Progress of expanding scope of Joint JOCS/AOCS Official Method Ch 3a-2019 for determination of FA Distribution in TAG

Joint JOCS/AOCS Official Method Ch 3a-19 is an improvement over the older methods including ISO 6800 and AOCS Ch 3-91 that determine FA distribution in TAG molecule by 1(3)-position selective hydrolysis with pancreatic lipase. PUFA containing oils such as fish oils and algal oils, and short chain FA-containing milk fats are out of scope in the older methods. In contrast, the scope of the Official Method Ch 3a-19, using Candida antarctica lipase B to prepare 2-MAG from TAG, is broader and includes oils containing PUFA and short chain FAs.

By combining the lipid extraction methods with Official Method Ch 3a-19, FA distribution of TAG in food and various materials can be determined. A single extraction step using pre-packed columns MAK174 (Sigma-Aldrich) from fish meat was found to be advantageous in terms that the extraction time to be reduced from 30 to 5 min/sample with similar or higher yield using half the volume of the extraction solvent compared to the liquid–liquid extraction with chloroform/MeOH.

Another method, hexane-isopropanol (HI) extraction, is halogen free and is currently preferred as environmentally-friendly method. The HI extraction was successfully applied to extract lipids from various fish meat, insects, milk and infant formulae. When necessary, TAG in the extracted lipids could be purified by silica gel chromatography using hexane/diethyl ether 87:13 as developing solvent, before applied to Official Method Ch 3a-19. Recent analyses of FA distribution in fish and milk TAG revealed that PUFAs in the cetacean milk fat distributed mainly in sn-1(3), in contrast that they were distributed in sn-2 in TAGs of their dietary fish. Therefore, the Official Method Ch 3a-19 may contribute to estimate the biosynthetic and secretion pathways of milk lipid.