TRANSESTERIFICATION PROCESS

Abstract: Transesterification of a triglyceride is carried out in the presence of a lipase in a thermodynamically stable solution comprising a hydrophobic part, a surface active part and water.

Description: The present invention relates to a process for the transesterification of triglycerides in a thermo­ dynamically stable solution containing a hydrophobic part, a surface-active part, and water. Enzymatic processes are traditionally carried out in an aqueous solution. The reason for this is that water is the natural environment for enzymes which are proteins and thus hydrophilic. Many of the more common enzymes, such as proteases which split proteins, and lipases which split lipids, also use water as a reactant in the reaction which they catalyse. For example, mention may be made of the lipase-catalysed hydrolysis of a triglyceride: It has been found recently that some enzymes, among them the above-mentioned lipases, also function in many organic solvents. Surprisingly, it was found that the solvents which, besides water, are the best in respect of enzyme stability are pure hydrocarbons of the type hexane and petroleum ether. Water-miscible solvents, such as ethanol and acetone, are not as good in this respect, and especially mixtures of such organic solvents and water frequently have a purely denaturating effect on enzymes. This effect is utilised in, inter alia, the disinfecting alcoholic solution which is used in the medical service and which consists of about 70 parts ethanol and 30 parts water. If enzymes which normally catalyse hydrolysis reactions can be activated in an anhydrous environment, the reaction instead occurs in the opposite direction, i.e. the condensation process is catalysed. In such a case, lipases can catalyse the reaction between fatty acid and glycerol, while forming triglyceride. However, these reverse enzyme-catalysed reactions do not take place entirely without water. It seems as if the enzyme in its nearest surroundings requires an aqueous environment. The content of such "hydrate water" may, however, be very low, frequently far below l%, based on the weight of the entire solution. The water can be distributed in the organic environment by hydration of some mineral, such as celite or calcium carbonate, which is then dispersed by stirring. The fact that some enzymes can function also in an essentially anhydrous environment, has opened new possibilities of enzymatic reactions in organic process chemistry. Besides hydrolysis, also condensation reactions can be carried out, and furthermore many solubility problems with organic substrates in water can be avoided since use may be made of organic solvents. As regards lipases in organic environment, the possibility of carrying out a triglyceride synthesis has no great practical interest because triglyceride is the raw material from which glycerol and the majority of fatty acids are produced. On the other hand, it is of considerable commercial interest to be able to carry out so-called transesterification by means of lipases in organic environment, i.e. substituting new fatty acids for one or more fatty acids on a triglyceride. Proceeding from mixtures of inexpensive triglycerides and fatty acids, various types of new triglycerides can be produced in this manner, also such as do not exist, or are rarely found, in nature. By using the selectivity which many enzymes exhibit, it is even possible to control the incorporation of a new fatty acid in a triglyceride such that it will either lie in any of the outer positions (positions l, 3) or be randomly distributed in all three positions. In several recently published works, this principle is utilised for transferring, by transesterification with the enzyme Rhizopus delemar (a lipase) inexpensive distillation fractions from palm and olive oil to a composition which corresponds to that of cocoa butter (K Yokozeki et al, Europ J Appl Microbiol Biotechnol, l4 , (l982) l; T Tanaka et al, Agric Biol Chem, 45 , (l98l) 2387; M H Coleman and A R Macrae, U S Patent 4,275,08l (l98l). Natural cocoa butter is at present in very short supply and highly expensive. The chemical reaction which takes place in this process may be illustrated, in simplified form, by the formula in which S is stearic acid, P is palmitic acid, and O is oleic acid. A mixture of stearic acid and a tri­ glyceride with palmitic acid residues in positions l and 3 and an oleic acid residue in position 2 has been converted into a mixture of palmitic acid and a new triglyceride where the stearic acid residue now is in positions l and 3. The lipase Rhizopus delemar is position specific, i.e. transesterification occurs in positions l and 3 and leaves position 2 intact. The above formula is, to some extent, a simpli­ fication. The palm or olive oil fraction is not a pure P-O-P triglyceride, and cocoa butter is not a pure S-O-P triglyceride. Nevertheless, the formula may be said to describe the process here concerned in broad outline. According to literature, the process preferably is carried out in hexane or similar hydrocarbon. However, the reaction rate is relatively low, and a fairly complete reaction requires reaction times in the order of 40-50 hours. The long reaction time is a disadvantage for the process that cannot be obviated by an increase in temperature because of insufficient enzyme stability above 40°C. It has now surprisingly been found that, if trans­ esterification instead is carried out in a so-called microemulsion, i.e. a thermodynamically stable solution consisting of a hydrophobic part, a surface-active part and water, the reaction rate will increase. The water content in the microemulsion preferably should not exceed 4% by weight. According to the invention, it is possible, by prior art technique, to reduce the reaction time to l/l0 of the reaction time required under otherwise the same reaction conditions. This brings, of course, considerable economic advantages. In a microemulsion, the surface-active component usually is a combination of a surface-active compound and a so-called auxiliary surfactant which usually is alcohol or a glycolether. The surface-active agent may be anionic, cationic, amphoteric or noninonic. The alcohol or the glycol ether usually is a low-molecular compound. Examples of conventional substances of this type are butanol, pentanol, hexanol, butyl glycol and butyl di­ glycol. In the context of this invention, is has proved especially advantageous to use a surface-active compound capable of forming microemulsions without the presence of an auxiliary surfactant. Such surface-active compounds are certain nonionic compounds in which the hydrophilic group is a polyalkene glycol chain prepared by polymer­ isation of ethylene oxide or combinations of ethylene oxide and propylene and/or butylene oxide as well as certain ionic compounds having the ionic, hydrophilic group in a nonterminal position on the hydrocarbon chain. Among non-ionic surfactants, polyethylene glycol is the preferred hydrophilic component, and the length of the polyglycol chain is between 3 and 8 ethylene oxide units on an average, in the most preferred case. The hydrophobic part may be derived from hydroxyl compounds or carboxyl compounds containing an alkyl chain which consists of 8-20 carbon atoms, or an alkylaryl group consisting of totally 9-24 carbon atoms. Examples of such compounds are ethylene oxide adducts of nonyl phenol octyl phenol and fatty alcohols. Monoglycerides are another preferred group of nonionic surfactants. For ionic surfactants, anionic groups, such as sulphonate, sulphate, carboxylate, phosphate, and phosphonate are preferred. Sulphonate is an especially preferred anionic group. These surfactants may, optionally, also contain alkyleneoxy groups, such as ethyleneoxy, as a coupler between the anionic group and the hydrophobic group. The hydrophobic part may consist of an alkyl chain, comprising l0-22 carbon atoms, or of an alkyl aryl group comprising 9-24 carbon atoms in all. The hydrophobic part may contain individual ether, ester or amide bonds. Other suitable ionic surfactants are phospholipids, which contain both a phosphate group and a quaternary ammonium group. Examples of suitable ionic compounds are di-(2-ethylhexyl)sulphosuccinate, lecithin, and carboxy-methylated nonyl phenol ethoxylate containing l-4 ethyleneoxy groups. The hydrophobic component of the microemulsion may, in principle, be any organic solvent immiscible with water. Aliphatic hydrocarbons, either pure and defined such hydro­ carbons, for example hexane or nonane, or broader distillation fractions, for example petroleum ether 60-80, are preferred. Frequently, the aqueous phase is a buffer solution, to provide a pH which is optimal for the enzyme. The aqueous phase may also be, for example, distilled water. Suitable microemulsions for the process according to the invention contain 8l-99.8, preferably 93-99.0% by weight of the hydrophobic part; 0.l-l5, preferably 0.3-8% by weight of the surface-active part, and 0.l-4, preferably 0.3-2% by weight of water. This shows that the water content is relatively low. If it is increased, the hydrolysis reaction will be favoured. To further illustrate the invention, the following Examples are given. Example l For enzymatic transesterification of a palm oil fraction with stearic acid, the reaction was carried out in the presence of a microemulsion having the fol­ lowing composition 2.7% by weight triethylene glycol ether of dodecyl alcohol 96.2% by weight technical nonane l.l% by weight buffer pH 8 The amount of palm oil/stearic acid (weight ratio 2:l) was 5.3 g per l00 g microemulsion. The enzyme employed was Rhizopus delemar in an amount of 34 mg per l00 g microemulsion. During the reaction, stirring was carried out at 35°C. Samples were taken after 4, 8, 24 and 48 hours. The triglyceride was separated chromatographically and analysed in respect of the fatty acid composition. The result is shown in the Table below. As will appear, the stearic acid has replaced parts of the palm­ itic acid and the oleic acid in the palm oil, and on the whole the reaction has terminated after 4 hours. For comparison, a transesterification of palm oil fraction with stearic acid in hexane was carried out in accordance with the prior art technique. A composition containing the following components per l00 g was prepared 5 g palm oil/stearic acid 2:l 0.3 g celite 94.6 g technical nonane 0.l g buffer pH 7 34 mg lipase Phizopus delemar During the reaction, stirring was carried out at 35°C. Samples were taken after 4, 8, 24 and 48 hours. The triglyceride was separated chromatographically and analysed in respect of the fatty acid composition. The result is shown in the Table below. A reaction time of about 40 hours is required in order to achieve a satisfactory reaction, i.e. the reaction time is about l0 times longer than in the process according to the invention.

