Thermal inactivation kinetics of pectin methylesterase and the impact of thermal treatment on the texture, electrical impedance characteristics and cell wall structure of Japanese radish (Raphanus sativus L.)

The thermal inactivation characteristics of pectin methylesterase (PME) from Japanese radish were described by the fractional conversion model at temperatures between 50 and 70 °C. The calculated values of the inactivation rate constant k exhibited an Arrhenius-type temperature dependence. The estimated value of the apparent activation energy Ea (190.29 kJ mol−1) was lower and the z-value (9.64 K) was higher than that of other agricultural products. The results suggest that PME from Japanese radish tissues is more thermally stable than PME from other agricultural products. The impact of changes in cell membrane function and cell wall structure on texture during thermal treatment was also examined. Changes in texture were observed to occur in two phases. In the first phase, the elastic properties decreased because of a decrease in cellular turgor caused by the loss of cell membrane function, as determined by electrical impedance analysis. In the second phase, observed at temperatures above 70 °C, the breaking force (firmness) of the tissues decreased due to the β-elimination-driven degradation of pectins present in the middle lamella of the tissues.