Preparation of β(1→3)/β(1→4) xylooligosaccharides from red alga dulse by two xylanases from Streptomyces thermogriseus.

Red alga dulse contains xylan with β(1→3)/β(1→4) linkages. We previously prepared xylooligosaccharides (XOSs) from dulse xylan; however, the product contained many D-xylose residues and fewer XOSs with β(1→3) linkages. To improve the efficiency of XOS production, we prepared two recombinant endoxylanases from Streptomyces thermogriseus (StXyl10 and StXyl11). Comparing the k/K values for dulse xylan, this value from StXyl10 was approximately two times higher than that from StXyl11. We then determined the suitable conditions for XOS production. As a result, dulse XOS was prepared by the successive hydrolysis of 10 mg/mL dulse xylan by 0.5 μg/mL StXyl10 for 4 h at 50 °C and then 2.0 μg/mL StXyl11 for 36 h at 60 °C. Xylan was converted into 95.8% XOS, including 59.7% XOS with a β(1→3) linkage and 0.97% D-xylose. Our study provides useful information for the production of XOSs with β(1→3) linkages.