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Rice straw (RS) is a by-product from rice production process. It is rich in cellulose, hemicellulose and lignin. RS hemicellulose mainly composes of arabinoxylan (AX). This research aimed to investigate the potential of microwave-pretreatment in AX extraction from RS and substrate to produce xylooligosaccharides (XOS) via enzymatic hydrolysis. The extractive-free RS was pretreated by microwave process at 160°C for 5-15 min, then the AX was extracted with 4% sodium hydroxide. The total sugar and reducing sugar content of AX exhibited that increasing microwave-pretreatment time increased the yield of AX. The highest AX content was found at 160°C for 10 min as 7.73%, reducing sugar content of 11.89 mg/g, and total sugar of 165.85 mg/g. The crude AX obtained by microwave-pretreatment was then used as a substrate for XOS production by two commercial xylanases of Pentopan mono BG (BG) and Ultraflo Max (UM), at the enzyme concentration of 50-300 U/g AX (50°C, pH 6.0) for 24 h.The reducing sugar content and sugar profiles were monitored by DNS assay,and thin layer chromatography (TLC) which revealed that BG 50 U/g at 12 h andUM 50 U/g at 24 h showed the promising reducing sugar of 16.4 and 25.44 mg/g,respectively. The composition of XOS derived from RS (RS-XOS) prepared by BGwas xylobiose (X2), xylotriose (X3), xylotretraose (X4), and xylopentaose (X5)while by UM was xylobiose (X2), xylotriose (X3) and xylotretraose (X5). Moreover,XOS produced by BG contained very low amount of xylose (X1). In addition, theRS-XOS could the growth of Lactobacillus brevis greater than commercial XOS.

The prebiotic properties of xylooligosaccharides (XOS) and arabino-xylooligosaccharides (AXOS) produced from rice husk (RH) using microwave treatment combined with enzymatic hydrolysis were evaluated. The RH was subjected to microwave pretreatment at 140, 160 and 180 °C for 5, 10 and 15 min to obtain crude arabinoxylan (AX). Increasing microwave pretreatment time increased sugar content. Crude AX was extracted with 2% (w/v) sodium hydroxide at 25 °C for 24 h and used as a substrate for XOS production by commercial xylanases. Results showed that oligosaccharides produced by Pentopan Mono BG and Ultraflo Max provided xylobiose and xylotriose as the main products. AXOS was also present in the oligosaccharides that promoted growth of Lactobacillus spp. and resisted degradation by over 70% after exposure to simulated human digestion.

Production of defatted rice bran arabinoxylan (DRB-AX) from defatted rice bran (DRB) is maximized using alkali extraction. Conversion of DRB-AX into xylooligosaccharide (XOS) by endoxylanase from Neocallimastix partriciarum, and refining enzymatic XOS liquor using activated carbon are also investigated. Chemical composition analysis of DRB indicates the richness of nutrients at 60.76% carbohydrate, 10.42% protein, and 32.69% total dietary fiber. Alkali extraction performed at 2.5 M NaOH solution for 12 h is the optimal condition to produce DRB-AX, with a crude yield of 52.82 g 100 g −1 containing 26.96% arabinoxylan, 26.07% arabinose, and 21.42% xylose with arabinose/xylose ratio 1.22. Endoxylanase from N. partriciarum partially hydrolyzes DRB-AX at 50 °C, pH 6.0 at enzyme concentration of 80 U g −1 substrate for 24 h. This enzymatic XOS production design yields 26.67 ± 0.69 mg g −1 DRB. Xylobiose and xylotriose including an unknown saccharide are short chain oligomer products. Refining XOS from DRB with 15% (w/v) activated carbon recover 55.7% (w/w) of initial XOS. Hence, DRB can be used as an alternative highly branched arabinoxylan source for novel substituted XOS production.

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