# Patent

## Title
Process modifications to enhance chlorophyll degradation

## Abstract

In one aspect, there is provided a process for treating a plant oil, comprising a step of contacting the oil with an enzyme, wherein the enzyme is capable of hydrolyzing an a′ or b′ stereoisomer of chlorophyll or a chlorophyll derivative.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is the U.S. National Stage of International Application PCT/IB2012/050715 filed Feb. 16, 2012, which designates the U.S. and was published by the International Bureau in English on Aug. 30, 2012, and which claims the benefit of U.S. Provisional Application No. 61/445,665, filed Feb. 23, 2011, both of which are hereby incorporated by reference in their entirety.


FIELD
The present invention relates to the industrial processing of plant-derived food and feed products, especially vegetable oils. The invention may be employed to reduce or eliminate contamination by chlorophyll and chlorophyll derivatives.
BACKGROUND
Chlorophyll is a green-coloured pigment widely found throughout the plant kingdom. Chlorophyll is essential for photosynthesis and is one of the most abundant organic metal compounds found on earth. Thus many products derived from plants, including foods and feeds, contain significant amounts of chlorophyll.
For example, vegetable oils derived from oilseeds such as soybean, palm or rape seed (canola), cotton seed and peanut oil typically contain some chlorophyll. However the presence of high levels of chlorophyll pigments in vegetable oils is generally undesirable. This is because chlorophyll imparts an undesirable green colour and can induce oxidation of oil during storage, leading to a deterioration of the oil.
Various methods have been employed in order to remove chlorophyll from vegetable oils. Chlorophyll may be removed during many stages of the oil production process, including the seed crushing, oil extraction, degumming, caustic treatment and bleaching steps. However the bleaching step is usually the most significant for reducing chlorophyll residues to an acceptable level. During bleaching the oil is heated and passed through an adsorbent to remove chlorophyll and other colour-bearing compounds that impact the appearance and/or stability of the finished oil. The adsorbent used in the bleaching step is typically clay.
In the edible oil processing industry, the use of such steps typically reduces chlorophyll levels in processed oil to between 0.02 to 0.05 ppm. However the bleaching step increases processing cost and reduces oil yield due to entrainment in the bleaching clay. The use of clay may remove many desirable compounds such as carotenoids and tocopherol from the oil. Also the use of clay is expensive, this is particularly due to the treatment of the used clay (i.e. the waste) which can be difficult, dangerous (prone to self-ignition) and thus costly to handle. Thus attempts have been made to remove chlorophyll from oil by other means, for instance using the enzyme chlorophyllase.
In plants, chlorophyllase (chlase) is thought to be involved in chlorophyll degradation and catalyzes the hydrolysis of an ester bond in chlorophyll to yield chlorophyllide and phytol. WO 2006009676 describes an industrial process in which chlorophyll contamination can be reduced in a composition such as a plant oil by treatment with chlorophyllase. The water-soluble chlorophyllide which is produced in this process is also green in colour but can be removed by an aqueous extraction or silica treatment.
Chlorophyll is often partly degraded in the seeds used for oil production as well as during extraction of the oil from the seeds. One common modification is the loss of the magnesium ion from the porphyrin (chlorin) ring to form the derivative known as pheophytin (see FIG. 1). The loss of the highly polar magnesium ion from the porphyrin ring results in significantly different physico-chemical properties of pheophytin compared to chlorophyll. Typically pheophytin is more abundant in the oil during processing than chlorophyll. Pheophytin has a greenish colour and may be removed from the oil by an analogous process to that used for chlorophyll, for instance as described in WO 2006009676 by an esterase reaction catalyzed by an enzyme having a pheophytinase activity. Under certain conditions, some chlorophyllases are capable of hydrolyzing pheophytin as well as chlorophyll, and so are suitable for removing both of these contaminants. The products of pheophytin hydrolysis are the red/brown-colored pheophorbide and phytol. Pheophorbide can also be produced by the loss of a magnesium ion from chlorophyllide, i.e. following hydrolysis of chlorophyll (see FIG. 1). WO 2006009676 teaches removal of pheophorbide by an analogous method to chlorophyllide, e.g. by aqueous extraction or silica adsorption.
Pheophytin may be further degraded to pyropheophytin, both by the activity of plant enzymes during harvest and storage of oil seeds or by processing conditions (e.g. heat) during oil refining (see “Behaviour of Chlorophyll Derivatives in Canola Oil Processing”, JAOCS, Vol, no. 9 (September 1993) pages 837-841). One possible mechanism is the enzymatic hydrolysis of the methyl ester bond of the isocyclic ring of pheophytin followed by the non-enzymatic conversion of the unstable intermediate to pyropheophytin. A 28-29 kDa enzyme from Chenopodium album named pheophorbidase is reportedly capable of catalyzing an analogous reaction on pheophorbide, to produce the phytol-free derivative of pyropheophytin known as pyropheophorbide (see FIG. 1). Pyropheophorbide is less polar than pheophorbide resulting in the pyropheophoribe having a decreased water solubility and an increased oil solubility compared with pheophorbide.
Depending on the processing conditions, pyropheophytin can be more abundant than both pheophytin and chlorophyll in vegetable oils during processing (see Table 9 in volume 2.2. of Bailey's Industrial Oil and Fat Products (2005), 6th edition, Ed. by Fereidoon Shahidi, John Wiley & Sons). This is partly because of the loss of magnesium from chlorophyll during harvest and storage of the plant material. If an extended heat treatment at 90° C. or above is used, the amount of pyropheophytin in the oil is likely to increase and could be higher than the amount of pheophytin. Chlorophyll levels are also reduced by heating of oil seeds before pressing and extraction as well as the oil degumming and alkali treatment during the refining process. It has also been observed that phospholipids in the oil can complex with magnesium and thus reduce the amount of chlorophyll. Thus chlorophyll is a relatively minor contaminant compared to pyropheophytin (and pheophytin) in many plant oils.
Each of the four chlorophyll derivatives, chlorophyll a and b and pheophytin a and b, exist as a pair of epimers determined by the stereochemistry of H and COOCH3 around the carbon number 132 (numbering according to the IUPAC system, marked with asterisk in FIG. 2). Thus chlorophyll a exists as the pair of epimers chlorophyll a and chlorophyll a′, and chlorophyll b comprises b and b′ forms. Likewise pheophytin a comprises the epimer a and a′ pair and pheophytin b comprises b and b′ forms. The prime (′) forms have S-stereochemistry and non-prime forms have R-stereochemistry about the carbon 132 atom. Epimerization of, for example, the a form to a′ form and vice versa can take place under certain conditions via a common enol, as described in “Epimerization in the pheophytin a/a′ system”, Chemistry letters (1984), 1411-1414. In solution there is typically an equilibrium which dictates the distribution of prime and non-prime chlorophyll compounds and this is often determined by physical parameters such as temperature, pH, solvent and so on.
In general enzymes typically act as stereospecific catalysts by having activity on only one stereoisomer. Previous analyses suggested that chlorophyllases possess a high degree of stereospecificity only catalyzing the hydrolysis of non-prime forms of chlorophyll compounds (see “The stereospecific interaction between chlorophylls and chlorophyllase” J. Biol. Chem. 267(31):22043-22047 (1992)).
In methods for the removal of chlorophyll and chlorophyll derivatives from plant oil which employ chlorophyllases or related enzymes, the stereospecificity of the enzyme may be problematic. In particular, depending on the distribution and equilibrium of the chlorophyll stereoisomers in the oil, a complete degradation of chlorophyll components can be very difficult. For instance, if a significant proportion of the chlorophyll or chlorophyll derivative exists in the prime form, this fraction of the chlorophyll derivatives present in the oil may be resistant to enzymatic degradation. Moreover, a number of enzymes show much lower activity on pyropheophytin than on, for example, pheophytin.
This problem with existing methods is illustrated in FIG. 3. FIG. 3 shows the epimerization of pheophytin a and the conversion to pyropheophytin. The pH of a water/crude plant oil mixture (e.g. comprising about 1-2% water) is typically around 5.0 at about 60° C. Under such conditions, in crude soy bean or rape seed oil the pheophytin a epimer distribution is typically around 70% pheophytin a (R-stereoisomer) and 30% pheophytin a′ (S-stereoisomer) and isomerization between the two epimers is slow. Moreover, variable amounts of pyropheophytin may be formed depending on reaction conditions. If the enzyme used in the reaction is predominantly active only on pheophytin a, a significant proportion of chlorophyll derivatives present in the oil cannot be hydrolyzed directly by the enzyme at unmodified pH.
There is a therefore a need for an improved process for removing chlorophyll and chlorophyll derivatives such as pheophytin and pyropheophytin from plant oils. In particular, there is a need for a process which enhances the removal of various forms of chlorophyll and chlorophyll derivatives from the oil.
SUMMARY
In one aspect, the present invention provides a process for treating a plant oil, comprising a step of contacting the oil with an enzyme, wherein the enzyme is capable of hydrolysing an a′ or b′ stereoisomer of chlorophyll or a chlorophyll derivative.
In one embodiment, the a′ or b′ stereoisomer comprises chlorophyll a′, pheophytin a′, chlorophyll b′ or pheophytin b′. Preferably the stereoisomer is an a′ stereoisomer of chlorophyll or the chlorophyll derivative, e.g. chlorophyll a′ or pheophytin a′.
In one embodiment, the enzyme has an activity ratio on an a stereoisomer of chlorophyll or a chlorophyll derivative, compared to an a′ stereoisomer of chlorophyll or the chlorophyll derivative, of less than 10, less than 5, or less than 2. In an alternative embodiment, the enzyme has an activity ratio on a b stereoisomer of chlorophyll or a chlorophyll derivative, compared to an b′ stereoisomer of chlorophyll or the chlorophyll derivative, of less than 10, less than 5, or less than 2.
In one embodiment, following treatment with the enzyme the oil comprises at least 50% a stereoisomers of chlorophyll or the chlorophyll derivative, based on the total amount of a and a′ stereoisomers of chlorophyll or the chlorophyll derivative in the oil. In an alternative embodiment, following treatment with the enzyme the oil comprises at least 50% b stereoisomers of chlorophyll or the chlorophyll derivative, based on the total amount of b and b′ stereoisomers of chlorophyll or the chlorophyll derivative in the oil.
In further embodiments, the enzyme has an activity ratio on pheophytin compared to pyropheophytin of less than 10, less than 8 or less than 5.
In further embodiments, the enzyme comprises chlorophyllase, pheophytinase and/or pyropheophytinase activity, i.e. hydrolytic activity on chlorophyll, pheophytin and/or pyropheophytin.
In further embodiments, the enzyme is derived from Arabidopsis thaliana or Ricinus communis. For instance, the enzyme may comprise a polypeptide sequence as defined in SEQ ID NO:2 or SEQ ID NO:13, or a functional fragment or variant thereof.
Preferably the enzyme comprises a polypeptide sequence having at least 75% sequence identity to SEQ ID NO:2 or SEQ ID NO:13 over at least 50 amino acid residues. In one embodiment, the enzyme comprises a polypeptide having at least 90% sequence identity to SEQ ID NO:2. In another embodiment, the enzyme comprises a polypeptide having at least 90% sequence identity to SEQ ID NO:13.
In a further aspect, the present invention provides a plant oil obtainable by a method according to any preceding claim.
In a further aspect, the present invention provides use of an enzyme which is capable of hydrolysing chlorophyll or a chlorophyll derivative, for removing an a′ or b′ stereoisomer of chlorophyll or the chlorophyll derivative from a plant oil.
As described herein, enzymes have been identified which surprisingly show hydrolytic activity on prime as well as non-prime forms of chlorophyll derivatives. Moreover such enzymes may also show increased hydrolytic activity on pyropheophytin compared to enzymes used in known methods. Such enzymes can be advantageously used to enhance the removal of various forms of chlorophyll derivatives from plant oils.



