EXTRACTION OF SOLUBLE DIETARY-FIBERS FROM DEFATTED RICE BRAN

The influence of extraction reagents on the properties of soluble dietary fiber was examined in defatted rice bran. The effect of soluble fiber preparations on hypocholesterolemic activity in cholesterol-fed rats was also investigated. The extraction reagents examined were: 1) pH 14 sodium hydroxide, 2) pH 12 calcium hydroxide, 3) pH 11 sodium carbonate, 4) pH 3 acetic acid, and 5) pH 0.5 hydrochloric acid solutions. The starch in the rice bran was previously digested with glucoamylase. The yields of soluble fiber extracted from 100 g of starch-free rice bran with extraction reagents 1-5 were: 8, 5, 2, 2, and 4 g, respectively. Composition, protein contamination, and coloration of the soluble fibers varied considerably with the extraction reagents. Soluble fibers extracted with alkaline solutions had the same arabinose-to-xylose ratio, but those extracted with acidic solutions were different. In the isolation of extract 2, trichloroacetic acid treatment could be omitted because the protein content was quite similar between treated and untreated fibers. Soluble fiber extracted with solution 2 had the least coloration, whereas that extracted with solution 1 had the most. Male Sprague-Dawley rats, aged four weeks, were fed a hypercholesterolemic diet containing 2% of each extracted soluble fiber for nine days. The soluble fibers extracted with solutions 1 and 2 suppressed the elevation of serum cholesterol levels. These results indicate that calcium hydroxide is appropriate for the extraction of soluble fiber from defatted rice bran because it produces the least color, gives a desirable composition and yield, and retains the hypocholesterolemic activity.