[Lactose--a potential dietary fiber. The regulation of its microecological effect in the intestinal tract. 2. The nutrient effect of lactose].

In the small intestine lactose is subjected to the hydrolytic impact of beta-galactosidase originating mainly from the mucosa. In rats about two thirds of the enzyme activity are located in the first part of the small intestine, and one third in the second one. A part of the mucosal enzyme does not remain in the mucosa. It becomes detached and can be determined in the chymus. The ratio of the transient to the resident proportion amounts to 1.8: 1 in germfree and 0.23: 1 in conventional rats. Bacterial settlement causes an increase in the mucosal mass resulting in higher total activity whereas the specific activity of the mucosal enzyme remains unchanged. Microorganisms occurring close to the small intestine mucosa take part in lactose degradation. Lactose-containing diet leads to an increase in both the bacterial and the mucosal activity, the latter one to varying degrees. Lactose concentration in the ileal chymus rises with increasing intake of lactose and decreasing protein and phosphate intake. Following a saturation kinetics the velocity of lactose hydrolysis is correlated with the lactose concentration of the diet. alpha-lactose is hydrolysed more rapidly in the small intestine of both human sucklings and rats than beta-lactose. As the results of a mathematical model show lactose mutarotation does not effect on the degree of lactose degradation in the small intestine. Depending on the intake of lactose and the food composition the rate of lactose hydrolysis amounts to: --max. 50% after small intestine perfusion in human sucklings, --max. 80% after small intestine perfusion in rats, --max. 60% in rats with ileostomata.