Cellobiose is extensively digested in the small intestine by β-galactosidase in rats

Abstract

Objective The bioavailability of cellobiose (CEB) was investigated with respect to small intestinal digestibility and cecal fermentation in rats. Further, whether small intestinal β-galactosidase is responsible for the hydrolysis of CEB was examined. Methods Ileorectostomized rats were fed diets including 6% CEB or fructo-oligosaccharide with or without 0.1% neomycin in drinking water for 7 d. The fecal excretion of the respective oligosaccharides was determined. In vitro digestion of CEB and lactose was characterized using mucosal enzymes of the small intestine from suckling and adult rats. Cecal fermentation in normal rats fed a control diet or a diet including 3% or 6% CEB for 14 d was examined. Results The small intestinal digestibility of CEB was 64%, irrespective of the presence of neomycin in drinking water, whereas the digestibility of fructo-oligosaccharide differed significantly between groups administered (26%) or not administered (35%) neomycin. The in vitro digestibility of lactose (62%) and CEB (36%) was three times greater with the enzymes from the suckling rats than with those from the adult rats. Michaelis constant (K m) and maximum velocity (V max) values for CEB were 25 and 7 times lower, respectively, than those for lactose. Normal rats fed the 6% CEB diet showed a greater cecal organic acid than those fed the control diet, but no differences were observed between those fed the control and 3% CEB diets. Conclusion Our results indicate that dietary CEB was extensively digested in the small intestine by β-galactosidase in rats, leading to complete digestion of CEB when dietary supplementation was limited.