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 shows the reactions involving chlorophyll and derivatives and enzymes used in the present invention.
FIG. 2 shows pheophytin a, where the C-132 according to the IUPAC numbering system is marked with an asterisk.
FIG. 3 shows epimerization of pheophytin a molecules and conversion to pyropheophytin a.
FIG. 4 shows amino acid and nucleotide sequences showing the fusion of a chlorophyllase gene to a His tag and thrombin site. The nucleotide sequence is provided as SEQ ID NO: 34 encoding the polypeptide provided as SEQ ID NO: 35.
FIG. 5 shows a schematic presentation of an E. coli. expression vector pET28-TRI_CHL containing the TRI_CHL gene encoding a chlorophyllase from Triticum aestivum (database acc. no. BT009214).
FIG. 6 shows amino acid and nucleotide sequences showing the fusion of a chlorophyllase gene to an AprE signal sequence and an AGK sequence. The nucleotide sequence is provided as SEQ ID NO: 36 encoding the polypeptide provided as SEQ ID NO: 37.
FIG. 7 shows a schematic presentation of a B. subtilis expression vector pBN-TRI_CHL containing the TRI_CHL gene encoding a chlorophyllase from Triticum aestivum (database acc. no. BT009214).
FIG. 8 shows amino acid and nucleotide sequences showing the fusion of a chlorophyllase gene directly to an AprE promoter. The nucleotide sequence is provided as SEQ ID NO: 38 encoding the polypeptide provided as SEQ ID NO: 39.
FIG. 9 shows a schematic presentation of a B. subtilis expression vector pBN-Spe-TRI_CHL containing the TRI_CHL gene encoding a chlorophyllase from Triticum aestivum (database acc. no. BT009214).
FIG. 10 shows amino acid and nucleotide sequence showing the fusion of a chlorophyllase gene to the Cel A signal sequence. The nucleotide sequence is provided as SEQ ID NO: 40 encoding the polypeptide provided as SEQ ID NO: 41.
FIG. 11 shows a schematic presentation of an S. lividans expression vector pKB-TRI_CHL containing the TRI_CHL gene encoding a chlorophyllase from Triticum aestivum (database acc. no. BT009214).
FIG. 12 shows the amino acid sequence of an Arabidopsis thaliana chlorophyllase (SEQ ID NO:1).
FIG. 13 shows the amino acid sequence of an Arabidopsis thaliana chlorophyllase (SEQ ID NO:2).
FIG. 14 shows the amino acid sequence of Citrus sinensis chlorophyllase (SEQ ID NO:3).
FIG. 15 shows the amino acid sequence of a Triticum aestivum chlorophyllase (SEQ ID NO:4).
FIG. 16 shows the amino acid sequence of a Triticum aestivum chlorophyllase (SEQ ID NO:5).
FIG. 17 shows the amino acid sequence of a Brassica oleracea chlorophyllase (SEQ ID NO:6).
FIG. 18 shows the amino acid sequence of a Brassica oleracea chlorophyllase (SEQ ID NO:7).
FIG. 19 shows the amino acid sequence of a Brassica oleracea chlorophyllase (SEQ ID NO:8).
FIG. 20 shows the amino acid sequence of a Zea Mays chlorophyllase (SEQ ID NO:9).
FIG. 21 shows the amino acid sequence of a Zea Mays chlorophyllase (SEQ ID NO:10).
FIG. 22 shows the amino acid sequence of a Phyllostachys edulis chlorophyllase (SEQ ID NO:11).
FIG. 23 shows the amino acid sequence of a Chenopodium album chlorophyllase (SEQ ID NO:12).
FIG. 24 shows the amino acid sequence of a Ricinus communis chlorophyllase (SEQ ID NO:13).
FIG. 25 shows the amino acid sequence of a Glycine max chlorophyllase (SEQ ID NO:14).
FIG. 26 shows the amino acid sequence of a Ginkgo biloba chlorophyllase (SEQ ID NO:15).
FIG. 27 shows the amino acid sequence of a Pachira macrocarpa chlorophyllase (SEQ ID NO:16).
FIG. 28 shows the amino acid sequence of a Populus trichocarpa chlorophyllase (SEQ ID NO:17).
FIG. 29 shows the amino acid sequence of a Sorghum bicolor chlorophyllase (SEQ ID NO:18).
FIG. 30 shows the amino acid sequence of a Sorghum bicolor chlorophyllase (SEQ ID NO:19).
FIG. 31 shows the amino acid sequence of a Vitis vinifera chlorophyllase (SEQ ID NO:20).
FIG. 32 shows the amino acid sequence of a Physcomitrella patens chlorophyllase (SEQ ID NO:21).
FIG. 33 shows the amino acid sequence of a Aquilegia chlorophyllase (SEQ ID NO:22).
FIG. 34 shows the amino acid sequence of a Brachypodium distachyon chlorophyllase (SEQ ID NO:23).
FIG. 35 shows the amino acid sequence of a Medicago truncatula chlorophyllase (SEQ ID NO:24).
FIG. 36 shows the amino acid sequence of a Piper betle chlorophyllase (SEQ ID NO:25).
FIG. 37 shows the amino acid sequence of a Lotus japonicus chlorophyllase (SEQ ID NO:26).
FIG. 38 shows the amino acid sequence of a Oryza sativa Indica chlorophyllase (SEQ ID NO:27).
FIG. 39 shows the amino acid sequence of a Oryza sativa Japonica chlorophyllase (SEQ ID NO:28).
FIG. 40 shows the amino acid sequence of a Oryza sativa Japonica chlorophyllase (SEQ ID NO:29).
FIG. 41 shows the amino acid sequence of a Picea sitchensis chlorophyllase (SEQ ID NO:30).
FIG. 42 shows the amino acid sequence of a Chlamydomonas chlorophyllase (SEQ ID NO:31).
FIG. 43 shows a phylogenetic tree of the plant chlorophyllases and the Chlamydomonas chlorophyllase (CHL_CHL) described herein.
FIG. 44 shows a Western blot analysis of E. coli extracts containing recombinant chlorophyllases derived from various species. Lane 1: BAM_CHL CoRe 112. Lane 2: CIT_CHL CoRe 113A. Lane 3: ARA_CHL CoRe 114A. Lane 4: CB_CHL CoRe 127. Lane 5: GlyMax_CHL CoRe 133. Lane 6: Sor_CFIL CoRe 134. Lane 7: ARA_CHL2 CoRe 135. Lane 8: BRA_CHL1 CoRe 136. See Tables 1 and 2 below for definitions of source species of the enzymes corresponding to the above abbreviations.
FIG. 45 shows a Western blot analysis of E. coli extracts containing recombinant chlorophyllases derived from various species. Lane 1: SORG_CHL CoRe 137A. Lane 2: TRI_CHL2 CoRe 138A. Lane 3: ZEA_CRL2 CoRe 139. Lane 4: TRI_CHL CoRe 20. Lane 5: BRACH_CHL CoRe 156. Lane 6: PIP_CHL CoRe 158. Lane 7: PICEA_CHL CoRe 163. Lane 8: Vector control. See Tables 1 and 2 below for definitions of source species of the enzymes corresponding to the above abbreviations.
FIG. 46 shows activity of recombinant enzymes derived from various species on pheophytin a, as demonstrated by total pheophytin a (pheophytin a+a′) levels in ppm remaining at various times after treatment with each enzyme.
FIG. 47 shows activity of recombinant enzymes derived from various species on pheophytin a, as demonstrated by pyropheophytin a levels in ppm remaining at various times after treatment with each enzyme.
FIG. 48 shows the percentage of a stereoisomers of pheophytin in an oil sample after treatment with recombinant enzymes derived from various species, based on the total amount of pheophytin a and pheophytin a′ stereoisomers in the oil sample after treatment.
FIG. 49 shows an HPLC chromatogram using absorbance detection (430 nm) indicating numbered peaks associated with: 1=chlorophyllide b; 2=chlorophyllide a; 3=neoxanthin; 3′=neoxanthin isomer; 4=neochrome; 5=violaxanthin; 6=luteoxanthin; 7=auroxanthin; 8=anteraxanthin; 8′=anteraxanthin isomer; 9=mutatoxanthin; 10=lutein; 10′=lutein isomer; 10′′=lutein isomer; 11=pheophorbide b; 12=pheophorbide a; 13=chlorophyll b; 13′=chlorophyll b′; 14=chlorophyll a; 14′=chlorophyll a′; 15=pheopytin b; 15′=pheophytin b′; 16=13-carotene; 17=pheophytin a; 17′=pheophytin a′; 18=pyropheophytin b; 19=pyropheophytin a.
FIG. 50 shows a diagrammatic representation of an oil refining process according to an embodiment of the present invention.
FIG. 51 shows the logarithm of substrate concentration for pheophytin a and a′ after 1⁄2 hr as a function of ARA_CRL2 (Arabidopsis chlorophyllase) dosage.



