食品添加剤

The use of ε-N-acetyl-L-lysine instead of L-lysine as food additive has been recommended previously in order to minimize the browning of foods, that encounters when lysine is enriched to the foods. Sanger synthesized ε-N-acetyl-L-lysine by acetylation of the lysine-Cu complex with acetic anhydride. An improved method for synthesizing this lysine derivative was presented by Benoiton, in which lysine-Cu complex was acetylated with p-nitrophenyl acetate. These methods, however, did not satisfactory with respects to the yield or economical standpoints. A new and more economical method for synthesizing ε-N-acetyl-L-lysine has been presented. The method consisted of two steps, i.e., conversion of lysine to its carbaminate and consequent acetylation of the carbaminate was made by adding 69.5 g Ba(OH)_2. 9H_2O (or 16.3 g Ca(OH)_2) to 500 ml of 3.66% lysine-HCl solution and bubbling carbon dioxide gas. The carbaminate thus formed was acetylated by alternate dropwise addition of 60 ml of 2N-NaOH and 12 g of acetic anhydride with stiring. After completion of acetylation, the acetyl-lysine-carbaminate was decomposed to acetyl-lysine by boiling of the mixture. The filtrate was loaded on a Dowex-50 NH_4^+ column and acetyl-lysine was eluted with 0.5N NH_4OH solution. This fraction was evaporated to dryness in vacuo, then ε-N-acetyl-L-lysine was crysterized in 80% ethanol. Yield, 72-75%. M.P., 246-253℃.