(113c) Kinetics of Yeast (Saccharomyces cerevisiae) Solubilization through Flash Hydrolysis for Recovery of Protein and Its Application As Nutrient Media

Yeast is produced in large quantities as a byproduct of fermentation by breweries, distilleries, biofuels, and food industry. Although, it has some low value applications as animal feed, it is generally considered as an organic waste. Its disposal is a concern as techniques currently used like incineration and landfills have environmental impacts. Yeast is a rich source of proteins and other useful compounds which can be recovered for various high value applications. A continuous-flow hydrothermal treatment called ‘flash hydrolysis’ was deployed for protein recovery and yeast disposal. A feed slurry with 1-15 wt% yeast was hydrolyzed at temperatures ranging between 160-280 °C for a very short residence time of 10±2 s. Using 10 wt% yeast at 240 °C, 66.5% carbon, 70.4% nitrogen and 61.0% overall yeast biomass was solubilized in liquid hydrolysate. The liquid hydrolysate in which 63.1% of analyzed amino acids in yeast feed were solubilized, was tested as nutrient for cultivation of E. coli in a continuous bioreactor. The steady-state E. coli concentration was 1.18 g L^-1 and 0.93 g L^-1 using liquid hydrolysate and commercial yeast extract, respectively. Finally, the kinetic parameters for yeast solubilization (reaction order, activation energy and pre-exponential factor) were found to be 0.86, 21.3 kJ mol^-1 and 19.36 [L g^-1]^n-1 s^-1, respectively.