Reviewer response for version 2

Abstract

Xylanase breaks xylan down to xylose which is used in industries such as pulp and paper, food, and feed, among others. The utilization of wastes for xylanase production is economical, hence, this work aimed at producing xylanase through solid-state fermentation and characterizing the enzyme. Xylanase-producing strains of Bacillus megaterium and Aspergillus niger GIO were inoculated separately in a 5 and 10 days solid fermentation study on maize straw, rice straw, sawdust, corn cob, sugarcane bagasse, conifer liters, alkaline-pretreated maize straw (APM), and combined-alkaline and biological-pretreated maize straw, respectively. The best substrate was selected for xylanase production. The crude enzyme was extracted from the fermentation medium and xylanase activity was characterized using parameters such as temperature, cations, pH, and surfactants. Among different substrates, the highest xylanase activity of 3.18 U/mL was recorded when Aspergillus niger GIO was grown on APM. The xylanase produced by Aspergillus niger GIO and Bacillus megaterium had their highest activities (3.67 U/mL, 3.36 U/mL) at 40 °C after 30 and 45 minutes of incubation, respectively. Optimum xylanase activities (4.58 and 3.58 U/mL) of Aspergillus niger GIO and Bacillus megaterium, respectively were observed at pH 5.0 and 6.2. All cations used enhanced xylanase activities except magnesium ion. Sodium dodecyl sulfate supported the highest xylanase activity of 6.13 and 6.90 U/mL for Aspergillus niger GIO and Bacillus megaterium, respectively. High yields of xylanase were obtained from Aspergillus niger GIO and Bacillus megaterium cultivated on alkaline pretreated maize straw.  The xylanase activities were affected by pH, temperature, surfactants, and cations.