Department of Food and Microbial Technology; Laboratory of Food Technology; Katholieke Universiteit Leuven; Kardinaal Mercierlaan 92; B-3001 Leuven; Belgium

Phone: 00-32-16-32.15.85, Fax: 00-32-16-32.19.60

e-mail: marc.hendrickc@agr.kuleuven.ac.be

http://www.agr.kuleuven.ac.be/lmt/vdt/general/foodtech.htm

Lipoxygenase is an enzyme that catalyzes the oxygenation of free fatty acids containing a cis,cis,1,4-pentadiene system. In vegetable products, especially in leguminosae, lipoxygenase is responsible for at least three detrimental effects: (i) There is a destruction of the essential fatty acids linoleic, linolenic and arachidonic acid. (ii) Lipoxygenase contributes to the development of off-flavors and bitter taste. (iii) Other compounds like vitamins and nutrients can be damaged by the free radicals produced in the reaction catalyzed by lipoxygenase. Hence, inactivation of lipoxygenase is pre-requisite for obtaining high-quality minimally processed vegetables. In this paper, the potential of high pressure as an alternative to water blanching for the inactivation of soybean lipoxygenase was kinetically investigated.

Isobaric-isothermal inactivation of soybean lipoxygenase (0.4 mg/ml in 0.01M Tris HCl at pH 9) was investigated in a pressure range of 0.1 to 650 MPa and a temperature range of 10 to 64°C. For all combinations studied (about 60), inactivation could be accurately described by a first order kinetic model. k-Values increased with increasing pressure at constant temperature. At constant pressure, however, k-values decreased with increasing temperature to obtain a minimal value in the temperature range between 30 and 40°C and then increased with further increase in temperature. Seemingly, lipoxygenase exerts maximal pressure stability at temperatures slightly higher than room temperature. This antagonistic effect of pressure and temperature likewise became clear from a pressure-temperature kinetic diagram. Subsequently, a mathematical model describing the inactivation rate constant as a function of pressure and temperature was formulated and the kinetic parameters were calculated. Finally, the proposed model and its concomitant parameters were validated under variable pressure and temperature conditions, including pulsated pressure treatments.