Citric acid production from raw wheat straw and sugarcane bagasse using A. niger ATCC 9142 and solid state fermentatio

Citric acid is a widely-used fermented product and several methods for decreasing its production cost have been developed. This study compared citric acid production from wheat straw and sugarcane baggase as inexpensive sources using A. niger and solid state fermentation. Process variables that influence production، such as pH and moisture of substrate، initial sugar concentration، inoculum size، age of spore، methanol concentration، nitrogen source، temperature، fermentation time، type of solvent، and steaming time were evaluated. A. niger ATCC 9142 was incubated at 30°C for 5 d on potato dextrose agar slants and the suspended spores were collected. The dried substrates were weighed and the pH and moisture recorded. Sugar and nitrogen content were adjusted accordingly. After autoclaving the substrate، inoculation and incubation were done. The medium was leached using distilled water or acetone، then separation was done by filtration and centrifuging. The maximum citric acid products were 47 g per kg for wheat straw and 94. 5 g per kg (dry) for sugar cane bagasse. The citric acid yield based on the consumed fermentable sugar of wheat straw was 93% and of sugar cane bagasse was 97%. The maximum productivity for wheat straw was 11. 21 g/kg day and for sugar cane bagasse was 22. 22 g/kg day. The results suggest that wheat straw and sugarcane baggase are effective and inexpensive substrates for production of citric acid. In addition، the fermented medium can be used as an animal feed component after leaching of the citric acid and decontamination.