Production of thermostable xylanase using Streptomyces thermocarboxydus ME742 and application in enzymatic conversion of xylan from oil palm empty fruit bunch to xylooligosaccharides

Abstract

Empty fruit bunch (EFB), the largest amount of biomass from a palm oil mill, is a promising renewable source for many value-added products. This study aimed to utilize EFB for production of xylanase by Streptomyces thermocarboxydus ME742 and applied the enzyme to the production of xylooligosaccharides (XOS) from EFB derived xylan (EFB-xylan). The strain ME742 produced the maximum xylanase (473.21 ± 6.55 U/mL) in a medium containing 50 g/L EFB supplemented with 3.0 g/L peptone at 40 °C for 4 days. Xylanase ME742 was purified 23.68 fold with specificity of 1229 U/mg by acetone precipitation and DEAE-Sepharose chromatography . It was stable in a wide range of pH (4.0–9.5) and in elevated temperatures up to 55 °C. Xylanase ME742 effectively hydrolyzed EFB-xylan. HPLC analysis revealed that the hydrolysate was composed of xylose and XOS with degree of polymerization between 2 and 5 and xylobiose was the predominant product. The XOS yield ranging in 95.01–151.19 mg/g EFB-xylan was generated from enzymatic processing for 12–72 h. Interestingly, arabinosyl-xylooligosaccharides were also predicted to be produced from EFB-xylan. XOS mixture exhibited high antioxidant activity (71.36 ± 0.57%) against DPPH at 100 μg/mL concentration and moderate activity (45.18 ± 1.56%) against ABTS radical. These findings reveal the potential use of Streptomyces thermocarboxydus ME742 and xylanase produced in a sustainable bioprocess to add value of EFB waste. • This study constituted a sustainable bioprocess to enrich value of oil palm waste. • Empty fruit bunch (EFB) was used to produce xylanase and xylan that both further used in XOS production. • Purified xylanase ME742 has characteristics favorable for industrial use in XOS production. • Purified xylanase ME742 generated arabinosyl-XOS from EFB-xylan. • XOS mixture contained arabinosyl-XOS had high antioxidant activity against DPPH radical.