Enhanced saccharification of rice straw using hypochlorite-hydrogen peroxide

Abstract

Rice straw is a lignocellulosic biomass, and has been recognized as a renewable organic substance and alternative energy source. In this study, rice straw was pretreated with hypochlorite-hydrogen peroxide (Ox-B) solution. The optimal pretreatment conditions were determined via response surface methodology, and the pretreated rice straw was hydrolyzed with exo-glucanase, endoglucanase, hemicellulase, and β-glucosidase Accellerase 1000™ (endo-glucanase equivalent activity of 1,250 carboxy methyl cellulose (CMC) U/g of rice straw pretreated for 24 h). The optimal conditions were as follows: 60 min pretreatment using Ox-B solution containing 0.6% hypochlorite and 25% hydrogen peroxide for 1 g of rice straw in a total reaction volume of 240 mL. Under these conditions, 406.8 mg of D-glucose and 224.0 mg of D-xylose were obtained from 1 g of rice straw. The fermentation of enzymatic hydrolysates containing 8.14 g/L D-glucose and 4.49 g/L D-xylose with Pichia stipitis generated 3.65 g/L of ethanol with a corresponding yield of 0.37 g/g. The maximum possible ethanol conversion rate is 72.54%.

Strain Isolation and Study on Process Parameters for Xylose-to-Xylitol Bioconversion

“…However, increasing further the xylose concentration to 160 g l -1 , led to a drastic decrease in cell growth and volumetric productivity. This phenomenon can be explained by substrate inhibition and/or osmotic pressure (12).…”

“…Generally, an increase in the initial sugar concentration leads to increases in the productivity and yield in a batch process if the microorganisms can tolerate a higher concentration of sugar and a higher osmotic pressure. However, the xylose inhibition on the growth of C. tropicalis W103 was even more severe than that on C. parapsilosis KFcc 10875 and C. tropicalis HY200, which were able to grow up to 150 g l -1 or 200 g l -1 xylose respectively (12,14). The profiles of xylitol bioproduction and the main enzymes (XR and XD) involved in xylose assimilation to xylitol were greatly influenced by the available oxygen (3).…”

“…Xylose can be converted to xylitol by several microorganisms including Pichia (17), Debaryomyces (6), Pachysolen (4), recombinant Escherichia coli (25), recombinant Saccharomyces cerevisiae (18) and also Candida (5,13,20). Among these, Candida ferments xylose to xylitol with high yield and productivity (12,14,16,23). Xylitol production involves complicated metabolic regulation including xylose transport, key enzymes formation, and cofactor regeneration (9).…”

Alkali Pretreatment of Wheat Straw (Triticum aestivum) at Boiling Temperature for Producing a Bioethanol Precursor

“…8) There are several different methods for biomass pretreatment which depend on the type, composition, and subsequent processing technology applied. 9) Physical treatment, including milling, grinding and chipping, aims to increase the surface area of biomass by reducing its particle size. 10) Acidic, alkaline, and organic solvents are employed to digest the hemicelluloses or lignin via chemical treatments.…”

Construction of Recombinant Escherichia coli JM109/LBH-10 and Comparison of Its Optimal Condition for Production of Carboxymethyl cellulase with Its Wild Type, Psychrobacter aquimaris LBH--10

“…Cellulosic materials have great potential for use as cheap and renewable feedstocks for fermentable sugars [1]. The complete enzymatic hydrolysis of cellulosic materials need at least three different types of cellulases; endoglucanase (Carboxymethyl cellulase), exocellobiohydrolase (avicelase), and β-glucosidase [2].…”