Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Preparing oxygen-containing organic compound
Reexamination Certificate
2001-11-02
2003-02-11
Tate, Christopher R. (Department: 1651)
Chemistry: molecular biology and microbiology
Micro-organism, tissue cell culture or enzyme using process...
Preparing oxygen-containing organic compound
C435S041000
Reexamination Certificate
active
06518049
ABSTRACT:
This invention relates to the lipase catalysed esterification of marine oils.
It is well known in the art to refine oil products of various kinds, including marine oils, with the aid of lipase catalysts whose specificity under the refining conditions employed enhances the recovery of a desired product.
For example, in PCT/WO95/00050 we disclosed a process for treating an oil composition containing saturated and unsaturated fatty acids in the form of triglycerides to transesterification reaction conditions with a C
1-6
alcohol such as ethanol under substantially anhydrous conditions in the presence of a lipase active to preferentially catalyse the transesterification of the saturated and monounsaturated fatty acids. With the preferred lipases, Pseudomonas sp. lipase (PSL) and
Pseudomonas fluorescens
lipase (PFL) it was possible to prepare from marine oil sources concentrates containing more than 70% by weight of the commercially and therapeutically important omega-3 polyunsaturated fatty acids EPA (eicosapentaenoic acid, C20:5) and DHA (docosahexaenoic acid, C22:6) in the form of glycerides.
A number of lipase-catalysed refining processes have utilised glycerol.
By way of example, JP 62-91188 (1987) teaches a process for preparing glycerides of polyunsaturated fatty acids (PUFA) in which the PUFA as free acid or ester is reacted with glycerol in the presence of a thermostable lipase. The fatty acid composition of the resulting glyceride product is substantially the same as in the starting PUFA.
WO91/16443 discloses a process for converting PUFA into triglycerides. The free fatty acids, for example mixtures of EPA and DHA, are reacted with about stoichiometric amounts of glycerol in the presence of a lipase, especially
Candida antarctica,
under essentially anhydrous, organic solvent-free, elevated temperature conditions with continuous removal of water and volatile alcohols. We are aware that there was little or no discrimination between EPA and DHA in this process.
In a paper in Int. J. Food Sci. Technol. (1992), 2, 73-76, Lie and Molin describe the esterification of a fish oil fatty acid concentrate with glycerol using three different lipases, including MML. Under the conditions used (5% water) they obtained a DHA-depleted free acid fraction (about 50% of the starting material) and a glyceride fraction with the same EPA content as the original fish oil concentrate. Thus, some selectivity was observed.
A paper by Myrnes et al in JAOCS, Vol. 72, No. 11 (1995), 1339-1344 discloses an organic solvent-free, lipase-catalysed glycerolysis of marine oils. A variety of different lipases are tested, and the reactions are run at low temperatures (12° C. or less) in the presence of relatively high (3.6%) amounts of water. Analysis of the resulting monoglyceride fraction showed, in some cases, good selectivity between unsaturated and saturated fatty acids, but no significant differences between individual PUFA.
Moore et al in JAOCS, Vol. 73, No. 11 (1996), 1409-1414 teach the hydrolysis of a fish oil in the presence of
Candida rugosa
lipase (CRL) to produce separate DHA-enriched and EPA-enriched fractions.
Subsequently, the EPA-enriched free fatty acid fraction is re-esterified with glycerol in the presence of
Rhizomucor miehei
lipase (MML).
A paper by McNeill et al in JAOCS, Vol. 73, No. 11 (1996), 1403-1407 discloses a MML-catalysed esterification of a n-3 PUFA concentrate with stoichiometric amounts of glycerol at 55° C. with continuous removal of water. The resulting triglyceride fraction contained the same level of DHA as the feed.
Finally, mention is made of WO96/37586 and WO96/37587. Example 3 of WO96/37586 discloses a process in which a free fatty acid concentrate originating in Chilean Fish Oil, comprising (after solvent fractionations of sodium salts) 25% EPA and 18% DHA, was directly esterified with glycerol using an immobilized
Candida rugosa
lipase (CRL) in the presence of 10% water at 35° C. After 120 hours, the extent of conversion had reached about 60%. In the glyceride mixture obtained, the triglycerides contained 28.2% EPA and 3.8% DHA and the monoglyceride fraction had 28.9% EPA and 4.5% DHA. The residual free fatty acids comprised 23.2% EPA and 31.5% DHA. This indicates good selectivity between EPA and DHA.
In contrast, in Examples 1 and 2, the MML catalysed re-esterification of a free fatty acid fraction with glycerol did not show significant selectivity between EPA and DHA.
The disclosure of WO96/37587 is similar to that of WO96/37586. Examples 1, 4, 6 and 8 show the glycerolysis of PUFA with MML without any discrimination between EPA and DHA.
It will be apparent from this, by no means exhaustive, discussion of the prior art that extensive research has been carried out in order to develop lipase-catalysed processes for isolating such commercially important PUFA as EPA and DHA from compositions such as fish oils containing them in relatively low concentrations.
We have now discovered a lipase-catalysed process for preparing concentrates of EPA and DHA by the direct esterification of free fatty acid from fish oil which, by selection of the lipase, permits the EPA/DHA contents of the resulting concentrate to be tailored to meet customers' different requirements.
More particularly, the present invention provides a process for esterifying a marine oil composition containing EPA and DHA as free fatty acids to form a free fatty acid fraction enriched in at least one of these fatty acids as compared to the starting composition, comprising the step of reacting said marine oil composition with glycerol in the presence of a lipase catalyst under reduced pressure and essentially organic solvent-free conditions, and recovering a free fatty acid fraction enriched in at least one of EPA and DHA.
The present invention is predicated on the discovery that glycerol can act as an excellent substrate for a lipase-catalysed direct esterification of marine oil free fatty acids, provided that certain critical reaction conditions are followed. This finding was not at all to be expected in view of the prior research using glycerol referred to above. The main esterification reaction can be schematically represented by the following equation in which the lipase catalyst is
Rhizomucor miehei
(MML):
The product also contains other types of EPA-enriched glycerides, not shown in the schematic equation.
As will be discussed in more detail below, and illustrated in Example 8, the selection of the lipase catalyst can crucially affect the nature of the product. In the case of MML used in the illustrated reaction scheme, the product is a DHA-enriched free fatty acid fraction and an EPA-enriched glyceride fraction.
A significant feature of the present process is that it takes advantage of the fact that the selectivity of a lipase towards individual fatty acids is greater when they are in the form of free acids rather than as glycerides, since complications related to lipase regioselectivity or positioned selectivity are avoided. Surprisingly, the reaction with glycerol is far less successful when the EPA and DHA are present as esters, rather than as free acids, as is shown in Example 10 (Comparative) below.
The use in accordance with the present invention of glycerol as the substrate has the further advantage that it aids separation of the glyceride and free fatty acid product fractions by molecular distillation. The reason for this is considered to be that the esters of a trioic alcohol such as glycerol are less volatile than similar esters of short-chain alcohols such as methanol, ethanol and propanol.
It has been found that the relative amounts of glycerol are important to make the esterification reaction succeed. Preferably, a molar ratio of glycerol to free fatty acids in the starting composition of from 1:1.5 to 1:3 should be used, more preferably from 1:1.5 to 1:2.5. In our experimental work to date we have found that a molar ratio of about 1:2 of glycerol to fatty acids is optimal (corresponding to a ratio of available hydroxyl groups to free fatty acids of 1.5:1).
It is essent
Haraldsson Gudmundur G.
Kristiansson Bjørn
Thorstad Olav
Norsk Hydro ASA
Tate Christopher R.
Winston Randall
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