Fermentation and downstream processing of yeast for production of single-cell proteins and exopolysaccharides

Yeasts are known to be sources of highly quality proteins and exopolysaccharides (EPS). The main goal in this study was to produce and process yeasts of biotechnological interest to investigate whether these species can be used as supplements in food and feeds. Candida utilis, Wickerhamomyces anomalus and Arxula adeninivorans were fermented several times on chicken meat hydrolysate and downstream processed to be able to characterize the cell walls of the yeast, measure the protein content, and to discover the bottlenecks in the different processing steps. The results from the protein analysis showed that W. anomalus and A. adeninivorans contained a higher amount of proteins than C. utilis. All the yeasts had glucose, mannose and N-acetyl-glucosamine in their cell walls according to the monosaccharide composition analysis. These monosaccharides are building blocks in the exopolysaccharides b-glucan, mannan and chitin. Earlier performed studies have reported that these exopolysaccharides often are percent in the yeast cell wall. The results from this study indicates that b-glucan, mannan and chitin are present in the cell walls of C. utilis, W. anomalus and A. adeninivorans as well. In addition, galactose was found in the cell wall of A. adeninivorans. In total seven downstream processing steps were performed on W. anomalus after optimization of the process. The final processing steps were; 2-phase separation, cell disruption, enzymatic treatment, acid treatment, centrifugation, ultrafiltration and nanofiltration. The obtained fractions after the filtrations contained both proteins and carbohydrates. In depth analysis of these fractions are subjected to ongoing analysis in the lab.