Document Type : Research Article
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Abstract
Nowadays, the use of natural antioxidants as alternative antioxidants is more acceptable than synthetic antioxidants mainly for negative effects such as carcinogenicity and toxicity. This has led to an increasing interest in the search for natural antioxidants. The objectives of this study were to measure total crude phenolic compounds and in sorghum grain as natural antioxidant sources, to determine antioxidant effect of extracted compounds in various concentrations on sheep tail fat and to compare antioxidant effect of crude extract with synthetic antioxidant (TBHQ). The crude phenolic compounds in the whole sorghum grain were extracted using the organic solvents (acetone and methanol) and its constituents were measured by HPLC method. Antioxidant effect of extracted compounds at three concentrations (500,1000 and 2000 ppm) was determined by measurement of peroxide value, Thiobarbitoric Acid Substances(TBAS) and induction period (rancimat) compared with control (sheep tail fat without extract) after 48 and 96 hours incubation at 80ºC. The antioxidant effect of crude phenolic extract at optimum concentration (1000 ppm) and TBHQ at 100 ppm was also determined by measurement of later factors compared with control at 4-day intervals during 20 days of storage at 80ºC. Total crude phenolic compounds were 1700 (mgGA/100gr) Phenolic acids (Gallic acid, Vanillic acid, Ferulic acid and Caffeic acid), flavonoids and anthocyanins were measured as main crude phenolic compounds that determined by HPLC. Anthocyanins were the main components of flavonoids. The most antioxidant effect on sheep tail fat was achieved by adding of 2000 ppm of crude phenolic extract from sorghum after 96 hours at 80ºC. The most effective concentration of crude phenolic extracts on sheep tail fat was determined 2000 ppm. Crude phenolic extract at 2000 ppm increase induction period significantly. Synthetic antioxidant (TBHQ) exhibits constant and higher antioxidant effect compared with crude phenolic extract during 20 days of storage. This antioxidant increase induction period of sheep tail fat more than crude phenolic extract. The results indicated that crude phenolic extract present in the sorghum grain may be introduced as natural antioxidant source with out any harmful effects on human health. But the presence of high amounts of anthocyanin as red pigment in crude phenolic extract and its negative effects on oil colour may limit use of this antioxidant.
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