Bi-phasic hydrolysis of corncobs for the extraction of total sugars and ethanol production using inhibitor resistant and thermotolerant yeast, Pichia kudriavzevii

Abstract

In order to have sustainable energy and to reduce the reliance on fossil fuels, transition to renewable bioenergy is highly desired. Adequate biomass conversion to ethanol requires total carbohydrate extraction from the feedstock with minimum inhibitors. The present study aimed at revealing the fermentation potential of toxin resistant and thermotolerant Pichia kudriavzevii for ethanol production. Corncobs being one of the most abundant renewable biomass, was chosen for sequential bioconversion process to ethanol. Firstly, the biomass was pretreated using 2% NaOH which resulted in 83.12 ± 1.07% delignification. Subsequently biomass was used for biphasic hydrolysis (ultrasound assisted dilute acid followed by enzyme) which resulted in 27.03 ± 0.91 gL-1 of xylose, 0.33 ± 0.03 gL-1 furans in the first phase and 27.33 ± 0.9 gL-1 glucose in the later phase. Fermentation efficiency of P. kudriavzevii was evaluated using enzyme and acid hydrolysates (detoxified and undetoxified) which resulted in 11.98 gL-1 ethanol with glucose, 3.83 gL-1 and 3.64 gL-1 ethanol with detoxified and undetoxified acid hydrolysates with theoretical yield of 85.95, 31.89% and 28% respectively at 42 °C. Though the efficiency with xylose was low, the strain was found to be one among very few Pichia strains that have ability to ferment xylose. Furthermore, developing a potential biological process that utilizes the renewable biomass for energy development will not only save a lot of foreign exchange, but also helps in waste management in a sensible way.