MEASURING OXIDATIVE STABILITY OF STRUCTURED LIPIDS BY PROTON NUCLEAR MAGNETIC RESONANCE

Abstract

ABSTRACT

The oxidative stability of enzymatically modified oils (structured lipids) and their unmodified counterparts were assessed using proton nuclear magnetic resonance (¹H NMR) spectroscopy. This methodology was used to monitor relative changes in the proton absorption pattern of the fatty acids of oils during storage at 60C. Relative changes of aliphatic to olefinic (R_ao) and aliphatic to diallylmethylene (R_ad) proton ratios during oil oxidation were determined by ¹H NMR spectroscopy. An increase in R_ao and R_ad values was obtained over the entire storage period. The oxidative stability of oils was also evaluated using conjugated dienes (CD) determination, 2-thiobarbituric acid reactive substances (TBARS) and headspace volatile analysis. A highly significant correlation (r = 0.930–0.992; P ≤ 0.005) existed between the CD values and changes in R_ao and R_ad during oxidation of all oils. The correlation coefficient between TBARS and changes in R_ao and R_ad values was in the range of 0.779–0.983 (P ≤ 0.05). A high correlation (r = 0.948–0.996; P ≤ 0.005) was found between hexanal content and R_ao and R_ad of oils. Propanal content was also highly correlated (r = 0.950–0.990; P ≤ 0.005) with R_ao and R_ad.

PRACTICAL APPLICATIONS

Assessment of the extent of lipid oxidation in food is of much interest to producers and scientists alike. Proton nuclear magnetic resonance spectroscopy provides a valuable tool for quantitation of oxidation of food lipids. This procedure was used for evaluating the oxidative state of structured lipids. The procedure is rapid and nondestructive, requires a small amount of material, and may be considered as “green” because it uses a very minimum amount of solvent and is readily applicable to edible oils and oils extracted from food and biological samples.