Citric acid production on three cellulosic supports in solid state fermentation

Abstract

Six strains of Aspergillus niger were screened in liquid medium and strain LPB 21 was selected for further studies on three different agro-industrial wastes/residues for production of citric acid by solid state fermentation. Cassava bagasse was found to be a better substrate than vegetable sponge and sugar cane bagasse. Citric acid production and yields were 13.64 g/100 g dried substrate and 41.78 %, respectively with the use of cassava bagasse. Studies on optimization of parameters for production of citric acid by A. niger LPB 21 in cassava bagasse medium indicated that 50% of initial moisture content, initial pH of 2.0, aeration rate of 60 ml/min/column and 26°C fermentation temperature are the optimum values. Under these optimized conditions, the production of citric acid was 280 g/kg dry substrate at 120 hours, which corresponds to the yield of 70% based on sugars consumed. Data on kinetics of pH changes, moisture level, loss of weight of the substrate, starch utilization and alpha-amylase production give insights in the process.