Lanthionine racemization

Scheme 6 Protected Partially Racemic Lanthionine Formation via Michael Addition of L-Cysteine to Dehydroalanine Derivatives133 ...

Nutritional and Physiological Effects of Alkali-Treated Proteins. The first effect of the alkaline treatment of food proteins is a reduction in the nutritive value of the protein due to the decrease in (a) the availability of the essential amino acids chemically modified (cystine, lysine, isoleucine) and in (b) the digestibility of the protein because of the presence of cross-links (lysinoalanine, lanthionine, and ornithinoalanine) and of unnatural amino acids (ornithine, alloisoleucine, / -aminoalanine, and D-amino acids). The racemization reaction occurring during alkaline treatments has an effect on the nitrogen digestibility and the use of the amino acids involved. 

These effects were described by de Groot and Slump (99) followed by Provansal et al. (94). Later, it was confirmed that the lysine moiety of lysinoalanine was completely unavailable to the rat and only partly available to the chick, while a certain part of the cysteine moiety of lanthionine (32% to 52% according to the racemic mixture) was available to chicks (100) (see Table I). 

Alkali has long been used on proteins for such processes as the retting of wool and curing of collagen, but more recently it has received interest from the food industry. Alkali can cause many changes such as the hydrolysis of susceptible amide and peptide bonds, racemization of amino acids, splitting of disulfide bonds, beta elimination, and formation of cross-linked products such as lysinoalanine and lanthionine. 

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