Effects of integrated wet-milling and alkali pretreatment on the properties and enzymatic hydrolysis of rice straw

Rice straw is a sort of biomass resource in abundance.However,it is difficult to convert the cellulose and hemicellulose contained in the rice straw into fermentable sugars because of its complex chemical composition and structure.An integrated wet-milling and alkali pretreatment was applied to the rice straw for 1 h.The effects of NaOH concentration in the pretreatment on chemical composition,structure and reducing-sugar yield of rice straw were investigated.The Michaelis constant(Km) and maximum reaction rate(rmax)of Michaelis-Menten equation were determined for the enzymatic reaction.It was shown that the lignin content was decreased from 12.4% to 10.4%;the crystalline structure was disrupted;and the water retention value(WRV) was increased from 639.6% to 1044.6% for rice straw by the pretreated with 1% NaOH.The reducing-sugar yield was 13.4%;the Km was 66.8 mg/mL;and the rmax was 312.5 μmol/(min.mL) in the enzymatic hydrolysis of untreated rice straw.The reducing-sugar yield was 41.4%;the Km was 15.9 mg/mL;and the rmax was 666.7 μmol/(min.mL) in the enzymatic hydrolysis of rice straw pretreated with 1% NaOH.The improvement of enzymatic reaction rate and reducing-sugar yield was resulted from the lignin removal,crystalline-structure disruption and accessibility increase in rice straw.