Browsing by Author "Feleke Hailemariam"

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    Small-Scale Citric Acid Production on Solid-State Fermentation Using Aspergillus Niger
    (Addis Ababa University, 2010-06) Feleke Hailemariam; Abate Dawit (PhD)
    Citric acid is used in the food, beverage, pharmaceutical, chemical, cosmetic and other industries for applications such as acidulation, anti oxidation, flavour enhancement, preservation, and as a synergistic agent. It is used to flavour the drinks, jams and jellies, candies, water ice and wines. In recent years, a great deal of attention is given to alternative methods for citric acid production using agro-industrial residues. A citric acid producing Aspergillus niger isolate designated as ASGS was isolated from the Faculty of science Addis Ababa University green house soil. The isolate produced citric acid in solid state fermentation (SSF) using different agricultural products and by products (Maize, Rice and wheat bran) as substrates. Out of the three substrates, rice(R) was found to be better followed by the combination of wheat bran and rice (WR). The highest level of citric acid (110.6g/kg DR) was produced in Rice, with Rice-to- moisture ratio of 1:4 (w/v) at 30ºC and 72 hr. The weakest substrate for citrate fermentation was wheat bran with only 7g/kg citrate production. Maximum growth of the isolate was shown at 30◦c, it also showed growth and biomass accumulation at 35◦c. Wrinkled, dense, white mycelium was observed in the flask at 30◦c while at 25◦c was not shown. Citrate accumulation increased exponentially after 48hrs of fermentation and the maximum citric acid (82.6g/kg DR) was obtained at 72hr which declined gradually. Initial rice moisture content had a considerable effect on citric acid production by ASGS. A maximum citric acid production (91g/kg DR) was obtained with 80% moisture content. Citrate accumulation also increased significantly with increase in temperature from 25 to 30◦c and production slightly declined up to 35◦c. The highest value of citric acid concentration (98g/kg DR) was achieved at an initial pH of 4.5. Recovery trial yielded 1.2g citric acid from 10g of dry rice substrate which was white and solid crystalline. Key phrases: Aspergillus niger strain; Solid state fermentation; Citric acid.