标题：Optimization of Solid-state Fermentation for Acidophilic Pectinase Production by Aspergillus niger Jl-15 Using Response Surface Methodology and Oligogalacturonate Preparation
摘要：Polygalacturonases that hydrolyzed the α-(1,4) glycosidic linkages of pectin is one of widely used industrial enzymes and applied in food, feed, paper and pulp, fruit juice and textile industries. To improve the production of extracellular pectinase (PgA) by a newly isolated Aspergillus niger JL-15 strain, the conditions of solid-state fermentation (SSF) were optimized by response surface methodology (RSM). The maximum pectinase activity (525.70 IU g-1 dry fermentation product) was obtained at 12.10% orange peel powder, 3.20% ammonium sulfate employing wheat bran as the solid substrate, 51.10% moisture content and 75.00 h fermentation and was 4.10 times as high as that of the basic medium (125.80 IU g-1). SDS-PAGE analysis showed that the molecular mass of PgA was about 40.0 kDa. The PgA was optimally active at 45°C and pH 4.0 and was stable over a broader pH range (4.0-8.0). The Michaelis-Menten constant (Km) and maximal velocity (Vmax) of PgA for citrus pectin was 4.04 mg mL-1 and 40.16 μmol min-1 mL-1, respectively. The enzyme mediates a decrease in the viscosity of pectin associated with a release of small amounts of reducing sugar. High performance liquid chromatography (HPLC) analysis revealed that PgA liberated a series of oligogalacturonate from pectin with the digalacturonate (G2) and trigalacturonate (G3) as major products. The mode of action study showed that the enzyme was an endo-acting polygalacturonase.
