Analysis of fatty acid distribution in lipid extracts of infant formulas

Abstract

　Triacylglycerols (TAG) are the major neutral lipids in mammalian breast milk and they are known to have certain unique structural features. In these TAG, 16:0 fatty acids are located predominantly at the sn-2 position, whereas the short chain (SC) and unsaturated fatty acids (FAs) are located largely at the sn-1(3) position. In infant formula, a substitute for human breast milk, the positional distribution of FA in the TAG is of central importance in the compositional design for proper efficacy of lipid absorption and nutrition for the infant. Some infant formulas contain polyunsaturated (PU) FAs to improve nutritional benefits. However, the pancreas lipase used in the conventional method for identifying the FA occupying the sn-2 position of TAG, ISO 6800, is unsuitable for use with oils containing SCFA or PUFA.

　This study aimed to develop an experimental protocol to analyse the FA distribution in the TAG of infant formula. First, lipids in infant formulas were extracted using AOAC Official Method 932.02, generally known as the Röse-Gottlieb method. Recoveries in the range of 88～96％ from both liquid and powdered types of formulas were obtained. Because the PUFA contents in a fish oil mixture did not change significantly after extraction with Röse-Gottlieb method, the PUFAs were stable during the extraction procedure.

　The lipids extracted from infant formulas were subjected to Joint JOCS/AOCS official method Ch 3a-19 (JOCS Standard method 2.4.5) to determine the FA in the sn-2 position of TAG; this method is suitable for use with TAG containing SCFA and PUFA. In most of the infant formulas analysed in this study, 16:0 FA was mainly located at the sn-2 position. Docosahexaenoic acid was also located mainly at the sn-2 position in the PUFA-containing formulas.