DETAILED DESCRIPTION
In one aspect the present invention relates to a process for treating a plant oil. Typically the process is used to remove chlorophyll and/or chlorophyll derivatives from the oil, or to reduce the level of chlorophyll and/or chlorophyll derivatives in the oil, for instance where the chlorophyll and/or chlorophyll derivatives are present as a contaminant.
Chlorophyll and Chlorophyll Derivatives
By “chlorophyll derivative” it is typically meant compounds which comprise both a porphyrin (chlorin) ring and a phytol group (tail), including magnesium-free phytol-containing derivatives such as pheophytin and pyropheophytin. Chlorophyll and (phytol-containing) chlorophyll derivatives are typically greenish is colour, as a result of the porphyrin (chlorin) ring present in the molecule. Loss of magnesium from the porphyrin ring means that pheophytin and pyropheophytin are more brownish in colour than chlorophyll. Thus the presence of chlorophyll and chlorophyll derivatives in an oil, can give such an oil an undesirable green, greenish or brownish colour. In one embodiment, the present process may be performed in order to remove or reduce the green or brown colouring present in the oil. Accordingly the present process may be referred to as a bleaching or de-colorizing process.
Enzymes used in the process may hydrolyse chlorophyll and phytol-containing chlorophyll derivatives to cleave the phytol tail from the chlorin ring. Hydrolysis of chlorophyll and chlorophyll derivatives typically results in compounds such as chlorophyllide, pheophorbide and pyropheophorbide which are phytol-free derivatives of chlorophyll. These compounds still contain the colour-bearing porphyrin ring, with chlorophyllide being green and pheophorbide and pyropheophorbide a reddish brown colour. In some embodiments, it may also be desirable to remove these phytol-free derivatives and to reduce the green/red/brown colouring in the oil. Thus in one embodiment of the invention, the process may further comprise a step of removing or reducing the level of phytol-free chlorophyll derivatives in the oil. The process may involve bleaching or de-colorizing to remove the green and/or red/brown colouring of the oil.
The chlorophyll or chlorophyll derivative may be either a or b forms. Thus as used herein, the term “chlorophyll” includes chlorophyll a and chlorophyll b. In a similar way both a and b forms are covered when referring to pheophytin, pyropheophytin, chlorophyllide, pheophorbide and pyropheophorbide.
As described herein, chlorophyll and chlorophyll derivatives may exist as a pair of epimers determined by the stereochemistry around the carbon number 132 (numbering according to the IUPAC system, marked with asterisk in FIG. 2). Thus chlorophyll a exists as the pair of epimers chlorophyll a and chlorophyll a′, and chlorophyll b comprises b and b′ forms. Pheophytin a comprises the epimers a and a′ and pheophytin b comprises b and b′ forms. The prime (′) forms have S-stereochemistry and non-prime forms have R-stereochemistry about the carbon 132 atom. When used generally herein, the term “chlorophyll and chlorophyll derivatives” includes both prime and non-prime forms.
Plant Oils
Any plant oil may be treated according to the present process, in order to remove undesirable contamination by chlorophyll and/or chlorophyll derivatives. The oil may be derived from any type of plant, and from any part of a plant, including whole plants, leaves, stems, flowers, roots, plant protoplasts, seeds and plant cells and progeny of same. The class of plants from which products can be treated in the method of the invention includes higher plants, including angiosperms (monocotyledonous and dicotyledonous plants), as well as gymnosperms. It includes plants of a variety of ploidy levels, including polyploid, diploid, haploid and hemizygous states.
In preferred embodiments, the oil may comprise a vegetable oil, including oils processed from oil seeds or oil fruits (e.g. seed oils such as canola (rapeseed) oil and fruit oils such as palm). Examples of suitable oils include rice bran, soy, canola (rape seed), palm, olive, cottonseed, corn, palm kernel, coconut, peanut, sesame, Moringa or sunflower. The process of the invention can be used in conjunction with methods for processing essential oils, e.g., those from fruit seed oils, e.g. grapeseed, apricot, borage, etc. The process of the invention can be used in conjunction with methods for processing high phosphorus oils (e.g. a soy bean oil). Preferably the oil is a crude plant oil.
Chlorophyll and Chlorophyll Derivatives in Oil
The chlorophyll and/or chlorophyll derivatives (e.g. chlorophyll, pheophytin and/or pyropheophytin) may be present in the oil naturally, as a contaminant, or as an undesired component in a processed product. The chlorophyll and/or chlorophyll derivatives (e.g. chlorophyll, pheophytin and/or pyropheophytin) may be present at any level in the oil. Typically chlorophyll, pheophytin and/or pyropheophytin may be present as a natural contaminant in the oil at a concentration of 0.001 to 1000 mg/kg (0.001 to 1000 ppm, 10−7 to 10−1 wt %), based on the total weight of the oil. In further embodiments, the chlorophyll and/or chlorophyll derivatives may be present in the oil at a concentration of 0.1 to 100, 0.5 to 50, 1 to 50, 1 to 30 or 1 to 10 mg/kg, based on the total weight of the oil.
Phytol-free chlorophyll derivatives may also be present in the oil. For instance, chlorophyllide, pyropheophorbide and/or pyropheophorbide may be present at any level in the oil. Typically chlorophyllide, pyropheophorbide and/or pyropheophorbide may be present in the oil, either before or after treatment with an enzyme according to the method of the present invention, at a concentration of 0.001 to 1000 mg/kg (0.001 to 1000 ppm, 10−7 to 10−1 wt %), based on the total weight of the oil. In further embodiments, the chlorophyllide, pyropheophorbide and/or pyropheophorbide may be present in the composition at a concentration of 0.1 to 100, 0.5 to 50, 1 to 50, 1 to 30 or 1 to 10 mg/kg, based on the total weight of the composition.
Enzymes Hydrolysing Chlorophyll or a Chlorophyll Derivative
The process of the present invention comprises a step of contacting the oil with an enzyme which is capable of hydrolysing chlorophyll or a chlorophyll derivative, particularly prime stereoisomers (e.g. a′ or b′) thereof. Typically “hydrolyzing chlorophyll or a chlorophyll derivative” means hydrolysing an ester bond in chlorophyll or a (phytol-containing) chlorophyll derivative, e.g. to cleave a phytol group from the chlorin ring in the chlorophyll or chlorophyll derivative. Thus the enzyme typically has an esterase or hydrolase activity. Preferably the enzyme has esterase or hydrolase activity in an oil phase, and optionally also in an aqueous phase.
Thus the enzyme may, for example, be a chlorophyllase, pheophytinase or pyropheophytinase. Preferably, the enzyme is capable of hydrolysing at least one, at least two or all three of chlorophyll, pheophytin and pyropheophytin. In a particularly preferred embodiment, the enzyme has chlorophyllase, pheophytinase and pyropheophytinase activity. In further embodiments, two or more enzymes may be used in the method, each enzyme having a different substrate specificity. For instance, the method may comprise the combined use of two or three enzymes selected from a chlorophyllase, a pheophytinase and a pyropheophytinase.
Any polypeptide having an activity that can hydrolyse chlorophyll or a chlorophyll derivative, and in particular prime stereoisomers thereof, can be used as the enzyme in the process of the invention. By “enzyme” it is intended to encompass any polypeptide having hydrolytic activity on prime stereoisomers (e.g. a′ or b∝) of chlorophyll or a chlorophyll derivative, including e.g. enzyme fragments, etc. Any isolated, recombinant or synthetic or chimeric (or a combination of synthetic and recombinant) polypeptide can be used.
In embodiments of the present invention, the enzyme is capable of hydrolysing an a′ or b′ stereoisomer of chlorophyll or a chlorophyll derivative. By this it is meant that the enzyme has hydrolytic activity on a prime (′) form of chlorophyll or a chlorophyll derivative. The prime (′) designation refers to the stereochemistry around the carbon number 132 in chlorophyll or the chlorophyll derivative.
Thus prime forms of chlorophyll or chlorophyll derivatives which may be hydrolysed in embodiments of the present invention include chlorophyll a′, chlorophyll b′, pheophytin a′ and pheophytin b′. Preferably the enzyme is capable of hydrolyzing at least a prime form of an a type chlorophyll derivative, i.e. chlorophyll a′ or pheophytin a′.
Typically the enzyme also has hydrolytic activity on non-prime forms of chlorophyll or chlorophyll derivatives. The enzymes used in the present invention may have reduced stereospecificity, i.e. the enzymes used herein are less specific for non-prime forms of chlorophyll or chlorophyll derivatives than other known chlorophyllases (such as Triticum aestivum chlorophyllase, see SEQ ID NO:4).
In one embodiment, the enzyme has an activity ratio on a non-prime (e.g. a or b) stereoisomer of chlorophyll or a chlorophyll derivative, compared to a prime (e.g. a′ or b′) stereoisomer of chlorophyll or the chlorophyll derivative, of less than 100. Preferably the activity ratio is less than 50, less than 10, less than 5, less than 3, less than 2, less than 1.5, less than 1 or less than 0.5. By “activity ratio” it is meant to refer to the relative activity of the enzyme on the prime form compared to the non-prime form under the same conditions. Thus the activity ratio may be determined by determining (a) hydrolytic activity of the enzyme on a non-prime stereoisomer, and (b) hydrolytic activity of the enzyme on a corresponding prime stereoisomer, and dividing (a) by (b). A low activity ratio is thus indicative of a relatively high activity on prime forms.
Hydrolytic activity may be determined, for example, using methods described below. Typically the activity ratio may be determined under conditions which do not favour epimerization (i.e. transition between prime and non-prime isomers). For instance, the activity ratio may be determined by measuring hydrolytic activity on prime and non-prime isomers in a crude oil with greater than 0.5 ppm pheophytin, about 2% water and at pH 5.0 to 5.5. In one embodiment, the hydrolytic activity of the enzyme on pheophytin a or pheophytin a′ is calculated at half of the original substrate concentration (see e.g. Example 4)
In another embodiment, the enzyme has an activity ratio on pheophytin compared to pyropheophytin of less than 80, less than 50, less than 10, less than 8, less than 7 or less than 5. For example, the enzyme may have a pheophytinase to pyropheophytinase activity ratio of 0.1 to 10, 1 to 10 or 1 to 5. The pheophytinase to pyropheophytinase activity ratio may be calculated by determining pheophytinase activity and pyropheophytinase activity under the same conditions using methods described below, and dividing the pheophytinase activity by the pyropheophytinase activity. Activity ratios within the above ratios may be determined in respect of corresponding species of pheophytin and pyropheophytin, e.g. pheophytin a (comprising both a and a′ forms) to pyropheopytin a.
Enzyme (Chlorophyllase, Pheophytinase or Pyropheophytinase) Activity Assay
Hydrolytic activity on chlorophyll or a chlorophyll derivative, including on prime and non-prime forms thereof, may be detected using any suitable assay technique, for example based on an assay described herein. For example, hydrolytic activity may be detected using fluorescence-based techniques. In one suitable assay, a polypeptide to be tested for hydrolytic activity on chlorophyll or a chlorophyll derivative is incubated in the presence of a substrate, and product or substrate levels are monitored by fluorescence measurement. Suitable substrates include e.g. chlorophyll, pheophytin and/or pyropheophytin, including a and b and prime and non-prime forms thereof. Products which may be detected include chlorophyllide, pheophorbide, pyropheophorbide and/or phytol.
Assay methods for detecting hydrolysis of chlorophyll or a chlorophyll derivative are disclosed in, for example, Ali Khamessan et al. (1994), Journal of Chemical Technology & Biotechnology, 60(1), pages 73-81; Klein and Vishniac (1961), J. Biol. Chem. 236: 2544-2547; and Kiani et al. (2006), Analytical Biochemistry 353: 93-98.
Alternatively, a suitable assay may be based on HPLC detection and quantitation of substrate or product levels following addition of a putative enzyme, e.g. based on the techniques described below. In one embodiment, the assay may be performed as described in Hornero-Mendez et al. (2005), Food Research International 38(8-9): 1067-1072. In another embodiment, the following assay may be used:
170 μl mM HEPES, pH 7.0 is added 20 μl 0.3 mM chlorophyll, pheophytin or pyropheophytin dissolved in acetone. The enzyme is dissolved in 50 mM HEPES, pH 7.0. 10 μl enzyme solution is added to 190 μl substrate solution to initiate the reaction and incubated at 40° C. for various time periods. The reaction was stopped by addition of 350 μl acetone. Following centrifugation (2 min at 18,000 g) the supernatant was analyzed by HPLC, and the amounts of (i) chlorophyll and chlorophyllide (ii) pheophytin and pheophorbide or (iii) pyropheophytin and pyropheophorbide determined. Prime and non-prime forms of chlorophyll and chlorophyll derivatives may be distinguished by HPLC analysis, as shown in FIG. 49.
One unit of enzyme activity is defined as the amount of enzyme which hydrolyzes one micromole of substrate (e.g. chlorophyll, pheophytin or pyropheophytin) per minute at 40° C., e.g. in an assay method as described herein.
In preferred embodiments, the enzyme used in the present method has chlorophyllase, pheophytinase and/or pyropheophytinase activity of at least 1000 U/g, at least 5000 U/g, at least 10000 U/g, or at least 50000 U/g, based on the units of activity per gram of the purified enzyme, e.g. as determined by an assay method described herein. Preferably the enzyme has a hydrolytic activity of at least 1000 U/g, at least 5000 U/g, at least 10000 U/g, or at least 50000 U/g, based on the units of activity per gram of the purified enzyme, on a prime (e.g. a′ or b′) stereoisomer of chlorophyll or a chlorophyll derivative (e.g. chlorophyll a′, chlorophyll b′, pheophytin a′ or pheophytin b′).
In a further embodiment, hydrolytic activity on chlorophyll or a chlorophyll derivative may be determined using a method as described in EP10159327.5.
Chlorophyllases
In one embodiment, the enzyme is capable of hydrolyzing at least a prime (e.g. a′ or b′) stereoisomer of chlorophyll. A polypeptide that catalyses the hydrolysis of a chlorophyll a′ or b′ ester bond to yield chlorophyllide a′ or b′ and phytol can be used in the process. In one embodiment the enzyme is a chlorophyllase classified under the Enzyme Nomenclature classification (E.C. 3.1.1.14). An isolated, recombinant or synthetic or chimeric (a combination of synthetic and recombinant) polypeptide (e.g., enzyme or catalytic antibody) can be used, see e.g. Marchler-Bauer (2003) Nucleic Acids Res. 31: 383-387.
In one embodiment, the enzyme may be derived from Arabidopsis thaliana. For instance, the enzyme may be a polypeptide comprising the sequence of SEQ ID NO:2 (see FIG. 13).
In another embodiment, the chlorophyllase is derived from castor bean, e.g. from Ricinus communis. For example, the chlorophyllase may be polypeptide comprising the sequence of SEQ ID NO:13 (see FIG. 24).
Further provided herein are enzymes comprising a polypeptide sequence as defined in any one of SEQ ID NO:s 1 to 31, as well as functional fragments and variants thereof, as described below.
Variants and Fragments
Functional variants and fragments of known sequences which hydrolyse prime forms is of chlorophyll or a chlorophyll derivative may also be employed in the present invention. By “functional” it is meant that the fragment or variant retains a detectable hydrolytic activity on a prime (e.g. a′ or b′) stereoisomer of chlorophyll or a chlorophyll derivative. Typically such variants and fragments show homology to a source chlorophyllase, pheophytinase or pyropheophytinase sequence, e.g. at least about 50%, 60%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or more sequence identity to a source chlorophyllase, pheophytinase or pyropheophytinase amino acid sequence, e.g. to SEQ ID NO:2 or SEQ ID NO: 13, e.g. over a region of at least about 10, 20, 30, 50, 100, 200, 300, 500, or 1000 or more residues, or over the entire length of the sequence.
