The effect of the addition of proteases and glucanases during yeast autolysis on the production and properties of yeast extracts.

Yeast extracts (YE) were produced with the addition of proteases or glucanases during bakers' yeast (Saccharomyces cerevisiae) autolysis. Chemical composition, physical properties, and biological value of the YE were examined. Proteases had the highest impact on the turbidity and filterability of YE. All 11 proteases and two glucanases increased YE yields (% yeast solids solubilized) obtained from heated (80 degrees C/15 min) bakers' yeast creams (BYC). However, when proteases were added to native (unheated) BYC during autolysis, few increased YE yields, with papain being the most effective. The increased yields were generally related to increased levels of total nitrogen (TN) and alpha-amino nitrogen (alpha-AN) in the YE. Media were supplemented with the various yeast extracts, and the highest growth rates (mumax) and biomass values (ODmax) of Lactobacillus acidophilus were noted. The best growth was obtained with YE produced with native BYC treated with a fungal protease, and results of this study show that some enzymes could be used to produce improved YE for microbiological media.