Pascual Lopez

Free radical production by manothermosonication

Abstract The use of manothermosonication (MTS), a combined treatment of heat and ultrasound (20 kHz frequency) under moderate pressure, has been recently proposed as an alternative to conventional heat treatment of liquid foods. The efficiency of MTS has been proved on several enzymes of interest in food industry. One of the MTS enzyme inactivation mechanisms proposed is the interaction of free radicals produced by water sonolysis with some amino acid residues. In this paper we examine the rate of free radical production of the MTS system under different conditions of temperature, pressure and ultrasound amplitude using the terephtalate dosimeter. The ultrasound amplitude was varied between 20 and 145 μm at two different temperatures and pressures ( 70 ° C 200 kPa and 130 ° C 500 kPa ). In both cases, free radical production rate increases linearly with increasing ultrasound amplitude. The pressure effects on free radical production was studied under two different conditions at 117 μm: 70 °C and 130 °C. At 70 °C an increase of hydrostatic pressure results in an increase in free radical production rate, whereas increasing hydrostatic pressure at 130 °C had a negligible effect on free radical production rate. Temperature effects were studied between 30 and 140 °C at 117 μm ultrasound amplitude. Results show that increasing temperature results in a decrease in hydroxyl radical rate production.

Temperature dependence of lipoxygenase heat inactivation; evaluation with linearly increasing temperature profiles

ZusammenfassungEine nicht isotherme kinetische Methode zur Bewertung der Temperaturabhängigkeit der Hitzeinaktivierung von Enzymen wurde aus theoretischen Grundlagen entwickelt. Mittels eines nicht linearen Regressions-Computerprogrammes und Enzymaktivitätbestimmungen entlang linear steigender Temperaturprofile wurden z-Werte von Lipoxygenase in einzelnen Versuchen bestimmt. Auf diese Weise werden Zeit, Kosten und Laborarbeit erspart. Die so bestimmten z-Werte waren von der Erhitzungsgeschwindigkeit leicht abhängig; z-Werte von 4,11 °C bis 4,66 °C wurden bei Erhitzungsgeschwindigkeiten von 2,56 °C/Minute bzw. 1,48 °C/Minute bestimmt.AbstractA non-isothermal kinetic method for evaluating the temperature dependence of enzyme heat inactivation has been developed from theoretical considerations. By using a non-linear regression software programme and enzyme activity data obtained along linearly increasing temperature profiles, z values of lipoxygenase were obtained in single experiments, substantially reducing time, cost, and labour. The z values so obtained were slightly dependent on heating rate, varying from 4.11° C at a rate of heating of 2.56° C/min to 4.66° C at a heating rate of 1.48° C/min.