Influence of Different Storage Conditions on Rapeseed Oils Quality

Abstract

Aims: The aim was to determine the impact of various storage conditions on the stability of rapeseed oil, which determines the content of free fatty acids, peroxides, aldehydes, conjugated compounds and fatty acid composition. Study Design: Storage experiment was performed in 6 months period; Quality of oils was analysed using standard methods. Fatty acid composition of oils was determined using gas chromatography. The data were analysed using Statistica v. 12.5 software. Place and Duration of Study: Chair of Food Plant Chemistry and Processing, Olsztyn, Poland between December 2014 and July 2015. Methodology: The material consisted of 24 commercial samples of rapeseed oils. Samples were stored in brown glass bottles for six months in different conditions - in the dark at +20°C, in a refrigerator at +4°C, and in a freezer at -20°C. The quality of rapeseed oil was determined by measuring the acid value, peroxide value and anisidine value. The fatty acid composition and the content of conjugated dienes and trienes were also analyzed.  Results: In control samples cold pressed oils were characterized by the highest acid value and the lowest anisidine and peroxide values. Cold pressed oil samples stored at -20°C had the highest acid value (an increase by 9.21%); however, unlike fresh oils, they also had the highest peroxide value (an increase by 5.17%). The greatest increase in the content of saturated fatty acids during storage was noted for refined hot pressed oils (6.33%). A permanent trend was an increase in the share of monounsaturated fatty acids, and a decrease in the share of polyunsaturated fatty acids. The share of MUFAs increased most following storage at 20°C for refined hot pressed oils (9.38%), and pressed and extracted oils (9.35%). In the same samples, the greatest decrease in the content of PUFAs also occurred by, respectively, 30.78% and 31.22%. Conclusion: Higher temperatures are more conducive to oxidative changes in oils, which are indicated by higher values of all the analyzed distinguishing quality features of oils. Refined oils are more susceptible to these changes as in the process of purification a number of substances with antioxidant properties are removed.