Growing of vegetables in the field, harvesting, handling in the packing house and storage are events in the lifetime of vegetables that are analysed from the point of view of the complex series of physiological transitions taking place in each of these events. Water is the major factor limiting plant metabolism and plants have developed fascinating mechanisms to cope with this limiting factor. Therefore, water relations (water, pressure and osmotic potential) are used as criteria for discussing plant stress physiology aspects such as osmotic, elastic adjustment and cold acclimation, as well as mechanical stress when the vegetable is harvested and during handling in the packing house. Consequences for the storage potential and quality of the vegetable are discussed. After harvesting, the postharvest cell has the ability to complete a complex series of physiological transitions that will influence vegetable quality andfurther processing operations. Metabolic changes in the cytosol, cell membrane and cell wall are described.

a b s t r a c tEfforts are currently directed towards improving the quality of sensitive tissues of fruits and vegetables after freezing and thawing. One of the methods under investigation is the combination of vacuum impregnation (VI) with cryoprotectants and pulsed electric field (PEF), applied to the plant tissue prior exposure to freezing. The influence of these processes on the freezing temperature and ice propagation rate of spinach baby leaves are here studied. Leaves impregnated with trehalose, sucrose, glucose and mannitol exhibited significantly lower ice propagation rate and higher freezing temperatures in comparison to non-treated controls. Leaves subjected to PEF also showed increased freezing temperatures compared to the non-treated leaves; however the ice propagation rate was not influenced by PEF for the cryoprotectants used in the study, except for leaves impregnated with trehalose, where it was significantly increased and water, where it was significantly decreased. The combination of VI and PEF resulted in comparable freezing temperatures and ice propagation rates as the leaves subjected only to VI.

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