Exo-Inulinase Production by a Catabolite Repression-Resistant Mutant Thermophilic Aspergillus tamarii-U4 in Solid State Fermentation

Abstract

In this study, spores of inulinase-producing thermophilic Aspergillus tamarii were subjected to UV mutagenesis, and colonies obtained were screened for inulinase production on inulin-glucose agar. The thermal stability of the inulinase was also investigated. A mutant strain U4 was found to produce 2.8 times inulinase titre (62.1U/mL) as against the wild strain (22.2U/mL). Inulinase production by this U4 strain was also found not to be significantly (P≤0.05) affected by the presence of glucose. The inulinase produced retained 64% of its activity after incubation at 65ºC for three hours. Solid-state fermentation for inulinase production by the strain U4 showed that wheat bran supported the highest inulinase titre 218.3U/gds while banana peels supported the lowest inulinase production titre of 80.5U/gds. Further optimization of cultural parameters revealed that incubation time of 5 days, 60% initial moisture content of the substrate, 2% inoculum density 2%, temperature 55ºC and pH 4.5 were optimal for inulinase production. Under optimized conditions, inulinase titre of 426.6 U/gds was observed. The pattern of inulin hydrolysis by the inulinase revealed the presence of monosaccharide as the main product of hydrolysis. Inulinase production at elevated temperatures by the mutant Aspergillus tamarii-U4 and its catabolite resistant properties showed that the organism is a potential industrial candidate for the production of exo-acting inulinases.