ABSTRACT
Water loss from harvested horticultural commodities will continue to be a problem as long as warm products need to be cooled and kept cold during storage and marketing. Even a small amount of water loss can adversely affect product quality, marketability, and storability. Apart from the loss of fresh weight that accompanies water loss, a few percent water loss can stimulate physiological changes that hasten senescence. The physics of heat transfer in a mechanical refrigeration system necessitates that the air in a cold room will have a vapor pressure less than that of the commodity. This inherent difference in the vapor pressure between water near the surface of fresh fruits, vegetables, and ornamentals and the ambient cooling air is the prominent force that determines the rate of water loss. Increasing the relative humidity of the surrounding air or the resistance of the surface of the commodity to the diffusion of water vapor will decrease the rate of water loss. This can be done by applying a wax or edible coating to the surface of whole or fresh-cut commodities, by enclosing them in a package that raises the ambient humidity, and by using harvest and postharvest practices that reduce injuries (e.g., bruises, wounds, abrasions, etc.) that decrease the ability of the surface to retard water loss. Preharvest factors (e.g., cultivar selection, growing environment, cultural practices, and maturity at harvest) can have signicant effects on rates of water loss. Familiarity with the
W A T E R L O S S
psychrometric chart provides insights into the relationships among vapor pressures, relative humidity, and product temperature. Rapid cooling of warm-harvested commodities and maintaining a high relative humidity in the cold room is essential to minimize the initial and subsequent level of water loss.
