AIM:To investigate the impact of agitation speed on pectinase production and morphological changing of Aspergillus niger (A. niger ) HFD5A-1 in submerged fermentation. METHODS:A. niger HFM5A-1 was isolated from a rotted pomelo. The inoculum preparation was performed by adding 5.0 mL of sterile distilled water containing 0.1% Tween 80 to a sporulated culture. Cultivation was carried out with inoculated 1 × 10 7 spores/mL suspension and incubated at 30 ℃ with different agitation speed for 6 d. The samples were withdrawn after 6 d cultivation time and were assayed for pectinase activity and fungal growth determination. The culture broth was filtered through filter paper (Whatman No. 1, London) to separate the fungal mycelium. The cell-free culture filtrate containing the crude enzyme was then assayed for pectinase activity. The biomass was dried at 80 ℃ until constant weight. The fungal cell dry weight was then expressed as g/L. The 6 d old fungal mycelia were harvested from various agitation speed, 0, 50, 100, 150, 200 and 250 rpm. The morphological changing of samples was then viewed under the light microscope and scanning electron microscope. RESULTS:In the present study, agitation speed was found to influence pectinase production in a batch cultivation system. However, higher agitation speeds than the optimal speed (150 rpm) reduced pectinase Effect of agitation speed on the morphology of Aspergillus niger HFD5A-1 hyphae and its pectinase production in submerged fermentation ORIGINAL ARTICLE Basic StudyDarah Ibrahim, Haritharan Weloosamy, Sheh-Hong Lim production which due to shear forces and also collision among the suspended fungal cells in the cultivation medium. Enzyme activity increased with the increasing of agitation speed up to 150 rpm, where it achieved its maximal pectinase activity of 1.559 U/mL. There were significant different (Duncan, P < 0.05) of the pectinase production with the agitation speed at static, 50, 100, 200 and 250 rpm. At the static condition, a well growth mycelial mat was observed on the surface of the cultivation medium and sporulation occurred all over the fungal mycelial mat. However with the increased in agitation speed, the mycelial mat turned slowly to become a single circular pellet. Thus, it was found that agitation speed affected the morphological characteristics of the fungal hyphae/mycelia of A. niger HFD5A-1 by altering their external as well as internal cell structures. CONCLUSION:Exposure to higher shear stress with an increasing agitation speed could result in lower biomass yields as well as pectinase production by A. niger HFD5A-1. Core tip:We report the influence of agitation speed on pectinase production on our newly isolate Aspergillus niger (A. niger ) HFM5A-1 in submerged fermentation.The agitation speed was found to influence pectinase production in a batch cultivation system. However, higher agitation speeds than the optimal speed (150 rpm) reduced pectinase production which due to shear forces and also collision among the suspended fungal cells in...

The aim of this work was to develop an effective bioprocess to enhance the pectinase production by solid-state cultures of Aspergillus niger HFM-8. Methodology and results: The pectinase production produced by A. niger HFM-8 was studied under solid state fermentation using Malaysian pomelo (Citrus grandis) peel as the substrate. This local agricultural waste is rich with lignocellulolytic material including pectin acts as the inducer of pectinase production. Under optimized conditions, 5 g of 0.75 mm pomelo peel size, moisture content of 60% (v/w) sterile distilled water pH 5.0, inoculums size of 1x10 4 spores/mL, cultivation temperature of room temperature (30 ± 2 °C), no mixing incurred and with the addition of 1% (w/w) citrus pectin and 0.1% (w/w) urea has produced pectinase production of 306.89 U/g substrate and 0.78 mg glucosamine/g substrate of fungal growth on the 8 th day of cultivation. Conclusion, significance and impact of study: There was 48.82% increment in enzyme production after the improvement of parameters. It was found that pomelo peel is a suitable feedstock for pectinase production.

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