Optimisation of solid-state fermentation of Aspergillus niger JL-15 for xylanase production and xylooligosaccharides preparation

Abstract

The production of xylanase (XylA) by Aspergillus niger JL-15 in solid-state fermentation (SSF) on orange peel was optimised by the response surface methodology (RSM). The results revealed that four factors had significant effects on the XylA production (P < 0.05), that is the concentrations of the added glycerin and ammonium sulfate, the moisture content, and fermentation time. Exploying orange peel as the solid substrate, maximum xylanase activity (917.7 U/g dry fermentation product) was obtained at 4.2% glycerin, 3.1% (NH4)2SO4, 61% moisture content, and 73.4-h fermentation, this activity being close to the predicted one and 3.2 times higher than that of the basic medium (218.5 U/g). Optimum temperature and pH for XylA activity were 55°C and pH 5.0, respectively. SDS-PAGE analysis showed that the relative molecular mass of XylA was about 30.0 kDa. XylA exhibited Km and Vmax values of 9.24 mg/ml and 54.05 μmol/min/ml, respectively. XylA liberated mainly xylotriose from birchwood xylan and wheat bran, respectively. XylA was an endo-acting xylanase with transglycosylation activity, with the ability to hydrolyse, xylobiose, xylotriose, xylotetraose, xylopentaose, and xylohexaose.

Keywords

• xylanase
• response surface methodology (rsm)
• solid-state fermentation (ssf)
• xylooligosaccharides
• hplc