Solid state fermentation of BSG for citric acid production

Abstract

Brewers' spent grain (BSG) is the major by-product of the brewing industry, representing around 85 % of the total by-products generated. BSG is a lignocellulosic material containing about 17 % cellulose, 28 % non-cellulosic polysaccharides, chiefly arabinoxylans, and 28 % lignin. Nevertheless, due to its high content of protein and fibre (around 20 and 70 % dry basis, respectively), it can also serve as an attractive adjunct in human nutrition. The present investigation was carried out on citric acid production from Brewer’s spent grain using Aspergillus niger. The chemical qualitative characterization of Brewer’s spent grain showed that it contained a considerable amount of carbohydrate (6.4 %) and protein (20 %) that could be a good source for microorganism’s growth and metabolic activities. Effect of different supplements was studied on solid state fermentation of Brewers’ spent grain. Among the different constituents, the organic nitrogen that is peptone was found to give significant results at 0.1 % concentration which increases the citric acid production up to 0.19 % as compared to yeast extract which did not give significant result in the fermentation medium. The effect of inorganic constituents on the fermentation showed that potassium dihydrogen phosphate was also found best at 0.1 % which led to increase in the production of citric acid i.e (0.22 %). The mineral constituents such as ammonium sulphate and magnesium sulphate were found effective at 0.1 % concentration. From this investigation, it can be concluded that BSG can be used as a cheap raw material for the production of citric acid by A. niger.