9.2.1 Enzymatic hydrolysis followed by analysis of both MAG and
DAG
This method utilizes the high 1,3-regioselectivity of pancreatic lipase. Partial hydro-
lysis of TAG by porcine pancreatic lipase gives rise to 2-MAG, which is then se-
parated by TLC. However, this method has two drawbacks. First, partial lipase hy-
drolysis of TAG may cause acyl migration, resulting in erroneous identification of
acyl positional distribution. Second, the lipase method is not reliable for a TAG that
contains significant amounts of short- and/or medium-chain fatty acids and very
long-chain PUFA (Battino et al., 1967; Yang et al., 1990), because it hydrolyzes
short- and medium-chain fatty acid esters preferentially and the ester bond of
PUFA is resistant to its cleavage.
9.2 Monitoring the reaction 151
Table 2.Peak identification for the transesterification reaction between EPAEE and tricaprylin by silver-
ion HPLC.
Peak
no.
Chemical species Possible
isomersMolecular
weightNumber of
double bonds1 Tricaprylin, caprylic acid ethyl ester
2 Caprylic acid, dicaprylin
3 Dioctanoyleicosapentaenoylglycerol
(TAG-A)
C 8 (EPA)C 8
(TAG-A3)629 54 Dioctanoyleicosapentaenoylglycerol
(TAG-A)
(EPA)C 8 C 8
(TAG-A1)
C 8 C 8 (EPA)
(TAG-A2)629 55 Eicosapentaenoic acid ethyl
ester (EPAEE)
331 56 Eicosapentaenoyloctanoyl
diacylglycerol (DAG-A)
(EPA)C 8 (OH),
C 8 (EPA)(OH)
(OH)(EPA)C 8 ,
(OH)C 8 (EPA)
(EPA)(OH)C 8 ,
C 8 (OH)(EPA)503 57 Eicosapentaenoic acid (EPA) 303 5
8 Dieicosapentanoyloctanoyl
triacylglycerol (TAG-B)
(EPA)C 8 (EPA),
(EPA)(EPA)C 8 ,
C 8 (EPA)(EPA)787 109 Dieicosapentaenoyl diacylglycerol
(DAG-B)
(EPA)(EPA)(OH),
(EPA)(OH)(EPA),
(OH)(EPA)(EPA)661 1010 Trieicosapentaenoylglycerol (TAG-C) (EPA)(EPA)(EPA) 945 15