Correlations between H-1 NMR and conventional methods for evaluating soybean oil deterioration during deep frying

摘要

H-1 NMR was applied as a fast method to determine soybean oil deterioration during deep frying and its correlations with conventional analytical methods were evaluated. Very high correlations (R = 0.925-0.968) were observed between the secondary oxidation products (n-alkanals, aldehyde, (E,E)-2,4-alkadienals) determined by H-1 NMR and the total polar compounds (TPCs) determined by conventional silica gel column method. Strong correlations were found between H-1 NMR and conventional gas chromatography method for analyzing linoleic (correlation coefficient R = 0.988), inolenic (R = 0.946) and oleic acids (R = 0.869). Moderate correlations (R = 0.664-0.742) were presented between the secondary oxidation products (n-alkanals, aldehyde, (E,E)-2,4-alkadienals) determined by H-1 NMR and p-anisidine value (AnV) determined by conventional spectrophotometer method. The very high correlations between the formation of aldehydes and TPCs found in this study makes H-1 NMR a potential tool to predict the maximum number of times that oil can be re-used during frying.