Investigation of gluconic acid production in bioreactor from sugar beet molasses by Escherichia coli W pqq+ vgb+ recombinant strain

In this study, gluconic acid (GA) was produced from sugar beet molasses and sugar beet pulp, which is an economical carbon source, by using recombinant strain of Escherichia coli W pqq+ vgb+ developed within the scope of TUBİTAK 1001 (117R003) project. The fermentation medium to be used is optimized; the effects of semi-solid state fermentation and operating parameters of the rotary drum bioreactor were investigated for gluconic acid production. In the first stage, screening experiments were carried out with Placket-Burman (PB), one of the Response Surface Methods (RSM), and fermentation media components which are effective on GA production were determined. In the second stage, the optimum values of the effective parameters were determined with the Central Composite Design (CCD) method. Four independent variables were found to have the greatest effect on GA production: Sugar Beet Pulp (g/L), Sugar Beet Molasses (g/L), CaCO3 (g/L) and inoculation rate (v/v, %). In the environment where maximum GA production is achieved, the amount of pulp is 5 g/L, CaCO3 is 13 g/L, the total sugar concentration in molasses is 75 g/L, and the inoculation rate is 7.5%. These studies were carried out in a rotary drum bioreactor with a working volume of 3 L using the optimum fermentation medium. As a result of these experiments, maximum GA production found as 38.5 g/L under the conditions of 1.85 L/min aeration rate, 34.2 rpm rotation speed and 6.56 pH. Result of our experiments suggest that the fermentation process of the recombinant strain obtained from the E. coli W strain is faster than the microorganisms classically used in the production of GA such as Aspergillus niger. These new findings provide an alternative way of producing GA which is highly efficient and low cost in terms of carbon source.