Prevention of Hydrolytic Rancidity in Rice Bran during Storage

The effect of microwave heating, packaging, and storage temperature on the production of free fatty acids (FFA) in rice bran was examined. Freshly milled raw rice bran was adjusted to 21% moisture content and heated in a microwave oven at 850 W for 3 min. Raw and microwave-heated rice bran were packed in zipper-top bags or vacuum-sealed bags and stored at 4−5 or 25 °C for 16 weeks. FFA content of bran was measured at 4-week intervals. Total FFA increased rapidly over the 16-week period from the initial value of 2.5% in raw bran stored at 25 °C to 54.9% in vacuum bags and 48.1% in zipper-top bags. However, total FFA of raw bran stored at 4−5 °C increased at a slower rate from an initial value of 2.5 to 25.4% in vacuum bags and 19.5% in zipper-top bags. After 16 weeks of storage, total FFA of microwave-heated bran stored at 25 °C increased from 2.8 to 6.9 and 5.2%, respectively, for samples stored in vacuum bags and zipper-top bags. Total FFA of microwave-heated samples stored at 4−5 °C did not change significantly with storage time. Results showed that hydrolytic rancidity of rice bran can be prevented by microwave heating and that the recommended storage condition for microwaved rice bran is 4−5 °C in zipper-top bags. Keywords: Rice bran; free fatty acid; hydrolytic rancidity; microwave heat; storage