摘要:

Immobilized enzymes, advantageous for use in bioreactors, are difficult to decontaminate. Inactivation of microorganisms by high hydrostatic pressure could be a gentle decontamination method, provided the immobilized enzyme is stable enough. Loss in activity of α‐amylase fromBacillus subtiliscovalently bound to sepharose, after 10–30 minutes of pressure treatment at 300, 450 und 600 MPa at 50 and 70 °C and pH 8, and after 10–30 minutes of heat treatment at 50 and 70 °C and pH 8, was distinctly lower than that of equally treated non‐immobilizedB. subtilis α‐amylase with and without sepharose. At 100 MPa reaction was accelerated by 5 %.

ISSN:0890-5436    

DOI:10.1080/08905439609549904

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The kinetic parameters for thermal inactivation ofBacillus subtilis α‐amylase (15 mg/ml in Tris HCI buffer at pH 8.6) were determined from isothermal experiments using a two step linear regression method. At ambient pressure, the inactivation ofBacillus subtilis α‐amylase could be described by a first order kinetic model. The activation energy (Ea) was 266 kJ/mole and the rate constant (kref) at reference temperature (50°C) 6.3*10−5min−1. Subsequently the inactivation due to combined pressure and temperature was investigated in a pressure range of 0 to 550 MPa and a temperature range of 40 to 80°C. The kinetic parameters for pressure‐temperature inactivation of BSA were estimated applying a non‐linear regression method on a first order kinetic model. Ea‐values were found to decrease and kref‐values to increase with increasing pressure. Furthermore, the influence of glycerol on the thermal and pressure‐temperature stability ofBacillus subtilis α‐amylase was investigated. In both cases, glycerol seemed to enhance the stability since it caused a decrease of the krefvalues at any pressure. At ambient pressure, the kinetic parameters for thermal inactivation in the presence of glycerol were an Ea‐value of 265 kJ/mole and a kref‐value of 4.1 *10−6min−1. Adding glycerol lowered the kref‐value, but had no significant influence on the activation energy. Finally, the activation volume for pressure‐temperature inactivation of BSA was calculated. At reference temperature the activation volume was ‐39.7 cm3/mole and it decreased linearly with increasing temperature. In the presence of glycerol, the activation volume at reference temperature was ‐55.1 cm3/mole.

ISSN:0890-5436    

DOI:10.1080/08905439609549905

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The stability and the catalytic activity of a carboxypeptidase from the extreme thermophilic archaebacteriaS. solfataricuswas studied over a wide range of temperature (30–95 °C) and pressure (0.1 ‐ 400 MPa), and compared to carboxypeptidase A. The thermostability of both carboxypeptidases could be increased at high pressure. The catalytic activity of the enzyme fromS. solfataricusshowed two temperature dependent domains. Below 60°C, the values of the activation energy and activation volume were large: ?H‡= 44 kJ/mol, ?V‡= 21 ml/mol, suggesting a conformation with a high structural rigidity. In the high temperature domain (above 60 °C), both terms were quite small (?H‡= 9 kJ/mol, ?V‡= 6 ml/mol), comparable to those of carboxypeptidase A which were always small (?H‡= 24 kJ/mol, ?V‡= 0.5 ml/mol), regardless of the temperature. High pressure appeared to shift the enzyme conformation to the properties of the low temperature domain. These results point to the possibility that the thermostability of carboxypeptidase fromS. solfataricusis explained by hydrophobic hydration. This enzyme appears to be an interesting model system for the understanding of the thermo‐ and barostability of proteases.

ISSN:0890-5436    

DOI:10.1080/08905439609549906

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

High hydrostatic pressure thawing (600 MPa, 25 and 50°C, 15 min) of frozen strawberries was applied as a pretreatment in the thermal processing of strawberry preparations when comparing this process with thawing of strawberries at atmospheric pressure prior to thermal processing (92°C, 20 min) increases in sucrose uptake were observed for strawberry slices (21%) as well as for whole fruit (140%) reaching maximum sucrose contents of 45.6±2.4°Brix and 34.7±0.9°Brix respectively. In addition high pressure treatment of strawberries proved sufficient to reduce total microbial counts by two log cycles.

ISSN:0890-5436    

DOI:10.1080/08905439609549907

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Inactivation of vegetativeBacillus subtilisATCC 9372 by high hydrostatic pressure treatment (200 ‐ 450 MPa) was tested at 20, 30 and 40°C. Time ‐ inactivation curves of the bacteria suspended in Ringer's solution showed sigmoid asymmetric shapes when plotted in logarithmic scale. Kinetic analysis of the survivor data was performed by fitting a two‐step‐model. It was assumed that during pressure treatment, the bacterial cells pass through a metastable intermediate state which is reached after endogenous homeostatic mechanisms balancing the pressure induced displacements of equilibria can no longer be maintained. Combined pressure‐temperature‐pH effects may target this state and cause lethal cell damage. Modelling this concept, a distributive function describing the initial transition was used in combination with a first‐order reaction which was assumed to govern the irreversible second step. Regressively derived characteristic parameters showed logarithmic‐linear behaviour. Applicability of the model on dynamic treatments with constant rate of pressure increase could be proven.

ISSN:0890-5436    

DOI:10.1080/08905439609549908

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Production of hydrogen peroxide is commonly the first of various biochemical reactions of plant cells to stress. For monitoring this oxidative stress response of plant cells pyranine, a fluorescent dye, is a useful system, because of its rapid bleaching by plant peroxidases. Measurement of the reduction of fluorescence can provide valuable information about the stress effects of processing operations on plant foods. The effect of high pressure treatment at 50 and 90 MPa, a thermal process at 50 °C, and a freeze‐thaw cycle on tomato cell cultures as model system was examined. Thermal treatment, freezing as well as pressures of 90 MPa caused destruction and the death of the plant cells, consequently no hydrogen peroxide production occured. Pressure treatments for 10 minutes at 50 MPa and room temperature were shown to induce stress responses in the plant cells. In contrast to elicitation with chitosan the cells showed a lag‐time in their reaction after high pressure treatment. The addition of pectolytic enzymes to the cell culture system resulted in delayed stress reaction most likely due to the formation of degradation products of pectin. We suggest that chemical and physical elicitation provoke different ways of signal transduction.

ISSN:0890-5436    

DOI:10.1080/08905439609549909

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Genetically Modified Foods ‐ Safety Aspects Karl‐Heinz Engel, Gary R. Takeoka and Roy TeranishiAmerican Chemical Society, Washington, DC 1195 243 pages, ISBN 0–8412–3320–9

ISSN:0890-5436    

DOI:10.1080/08905439609549910

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0890-5436    

DOI:10.1080/08905439609549903

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor