Effect Of White Rice Protein, Brown Rice Protein And Their Hydrolysates On Lipid Metabolism

Dietary protein is not only the source of essential amino acids required for growth or maintenance but alsocontains amino acid sequences for peptides that have antimicrobial, blood pressure-lowering (ACE inhibitor),anti-oxidative, and cholesterol-lowering properties. Rice (Oryza sativa) accounting for about25%of the worldcereal grain production is the staple food in most Asian countries. White rice protein (WRP) has been shown tohave hypocholesterolemic properties in several studies, but to our knowledge the hypocholesterolemic ability ofwhite rice protein hydrolysates (WRPH), brown rice protein (BRP), and brown rice protein hydrolysates (BRPH)has not been reported.WRP, BRP, and soybean protein (SP) were hydrolyzed by peptidases Alcalase2.4L. The cholesterollowering ability of WRP, BRP, SP, WRPH, BRPH, and soybean protein hydrolysates (SPH) was identified usingcholesterol micellar solution and Caco-2cell and their bile acid binding ability was indentified using artificial bileacid solution. The results showed all original proteins and their hydrolysates had cholesterol-lowering and bileacid binding abilities.The effects on lipid metabolism of WRP, BRP, SP, and their hydrolysates were studied using Male SyrianGolden hamsters fed high-fat and-cholesterol diets. Compared with casein, the final body weight and weight gainwere significantly (P <0.05) reduced12%and76%in BRPH diet group. Fecal dry weight, lipid, triglyceride andnitrogen contents were negatively correlated, r=-0.785, r=-0.871, and r=-0.795, respectively, with final bodyweight (P <0.05). In WRPH, BRP, BRPH, SP, and SPH diet groups, the plasma very low-density lipoproteincholesterol (VLDL-C) and hepatic total cholesterol contents were significantly (P <0.05) lower compared withthe control group. WRPH, BRP, BRPH, and SPH significantly (P <0.05) increased the fecal total lipid content(64%-280%) compared with casein. Compared with the control group, WRPH and BRPH significantly (P <0.05)increased the fecal total cholesterol excretion (206%and108%) and WRP, WRPH, BRPH, and SP significantly(P <0.05) increased the fecal total bile acid excretion (67%-75%).Hamsters fed the BRPH supplemented diet had the lowest mRNA level of lipid biosynthesis gene SCD1andhighest mRNA levels of lipid oxidation gene, PPARα, ACOX1, and CPTI. In WRPH, BRP, BRPH, and SPH dietgroups, there were negative correlations between mRNA level of CPTI and final body weight (r=-0.883, P=0.063) and body weight gain (r=-0.775, P=0.1). The negative correlation was also observed between mRNAlevel of ACOX1and final body weight (r=-0.869, P=0.1). Correlations between fecal total lipid concentrationand mRNA levels of CPTI (r=0.946, P <0.05) and ACOX1(r=-0.883, P <0.05) were observed. The mRNAlevels of CYP51and CYP7A1were up-regulated in WRPH, BRP, BRPH, and SPH. In the BRPH diet group,hepatic and fecal total cholesterol concentrations were negatively (r=-0.969, P <0.05) and positively (r=0.758,P=0.1) correlated, respectively, with the expression of CYP51.The effects on lipid metabolism of soybean protein peptides LPYPR and WGAPSI, with micellar cholesterolinhibition ability in vitro were identified using mice fed high-fat and-cholesterol diets. Except the reduction ofVLDL-C and triglyceride concentrations, the peptides containing diets increased the plasma cholesterolconcentration with increasing dose of the peptides. Mice fed diets supplemented with the peptides also had lowerfecal bile acid excretion. The mRNA levels of the genes CYP51, LDLR, and CYP7A1were up regulated in micefed diets supplemented with peptides except the WGAPSI (0.45g/kg diet) diet group.