Abstract
Microbial conversion of corn stover by white rot fungi has the potential to increase its ligninolysis and nutritional value, thereby transforming it into protein-enriched animal feed. Response surface methodology was applied to optimize conditions for the production of lignocellulolytic enzymes by Trametes versicolor during solid-state fermentation of corn stover, as well as enhance ligninolysis and increase the crude protein content. The effects of an additional carbon source (glucose), copper sulfate (CuSO4) and initial moisture content on lignocellulolytic enzymes, changes in chemical constituents and the crude protein content of corn stover were investigated. T. versicolor produced high laccase, moderate xylanase, and low CMCase activity, whereas neither LiP nor MnP activity was detected. An overall 20-fold increase in laccase activity (45.1 U/g corn stover) was achieved under the optimized conditions. The maximum degradation of lignin and hemicellulose was up to 34.8 and 21.9%, respectively. However, the maximum cellulose loss was less than 10.5%. The crude protein content of the fermented corn stover was doubled under the optimized conditions. Therefore, T. versicolor is a potential organism for laccase production using solid-state fermentation, as well as the simultaneous enhancement of delignification and improvement of the crude protein content in corn stover. Key words: Corn stover, central composite design, laccase, ligninolysis, Trametes versicolor, crude protein.
Highlights
Agricultural straw, which mainly consists of cellulose, hemicellulose and lignin, is the most abundant renewable lignocellulosic biomass
Response surface methodology was applied to optimize conditions for the production of lignocellulolytic enzymes by Trametes versicolor during solid-state fermentation of corn stover, as well as enhance ligninolysis and increase the crude protein content
T. versicolor is a potential organism for laccase production using solid-state fermentation, as well as the simultaneous enhancement of delignification and improvement of the crude protein content in corn stover
Summary
Agricultural straw, which mainly consists of cellulose, hemicellulose and lignin, is the most abundant renewable lignocellulosic biomass. Lignin is quite resistant to microbial degradation under natural conditions, it plays a key role in limiting the quality of lignocellulosic biomass as animal feed Faced with these problems, a potential solution is available, that is, the utilization of microorganisms, mainly fungi, to convert agroindustrial residues to obtain products with higher nutritive value, especially in terms of CP and enhanced ligninolysis (Villas-Bôas et al, 2002; Mukherjee and Nandi, 2004). A number of microorganisms, mainly white rot fungi, have been used for producing microbial proteins and lignocellulolytic enzymes by SSF from different agricultural residues (Bisaria et al, 1997; Niladevi et al, 2007; Arora and Sharma, 2009; Zeng et al, 2011). Central composite design was applied to optimize additional glucose, CuSO4 and the initial moisture content during SSF
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