Effect of Ethanol on Autolysis of Spent Baker’s Yeast Generated from Sago Bioethanol

Spent Baker’s yeasts (Saccharomyces cerevisiae) have been increasingly utilised nowadays for various applications in food industry and livestock feeds, yet their disposal keeps growing and would eventually cause severe environmental pollution. Moreover, the knowledge on the optimisation of autolysis of spent yeasts is still lacking, particularly those obtained from sago bioethanol. These concerns drive this work to focus on valorising spent yeast cells by autolysis. Here, this work aims to study the effect of ethanol on the autolysis of spent yeast generated from sago bioethanol fermentation. Ethanol (10, 15 and 20% v/v) was applied to the yeast suspension before the autolysis, and the efficiency of each treatment was analysed based on protein and carbohydrate released in the lysate using Lowry assay and phenol–sulfuric acid method, respectively. Additionally, scanning electron microscopic analysis was performed to observe the morphological alterations of the autolysed yeast cells. The results showed that ethanol stress could accelerate the lysis of yeast cells and enhance the extract yields. The protein concentration reached the maximum value (13455 μg/ml) during 20% ethanol treatment, whereas the highest carbohydrate concentration (3511.07 μg/ml) was achieved by 15% ethanol treatment. The final concentrations of protein and carbohydrate in the yeast lysate achieved by the optimised conditions were 3.4-fold and 6.9-fold higher than the contents in the control samples, respectively. Meanwhile, the microscopic study of lysed yeast cells revealed a substantial change in surface morphology, parallel with the autolytic events that occurred during the incubation. In conclusion, plasmolysis by ethanol was proven as a promising method for optimising the autolysis performance and the release of intracellular contents. This finding would improve the extraction procedure of yeast autolysates, boost the spent yeast’s market commodity, and increase the source of raw materials for the industrial sector