Determination of 2-Acyl Positional Fatty Acid Distribution in Vegetable Oils by High Resolution ¹³C Nuclear Magnetic Resonance Spectroscopy

Abstract

2-Acyl positional fatty acid distribution of edible vegetable oils was determined by high resolution ¹³C nuclear magnetic resonance spectroscopy. Quantitative analysis of each 2-acylpositional fatty acids were carried out by dividing each peak area by that of total carbonyl or olefinic carbon on ¹³C-NMR. Individual chemical shifts were observed for the fatty acids with resolution enhancement. The carbonyl region could be used to identify oils containing only saturates, oleyl and linoleyl group at 2-acyl position. The olefinic region was useful for determining the number of acyl groups that gave rise to superimposed carbonyl peaks, as in the case of linoleyl and linolenyl.
¹³C-NMR conditions which affect time saving and quantitative analsis was examined. As a result, total time required to obtain the data from olefinic region is reduced to about 3h per each sample. The ¹³C-NMR method was assessed for capacity in making quantitative determinating using the Lipase-GC method. Regression of data obtained by the two methods showed satisfactory correlation. The olefinic and carbonyl spectral regions when used together provide information essential for determining full acyl positional distribution.