The resolution of DL-methionine

The virtue of the enzymes in the manufacture of fructose and glucose, and of 6-APA, is the mild conditions under which they act. This prevents the development of colours and off-flavours in the sugars, and the loss of the jS-lactam nucleus from the penicillins. One of their other virtues is their stereochemical specificity. This is well illustrated by the process used to resolve DL-methionine and other racemic amino-acids. 

The enzyme for such a process is usually isolated from Aspergillus oryzae. In the period between 1953 and 1969 this mould was used to carry out the hydrolysis in batch reactors. The process was similar to that originally used to manufacture 6-APA however, soluble enzyme is now extracted from the cells 

When this process was introduced in 1969 it was the first to use an immobilized enzyme. The scale of the process is not large (see Table 6.10), but where the chemical synthesis of DL-amino acids is cheap it provides an efficient route through to the L-isomer. 

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Considering that sodium glutamate, like other amino acids, is contained in soy sauce, which is a traditional Japanese food, it is not surprising that Japan should have become interested very early in this type of fermentation. Firms like Ajinomoto and Kyowa Hakko dominate the world market for amino acids and particularly for glutamic acid and l-lysine. It is also through enzymes that the resolution of dl-methionine into its optical isomers is achieved since its laboratory synthesis yields the racemic form. 

Figure 6.28 Process for the resolution of DL-methionine with amino acid acylase...

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