Method of preparing an emulsion spread using a wet gelatine retentate

A method of preparing a water-in-oil emulsion spread by mixing a wet gelatin retentate wherein the off flavor has been reduced by membrane filtration to remove a low molecular weight fraction, with a fat phase.

The present invention is concerned with treatment of gelling agents, more 
particularly applicable to the treatment of gelatins, so as to remove or 
reduce off-flavours. 
Gelatine is a well known proteinaceous gelling agent which is widely used 
in food manufacture and in the photographic and pharmaceutical industries. 
Gelatine is produced from animal tissues, often as a slaughter-house 
by-product, by a process involving physical and chemical treatment 
followed by hot-water extraction. In the food industry gelatine is 
employed in a remarkable range of products including wine-gums, sweets, 
corned beef, low-fat spreads, sausage coatings, aspic products and 
ice-cream. Gelatine is also employed as a "fining" in wine-making. 
The gel-strength of gelatine is related to the so-called "Bloom" value. 
From which a theoretical estimate of the gel-strength can be obtained with 
a expected error of approximately 10% from the measured value. 
Chemically, gelatine comprises partially hydrolysed collagen, the most 
common structural component of many animal tissues. The molecular weight 
of collagen is believed to lie in the region of 340 kD, and the intact 
collagen macro-molecule is believed to comprise three sub-units each of 
around 100 kD. Gelatine is not a globular protein. The transition 
temperature from collagen to gelatine differs from one species to another, 
but is characterised by a contraction of the collagen fibres to about one 
third of their original length and a radical modification of the X-ray 
diffraction pattern. 
Gelatine has long been known to be a nutritionally incomplete protein, as 
it lacks the essential amino-acid tryptophane and methionine is only 
present in small quantities, it does however contain sufficient 
hydroxyproline to allow it's specific presence to be detected in products. 
In the conventional process for the manufacture of gelatine, collagen rich 
tissues such as calf- and pig-skin trimmings, white connective tissue and 
large bones are limed and washed before being macerated in acid or 
alkaline solution while being heated in a kettle. The heating process 
continues for many hours during which time several fractions are taken. 
The first fractions are of markedly better quality than the later 
fractions, being less degraded, and therefore command a higher market 
value. The immediate product of this process is not unlike thin soup. 
In a known process for dewatering of the crude gelatine liquor (the 
"soup"), the raw solution is concentrated to about 20% wt in a triple 
effect evaporator, filtered and further concentrated to about 35% wt in a 
single stage climbing-film evaporator. Final processing involves chilling, 
air drying to about 90% wt gelatine followed by crushing, testing, 
blending and packaging. 
As an alternative to the abovementioned evaporative dewatering process, 
ultra-filtration has been suggested for concentration of the gelatine 
liquor. Such a process is described by Fane and Friend (Chemeca 77, 
Canberra, 14-16 Sep. 1977). An observed benefit of the ultra-filtration 
process was the de-ashing of the product which accompanied 
ultra-filtration; that is, the removal of calcium. However it was noted 
that while proteins were almost completely rejected by the 
ultra-filtration membrane, inorganic species such as sulphur-dioxide were 
anomalously also rejected. The authors of the abovementioned document 
concluded that for economic reasons ultra-filtration was a viable 
alternative in the initial dewatering and de-ashing of the gelatine 
liquor, which is then dried. 
Typically, high grade gelatine produced by the conventional methods has a 
mild off-flavour which has been described as sickly, musty, cardboard-like 
or animal-like. While this does not present a problem in products such as 
wine gums or strongly-flavored sweets, use of gelatine in relatively bland 
products such as edible spreads, particularly low-fat spreads, is hindered 
by the characteristic off-flavour of gelatine. Notwithstanding this, such 
are the advantages to be gained by the use of gelatine in spreads, 
particularly as regards the melting behaviour of the gels obtained, that 
medium fat products containing gelatine have enjoyed some commercial 
success. However, as the mass fraction of gelatine present in a product is 
increased the off-flavour associated with its use becomes progressively 
more noticeable and the products become progressively less acceptable. For 
this reason, spreads manufactures are restricted to the use of 
high-quality gelatines obtained in the early part of the gelatine 
extraction process. As mentioned above, these high-quality fractions are 
expensive. 
As is obvious from the production process, lower quality gelatines are also 
produced. These range in quality from those suitable for use in highly 
flavored foods through those suitable for animal foods, particularly "pet 
foods", to those only suitable for non-food usage. The market for these 
materials is relatively stable. As the demand for high quality gelatine 
increases so the production of low quality gelatine must also increase and 
difficulties have been encountered in disposing of these materials 
commercially. This restricts the supply of high quality gelatine and may 
elevate the price. 
