Abstract
Investigations were carried out in order to elucidate the reason for the nutritive value reduction of browned protein by using casein labeled with U-14C-L-lysine. When the browned casein was ingested by growing rats, high radioactivity was found in a lysine derivative present in the small intestinal TCA-soluble fraction obtained 3 and 7hr after feeding. Experiments were done to identify the lysine derivative as absorption-delayed material. This material was identified by an amino acid auto-analyzer, paper chromatography and radioactive analysis as 1-deoxy-l-(ε-N-L-lysino)-D-fructose (ε-fructoselysine), which accounted for about 70% of the total radioactivity in the small intestinal TCA-soluble fraction obtained 7hr after feeding. Lysine which was found after 3hr, was disappeared from the intestinal TCA-soluble fraction taken 7hr after feeding, but ε-fructoselysine remainded. Its content as acetate found 7hr after one-dosal feeding of 600mg browned labeled casein (700, 000 dpm) was 18.3 and 19.0mg/each rat, respectively. These values accounted for about 40% of the lysine content in the ingested browned casein.
