Rice Protein Extracted by Different Methods Affects Cholesterol Metabolism in Rats Due to Its Lower Digestibility

Abstract

To elucidate whether the digestibility is responsible for the hypocholesterolemic action of rice protein, the effects of rice proteins extracted by alkali (RP-A) and α-amylase (RP-E) on cholesterol metabolism were investigated in 7-week-old male Wistar rats fed cholesterol-free diets for 3 weeks. The in vitro and in vivo digestibility was significantly reduced by RP-A and RP-E as compared to casein (CAS). The digestibility was lower in RP-E than that of RP-A. Compared with CAS, the significant cholesterol-lowering effects were observed in rats fed by RP-A and RP-E. Fecal excretion of bile acids was significantly stimulated by RP-E, but not by RP-A. The apparent cholesterol absorption was more effectively inhibited by RP-E than RP-A because more fecal neutral sterols were excreted in rats fed RP-E. There was a significant correlation between protein digestibility and cholesterol absorption (r = 0.8662, P < 0.01), resulting in a significant correlation between protein digestibility and plasma cholesterol level (r = 0.7357, P < 0.01) in this study. The present study demonstrates that the digestibility of rice protein affected by extraction method plays a major role in the modulation of cholesterol metabolism. Results suggest that the hypocholesterolemic action induced by rice protein with lower digestibility primarily contribute to the inhibition of cholesterol absorption.

Rice protein improves oxidative stress by regulating glutathione metabolism and attenuating oxidative damage to lipids and proteins in rats

“…The hepatic total cholesterol concentrations were significantly lower in rats fed RP than those fed CAS (P b 0.05) ( Table 2), consistent with previous studies (Yang et al, 2007(Yang et al, , 2011a. In parallel, hepatic triglyceride levels decreased by 35.22% in RP compared to CAS (P b 0.05).…”

“…As shown in Table 2, less liver swelling was observed in rats fed RP (P b 0.05) than in those fed CAS, as suggested by previous studies (Yang et al, 2007(Yang et al, , 2011a.…”

“…The present experiment was performed in compliance with the Guidelines of the Committee for Animal Experimentation of Harbin Medical University and followed the same protocol used in previous studies (Yang et al, 2011a(Yang et al, , 2012b. Seven-week-old male Wistar rats were purchased from the Animal Center of Harbin Medical University (Harbin, China) and individually housed in metabolic cages in a room maintained at 22 ± 2°C under a 12 h light-dark cycle (07:00-19:00 light).…”

“…The lipids in the liver were extracted and purified as described by Folch et al (1957) and analyzed as described by Yang et al (2011a). Samples of liver were extracted with chloroform/methanol (2:1, v/v).…”

“…Longjing 26 (Rice Research Institute of Heilongjiang Academy of Agricultural Sciences, Jiamusi, China) and casein (CAS) (Gansu Hualing Industrial Group, Gansu, China) were used as the dietary protein sources in the present study. RP was prepared by the alkaline extraction method (Yang et al, 2011a(Yang et al, , 2012b.…”