Produce Degradation Pathways and Prevention

Water and Its Relation to Fresh Produce 285

9.7.6 AIR MOVEMENT AND AIR PRESSURE

Air movement is important in freshly harvested produce because it removes heat
from the produce. The vapor pressure of the thin air layer just above the produce is
generally in equilibrium with that of the produce. Air movement around the produce
reduces the thickness of the boundary layer and thus increases the vapor pressure
difference, resulting in increased water loss. Reduced air pressure increases the rate
of water loss, but this can be minimized by misting with water or providing moisture
barrier packaging (Ben-Yehoshua, 1987; Kays, 1997).

9.8 WATER LOSS AND ITS IMPACT ON PRODUCE QUALITY

Freshly harvested produce is sold based on weight; therefore, any loss in weight has
great impact not only on the quality but also the economic value of the produce and
its profitability. It is therefore important to take steps that minimize water loss soon
after harvest and during storage. Water loss of fresh produce affects its appeal to
consumers because transpiration from fresh produce induces wilting, shrinkage, loss
of firmness and crispness, and succulence, all of which are components of freshness
(Ben-Yehoshua, 1987). Table 9.5 shows the effect of water loss on quality in mature
green bell peppers (Cantwell et al., 2001). A weight loss of 2 to 4% reduced bell
peppers’ firmness, gloss, and visual quality, and increased their dehydration score.
In some fresh produce, water is added back by misting, water baths, and increasing
humidity. However, the presence of excessive moisture may result in growth of
microorganisms and decay, physical damage such as splits in fruits, undesirable
growth and sprouting, and color changes. Quality of fresh produce includes a com-
bination of visual appearance (freshness, color, absence of defects, and decay),
texture (crispness, turgidity, firmness, toughness, and tissue integrity), flavor (taste
and smell), nutritive value (vitamins A and C, minerals, and dietary fiber), and safety

TABLE 9.5

Quality Attributes of Mature Green Bell Peppers

in Relation to Weight Loss at 20°C

Actual Weight

Loss (%)

Visual Quality

Scorea

Dehydration

Scoreb

Firmness

(N)c

Gloss Meter

Valued

0.3 8.4 1.1 23.3 6.7

2.0 7.2 2.3 16.2 5.8

2.8 5.9 2.8 12.5 4.7

3.9 4.8 3.1 7.1 3.4

aVisual score based on scale of 1 to 9; 1 = unsalable and 9 = excellent.

bDehydration score based scale of 1 to 5; 1 = none and 5 = severe dehydration.

cNewtons.

dGloss value: the higher the value, the glossier the produce.

Source:Cantwell, M. et al., Perishables Handling Q., 107, 17, 2001. With permission.