Isolation and identification of thermotolerant yeast strains producing bioethanol from agro-food wastes.

Bioethanol production from agro-food industry waste is one of the suitable alternatives to fossil fuels. In this study, six agro-food wastes were evaluated to select those with a high concentration of starch or fermentable sugars for bioethanol processing. Yeast's ability to produce biofuels by fermentation is affected by temperature. In this study, thermotolerant yeasts, obtained from natural sources in Algeria (soil and agro-food waste), were selected for their capacity to produce and tolerate bioethanol. Three wastes were selected, two of which had significant starch content. In order to get fermentable sugars, these wastes underwent chemical and enzymatic hydrolysis. The selected yeasts were identified by morphological, physiological, biochemical, and molecular characterization. Enzymatic and acid hydrolysis of whole potato and durum wheat bran released (190 g/L and 130 g/L) and (138.40 g/L and 90.03 g/L) reducing sugars, respectively. Among the isolated strains, three were found to be able to produce bioethanol, namely Candida tropicalis, Candida glabrata, and Saccharomyces cerevisiae. These strains were identical to those stored in the data bank with 99%, 100%, and 100%, respectively. In addition, C. glabrata and C. tropicalis exhibited an ethanol tolerance of up to 14%, while S. cerevisiae tolerates up to 15%. Interestingly, enzymatic hydrolysis–treated potatoes produced a considerable amount of bioethanol after 48 h of fermentation by S. cerevisiae (7.525% (v/v)), C. glabrata (6.80% (v/v)), and C. tropicalis (4.50% (v/v)). Taken together, our findings suggest that S. cerevisiae and whole potato waste could be considered good candidates for industrial bioethanol production at high temperatures. [ABSTRACT FROM AUTHOR]