Rapid and direct quantitative analysis of positional fatty acids in triacylglycerols using ~(13)C NMR

摘要

There is increasing evidence that the positional fatty acid composition (FAC) of TAG is more important than total FAC with regard to nutrition values of edible oils and fats. A rapid and direct regiospecific analysis of positional fatty acids in TAG using ~(13)C NMR was developed to overcome the tedious conventional methods which involve enzymatic hydrolysis, Grignard chemical degradation, and chromatography analysis. A set of NMR data acquisition parameters and processing methods had proven their excellent versatility and applicability on various types of oils and fats, with systematic error of 1.0 mol%. It was found that there are discrepancies between the regiospecific analysis results obtained by the current method and by conventional methods. Probable acyl migration occurring in the hydrolysis process in conventional methods is a noted problem. As the current ~(13)C NMR method is a direct measurement and no hydrolysis of the sample is needed, acyl migration during the analysis is eliminated. As a result, the saturation level is always higher at sn-1, 3 positions and lower at sn-2 position in TAG structure of oils in the regiospecific data obtained from the current ~(13)C NMR than that from conventional methods. In the absence of laborious chemical derivatization, this method is simple, accurate, and user-friendly for researchers, especially for nutritionists to support their nutritional studies from the perspective of positional FAC of edible oils and fats.