Suitability of Some Lignocellulosic Materials for Xylan and Xylanase Production using Aspergillus flavus

Abstract

Xylan, a major hemicellulosic polysaccharide in plant cell walls, and the hydrolytic enzyme, xylanase, have attracted increasing attention due to their wide industrial applications in the food, textile, paper industries and in prebiotic (xylooligosaccharide) production. However, xylan and xylanase remain commercially expensive and not sufficiently available for industrial purposes. In this study, thirteen agricultural biomasses were screened for their xylan content, their ability to support the growth of xylanolytic fungi and production of xylanase. Among them, ‘Goruba’ fruit waste exhibited the highest xylan content of 34.35 ± 1.02%. Nine xylanase-producing fungi were isolated from the ‘Goruba’ sample and one of the strains gave the highest zone of hydrolysis of 3.7±0.71mm. Cultural and molecular identification confirmed the strain as Aspergillus flavus with query coverage and identity of 99 and 99.21% respectively. Crude xylanase production using solid-state fermentation yielded 362.3 mg/mL protein with a total activity of 2829 µmol/min and a specific activity of 7.81µmol/min/mg. The partially purified enzyme had 41.17 mg of total protein after ammonium sulphate precipitation with a specific activity of 66.48 µmol/min /mg. The enzyme displayed optimum activity at 50 °C, pH 6.0, after 4 hours of incubation, with Km value of 4.08 mg/mL and Vmax of 2857 μmol/min/mg protein. These findings showed that ‘Goruba’ fruit waste is a promising substrate for xylan production and locally isolated A. flavus can efficiently produce xylanase using cheaper and readily available ‘Goruba’ fruit waste biomass for our industrial and biotechnological applications in Nigeria.