Abstract
Abstract Background Polygalacturonase is one kind of pectinases which hydrolyze the alpha-1,4 glycosidic bond between galacturonic acid residue. Polygalacturonase has been widely used in the fields of food, biofuel, and textile industries, in which thermostable polygalacturonase is often demanded at high temperatures of 50–60 °C. Herein, we reported a thermostable polygalacturonase producing from Aspergillus fumigatus isolated from the pile fermentation of Pu’er tea in China. Results The thermophilic polygalacturonase-producing strain was identified as A. fumigatus L45 on basis of its morphology, physicochemical properties, and 18S rDNA analysis. The crucial fermentation parameters affecting polygalacturonase activity were optimized by response surface methodology (RSM); the optimum fermentation parameters were the following: inoculums concentration of 0.07 % (v/v), fermentation time of 36 h, pH of 5.0, and temperature of 45 °C. Under the optimized conditions, the highest polygalacturonase activity of 359.1 ± 10.1 U/mL was obtained. The polygalacturonase showed good thermostability and pH stability. The enzyme was activated by metal ions Zn2+ and Mg2+, but inhibited by K+. However, Na+ and Ca2+ showed little effects on its activity. K m and V max values were estimated to be 35.0 mg/mL and 7.69 μmol/mL/min, respectively. Conclusions A polygalacturonase from A. fumigatus L45 was preliminarily investigated, the crucial fermentation parameters were optimized by RSM, and the properties of polygalacturonase was examined. The polygalacturonase showed good thermostability and pH stability, which suggested the enzyme has potential applications in the biofuel and textile industries.
Highlights
Polygalacturonase is one kind of pectinases which hydrolyze the alpha-1,4 glycosidic bond between galacturonic acid residue
The results showed that 57 isolates (28.5 %) could not grow on the Congo red medium, while 143 isolates (71.5 %) showed different diameters of pectin degradation halos, indicating that they have extracellular pectinolytic activities
The propagating stability of strain L45 was evaluated, and the results showed that the polygalacturonase activity could maintain ca. 94 % after five generations
Summary
Polygalacturonase is one kind of pectinases which hydrolyze the alpha-1,4 glycosidic bond between galacturonic acid residue. Polygalacturonase has been widely used in the fields of food, biofuel, and textile industries, in which thermostable polygalacturonase is often demanded at high temperatures of 50–60 °C. Pectinases, called pectinolytic enzymes, are a group of enzymes hydrolyzing pectin substrates in plant cell [1]. Pectinases from A. niger reported by Kittur et al showed the maximal activity at 47 °C [17]. Singh and Appu Rao [18] claimed that two endo-polygalacturonases from A. niger could achieve their maximal activities at 43 and 45 °C. A polygalacturonase from Saccharomyces cerevisiae isolated from marsh grape fruit pulp possessed the maximal activity at 45 °C [19]. Thermostable pectinases are highly demanded in these modern industries
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