Certain cultivated and wild plants yield edible fruits. There are various kinds of edible fruits, including pomes (apple, pear, quince), drupes (apricot, plum, cherry, peach), citruses (orange, lemon, mandarin, grapefruit), subtropical and tropical fruits (fig, mango, pomegranate, pineapple, banana, avocado), berries (currant, gooseberry, grape, cranberry), and melons (muskmelon, watermelon). Fruits are very important in human nutrition; their pleasant taste and biological value are due to the presence of a large quantity of useful substances (see Table 1).
|Table 1. Chemical composition of various edible fruits|
|Sugars (percent)||Acids (percent)||Vitamin C (mg percent)|
Fruits are a source of readily assimilated carbohydrates. Pomes are particularly rich in fructose, and drupes in glucose and sucrose. Sucrose is least abundant in berries and most abundant in bananas, pineapples, oranges, and mandarins. Bananas are high in starch. Fruits contain carotene and many vitamins, including ascorbic acid (vitamin C) and vitamin P. Citruses have a vitamin content of 50–90 mg percent. They retain most of their original vitamins during storage; the enzymes that oxidize ascorbic acid are absent in citruses. Strawberries, raspberries, and gooseberries are high in vitamin C. Some fruits appear to be natural vitamin concentrates: for example, the dog rose contains about 1,500 mg percent vitamin C and 5 mg percent carotene; chokeberry, 50 and 8 mg percent, respectively; and the sea buckthorn, 120 and 8 mg percent. The black currant has a vitamin C content reaching 400 mg percent. The caloric content of fruits is low, averaging 50–70 kcal in 100 g (1 kcal = 4.19 kj). The Institute of Nutrition of the Academy of Medical Sciences of the USSR has set the annual standard of fruit consumption at 106 kg per person. According to the Food and Agriculture Organization of the United Nations, the world production of fruits in 1974 was 213,276,000 tons, including 63,069,000 tons of grapes; the corresponding figures in the USSR were 12,441,000 tons and 4,760,000 tons.
The substances found in fruits play an important part in the digestive and metabolic processes. The organic acids are powerful stimulants of pancreatic secretion and intestinal activity. Of the tannic substances, tannin and the catechins have the most marked biological action. Whortleberries, pears, quinces, and cornels are rich in tannin. Many fruits are used as therapeutic agents (for example, raspberries) and in dietetics.
Many kinds of fruits remain tasty and fresh for a long time when properly refrigerated and exposed to a controlled gaseous atmosphere. Apples, pears, citrus, grapes, and bananas can be stored the longest. Fruits can be frozen, vacuum dried, or preserved (jam, compote).
REFERENCESTserevitinov, F. V. Khimiia i tovarovedenie svezhikh plodov i ovoshchei, 3rd ed, vols. 1–2. Moscow, 1949.
Spravochnik tovaroveda prodovol’s tvennykh tovarov, vols. 1–2. Moscow, 1968–69.
Shirokov, E. P. Tekhnologiia khraneniia i pererabotki plodov i ovoshchei. Moscow, 1970.
E. P. SHIROKOV