Oxidation of walnut oil (Juglans regia L.) at heat treatment: primary and secondary oxidation products accumulation

Abstract

In this work heat treatment experiment was set up to determine the intensity of oxidation products accumulation in walnut oil with particular reference to the walnut oil sample at room temperature. The influence of the heat treatment conditions was assessed by measuring the primary and secondary oxidation products in oil samples immediately after treatment up to the highest temperature of 180 0C. Primary oxidation products of walnut oil samples were evaluated by measuring peroxide value and conjugated dienes & trienes content. The peroxide value was in the range of 5.81 – 26.55 mmol/kg of walnut oil. The conjugated dienes content of the walnut oil samples ranged from 6.23 to 12.75 μmol/g, while the conjugated trienes content ranged from 1.58 to 6.25 μmol/g. Secondary oxidation products of walnut oil samples were evaluated by measuring p-anisidine value and 2-thiobarbituric acid value. The p-anisidine value was in the range of 2.98 – 16.91 c.u. The 2-thiobarbituric acid value of the walnut oil samples ranged from 0.027 to 0.048 mg/kg. Walnut oil retained acceptable quality for heat treatment at 120 0C and quality deteriorated significantly for heat treatment of walnut oil at 160 0C and 180 0C.