Small-scale Citric Acid Production On Solid-state Fermentation Using Aspergillus Niger

Citric acid is used in the food, beverage, pharmaceutical, chemical, cosmetic and other industriesrnfor applications such as acidulation, anti oxidation, flavour enhancement, preservation, and as arnsynergistic agent. It is used to flavour the drinks, jams and jellies, candies, water ice and wines.rnIn recent years, a great deal of attention is given to alternative methods for citric acid productionrnusing agro-industrial residues. A citric acid producing Aspergillus niger isolate designated asrnASGS was isolated from the Faculty of science Addis Ababa University green house soil. Thernisolate produced citric acid in solid state fermentation (SSF) using different agricultural productsrnand by products (Maize, Rice and wheat bran) as substrates. Out of the three substrates, rice(R)rnwas found to be better followed by the combination of wheat bran and rice (WR). The highestrnlevel of citric acid (110.6g/kg DR) was produced in Rice, with Rice-to- moisture ratio of 1:4rn(w/v) at 30ºC and 72 hr. The weakest substrate for citrate fermentation was wheat bran with onlyrn7g/kg citrate production. Maximum growth of the isolate was shown at 30◦c, it also showedrngrowth and biomass accumulation at 35◦c. Wrinkled, dense, white mycelium was observed inrnthe flask at 30◦c while at 25◦c was not shown. Citrate accumulation increased exponentially afterrn48hrs of fermentation and the maximum citric acid (82.6g/kg DR) was obtained at 72hr whichrndeclined gradually. Initial rice moisture content had a considerable effect on citric acidrnproduction by ASGS. A maximum citric acid production (91g/kg DR) was obtained with 80%rnmoisture content. Citrate accumulation also increased significantly with increase in temperaturernfrom 25 to 30◦c and production slightly declined up to 35◦c. The highest value of citric acidrnconcentration (98g/kg DR) was achieved at an initial pH of 4.5. Recovery trial yielded 1.2g citricrnacid from 10g of dry rice substrate which was white and solid crystalline.rnKey phrases: Aspergillus niger strain; Solid state fermentation; Citric acid.

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