Abstract
In order to determine the relationship between color development and the nutritive value of food protein subjected to non-enzymatic browning, browned casein was examined biologically and biochemically. Development of the brown color (420nm) of a casein-glucose mixture (liquid state) during autoclaving (121°C, 10-60 min) increased as the ratio of glucose to casein increased to surpass that of a casein-glucose mixture (solid state) stored at 37°C (RH 58%, 1-4 week). Inversely, in vitro digestibility by trypsin and the growth of Tetrahymena pyriformis W were decreased to a greater extent in medium containing casein stored with glucose than in that containing casein autoclaved with glucose. These tendencies were also reflected by the changes in FDNB-reactive lysine content. Rat growth was completely suppressed by feediag a diet containing 10% casein stored with glucose. However, the diet containing 10% casein autoclaved with glucose suppressed rat growth only slightly. Supplementation of L-lysine (0.48%) to diets containing browned casein restored the growth of rats completely to normal. These findings suggest that the difference in protein quality between the two types of browned casein might be dependent on the content of available lysine, rather than that of the substance related to browning intensity.
