Food-grade single-cell protein production, characterization and ultrafiltration recovery of residual fermented whey proteins from whey

This study was carried out to characterize and recover residual soluble proteins after cultivation of mono- (Kluyveromyces marxianus) and mixed culture (K. marxianus and Saccharomyces cerevisiae) on whey, to serve as food-grade single-cell protein (SCP). Batch fermentation was carried out at 35 °C and pH 5.5 for mono-culture and 30 °C and pH 6.5 for mixed culture. The yeasts biomass was separated from the fermented broth by centrifugation leaving residual soluble proteins in the fermented whey supernatant (FWS). The yeasts biomass was treated in two-step with a novel combination of chemicals (N-lauroyl sarcosine and NH4OH), which reduced the nucleic acid content in the biomass to the desired level (below 2% w/w) for food-grade SCP. The characteristics of the proteins were evaluated by electrophoresis. During fermentation, a fraction of the whey proteins was consumed. The electrophoresis results revealed that the fermented proteins were different from the native whey proteins and that they were partially hydrolyzed. The ultrafiltration operational parameters were optimized (in series) using 10 kDa and 1 kDa membranes. A permeate flux of 413 LMH and transmembrane pressure-TMP of 80 kPa resulted in the highest recovery with the 10 kDa membrane followed by a permeate flux of 2760 LMH and a TMP of 210 kPa were determined for the 1 kDa membrane. Recovery of the total proteins under these optimized conditions was 84% and 92% from mono- and mixed culture FWS, respectively.