Production of L-glutamic acid using Corynebacterium glutanicum and glucose derived from sweet potato flour
1992
Phung Huu Hao
Gelatinized sweet potato flour was liquefied by crude alpha-amylase (obtained from Bacillus subtilis NRRL 3411) to the level of 25% dextrose equivalent (DE). The liquefied sweet potato flour was then saccharified with the local crude glucoamylase which was obtained from Aspergillus oryzae 3078 by the solid culture method. The standard conditions for saccharification of the liquefied sweet potato flour with local crude glucoamylase were: temperature 55 deg C; pH 5.0; and enzyme concentration, 300 ml/kg dry weight flour. Under these conditions, the maximum DE of 54% (dry basis) was obtained after 24 hr saccharification which corresponded to a 63% conversion of the initial starch into glucose. The low conversion rate could be due to repolymerization of glucose molecules in the presence of transglucosylase in the local crude glucoamylase. Other possible reasons are: 1.) high level of alpha-amylase in the local glucoamylase which resulted in production of syrups of high maltose and glucose content (lower DE value) and, 2.) condensation of glucose with sweet potato protein or with amino acids in the crude enzyme via the Maillard reaction. Optimization of the batch process conditions for the production of L-glutamic acid by Corynebacterium glutamicum CgAC 1188 and glucose derived from sweet potato flour was conducted. The optimum conditions for the process were: reducing sugar concentration: 80 g/L; pH 7.0; and no biotin added. The highest L-glutamic acid concentration obtained was 35.9 g/L with a yield conversion rate of 62% after 48 hr fermentation process.
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