Enthalpy entropy compensation during thermal degradation of chlorophyll in mint and coriander puree

Abstract

Enthalpy entropy compensation effect has been a debatable topic for explaining the thermodynamic parameters in chemical reactions. Kinetic data for thermal degradation of chlorophylls ( a, b and total) at 105–145 °C in coriander and mint leaf puree at pH 5.5–8.5 was used for this study. By applying the modified transition state theory and Krug’s unbiased statistical regression procedure, the existence of thermodynamic compensation was tested for chlorophyll degradation. Enthalpy of activation (Δ H #) for the coriander and mint purees ranged from 2.36 to 91.99 kJ/mol while entropy (Δ S #) ranged from −0.047 to −0.713 kJ/(mol K). Though the enthalpy and entropy values exhibited an excellent linear relationship ( R 2 > 0.96), a critical analysis of the results indicated absence of any extra-thermodynamic effect or thermodynamic compensation for chlorophylls degradation. The presence of isokinetic point was also not detected.