TMAH-Catalyzed Transesterification of EPA and DHA in Encapsulated Fish Oil Products |
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Authors: | Cheng-Jung Tsai Chih-Cheng Liu Lang-Bang Hung Bonnie Sun Pan |
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Affiliation: | (1) Department of Food Science, National Taiwan Ocean University, 2 Pei-Ning Road, Keelung, 202, Taiwan, ROC;(2) Department of Food Science, Ching Kuo Institute of Management and Health, Keelung, Taiwan, ROC; |
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Abstract: | Tetramethylammonium hydroxide (TMAH)-catalyzed transesterification was developed as a rapid and reliable method using gas
chromatography (GC) to determine the total fatty acid profile and to quantify the ethyl esters of eicosapentaenoic acid (EPA)
and docosahexaenoic acid (DHA) in 20 brands of encapsulated fish oil products. The AOAC method with boron trifluoride (BF3) as a catalyst was used as a reference. After the respective transesterifications of BF3 and TMAH, seven brands of encapsulated fish oil showed a single peak of EPA or DHA in the chromatograms, while 13 brands
showed a single peak in the chromatograms after BF3 esterification, but doublet peaks of EPA or DHA after TMAH esterification. By comparing with the GC/MS NIST library and authentic
standard fatty acids of ethyl esters, the two pairs of doublet peaks were confirmed the ethyl and methyl esters of EPA and
DHA, while the sum of the peak areas of the doublet represented the content of EPA or DHA. The reaction time course concluded
that optimal TMAH transesterification was obtained at 25 °C for 10 min and using GC columns of low to medium polarity including
Rtx-wax and Rtx-2330 were able to differentiate and quantify the ethyl- and methyl-esterified EPA and DHA, while RT-2560 column
with higher polarity than the two other columns was unable to resolve the ethyl ester from the methyl ester of EPA or DHA.
An EPA/DHA ratio of ≥1.10 may serve as an indicator of fish oil fortified with the ethyl ester of EPA. |
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