Azevedo Melo

ABSTRACT

The production of bioethanol from lignocellulosic biomass remains a major challenge due to the high xylose content that conventional ethanol-producing yeasts, such as Saccharomyces cerevisiae, are unable to efficiently ferment. Although S. cerevisiae is widely favored for industrial ethanol production because of its robustness and tolerance to ethanol and fermentation inhibitors, its incapacity to utilize xylose significantly reduces overall process efficiency. This study focuses on exploring non-traditional yeast species capable of co-fermenting glucose and xylose to enhance bioethanol yield. Two yeast strains were isolated from decomposed apple samples and molecularly identified through ITS sequencing as Meyerozyma and Lodderomyces. Fermentation was carried out using a mixed sugar medium with a glucose-to-xylose ratio of 2:1 over a period of 96 hours. Both strains rapidly metabolized glucose, and more than one-third of the xylose was consumed within the first 24 hours. The resulting ethanol yields were 0.344 g/g for Meyerozyma and 0.327 g/g for Lodderomyces, corresponding to an approximate fermentation efficiency of 65%. In addition, these isolates demonstrated significant tolerance to common lignocellulosic inhibitors, including furfural and 5-hydroxymethylfurfural (HMF), at concentrations typically encountered in pretreated biomass hydrolysates. The findings highlight, for the first time, the ability of Meyerozyma and Lodderomyces to efficiently co-utilize mixed sugars for ethanol production, positioning them as promising candidates for industrial bioethanol processes. This study opens avenues for exploiting non conventional yeasts to improve the conversion of lignocellulosic feedstocks into renewable fuels.