Effect of pH and temperature on the production and activity of Schwanniomyces polymorphus extracellular proteases in fermentation medium

Proteases are among the most studied enzymes due to the great interest with regard to their cleavage of peptide bonds in industrial applications. With the goal of maximizing the advantages of these biocatalysts, new producers of proteolytic enzymes are being prospected from various microhabitats. This study aimed to select a yeast strain with high yield of extracellular proteolytic enzyme and characterize the yield and activity of theses enzymes. Among the 521 yeast isolates tested for proteolytic activity on solid medium, 20 isolates were selected for the determination of proteolytic activity in liquid medium. Enzymatic assay was performed using azocasein as substrate, and one unit of protease activity was defined as the amount of enzyme able to produce an increase in absorbance of 0.001/min and expressed in U/mL. A yeast extracted from Jabuticaba fruit, identified as Schwanniomyces polymorphus through the analysis of its rDNA sequence, showed the highest proteolytic activity. The optimal conditions for protease production, with a maximum value of 289.9 U.mL-1, were pH 7.8, 28ºC and 72 h of fermentation. The activity of extracellular proteases contained in the culture supernatant was subjected to enzymatic characterization: the optimal pH was 8.0 and the optimal temperature was 35ºC. Therefore, among the yeasts isolated from tropical fruits, S. polymorphus presented the highest proteolytic enzyme activity under conditions of minimal fermentation, at temperature of 28ºC and pH of 7.8.