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Determination of the conjugated linoleic acid‐containing triacylglycerols in New Zealand bovine milk fat
Author(s) -
Robinson Nicholas P.,
MacGibbon Alastair K. H.
Publication year - 2000
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/s11745-000-0587-x
Subject(s) - tripalmitin , conjugated linoleic acid , chromatography , chemistry , triolein , high performance liquid chromatography , linoleic acid , fatty acid , biochemistry , lipase , enzyme
Reversed‐phase high‐performance liquid chromatography (HPLC) with ultraviolet (UV) detection at 233 nm was used to separate, quantify, and identify the triacylglycerols (TAG) of milk fat that contain conjugated linoleic acid (CLA). The absorbance at 233 nm was substantially due to CLA‐TAG (chromatography of some representative TAG devoid of CLA, such as tripalmitin and triolein, showed poor responses at 233 nm, 1/800th that of CLA‐TAG). A CLA molar extinction coefficient at 233 nm of 23 360 L mol −1 cm −1 and an HPLC UV response factor were obtained from a commercially available cis ‐9, trans ‐11‐CLA standard. This molar extinction coefficient was only 86% reported literature values. Summation of all chromatographic peaks absorbing at 233 nm using the corrected response factor gave good agreement with independent determinations of total CLA by gas chromatography and UV spectrophotometry. This agreement allowed quantification of individual CLA‐TAG peaks in the HPLC separation of a typical New Zealand bovine milk fat. Three CLA‐containing TAG, CLA‐dipalmitin, CLA‐oleoyl‐palmitin and CLA‐diolein, were prepared by interesterification of tripalmitin with the respective fatty acid methyl esters and used to assign individual peaks in the reversed‐phase chromatography of total milk fat, of which CLA‐oleoyl‐palmitin was coincident with the largest UV peak. Band fractions from argentation thin‐layer chromatography of total milk fat were similarly employed to identify five predominant CLA‐TAG groups in total milk fat: CLA‐disaturates, CLA‐oleoyl‐saturates, CLA‐vaccenyl‐saturates, CLA‐vaccenyl‐olein, and CLA‐diolein.