The percentage of sequence identity may be determined by analysis with a sequence comparison algorithm or by a visual inspection. In one aspect, the sequence comparison algorithm is a BLAST algorithm, e.g., a BLAST version 2.2.2 algorithm.
Other enzymes having activity on prime forms of chlorophyll or a chlorophyll derivative suitable for use in the process may be identified by determining the presence of conserved sequence motifs present e.g. in known chlorophyllase, pheophytinase or pyropheophytinase sequences. For example, the motif GHSRG (SEQ ID NO: 32) containing the Ser active site is highly conserved in chlorophyllase sequences. In some embodiments, an enzyme for use in the present invention may comprise such a sequence. Polypeptide sequences having suitable activity may be identified by searching genome databases, e.g. the microbiome metagenome database (JGI-DOE, USA), for the presence of these motifs.
Isolation and Production of Enzymes
Enzymes for use in the present invention may be isolated from their natural sources or may be, for example, produced using recombinant DNA techniques. Nucleotide sequences encoding polypeptides having chlorophyllase, pheophytinase and/or pyropheophytinase activity may be isolated or constructed and used to produce the corresponding polypeptides.
For example, a genomic DNA and/or cDNA library may be constructed using chromosomal DNA or messenger RNA from the organism producing the polypeptide. If the amino acid sequence of the polypeptide is known, labeled oligonucleotide probes may be synthesised and used to identify polypeptide-encoding clones from the genomic library prepared from the organism. Alternatively, a labelled oligonucleotide probe containing sequences homologous to another known polypeptide gene could be used to identify polypeptide-encoding clones. In the latter case, hybridisation and washing conditions of lower stringency are used.
Alternatively, polypeptide-encoding clones could be identified by inserting fragments of genomic DNA into an expression vector, such as a plasmid, transforming enzyme-negative bacteria with the resulting genomic DNA library, and then plating the transformed bacteria onto agar containing an enzyme inhibited by the polypeptide, thereby allowing clones expressing the polypeptide to be identified.
In a yet further alternative, the nucleotide sequence encoding the polypeptide may be prepared synthetically by established standard methods, e.g. the phosphoroamidite method described by Beucage S. L. et al (1981) Tetrahedron Letters 22, p 1859-1869, or the method described by Matthes et al (1984) EMBO J. 3, p 801-805. In the phosphoroamidite method, oligonucleotides are synthesised, e.g. in an automatic DNA synthesiser, purified, annealed, ligated and cloned in appropriate vectors.
The nucleotide sequence may be of mixed genomic and synthetic origin, mixed synthetic and cDNA origin, or mixed genomic and cDNA origin, prepared by ligating fragments of synthetic, genomic or cDNA origin (as appropriate) in accordance with standard techniques. Each ligated fragment corresponds to various parts of the entire nucleotide sequence. The DNA sequence may also be prepared by polymerase chain reaction (PCR) using specific primers, for instance as described in U.S. Pat. No. 4,683,202 or in Saiki R K et al (Science (1988) 239, pp 487-491).
The term “nucleotide sequence” as used herein refers to an oligonucleotide sequence or polynucleotide sequence, and variant, homologues, fragments and derivatives thereof (such as portions thereof). The nucleotide sequence may be of genomic or synthetic or recombinant origin, which may be double-stranded or single-stranded whether representing the sense or antisense strand.
Typically, the nucleotide sequence encoding a polypeptide having chlorophyllase, pheophytinase and/or pyropheophytinase activity is prepared using recombinant DNA techniques. However, in an alternative embodiment of the invention, the nucleotide sequence could be synthesised, in whole or in part, using chemical methods well known in the art (see Caruthers M H et al (1980) Nuc Acids Res Symp Ser 215-23 and Horn T et al (1980) Nuc Acids Res Symp Ser 225-232).
Modification of Enzyme Sequences
Once an enzyme-encoding nucleotide sequence has been isolated, or a putative enzyme-encoding nucleotide sequence has been identified, it may be desirable to modify the selected nucleotide sequence, for example it may be desirable to mutate the sequence in order to prepare an enzyme in accordance with the present invention.
Mutations may be introduced using synthetic oligonucleotides. These oligonucleotides contain nucleotide sequences flanking the desired mutation sites. A suitable method is disclosed in Morinaga et al (Biotechnology (1984) 2, p 646-649). Another method of introducing mutations into enzyme-encoding nucleotide sequences is described in Nelson and Long (Analytical Biochemistry (1989), 180, p 147-151).
Instead of site directed mutagenesis, such as described above, one can introduce mutations randomly for instance using a commercial kit such as the GeneMorph PCR mutagenesis kit from Stratagene, or the Diversify PCR random mutagenesis kit from Clontech. EP 0 583 265 refers to methods of optimising PCR based mutagenesis, which can also be combined with the use of mutagenic DNA analogues such as those described in EP 0 866 796. Error prone PCR technologies are suitable for the production of variants of enzymes which hydrolyse chlorophyll and/or chlorophyll derivatives with preferred characteristics. WO0206457 refers to molecular evolution of lipases.
A third method to obtain novel sequences is to fragment non-identical nucleotide sequences, either by using any number of restriction enzymes or an enzyme such as Dnase I, and reassembling full nucleotide sequences coding for functional proteins. Alternatively one can use one or multiple non-identical nucleotide sequences and introduce mutations during the reassembly of the full nucleotide sequence. DNA shuffling and family shuffling technologies are suitable for the production of variants of enzymes with preferred characteristics. Suitable methods for performing ‘shuffling’ can be found in EP0752008, EP1138763, EP1103606. Shuffling can also be combined with other forms of DNA mutagenesis as described in U.S. Pat. No. 6,180,406 and WO 01/34835.
Thus, it is possible to produce numerous site directed or random mutations into a nucleotide sequence, either in vivo or in vitro, and to subsequently screen for improved functionality of the encoded polypeptide by various means. Using in silico and exo mediated recombination methods (see WO 00/58517, U.S. Pat. No. 6,344,328, U.S. Pat. No. 6,361,974), for example, molecular evolution can be performed where the variant produced retains very low homology to known enzymes or proteins. Such variants thereby obtained may have significant structural analogy to known chlorophyllase, pheophytinase or pyropheophytinase enzymes, but have very low amino acid sequence homology.
As a non-limiting example, in addition, mutations or natural variants of a polynucleotide sequence can be recombined with either the wild type or other mutations or natural variants to produce new variants. Such new variants can also be screened for improved functionality of the encoded polypeptide.
The application of the above-mentioned and similar molecular evolution methods allows the identification and selection of variants of the enzymes of the present invention which have preferred characteristics without any prior knowledge of protein structure or function, and allows the production of non-predictable but beneficial mutations or variants. There are numerous examples of the application of molecular evolution in the art for the optimisation or alteration of enzyme activity, such examples include, but are not limited to one or more of the following: optimised expression and/or activity in a host cell or in vitro, increased enzymatic activity, altered substrate and/or product specificity, increased or decreased enzymatic or structural stability, altered enzymatic activity/specificity in preferred environmental conditions, e.g. temperature, pH, substrate.
As will be apparent to a person skilled in the art, using molecular evolution tools an enzyme may be altered to improve the functionality of the enzyme. Suitably, a nucleotide sequence encoding an enzyme (e.g. a chlorophyllase, pheophytinase and/or pyropheophytinase) used in the invention may encode a variant enzyme, i.e. the variant enzyme may contain at least one amino acid substitution, deletion or addition, when compared to a parental enzyme. Variant enzymes retain at least 1%, 2%, 3%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 97%, or 99% identity with the parent enzyme. Suitable parent enzymes may include any enzyme with hydrolytic activity on prime forms of chlorophyll and/or a chlorophyll derivative.
Polypeptide Sequences
The present invention also encompasses the use of amino acid sequences encoded by a nucleotide sequence which encodes an enzyme for use in any one of the methods and/or uses of the present invention.
As used herein, the term “amino acid sequence” is synonymous with the term “polypeptide” and/or the term “protein”. In some instances, the term “amino acid sequence” is synonymous with the term “peptide”. The amino acid sequence may be prepared/isolated from a suitable source, or it may be made synthetically or it may be prepared by use of recombinant DNA techniques. Suitably, the amino acid sequences may be obtained from the isolated polypeptides taught herein by standard techniques.
One suitable method for determining amino acid sequences from isolated polypeptides is as follows. Purified polypeptide may be freeze-dried and 100 μg of the freeze-dried material may be dissolved in 50 μl of a mixture of 8 M urea and 0.4 M ammonium hydrogen carbonate, pH 8.4. The dissolved protein may be denatured and reduced for 15 minutes at 50° C. following overlay with nitrogen and addition of 5 μl of 45 mM dithiothreitol. After cooling to room temperature, 5 μl of 100 mM iodoacetamide may be added for the cysteine residues to be derivatized for 15 minutes at room temperature in the dark under nitrogen.
135 μl of water and 5 μg of endoproteinase Lys-C in 5 μl of water may be added to the above reaction mixture and the digestion may be carried out at 37° C. under nitrogen for 24 hours. The resulting peptides may be separated by reverse phase HPLC on a VYDAC C18 column (0.46×15 cm; 10 μm; The Separation Group, California, USA) using solvent A: 0.1% TFA in water and solvent B: 0.1% TFA in acetonitrile. Selected peptides may be re-chromatographed on a Develosil C18 column using the same solvent system, prior to N-terminal sequencing. Sequencing may be done using an Applied Biosystems 476A sequencer using pulsed liquid fast cycles according to the manufacturer's instructions (Applied Biosystems, California, USA).
Sequence Comparison
Here, the term “homologue” means an entity having a certain homology with the subject amino acid sequences and the subject nucleotide sequences. Here, the term “homology” can be equated with “identity”. The homologous amino acid sequence and/or nucleotide sequence should provide and/or encode a polypeptide which retains the functional activity and/or enhances the activity of the enzyme.
In the present context, a homologous sequence is taken to include an amino acid sequence which may be at least 75, 85 or 90% identical, preferably at least 95 or 98% identical to the subject sequence. Typically, the homologues will comprise the same active sites etc. as the subject amino acid sequence. Although homology can also be considered in terms of similarity (i.e. amino acid residues having similar chemical properties/functions), in the context of the present invention it is preferred to express homology in terms of sequence identity.
In the present context, a homologous sequence is taken to include a nucleotide sequence which may be at least 75, 85 or 90% identical, preferably at least 95 or 98% identical to a nucleotide sequence encoding a polypeptide of the present invention (the subject sequence). Typically, the homologues will comprise the same sequences that code for the active sites etc. as the subject sequence. Although homology can also be considered in terms of similarity (i.e. amino acid residues having similar chemical properties/functions), in the context of the present invention it is preferred to express homology in terms of sequence identity.
Homology comparisons can be conducted by eye, or more usually, with the aid of readily available sequence comparison programs. These commercially available computer programs can calculate % homology between two or more sequences. % homology may be calculated over contiguous sequences, i.e. one sequence is aligned with the other sequence and each amino acid in one sequence is directly compared with the corresponding amino acid in the other sequence, one residue at a time. This is called an “ungapped” alignment. Typically, such ungapped alignments are performed only over a relatively short number of residues.
Although this is a very simple and consistent method, it fails to take into consideration that, for example, in an otherwise identical pair of sequences, one insertion or deletion will cause the following amino acid residues to be put out of alignment, thus potentially resulting in a large reduction in % homology when a global alignment is performed. Consequently, most sequence comparison methods are designed to produce optimal alignments that take into consideration possible insertions and deletions without penalising unduly the overall homology score. This is achieved by inserting “gaps” in the sequence alignment to try to maximise local homology.
However, these more complex methods assign “gap penalties” to each gap that occurs in the alignment so that, for the same number of identical amino acids, a sequence alignment with as few gaps as possible—reflecting higher relatedness between the two compared sequences—will achieve a higher score than one with many gaps. “Affine gap costs” are typically used that charge a relatively high cost for the existence of a gap and a smaller penalty for each subsequent residue in the gap. This is the most commonly used gap scoring system. High gap penalties will of course produce optimised alignments with fewer gaps. Most alignment programs allow the gap penalties to be modified. However, it is preferred to use the default values when using such software for sequence comparisons.
Calculation of maximum % homology therefore firstly requires the production of an optimal alignment, taking into consideration gap penalties. A suitable computer program for carrying out such an alignment is the Vector NTI AdvanceTM 11 (Invitrogen Corp.). Examples of other software that can perform sequence comparisons include, but are not limited to, the BLAST package (see Ausubel et al 1999 Short Protocols in Molecular Biology, 4th Ed—Chapter 18), and FASTA (Altschul et al 1990 J. Mol. Biol. 403-410). Both BLAST and FASTA are available for offline and online searching (see Ausubel et al 1999, pages 7-58 to 7-60). However, for some applications, it is preferred to use the Vector NTI AdvanceTM 11 program. A new tool, called BLAST 2 Sequences is also available for comparing protein and nucleotide sequence (see FEMS Microbiol Lett 1999 174(2): 247-50; and FEMS Microbiol Lett 1999 177(1): 187-8).
Although the final % homology can be measured in terms of identity, the alignment process itself is typically not based on an all-or-nothing pair comparison. Instead, a scaled similarity score matrix is generally used that assigns scores to each pairwise comparison based on chemical similarity or evolutionary distance. An example of such a matrix commonly used is the BLOSUM62 matrix—the default matrix for the BLAST suite of programs. Vector NTI programs generally use either the public default values or a custom symbol comparison table if supplied (see user manual for further details). For some applications, it is preferred to use the default values for the Vector NTI AdvanceTM 11 package.
Alternatively, percentage homologies may be calculated using the multiple alignment feature in Vector NTI AdvanceTM 11 (Invitrogen Corp.), based on an algorithm, analogous to CLUSTAL (Higgins D G & Sharp P M (1988), Gene 73(1), 237-244). Once the software has produced an optimal alignment, it is possible to calculate % homology, preferably % sequence identity. The software typically does this as part of the sequence comparison and generates a numerical result.
Should Gap Penalties be used when determining sequence identity, then preferably the default parameters for the programme are used for pairwise alignment. For example, the following parameters are the current default parameters for pairwise alignment for BLAST 2:















