Chapter 6 - Postharvest changes

Abstract

Quality changes in the harvested fruit can be studied from two different angles, namely, postharvest physiology and postharvest pathology. Respiration is the predominant physiological process in harvested fruits. In contrast to most other fruits, citrus fruits are nonclimacteric. Their rate of postharvest respiration is low and does not show a tendency to increase. Detached citrus fruit does not ripen. The rate of respiration is faster at higher temperature. As long as the oxygen supply is adequate, the respiration quotient is close to unity. Respiration quotient values higher than unity indicate that fermentative processes are taking place, in addition to respiration. Respiration can be depressed by decreasing the concentration of oxygen or increasing the concentration of carbon dioxide in the atmosphere surrounding the fruit. In essence, this is the technology of “controlled atmosphere.” Another important postharvest change is moisture loss due to transpiration, partially depressed by waxing. Postharvest changes in mechanical properties include softening. Postharvest deterioration of taste and aroma is particularly important in mandarins. Chilling injury is observed most frequently when fruit, previously stored at low temperature for a few weeks, is exposed to ambient temperature. The most common type of chilling injury in citrus is “pitting,” to which grapefruit is particularly susceptible. The most common postharvest pathogens of citrus fruit are fungi and particularly Penicillium digitatum and Penicillium italicum, known as the green and blue molds, respectively. The most commonly applied fungicides are sodium orthophenyl phenate and thiabendazole. Most frequently recommended storage conditions are temperatures of 5–9°C for oranges, 7–12°C for lemons, 9–12°C for grapefruit, 3–9°C for tangerines and mandarins, and 9–12°C for limes, high relative humidity and adequate aeration.