Alkyl β-D-xyloside synthesis from black liquor xylan using Aureobasidium pullulans CBS 135684 β-xylosidases immobilized on spent expanded perlite

The crude beta-xylosidase from Aureobasidium pullulans CBS 135684 was immobilized on the surface of the modified spent expanded perlite via (3-aminopropyl) triethoxy-silane and glutaraldehyde cross-linking reaction. Over 80% of the initial free enzyme activity was detected on the bound enzyme. The immobilized beta-xylosidase (204.7 +/- 6.5 U g(-1) of perlite) exhibited transxylosylation activity when sugars from black liquor xylan hydrolysate and a variety of alcohols (C1-6) were used as donor and acceptor molecules, respectively, yielding a number of alkyl xylosides. The synthesized hexyl xyloside exhibited some interesting properties comparable with those of a commercial hexyl glucoside, including an antioxidant activity (IC50 = 8.9 +/- 2.0 mg mL(-1)), wetting time (43 s), and critical micelle concentration value (252 mmol L-1). Optimization for hexyl xyloside synthesis was performed via statistical analysis using a Box and Behnken design. The maximum predicted yield of hexyl xyloside (499.0 +/- 1.1 mg g(-1) xylan hydrolysate) was obtained with 10% (w/v) xylan hydrolysate, 10 U g(-1) immobilized beta-xylosidase, and 13% (v/v) hexanol at 70 degrees C, pH 6.0 for 4 h, and it was validated by the following experimental yield (498.9 +/- 4.8 mg g(-1) xylan hydrolysate). The maximum production yield remained relatively stable after the immobilized enzyme was reused for 12 cycles with a 471.5 +/- 15.1 mg g(-1) hexyl xyloside yield (94.4% of the first cycle). Thus, the immobilized beta-xylosidase has a high potential as a robust catalyst for application in alkyl xyloside production.