White-rot basidiomycetous (WRB) fungi are a group of wood-decaying fungi that are known to be endowed with the ability to secrete enzymes that can catalyze decomposition of a range of plant cell wall polysaccharides, including cellulose and lignin. Expression of these enzymes is induced by the substrate and the enzyme yields obtained depend on the growth of the fungi and thus the mode of cultivation. In order to exploit WRB fungi for local enzyme production for converting lignocellulosic materials in biorefinery processes, the fungi can principally be cultivated in either solid-state (SSC) or submerged cultivation (SmC) systems. In this review, we quantitatively assess the data available in the literature on cellulase production yields by WRB fungi cultivated by SSC or SmC. The review also assesses cellulolytic enzyme production rates and enzyme recovery when WRB fungi are cultivated on different biomass residues in SSC or SmC systems. Although some variation in cellulase production yields have been reported for certain substrates, the analysis convincingly shows that SmC is generally more efficient than SSC for obtaining high cellulase production yields and high cellulase production rates on the substrate used. However, the cultivation method also affects the enzyme activity profile obtained, and the resulting enzyme titers and significant dilution of the enzymes usually occurs in SmC. The review also highlights some future approaches, including sequential cultivations and co-cultivation of WRB fungi for improved enzyme expression, as well as on-site approaches for production of enzyme blends for industrial biomass conversion. The quantitative comparisons made have implications for selection of the most appropriate cultivation method for WRB fungi for attaining maximal cellulase production.
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This study investigated the potential of pito mash (waste from sorghum brewing) as alternative and cost-effective feedstock for bioethanol production by means of fermentation using Zymomonas mobilis and Saccharomyces cerevisiae isolated from freshly tapped palm wine. Fermentation parameters such as pH, temperature and incubation period were studied. The fermentation microbes, Z. mobilis and S. cerevisiae were identified using API TM test kit and morphological characteristics, respectively. Analysis of reducing sugar residue was performed using dinitrosalicylic acid (DNS) method, while analysis of ethanol content was performed using gas chromatography. Pito mash recorded total starch content of 6.69%, reducing sugar content of 11.1 mg ml-1 and cellulose content of 0.41 mg g-1. Saccharification by malting increased reducing sugar content by 77.9% (19.75 mg ml-1). The optimum fermentation conditions (pH, temperature and incubation period) for Z. mobilis and S. cerevisiae were 5.5, 35°C, 3 days and 6.0, 30°C, 4 day, respectively. The maximum ethanol yield of 3.03 g l-1 and efficiency of 62% were obtained for S. cerevisiae while yield of 3.63 g l-1 and efficiency of 74.2% were obtained for Z. mobilis. Z. mobilis conclusively may be better organism for ethanol production from pito mash.
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