Variation in the composition and oxidative stability of commercial rapeseed oils during their shelf life

Abstract

This study was conducted to evaluate the variation in chemical composition and oxidative stability of 21 different commercial rapeseed oils. Their composition was estimated immediately after opening the packaging and for the same oils at the end of their induction period. The oxidation of oils was conducted at 110°C in an oven test, while the induction time was determined in a Rancimat test at the same temperature. It was found that the initial ratio of n‐6 to n‐3 fatty acids was close to 2.2 to 1. These oils differed mainly in minor acids, such as C16:0 and C20:1. At the end of their shelf life, a reduction of C18:2 and C18:3 acids shares was found, which was accompanied by a slight increase of n‐6 to n‐3 ratio. The most variable oil‐soluble compounds of oils were carotenoids, chlorophylls, and phenolics, while the tocopherols were the most stable. Induction time was the most positively correlated with the oil‐soluble phenolics (r = 0.76 for all samples) and chlorophylls (r = 0.77 for refined oils), while carotenoids generally acted as pro‐oxidants (r = −0.66 for all oils). The degradation degree of tested compounds during oxidation (on average) was as follows: phytosterols > tocopherols > carotenoids > phenolic compounds > chlorophylls.Practical applications: Rapeseed oil is a popular edible oil and may be a good source of oil‐soluble vitamins, polyunsaturated fatty acids and antioxidants in human diet. However, its composition depends mainly on the rape genotypes, cultivation conditions, industrial practices, and storage conditions. In this study, we evaluated the variability in chemical composition of typical commercial rapeseed oils immediately after opening the package and at the end of their induction time. We have shown that fatty acids composition of tested oils was relatively stable, while their minor compounds content were significantly different. Oils oxidative stability was mainly related to phenolic compounds. These informations are important both for the consumers (nutrition facts), and industry (phenolics as antioxidants).Score plot of the two first principal components after PCA analysis of oil‐soluble minor components of fresh (1‐21) and oxidized (1’‐21’) rapeseed oils with an indication by ellipses samples of cold pressed oils before (green) and after oxidation (yellow); 1‐3 – cold pressed, unrefined oils, 4‐21 – refined mixture of pressed and extracted oils.