Effect of Microwave Treatment on the Changes in Lipids of Rice during Storage

The aim of this study was to reveal the changes of lipids in rice with and without microwave pretreatment during storage. Different varieties of rice (Jindao 919, Chaobei 2, and Daohuaxiang 2) were microwaved at 850 W for 50 s and stored under different conditions for up to three months. The changes of lipase, lipoxygenase, peroxidase and catalase activity, fatty acid value (FAV), peroxide value (POV), and carbonyl value (CV), water distribution and volatile components were evaluated. The results showed that microwave treatment effectively reduced the water activity of rice, changed the microstructure of rice grains, and inactivated the activity of lipases. After microwave treatment, the activities of lipase, lipoxygenase, peroxidase and catalase decreased by an average of 54.03%, 71.11%, 95.94%, and 46.04% for Jindao 919, Chaobei 2, Daohuaxiang 2, respectively. After storage at 37 ℃ for 90 days, FAV, POV and CV were only increased by 0.716-1.436 mg/100 g, 2.859-6.734 mmol/kg and 3.697-5.308 mmol/kg, respectively. It was demonstrated that microwave treatment could effectively deactivate the activity of lipolytic enzymes, and reduce the production of free fatty acids and hydroperoxides from the hydrolysis and oxidation of rice lipids and the production of volatile aldehydes and ketones, thereby delaying quality deterioration in rice during the storage process.