FOR BLAST2
DNA
PROTEIN




















EXPECT
10
10



THRESHOLD



WORD SIZE
11
3



SCORING



PARAMETERS



Match/Mismatch
2, −3
n/a



Scores



Matrix
n/a
BLOSUM62



Gap Costs
Existence: 5
Existence: 11




Extension: 2
Extension: 1










In one embodiment, preferably the sequence identity for the nucleotide sequences and/or amino acid sequences may be determined using BLAST2 (blastn) with the scoring parameters set as defined above.
For the purposes of the present invention, the degree of identity is based on the number of sequence elements which are the same. The degree of identity in accordance with the present invention for amino acid sequences may be suitably determined by means of computer programs known in the art such as Vector NTI AdvanceTM 11 (Invitrogen Corp.). For pairwise alignment the scoring parameters used are preferably BLOSUM62 with Gap existence penalty of 11 and Gap extension penalty of 1.
Suitably, the degree of identity with regard to a nucleotide sequence is determined over at least 20 contiguous nucleotides, preferably over at least 30 contiguous nucleotides, preferably over at least 40 contiguous nucleotides, preferably over at least 50 contiguous nucleotides, preferably over at least 60 contiguous nucleotides, preferably over at least 100 contiguous nucleotides. Suitably, the degree of identity with regard to a nucleotide sequence may be determined over the whole sequence.
Amino Acid Mutations
The sequences may also have deletions, insertions or substitutions of amino acid residues which produce a silent change and result in a functionally equivalent substance. Deliberate amino acid substitutions may be made on the basis of similarity in polarity, charge, solubility, hydrophobicity, hydrophilicity, and/or the amphipathic nature of the residues as long as the secondary binding activity of the substance is retained. For example, negatively charged amino acids include aspartic acid and glutamic acid; positively charged amino acids include lysine and arginine; and amino acids with uncharged polar head groups having similar hydrophilicity values include leucine, isoleucine, valine, glycine, alanine, asparagine, glutamine, serine, threonine, phenylalanine, and tyrosine.
Conservative substitutions may be made, for example according to the Table below. Amino acids in the same block in the second column and preferably in the same line in the third column may be substituted for each other:

















