Phenolics in buckwheat hull extracts and their antioxidant activities on bulk oil and emulsions

Abstract

Buckwheat hulls are discarded as waste, although they have more phenolic compounds than buckwheat groats. The antioxidant activities of buckwheat hull extracts prepared with water, 50% ethanol, and 100% ethanol were investigated in bulk oil, oil-in-water (O/W), and water-in-oil (W/O) emulsions. The relationship between the phenolic compositions of the extracts and their antioxidant activities in the three different lipid systems was also evaluated. Fifty percent ethanol extract had the highest total phenolic content (327 mg gallic acid equivalent [GAE]/g extract) followed by water and 100% ethanol extracts (211 and 163 mg GAE/g extract, respectively). The total oxidation rate (k) was not significantly different among the bulk oils added with the buckwheat hull extracts. However, in the O/W emulsion, the k was more reduced by the 50% and 100% ethanol extracts than by the water extract at the concentration of 100 µg GAE/g (2.9, 2.8, and 3.7 Totox/day, respectively). The k of the W/O emulsion was more reduced by the 100% ethanol extract than by the water and 50% ethanol extract at the concentration of 100 µg GAE/g (3.8, 4.7, and 4.5 Totox/day, respectively). Multivariate statistical analysis revealed that the contents of phenolic acids and their derivatives were the highest in the water extract among the extracts, while the contents of flavonoid glycosides and methylated polyphenols were the highest in the 50% and 100% ethanol extracts, respectively. The results suggest that flavonoid glycosides and methylated polyphenols could be potential candidates for retarding the oxidation of the emulsion system. K E Y W O R D Sbuckwheat hulls, lipid antioxidation, multivariate statistical analysis Practical Application: Buckwheat hull extracts could retard lipid oxidation. Flavonoid glycosides and methylated polyphenols in buckwheat hull extracts may have an antioxidative effect on lipids. Thus, buckwheat hulls could be used as an antioxidant in lipid systems, as flavonoid glycosides and methylated polyphenols are properly extracted from buckwheat hulls.

Effects of roasting and ultrasound‐assisted enzymatic treatment of Nigella sativa L. seeds on thymoquinone in the oil and antioxidant activity of defatted seed meal

“…Specifically, the TQ and TPC contents in the UAET‐treated samples were significantly higher than those of the other groups ( P < 0.05), although no significant differences were observed for the other parameters. As per previous studies, TPC has been found to be positively correlated with antioxidant activity 28 . Results in this study were aligned with this notion, as the UAET treatment group with the highest TPC content exhibited the highest antioxidant activity.…”

“…As per previous studies, TPC has been found to be positively correlated with antioxidant activity. 28 Results in this study were aligned with this notion, as the UAET treatment group with the highest TPC content exhibited the highest antioxidant activity. The UT treatment group was found to have the second-highest TQ and TPC content following UAET treatment, while its TFC content was either similar to or lower than that of the untreated group.…”