After removing microorganisms growing on the rice straw as
completely as possible, pretreated rice straw was enzymatically
solubilized in a 50 mM sodium citrate buffer (pH 5.0). Hydrolysis
experiments were conducted in a shaking water bath at 120 rpm
and 40 C for 48 h. Cellulase (Cellulase Y-NC; Yakult Pharmaceutical
Industry, Tokyo, Japan) was used at a protein concentration of
100 mg L 1.After removing microorganisms growing on the rice straw as
completely as possible, pretreated rice straw was enzymatically
solubilized in a 50 mM sodium citrate buffer (pH 5.0). Hydrolysis
experiments were conducted in a shaking water bath at 120 rpm
and 40 C for 48 h. Cellulase (Cellulase Y-NC; Yakult Pharmaceutical
Industry, Tokyo, Japan) was used at a protein concentration of
100 mg L 1. The specific activity of cellulase was 30,000 U g 1,
according to the manufacturers' data. Carboxymethyl cellulose
was used as a substrate to measure cellulase activity. The concentration
of pretreated rice straw was 10 g L 1. After an appropriate
incubation time, the reaction mixture was centrifuged (8000 g
for 5 min), and the supernatant was filtrated with a glass filter
(G-100; Advantec Toyo, Tokyo, Japan) to remove the residual substrate.
Total soluble sugar and glucose in the resulting filtrate were
determined using the phenol–sulfuric acid method (Masai et al.,
2007) and high performance liquid chromatography using a Bio-
Rad HPX-87H column, respectively.
The net yields of total soluble sugar (TS) and glucose (G) were
determined on the basis of the amounts of holocellulose (H: cellulose
and hemicellulose) and cellulose (C) in untreated rice straw,
respectively, as follows:
Net yield of TS (%) = {(amount of TS produced from residual
straw after pretreatment)/(amount of H in untreated straw)}
162/180 100.
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