High pressure inactivation of lipoxygenase in soy milk and crude soybean extract

The high pressure inactivation of lipoxygenase (LOX) in soy milk and crude soybean extract was studied in the pressure range 0.1–650 MPa with temperature varying from 5 to 60 °C. For both systems, the isobaric–isothermal inactivation of LOX was irreversible and followed a first-order reaction at all pressure–temperature combinations tested. In the entire pressure–temperature area studied, the LOX inactivation rate constants increased with increasing pressure at constant temperature for both systems; the rate constants were somewhat smaller in soy milk system than in crude soybean extract. At constant elevated pressure, LOX exhibited the greatest stability around 20 °C in both systems, indicating that the Arrhenius equation was not valid over the entire temperature range. For both systems, the temperature dependence of the LOX inactivation rate constants at high temperature decreased with increasing pressure, while the highest sensitivity of the LOX inactivation rate constants to pressure was observed at about 30 °C. The pressure–temperature dependence of the LOX inactivation rate constants was successfully described either using an empirical mathematical model or using a thermodynamic kinetic model for both systems. On a kinetic basis, neither the reaction order of inactivation nor the pressure and temperature sensitivities of the inactivation rate constants were influenced by the different levels of food complexity between the two systems.