Corn pericarp pretreated with dilute acid: bioconversion of sugars in the liquid fraction to ethanol and studies on enzymatic hydrolysis of the solid fraction

Abstract

Corn pericarp (CP) results from wet milling of the corn industry. It is an abundant agro-industrial byproduct in Mexico, with potential use as sugars source to obtain ethanol and other economically relevant chemicals. In this work, CP was pretreated with dilute sulfuric acid at 121 °C; using a 23 full factorial design, factors were sulfuric acid, reaction time, and CP concentration. After pretreatment, the capacity of activated charcoal to remove inhibitory compounds in the liquid fraction was studied. Then, the detoxified liquid fraction was fermented using Scheffersomyces stipitis, whereas the solid fraction was exposed to enzymatic hydrolysis by a commercial cellulase (Cellic® CTec2). The most promising pretreatments utilized 2% (v/v) sulfuric acid, 20% (w/v) of CP, and 30 min reaction time producing 109.38 ± 6.73 g/L reducing sugars. The solid fraction obtained from CP pretreatment resulted in cellulose conversion up to 85.60% ± 1.87% after 94 h, significantly higher than conversion achieved using untreated CP of 32.54% ± 5.58%. The detoxification process allowed yeast fermentation to reach ethanol yields (g ethanol/g consumed substrate) between 0.09 ± 0.02 and 0.29 ± 0.006. S. stipitis was able to produce between 4.62 ± 1.73 and 14.22 ± 0.98 g/L of ethanol from the hydrolyzed liquid fraction. The dilute acid pretreatment on CP produced a solid fraction, which upon enzymatic treatment caused high cellulose conversion into reducing sugars. Additionally, the fermentability of the sugars present in the liquid fraction was increased after the detoxification process. Thus, CP is a material that shows good potential to obtain value-added products such as ethanol.