GROWTH, MATURITY, GRADE STANDARDS, AND PHYSICO-MECHANICAL CHARACTERISTICS OF FRUIT

Citrus fruit growth and quality are dependent on climatic conditions in addition to soil type, water availability, cultural practices, and nutrient supply. The duration of growth and maturation differs with variety. The development of a citrus flower's ovary into a fruit ready to harvest takes 6–18 months or more depending upon the type of fruit, particular cultivar, and climate. The growth can be shown as a single sigmoid curve—two stages of slow growth with a period of rapid growth in between. With respect to maturation, the fruits are non-climacteric—they ripen on the tree. They neither ripen after harvest, nor do they show any respiratory rise accompanied by major changes in flavor and biochemical composition. Indices of maturity, fruit grades, and standards are discussed. Sweet oranges, mandarins, grapefruits, and pummelos are considered mature when their juice content and total soluble solids and acidity ratio have attained certain minimum limits for palatability. Fruit grades are mostly related to size, appearance, extent of defects, shape, and color of the fruit. European citrus-growing countries, South Australia, California, and other places with Mediterranean-type climates (cool winter nights, bright days, and low rainfall) can rely almost entirely on external standards to sell their fruit. It is essential to know the physical and mechanical properties of various citrus fruits for designing mechanical systems, optimal harvesting, and handling capacities with minimum damage to fruit.