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Comparison of methylation methods for fatty acid analysis of milk fat

Liu, Zhiqian, Ezernieks, Vilnis, Rochfort, Simone, Cocks, Ben
Food chemistry 2018 v.261 pp. 210-215
catalysts, conjugated linoleic acid, fatty acid composition, fatty acid methyl esters, free fatty acids, methylation, milk, milk fat, phospholipids, potassium hydroxide, temperature, transesterification, triacylglycerols
Three acid- and alkaline-catalysed transesterification methods were compared with the aim to validate a simple yet reliable protocol for fatty acid (FA) profiling of milk fat. While both the acid- and alkaline-catalysed methods were able to convert completely triglycerides and phospholipids into fatty acid methyl esters (FAMEs), the acid catalyst caused significant degradation of conjugated linoleic acid C18:2c9t11 at high temperature. Although a milder temperature can mitigate this negative impact, a long reaction time (2 h) is required to achieve full methylation. By contrast, despite being unable to methylate free fatty acids (FFA), the alkaline-catalysed transesterification yielded comparable results for all major FA due to the very low level of FFA in milk. The alkaline-catalysed methylation is benign for C18:2c9t11. We recommend here a simple one-step protocol based on 0.2 M methanolic KOH, a short reaction time (20 min) and a mild reaction temperature (50 °C) for milk FAME preparation.