The present technical problem is therefore how the cost of high-quality 
gelatines for food use can be reduced by facilitating the use of lower 
quality fractions in products fit for human consumption. 
We have now determined that the off-flavour may be reduced by a membrane 
filtration specifically to remove a low-molecular weight fraction of the 
gelatine. 
Accordingly, a first aspect of the present invention provides gelatine 
substantially without a low molecular weight fraction. 
Other advantages are found in the provision of such a gelatine, especially 
where the gelatine has been mistreated during production or transport or 
in other circumstances where it is necessary to remove low molecular 
weight contaminants or degradation products. 
According to a second aspect of the present invention there is provided a 
process for the purification of gelatine which comprises removal of a 
low-molecular weight fraction by membrane filtration, preferably 
diafiltration. 
Diafiltration apparatus is similar to ultrafiltration apparatus, in that 
the apparatus comprises an extensive membrane surface through which a 
solvent may pass but which retains relatively large molecules. However, it 
should be noted that in ultrafiltration the objective is to remove only 
the solvent and very low-molecular weight salts, whereas in diafiltration 
species with moderate molecular weights may cross the membrane. The 
diafiltration process of the present invention is therefore not identical 
to the dewatering process of Fane and Friend (cit. ultra) as described in 
the prior art. Moreover, in preferred embodiments of the present invention 
the gelatine is not dried after the diafiltration step. It is believed 
that drying of diafiltered gelatine and/or subsequent milling and dry 
storage may re-introduce the off-flavour components removed by the 
filtration step. 
Analysis has shown that the membrane permeate contains species of a 
molecular weight below 100 kD. Peak absorbtion of light of a wave-length 
of 214.4 nm was noted at 20 kD mass equivalent. It should be noted that 
the this 20 kD molecular weight is expressed in terms of the molecular 
weight of a globular marker protein of this mass. Gelatine and its 
oligo-peptidic digests are not globular proteins. 
It is believed that the species present in the permeate comprise in part 
both oligopepitides derived from collagen by hydrolysis and other 
proteinaceous matter present in the original feedstock. In addition 
low-molecular weight organic species such as aldehydes, ketones and 
metabolites are believed to be removed. Analysis has indicated that other 
low-molecular weight components, particularly -2-propanon, toluene, 
hexanol, octanol and nonanol are removed by the process of the present 
invention. 
In particular, it is believed that 4 and 5-methyl indane are removed by the 
filtration process. Accordingly, a further aspect of the present invention 
provides gelatine substantially free of 4 and 5-methyl indane. 
4 and 5-methyl indane are not compounds which have previously been 
associated with the presence of off-flavours in gelatine. Consequently, it 
is believed that the it is not the methyl indanes per se which are 
responsible for the off taste, but rather compounds which presently remain 
in part unidentified but which are separated into the membrane permeate 
together with the methyl indanes in the process of the present invention. 
Thus, the methyl indanes can be seen as markers for the unspecified 
off-flavour promoting species removed in the process of the present 
invention. 
Accordingly, a yet further aspect of the present invention provides a 
gelatine preparable by membrane filtration under such conditions as to 
substantially remove 4 and 5-methyl indane. 
The origin of these indane compounds in the gelatine is obscure, as it is 
known (and mentioned above) that gelatine does not contain the indole-ring 
derived amino-acid tryptophane. 
Typically, the process comprises the steps of; 
a) dissolving dried gelatine in water, 
b) subjecting the gelatine solution obtained in step (a) to membrane 
filtration to remove at least 10% wt of the gelatine solution, 
c) optionally, repeating step (b) until a solution is obtained which is 
substantially free of 4 and 5-methyl indane. 
By performing the process after drying of the gelatine, it is believed that 
off-flavour components generated during the drying process are removed. 
During the process of the present invention it is possible either to 
prepare a dilute solution of gelatine and concentrate this solution by a 
membrane filtration to the desired final concentration, or alternatively, 
it is possible to first concentrate the gelatine solution to a solution 
more concentrated than that desired before dilution to the required 
concentration. 
As the gelatine is intended for use as a gelling agent it is important that 
the final gel strength is not adversely affected by the treatment process. 
It has been determined experimentally that the gel strength is not 
significantly reduced by the method of the present invention, as the 
reduction in gel strength following treatment according to the present 
invention is within the 10% variation in calculated and observed gel 
strength mentioned above.

EXAMPLE ONE 
Purification of Gelatine 
High quality gelatine obtained in the marketplace from "Extraco Nobel 
Industrier" and sold under the trademark "GELTEC UG-719-N" was membrane 
filtered, in batch, as follows; 
2.5 kg of dry gelatine was dissolved, with stirring for ten minutes, in 
demineralized water at 60.degree. C. in a thermostatted, heat-jacketed 
kettle and made-up to a concentration of 2.5 wt % in approximately 100 
liters of solution. The solution was allowed to stand for 30 min at 
55.degree.-60.degree. C. to deaerate. 
