Effects of lactose and mode of sterilization of a lactose diet on mineral metabolism in germ-free and conventional rats.

Abstract

Mineral balances of Ca, P, Mg, K, Na, Zn, Mn, Cu were carried out on 6-week old Fisher rats for 14 consecutive days. Four lots of germfree (GF) and 4 lots of conventional (CV) rats were fed a semi-synthetic diet at weaning containing either 0 or 10 p. 100 of lactose (L). The diet was sterilized either by irradiation (I) or by autoclave (Au). Lactose, when added to the diet, caused very variable modifications of the mineral metabolism, depending on the mineral studied and the mode of sterilization. Thus, retention and apparent absorption of iron were hardly changed by the presence of lactose. On the other hand, those of Mn were strongly enhanced by the lactose. The action of the other minerals was complex; it was modulated either by the mode of diet sterilization, the flora, or by both factors simultaneously. The IL diet increased retention of most of the minerals; in some cases (Na, Zn, P, Ca) it was only evidenced in CV rats; in other cases (Mn, Mg, Cu) its action was visible in both CV and GF animals. Steam-sterilized lactose (AuL) considerably reduced this effect and even reversed it. This change in lactose action under the effect of steam sterilization especially affected absorption, which declined for all the minerals, except Zn and Mn. It was accompanied by a drop in the digestive efficiency ratio which was particularly pronounced in GF rats. The destruction of 1/3 of dietary lactose by steam sterilization could not alone explain the differences between the effects of IL and AuL. Other factors, such as the products of the Maillard reaction formed by steam sterilization of the diet, might be implicated.