Enzymatic hydrolysis of tropical weed xylans using xylanase from Aureobasidium melanogenum PBUAP46 for xylooligosaccharide production

Abstract

The maximum yield of xylanase from Aureobasidium melanogenum PBUAP46 was 5.19 ± 0.08 U ml⁻¹ when cultured in a production medium containing 3.89% (w/v) rice straw and 0.75% (w/v) NaNO₃ as carbon and nitrogen sources, respectively, for 72 h. This enzyme catalyzed well and was relatively stable at pH 7.0 and room temperature (28 ± 2 °C). The produced xylanase was used to hydrolyze xylans from four tropical weeds, whereupon it was found that the highest amounts of reducing sugars in the xylan hydrolysates of cogon grass (Imperata cylindrical), Napier grass (Pennisetum purpureum), and vetiver grass (Vetiveria zizanioides) were at 20.44 ± 0.84, 17.50 ± 0.29, and 19.44 ± 0.40 mg 100 mg xylan⁻¹, respectively, but it was not detectable in water hyacinth (Eichhornia crassipes) hydrolysate. The highest combined amount of xylobiose and xylotriose was obtained from vetiver grass; thus, it was selected for further optimization. After optimization, xylanase digestion of vetiver grass xylan at 27.94 U g xylan⁻¹ for 92 h 19 min gave the highest amount of reducing sugars (23.65 ± 1.34 mg 100 mg xylan⁻¹), which were principally xylobiose and xylotriose. The enriched XOs exhibited a prebiotic property, significantly stimulating the growth of Lactobacillus brevis and L. casei by a factor of up to 3.5- and 6.5-fold, respectively, compared to glucose.