The solution was continuously drawn from the kettle via a positive 
displacement pump (capacity 4 m.sup.3 /h, 40 bar) and fed to the membrane 
filtration apparatus at a throughput of 50 liters/min. 
The membrane filtration apparatus-was a STORK-WAFILIN "Universal Pilot 
Plant" ultrafiltration installation, using 6.8 sqr. meter of a WFA 4010 
membrane, available in the marketplace from STORK-WAFILIN N.V. The 
above-mentioned membrane was housed in four tubes arranged in two parallel 
flow-paths each containing two tubes connected in series, to give a flow 
path length of 76 meter. Each tube comprised nineteen filtration sections 
coupled in series and disposed in a serpentine configuration within a 
housing to collect permeate. Retentate was re-circulated to the kettle, 
with an approximate volume reduction of 1% per pass. The permeate flow 
rate was 25 liters/meter.sup.2 hour. The average trans-membrane pressure 
was 300 kilo-pascal. 
This process was continued until the volume of the process stream had 
reduced to 50 liters, with an approximate gelatine concentration slightly 
lower than 5% wt. 
The retentate was diluted with 50 liters of de-mineralized water at 
60.degree. C. and the abovementioned process repeated. In all, the cycle 
of concentration and dilution was repeated four times to give a final 
gelatine concentration of slightly less than 5% wt. 
The final solution was pale-yellow in hue and had a faint odour which was 
not unpleasant. 
The above experiment was repeated with "Delftse" bloom 120 gelatine, 
available in the marketplace from "Delftse Lijm en Gelatine Frabriken", 
The Netherlands. This is a gelatine with a strong off-flavour and while of 
edible quality is not considered suitable for use in spreads. The starting 
solution in this second instance was distinctly ochre in hue and had a 
pronounced, unpleasant odour described as "dog-like". The final solution 
was pale yellow in hue and had a faint odour which was not unpleasant. 
EXAMPLE 2 
Preparation of a Spread 
A 40% fat, edible water-in-oil spread was prepared as is known in the art 
at factory scale using products similar to the products of EXAMPLE 1 as 
the basis of the aqueous phase. The difference between the gelatine 
purification method of EXAMPLE 1 and that employed in the purification of 
the gelatine used in the present example were minor, in that a membrane 
type WFS8081 (cut-off 10 kD, available from Stork Wafilin) was used and 
the final concentration of the gelatine solution was 15%. This higher 
concentration was necessary to ship the concentrated, purified solution 
from the filtration plant (in Holland) to the factory (in Sweden). In 
order to ensure microbiological safety during shipping potassium sorbate 
was added to the gelatine solution. 
The only difference between the spread-type products prepared was in 
respect of the type of gelatine used and the presence or absence of 
potassium sorbate included in the product. 
The following products were prepared: 
______________________________________ 
2A) 3% EXTRACTO gelatine (unpurified) 
2B) 3% EXTRACTO gelatine + sorbate 
(unpurified) 
2C) 3% UF-DELFTSE gelatine + sorbate 
2D) 3% DELFTSE gelatine (unpurified) 
______________________________________ 
It can be seen that the purified gelatine of the present invention was used 
only in example (2C). 
The fresh products made with high quality and upgraded gelatine did not 
differ significantly. 
Isolated waterphases were scored and described as follows by a trained 
panel of assessors and scored in a ranking test with 1=best and, higher 
scores indicating progressively worse products. The following results were 
obtained: 
______________________________________ 
2A) score: 2.3 gluey, sweet, fungid 
2B) score: 3.8 stuffy, sweet 
2C) score: 4.0 stuffy, sweet 
2D) score: 4.3 like burned rubber 
______________________________________ 
Although the product of example 2A was described as "gluey, sweet and 
fungid" only a faint impression of this taste was noted. It is clear from 
the results that sorbate, a common ingredient of edible spreads, has a 
deleterious effect on the taste but it can be seen that even without the 
presence of sorbate the score for example 2D was the worst obtained. 
It can be seen that the products 2B and 2C are comparable, demonstrating 
the upgraded products of the present invention are at least as good as the 
products obtained by the methods of the prior art using the higher quality 
gelatine. 
EXAMPLE 3 
A further sample of a 40% spread was prepared using the first 
above-described method and the WFA 4010 membrane. The spread was presented 
to an experienced tasting panel for evaluation of off flavour, by 
comparison between low and high quality gelatine, both treated according 
to the present invention and untreated. Experiments were performed both on 
fresh samples and on samples which has been stored for six weeks. 
