Single cell protein production from digested and undigested poultry litter by Candida utilis: optimization of process parameters using response surface methodology

In this study, production of single cell protein (SCP) was carried out using Candida utilis from undigested poultry litter (UPL) and digested poultry litter (DPL). UPL and DPL were hydrolyzed by acid hydrolysis initially and the resulting crude hydrolysates were used for SCP production. Fermentation variables of the production medium were optimized by single variables optimization methodology. By this conventional approach, SCP production from UPL and DPL has increased to 25 and 20 %, respectively. The proportional analysis of these results revealed that UPL was the suitable substrate than DPL for the production of SCP by C. utilis. Further, 2³ central composite design was applied to determine the optimal process parameters for SCP production using UPL as substrate. The analysis of treatment combinations showed that a second-order polynomial regression model was in good agreement with experimental results at R ² value −0.98 (P < 0.05). These results suggest that UPL concentration was the most influential factor affecting the SCP production with a P value of 2.22E-09 followed by yeast extract and pH at 0.0339 and 0.0439, respectively. Based on contour plots, the optimum conditions for SCP production were found to be the UPL concentration—5.6 % w/v, yeast extract concentration—2.3 % w/v, and pH—7. After statistical optimization, SCP production by C. utilis strain has increased 29 %. It is understood from this study that UPL could be used effectively as substrate for the production of animal feed supplement with benefit of reducing feed cost as well as mitigating environmental problems associated with poultry litter.