Protein Enrichment of Sweet Potato Beverage Residues Mixed with Peanut Shells by Aspergillus oryzae and Bacillus subtilis Using Central Composite Design

Abstract

The present study aimed at reducing the pollution of the waste generated by the sweet potato beverage industry to the environment and transforming the residues mixed with peanut shells into biomass protein to be used as animal feed. Six different microbial strains were evaluated for their ability to produce true protein using the mixed substrates as a nature medium under solid-state fermentation. The experimental results revealed that the highest true protein content was obtained when the substrates were fermented with a combination of Aspergillus oryzae and Bacillus subtilis. The optimal process parameters for protein enrichment by solid-state fermentation using A. oryzae and B. subtilis through Central Composition Design (CCD) included initial moisture content of 63.7%, incubation of temperature 26.9 °C and fermentation time of 67.5 h. Expression profile of protein system was characterized using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The fermentation products appeared as five major protein bands, indicating that the protein components had increased after solid-state fermentation by A. oryzae and B. subtilis. This study developed an efficient and reliable fermentation method to utilize the industrial wastes of sweet potato beverage residues and peanut shells for the animal protein feed.