Claims: 1. A process for transesterification of a triglyceride with a fatty acid in the presence of a lipase, characterised in that the transesterification is carried out in a thermodynamically stable solution, which contains 8l-99.8% by weight of a hydrophobic part, 0.l-l5% by weight of a surface active part, and 0.l-2% by weight of water. 2. A process acccording to claim l, characterised in that the hydrophobic part is a hydrocarbon. 3. A process according to claim 2, characterised in that the surface active part is a surface active compound. 4. A process according to claim 3, characterised in that the surface active compound is nonionic. 5. A process according to claim 4, characterised in that the nonionic surface active compound has 3-8 ethylene oxide units in the hydrophilic part. 6. A process according to claim 3, characterised in that the surface active compound is anionic or amphoteric. 7. A process according to claim 6, characterised in that the anionic group is situated on a non-terminal carbon atom in the hydrocarbon chain. 8. A process according to claim 6, characterised in that the amphoteric compound is a phospholipid. 9. A process according to claims l-8, characterised in that the hydrophobic part constitutes 93-99.5%, the surface active part 0.3-8%, and water 0.3-2%, based on the weight of the thermodynamically stable solution. l0. A process according to claim l-9, characterised in that palm or olive oil is reacted with stearic acid.

Inventors: HOLMBERG, KRISTER, OSTERBERG, EVA, Österberg, Eva
Applicants: BEROL KEMI AB
Application year: 1987
Main classification: C11C3
IPC codes: C11C3