Hot air-assisted radio frequency heating for stabilization of rice bran: Enzyme activity, phenolic content, antioxidant activity and microstructure

Stabilization treatment of rice bran (RB) for reducing enzyme activity and improving storability is a key step to develop its value-added utilization. Hot air-assisted radio frequency (HA-RF) heating was investigated as a stabilization method for RB, and associated quality attributes were evaluated and compared with samples subjected to extrusion stabilization. Results showed that two HA-RF stabilization treatments (low-temperature HA-RF: 100-105 degrees C, 15 min; high-temperature HA-RF: 110-115 degrees C, 6 min) reduced lipase and polyphenol oxidase activities to 20-30% of fresh RB. HA-RF stabilized RB was darker than that of fresh RB. HA-RF stabi-lization had no significant (p > 0.05) effect on protein, lipid, total tocotrienol and total tocopherol contents, and fatty acid composition, but reduced free phenolic content of RB. HA-RF stabilized RB also showed higher free flavonoid content, higher antioxidant ability, and less damage to the microstructure than extruded RB. This study provides useful information for making HA-RF heating as an industrial stabilization method for RB.