Production and characterization of polygalacturonase from thermophilic Thermoascus aurantiacus on submerged fermentation

Preliminary investigations on a polygalacturonase from Aspergillus fumigatus in Chinese Pu’er tea fermentation

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.

Purification and Properties of Polygalacturonase Produced by Thermophilic Fungus Thermoascus aurantiacus CBMAI-756 on Solid-State Fermentation

Polygalacturonases are enzymes involved in the degradation of pectic substances, being extensively used in food industries, textile processing, degumming of plant rough fibres, and treatment of pectic wastewaters. Polygalacturonase (PG) production by thermophilic fungus Thermoascus aurantiacus on solid-state fermentation was carried out in culture media containing sugar cane bagasse and orange bagasse in proportions of 30% and 70% (w/w) at 45°C for 4 days. PG obtained was purified by gel filtration and ion-exchange chromatography. The highest activity was found between pH 4.5 and 5.5, and the enzyme preserved more than 80% of its activity at pH values between 5.0 and 6.5. At pH values between 3.0 and 4.5, PG retained about 73% of the original activity, whereas at pH 10.0 it remained around 44%. The optimum temperature was 60–65°C. The enzyme was completely stable when incubated for 1 hour at 50°C. At 55°C and 60°C, the activity decreased 55% and 90%, respectively. The apparent molecular weight was 29.3 kDa, K_m of 1.58 mg/mL and V_max of 1553.1 μmol/min/mg. The presence of Zn⁺², Mn⁺², and Hg⁺² inhibited 59%, 77%, and 100% of enzyme activity, respectively. The hydrolysis product suggests that polygalacturonase was shown to be an endo/exoenzyme.