The influence of dietary tea, coffee and cocoa on protein and energy utilization of soya-bean meal and barley in rats.

Two series of balance experiments were performed with growing rats to test the effect of black tea, green tea, coffee and cocoa on protein and energy utilization. In Expt 1 soya-bean meal was fed as a basal diet and supplemented with freeze-dried materials from 11 black tea, green tea or coffee/500 g dry matter. Cocoa powder, corresponding to 11 of the beverage, was also added to the basal diet. In Expt 2 the procedure was repeated with a barley-based diet. In both experiments both tea varieties and coffee had significantly negative effects on true protein digestibility and biological value, while digestible energy was only slightly affected in the barley-based diet. Cocoa had no effect on protein or energy utilization in either soya-bean meal or barley diets, although the protein in cocoa powder was completely indigestible. As the tannin concentration in both tea varieties and coffee was very high it is assumed that the observed deleterious effects might, in part, be explained by anti-nutritional effects of tannin. The strongest deleterious effect was recorded for black tea.