Effect of substrate on the in vitro protein digestibility of extracts generated by Saccharomyces cerevisiae

The in vitro crude protein (CP) digestibility (D-ivcp), true protein digestibility (D-tp) and degradation rate (kd(cp)) were measured in different protein extracts of Saccharomyces cerevisiae (Sc) yeast. These extracts were generated through a biotechnological method (solid state fermentation). Wheat straw (TWS), barley straw (TBS), chili stubble (TCS), oats hull (TOH) and starch-glucose powder (TSP; control) were used as substrates for fermentation by Sc, and their effect on the aforementioned kinetic parameters in the generated cellular biomass was evaluated. In 12 mL cultivation medium, 2 mL Sc solution inoculum (6.7x10(6) spores mL(-1)) was added together with 2 g vegetable substrate (dry) and additional nitrogen source, and the mixture was incubated for 7 days at a constant temperature (26 degrees C at pH 5) under aerobic conditions. The average CP content of the yeast biomass (DM) was of 45%. The D-ivcp and D-tp were analyzed (two phases: pepsin/trypsin-pancreatin) after the extraction of the yeast biomass, and an effect of the fermented substrate on these values (P <= 0.001 and P <= 0.01, respectively) was observed. The greatest digestibility (D-ivcp) was obtained with TSP (78.9% CP) and the lowest with TCS (67.1% CP). In addition, differences in the kd(cp) between the treatments were also observed (P <= 0.01). The high contents of CP, D-ivcp (71.8% on average) and kd(cp) (16.4% h(-1) on average) suggest that Sc yeast biomass has the potential to become an alternative for the production of animal protein supplements.