Sequential Fermentation of Coffee Husks by Aspergillus japonicus URM5620 for Cellulases Production: Biochemical Characterization and Kinetic/Thermodynamic Study

Cellulases catalyze the hydrolysis of cellulose and can be produced through fermentation processes, such as sequential fermentation (SeqF), which combines submerged and solid-state fermentation. The objective of this study was to evaluate the production of cellulases (endoglucanase and β-glycosidase) by fungi of the genus Aspergillus using coffee husks as substrate. Three Aspergillus strains were evaluated, with A. japonicus URM5620 showing the highest endoglucanase (0.368 U mL−1) and β-glucosidase (0.652 U mL−1) activities by SeqF. Based on the complete factorial design 22, a 9-fold and 3-fold increase in the production of endoglucanase (3.44 U mL−1) and β-glucosidase (2.12 U mL−1), respectively, was observed. Both enzymes showed maximum activity at 60 °C and pH 5.0. The kinetic/thermodynamic parameters indicated a high affinity of the enzymes for their respective substrates and a high catalytic potential. In addition, the half-life and decimal reduction values demonstrate the good thermal stability of endoglucanase (t1/2 = 8.82 ± 0.34 and D = 29.32 ± 1.13 h) and β-glucosidase (t1/2 = 26.61 ± 0.74 and D = 88.38 ± 2.47 h) at 60 °C. The thermostability results indicate potential for use in the pretreatment of raw materials.