Recovery of Sustainable Yeast Proteins: A Mechanistic Study of Autolysis and Enzyme Proteolysis as Pretreatments for Mechanical Cell Rupture

Single-cell protein from yeast can provide a sustainable means to meet increasing protein demands. For yeast protein to be digestible it must be released from within the cells using methods such as autolysis, enzyme proteolysis, and mechanical rupture. This study investigates the combination of autolysis or proteolysis and subsequent mechanical rupture on the protein release. The effects of autolysis and proteolysis using papain on the size, wall thickness, and internal structure of freshly harvested and 7 day stored Saccharomyces cerevisiae cells were investigated using particle sizing and electron microscopy. Samples were then subjected to high-pressure homogenization (single pass, 800 bar) and the extent of cell rupture and protein solubilization determined. During autolysis and proteolysis, intracellular contents were released, shrinking the cells, allowing the elastic walls to contract and thicken. Autolyzed cells were mostly deformed rather than ruptured by high-pressure homogenization, which expelled cell contents. Intact untreated cells with thin, stretched cell walls burst during high-pressure homogenization, with the proteins mostly remaining unsolubilized. Stored cells were smaller with thicker cell walls and generally more difficult to rupture. These findings can assist in developing efficient processes for recovering sustainably produced proteins from yeast and other microorganisms.