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MATURITY, RIPENING, AND QUALITY RELATIONSHIPS OF FRUIT-VEGETABLES
Fruit-vegetables include two groups: (1) immature fruit-vegetables, such as green bell pepper, green chili pepper, cucumber, summer (soft-rind) squash, chayote, lima beans, snap beans, sweet pea, edible-pod pea, okra, eggplant, and sweet corn; and (2) mature fruit-vegetables, such as tomato, red peppers, muskmelons (cantaloupe, casaba, crenshaw, honeydew, persian), watermelon, pumpkin, and winter (hard-rind) squash.
For group (1), the optimum eating quality is reached before full maturity and delayed harvesting results in lower quality at harvest and faster deterioration rate after harvest.
For group (2) most of the fruits reach peak eating quality when fully ripened on the plant and, with the exception of tomato, all are incapable of continuing their ripening processes once removed from the plant.
Fruits picked at less than mature stages are subject to greater shriveling and mechanical damage, and are of inferior flavor quality.
Overripe fruits are likely to become soft and/or mealy in texture soon after harvest.
The necessity of shipping mature fruit-vegetables long distances has often encouraged harvesting them at less than ideal maturity, resulting in suboptimal taste quality to the consumer.
Several factors in addition to maturity at harvest have major impacts on postharvest behaviour and quality of fruit-vegetables.
Fruits of group (1) normally produce only very small quantities of ethylene.
However, they are very responsive to ethylene and can be damaged by exposure to 1 ppm or higher concentrations.
Ethylene exposure accelerates chlorophyll degradation, induces yellowing of green tissues, encourages calyx abscission (eggplant), and accelerates fruit softening.
Most of the fruits in group (2) produce larger quantities of ethylene in association with their ripening, and exposure to ethylene treatment will result in faster and more uniform ripening as indicated by loss of chlorophyll (green color), increase of carotenoids (red, yellow, and orange colors), flesh softening and increased intensity of characteristic aroma volatiles.
All fruit-vegetables, except peas and sweet corn, are susceptible to chilling injury if exposed to temperatures below 5°C (cantaloupe, lima bean, snap bean), 7.5°C (peppers), 10°C (cucumber, soft-rind squash, eggplant, okra, chayote), or 12.5°C (tomato, muskmelons other than cantaloupe, pumpkin, hard-rind squash). A relative humidity range of 90 to 95% is optimum for all fruit-vegetables except pumpkin and hard-rind squash where it should be 60 to 70%. Atmospheric modification (low oxygen and/or elevated carbon dioxide concentrations) can be a useful supplement to proper temperature and relative humidity in maintaining postharvest quality of some fruit-vegetables, such as tomato and muskmelons.