A comparative study on pretreatment of rice straw and saccharification by commercial and isolated cellulase–xylanase cocktails towards enhanced bioethanol production

Abstract

The aim of this work was to study the efficiency of native lignocellulolytic enzymes obtained from isolated bacteria towards enhanced bioethanol production from lignocellulosic biomass. Maximum cellulose (199.33 ± 0.2 mg/g) and hemicellulose (62.21 ± 0.22 mg/g) content was measured from rice straw in alkali condition compared to acid and biological pretreatment, while significant lignin removal has been observed in biological pretreatment. Saccharification of rice straw using isolated cellulase–xylanase enzymes exhibited 60.33% production of total reducing sugar obtained by commercial cellulase–xylanase cocktail. Maximum glucose, xylose, and total reducing sugar yield of 309 ± 0.32, 190.7 ± 0.42, and 499.7 ± 0.37 mg/g, respectively, at 37.5 °C, pH-7, rice straw concentration of 2.5 g/100 mL, enzyme loading 175 μl, and incubation period 42 h by commercial cellulase–xylanase enzyme mediated hydrolysis. While in case of using the native cellulase–xylanase cocktail from the isolated bacterial strains, highest yields of glucose, xylose and total reducing sugar production was 253.52 ± 0.56 mg/g, 47.94 ± 0.78 mg/g, and 301.46 ± 0.67 mg/g, respectively. While applying the isolated enzymes on alkali-pretreated rice straw, bioethanol concentration of around 32.57 ± 0.25 g/L was recorded after the simultaneous saccharification and fermentation by Saccharomyces cerevisiae. The above mentioned bioethanol concentration was obtained at a process parameter of temperature 35 °C, incubation time 58 h, and pH 5.5 for isolated cellulase–xylanase enzymes. A maximum bioethanol concentration using isolated cellulase–xylanase enzymes was nearly 93.89% of bioethanol concentration (34.69 ± 0.28 g/L) obtained using commercial cellulase–xylanase. The present study interpreted that the cutting-edge approach for the native enzymes along with metabolic engineering of the isolated bacteria could be promising towards enhanced bioethanol production.