Optimization of enzymatic hydrolysis and fermentation of bleached garlic straw for bioethanol production

Converting food waste, such as garlic straw, into bioethanol offers a promising solution for both food waste management and meeting the increasing energy demands of a growing population. As a low-cost and renewable agro-industrial substrate, garlic straw holds significant potential for bioethanol production. To optimize the enzymatic conversion, pretreatment was performed to facilitate the enzymatic saccharification process by alkaline peroxide and sodium chlorite, resulting in a substrate consisting of 83.07% cellulose, 6.13% hemicelluloses, and 2.09% lignin. The bleached garlic straw (BGS) was hydrolyzed using a cellulolytic complex produced by the hypercellulosic mutant Penicillium occitanis Pol6, aiming to convert cellulose into glucose. The BGS was treated with various enzyme loading (10–50 FPU/g), at different BGS concentration (20–80 g/L) and tween 80 concentration (0–8 g/L) and at different reaction time (24–72 h). The hydrolysis yield from enzymatic saccharification of BGS were evaluated using a Box–Behnken Design. The optimum conditions for the hydrolysis yield were obtained based on surface and contour plots. The maximum predicted hydrolysis yield of 54.08% was obtained as follows: enzyme loading 40 FPU/g, BGS concentration 22 g/L, Tween 80 concentration 6 g/L and hydrolysis time 72 h. Fermentation of hydrolysates of bleached garlic straw (HBGS) carried out using Saccharomyces cerevisiae for 24 h showed that the sugar content decreased over time, while ethanol production increased. Besides, the highest bioethanol production (11.9 g/L) was observed in the 4% HBGS sample after 6 h of alcoholic fermentation. These findings proved the economical production of ethanol using garlic straw as a cheap waste material and also using a low-cost enzymes derivated from filamentous fungi.