Characteristics of blackberry, black raspberry and blueberry seed oils and importance of their minor components to autoxidative and photooxidative stabilities
The cold-pressed blackberry, black raspberry, and blueberry seed oils were evaluated for their fatty acid composition and their positional distribution within triacylglycerols, triacylglycerol profile, total phenolic content (TPC), and oxidative stability. All three seed oils were stripped of their minor components using a silicic acid column. The hexane extracted oils had a higher oil recovery than their column extracted counterparts, but retained some of the minor components, such as tocopherols. Accelerated oxidation under Schaal oven and photoxidative conditions demonstrated that the oxidative stability among non-stripped, column stripped and hexane stripped seed oils was different. Pigments, including carotenoids and chlorophylls, were also measured by UV-visible spectrophotometry and were found to influence the stability of the oils by singlet oxygen scavenging and photosensitization, respectively when exposed to light.
All tested seed oils contained significant levels of α-linolenic acid ranging from 16.4 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 (LnLnLn, LnLLn, LLLn, LLL, OLL and OLLn were detected where L, O, and Ln, are linoleoyl, oleoyl, and linonenoyl fatty acids, respectively) in the berry seed oils were determined as primary triacylglycerols as determined by high-performance liquid chromatography. Total tocopherol contents were 246.6−1302.9 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. All tested berry seed oils directly reacted with and quenched DPPH radicals in a dose- and time-dependent manner. All three tested berry seed oils suggest that berry seed oil lipid oxidation is affected by triacylglycerol profiles, positional distribution of fatty acids, storage condition and minor components. These data suggest that the cold-pressed berry seed oils may also serve as potential dietary sources for tocopherols, α-linolenic acid and natural antioxidants, but must be well protected from oxidative deterioration by proper storage in the dark and in the absence of air and with minimal processing to retain their minor components.
Keywords: α-Linolenic acid; fatty acid composition; triacylglycerol profiles; antioxidant; total phenolic content; tocopherol, berry seed oil