transpiration continues. Translocation of plant hormones from the roots
(e.g., cytokinins) is also interrupted but bruises and lesions may intro-
duce stress metabolism in the wounded tissue initiating synthesis of eth-
ylene with an enhanced respiration. Wounding also facilitates entrance
of various pathogenes resulting in postharvest decay. Taken together,
vegetables must be harvested with special care in order to avoid delete-
rious postharvest processes resulting in severe reduction of the keeping
quality and losses of such freshness attributes as appearance, texture and
flavor.
Vegetables make up a very heterogeneous group of food from plants
compared with cereals. The type of plant organ harvested and its role in
the ontogeny of the growing plant has a strong influence on storage po-
tential and shelf life. The physiological basis for maintaining quality dur-
ing postharvest handling is therefore closely related to the ability of the
plant organ harvested to maintain metabolic homeostasis for a period of
suitable length provided the storage conditions are close to optimal. Con-
sequently, vegetables have been divided into subgroups with more or
less similar behavior and storage potential.
Leaves, Stems, Flower Buds and Inflorescences
Most vegetables within this group are harvested at a stage of horti-
cultural maturity (Watada et al., 1984) determined by consumer demands
or suitability for processing rather than the degree of physiological ma-
turity and suitability for postharvest storage and subsequent shelf life.
Vegetables harvested can consist of the whole overground plant (lettuce,
Chinese cabbage, leek), a section of the plant (broccoli, cauliflower) or
single leaves (parsley, spinach). Due to the large proportion of young
tissue, preharvest respiration and overall cell metabolism are on a high
level and continue in the harvested plant material. The stage of devel-
opment at harvest is often crucial due to ongoing quality-reducing
processes, e.g., cell wall lignification in asparagus spears or accumula-
tion of starch in green peas and sweet corn. The epidermis or periderm
exerts little protection against postharvest water loss. Rapid precooling
of the produce immediately after harvest, aimed at slowing down cell
metabolism and transpiration, followed by an unbroken cool chain is a
prerequisite for achieving an acceptable postharvest quality retention.
However, since the tissue of these vegetables is programmed for posthar-
vest senescence rather than dormancy, the inherent storage potential is
limited due to progressive senescence. Shelf life of such highly perish-
able vegetables is therefore limited from a few days to a few weeks.