Abstract: Rice bran was fermented to produce soluble dietary fiber (SDF) with Aspergillus niger. The optimum fermentation conditions for higher yield of SDF were determined by one-factor-at-a-time method and Box-Behnken response surface methodology and the structural and physicochemical change of SDF before and after fermentation was examined. The maximum yield of SDF of 38.23% was achieved after fermentation at 26 ℃ and pH 5.0 with a solid-to-solvent ratio of 1:11 (g/mL) at a shaking speed of 150 r/min, which was improved by 29.58% compared with that before optimization. The swelling force, water-holding capacity and oil-holding capacity of SDF were increased respectively by 84.44%, 79.30% and 73.25% after fermentation. The result of scanning electron microscopy showed that fermented SDF displayed a rough surface and porous structure.

Key words: rice bran, soluble dietary fiber, Aspergillus niger, response surface methodology, physiochemical properties