[Degradation and uptake of 14C labeled casein peptides by mixed bacteria of the rumen].

This work studied the in vitro degradation by mixed rumen bacteria of various 14C-labelled fractions of casein peptides, of known molecular size, added to a total unlabelled casein hydrolysate. Size exclusion HPLC was used in order to segregate the casein peptides according to their molecular weights. Radioactivity associated with the bacteria increased over time. The way 14C was incorporated into the bacteria depended on the size of the labelled peptides initially added. Small peptides (1 to 2 kDa) were very rapidly assimilated, whereas radioactivity coming from larger peptides (5 to 10 kDa) tended to accumulate far more slowly in the bacterial pellet. The disappearance rates of the radioactivity differed between the fractions. The longest peptides disappeared more quickly than the medium-sized ones, which in turn were hydrolysed more rapidly than the smallest ones. Here, the uptake of small peptides seems to be the limiting step of the peptides utilization by bacteria.