Modification of rice bran dietary fiber concentrates using enzyme and extrusion cooking

Abstract

Rice bran (RB) is an underutilized by-product of rice milling industry that is rich in insoluble dietary fiber (IDF) but low in soluble dietary fiber (SDF). SDF has proven health benefits and potential to improve the sensory and physicochemical properties of foods. Thus, conversion of RB-IDF to RB-SDF would be beneficial in value addition to the rice bran as a functional food ingredient. The objective of this study was to maximize soluble pentosan content in RB, using physical (extrusion) and enzymatic (xylanase) technologies individually and/or in combination on water-washed RB. Water-washing was necessary to remove water soluble compounds, all in order to increase the proportion of total dietary fiber (IDF + SDF) that could be converted to SDF. Although water-washing led to loss of native SDF along with starch and other solubles, this step substantially increased the content of IDF. Both enzyme treatment and extrusion improved the solubility of RB dietary fiber and other soluble components, especially the sequential extrusion-enzyme treatment significantly increased the total soluble pentosan content compared to individual or simultaneous treatments. Warm-water (37 °C) soluble pentosan content of treated RB was 6.5% in the sequential extrusion-enzyme treatment, and 4% by either extrusion alone or xylanase treatment alone or simultaneous extrusion-enzyme treatment. The total hot-water (100 °C) solubility was 25% (including 10.5% soluble pentosans) in the sequential extrusion-enzyme treatment, which was approximately a four-fold increase compared to the untreated RB, superior to extrusion alone or xylanase treatment alone.