ALIPHATIC
Non-polar
G A P





I L V




Polar - uncharged
C S T M





N Q




Polar - charged
D E





K R



AROMATIC

H F W Y










The present invention also encompasses homologous substitution (substitution and replacement are both used herein to mean the interchange of an existing amino acid residue, with an alternative residue) that may occur i.e. like-for-like substitution such as basic for basic, acidic for acidic, polar for polar etc. Non-homologous substitution may also occur i.e. from one class of residue to another or alternatively involving the inclusion of unnatural amino acids such as ornithine (hereinafter referred to as Z), diaminobutyric acid ornithine (hereinafter referred to as B), norleucine ornithine (hereinafter referred to as O), pyriylalanine, thienylalanine, naphthylalanine and phenylglycine. Replacements may also be made by unnatural amino acids.
Variant amino acid sequences may include suitable spacer groups that may be inserted between any two amino acid residues of the sequence including alkyl groups such as methyl, ethyl or propyl groups in addition to amino acid spacers such as glycine or β-alanine residues. A further form of variation, involves the presence of one or more amino acid residues in peptoid form, will be well understood by those skilled in the art. For the avoidance of doubt, “the peptoid form” is used to refer to variant amino acid residues wherein the α-carbon substituent group is on the residue's nitrogen atom rather than the α-carbon. Processes for preparing peptides in the peptoid form are known in the art, for example Simon R J et al., PNAS (1992) 89(20), 9367-9371 and Horwell D C, Trends Biotechnol. (1995) 13(4), 132-134.
Nucleotide Sequences
Nucleotide sequences for use in the present invention or encoding a polypeptide having the specific properties defined herein may include within them synthetic or modified nucleotides. A number of different types of modification to oligonucleotides are known in the art. These include methylphosphonate and phosphorothioate backbones and/or the addition of acridine or polylysine chains at the 3′ and/or 5′ ends of the molecule. For the purposes of the present invention, it is to be understood that the nucleotide sequences described herein may be modified by any method available in the art. Such modifications may be carried out in order to enhance the in vivo activity or life span of nucleotide sequences.
The present invention also encompasses the use of nucleotide sequences that are complementary to the sequences discussed herein, or any derivative, fragment or derivative thereof. If the sequence is complementary to a fragment thereof then that sequence can be used as a probe to identify similar coding sequences in other organisms etc.
Polynucleotides which are not 100% homologous to the sequences of the present invention but fall within the scope of the invention can be obtained in a number of ways. Other variants of the sequences described herein may be obtained for example by probing DNA libraries made from a range of individuals, for example individuals from different populations. In addition, other viral/bacterial, or cellular homologues particularly cellular homologues found in plant cells, may be obtained and such homologues and fragments thereof in general will be capable of selectively hybridising to the sequences shown in the sequence listing herein. Such sequences may be obtained by probing cDNA libraries made from or genomic DNA libraries from other plant species, and probing such libraries with probes comprising all or part of any one of the sequences in the attached sequence listings under conditions of medium to high stringency. Similar considerations apply to obtaining species homologues and allelic variants of the polypeptide or nucleotide sequences of the invention.
Variants and strain/species homologues may also be obtained using degenerate PCR which will use primers designed to target sequences within the variants and homologues encoding conserved amino acid sequences within the sequences of the present invention. Conserved sequences can be predicted, for example, by aligning the amino acid sequences from several variants/homologues. Sequence alignments can be performed using computer software known in the art. For example the GCG Wisconsin PileUp program is widely used.
The primers used in degenerate PCR will contain one or more degenerate positions and will be used at stringency conditions lower than those used for cloning sequences with single sequence primers against known sequences.
Alternatively, such polynucleotides may be obtained by site directed mutagenesis of characterised sequences. This may be useful where for example silent codon sequence changes are required to optimise codon preferences for a particular host cell in which the polynucleotide sequences are being expressed. Other sequence changes may be desired in order to introduce restriction polypeptide recognition sites, or to alter the property or function of the polypeptides encoded by the polynucleotides.
Polynucleotides (nucleotide sequences) of the invention may be used to produce a primer, e.g. a PCR primer, a primer for an alternative amplification reaction, a probe e.g. labelled with a revealing label by conventional means using radioactive or non-radioactive labels, or the polynucleotides may be cloned into vectors. Such primers, probes and other fragments will be at least 15, preferably at least 20, for example at least 25, 30 or 40 nucleotides in length, and are also encompassed by the term polynucleotides of the invention as used herein.
Polynucleotides such as DNA polynucleotides and probes according to the invention may be produced recombinantly, synthetically, or by any means available to those of skill in the art. They may also be cloned by standard techniques.
In general, primers will be produced by synthetic means, involving a stepwise manufacture of the desired nucleic acid sequence one nucleotide at a time. Techniques for accomplishing this using automated techniques are readily available in the art.
Longer polynucleotides will generally be produced using recombinant means, for example using a PCR (polymerase chain reaction) cloning techniques. This will involve making a pair of primers (e.g. of about 15 to 30 nucleotides) flanking a region of the enzyme sequence which it is desired to clone, bringing the primers into contact with mRNA or cDNA obtained from a plant cell, performing a polymerase chain reaction under conditions which bring about amplification of the desired region, isolating the amplified fragment (e.g. by purifying the reaction mixture on an agarose gel) and recovering the amplified DNA. The primers may be designed to contain suitable restriction enzyme recognition sites so that the amplified DNA can be cloned into a suitable cloning vector.
Enzyme Formulation and Dosage
Enzymes used in the methods of the invention can be formulated or modified, e.g., chemically modified, to enhance oil solubility, stability, activity or for immobilization. For example, enzymes used in the methods of the invention can be formulated to be amphipathic or more lipophilic. For example, enzymes used in the methods of the invention can be encapsulated, e.g., in liposomes or gels, e.g., alginate hydrogels or alginate beads or equivalents. Enzymes used in the methods of the invention can be formulated in micellar systems, e.g., a ternary micellar (TMS) or reverse micellar system (RMS) medium. Enzymes used in the methods of the invention can be formulated as described in Yi (2002) J. of Molecular Catalysis B: Enzymatic, Vol. 19, pgs 319-325.
The enzymatic reactions of the methods of the invention, e.g. the step of contacting the oil with an enzyme which hydrolyses a prime (e.g. a′ or b) stereoisomer of chlorophyll or a chlorophyll derivative, can be done in one reaction vessel or multiple vessels. In one aspect, the enzymatic reactions of the methods of the invention are done in a vegetable oil refining unit or plant.
The method of the invention can be practiced with immobilized enzymes, e.g. an immobilized chlorophyllase, pheophytinase and/or pyropheophytinase. The enzyme can be immobilized on any organic or inorganic support. Exemplary inorganic supports include alumina, celite, Dowex-1-chloride, glass beads and silica gel. Exemplary organic supports include DEAE-cellulose, alginate hydrogels or alginate beads or equivalents. In various aspects of the invention, immobilization of the enzyme can be optimized by physical adsorption on to the inorganic support. Enzymes used to practice the invention can be immobilized in different media, including water, Tris-HCl buffer solution and a ternary micellar system containing Tris-HCl buffer solution, hexane and surfactant. The enzyme can be immobilized to any type of substrate, e.g. filters, fibers, columns, beads, colloids, gels, hydrogels, meshes and the like.
The enzyme may be dosed into the oil in any suitable amount. For example, the enzyme may be dosed in a range of about 0.001 to 10 U/g of the composition, preferably 0.01 to 1 U/g, e.g. 0.01 to 0.1 U/g of the oil. One unit is defined as the amount of enzyme which hydrolyses 1 μmol of substrate (e.g. chlorophyll a or b, pheophytin a or b and/or pyropheophytin a or b, or a prime (e.g. a′ or b′) stereoisomer thereof) per minute at 40° C., e.g. under assay conditions as described in J. Biol. Chem. (1961) 236: 2544-2547.
Enzyme Reaction Conditions
In general the oil may be incubated (or admixed) with the enzyme between about 5° C. to and about 100° C., more preferably between 10° C. to about 90° C., more preferably between about 15° C. to about 80° C., more preferably between about 20° C. to about 75° C.
At higher temperatures pheophytin is decomposed to pyropheophytin, which is generally less preferred because some chlorophyllases are less active on pyropheophytin compared to pheophytin. In addition, the chlorophyllase degradation product of pyropheophytin, pyropheophorbide, is less water soluble compared to pheophorbide and thus more difficult to remove from the oil afterwards. The enzymatic reaction rate is increased at higher temperatures but it is favourable to keep the conversion of pheophytin to pyropheophytin to a minimum.
In view of the above, in particularly preferred embodiments the oil is incubated with the enzyme at below about 80° C., preferably below about 70° C., preferably at about 68° C. or below, preferably at about 65° C. or below, in order to reduce the amount of conversion to pyropheophytin. However, in order to keep a good reaction rate it is preferred to keep the temperature of the oil above 50° C. during incubation with the enzyme. Accordingly preferred temperature ranges for the incubation of the enzyme with the oil include about 50° C. to below about 70° C., about 50° C. to about 65° C. and about 55° C. to about 65° C.
Preferably the temperature of the oil may be at the desired reaction temperature when the enzyme is admixed therewith. The oil may be heated and/or cooled to the desired temperature before and/or during enzyme addition. Therefore in one embodiment it is envisaged that a further step of the process according to the present invention may be the cooling and/or heating of the oil.
Suitably the reaction time (i.e. the time period in which the enzyme is incubated with the oil), preferably with agitation, is for a sufficient period of time to allow hydrolysis of chlorophyll and chlorophyll derivatives, especially prime (e.g. a′ or b) stereoisomers thereof, to form e.g. phytol and chlorophyllide, pheophorbide and/or pyropheophorbide. For example, the reaction time may be at least about 1 minute, more preferable at least about 5 minutes, more preferably at least about 10 minutes. In some embodiments the reaction time may be between about 15 minutes to about 6 hours, preferably between about 15 minutes to about 60 minutes, preferably about 30 to about 120 minutes. In some embodiments, the reaction time may up to 6 hours.
Preferably the process is carried out between about pH 4.0 and about pH 10.0, more preferably between about pH 5.0 and about pH 10.0, more preferably between about pH 6.0 and about pH 10.0, more preferably between about pH 5.0 and about pH 7.0, more preferably between about pH 5.0 and about pH 7.0, more preferably between about pH 6.5 and about pH 7.0, e.g. at about pH 7.0 (i.e. neutral pH). In one embodiment preferably the process is carried out between about pH 5.5 and pH 6.0.
Suitably the water content of the oil when incubated (or admixed) with the enzyme is between about 0.5 to about 5% water, more preferably between about 1 to about 3% and more preferably between about 1.5 and about 2%.
When an immobilised enzyme is used, suitably the water activity of the immobilised enzyme may be in the range of about 0.2 to about 0.98, preferably between about 0.4 to about 0.9, more preferably between about 0.6 to about 0.8.
Oil Separation
Following an enzymatic treatment step using an enzyme according to the present invention, in one embodiment the treated liquid (e.g. oil) is separated with an appropriate means such as a centrifugal separator and the processed oil is obtained. Upon completion of the enzyme treatment, if necessary, the processed oil can be additionally washed with water or organic or inorganic acid such as, e.g., acetic acid, citric acid, phosphoric acid, succinic acid, and the like, or with salt solutions.
Chlorophyll and/or Chlorophyll Derivative Removal
The process of the present invention involving an enzyme treatment typically reduces the level of chlorophyll and/or chlorophyll derivatives in the oil, especially prime (e.g. a′ or b′) stereoisomers thereof. For example, the process may reduce the concentration of chlorophyll a or b, pheophytin a or b and/or pyropheophytin a or b, or prime (e.g. a′ or b′) stereoisomers thereof by at least 5%, at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% or at least 99%, compared to the concentration of chlorophyll, pheophytin and/or pyropheophytin (by weight) present in the oil before treatment. Thus in particular embodiments, the concentration of chlorophyll and/or chlorophyll derivatives, or prime (e.g. a′ or b′) stereoisomers thereof, in the oil after treatment may be less than 100, less than 50, less than 30, less than 10, less than 5, less than 1, less than 0.5, less than 0.1 mg/kg or less than 0.02 mg/kg, based on the total weight of the oil.
If an enzyme which is stereospecific for non-prime forms of chlorophyll or chlorophyll derivatives is used, following treatment with the enzyme the oil typically comprises a reduced proportion of non-prime stereoisomers, compared to the total amount of non-prime and prime stereoisomers remaining in the oil (see Example 3 and FIG. 48 below). In contrast, in embodiments of the present invention, the enzymes used in the present method typically have reduced stereospecificity for non-prime forms of chlorophyll and chlorophyll derivatives, i.e. the enzymes are typically capable of hydrolyzing both prime and non-prime forms. Consequently following a treatment step of the present invention, the proportion of non-prime stereoisomers remaining in the oil typically falls less than when a stereospecific enzyme is used.
It has been found that under typical conditions, crude oils (e.g. crude soy bean oil or rape seed oil) may comprise around 70% non-prime (e.g. pheophytin a) and 30% prime (e.g. pheophytin a′) stereoisomers. In one embodiment, following treatment with the enzyme the oil comprises at least 50% non-prime (e.g. a and/or b) stereoisomers of chlorophyll or the chlorophyll derivative, based on the total amount of non-prime (e.g. a and/or b) and prime (e.g. a′ and/or a′) stereoisomers of chlorophyll or the chlorophyll derivative in the oil. More preferably, the oil comprises at least 55%, at least 60% or at least 65% non-prime stereoisomers of chlorophyll or the chlorophyll derivative after treatment.
In one embodiment, following treatment with the enzyme the oil comprises at least 50%, at least 60% or at least 65% pheophytin a, based on the total amount of pheophytin a and pheophytin a′ in the oil. In one embodiment, following treatment with the enzyme the oil comprises at least 50%, at least 60% or at least 65% pheophytin b, based on the total amount of pheophytin b and pheophytin b′ in the oil.
In these embodiments, typical conditions may be, for example, about 20° C. to about 70° C. (e.g. about 40° C. or about 60° C.), pH 5 to 8 (e.g. about pH 6.0 or about pH 7.0) and water content of 1 to 3% (e.g. about 2%). The treatment time may comprise, for example, at least 1 hour, preferably 2 hours or more, more preferably 4 hours or more.
Further Processing Steps
In a typical plant oil processing method, oil is extracted in hexane, the crude vegetable oil is degummed, optionally caustic neutralized, bleached using, e.g. clay adsorption with subsequent clay disposal, and deodorized to produce refined, bleached and deodorized or RBD oil (see FIG. 50). The need for the degumming step depends on phosphorus content and other factors. The process of the present invention can be used in conjunction with processes based on extraction with hexane and/or enzyme assisted oil extraction (see Journal of Americal Oil Chemists' Society (2006), 83 (11), 973-979). In general, the process of the invention may be performed using oil processing steps as described in Bailey's Industrial Oil and Fat Products (2005), 6th edition, Ed. by Fereidoon Shahidi, John Wiley & Sons.
In embodiments of the present invention, an enzymatic reaction involving application of the enzyme capable of hydrolyzing chlorophyll or a chlorophyll derivative may be performed at various stages in this process, are shown in FIG. 50. In particular embodiments, the enzyme is contacted with the oil before the degumming step. In another embodiment, the enzyme may be contacted with the oil during a water degumming step. In another embodiment, the enzyme is contacted with water degummed oil, but before degumming is complete (e.g. before a total degumming or caustic neutralization step).
Further processing steps, after treatment with the enzyme, may assist in removal of the products of enzymatic hydrolysis of chlorophyll and/or chlorophyll derivatives. For instance, further processing steps may remove chlorophyllide, pheophorbide, pyropheophorbide and/or phytol.
Degumming
The degumming step in oil refining serves to separate phosphatides by the addition of water. The material precipitated by degumming is separated and further processed to mixtures of lecithins. The commercial lecithins, such as soybean lecithin and sunflower lecithin, are semi-solid or very viscous materials. They consist of a mixture of polar lipids, primarily phospholipids such as phosphatidylcholine with a minor component of triglycerides. Thus as used herein, the tem “degumming” means the refining of oil by removing phospholipids from the oil. In some embodiments, degumming may comprise a step of converting phosphatides (such as lecithin and phospholipids) into hydratable phosphatides.
The process of the invention can be used with any degumming procedure, particularly in embodiments where the chlorophyll- or chlorophyll derivative-hydrolyzing enzyme is contacted with the oil before the degumming step. Thus suitable degumming methods include water degumming, ALCON oil degumming (e.g., for soybeans), safinco degumming, “super degumming,” UF degumming, TOP degumming, uni-degumming, dry degumming and ENZYMAXTM degumming. See e.g. U.S. Pat. Nos. 6,355,693; 6,162,623; 6,103,505; 6,001,640; 5,558,781; 5,264,367, 5,558,781; 5,288,619; 5,264,367; 6,001,640; 6,376,689; WO 0229022; WO 98118912; and the like. Various degumming procedures incorporated by the methods of the invention are described in Bockisch, M. (1998), Fats and Oils Handbook, The extraction of Vegetable Oils (Chapter 5), 345-445, AOCS Press, Champaign, Ill.
Water degumming typically refers to a step in which the oil is incubated with water (e.g. 1 to 5% by weight) in order to remove phosphatides. Typically water degumming may be performed at elevated temperature, e.g. at 50 to 90° C. The oil/water mixture may be agitated for e.g. 5 to 60 minutes to allow separation of the phosphatides into the water phase, which is then removed from the oil.
Acid degumming may also be performed. For example, oil may be contacted with acid (e.g. 0.1 to 0.5% of a 50% solution of citric or malic acid) at 60 to 70° C., mixed, contacted with 1 to 5% water and cooled to 25 to 45° C.
Further suitable degumming procedures for use with the process of the present invention are described in WO 2006/008508. In one embodiment the process comprises contacting the chlorophyll- or chlorophyll derivative-hydrolyzing enzyme with the oil and subsequently performing an enzymatic degumming step using an acyltransferase as described in WO 2006/008508. Acyltransferases suitable for use in the process are also described in WO 2004/064537, WO 2004/064987 and WO 2009/024736. Any enzyme having acyltransferase activity (generally classified as E.C.2.3.1) may be used, particularly enzymes comprising the amino acid sequence motif GDSX, wherein X is one or more of the following amino acid residues: L, A, V, I, F, Y, H, Q, T, N, M or S. In one embodiment, acyltransferase is a mutant Aeromonas salmonicida mature lipid acyltransferase (GCAT) with a mutation of Asn80Asp.
In another embodiment, the process comprises a degumming step using a phospholipase. Any enzyme having e.g. a phospholipase A1 (E.C.3.1.1.32) or a phospholipase A2 (E.C.3.1.1.4) activity may be used, for example Lecitase Ultra® or pancreatic phospholipase A2 (Novozymes, Denmark). In one embodiment the process comprises contacting the chlorophyll- or chlorophyll derivative-hydrolyzing enzyme with the oil before an enzymatic degumming step using a phospholipase, for example using a degumming step as described in U.S. Pat. No. 5,264,367, EP 0622446, WO 00/32758 or Clausen (2001) “Enzymatic oil degumming by a novel microbial phospholipase,” Eur. J. Lipid Sci. Technol. 103:333-340.
In another embodiment, the degumming step may be a water degumming step. In a further embodiment, an enzymatic degumming step using an enzyme such as phospholipase C (IUB 3.1.4.1) may be used. Polypeptides having phospholipase C activity which are may be used in a degumming step are disclosed, for example, in WO2008143679, WO2007092314, WO2007055735, WO2006009676 and WO03089620. A suitable phospholipase C for use in the present invention is Purifine®, available from Verenium Corporation, Cambridge, Mass.
Acid Treatment/Caustic Neutralization
In some embodiments, an acid treatment/caustic neutralization step may be performed in order to further reduce phospholipid levels in the oil after water degumming. In another embodiment, a single degumming step comprising acid treatment/caustic neutralization may be performed. Such methods are typically referred to as total degumming or alkali refining.
It has been found that an acid treatment/caustic neutralization step is particularly effective in removing products of the enzymatic hydrolysis of chlorophyll, e.g. chlorophyllide, pheophorbide and pyropheophorbide. Thus this step may be performed at any stage in the process after the enzyme treatment step. For example, such a step may comprise addition of an acid such as phosphoric acid followed by neutralization with an alkali such as sodium hydroxide. Following an acid/caustic neutralization treatment compounds such as chlorophyllide, pheophorbide and pyropheophorbide are extracted from the oil in an aqueous phase.
In such methods, the oil is typically first contacted with 0.05 to 0.5% by weight of concentrated phosphoric acid, e.g. at a temperature of 50 to 90° C., and mixed to help precipitate phosphatides. The contact time may be, e.g. 10 seconds to 30 minutes. Subsequently an aqueous solution of an alkali (e.g. 1 to 20% aqueous sodium hydroxide) is added, e.g. at a temperature of 50 to 90° C., followed by incubation and mixing for 10 seconds to 30 minutes. The oil may then be heated to about 90° C. and the aqueous soap phase separated from the oil by centrifugation.
Optionally, further wash steps with e.g. sodium hydroxide or water may also be performed.
Chlorophyllide, Pheophorbide and Pyropheophorbide Removal
The method of the present invention may optionally involve a step of removing phytol-free derivatives of chlorophyll such as chlorophyllide, pheophorbide and pyropheophorbide, including prime and non-prime forms thereof. Such products may be present in the composition due to the hydrolysis of chlorophyll or a chlorophyll derivative by the enzyme of the invention, or may be present naturally, as a contaminant, or as an undesired component in a processed product. Pyropheophorbide may also be present in the composition due to the breakdown of pheophorbide, which may itself be produced by the activity of an enzyme having pheophytinase activity on pheophytin, or pheophorbide may be formed from chlorophyllide following the action of chlorophyllase on chlorophyll (see FIG. 1). Processing conditions used in oil refining, in particular heat, may favour the formation of pyropheophorbide as a dominant component, for instance by favouring the conversion of pheophytin to pyropheophytin, which is subsequently hydrolysed to pyropheophorbide.
In one embodiment the process of the present invention reduces the level of chlorophyllide, pheophorbide and/or pyropheophorbide in the oil, compared to either or both of the levels before and after enzyme treatment. Thus in some embodiments the chlorophyllide, pheophorbide and/or pyropheophorbide concentration may increase after enzyme treatment. Typically the process involves a step of removing chlorophyllide, pheophorbide and/or pyropheophorbide such that the concentration of such products is lower than after enzyme treatment. Preferably the chlorophyllide, pheophorbide and/or pyropheophorbide produced by this enzymatic step is removed from the oil, such that the final level of these products in the oil is lower than before enzyme treatment.
For example, the process may reduce the concentration of chlorophyllide, pheophorbide and/or pyropheophorbide, including prime and non-prime forms thereof, by at least 5%, at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% or at least 99%, compared to the concentration of chlorophyllide, pheophorbide and/or pyropheophorbide (by weight) present in the oil before the chlorophyllide, pheophorbide and/or pyropheophorbide removal step, i.e. before or after enzyme treatment. Thus in particular embodiments, the chlorophyllide, pheophorbide and/or pyropheophorbide concentration in the oil after the removal step may be less than 100, less than 50, less than 30, less than 10, less than 5, less than 1, less than 0.5, less than 0.1 mg/kg, or less than 0.02 mg/kg, based on the total weight of the composition (e.g a vegetable oil).
It is an advantage of the present process that reaction products such as chlorophyllide, pheophorbide and/or pyropheophorbide may be simply and easily removed from the oil by a step such as acid treatment/caustic neutralization. Thus in preferred embodiments chlorophyll and chlorophyll derivatives may be substantially removed from the oil without the need for further processing steps such as clay and/or silica treatment and deodorization (as indicated by the dashed boxes shown in FIG. 50).
Clay Treatment
It is particularly preferred that the process does not comprise a clay treatment step. Avoiding the use of clay is advantageous for the reasons described earlier, in particular the reduction in cost, the reduced losses of oil through adherence to the clay and the increased retention of useful compounds such as carotenoids and tocopherol.
In some embodiments, the process may be performed with no clay treatment step and no deodorization step, which results in an increased concentration of such useful compounds in the refined oil, compared to a process involving clay treatment.
Silica Treatment
Although not always required, in some embodiments the process may comprise a step of silica treatment, preferably subsequent to the enzyme treatment. For example, the method may comprise use of an adsorbent-free or reduced adsorbent silica refining devices and processes, which are known in the art, e.g., using TriSyl Silica Refining Processes (Grace Davison, Columbia, Md.), or, SORBSIL RTM silicas (INEOS Silicas, Joliet, Ill.).
The silica treatment step may be used to remove any remaining chlorophyllide, pheophorbide and/or pyropheophorbide or other polar components in the oil. For example, in some embodiments a silica treatment step may be used as an alternative to an acid treatment/caustic neutralization (total degumming or alkali refining) step.
In one embodiment the process comprises a two-stage silica treatment, e.g. comprising two silica treatment steps separated by a separation step in which the silica is removed, e.g. a filtration step. The silica treatment may be performed at elevated temperature, e.g. at above about 30° C., more preferably about 50 to 150° C., about 70 to 110° C., about 80 to 100° C. or about 85 to 95° C., most preferably about 90° C.
Deodorization
In some embodiments, the process may comprise a deodorization step, typically as the final refining step in the process. In one embodiment, deodorization refers to steam distillation of the oil, which typically removes volatile odor and flavor compounds, tocopherol, sterols, stanols, carotenoids and other nutrients. Typically the oil is heated to 220 to 260° C. under low pressure (e.g. 0.1 to 1 kPa) to exclude air. Steam (e.g. 1-3% by weight) is blown through the oil to remove volatile compounds, for example for 15 to 120 minutes. The aqueous distillate may be collected.
In another embodiment, deodorization may be performed using an inert gas (e.g. nitrogen) instead of steam. Thus the deodoriztion step may comprise bubble refining or sparging with an inert gas (e.g. nitrogen), for example as described by A. V. Tsiadi et al. in “Nitrogen bubble refining of sunflower oil in shallow pools”, Journal of the American Oil Chemists' Society (2001), Volume 78 (4), pages 381-385. The gaseous phase which has passed through the oil may be collected and optionally condensed, and/or volatile compounds extracted therefrom into an aqueous phase.
In some embodiments, the process of the present invention is performed with no clay treatment but comprising a deodorization step. Useful compounds (e.g. carotenoids, sterols, stanols and tocopherol) may be at least partially extracted from the oil in a distillate (e.g. an aqueous or nitrogenous distillate) obtained from the deodorization step. This distillate provides a valuable source of compounds such as carotenoids and tocopherol, which may be at least partially lost by entrainment in a process comprising clay treatment.
The loss of tocopherol during bleaching depends on bleaching conditions and the type of clay applied, but 20-40% removal of tocopherol in the bleaching step has been reported (K. Bold, M, Kubo, T. Wada, and T. Tamura, ibid., 69, 323 (1992)). During processing of soy bean oil a loss of 13% tocopherol in the bleaching step has been reported (S. Ramamurthi, A. R. McCurdy, and R. T. Tyler, in S. S. Koseoglu, K. C. Rhee, and R. F. Wilson, eds., Proc. World Conf. Oilseed Edible Oils Process, vol. 1, AOCS Press, Champaign, Ill., 1998, pp. 130-134).
Carotenoids may be removed from the oil during deodorization in both clay-treated and non-clay-treated oil. Typically the removal of coloured carotenoids is controlled in order to produce an oil having a predetermined colour within a specified range of values. The level of carotenoids and other volatile compounds in the refined oil can be varied by modifying the deodorization step. For instance, in an embodiment where it is desired to retain a higher concentration of carotenoids in the oil, the deodorization step may be performed at a lower temperature (e.g. using steam at 200° C. or below). In such embodiments it is particularly preferable to avoid a clay treatment step, since this will result in a higher concentration of carotenoids in the refined oil.
Further Enzyme Treatments
In further aspects, the processes of the invention further comprise use of lipid acyltransferases, phospholipases, proteases, phosphatases, phytases, xylanases, amylases (e.g. α-amylases), glucanases, polygalacturonases, galactolipases, cellulases, hemicellulases, pectinases and other plant cell wall degrading enzymes, as well as mixed enzyme preparations and cell lysates. In alternative aspects, the processes of the invention can be practiced in conjunction with other processes, e.g., enzymatic treatments, e.g., with carbohydrases, including cellulase, hemicellulase and other side degrading activities, or, chemical processes, e.g., hexane extraction of soybean oil. In one embodiment the method of the present invention can be practiced in combination with a method as defined in WO 2006031699.
The invention will now be further illustrated with reference to the following non-limiting examples.
EXAMPLE 1
Identification and Cloning of Chlorophyllases
Using different approaches (including BLAST) to search the NCBI databases, several sequences were identified as chlorophyllases or sequences having homology to chlorophyllases. The names of the sequences, their origin and NCBI database accession numbers are listed in Table 1.







