268 Produce Degradation: Reaction Pathways and their Prevention
9.1 INTRODUCTION
Water is the most important component of plant tissues, and it plays a significant role
in the quality of harvested fresh produce. It accounts for as much as 60 to 95% of the
weight of fresh produce, and carrots, lettuce, apples, and peaches contain as much as
84 to 96% of water (Table 9.1). Important plant functions, including exchange of
resources, cell expansion, physical and chemical integrity of cell walls, and cell con-
stituents depend on water and its unique properties (Nilsen and Orcutt, 1996). Water
creates a medium in which most of the biochemical reactions necessary for plant
survival occur and participates in many important biochemical reactions. Water con-
tributes to the quality of fresh produce and has great impact on shelf life, textural
properties, and processing potential. Fresh produce is maintained fresh due to its high
water content; however, this high water content limits the stability of its shelf life.
The transportation and redistribution of essential life-supporting chemical com-
ponents of plants is dependent on the movement of water. During plant growth, the
elaborate xylem and phloem tissue system facilitates the movement of water and
many chemical components throughout the plant. The continuous redistribution of
water is essential in the replenishment of water lost through transpiration and evap-
oration to the environment. This process continues in harvested fruits and vegetables
but occurs over a short distance and is much slower compared to that in living plants.
It is the loss of water that affects shelf life, quality, and marketability of fresh fruits
and vegetables. Hruschka (1977) reported weight losses of 4 to 41% in harvested
snap beans, cabbage, sweet peppers, squash, and tomatoes, resulting in shriveled
products. Maguire et al. (2001) in their review reported that excessive weight loss
from fruits can lead to a shriveled appearance; as a result of decreased turgidity this
can cause undesirable textural and flavor changes and thus make the produce unsalable.
TABLE 9.1
Approximate Water Content of Some
Selected Fruits and Vegetables
Fruit Water (%) Vegetable Water (%)Apple 85 Broccoli 91
Banana 75 Cabbage 92
Blueberry 85 Carrot 88
Cherry 86 Cauliflower 95
Grape 81 Cucumber 96
Peach 89 Lettuce 96
Pear 84 Pea 79
Raspberry 86 Potato 83
Strawberry 91 Spinach 91
Watermelon 92 Tomato 94
Source:USDA Nutrient Data Laboratory
(www.nal.usda.gov/fnic/cgi-bin/nut_search.pl).