Seasonal variation in fatty acid and triacylglycerol composition of bovine milk fat

摘要

The aim of this study was to assess the effects ofseasonal variation on the changes of the fatty acid (FA)and triacylglycerol (TAG) composition of bovine milkfat (MF) in a nonseasonal milking system. Weekly milksamples were collected from 14 dairy factories andpooled per week as representative samples of the averageDutch bovine milk. The sample collection startedin May 2017 and finished in April 2018, resulting in atotal of 52 samples, corresponding to each week of theyear. The samples were analyzed for MF content (%)and FA and TAG composition using gas chromatographywith flame-ionization detection. The increasedintake of C18:3 cis-9,12,15 through grass feeding inspring and summer was associated with major changesin MF FA composition, including reduced proportionsof de novo synthesized FA and presence of several rumenbiohydrogenation products and conjugated linoleicacid isomers in MF. These changes in seasonal FAcomposition had an effect on TAG seasonal variation.The TAG seasonal variation showed that all TAGgroups were significantly different between months.The low molecular weight and the medium molecularweight TAG groups increased in winter and decreasedin summer, whereas the high molecular weight TAGgroups increased in summer and decreased in winter.Based on pooled monthly samples, MALDI-TOF-massspectrometry allowed the analysis of even- and oddchainTAG species in MF based on their total carbonnumber and number of double bonds. These analysesindicated saturated TAG species to be greatest in winter,whereas monounsaturated, polyunsaturated, andodd-chain TAG species were greatest in summer. Ourstudy showed that TAG seasonal variation in a nonseasonalmilking system is influenced by the variation inFA composition throughout the seasons.