Cholesterol-Lowering by Rice Bran and Rice Bran Oil Unsaponifiable Matter in Hamsters

Abstract

Cereal Chem. 73(1):69‐74 Unsaponfiable matter (U) was prepared from both raw and extrusion stabilized (130°C) rice bran and tested for cholesterol-lowering activity in hamsters by addition to diets containing cellulose, raw rice bran, or stabilized rice bran at either the level found in the rice bran diet (0.4%, 1X) or twice that level (2X). All diets contained 0.3% cholesterol, 10% total dietary fiber, 10.1% fat, and 3% N (same plant-to-animal N ratio). After 21 days, plasma cholesterol was significantly reduced by rice bran diets containing added U compared to the cellulose control diet, while the high density lipoprotein cholesterol-to-low density lipoprotein cholesterol ratio remained unchanged in all treatment groups. Liver cholesterol was significantly reduced by all rice bran-containing diets and with cellulose diets containing 2X added U when compared to the control diet. Rice bran diets plus added U resulted in cholesterol values lower than cellulose diets containing the same level of U. Stabilization of rice bran did not appear to affect the plasma and liver cholesterol responses to the unsaponifiable matter prepared from the extracted o il. There appears to be a dose response to rice bran unsaponifiable matter in plasma and liver cholesterol reductions. After 2 weeks, fecal fat and neutral sterol excretion were significantly greater with all treatment diets compared to the control diet. Fecal fat was negatively correlated with liver as well as plasma cholesterol (r = ‐0.97, P ≤ 0.0001 and ‐0.91, P ≤ 0.0006, respectively). Under the conditions of this study, cholesterol-lowering activity of rice bran is present in its unsaponifiable matter in add ition to other components. Increased fecal excretion of fat and neutral sterols appears to be a possible mechanism for cholesterol-lowering by rice bran. Hypocholesterolemic effects of rice bran and some of its fractions (neutral detergent fiber, hemicellulose, rice bran oil, and unsaponifiable matter) have been observed (Suzuki and Oshima 1970; Ayano et al 1980; Ishibashi and Yamamoto 1980; Suzuki 1982; Sugano et al 1984; Sharma and Rukmini 1986, 1987; Seetharamaiah and Chandrasekhara 1988, 1989; Raghuram et al 1989; Hegsted et al 1992; Nicolosi et al 1991). We have previously reported plasma and liver cholesterol-lowering with stabilized full-fat rice bran, and liver cholesterol-lowering with defatted rice bran when combined with rice bran oil or degummeddewaxed rice bran oil (Kahlon et al 1990; 1992a,b) in cholesterolfed hamsters. In the study reported here, male hamsters were fed 0.3% cholesterol diets to evaluate the cholesterol-lowering activity of raw vs. extrusion-stabilized (130 °C) rice bran and of unsaponifiable matter (U) prepared from raw or stabilized rice bran and added to diets at two concentrations. Raw rice bran and its U were investigated to determine the effects of the stabilization process on cholesterol-lowering properties.