Effects of Harvesting Methods and Microwave Pretreatment on the Quality of Pressed Rapeseed Oil

The rapeseeds,collected by one-time and two-stage harvesting,were treated with microwave oven(2450 MHz,800 W)for 7 min,then pressed at low temperature. The changes in quality of rapeseed oil under different harvesting and pretreatment methods were analyzed and compared. The results showed that there were significant differences in fatty acid composition,acid value and peroxide value of rapeseed oil under different harvesting methods(P<0.05). Compared with two-stage harvesting of raw material oil,the phytosterols and vitamin E in one-time harvested of the raw material rapeseed oil were 16.31% and 6.56% higher,respectively. The total phenolic content(TPC)decreased by 36.90%,1,1-diphenyl-2-trinitrophenylhydrazine(DPPH)free radical scavenging ability,the iron ion reduction antioxidant capacity(FRAP)were reduced by nearly 50%,and oxidation induction period(IP)was shortened by 0.55 h. Compared with control group,the increases of vitamin E and total sterol in the microwave pretreatment groups were 18.76~19.90 and 378.25~548.81 mg/kg.Canolol and TPC increased by 595.16~835.77 μg/g and 119.24~130.29 mg/100 g,respectively. DPPH,FRAP and IP values of microwave pretreatment groups increased by 20.72~33.13 times,22.98~31.62 times,2.11~2.43 times of the control group. Therefore,microwave pretreatment could effectively improve the content of trace components in rapeseed oil,and give it better oxidative stability and higher nutritional value.