Abstract
The aim of this study was to investigate the physicochemical properties (extraction yield, color development, fatty acid profile, iodine value, saponification value, phytosterol profile(, DPPH radical scavenging activity and oxidative stability of cold pressed walnut oil extracted from microwave pretreated kernels (0, 2.5, 5 and 7.5 min, 600 W). Results showed that microwave pretreatment of persian walnut kernel increased the oil extraction yield, color development, the polyunsaturated to saturated fatty acids (PUFA/SFA) ratio and phytosterols of all oil samples. Also, no significant differences (p≥ 0.05) were observed during microwave pretreatment in saponification value (192.71-193.73 mg KOH/g oil), iodine value (150.12-151.81gI2/100 g oil) and SFA, MUFA, PUFA values of walnut kernel oil samples. The predominant unsaturated fatty acids in oil samples in all treatments were determined as linoleic acid C18:2c (55.67%- 56.49%) and oleic acid C18:1c (20.70%- 21.56%), respectively. The predominant phytosterols in oil samples in all treatments were determined as β-sitosterol, Δ-5-Avenasterol, Campesterol,Δ-7-Avenasterol and Δ -7-Stigmasterol. The highest DPPH radical scavenging activity were observed in oil samples of MW-0 (90.62%) and MW-2.5 (73.96%), respectively. In addition, peroxide value, anisidine value and totox value of control walnut oil (MW-0) and pretreated walnut oil (MW-2.5) at an oven temperature of 160 ° C at 0, 3, 6 and 9 h intervals were determined. Also oxidative stability index (OSI) was determined by rancimat test at 120 ° C. The results indicated that microwave pretreatment is a promising strategy for amplification of oil extraction yield, the content of phytosterols and PUFA/SFA) ratio in obtained oil from persion walnut kernels.
Keywords: Cold press, Microwave roasting, Oxidative stability, Walnut kernel Oil, Phytosterol.