Browsing by Author "Saraiva, J."
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- Analysis of the inactivation kinetics of freeze-dried á-amylase from bacillus amyloliquefaciens at different moisture contentsPublication . Saraiva, J.; Oliveira, J. C.; Hendrickx, M.; Oliveira, F. A. R.; Tobback, P.The thermal inactivation kinetics of freeze-dried á-amylase in a solid matrix was studied at water contents ranging from 1.5 to 23.9 g water per 100 g dry solid. These conditions were obtained by equilibration in dry environments, with water activities ranging between 0.11 and 0.88. Isothermal inactivation experiments in the range 135 to 150 °C were performed. Results were analysed with both the Bigelow and Arrhenius models. It was concluded that there was no statistical significance to suggest that the water content influenced the kinetic parameters. An activation energy of 128 kJ/mol and pre-exponential factor with a logarithm of 33.9 described all the results well.
- The effect of high pressure on microbiological quality of AlheirasPublication . Castro, S.M.; Noronha, L.; Queirós, R.; Silva, Joana; Saraiva, J.; Teixeira, Paula
- The influence of water activity on thermal stability of horseradish peroxidasePublication . Hendrickx, M.; Saraiva, J.; Lyssens, J.; Oliveira, J.; Tobback, P.The thermal stability of horseradish peroxidase in the solid state was studied as a function of water activity, from 0.11 to 0.88. At all activities the enzyme was found to be much more stable in the solid state than in solution. Inactivation temperatures were in the range of 140–160°C. Inactivation curves show a biphasic behaviour which can be described by a model assuming two fractions (heat labile and heat stable) with independent first order inactivation kinetics. The labile fraction represents approximately 30% of the total activity. The z-value for both stable and labile fractions depends on water activity (moisture content) and has a maximum at aw= 0.76 (44.4°C and 43.8°C, respectively).
- Thermal inactivation kinetics of suspensions of bacillus amyloliquefaciens a-amylase in hydrophobic organic solventsPublication . Saraiva, J.; Oliveira, J.; Hendrickx, M.The thermal inactivation of suspensions of á-amylase from Bacillus amyloliquefaciens equilibrated at three low moisture contents and with added hydrophobic organic solvents of different hydrophobicity (dodecane, octane and 1-octanol) was systematically studied at temperatures between 135 to 150°C. The inactivation kinetics showed a first order decay in all cases. The enzyme is much more thermostable and less temperature sensitive than in aqueous solution. The behaviour was compared to inactivation in dry atmospheres, at similar water contents, without solvents. The organic solvents caused a larger influence of the water content and some environments caused significant changes in the rate constants, but the activation energy was not significantly affected. The solvent showing a higher impact on the kinetic parameters was 1-octanol.