Keto acids recovery

The data of Table IV seem to indicate slightly less damage to amino acids with 7-irradiation than with 24 m.e.v. electrons. The marked stability of these amino acids in beef to 7-irradiation has also recently been observed by Rhodes and Southern (39) and is somewhat in contrast to the earlier report of Tsien and Johnson (50). The rather extensive losses of glutamate reported in the earlier work may have been caused by incomplete recoveries from the analytical columns or by differences in irradiation procedure. Our samples were irradiated from a cobalt-60 source, while the earlier samples were irradiated from spent fuel rods. It has recently been reported (15) that 7-ray irradiation of glutamic acid yields the corresponding a-keto acid, the amount obtained depending on irradiation conditions. 

In addition to the identification of the appropriate biosynthetic enzyme, the feasibility of all biotransformation processes depends heavily on other criteria, such as the availability of inexpensive starting materials, the reaction yield, and the complexity of product recovery, hi the case of transaminase processes, the reversible nature of the reaction (Scheme 3.1) and the presence of a keto acid by-product is a concern that limits the overall yield and purity of product and has led to efforts to increase the conversion beyond the typical 50% yield of product.99 100 Additionally, there are cost considerations in the large-scale preparation of keto acid substrates such as 2-ketobutyrate, which are not commodity chemicals. 

In 1935, Krebs published a technique for Isomer analysis that employs D-amino acid oxidase, an enzyme which selectively deaminates D-isomers. This method allowed measurement of D-amino acids via the resultant keto acids that were formed or by recovery of intact L-amino acids (28). Other enzymatic methods based on L-amino acid decarboxylases (25,43), L-amino acid acylases and amidases (44) also have been used. Other biologically-based techniques employing selective utilization of L-amino acids by microorganisms appeared as early as 1949 (29,30), but due to their complexity, have not been used widely. 

Synthesis of vitamin C (ascorbic acid) is conventionally performed via the Reichstein-Griissner procedure, which involves the fermentation of glucose followed by five chemical steps. Cerestar/ BASF recently developed a new process that consists of one fermentation step and two simple chemical steps (via 2-keto-L-gluconic acid). It is predicted that soon a fermentation process will be developed to convert glucose into vitamin C in a single step, eliminating several recovery steps and reducing extraction solvents. 

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