Concentration-dependent displacement of cholesterol in micelles by hydrophobic rice bran protein hydrolysates

Rice bran, containing about 100-150 g kg(-1) protein, is a by-product of rice milling that has only become an available ingredient in recent years owing to the centralisation of rice milling. Rice bran, but not its protein fraction or hydrolysates, has been shown to have a hypocholesterolaemic effect. Peptides from soy, milk and other foods have been proposed to have hypocholesterolaemic effects based on their ability to lower cholesterol solubility in bile acid/phosphotidyl choline micelles.

Rice bran protein hydrolysates (RBPHs) were prepared and investigated for their potential to lower cholesterol concentration in micelles. The RBPHs were produced by digestion using four different peptidases, alcalase 2.4L(®), neutrase 0.8L(®), papaya latex papain and porcine pancreas trypsin, and then fractionated by hydrophobicity using styrene/divinylbeneze resins. Alcalase 2.4L(®) produced the highest degree of hydrolysis, and the resulting hydrolysates had the highest micellar cholesterol inhibition ability in an in vitro hypocholesterolaemic test. The adsorption dynamics of four different macroporous resins, DA201-C, Sepabeads SP207 and SP825 and Diaion HP20, were determined using the Langmuir isotherm model. DA201-C had the highest adsorption capacity with an equilibrium concentration of 220 mg g(-1). The hydrolysates eluted with 25, 50, 75 and 95% (v/v) ethanol lowered the micellar cholesterol concentration by 11.88, 14.76, 19.37 and 7.56% respectively.

A hydrophobic fraction of RBPH had the highest inhibitory activity on micellar cholesterol, which suggests that it may have hypocholesterolaemic properties.