Abstract
Among the enzymes of the cellulolytic complex, β-glucosidases are noteworthy due to the possibility of their application in different industrial processes, such as production of biofuels, winemaking, and development of functional foods. This study aimed to evaluate the production and characterization of β-glucosidase from the filamentous fungus Gongronella butleri, recently isolated from Cerrado soil and cultivated in agro-industrial residue substrates. The highest production of β-glucosidase, about 215.4 U/g of dry substrate (or 21.5 U/mL), was obtained by cultivation of the microorganism on wheat bran with 55% of the initial moisture, for 96 h at 30°C. This β-glucosidase showed higher catalytic activity at pH 4.5, and a temperature of 65°C. The original enzymatic activity was recovered in a pH range of 3.0-7.5 after 24 h of incubation. The enzyme retained 80% of its catalytic activity when incubated for 1 h at 50°C. The enzyme was strongly inhibited by glucose, an effect that was completely reversed by increasing substrate concentration in the reaction mixture, which is typical for competitive inhibition. High catalytic activity was observed in solutions containing up to 20% ethanol, allowing the application of this enzyme in processes with high alcohol concentrations (for example beverages and biofuels). The significant production of β-glucosidase by the selected strain, along with these enzyme characteristics, highlights the biotechnological potential of the fungus G. butleri. Key words: Microbial enzyme, biofuels, agro-industrial residues, cellulases, hemicellulases.
Highlights
The enzyme was strongly inhibited by glucose, an effect that was completely reversed by increasing substrate concentration in the reaction mixture, which is typical for competitive inhibition
Agro-industrial residues are usually discarded in the environment, yet their composition allows the use of such materials as nutrient sources in fermentation processes
Different agro-industrial residues were tested for βglucosidase production by the fungus G. butleri, for which other fermentation parameters were fixed, including moisture (60%), temperature (28°C) and cultivation time (96 h)
Summary
Agro-industrial residues are usually discarded in the environment, yet their composition allows the use of such materials as nutrient sources in fermentation processes. In this context, solid-state fermentation is essential in the use of residues as substrates for the synthesis of various compounds of industrial interest, in addition to being. For efficient conversion of cellulose into fermentable sugars, an enzymatic system constituted of at least three groups of enzymes is necessary: (1) endoglucanases (EC 3.2.1.4), which internally hydrolyze cellulose chains, resulting in a rapid reduction in the degree of polymerization; (2) exoglucanases (EC 3.2.1.91), which hydrolyze glycosidic bonds at the ends of chains, releasing principally cellobiose; and (3) β-glucosidases (EC 3.2.1.21), which finalize hydrolysis, converting cellobiose to glucose. The glucose from lignocellulosic biomass can be converted into ethanol through fermentation by microorganisms, which has aroused great interest in biofuel industries (Bansal et al, 2012)
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