Ethanol production from non-sterilized beet molasses by free and immobilized Saccharomyces cerevisiae cells using fed-batch culture

Abstract

The production of ethanol from non-sterilized beet molasses by free and immobilized S. cerevisiae cells in batch and fed-batch culture was investigated. Fed-batch culture proved to be a better fermentation system for the production of ethanol than batch culture. In fed-batch culture, both free and immobilized S. cerevisiae cells gave the same maximum ethanol concentration (53 g/litre) at an initial sugar concentration of 250 g/litre and F = 250 ml/h. In the free cells system, the maximum ethanol productivity (3.8 g/litre h) was obtained at a substrate concentration of 250 g/litre and F = 500 ml/h with 30.6% ethanol yield and 81% sugars utilization. In the immobilized cells system, a maximum ethanol productivity of 3.5 g/litre h was achieved at an initial sugar concentration of 250 g/litre and F = 500 ml/h with 31.2% ethanol yield and 73.3% sugars utilization. In repeated fed-batch culture, immobilized S. cerevisiae cells gave higher overall ethanol concentration compared to the free cells. In this case, the immobilized S. cerevisiae cells in Ca-alginate beads retained their ability to produce ethanol for 8 days.