Sustainable approach to produce bioethanol from Karanja (Pongamia pinnata) oilseed residue

Agricultural biomass is the world’s largest, most sustainable, and most promising renewable energy source. This study investigated the potential of Karanja (Pongamia pinnata) oilseed residual waste (defatted kernel, hull, and their mixture) as a source of ethanol. The pretreatment of the finely ground samples was carried out using dilute sulfuric acid (0.5%) hydrolysis at a higher temperature of 121 °C and 15 psi pressure for 90 min. The pretreatment usually removes the lignin and facilitates the hydrolysis of cellulose and hemicelluloses. They were further hydrolyzed using 5% H2SO4 at 50 °C for 70 h. The analyses of hydrolyzed products have shown the presence of 66.06–67.12 mg g^–1 of total reducing sugars, 0.41–0.47 mg g^–1 of glucose, and 0.36–0.45 mg g^–1 of xylose, from which the rate of hydrolysis and conversion percentage of cellulose to glucose (44.44%–55.16%) and hemicelluloses to xylose (53.76%–67.17%) was obtained. The hydrolyzed product of complex polysaccharide was further converted into ethanol by fermentation at 32 °C on an orbital shaker using commercial yeast. The results showed ethanol yield of about 10.3%, 8.3%, and 3.3%, respectively in fermentation broths of kernel, mixture, and hull samples, thus indicating Karanja oilseed wastes as potential sources for ethanol production.