Water and Its Relation to Fresh Produce 283
has long been used successfully to reduce moisture loss from produce during storage,
shipment, and display by reducing the magnitude of the moisture vapor deficit
between the produce and immediate in-package environment (Schlimme and
Rooney, 1994). The permeability of the packaging material to water vapor migration
determines water loss from fresh produce, and materials such as polyethylene films
are excellent vapor barriers. Selection of packaging material and understanding the
storage environment for fresh produce are important in reducing water loss. Thin
plastic films are ideal in storage environments that are vapor-saturated without the
associated problems of condensation. Miller et al. (1983) found that strawberries in
rigid plastic baskets with solid plastic covers lost significantly less weight than those
stored in mesh plastic baskets with and without covers. Presently, perforated and
unperforated packaging materials are used to minimize moisture loss, reduce respi-
ration rate, maintain product quality, and extend shelf life. Edmond et al. (1995)
also found that perforated films tested on 11 horticultural products significantly
reduced water loss and formation of condensation and extended the marketability
of fresh fruits and vegetables in displays.
9.7.3.1 Modified Atmosphere Packaging (MAP) in Reducing
Water LossModified atmosphere packaging is the packaging of produce in polymeric films to
establish a modified atmosphere around the produce. The produce is sealed in a
polymeric bag with selected gas permeability characteristics and stored at low
temperature. The relative humidity created inside the package is significant in attain-
ing optimum shelf life and storage quality of fresh produce (Shamaila et al., 1992;
Gonzalez-Aguilar et al., 2000; Bai et al., 2001). Howard et al. (1999) found that
simply placing broccoli, carrots, and green beans in Ziploc® bags at a refrigeration
temperature of 4°C resulted in moisture retention. Nunes et al. (1998) used PVC
film to retard water loss in strawberries and found that water loss had a great effect
on the retention of ascorbic acid. Although few differences were found in wrapped
and unwrapped strawberries stored at 1°C and 10°C, a much greater (fivefold) loss
occurred at 20°C storage. Most packages used for MAP have low permeability to
water vapor and maintain a relative humidity of greater than 85%. Relative humidity
below 85% results in excessive loss of moisture, leading to wilting and shriveling
(Schlimme and Rooney, 1994). However, higher relative humidity nearing 100% in
the bag may lead to condensation of water on the inside of the bag and loss in
produce quality in the form discoloration and decreased nutritional quality.
9.7.4 WAXING OF FRESH PRODUCE
Water loss from fresh produce occurs through any openings such as lenticels and
stomata on the plant surface and can also result from damage at harvest. Therefore,
any method such as waxing that seals these openings will reduce the amount of
water lost from the product.
Waxing of fresh produce is carried out to restore the natural wax lost in pro-
cessing, but it also aids in slowing down water loss that causes dehydration. Waxes