Enzymes and Quality Factors of Fruits and Vegetables

Abstract

In harvested plant products, quality is the composite of those characteristics that differentiate individual units of the product and have significance in determining the units’ degree of acceptability to the user (Arthey, 1975; Kramer and Twigg, 1970). The degree of acceptability of fresh fruits and vegetables and their products is a combination of attributes, properties, or appearances that give each commodity value in terms of human food. The relative importance of each quality factors depends upon the commodity and its intended use and varies among producers, handlers, and consumers. To producers a given commodity must have high yield and good appearance, must be easy to harvest, and must withstand long distance shipping to markets. Appearance quality, firmness and shelf life are important from the point of view of wholesale and retail marketers. Consumers judge quality of fresh fruits and vegetables on the basis of appearance and firmness at the time of initial purchase. Subsequent purchases depend upon the consumer’s satisfaction in terms of flavor quality of the product (Kader, 1999). But fruits and vegetables quality declines rapidly after harvest, especially if proper postharvest handling procedures are not followed. Changes in color, texture, nutrition, and flavor all affect the market quality of the fruits and vegetables; meanwhile quality of processed products using superior fruits and vegetables is reduced. Any attribute or characteristic that make fruit attractive and pleasant to eat adds to its desirable quality. Certain fruits including grapes and citrus fruits attain optimal quality at the time of harvest and undergo deteriorative changes during storage. Postharvest techniques cannot further improve the quality of these fruits. However, other fruits including pears and bananas go through the ripening process during the postharvest period and improve in eating quality because of an increase in juiciness, development of flavor and conversion of starch to sugars. Quality of these fruits declines rapidly after they are fully ripe. Thus, the postharvest behavior and quality retention vary from one commodity to another (Wang, 1999). Changes that cause quality deterioration after harvest include high respiration rate, high metabolic activity, moisture losses, softening, yellowing, and/or loss of flavor and nutritional value. Factors that accelerate quality deterioration are mechanical injury, physical disorders, and pathological diseases. Biochemical changes underlying postharvest deterioration in quality encompass oxidative damage and free