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.

Composition

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.

1 For further information, note "Uses of Fruit as Food." Farmer's Bulletin No. 293, U. S. Dept. of Agriculture, Washington, D. C.

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

Digestibility of fruits varies with the kind of fruit eaten and its mode of preparation; stewed fruits are more easily digested than raw fruits. Personal idiosyncracy 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.

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.

The apple exerts a most excellent influence upon the liver and kidneys, and is valuable in cases of acidity of the stomach.

The juice of the ripe pineapple contains a remarkable active digestive principle, similar to pepsin, termed bromelin, and so powerful is its action upon proteids that it will digest as much as one thousand times its weight within a few hours. It is especially valuable in diphtheria and diabetes.

Figs and prunes are valuable for inactivity of the liver and most excellent laxatives.

The banana contains a large amount of starch, as much as the potato; therefore it should not be eaten in an unripe state. For invalids and children and others of delicate digestion, it should always be cooked.

Grape juice and other freshly expressed juices are refreshing and wholesome beverages, and can often be given to invalids when the pulp would prove irritating.

Nutritive Value

Fresh fruits are chiefly valuable for their refreshing, appetizing qualities, and for their mineral constituents. The organic acids form carbonates in the body, and by their alkalinity assist in the regulation of body processes.

In disturbed conditions of metabolism it is often important to know just what salts and acids fruits contain.

As already stated, the chief nutrients are carbohydrates. In fuel value, fresh fruits resemble given vegetables, as is shown by the following figures:

The dried fruits compare favorably with bread, dried beans and similar foods as to energy value, but the latter contain protein in considerable amounts, while in fruits it occurs only in small quantities. The fuel value of fruits is often increased by the sugar added in cooking or serving.

Fruits are also valuable for bulk, which is an essential factor in diet. Most of them contain a considerable proportion of indigestible matter. Intelligently used, fruits are a valuable part of a well-balanced diet, and their use should be encouraged.