278 Produce Degradation: Reaction Pathways and their Prevention
loss than intact fruits; this was attributed to the removal of the protective epidermal
cells and the resulting increase in the surface area/mass rate. They concluded that
storage temperature, degree of tissue damage, and microatmospheric gas composi-
tion were important factors for quality retention of fresh-cut kiwifruit slices in
relation to water loss.
When subjected to temperatures between freezing and 12.5°C, many fruits and
vegetables undergo physiological injury, called chilling injury since it does not
involve freezing (Rolle and Chism, 1987). The injury is attributed to several factors,
including impairment of membrane function, changes in cellular membrane, and
effects on lipid components. Physiological damage caused by chill injury contributes
to water loss and deterioration in quality of many fruits and vegetables. Purvis (1984)
implicated moisture loss in grapefruit as one of the factors causing chill injury and
noted that the diffusive resistance was lower on the surfaces that showed symptoms
of chill injury. However, hydrocooling was found to reduce moisture loss and chilling
injury due to a reduced vapor pressure gradient. Cohen et al. (1994) found a signif-
icant effect of storage temperature and chill on moisture loss of grapefruit and
lemons. Although there was higher moisture and weight loss of fruit stored at 13°C
compared to that held at 2°C, transfer of fruit to 20°C showed fruit previously stored
at 2°C to have higher water loss. They attributed this high water loss to chill injury
that caused microscopic cracks in the peel.
9.7 METHODS OF PREVENTING WATER LOSS FROM
FRESH PRODUCEMost fruits and vegetables contain the highest amount of moisture content at harvest
and gain little or no moisture during storage. Any loss in water after harvest affects
the quality and economic value of the produce. Table 9.3 shows the effect of water
loss on the shelf life of selected fruits and vegetables and the maximum possible
loss in water before the product becomes unsalable (Robinson et al., 1975). The
amount of water loss that affects salability varies depending on the produce; succu-
lent produce is greatly affected with minimal loss of water. It is therefore important
to limit any further loss of water from the produce. The most ideal techniques to
reduce loss of water from harvested products are to minimize the water vapor
pressure deficit and the resistance to water exchange between the produce and its
immediate surroundings. This can be achieved by lowering the temperature and/or
increasing the relative humidity of the surrounding environment to specific levels,
resulting in a reduced vapor pressure difference between the produce and its envi-
ronment (Wills et al., 1998).
Both humidity and temperature are important in minimizing the difference in
water vapor pressure between the harvested fresh produce and its environment. The
humidity of the surrounding environment and that of the internal atmosphere of the
produce should be as close to equilibrium as possible. Relative humidity of 95 to
99% is recommended for high-moisture fresh products (Table 9.2), while low humid-
ity can be applied to products that have high resistance to water exchange (Robinson
et al., 1975).