Production of Citric Acid from Starch by Submerged Culture of Aspergillus niger

Abstract

Citric acid can be produced by submerged culture of Aspergillus niger from starch at low pH. The optimum conditions for the production of the acid in a medium of 15% soluble starch (potato) were investigated by using a 10 l jar fermentor with 8 l working volume. The agitation rate was varied from 600 rpm to 800 rpm to keep aerobic condition while aeration rate was kept at 1 vvm throughout the experiment. The fermentation was carried out at 30ºC. A higher yield was obtained by dynamic control of pH at 2.0 after 12 h by addition of 1% CaCO3 or 6N NaOH resulted in almost the same yield of citric acid. The highest citric acid production was 91.4 g/l after 5 days cultivation. Utilization of cassava as a raw material was also investigated using a 2.5 l jar fermentor. Cassava starch was liquefied by a-amylase beore use. The working volume was 1.5 l and dissolved oxygen was controlled to 10-30% saturation by varying agitation rate. The amount of citric acid produced from cassava starch was 109.3 l after 6 days cultivation. The production of citric acid by tower fermentors was tested. A 6 l glass column was used with a working volume of 5 l. Air was supplied by a glass sparger at the bottom of the column and the fermentation was carried out for 7-9 days. Citric acid production was low due to inefficiency of oxygen supply.