Abstract:
The soluble phenols were extracted from the seeds of sumac (Rhus coriaria L.) and fennel (Foeniculum vulgare) with 70% aqueous ethanol, and the bound phenols were liberated by alkaline hydrolysis with 2M NaOH. The soluble- and bound-phenolics fractions from sumac and fennel were added to sunflower oil at concentrations of 400 and 800 ppm. Sunflower oil (Control), the sumac- and fennel-treated samples, and sunflower oil containing 200 ppm of butylated hydroxy anisole (BHA) were stored at 60oC and the evolution of the primary and secondary lipid oxidation products was monitored for 35 days. The soluble- and bound phenols from both seeds inhibited lipid oxidation as reflected by the decrease (P<0.05) in peroxide value (PV), conjugated dienes (CD), anisidine value (AnV), and the increase in the induction period (P<0.05) as measured by the Rancimat, relative to the control, during storage. The soluble-phenolic fractions of both fennel and sumac were generally more effective in inhibiting (P<0.05) sunflower oil oxidation than their bound-phenolic counterparts. Further, both fractions of sumac exerted a more pronounced decrease (P<0.05) in AnV, CD, and PV, and an increase (P<0.05) in the induction period, relative to the control, than their fennel counterparts during storage of sunflower oil. The samples treated with an 800-ppm soluble fraction of sumac exhibited similar patterns of change in the lipid oxidation indices and the induction periods of the 200-ppm BHA-containing samples, thereby indicating the sumac soluble-phenolic fraction can substitute the synthetic BHA at the indicated levels.