TABLE 1







Chlorophyllases with accession numbers and names used herein.









Organism
Database acc. no.
CHL name





Arabidopsis thaliana
AAG12547
ARA_CHL


Arabidopsis thaliana
NP_199199
ARA_CHL2


Citrus sinensis
AAF59834
CIT_CHL


Triticum aestivum
BT009214
TRI_CHL


Triticum aestivum
BT008923
TRI_CHL2


Brassica oleracea
AAN51935
BRA_CHL


Brassica oleracea
AAN51933
BRA_CHL1


Brassica oleracea
AAN51934
Brass_CHL2


Zea Mays
ACN32030
ZEA_CHL


Zea Mays
ACG44273
ZEA_CHL2


Phyllostachys edulis
FP092915
BAM_CHL


Chenopodium album
Q9LE89
CHE_CHL


Ricinus communis
XP_002517075
CB_CHL


Glycine max
BAF43704
GlyMax_CHL


Ginkgo biloba
AAP44978
Gin_CHL


Pachira macrocarpa
ACO50429
PAC_CHL2


Populus trichocarpa
XP_002315752
POP_CHL


Sorghum bicolor
XP_002459848
Sor_CHL


Sorghum bicolor
XP_002445588
SORG_CHL


Vitis vinifera
XP_002273926
Vitis_CHL


Physcomitrella patens
EDQ81786
PHYS_CHL


Aquilegia

AQU_CHL


Brachypodium distachyon
ADDN01001446
BRACH_CHL


Medicago truncatula
ACJ85964
MED_CHL


Piper betle
ABI96085
PIP_CHL


Lotus japonicus
AK338339
LOTUS_CHL


Oryza sativa Indica
EEC66959
ORYI_CHL


Oryza sativa Japonica
NP_001064620
ORYJ1_CHL


Oryza sativa Japonica
EEE50970
ORYJ2_CHL


Picea sitchensis
ACN40275
PICEA_CHL


Chlamydomonas
XP_001695577
CHL_CHL









Chlorophyllase Sequences

The chlorophyllase sequences identified from the search in NCBI databases are listed in Table 1 and the amino acid sequences are shown in FIGS. 12 to 42 (SEQ ID NO:s 1 to 31). Multiple sequence alignment of the selected chlorophyllase amino acid sequences showed several conserved residues distributed throughout the sequences. The motif GHSRG (SEQ ID NO: 32) containing the Ser active site is highly conserved. The alignment resulted in a phylogenetic tree as shown in FIG. 43.
Cloning in E. Coli 
Synthetic genes encoding the chlorophyllases shown in Table 1 were prepared. Each gene was codon optimized for expression in E. coli. For cloning purposes the genes were extended in the 5′-end to contain a restriction site for NheI and in the 3′-end to contain a restriction site for XhoI.
Following digestion with NheI and XhoI restriction enzymes the synthetic DNA was ligated into the E. coli expression vector pET-28a(+) (Novagen) digested with the same restriction enzymes. This vector includes a T7 promoter with a Lac operator for controlling expression of inserted genes. The chlorophyllase genes were fused in frame to a His tag and a thrombin cleavage site for purification (example shown in FIG. 4). The resulting constructs (an example pET28-TRI_CHL is shown in FIG. 5), were transformed into competent E. coli TOP10 cells (Invitrogen), and plasmids were isolated from transformed colonies and subjected to nucleotide sequencing to verify the correct sequence and that all fusions were as expected.
Expression in E. Coli 
For expression the plasmids were transformed into the expression host E. coli BL21(DE3) (Novagen). The cells were cultured at 37° C. in LB containing carbenicillin (50 mg/ml) until OD600 0.6-0.8. For induction the culture was added 1 mM IPTG and incubated at 25° C. for another 20-24 h before harvesting the cells by centrifugation. The recombinant chlorophyllases were released from the cell pellet by sonication and cellular debris removed by centrifugation.
Cloning in B. Subtilis 
For cloning and expression in B. subtilis the synthetic genes encoding the chlorophyllases (Table 1) were codon optimized for B. subtilis. The genes were cloned in two different plasmids, one for intracellular expression and one for secretion into the culture medium (extracellular expression).
Extracellular Expression
The genes were extended in the 5′-end to contain a restriction site for BssHII and part of an AprE signal sequence for in frame fusion to the AprE signal sequence as well as a sequence encoding the amino acids A G K to facilitate signal sequence cleavage. In the 3′ end the genes were extended with a restriction site for Pad. The BssHII and Pad digested genes were ligated into B. subtilis expression vector pBN digested with the same restriction enzymes. The pBN vector contains an AprE promoter and an AprE signal sequence. An example of the resulting fusion of the chlorophyllase genes with the AprE signal sequence is shown in FIG. 6. The final constructs (an example pBN-TRI_CHL is shown in FIG. 7), were transformed into competent E. coli TOP10 cells (Invitrogen), and plasmids were isolated from transformed colonies and subjected to nucleotide sequencing to verify the correct sequence and that all fusions were as expected.
For expression the plasmids were transformed into the expression host B. subtilis BG6002. The cells were cultured at 33° C. in Grant's II medium for 68 h. The recombinant chlorophyllases were isolated from the culture medium after precipitation of the cells by centrifugation.
Intracellular Expression
The genes were extended in the 5′-end to contain a restriction site for SpeI to allow fusion of the genes directly to the AprE promoter in a B. subtilis expression vector pBN without the AprE signal sequence. In the 3′ end the genes were extended with a restriction site for HindIII. The fusion of a chlorophyllase gene to the AprE promoter is shown in FIG. 8. The resulting constructs (an example pBN-Spe-TRI_CHL is shown in FIG. 9), were transformed into compentent E. coli TOP 10 cells (Invitrogen), and plasmids were isolated from transformed colonies and subjected to nucleotide sequencing to verify the correct sequence and that all fusions were as expected.
For expression the plasmids were transformed into the expression host B. subtilis BG6002. The cells were cultured at 33° C. in Grant's II medium for 68 h. The recombinant chlorophyllases were released from the cultures by treatment with 1 mg/ml Lysozyme for 1 h at 30° C. Cellular debris was removed by centrifugation and the chlorophyllases were recovered from the supernatant.
Cloning in S. Lividans 
For cloning and expression in S. lividans the synthetic genes encoding the chlorophyllases (Table 1) were codon optimized for S. lividans. For cloning purposes the genes were extended in the 5′-end to contain a restriction site for NheI and part of a Cel A signal sequence for in frame fusion to the Cel A signal sequence. The 3′-end was extended to contain a restriction site for BamHI. The fusion of a chlorophyllase gene (TRI_CHL) to the Cel A signal sequence is shown in FIG. 10. The resulting constructs (an example pKB-TRI_CHL is shown in FIG. 11), were transformed into compentent E. coli TOP10 cells (Invitrogen), and plasmids were isolated from transformed colonies and subjected to nucleotide sequencing to verify the correct sequence and that all fusions were as expected.
Expression in S. Lividans 
For expression plasmids were transformed into protoplasts of the expression host S. lividans strain g3s3. The cells were pre-cultured for 48 h at 30° C. in TSG medium supplemented with thiostrepton. The pre-cultures were diluted 10× in Strept Pdxn2 modified medium and incubated at 30° C. for 96 h. The recombinant chlorophyllases were isolated from the culture medium after precipitation of the cells by centrifugation.
EXAMPLE 2
Activity of Chlorophyllases
A number of chlorophyllases were identified by genome mining as described above and expressed in E. coli. The extracts from E. coli harboring plasmids containing the chlorophyllase gene were analyzed for pheophytinase activity. The assay may be performed as described in EP10159327.5. Alternatively pheophytinase activity may be determined by a method as described above, e.g. HPLC-based methods. The results are shown in Table 2.
Pheophytinase activity may be determined based on hydrolysis of pheophytin a in a reaction buffer followed by fluorescent measurement of the generated pheophorbide a. The assay can also be adapted to employ pyropheophytin as a substrate. 1 U of enzyme activity is defined as hydrolysis of 1 μmole of pheophytin a or pyropheophytin per minute at 40° C.







