Production of exo-inulinase from Aspergillus niger and Candida oleophila for degradationof chicory root inulin and ethanol production

Abstract

Exo-inulinase is an enzyme that is capable of breaking down inulin to produce fructosemolecules. This enzyme produced by various fungal strains belonged to genera of Aspergillus,Trichoderma, Penicillium, Saccharomyces and Candida. Two fungal strains (Aspergillus niger andCandida oleophila) were selected among of 12 the tested strains which gave the highest inulinaseactivity (I) on chicory root, giving 40 and 35 mm of clear zone diameter on an agar plate and 55.93 and46.38 U/ml in broth medium, respectively. The selected two also strains gave the highest invertaseactivity (S) on sucrose 95.04 and 86.94 U/ml with high values of I/S ratio (0.59 and 0.53). Bothenzymes were better produced using co-cultures of A. niger and C. oleophila than using single culture.Optimization of fermentation parameters (11 factors) for both enzymes production from the tested co-cultures was carried out using the design of Taguchi orthogonal array (OA). Results showed that 5(inulin, corn steep liquor (CSL), temperature degree, pH and KH2PO4) and 3 (inulin, CSL andtemperature degree) were most significant factors affecting on production of inulinase (102.3 U/ml) andinvertase (139.5 U/ml)which were closely related with predicted values of 103.6 and 140.1 U/ml,respectively. Fungal inulinase was applied to chicory inulin hydrolysis compared to pure inulin for theproduction of fructose with content of 61% and 75%, respectively, after 60 min of reaction time. It wasalso found that ethanol production by inulinase was achieved using 3 processes, which were directconversion (DC) of inulin into ethanol by mixed cultures A. niger and C. oleophila, separate hydrolysisand fermentation (SHF) and simultaneous saccharification and fermentation (SSF). The SHF and SSFmethods were inoculated with Saccharomyces cerevisiae for fermentation sugars into ethanol. Thehighest ethanol yield was recorded during SSF process (15.60 g/L) compared with SHF (7.36 g/L) andDC (2.83 g/L) processes

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