Ethanol producing yeast isolated from Indonesian flower nectar and wild forrest honey

Biofuel is a form of energy produced from natural biomass and is thought to replace fossil fuels. One of the commonly used biofuels is ethanol. Ethanol is generally fermented by yeast using plant based materials with relatively low sugar content. The low levels of sugar results low ethanol yield per batch. It will be more economically efficient if the initial sugar concentration is high, hence resulting higher ethanol. However, osmotolerant yeast is needed to do the conversion. The purpose of this study was to explore osmotolerant yeast isolates that can produce high yield ethanol from environments with high sugar content, namely honey and flower nectar. The methods used were qualitative and quantitative screening of the ability to produce ethanol, with the highest producing isolate optimized with two different factors, namely sugar content and incubation temperature. Isolate with the highest ethanol production were tested further by ethanol tolerance test and monitored the isolate�s ethanol production and biomass growth. Ethanol content was measured by redox titration method. Qualitative screening showed 23 isolates with positive fermentation from 50 isolates tested. These isolates then screened quantitatively, with three highest ethanol content by BL 6.4, BL 8.21, and BL 8.22 with 19.6, 21.8, and 19.1 mL/L ethanol respectively. Ethanol production of the three isolates then optimized by varying glucose concentration (10, 15, 20, 25, 30 (v/v)) and incubation temperatures (25, 28, 30 and 47^oC). The optimization results showed that 10 glucose concentration with incubation temperature of 28^oC produced highest ethanol content of 4.67 (v/v) by BL 8.21. Ethanol tolerance test showed a significant decrease (around 40) in growth at 8 (v/v) ethanol concentration. Ethanol production and biomass growth of BL 8.21 were monitored and showed after day three biomass growths became stagnant while ethanol production increased. The highest ethanol concentration was obtained on the fifth day, amounting to 4.69 (v/v). We concluded the isolate is not a potential ethanol producer, hence further exploratory studies at different environments are suggested. © 2020 Elsevier B.V., All rights reserved.