Optimization of media components and fermentation conditions for citric acid production from sweet potato peel starch hydrolysate by Aspergillus niger

This study investigated sweet potato peel waste as the main carbon source and determine the effect of media components and operating conditions on citric acid (CA) production by Aspergillus niger under submerged fermentation. The sweet potato peel waste is of low-cost readily-available and serve as hydrolysate for CA production. Two sets of experiments were performed using experimental design technique. The first set was designed using a low resolution 2-level factorial which was deployed for parameter screening. The other set of experiments was designed using 3-level design algorithm and was deployed for model development and optimization. The results from parameter screening showed that carbon source (CS), nitrogen concentration (NC), fermentation time (FT) and pH were the "heavy hitters" with significant impact on CA production. The developed model is predictive (R-2 = 0.948) with optimum CA (3.22 mg/mL) obtained at CS (97.25%), NC (1.25%w/v), FT (7 days), and pH (6.5). This setting was validated experimentally and resulted in CA yield of 4.36 +/- 006 mg/ml, representing a 135%-fold increase over the predicted yield. The present investigation shows that sweet potato peels hydrolysate is a viable and sustainable substrate for CA production. (C) 2020 The Authors. Published by Elsevier B.V. on behalf of African Institute of Mathematical Sciences / Next Einstein Initiative.