Optimization of β-alanine production from β-aminopropionitrile by resting cells of Rhodococcus sp. G20 in a bubble column reactor using response surface methodology

Resting cells of Rhodococcus sp. G20 were used for the transformation of β-aminopropionitrile to β-alanine, an important beta amino acid. A 23 central composite experimental design was performed with the purpose of optimizing the β-alanine production in a bubble column reactor with 200 mL working volume using response surface methodology (RSM). The individual and interactive effects of three independent variables (cells loading, substrate concentration, airflow rate) on β-alanine production were investigated. A quadratic polynomial predictive model was obtained after statistical analysis to predict the optimum biotransformation conditions. The optimum bioconversion conditions of β-aminopropionitrile in a batch operation for β-alanine production were as follows: cells loading of 16.50 gww/200 mL, substrate concentration of 1.29% (v/v), and airflow rate of 86.56 L/h, under which an overall 40.6% increase in productivity of β-alanine was obtained. The influences of the temperature and pH on the conversion were also studied, and the optimums were 30 °C and pH 7.5. The measured activation energy (Ea) was found to be 22,199 J/mol, thus indicating the presence of diffusional resistance.