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 hydrolyse the alpha-(1,4) glycosidic linkages of pectin are widely used in the food, feed, paper and pulp, fruit juice and textile industries. To improve production of extracellular pectinase (PgA) by the newly isolated Aspergillus niger JL-15 strain, conditions for solid-state fermentation (SSF) were optimized by response surface methodology (RSM). Max. pectinase activity (525.70 IU g-1 dry fermentation product) was obtained using 12.10% orange peel powder, 3.20% ammonium sulfate with wheat bran as the solid substrate and a 51.10% moisture content after 75 h of fermentation, and was 4.10 times as high as that achieved using the basic medium (125.80 IU g-1). SDS-PAGE analysis showed that the molecular mass of PgA was approx. 40.0 kDa. The PgA was optimally active at 45 degrees C and pH 4.0 and was stable over a broader pH range (4.0-8.0). K_m and V_max of PgA for citrus pectin were 4.04 mg ml-1 and 40.16 mumol min-1 ml-1, respectively. The enzyme mediated a decrease in the viscosity of pectin associated with a release of small amounts of reducing sugar. HPLC revealed that PgA liberated a series of oligogalacturonates from pectin with digalacturonate and trigalacturonate as major products. The enzyme was found to be an endo-polygalacturonase.