RESUMO
Background: Enzymatic hydrolysis of lactose is one of the most important biotechnological processes in the food industry, which is accomplished by enzyme beta-galactosidase [beta-gal, beta-D-galactoside galactohydrolase, EC 3.2.1.23], trivial called lactase. Orthogonal arrays design is an appropriate option for the optimization of biotechnological processes for the production of microbial enzymes
Methods: Design of experimental [DOE] methodology using Taguchi orthogonal array [OA] was employed to screen the most significant levels of parameters, including the solid substrates [wheat straw, rice straw, and peanut pod], the carbon/nitrogen [C/N] ratios, the incubation time, and the inducer. The level of beta-gal production was measured by a photometric enzyme activity assay using the artificial substrate ortho-Nitrophenyl-beta-D-galactopyranoside
Results: The results showed that C/N ratio [0.2% [w/v], incubation time [144 hour], and solid substrate [wheat straw] were the best conditions determined by the design of experiments using the Taguchi approach
Conclusion: Our finding showed that the use of rice straw and peanut pod, as solid-state substrates, led to 2.041-folds increase in the production of the enzyme, as compared to rice straw. In addition, the presence of an inducer did not have any significant impact on the enzyme production levels
RESUMO
Listeria monocytogenes is slowly becoming drug resistant, study on resistance of this pathogen is important to ensure effective treatment of human listeriosis. The aim of this work was evaluating the changes in susceptibility to antibiotics and cell survival of L. monocytogenes PTCC1297 [serotype 4a] after exposure to some stresses. In this descriptive-analytic study L. monocytogenes PTCC1297 subjected to sub-lethal environmental stresses including ethanol [5% v/v], sodium chloride [7% w/v], acid [HCl, pH=5.0], hydrogen peroxide [600 ppm] and heat [45[degree]C]. After the stress treatments, antibacterial susceptibility and cell survival were determined. Exposing to hydrogen peroxide [600 ppm] and heat [45[degree]C] significantly [p< 0.05] increased resistance to all selective antibiotics. But treating to stresses such as hydrochloric acid [pH=5.0], sodium chloride [7% w/v] and ethanol [5% v/v] decreased resistance [p< 0.05] to antibiotics. L. monocytogenes PTCC1297 cell survival was decreased at 60[degree]C which is considered as lethal condition. Exposing to sub-lethal acid stress increased survival to high acidic conditions [pH=3.0]. But upon increasing hydrogen peroxide the viability of cell decreased. Treating the cells with ethanol [14% v/v] and NaCl [20% w/v] increased cell survival. Adaptation to some stresses including hydrogen peroxide and heat increase resistance to antibiotics. Stresses such as ethanol, hydrochloric acid and sodium chloride act in adverse. Exposing to some sub-lethal stresses increased cell survival when lethal doses of the same stress such as acid, ethanol and sodium chloride were used. But, when we treating the cells to sublethal doses of H[2]O[2] and heat the cell survival decreased
RESUMO
In this study, urease production was investigated among thirteen strains of Aspergillus niger; seven strains isolated from soils of Semnan province in Iran and six strains obtained from Persian Type Culture Collection [PTCC]. The enzyme production was screened in two submerged media quantitatively. The registered PTCC 5011 and the native S31 strains showed more urease production than the other eleven strains. The maximum enzyme productions by PTCC 5011 and S31 strains were 106 and 109 U.g-1dry mass in submerged culture, respectively. Also, we used two solid media for screening all of the strains for urease production semi quantitatively. Due to the acceptable correlations between the two methods, the latter can be used as an ancillary method to mass screening of urease production by filamentous fungi