The differences of three pretreatment methods (acetyl chloro carbinol esterification, acid hydrolysis esterification and alkali hydrolysis esterification) for the detection of four polyunsaturated fatty acids (docosahexaenoic acid, arachidonic acid, linoleic acid and α -linolenic acid) in infant formula milk powder were discussed. Acetyl chloro carbinol esterification and acid hydrolysis esterification were found to be significantly better than alkali hydrolysis esterification. The sample digestion and fat methyl esterification were carried out simultaneously in the acetyl chloro carbinol esterification method, where the two processes seemed to enhance each other. This allowed the complete release and methyl esterification of the fats. The accuracy of the methods was determined by investigating the reaction processes and recovery rates. Acid and alkali hydrolysis esterification methods were employed to hydrolyze the samples using a hydrochloric acid solution and an ammonia solution, respectively. Then, the fats were extracted for subsequent methyl esterification. These two methods were compared in terms of the digestion efficiency, extraction efficiency, and methylation efficiency. The results showed that the digestion efficiency is the main factor determining the differences between the acid and alkali hydrolysis methods. The accuracies of acetyl chloro carbinol esterification and acid hydrolysis esterification methods were further verified in the detection of samples, providing a basis for the determination of fatty acids in other foods.
Keywords: acetyl chloro carbinol esterification; acid hydrolysis esterification; alkali hydrolysis esterification; differences; infant formula milk powder; polyunsaturated fatty acid.