No significant differences were noted between the freshly prepared spreads, 
whether or not the gelatine was treated according to the present 
invention. 
Significant improvement in organoleptic properties were noted after six 
weeks when the treated and untreated low-quality gelatines were compared. 
On average the members of the panel reported an improvement in the 
organoleptic properties of the spread prepared with the upgraded 
low-quality gelatine as compared to the native low-quality gelatine. In 
particular the spread was described as less musty, less tart, less 
astringent in the throat, less bitter and more watery. No significant 
differences were noted between the treated and untreated high-quality 
gelatine. 
From the above results it is clear that there is perceived variation in the 
quality of the low-quality gelatine. This variation is significant enough 
that the lower-quality gelatine can on occasion appear suitable for use in 
edible spreads, but the quality of products made with this material 
degrades within the shelf-life of the products. 
In order to better characterise which off-flavour promoting species had 
been removed by the membrane filtration, samples of the low-quality 
gelatine from both before and after membrane filtration were analyzed by 
gel chromatography and gas chromatography in combination with mass 
spectrometry. It should be noted that although the reduction in 
off-flavour could be easily observed in a comparative organoleptic test, 
it was difficult to be entirely precise about the chemical species 
contributing to the off-flavour. 
EXAMPLE 4 
Gel Chromatography of Retentate 
A sample of the high quality untreated commercial gelatine and a sample of 
the same gelatine membrane-filtered according to the present invention 
were each taken at 5% solution in water. Both samples were heated for 20 
min at 50.degree. C. in a thermostatted water bath to melt the gelatine 
and promote effective mixing during subsequent dilution. 
The heat-treated solutions were diluted with elution buffer pre-heated to 
50.degree. C. (0.05 Molar sodium phosphate/0.15 Molar sodium chloride, pH 
7.2) to a final concentration of 0.9% wt. The diluted solutions were 
cooled to room temperature and filtered through 0.22 m low protein-binding 
filter ex. "MILLIPORE" (Registered Trade Mark). The samples were 
separately run on gel filtration columns packed with "SUPEROSE 12" 
(Registered Trade Mark) ex. "PHARMACIA". Two-hundred and fifty microliters 
of the samples prepared as above being loaded onto each column. 
Detection of the sample components was performed by an optical 
spectrophotometer of the "Diode Array Detection System" type HP 1040 at a 
wavelength of 280.4 nm, a characteristic absorbtion wavelength for 
proteinaceous matter. The gelatine recovery of the column measured 
spectrophotometrically was 92% of feed. The elution buffer throughput was 
0.7 ml/min. 
FIG. 1 shows chromatograms of both (A) membrane filtered and (B) untreated 
gelatine. The results show that there has been some change in the content 
of species (indicated in the figure by arrows) which exhibit a relatively 
long residence time in the column, i.e species with relatively low 
molecular weight. However it was difficult to characterise the precise 
manner of purification by this analytical technique. 
EXAMPLE 5 
Gel Chromatography of Permeate 
EXAMPLE 4 was repeated with a sample of permeate, produced according to the 
method of EXAMPLE 1, from the low-quality gelatine. FIG. 2, shows the 
optically resolved gel-filtration chromatogram viewed at a wavelength of 
214.4 nm. Myoglobin of molecular weight 17 kD was used as a marker. It can 
be seen that the permeate is rich is species eluted at a time consistent 
with a molecular weight of around 20 kD (relative to the marker in this 
chromatographic method). It is again noted that the molecular weight of 
intact collagen is in the region of 340 kD (absolute), and the collagen 
subunits each have a molecular weight of around 100 kD (absolute). 
EXAMPLE 6 
Gas Chromatography of Retentate 
A chromatography column was packed with the commercially available resin 
"XAD-2", known to adsorb apolar materials. 5% wt solutions of both 
membrane filtered and un-purified low-quality gelatine were eluted over 
the column. Following drainage of the solutions species retained on the 
column were eluted with ether and subsequently separated by gas 
chromatography with detection in a mass spectrometer. 
The presence of 4 and 5-methyl indane was observed in the eluate of the 
untreated low-quality sample as compared with the absence of detectable 
quantities of these compounds in the eluate of the treated sample. The 
untreated samples did not comprise any clearly detectable free amino 
acids. 
From the abovementioned taste studies it is concluded that the organoleptic 
properties of low-quality gelatine in spreads can be significantly 
improved by treatment according to the present invention. Although 
attempts to characterise the particular components responsible for the 
off-flavour development have been unsuccessful, it is believed that the 
off-flavours are removed under conditions which remove the 4 and 5-methyl 
indanes, and for this reason the 4 and 5-methyl indanes provide a useful 
analytical marker for the process of the present invention.