Comparison of citric acid production from Aspergillus niger in solid and suspension state fermentation

Abstract

Aim: Due to huge demand of citric acid, there is a need to find alternatives for its efficient production either using low-cost substrates or by improving the potency of the fermentation microorganisms. Materials and Methods: In this study, microbial production of citric acid was performed by Aspergillus niger. Solid and suspension state fermentation was carried out using biodiesel waste, i.e. the oilseed cake of Pongamia pinnata (honge) as a substrate for the comparative study of citric acid production using A. niger. After the estimation, the concentration of citric acid was found to be more in suspension state fermentation than in solid state. Hence, the further analysis was carried out using suspension culture. In the first stage, weight was varied, and the optimum weight was found out to be 12.5 g. Then keeping this optimum weight as constant, the inoculum size was varied, also keeping the optimum pH 6 and temperature 32°C constant. The rpm of suspension state was kept 100. Through this, optimum inoculum size was obtained. Results and Discussion: The yield of citric acid in solid state fermentation (SSF) was found to be 4.74 mg in 12.5 g of substrate and suspension state was 9.6 mg/ml. Conclusion: Suspension state fermentation method gives a higher yield of citric acid using oil seed cake as the substrate from A. niger than SSF method. The highest yield of 10.43 mg/ml of citric acid was obtained by taking substrate weight 12.5 g and inoculum size 275*104 spores/ml by suspension state fermentation method.