Modern Industrial Microbiology and Biotechnology

Production of Amino Acids by Fermentation 385Fig. 21. 2 World Production of Amino Acids, 1996 (from Mueller and Huebner, 2003)(i) Protein hydrolysis: Protein hydrolysis was the original method of amino manufacture.Hair, keratin, blood meal and feathers are hydrolyzed using acid and the amino acidextracted. It is not very popular because it depends on the availability of hair, feathersand the other raw materials. However, cysteine and cystine are still produced byisolating them from chemically hydrolyzed keratin protein in hair and feathers whileproline and hydroxyproline are precipitated from gelatin hydrolysates.(ii) Chemical synthesis: Glycine, L-alanine, and DL- methionine are produced bychemical synthesis. Chemical synthesis can only produce the D,L- (recemic) forms ofamino acids and an additional step involving the use of an immobilized enzyme,aminoacylase, produced by Aspergillus niger is necessary to obtain the biologically activeL-form. (Fig. 21. 3). This step is expensive and on account of this, few amino acids areprepared by chemical synthesis. Amino acids produced by chemical synthesis areglycine and methionine; methionine is said to have the same effect as an animal feedadditive whether in the L- or in the D, L- form.(iii) Microbiological methods: Microbiological methods are of three types:1. Semi-fermentation;2. Use of microbial enzymes or immobilized cells;3. Direct fermentation.Fig. 21.3Action of Aminoacylase on Racemic Mixtures of Amino Acids