Oxidative stability of blackberry, black raspberry and blueberry seed oils as affected by their structural features, minor components, and storage conditions

Li, Quanquan (2014) Oxidative stability of blackberry, black raspberry and blueberry seed oils as affected by their structural features, minor components, and storage conditions. Masters thesis, Memorial University of Newfoundland.

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Abstract

Cold-pressed blackberry, black raspberry, and blueberry seed oils were evaluated for their fatty acid composition, positional distribution of fatty acids within triacylglycerols, triacylglycerol (TAG) profile, total phenolic content (TPC), tocol profile, and oxidative stability (in the dark at 60°C and under fluorescent light at 27°C), before and after the removal of their minor components. All three berry seed oils were stripped of their minor components using a silicic acid column and a hexane/methanol solvent partitioning system, respectively. Accelerated oxidations under Schaal oven and photooxidative conditions demonstrated that the oxidative stability of non-stripped, and column-stripped oils was different. Tocopherols and tocotrienols, collectively known as tocols, were determined by high performance liquid chromatography, and found to affect the stability of oils by donating hydrogen atoms in the dark at 60°C. Pigments, including carotenoids and chlorophylls, were also measured by UV-visible spectrophotometry and were found to influence the stability of the oils. The stability of the oils was dictated by their fatty acid composition, TAG profile, and the type and quantity of their total tocols and pigments present. All tested seed oils contained significant levels of α-linolenic acid, ranging from 13.4 to 33.7 g per 100 g of oil, along with a low ratio of n−6/n−3 fatty acids (1.49−3.86). Six triacylglycerols, namely LnLnLn, LnLLn, LLLn, LLL, OLL and OLLn were detected by high-performance liquid chromatography in berry seed oils tested, where O, L and Ln, are oleoyl, linoleoyl, and linonenoyl fatty acids, respectively. Total tocol contents were 286.3−1302.9 ppm, and included α-, γ-, and δ-tocopherols as well as δ-tocotrienol. The highest TPC of 0.48 mg gallic acid equivalents per gram of oil was observed in the black raspberry seed oil. Oxidative stability of the three berry seed oils tested was affected by their triacylglycerol profiles, positional distribution of fatty acids, storage conditions and minor components. These data suggests that the cold-pressed berry seed oils may also serve as potential dietary sources for tocols, α-linolenic acid (ALA) and natural antioxidants. These oils must be well protected from oxidative deterioration by proper storage in the dark and in the absence of oxygen and with minimal processing in order to retain their integrity and health promoting minor components.

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