Study on the Antioxidant Effects of Extract and Powder of Green Walnut Hulls on the Oxidation of Sunflower Oil

One way to protect the oil against oxidation is using antioxidants. Since the most used synthetic antioxidants are harmful to health, due to safety concerns, there is an increasing trend among food scientists to replace synthetic antioxidants with natural ones, which, in general, are supposed to be safer. Walnut hulls, due to having high antioxidant effects, is a good choice as a natural antioxidant. The aim of this study, is investigation of the antioxidant effects of the extract and powder of green walnut hall on the oxidation of sunflower oil. Green walnut hull extract was prepared with Maceration and Soxhlet extraction methods and the amount of phenolic compounds and antioxidant activity, respectively, was determined by Folin-Ciocalteu and DPPH radical trap methods. Antioxidant effects of different concentrations (100, 250, 500 and 1000 mg/kg) of green hull extract and powder (500 and 1000 mg/kg) were compared with the control and artificial antioxidant TBHQ in the maximum limit amount (200 mg/kg) through evaluation of acidity, peroxide value and thiobarbituric (TBA) on days 0, 5, 10 and 15 days of storage at 70°C. The amount of total phenolics and flavonoids for Maceration method was 17.81 and 1.59 and for Soxhlet method was 98.07 and 38.7, respectively, on the basis of gallic acid and catechin (mg/g sample) for phenols and flavonoids obtained. The walnut hulls’ EC50 was 0.15 mg/ml. The data showed that peroxide value and thiobarbituric oxidation rate increase over time, but the samples containing extract and powder of walnut hulls compared to the control in most concentrations showed less oxidation. The use of high concentrations of green walnut hull extract increased oil oxidation, and the best result was obtained for 100 mg/kg that could well slow the oxidation process and compete with TBHQ at 200 mg/kg. Soxhlet extraction method leads to higher levels of polyphenols than the Maceration method. Less concentration of green hull extract is more effective than higher concentrations in reducing oxidation. Green walnut hull is presented as a source of high antioxidant effect with low price to replace with synthetic antioxidants.