Water loss
• 90 to 95% of the commodity is water.• milk has more solids than cucumber (weight basis).• water loss resulting in direct loss of salable weight, in
addition to quality loss.• Appearance quality - wilting, shriveling, accelerateddevelopment of injuries.• Textural quality – loss of crispness, juiciness, etc.• Nutritional quality – e.g. vitamins A & C.• Thus, managing water content of commodities iscritically important.
Loss of marketability due to water loss
Commodity% water Loss
Asparagus8
Brussels sprouts8
Spinach7
Lettuce5
Celery3
Cabbage3
Water loss (%)Potential effects
0.5%Increased activity of some cell wall enzyme.
1%Increased CO2 and ethylene production. Faster
ripening, yellowing and abscission. Reduce wound
healing (periderm formation).
2%Reduced turgor. Reduced susceptibility to chilling
injury. Accelerated loss of volatiles.
3%Loss of membrane integrity.
4%Faster loss of vitamins A and C. Loss of flavor.
Discoloration of mechanical injuries.
5%Loss of color intensity and gloss. Increase severity
of pitting associated with chilling injury. Wilting and
shriveling.
6%Loss of textural quality: softening, limpness,
flaccidity, and loss of crispness and juiciness.
Effects of Water Loss
Physical Effects:• Reduced turgor pressure
from as little as 2% water loss enhances:
- Wilting & flaccidity of vegetables.
- Shriveling and wrinkling of fruit.
• Shrinking produce within a package allows it to move or vibrate during transport = damage.
Effects of Water Loss
Economic Effects:
• Reduced quality or grade of the commodity reduces its value.
• Commodities are often sold on a weight basis.
Less weight = lower price
Effects of Water Loss
Physiological Effects:• Increased respiration & ethylene production (1%).• Reduced periderm formation in some roots and tubers (1%).• Faster ripening, yellowing & senescence (1%).• Reduction in volatiles (2%).• Faster loss of vitamins A and C (4%).
Properties of WaterHigh heat of vaporization (540 kcal/kg/oC).• Water that evaporates absorbs a great amount of heat =>
cools the plant tissue (transpiration).High heat of fusion (80 kcal/kg).• When water cools from a liquid to a solid (ice),
it releases heat energy. • Therefore, water absorbs energy at the transition from
solid (ice) to liquid. This is the added benefit for top-icing.
Relative humidity (R.H.%)
• Corresponds to the ratio of actual water content of the air to the maximum water content at a given temperature.
Water vapors and liquid water
• Air water content (vapor pressure or humidity ratio) increases rapidly with increasing temperature.
• Warm air can hold more water than cold air.• When warm, moist air is cooled, RH increases until it reaches
its dew-point.• Air cooled below its dew-point begins to loose water as
condensation.• Placing a cold commodity in a warm room with moist air, cools
the air that contacts the commodity to below the dew-point.• Condensation will form on the commodity surface (“sweating”).
• Placing a warm commodity in room with cold, moist air will warm the air contacting the commodity and reduce the humidity around the commodity.
• water loss increased until the commodity is cooled.Delayed cooling results in greater water loss.
Water vapors and liquid water
Factors affecting water loss
Commodity factors:
• Surface to volume ratio.
• Cell type (epidermal cells vs. periderm and other cells).
• Structure of the surface: Stomates, Curticular waxes,
Lenticels, Trichomes ect.
Trichomes
Stomates
Factors affecting water loss
Commodity factors:
• Physiological state of the commodity.
• Stage of maturity or stage of ripeness.
• Cultivar.
• Cultural conditions.
• Weather and growing practices.
Factors affecting water lossEnvironmental factors:Humidity: Lower humidity → greater water loss.• Diffusion shells and air velocity: Outside the epidermis, there is a thin layer of air
that maintains high humidity (“diffusion shell”). Surface features (e.g. trichomes) influence the thickness of this shell.
Faster air flow↓
decreases thickness of the diffusion shell ↓
increases water loss.
Factors affecting water loss
Environmental factors:
Temperature:
• Higher temperatures → greater water loss.
Atmospheric pressure:
• Lower pressures (at high altitudes) increases water loss.
Water loss reduction
• Addition of water to some commodities
(cut flowers, potted plants).• Careful handling.
Injury and puncture of surfaces greatly increase water loss.
• Curing of certain root, bulb, and tuber vegetables.• Waxing and other surface coatings.
Water loss reduction
• plastic films (wraps): act as moisture barriers.• Packaging: Polyethylene or plastic liners.• Wood or plain fiberboard boxes can absorb water.
Water loss reduction
Water loss reduction
Influencing the environment:• Additional moisture to the air
(humidifiers).• Minimizing air movement
around the commodity and reducing room air exchanges.
• Maintaining temperature of refrigeration coils within 1oC of the air temperature.
Water loss reductionInfluencing the environment:
Moisture barriers:
• In the walls of storage rooms and transport vehicles.
• Polyethylene liners or curtains within shipping containers.
• Polymeric films for packaging produce.
• Wet the floor in storage rooms.
Influencing the environment:
Use 0f crushed ice in shipping containers and in retail
display of commodities that tolerate direct contact with ice.
Water loss reduction
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