Value-added bioethanol from spent ginger obtained after oleoresin extraction

Spent ginger obtained after extraction of oleoresin constitutes more than 90% of the raw material and rich in carbohydrates that could be used as a substrate for the production of bioethanol. Proximate analysis and carbohydrate profiling showed it to contain 60–75% carbohydrates of which starch was the major constituent. This study was undertaken to optimize acid and enzyme hydrolysis for maximum release of fermentable sugars and subsequent fermentation to bioethanol. Enzymatic hydrolysis of the spent samples using Stargen® 002 (pH 4.5, 50 °C, 20 U, 20% substrate load, 48 h) was found to be better than acid hydrolysis as seen from the hydrolytic efficiency and growth of Saccharomyces cerevisiae NCIM 3095 therein. Hydrolytic efficiency of 89.89 and 91.35% were obtained under optimized conditions for the two samples chosen in the study. Fermentation of enzyme hydrolyzed medium showed a maximum fermentation efficiency of 81.53%, and resulted in maximum ethanol production of 43.4 g/l.

► Utilization of spent ginger for bioethanol production.
► Optimization of saccharification using acid and enzymes.
► Pretreatment of biomass to enhance saccharification.
► Optimization of fermentation parameters for bioconversion of sugars to bioethanol.