Environmental factors affecting deterioration
Several external environmental and physical factors affect the rate of deterioration and postharvest life of tropical and subtropical fruits via their effects on the internal, biological factors listed in the previous section. Stresses related to environmental factors such as excessive heat, cold, or improper mixtures of environmental gases, such as oxygen, carbon dioxide, and ethylene, can also cause certain physiological disorders, which negatively affect fruit quality and reduce its postharvest life. Several of these disorders can be initiated before harvest and expressed either before or after harvest. Some disorders may also be caused by mechanical damage. All of these disorders are abiotic in origin (i.e. not caused by disease organisms); however, abiotic disorders often weaken the natural defenses of fresh produce, making it more susceptible to biotic diseases that are caused by disease organisms. Furthermore, in many cases injuries caused by chilling, bruising, sunburn, senescence, poor nutrition and other factors can mimic biotic diseases. The effects of external factors are cumulative during the time between harvest and consumption. The different environmental and physical factors affecting fruit quality and the physiological disorders they cause are described below.