Gluconic acid production from sugar beet molasses by using A. niger

In this study, gluconic acid production by fermentation has been investigated from molasses which is obtained as a by-product during sugar production from beet by using A. niger. The experimental conditions have been optimized for gluconic acid production by deep, semi solid state and solid state fermentation routes by using Response Surface Methodology (RSM) and Central Composite Design (CCD) technique. The optimum conditions for gluconic acid production by deep fermentation were determined as 257.8 g/L of molasses concentration, 30 g/L of CaCO3 amount, 31.8 oC of temperature and 135.2 rpm of shaking speed and the maximum gluconic acid concentration was obtained as 58.76 g/L under this conditions for 192 h of fermentation period. The optimum conditions for semi solid state fermentation were determined as 245 g/L of molasses concentration, 15.5 g/L beet pulp amount, 30 g/L CaCO3 amount, 30.2 oC of temperature and 145.7 rpm of shaking speed and the maximum gluconic acid concentration was 74.64 g/L under these conditions at the end of 192th hour of fermentation period. For the solid state fermentation, maximum gluconic acid production was obtained as 0.262 g/g absolute solid substrate at the end of 9-day fermentation period under the conditions of 0.18 of molasses ratio, 0.22 of beep pulp ratio, 0.03 of CaCO3 ratio and 30.9 oC of temperature. It has been determined that citric and oxalic acid productions together with gluconic acid are being occurred in the significant levels for all three fermentation shapes. It was also investigated that the effect of beet pulp particle size on the gluconic acid production by semi solid and solid state fermentation and it was determined that the production increases in a moderate extent by the decreasing of particle size.