282 Produce Degradation: Reaction Pathways and their Prevention
lose a large amount of weight but that the weight loss was minimal in a controlled
atmosphere containing humidified gases. The increased relative humidity of the air
reduces the vapor pressure deficit between the fresh produce and the immediate air,
resulting in an air-saturated environment. Gaffney (1978) reported that total moisture
loss from fresh produce can be reduced by decreasing the time of exposure to a vapor
pressure difference by cooling the produce surfaces close to the surrounding air tem-
perature as quickly as possible and also maintaining the surrounding air as close to
saturation as possible. van den Berg and Lentz (1978) found substantially less quality
and water loss at higher humidity in cabbage, cauliflower, and potatoes, while at relative
humidity of less than 95%, softening and shriveling of commodities occurred.
Relative humidity can be increased by spraying water as a mist, introduction of
steam, or increasing temperature of refrigeration coils. Baldwin (1994) concluded that
fruits and vegetables are often stored in a high-humidity environment (90 to 98% relative
humidity) to minimize water loss and subsequent weight loss and shriveling. Automatic
misting designed to spray the produce with a fine mist of water at timed intervals is
commonly used to prevent dehydration, extend shelf life, and improve the appearance
of fresh produce in retail display cases. Barth et al. (1990) found that misting promoted
a high retention of ascorbic acid and moisture content over a 72-h storage period in
broccoli. Proper control of increased relative humidity is important since very high
levels of moisture in the environment promote growth of microbials.
9.7.3 PACKAGING OF FRESH PRODUCE
Packaging is one of the most effective methods for reducing water loss from fresh
produce since it acts as physical barrier and also reduces air movement across the
produce’s surface. James et al. (1999) found that Muscadine grapes wrapped with
polyethylene bags lost a minimal weight of 0.5 to 1.0% compared to unwrapped
grapes, which lost 15% weight, and they were able to correlate the loss in weight
to the decrease in fruit firmness. Collins and Perkins-Veazie (1993) packaged ‘Car-
dinal’ strawberries in plastic boxes with dome lids or polyethylene (PE) wrap and,
after warming the fruit to 25°C, stored it at 1 and 5°C to simulate retail storage
conditions. They found that strawberries stored in boxes covered with PE accumu-
lated CO 2 , lost less weight, and had better color retention than fruit in boxes with
plastic dome lids at both 1 and 5°C. Similarly, the quality of green beans, bell
peppers, and spinach packaged in polyethylene bags and stored at two different
temperatures was studied by Watada et al. (1987). They found that packaging in PE
reduced weight loss of green beans and spinach kept stored at 20°C, and reduced
chlorophyll loss of green beans at 10°C and of spinach at 20°C. More ascorbic acid
was also retained in the vegetables. Ben-Yehoshua (1985) reviewed individual seal-
packaging of fruits and vegetables and noted that this technique was mainly used
to extend shelf life and reduce shrinkage, weight loss, the occurrence of various
blemishes, and refrigeration costs. It was further concluded that individual seal-
packaging helped in securing the beneficial aspects of a water-saturated atmosphere.
Fresh produce can be packaged into bags, boxes, cartons, or mesh bags and
covered with tarpaulins. Any form of close packing that restricts the passage of air
around individual products reduces water loss. Perforated polymeric packaging film