Engineering Coffee Cherry Pulp-derived Activated Carbon for Cellulase Immobilization and its Role in Regulating Non-Sterile Coffee Fermentation

Abstract

During non-sterile coffee fermentation, microbial activity and substrate availability change as the mucilage is degraded. Activated carbon prepared from Arabica coffee cherry pulp by carbonization and ZnCl₂ activation was used as a support for cellulase immobilization. Cellulase produced by Cytobacillus sp. isolated from civet (Paradoxurus hermaphroditus) feces was immobilized by adsorption and used as part of the fermentation starter system. The immobilization efficiency was 80% and the immobilized cellulase had a specific activity of 613.22 U/mg. During fermentation, cellulase activity decreased from 2.45 U/mL at 0 h to 1.71 U/mL at 72 h, with approximately 70% of the initial activity remaining. At 48 h, the reducing sugar concentration was 10.7 mg/mL in the fermentation with immobilized cellulase, compared with 6.1 mg/mL in the control. The microbial growth rate was 0.132 h⁻¹ with immobilized cellulase and 0.084 h⁻¹ in the control. Pearson correlation coefficients were 0.93 between cellulase activity and reducing sugar concentration, 0.91 between reducing sugar concentration and microbial growth, and 0.88 between cellulase activity and microbial growth rate. Immobilized cellulase was associated with changes in sugar availability and microbial growth during non-sterile coffee fermentation.