Determination of the conjugated linoleic acid-containing triacylglycerols in New Zealand bovine milk fat

Reversed-phase high-performance liquid chromatography (HPLC) with ultraviol et (UV) detection at 233 nm was used to separate, quantify, and identify th e triacylglycerols (TAC) of milk fat that contain conjugated linoleic acid (CLA). The absorbance at 233 nm was substantially due to CLA-TAG (chromatog raphy of some representative TAC devoid of CLA, such as tripalmitin and tri olein, showed poor responses at 233 nm, 1/800th that of CLA-TAG). A CLA mol ar 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% of reported literature values. Summation of all chromatographic peaks absorbing at 233 nm using the corrected response factor gave good agreement with independen t determinations of total CLA by gas chromatography and UV spectrophotometr y. This agreement allowed quantification of individual CLA-TAG peaks in the HPLC separation of a typical New Zealand bovine milk fat, Three CLA-contai ning TAG, CLA-dipalmitin, CLA-oleoyl-palmitin and CLA-diolein, were prepare d by interesterification of tripalmitin with the respective fatty acid meth yl esters and used to assign individual peaks in the reversed-phase chromat ography of total milk fat, of which CLA-oleoyl-palmitin was coincident with the largest UV peak. Band fractions from argentation thin-layer chromatogr aphy of total milk fat were similarly employed to identify five predominant CLA-TAG groups in total milk fat. CLA-disaturates, CLA-oleoyl-saturates, C LA-vaccenyl-saturates, CLA-vaccenyl-olein, and CLA-diolein.