Optimization of enzymatic hydrolysis of coffee (Coffea Arabica) pulp pretreated with sodium hydroxide for bioethanol production

Abstract

Coffee is one of the most important agricultural commodities in Brazilian agribusiness. The processing of coffee beans generates large volumes of residues with low environmental sustainability. Converting this biomass into bioethanol is a promising alternative, which requires pretreatment and enzymatic hydrolysis. This study aimed to optimize the hydrolysis of coffee pulp pretreated with 4% sodium hydroxide for ethanol production. Initially, different biomass loadings were evaluated, and 20 g/40 mL (14% w/v, dry basis) was selected due to its significantly higher cellulose-to-glucose conversion (Tukey, p < 0.05). A central composite rotational design (CCRD) assessed the effects of cellulase (1.5–43.5 FPU/g) and β-glucosidase (0–40 CBU/g) concentrations on the release of total sugars, reducing sugars, and glucose. The optimal conditions determined by the design were 25.78 FPU/g cellulase and 28.95 CBU/g β-glucosidase, resulting in an 85% conversion of cellulose to glucose. The central point treatments of the CCRD were used for fermentation with Saccharomyces cerevisiae CAT1 and Kluyveromyces marxianus CCT 4086, yielding ethanol concentrations of 25.63 and 21.71 g/L, respectively. The results demonstrate the technical feasibility of producing fermentable sugars and ethanol from coffee pulp through integrated pretreatment, enzymatic hydrolysis, and fermentation, contributing to waste valorization and sustainable biofuel production.