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High hydrostatic pressure enhances resistance to thermal denaturation, improves enzyme stability.

High-pressure processing has potential food preservation applications because it can inactivate microorganisms and enzymes. Before we implement this new technology, we need to understand the mechanism and kinetics of pressure-induced degradation, denaturation, activation and inactivation of several food compounds, such as microorganisms, enzymes and nutrients, and the way in which degradation, denaturation and the like are influenced by other parameters, such as temperature and pH.

We should be concerned with the factors that influence the effect of high pressure on enzymes that impact product quality. Since the first biosynthetic reactions involving enzymes were developed, various techniques have been employed to increase enzyme stability and activity, all of which have had varying degrees of success.

Scientists at the University of Florida indicate that high pressures can enhance resistance to thermal denaturation and increase enzyme activity. They found that moderate high pressures--between 150 MPa and 450 MPa--stabilize lipase activity in organic media, which allows processes to occur at temperatures higher that what is achievable at ambient pressure, because of enzyme denaturation and solvent evaporation.

In experiments, a commercial immobilized lipase was incubated in hexane at 80 C for 1 hour and 4 hours while simultaneously being exposed to pressure conditions ranging from 0.1 MPa to 700 MPa. At 400 MPa, the scientists found that increasing the incubation pressure increased the reaction rate, enabling it to reach a maximum of 100% of the relative rate, equal to that of the control enzyme not exposed to heat above 20 C.

Reaction rates decreased steadily above 400 MPa. The researchers determined the lipase activity at 400 MPa for the esterification of isoamyl acetate from isoamyl alcohol and acetic acid at temperatures ranging from 40 C to 80 C. Relative activity increased steadily from 40 C to 80 C, with activity at elevated pressures consistently greater than at ambient pressures.

High pressures enhanced the stability of lipase against thermal denaturation and increased its activity. Pressure does not always increase activity or stability. It depends on the enzyme. In the Florida laboratory, the scientists have verified the stabilizing effect in lipases, pectinases (pectin esterases and polygalacturonases) and some oxidases like glucose oxidase.

Further information. Jose I. Reyes-De-Corcuera, Citrus Research and Education Center, Food Process Engineering, University of Florida, 700 Experiment Station Rd., Lake Alfred, FL 33850; phone: 863-956-1151; email:
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Publication:Emerging Food R&D Report
Date:Jul 1, 2009
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