Front Matter

selective esterification withn-butanol (Mukherjee and Kiewitt, 1991). Using the

lipase fromC. rugosa, after a 1–h reaction period as much as 92 % of the fungal

oil fatty acids are esterified, and concomitantly the level ofc-linolenic acid in the

unesterified fatty acids is raised from 10 % to about 47 %, whereas virtually none of

thec-linolenic acid is converted to butyl esters (Mukherjee and Kiewitt, 1991). With

the lipase fromR. miehei, 91 % esterification of the fungal oil fatty acids occurs after

4 h of reaction; this results in an increase in the level ofc-linolenic acid in the un-

esterified fatty acids to 69 % (yield ofc-linolenic acid 59 %) (Mukherjee and Kie-

witt, 1991). With both lipases the enrichment ofc-linolenic acid is paralleled by a

decrease in the levels of palmitic, oleic and linoleic acid in the fatty acid fraction, and

some increase in the proportion of these acids in the butyl esters.

It has also been shown using several lipases that selective esterification of fungal

oil fatty acids withn-butanol, rather than selective hydrolysis of fungal oil triacyl-

glycerols, should be the method of choice for enrichment ofc-linolenic acid (Mu-

kherjee and Kiewitt, 1991).

2.2.3 Enrichment of n-3 polyunsaturated fatty acids

n-3 Polyunsaturated fatty acids are extensively used in nutraceutical preparations due

to their interesting biomedical properties (Innis, 1991).

The ability of the lipase from rape to discriminate against n-3 docosahexaenoic

acid has been utilized for the enrichment of this acid from a mixture of fatty acids

derived from cod liver oil via lipase-catalyzed selective esterification withn-butanol

(see Figure 3) (Hills et al., 1990b). Moreover, the ability of the lipase fromR. miehei

to discriminate against n-3 22 : 6 has been utilized for the enrichment of this fatty

acid from fish oil fatty acids via selective esterification with methanol (Langholz et

al., 1989). For example, esterification of fish oil fatty acids with methanol, catalyzed

byR. mieheilipase, raises the level of n-3 22 : 6 from about 8 % in the initial fatty

acid mixture to about 48 % in the unesterified fatty acids (Langholz et al., 1989).

Shortly thereafter, selective hydrolysis of fish oil triacylglycerols, catalyzed by li-

pases fromAspergillus nigerandC. rugosa, has been employed to concentrate n-3

polyunsaturated fatty acids, i.e. n-3 20 : 5 and n-3 22 : 6, that are enriched in the tri- +

di- + monoacylglycerol fraction (see Figure 4) (Hoshino et al., 1990) (see also chap-

ters 8-10).

Numerous publications have appeared since the above studies were published

(Table 3) on the selective hydrolysis of marine oil triacylglycerols for the enrich-

ment of n-3 polyunsaturated fatty acids in the unhydrolyzed acylglycerols (see Fig-

ure 4) and selective esterification of marine oil fatty acids for the enrichment of the

n-3 fatty acids in the unesterified fatty acid fraction (see Figure 3).

Thus, two successive hydrolyses of tuna oil triacylglycerols, catalyzed by lipase

fromG. candidum, result in enrichment of n-3 fatty acids, i.e., n-3 20 : 5 and n-3 22 : 6,

from about 32 % in the untreated oil to about 49 % in the fraction consisting of tri-, di-

andmonoacylglycerols(Shimadaetal.,1994).Similarly,inacommercialprocess,fish

oilispartiallyhydrolyzedbyC. rugosalipasetoyieldanacylglycerolfractionenriched

in n-3 20 : 5, and especially in n-3 22 : 6; the acylglycerol fraction is subsequently

32 2 Fractionation of Fatty Acids and Other Lipids Using Lipases