Citric acid production from Okara (soy-residue) by solid-state fermentation

Okara (soy-residue), a cellulosic byproduct of the soymilk and tofu (soypaneer) industry, was used for the production of citric acid by solid-state fermentation using a cellulolytic Aspergillus terreus and citric-acid-producing Aspergillus niger. Okara supplemented with ammonium sulphate (0•10% N) when fermented by A. niger with simultaneous saccharification using A. terreus at pH 8•3 and incubation temperature of 30°C resulted in production of 5•10 g citric acid/100 grams dry solids (gds) by the eleventh day.