CITRIC ACID Fermentation by Mutant Strain of Aspergillus Niger GCMC-7 in Stirred Fermentor

Abstract

Citric acid fermentation of cane-molasses by submerged fermentation in 15L stirred fermenter (working volume 9L) was carried out. The mutant strain of Aspergillus niger GCMC-7 was used in the present study and ferrocyanide treated molasses (200 ppm) medium containing sugar 150g/l was employed as the basal fermentation medium. Different cultural conditions such as volume of fermentation medium (60%), temperature (30°C), pH (6.0), aeration (1.0 I-1 I-1min) & agitation (200 rpm) and rate of acid production were employed to enhance citric acid production. Twenty four hours old vegetative inoculum was used at a level of 4%. Methanol as a stimulating agent was added, 24 hours after inoculation at the rate of 1%, based on the total working volume of fermenter. Among the mineral nutrient tested, ammonium nitrate (0.2%) potassium di hydrogen phosphate (0.10%) and magnesium sulphate (0.015%) were optimized as the best nitrogen, phosphorous and magnesium sources, respectively. Calcium Chloride (0.04%) and copper sulphate (0.025) were found to affect the mould morphology and thus have a positive effect on citric acid production. Fed-batch culture study was also carried out and found to give consistent yield of citric acid. Maximum amount of anhydrous citric acid obtained during the course of study was 77.65g/l, with a sugar consumption of 117g/l. Final pH ferrocyanide concentration and dry cell mas were 2.7, 40 ppm and 16.35 g/l, respectively. The mycelia were small round pellets in their morphology.