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Abstract : |
A local isolate identified as Aspergillus fumigatus was tested for inulinase and invertase production. Different carbon sources alone or in combination with inulin were tested. About 91% inulinase was found as extracellular enzyme in culture medium with inulin and wheat bran as sole C-source (1% for each). The activity towards sucrose (invertase enzyme) was detected only in the supernatant and represents about 26% from the inulinase activity. The production of both enzymes was inhibited with ammonical compounds as nitrogen source, whereas the maximum level (3.72, 0.35 U/ml for inulinase and invertase respectively) was observed when 0.38% KNO3 was used as nitrogen source. Beef extract, yeast extract, peptone and tryptone reduced the amount of inulinase by about 83-91%. Both enzymes were produced in a broad pH range between 4.0-8.0 as initial pH. Optimum temperature was found to be 30oC for inulinase and a dramatic reduction was observed above 35oC, while 40oC was observed for invertase. The properties of crude inulinase were also studied. The enzyme has optimum pH 5.5 in acetate buffer and optimum temperature 45oC. Fructose at concentrations higher than 0.2mg/reaction mixture inhibited the enzyme activity. The enzyme was stable for 30 min at 30oC and 40oC in pH 5.5 and for 24h at 4oC in pH 6 - 6.5. Addition of 10% glycerol protected the enzyme from deactivation at 45oC and 50oC for 30 min. The enzyme was completely inhibited by 1mM Ag+ and Hg2+ and activated by the presence of 1mM Ca2+ or Mn2+., |
