Effect of Maillard reaction products on protein digestion. In vivo studies on rats

The effect of a glucose-lysine reaction mixture on protein digestion in rats was studied by using 3H-labeled free lysine, 14C- or 3H-labeled protein-bound lysine and 35S-labeled protein-bound cystine in the experimental diets. The low-molecular-weight part of the glucose-lysine reaction mixture (1.5% wt/wt in the diet) affected the utilization of dietary protein-derived amino acids, as revealed by the ratio and the levels of different labels in plasma after feeding. The browned crust from a heated minced-meat loaf was less well digested and had a lower biological value than the crumb in a nitrogen-balance study with rats. When the water-soluble fraction of the crust was removed, the biological value of the crust was restored to the value of the crumb but the digestibility remained low. The addition of the water-soluble fraction of the crust had only a slight effect on the digestibility of the crumb. It is concluded that compounds in the glucose-lysine reaction model affect the dietary protein utilization of rats but were not present or otherwise could not explain the reduced utilization of proteins in the crust of the heated meat product.