Determination of the conjugated linoleic acid-containing triacylglycerols in New Zealand bovine milk fat |
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Authors: | Nicholas P Robinson Alastair K H MacGibbon |
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Affiliation: | (1) New Zealand Dairy Research Institute, Private Bag 11-029, Palmerston North, New Zealand |
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Abstract: | 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. |
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