초록
Optimization of citric acid production from Sweet Potato Starch Hydrolyzate (SPSH) using Aspergillus niger was investigated. Effect of five independent variables viz. concentrations of SPSH, (NH<SUB>4</SUB>)<SUB>2</SUB>HPO<SUB>4</SUB>, KH<SUB>2</SUB>PO<SUB>4</SUB>, fermentation time and pH on the response (citric acid concentration) and their reciprocal interactions were established using Response Surface Methodology (RSM). The central composite design was used to generate a total of 50 fermentation runs, which were subsequently conducted. A second-order mathematical model was obtained to predict the citric acid concentration as a function of the five variables. A statistical model predicted the highest citric acid concentration as 83.01 g L<SUP>-1</SUP>, at the optimal condition of SPSH of 153.77 g L<SUP>-1</SUP>, (NH<SUB>4</SUB>)<SUB>2</SUB>HPO<SUB>4</SUB> of 3.55 g L<SUP>-1</SUP>, KH<SUB>2</SUB>PO<SUB>4</SUB> of 2.58 g L<SUP>-1</SUP>, time of 8 days and pH of 6. The optimized condition was validated with the actual citric acid concentration of 83.00 g L<SUP>-1</SUP>. This work showed that SPSH could serve as alternative carbon source for citric acid production and the results could be scaled up to pilot production.