36 Food processing of cereal brans reduces blood cholesterol and precancerous colonic cells by changing bioavailability.

Wallace H. Yokoyama and Benny E. Knuckles. USDA, ARS, Western Regional Research Center, Albany, CA 94710.

The importance of physico-chemical factors on the bioavailability or activity of phytonutrients is often overlooked. Often analytical determination of phytonutrients is equated with bioavailibility. Soluble fibers, including beta-glucan (B-glucan) from oat and barley, reduce plasma cholesterol. Soluble fibers are usually highly viscous and this property has been associated with plasma cholesterol lowering. Viscosity of a given polymer is usually directly related to size. Hamsters fed oatrim, a processed oat product, had up to 36% lower total plasma cholesterol and 67% lower low density lipoprotein (LDL) cholesterol. The molar mass of the B-glucan polymer in the raw oat was 1.1 × 10(^6) daltons whereas the processed materials had been degraded to about 1/3 the original mass. Wheat bran is the source of dietary fiber that has shown the most consistent beneficial effect on colon cancer. Humans often consume wheat bran in the form of processed breakfast cereals. Rats fed processed wheat bran had up to 40% lower precancerous cells in the distal colon compared to rats fed raw wheat bran. Processing may increase bioavailability of beneficial components of wheat bran.