56
Handbook of Functional Lipids
often utilized in performing the selective esterification process. In the first step,
generation of FFAs by hydrolyzing GLA-containing oil using a lipase that acts on
PUFA/GLA as effective as on other constituent fatty acids is conducted. Then the
enrichment of PUFA in the FFA fraction is achieved by esterification of FFAs other
than GLA with an alcohol using a lipase that acts very weakly on GLA [54].
Shimada and group [54,60] have described a small-scale purification method
for GLA starting with borage oil that contained 22% GLA at the start and obtained
70% GLA-containing concentrate. Lipase from Pseudomonas spp., which was
found to be the most suitable for hydrolysis of borage acylglycerols, was used as
the catalyst to obtain FFAs in the first step in this process. Several factors that
affect hydrolysis reaction (e.g., oil-to-solvent ratio, enzyme-to-substrate ratio, reac-
tion time, and temperature) have been studied. Under the specified conditions
described by Shimada and group [60,61], hydrolysis of borage oil for 24 h resulted
in the release of FFAs (92%), including 93% recovery of GLA in the FFA fraction.
Free GLA obtained from this hydrolysis step was then selectively esterified with
lauryl alcohol catalyzed by Rhizopus delemer lipase; single-step esterification
resulted in a 74.2% recovery of GLA in the FFA fraction and concentration of GLA
was raised to 93.7% by a second step of selective esterification under the same
conditions [60]. This process has been adapted in large-scale preparation of GLA
concentrate [61]. In this scaled-up process, a molecular distillation step has been
included in removing the selectively esterified fatty acids. However, 15 to 20%
TABLE 3.3
Positional Fatty Acid Composition of Borage and Evening
Primrose Oil (Expressed as mol%)
Fatty Acid
Borage Oil
Evening Primrose Oil
Total
sn-1
a
sn-2
b
sn-3
c
Total
sn-1
a
sn-2
b
sn-3
c
16:0
11.5
20.2
–3.1
17.5
6.0
11.3
–0.4
7.1
18:0
4.2
4.9
1.4
6.4
2.2
3.9
0.7
2.0
18:1
18.0
17.5
18.9
17.5
9.0
9.8
7.8
9.4
18:2n-6
42.0
38.5
53.4
34.2
74.4
70.0
81.5
71.6
18:3n-6
17.7
3.6
32.2
17.4
8.5
4.9
10.3
10.2
20:1n-9
3.3
5.9
0.0
4.0
22:1n-9
2.0
6.1
–1.7
1.7
24:1n-9
1.2
3.5
–0.9
0.9
a
3
×
[TAG} – 2
×
[sn-2,3-DG urethane].
b
3
×
[TG] – [sn-1] – [sn-3].
c
3
×
[TG] – 2
×
[sn-1,2-DG urethane].
Source: Modified from Redden, P.R. et al., J. Chromatogr. A, 704, 99, 1995. With
permission.
2162_C003.fm Page 56 Monday, June 20, 2005 12:27 PM
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