No abstract

The effects of media temperature, agitation rate and molasses concentration on the yield of fermentation in xanthan gum production process were investigated. Xanthan gum was produced in batch fermentation by Xanthomonas campestris PTCC 1473 from molasses. At 32 °C, 500 rpm and media with 30 g/l of total sugar, maximum production of xanthan gum (17.1 g/l) was achieved. For the purity of the xanthan FTIR spectrum was obtained. The identified spectrum was compared with the commercial product. In batch culture, several kinetic models for the biochemical reactions were extensively studied. The growth kinetic parameters were evaluated by unstructured model and derived from the related equations. Based on Malthus and Logistic rate equations, the maximum specific growth rate, μ max , and initial cell dry weight, X 0 , were defined. Luedeking-Piret and Modified Luedeking-Piret models were applied for the product formation and substrate consumption rates. In batch experiments, the kinetic parameters for the growth associated (m, a) and non-growth associated (n, b) parameters were determined.

No abstract

S-naproxen by enantioselective hydrolysis of racemic naproxen methyl ester was produced using immobilized lipase. The lipase enzyme was immobilized on chitosan beads, activated chitosan beads by glutaraldehyde, and Amberlite XAD7. In order to find an appropriate support for the hydrolysis reaction of racemic naproxen methyl ester, the conversion and enantioselectivity for all carriers were compared. In addition, effects of the volumetric ratio of two phases in different organic solvents, addition of cosolvent and surfactant, optimum pH and temperature, reusability, and inhibitory effect of methanol were investigated. The optimum volumetric ratio of two phases was defined as 3:2 of aqueous phase to organic phase. Various water miscible and water immiscible solvents were examined. Finally, isooctane was chosen as an organic solvent, while 2-ethoxyethanol was added as a cosolvent in the organic phase of the reaction mixture. The optimum reaction conditions were determined to be 35 °C, pH 7, and 24 h. Addition of Tween-80 in the organic phase increased the accessibility of immobilized enzyme to the reactant. The optimum organic phase compositions using a volumetric ratio of 2-ethoxyethanol, isooctane and Tween-80 were 3:7 and 0.1% (v/v/v), respectively. The best conversion and enantioselectivity of immobilized enzyme using chitosan beads activated by glutaraldehyde were 0.45 and 185, respectively.

No abstract

In the present study, textural and structural characterizations of chitosan bead for immobilization of alpha amylase in detail by N2 adsorption-desorption, Microspore Analysis (MP), Barrett-Joyner-Halenda (BJH) plots and Field Emission Scanning Electron Microscope (FESEM) observations were investigated. Pore structure observation revealed chemical activation of chitosan bead by glutaraldehyde can change both the isotherm type of adsorption and pores shape. In consistence with textural analysis, the high value of pore volume distribution with range of mesopores region indicated the porosity of activated chitosan bead was uniformly increased. Intra-particle diffusion model designated that 97.6% of amylase was adsorbed inside the mesopores of activated chitosan bead owing to increase in kid (rate constant) and reduce of boundary layer effect on diffusion process. In addition, the stability experiments (pH, storage and thermal stability), enzyme leakage, Ca 2+ and salt concentration effects were evaluated for immobilized amylase and compared with its free activities. Ca 2+ concentration of 1 mM shows an excellent impact on relative activity of amylase on its free and immobilized forms. NaCl experiments indicated that 84% of amylase was covalently immobilized on activated chitosan beads. Further, the Michaelis-Menten kinetic coefficients, Km (~0.4mg/ml) and, Vmax(~227 U/mg Enzyme), point out strong affinity and high activity of immobilized enzym.