Abstract
Sixteen different mould cultures viz. Aspergillus, Alternaria, Arthroderma, Trichoderma, Fusarium, Penicillium, Rhizopus and Chochliobolus were isolated from the soil samples of Qatar by serial dilution method. The preliminary screening of isolates was done by selecting initial colonies showing relatively bigger zones of starch hydrolysis on nutrient agar plates. The isolates were then subjected to secondary screening by submerged fermentation (SmF). The 1,4-α-D-glucan glucohydrolase (GGH) activity ranged from 1.906-12.675 U/ml/min. The product yield was analysed in dependence of mycelial morphology, biomass level and protein content. The isolate Aspergillus oryzae llB-6 which gave maximum enzyme production was incubated in M3 medium containing 20 g/l starch, 10 g/l lactose, 8.5 g/l yeast extract, 6 g/l corn steep liquor (CSL), 1.2 g/l MgSO4.7H2O, 1.3 g/l NH4Cl, 0.6 g/l CaCl2.2H2O, pH 5 at 30±2°C and 200 rpm. On the basis of kinetic variables, notably Qp (0.058±0.01a U/g/h), Yp/s (0.308±0.03ab U/g) and qp (0.210±0.032abc U/g fungal biomass/h), A. oryzae IIB-6 was found to be a hyper producer of GGH (LSD 0.0345) compared to A. kawachii IIB-2. A noticeable enhancement in enzyme activity of over 30% was observed (13.917±1.01 U/ml/min) when the process parameters viz. cultural conditions (pH 5, incubation period 72 h) and nutritional requirements (6 g/l CSL, 9.5 g/l yeast extract, 10 g/l starch, 20 g/l lactose) were further optimized using a 2-factorial Plackett-Burman design. The model terms were found to be highly significant (HS, p≤0.05), indicating the potential utility of the culture (dof~3).
Highlights
The enzyme 1,4-α-D-glucan glucohydrolase (GGH, EC 3.2.1.3) is an exo-amylase which cleaves both α-1,4 and α-1,6 glycosidic bonds, yielding β-D-glucose from the non-reducing end of starch polymer chain
The isolates A. oryzae Institute of Industrial Biotechnology (IIB)-6 and A. kawachii IIB-2, being hyper producers of GGH were selected for kinetic comparison
A diversified mycelial morphology was noticed with other cultures A. oryzae IIB-6 exhibited mixed kind of mycelia
Summary
The enzyme 1,4-α-D-glucan glucohydrolase (GGH, EC 3.2.1.3) is an exo-amylase which cleaves both α-1,4 and α-1,6 glycosidic bonds, yielding β-D-glucose from the non-reducing end of starch polymer chain. GGH degrades starch to glucose in theoretically 100% yields. The reaction rate decreases with the decreasing chain length of the dextrin substrate. The enzyme is capable of catalysing a reverse of the normal hydrolysis reaction to produce mainly maltose and isomaltose (Rangabhashiyam et al 2011). It has wide range of applications in industries for the production of dextrose, high-fructose corn syrup (HFCS) and ethanol It is imperative to screen useful fungi for manufacturing of desired product (Oshoma et al 2010)
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