Fruits are the seed-bearing portions of plants. Some products of this class, such as melons, are sometimes called fruits and sometimes vegetables; and a few vegetable products which are not fruits in the strict sense, are included in this class of food products because they have a similar place in the diet.
Fresh fruits contain a high percentage of water, varying from about 75 per cent. to over 95 per cent. It has been suggested that those containing 80 per cent. or more of water be classed as flavor fruits, and those with less than 80 per cent. as food fruits: Bananas, grapes and fresh figs are the commonest examples of the latter class. When the water is removed by evaporation, as in drying, the percentage of moisture falls to 30 per cent. or less, and the proportion of nutrients is correspondingly raised, so that dried fruits would fall into the class of food fruits. Preserved fruits have their nutritive value raised by the addition of water, and usually by some loss of water in preparation.
As a class, fruits contain little or no fat. The olive is a remarkable exception. The proportion of protein is so low as to be practically negligible. Carbohydrates are the chief nutrient present. In ripe fruits these are almost wholly in the form of sugars and other soluble carbohydrates, commonly called pectin bodies. In unripe fruits starch is often found - notably in the ordinary banana. The principal sugars are sucrose or cane sugar, dextrose or grape sugar, and levulose or fruit sugar. A mixture of the last two is common, and is called invert sugar.
Fruits contain characteristic organic acids, such as malic in apples, citric in lemons, etc. These acids exist in the form of salts, usually of potassium. A little phosphoric acid, lime, iron, etc., also occur. The flavor is due partly to the sugars and acids, and partly to characteristic ethereal bodies present in small quantities. Chemists have isolated the ethers and oils which give the peculiar flavor to bananas, strawberries and other fruits.
Digestibility of fruits varies with the kind of fruit eaten and its mode of preparation; stewed fruits are, in general, more easily digested than raw fruits. Personal idiosyncrasy has also much to do with digestibility in case of this class of food materials. Oranges, lemons, grapes and peaches are very generally digested with ease. Oranges are much used in invalid dietaries, their juice being very effective in allaying thirst. Orange juice is also commonly administered to infants, especially if fed artificially, for the sake of the mineral matter and to prevent constipation and, in the case of infants fed on pasteurized or boiled milk or on proprietary foods, as an antiscorbutic. It is important to those who are obliged to exclude sugar from the dietary to know that fruits containing the least sugar are the plum, peach, apricot and raspberry. Those containing the largest amounts are the apple, sweet cherry, grape and pear.
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