Optimisation of β-Glucosidase Production in a Crude Aspergillus japonicus VIT-SB1 Cellulase Cocktail Using One Variable at a Time and Statistical Methods and its Application in Cellulose Hydrolysis

Abstract

Pulp and paper mill sludge (PPMS) is currently disposed of into landfills which are reaching their maximum capacity. Valorisation of PPMS by enzymatic hydrolysis using cellulases is an alternative strategy. Existing commercial cellulases are expensive and contain low titres of β-glucosidases. In this study, β-glucosidase production was optimised by Aspergillus japonicus VIT-SB1 to obtain higher β-glucosidase titres using the One Variable at a Time (OVAT), Plackett Burman (PBD), and Box Behnken design (BBD)of experiments and the efficiency of the optimised cellulase cocktail to hydrolyse cellulose was tested. β-Glucosidase production was enhanced from 0.4 to 10.13 U/mL, representing a 25.3-fold increase in production levels after optimisation. The optimal BBD production conditions were 6 days of fermentation at 20 °C, 125 rpm, 1.75% soy peptone, and 1.25% wheat bran in (pH 6.0) buffer. The optimal pH for β-glucosidase activity in the crude cellulase cocktail was (pH 5.0) at 50 °C. Optimal cellulose hydrolysis using the crude cellulase cocktail occurred at longer incubation times, and higher substrate loads and enzyme doses. Cellulose hydrolysis with the A. japonicus VIT-SB1 cellulase cocktail and commercial cellulase cocktails resulted in glucose yields of 15.12 and 12.33 µmol/mL glucose, respectively. Supplementation of the commercial cellulase cocktail with 0.25 U/mg of β-glucosidase resulted in a 19.8% increase in glucose yield.

Hyper β-glucosidase producer Beauveria bassiana SAN01—optimization of fermentation conditions and evaluation of saccharification potential

“…The p value < 0.05 indicates the significance of the corresponding factors, with the incubation time, KCl, NaCl, Bambara concentration, and agitation speed with p values ranging from <0.0001 to 0.0062 were established as the most significant factors (Table 4). These results are in agreement with the previous studies that identified incubation time [19,41] and agitation speed [38,41] as significant factors in Bgl production by different microorganisms. However, a negative correlation between KCl concentration and enzyme production was observed in this study; this is in contrast to a study on Aspergillus versicolor, where the same salt displayed a positive relationship with Bgl production [38].…”

“…4d). According to literature and the results obtained in this study, it can be inferred that further increase in Bgl production in different microorganisms is possible by optimization of medium components and physical components via statistical methods [38,41].…”