Biochemical and colour changes of watercress (Nasturtium officinale R. Br.) during freezing and frozen storage

The effects of water blanching, freezing, and frozen storage during 400 days at three different temperatures (-7, -15 and -30 °C), on watercress (Nasturtium officinale R. Br.) colour Hunter Lab parameters, chlorophyll degradation, vitamin C content loss and peroxidase (POD) activity were evaluated. The blanching induced significant changes on colour values and chlorophylls and vitamin C contents. POD activity was reduced 85% from its initial value. Freezing did not affect chlorophylls and vitamin C levels, however, promoted significant differences in colour values and POD residual activity. During frozen storage, ascorbic acid (AA) and POD activity degradations followed first-order kinetics, and colour parameters (L_H · a_H · b_H, -a_H/b_H, L_H · a_H/b_H, L_H/a_H · b_H and hue (h_H⁰)) were successfully described by zero-order kinetics. The storage temperature effect was successfully described by the Arrhenius law. Chlorophylls and dehydroascorbic acid (DHAA) contents were kept constant during frozen storage.