Sustainable Sugar Syrup Production from Rice Husk Using Aspergillus niger Carbohydrase

Cellulases play a crucial role in cellulose degradation and lignocellulosic biomass conversion. The cost-effective production of these enzymes can be achieved using Aspergillus niger in solid-state fermentation with low-cost substrates. In this study, the optimal composition of the substrate mixture (80% cocoa bean shell and 20% forage palm) was determined by using the Simplex-Centroid design. The optimal fermentation conditions (28 °C, 60% moisture for 96 h) were established through the Doehlert design. Enzymatic characterization revealed activity over a broad pH range (5-9) for up to 5 h, a thermal stability of 70% at 70 °C, and halophilic properties, with a 278% increase in activity in the presence of NaCl. Additionally, the enzymes were activated by Ca^{2 +} (+60%) and DMSO (+69%). The carbohydrase blend (CB) effectively hydrolyzed rice husk, generating 13 mg of reducing sugars per gram of biomass. HPLC analysis identified glucose (7.24 mg/L) and fructose (11.21 mg/L), confirming the synergistic activity of the endoglucanase and isomerase enzymes. These results underscore the innovative and biotechnologically relevant nature of the enzymatic formulation, particularly in the sustainable production of fructose-rich syrup from rice husk. The approach holds significant promise for applications in bioenergy generation and the valorization of food waste.