Induction of autolytic breakdown of RNA in yeast by addition of ethanol and by drying/rehydration

Autolytic degradation of RNA in suspensions of yeast at 50°C has been further studied as a means of preparing single‐cell protein (SCP) suitable for human consumption. Membrane disorganisation with initiation of autolysis was promoted by addition of ethanol (5 % v/v) or, more effectively, by first air‐drying yeast in a fluid‐bed dryer and rehydrating it at 4°C, or at 50°C, before incubation at 50°C. Water was a poor suspension medium, but nearly complete breakdown of RNA within 1.5 h was achieved with a buffer, or with a 0.5 m solution of NaCl. Salt in high concentration possibly destroyed ribosomal structure. With pressed commercial baker 's yeast, a consideration of its composition suggested that an ideal procedure for removing RNA would result in the loss of about 24% of dry matter, with the production of SCP containing 54% protein. With careful timing, SCP with 48% protein could be obtained from air‐dried yeast on extraction with 0.5 M‐NaCl, with a loss of 32% of the dry matter. Active dried baker 's yeast also autolysed rapidly at 50°C, and had a relatively low proteinase activity. After extensive autolysis of baker 's yeast, the residual nucleic acid (about 5 % of that initially present) was characterised by a relatively high ratio of adenine/guanine.