Autolytic methods for the reduction of the purine content of baker's yeast, a form of single‐cell protein

When a suspension of baker's yeast was incubated at 50°C, the cells became permeable to H+, a process completed in about 4 h. Cellular constituents of low molecular weight then diffused into the medium, but only after a long lag period were cell nucleic acids and proteins degraded by intracellular enzymes. The lag period was shorter at higher temperatures, when RNase and proteinases suffered some thermal denaturation. It was abolished if, before autolysis at 50°C, yeast was plasmolysed by ethyl acetate, or heated to 70°C for 1 min, treatments which, it is thought, disorganised the membrane of the yeast cell vacuole, within which the enzymes are located. Heat treatment, when effective, was sufficiently severe to disorganise the yeast cell plasma‐lemma, with the consequence that a single adjustment of pH immediately following heat treatment served to maintain a constant pH, without addition of buffer, during the subsequent incubation at 50°C. Autolysis was not found to be an entirely suitable procedure for the reduction of the nucleic acid content of baker's yeast, because of the concomitant and severe loss of protein.