Physiological differences of soluble and insoluble dietary fibre fractions of brown algae and mushrooms in pepsin activity in vitro and protein digestibility.

Soluble and insoluble dietary fibre fractions were separated from Konbu, Wakame and Hijiki seaweeds and Shiitake, Hiratake and Yanagimatsutake mushrooms, respectively, and the effects of the fractions on pepsin activity in vitro and of those from Wakame on apparent protein digestibility in vivo were studied. Addition of each dietary fibre fraction inhibited pepsin activity in vitro in all the dietary fibre fractions tested, particularly the inhibition by soluble dietary fibre fractions being significantly greater, by 62-99%, than that by insoluble dietary fibre fractions, by 22-36% (P< 0.01 in each food). This suggests that soluble dietary fibres in algae and mushrooms are likely to play a different physiological role from insoluble dietary fibres. Measurement of viscosity of each soluble dietary fibre fraction resulted in the correlation of viscosity with the inhibition of pepsin activity by the soluble fraction. Young adult rats given a normal protein diet containing 5% of the soluble dietary fibre fraction derived from the Wakame seaweed showed a greater decrease in apparent protein digestibility by 9.4% than those given the diet containing 5% of the insoluble one (P< 0.01). This may have resulted in the significantly lower body weight gain of the former rats than that of the latter rats.