Kinetics of batch single cell protein production from rice polishings with Candida utilis in continuously aerated tank reactors

Single cell protein was produced from the defatted rice polishings by fermentation with Candida utilis in an aerated 14-L fermentor to optimize bioprocess variables. Maximum values of specific growth rate coefficient (μ, h−1), cell mass yield (YX/S, g/g) and cell mass productivity (g/L h) were 0.31, 0.65, and 1.24, respectively under optimized conditions of aeration rate (1 v.v−1 m−1), dissolved oxygen (50%), corn steep liquor (5%), temperature (35 °C), and substrate concentration (90 g rice polishings/L) in yeast salt medium (pH 6.0). The kinetic parameters for 50-L fermentor under same conditions were 0.33 h−1, 0.66 g/g, 1.33 g/L h, 2.25 g/L h, 1.23 g/L h, 0.45 g/g substrate and 0.20 g/g cell h for μ, YX/S, QX, QS, QCP, YTP/S, and qCP, respectively and were significantly higher than their respective values reported on C. utilis in batch culture studies. This biomass protein contained 23.6%, 32.75%, 11.50%, 12.95%, 10.5%, and 0.275% true protein, crude protein, crude fiber, ash, cellulose and RNA content respectively. This implied that the fermentation process could be up scaled to manufacture animal feed. Gross metabolizable energy content of dried SCP was 29,711 kcal/kg and indicated that the SCP could serve both as energy as well as a protein source. Yeast can replace expensive feed ingredients currently being incorporated in poultry feed and can reduce cost of poultry ration by $0.33–$0.51/100 kg bag and improve the economics of feed production in our country.