Fermentation performance of the yeast Saccharomyces cerevisiae in media with high sugar concentration

Abstract

High sugar concentration is more preferred in industrial bioethanol production, as it can increase the amount of ethanol produced by the end of fermentation. However, when high sugar concentration is used in the media, yeast cells are exposed to high osmotic stress, which can affect the fermentation performance. The present experiment aimed to investigate the fermentation performance of the yeast S. cerevisiae at high sugar concentration, in poor (Yeast nitrogen base/YNB) and rich (yeast extract peptone/YEP) media. Growth parameters and sugar utilization were monitored during the fermentations. The results indicate that all three strains used had stuck fermentations, leaving 50 to 60% residual sugar. Therefore, a follow up experiment was conducted by using media of different nutritional value, including YNB with nitrogen supplementation and YEP, as well as different sugars (sucrose or glucose). Yeast cell grown in YEP had better fermentation performance indicated by higher sugar utilization. Addition of ammonium sulphate to YNB media did not change fermentation performance of the yeast cells. In YEP media, cells grown with glucose tended to maintain better viability than sucrose. Our study confirmed that nutrient availability is very important for fermentation performance. Comparison of YNB and YEP media indicates that nutritionally insufficient media are not suitable for high concentration sugar fermentation.