TABLE 2







Pheophytinase activity of enzymes











Enzyme
Ferment
Activity U/ml















BAM_CHL
CoRe 112
0.32



CIT_CHL
CoRe 113-A
0.25



ARA_CHL
CoRe 114-A
5.19



CB_CHL
CoRe 127
0.10



GlyMax_CHL
Core133
0.010



Sor_CHL
Core134
6.14



ARA_CHL2
Core135
0.94



BRA_CHL1
Core136
1.21



SORG_CHL
CoRe 137-A
0.78



TRI_CHL2
Core138 -A
0.19



ZEA_CHL2
Core139
0.03



TRI_CHL
CoRe 20
0.18



BRACH_CHL
CoRe 156
1.50



PIP_CHL
CoRe 158
0.01



PICEA_CHL
CoRe 163
0.05



Control
Empty vector
0.000










The enzymes described in Table 2 were analyzed by western blot analysis using a primary antibody raised in rabbit against purified TRI_CHI. FIGS. 44 and 45 show that all enzymes from Table 2 react with the raised antibody.
EXAMPLE 3
Hydrolysis of Chlorophyll Derivatives in Plant Oils
Some of the enzymes were tested for the ability to degrade chlorophyll components in an oil system. The recipe is shown in Table 3. Crude rapeseed oil is scaled in a Wheaton glass and heated with magnetic stirring to 60° C. Water and enzyme are added. The sample is treated with high shear mixing for 20 seconds and incubated at 60° C. with magnetic stirring. Samples are taken out after 0.5, 2 and 4 hours reaction time. The samples are centrifuged and analysed by HPLC-MS.







TABLE 3







Recipe for testing chlorophyllases in oil system
















Units/ml

1
2
3
4
5
6



















Crude rape seed


10
10
10
10
10
10


AKK extracted no 11


water

ml
0.200
0.152
0.159
0.011
0.191
0.162


ARA_CHL2
0.62
ml

0.0484


BRA_CHL1
3.62
ml


0.0414


CB_CHL
2.11
ml



0.189


TRI_CHL
54.19
ml




0.009


SORG_CHL
0.78
ml





0.0385


Units/g oil


0.000
0.0030
0.0150
0.0400
0.0500
0.003


% Water


2.000
2.000
2.000
2.000
2.000
2.000


Temperature

° C.
60
60
60
60
60
60









The total levels of pheophytin a (pheophytin a+a′) as determined by HPLC-MS are shown in FIG. 46. The degradation of pyropheophytin a is shown in FIG. 47. All 5 enzyme candidates can degrade pheophytin and pheophytin but especially the activity on pyropheophytin varies significantly among the 5 tested enzymes.
In the oil samples treated with chlorophyllase we also analyzed the distribution of pheophytin stereoisomers a and a′. Surprisingly we found large differences in the distribution depending on the enzyme applied (see FIG. 48). For the BRA_CHL1 and TRI_CHL, the percentage of pheophytin a drops to around half of the initial level whereas ARA_CHL2 and CB_CHL show a distribution which is comparable to the control and initial level. Retaining the initial distribution of stereoisomers throughout the reaction is a clear advantage as this means that the overall reaction rate is not dependent on the epimerization of pheophytin a′ to a. These findings also indicate that ARA_CHL2 and CB_CHL are not very sensitive to the groups at C-132. These two enzymes also show much better activity on pyropheophytin, which has 2 hydrogen atoms at C-132 (see FIG. 47).
Substrate Specificity in an In Vitro Assay
The relative activities of the above enzymes on pheophytin and pyropheophytin in an in vitro assay system, e.g. as described in EP10159327.5, were measured. Table 4 gives the ratio of pheophytin to pyropheophytin activity.







TABLE 4







Ratio of pheophytin to pyropheophytin activity








Enzyme
Ratio of activity on pheophytin to pyropheophytin











SORG_CHL
173


ARA_CHL2
4


CB_CHL
4


TRI_CHL
45









It is clear that SORG_CHL has a relatively lower activity on pyropheophytin compared to TRI_CHL. The CB_CHL and ARA2_CHL show a different substrate specificity which is much improved towards pyropheophytin. These findings correlate with what is shown in FIGS. 46 to 48.
EXAMPLE 4
Relative Activity of Chlorophyllases on Pheophytin a and a′
Dosage response of chlorophyllases in crude rapeseed oil was tested according to the recipe in Table 5
















TABLE 5








Units/g

1
2
3
4
5
6
7





Crude rape seed


10
10
10
10
10
10
10


no 11, AAK


water

ml
0.200
0.176
0.153
0.106
0.011
0.184
0.173


CB_CHL, CoRe
2.12
ml

0.0236
0.0472
0.0943
0.1887


127-A. 2.12 U/ml


ARA_CHL CoRe 135
0.94
ml





0.0160
0.0266


CoRe 137-A SORG_CHL
0.78


Units/g oil


0.000
0.005
0.010
0.020
0.040
0.0015
0.003


Water

%
2.000
2.000
2.000
2.000
2.000
2.000
2.000


Temperature

° C.
60
60
60
60
60
60
60


pH


4.85
5.52
5.29
5.56
5.55
5.40
5.36






Units/g

8
9
10
11
12
13
14





Crude rape seed


10
10
10
10
10
10
10


no 11, AAK


water

ml
0.147
0.047
0.006
0.091
0.187
0.162
0.072


CB_CHL, CoRe
2.12
ml


0.0943


127-A. 2.12 U/ml


ARA_CHL CoRe 135
0.94
ml
0.0532
0.0532


CoRe 137-A SORG_CHL
0.78





0.0128
0.0385
0.1282


Units/g oil


0.005
0.005
0.020
0.050
0.001
0.003
0.010


Water

%
2.000
1.000
1.000
1.000
2.000
2.000
2.000


Temperature

° C.
60
60
60
60
60
60
60


pH


5.28
4.99
5.06
4.82
5.01
5.49
5.55









Samples were taken out after 1⁄2, 2 and 4 hours reaction time and analysed by HPLC-MS. In order to compare the activity of different chlorophyllases on the two isomers, the enzyme activity on both isomers was calculated at a substrate concentration which is half of the original concentration. The natural logarithm of the substrate concentration is plotted as a function of enzyme dosage (Units/g), as shown in FIG. 51 for Arabidopsis chlorophyllase (ARA_CHL2).
Based on the graph in FIG. 51, the activity of the enzyme on pheophytin a and a′ is calculated for the substrate concentration which is half the original concentration, as shown in Table 6.







TABLE 6







Calculation of ARA-CHL2 activity on pheophytin a and pheophytin a′













Pheophytin a′
Pheophytin_a′

Pheophytin_a
Pheophytin_a



Units/g oil
Ln (substrate μg/g)

Units/g oil
Ln (substrate μg/g)

















0
−0.203

0
0.766



0.0015
−0.541

0.0015
0.409



0.0025
−0.685

0.0025
0.259


Conc 1⁄2

−0.896
Conc 1⁄2

0.073


Slope

−195.3
Slope

−205.5


Intercept

−0.216
Intercept

0.752


Units for

0.003
Units for

0.003


conc1⁄2


conc1⁄2


Reciproc

287.1
Reciproc

302.5


μg/u


μg/u


Reciproc

574.2
Reciproc

605.0


μg/u/hr


μg/u/hr









Based on the enzyme activity at half the original substrate concentration, it is possible to compare different enzymes under the same conditions. In Table 7 the results from two different chlorophyllases are compared.







TABLE 7







Chlorophyllase activity on pheophytin


a and a′ isomers in crude rape seed oil











Pheophytin_a′
Pheophytin_a
Relative activity


Enzyme
μg/Unit/hr
μg/Unit/hr
a′/a





ARA_CHL2,
574
605
0.95


CoRe135


CB_CHL,
141
343
0.41


CoRe 127-A









The results in Table 7 indicate that ARA_CHL2 has almost the same activity on pheophytin a and a′ isomers. This is in agreement with the observations that the ratio between the two isomers does not change during enzymatic degradation with ARA_CRL2 (see FIG. 48). In contrast CB_CHL also shows significant hydrolytic activity on pheophytin a′. Expressed in terms of an activity ratios on pheophytin a compared to pheophytin a′ (i.e. the inverse of that shown in Table 7), ARA_CRL2 has an activity ratio of 1.05 and CB_CHL has an activity ratio of 2.44.
CONCLUSION
We have identified 31 chlorophyllase sequences and furthermore cloned and expressed these in E. coli, B. subtilis or S. lividans. Based on expression in E. coli we have detected pheophytinase activity (Table 2) in nearly half of the identified chlorophyllases and all of these reacted with antibody raised against TRI_CHL (FIGS. 44 and 45). In the protein extracts without detectable pheophytinase activity we could not detect any expressed chlorophyllase enzyme based on western blots with antibody raised against TRI_CHL.
When testing the chlorophyllase candidates in oil applications we found major differences in specificity for the pheophytin and pyropheophytin substrates. The ARA_CHL2 and CB_CHL show much better activity on pyropheophytin compared to the other candidates tested (FIG. 47). For these two candidates we also observed that the ratio of pheophytin a to a′ did not change significantly during incubation in oil trials. For the other candidates tested we saw a clear decrease in this ratio during incubation. The improved activity towards pyropheophytin for ARA_CHL2 and CB_CHL in oil assay was also measured in the in vitro assay using pheophytin and pyropheophytin as substrates (Table 4).
HPLC Analysis
In the examples herein, chlorophyll derivatives may in general be quantified by HPLC analysis according to the following method. HPLC analysis is performed using a method in general terms as described in “Determination of chlorophylls and carotenoids by high-performance liquid chromatography during olive lactic fermentation”, Journal of Chromatography, 585, 1991, 259-266.
The determination of pheophytin, pheophorbide, pyropheophytin and pyropheophorbide is performed by HPLC coupled to a diode array detector. The column employed in the method is packed with C18 material and the chlorophylls were separated by gradient elution. Peaks are assigned using standards of chlorophyll A and B from SigmaAldrich, e.g. based on the representative HPLC chromatogram from Journal of Chromatography, 585, 1991, 259-266 shown in FIG. 49.
All publications mentioned in the above specification are herein incorporated by reference. Various modifications and variations of the described methods and system of the present invention will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. Although the present invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in biochemistry and biotechnology or related fields are intended to be within the scope of the following claims.

## Claims

1. A process for treating a plant oil comprising a step of contacting the oil with an enzyme, wherein the enzyme is capable of hydrolysing an a′ or b′ stereoisomer of chlorophyll or a chlorophyll derivative and wherein the enzyme comprises a polypeptide having at least 90% sequence identity with the polypeptide of SEQ ID NO: 13.

2. The process according to claim 1, wherein the a′ or b′ stereoisomer is chlorophyll a′, pheophytin a′, chlorophyll b′ or pheophytin b′.

3. The process according to claim 1, wherein the enzyme is capable of hydrolysing an a′ stereoisomer of chlorophyll or the chlorophyll derivative.

4. The process according to claim 1, wherein the enzyme has an activity ratio of less than 10, where said activity ratio is (a) the ratio of the activity of the enzyme on the a stereoisomer of chlorophyll or the chlorophyll derivative to the activity of the enzyme on the a′ stereoisomer of chlorophyll or chlorophyll derivative, or (b) the ratio of the activity of the enzyme on the b stereoisomer of chlorophyll or chlorophyll derivative to the activity of the enzyme on the b′ stereoisomer of chlorophyll or the chlorophyll derivative.

5. The process according to claim 1, wherein following treatment with the enzyme the oil comprises (a) at least 50% a stereoisomers of chlorophyll or the chlorophyll derivative, based on the total amount of a and a′ stereoisomers of chlorophyll or the chlorophyll derivative in the oil; or (b) at least 50% b stereoisomers of chlorophyll or the chlorophyll derivative, based on the total amount of b and b′ stereoisomers of chlorophyll or the chlorophyll derivative in the oil.

6. The process according to claim 1, wherein the enzyme has an activity ratio of less than 10, wherein said activity ratio is the ratio of the activity of the enzyme on pheophytin to the activity of the enzyme on pyropheophytin.

7. The process according to claim 1, wherein the enzyme comprises a chlorophyllase, pheophytinase and/or pyropheophytinase activity.

8. The process according to claim 1, wherein the enzyme comprises the amino acid sequence GHSRG (SEQ ID NO: 32).

9. The process according to claim 1, wherein the enzyme is derived from Ricinus communis.