Identification and quantification of dimethyl acetals from plasmalogenic lipids in lamb intramuscular fat under different derivatization procedures.

Meat lipids are mostly comprised by triacylglycerols, but small amounts of plasmalogens are also present in intramuscular fat. The purpose of this study was to evaluate the effect of lipid derivatization on the presence of dimethyl acetal (DMA) molecules from plasmalogenic lipids in intramuscular fat samples. Three different methods of methylation were assayed. Acid-catalyzed methanolysis using HCl, the traditional procedure to derivatize meat lipids, was compared to two base-catalyzed methanolysis based on the ISO International standard procedure using either KOH and/or NaOCH3 which, apparently, are only able to methylate fatty acids from triacylglycerols. DMA compounds were isolated by thin layer chromatography and then identified by gas chromatography-mass spectrometry. The most prominent DMA molecules detected were 16:0 and 18:0, but also minor amounts of monounsaturated and branched-chain DMA were quantified. Acid methylation yielded the highest amounts of DMA. However, the present article demonstrates that ISO standard based methylation procedures could also generate DMA derivatives in considerable quantities, which is not usually considered and may interfere with the determination of fatty acid methyl esters (FAME) from triacylglycerides. The current research warns scientist about possible FAME misidentifying and overestimations in intramuscular fat analysis using basic methylation and the need to consider the presence of DMA in samples that contain plasmalogens.

Dietary linseed oil increases trans-10,cis-15 18:2 in caprine milk fat.

Trans-10,cis-15 18:2 has been recently detected and characterized in digestive contents and meat and adipose tissue of ruminants, but its presence in milk and dairy products is hardly known. The aim of this study was to quantify trans-10,cis-15 18:2 in milk fat, better understand its metabolic origin, and help to elucidate the mechanisms of rumen biohydrogenation when the diet composition might affect ruminal environment. To address these objectives, 16 dairy goats were allocated to 2 simultaneous experiments (2 groups of goats and 2 treatments in each experiment). Experimental treatments consisted of basal diets with the same forage-to-concentrate ratio (33/67) and 2 starch-to-nonforage neutral detergent fiber (NDF) ratios (0.8 and 3.1), which were supplemented or not with 30 g/d of linseed oil for 25 d in a crossover design. Trans-10,cis-15 18:2 contents in milk fat were determined by gas chromatography fitted with an extremely polar capillary column (SLB-IL111). Levels of trans-10,cis-15 18:2 in individual milk fat samples ranged from 0 to 0.2% of total fatty acids, and its content in milk fat increased 8 fold due to linseed oil supplementation, substantiating the predominant role of α-linolenic acid in its formation. The trans-10,cis-15 18:2 levels in milk fat were similar in both experiments, despite the fact starch-to-nonforage NDF ratio of their respective basal diets greatly differed. In conclusion, trans-10,cis-15 18:2 was clearly related to linseed oil supplementation, and its increase in milk fat was comparable when the basal diets were rich in either nonforage NDF or starch.

Extensive analysis of milk fatty acids in two fat-tailed sheep breeds during lactation.

The profile of fatty acids (FA) in the milk fat of two Iranian fat-tailed sheep breeds, Sanjabi and Mehraban, was compared during lactation. Eight ewes of each breed, balanced in parity and carrying one foetus, were selected before parturition. Ewes were kept separated in individual pens during the experimental period, under the same management practices and fed the same diet, in order to eliminate any confounding effects on milk FA profile. Milk was sampled at biweekly intervals up to 10 weeks of lactation, starting 2 weeks after parturition. More than 100 FA were determined in milk fat by means of gas chromatography. The milk fat of Sanjabi ewes contained more cis-9 18:1, that of Mehraban ewes was richer in 10:0, 12:0 and 14:0, and no differences were found for 16:0 and 18:0. No breed differences were found for most branched-chain FA. Mehraban ewes showed a higher presence of vaccenic and rumenic acids in their milk fat. The milk fat of Sanjabi ewes had a lower atherogenicity index and n-6/n-3 FA ratio. The contents of several FA showed time-dependent changes, so breed differences were more apparent or disappeared as lactation progressed. The milk fat of Sanjabi ewes showed a better FA profile from the human health point of view.