Kinetic and thermodynamic investigation of mancozeb degradation in tomato homogenate during thermal processing

BACKGROUND: The kinetic and thermodynamic parameters of mancozeb degradation in tomato homogenates under the conditions prevailing in the manufacture of tomato products (at 60-100 degrees C for 0-60 min) were investigated. A gas chromatographymass spectrometry method was used to analyse residual mancozeb in tomato homogenate. Ethylenethiourea (ETU), the main toxic degradation product of mancozeb, was measured by high-performance liquid chromatography (HPLC)with photodiode array detector (PDA). RESULTS: The degradation of mancozeb and the formation of ETU in tomato homogenates were adequately described as first-order kinetics. Dependence of the rate constant followed the Arrhenius relationship. Apparent activation energies, temperature coefficients, half time and time to reduce to 90% of the initial value of mancozeb were calculated as kinetic parameters. The thermodynamic parameters of mancozeb were also described as Delta g(d) = -2.440 and 7.074 kJ mol(-1); Delta h(d) = -32.555 and -42.767 kJ mol(-1); Delta s(d) = -0.090 and -0.150 kJ mol(-1) K-1; K-e = 0.414 and 9.797 L g(-1) for 333 and 373 K respectively. CONCLUSION: Current findings may shed light on the reduction of mancozeb residue and its toxic degradation product during thermal processing of tomatoes and may also be valuable in awareness and prevention of potential risks from dietary exposure. (C) 2011 Society of Chemical Industry