This section is from the book "Practical Dietetics With Special Reference To Diet In Disease", by William Gilman Thompson. Also available from Amazon: Practical Dietetics with Special Reference to Diet in Disease.
The varieties of fruits which are consumed in all countries are innumerable, and their uses are various. Sweet fruits no doubt largely composed the diet of primordial man, as they do of every savage tribe to-day living outside of the Arctic Zone.
Pectin is a carbohydrate substance found in ripe pulpy fruits. It enables fruit to gelatinise when boiled. Its properties and composition are not thoroughly understood.
The organic acids exist mainly in union with alkalies, forming compounds which are readily split up in the system, leaving the alkalies free to combine as carbonates or phosphates.
The most important acids are citric, malic, and tartaric, which exist in various quantities and combinations.
Citric acid predominates in lemons, limes, and oranges; tartaric acid in grapes; malic acid in apples, pears, peaches, apricots, gooseberries, and currants.
Among the least acid of the common fruits are peaches, sweet pears, sweet apples, bananas, and prunes; moderately acid are strawberries. The most acid of all are currants and lemons.
Fruits contain a smaller proportion of earthy salts than other foods.
Certain fruits also hold a little nitrogenous material, chiefly as albumins, but, as a rule, the starches and sugars predominate, and the nutritive value of any fruit depends upon them chiefly. Most fruits contain too much water to constitute an economic diet if eaten alone. Some also contain a small quantity of fat and waxy matter, and most of them have more or less pigment.
Fruits which are especially rich in flavour, and which exhale a pleasant aroma, owe these conditions to the various essential oils and compound ethers which they possess in considerable amount.
Many fruits are only partially edible owing to the fact that they are composed of a pulp contained within an indigestible structure of cellulose or woody fibre.
Fruits are commonly classified into stone-bearing fruits, pomes, berries, capsules, and pepos. Some, such as the date, the plantain and its variety, the banana, afford sufficient nutriment to amply support life for a long time; others, like the apple, are wholesome, but slightly nutritious; while others again are of little value for nutritive purposes, and are mainly serviceable for their agreeable flavour to furnish variety in the diet.
Composition of Fruits (Bauer)
Orange, pulp only.
Other non - nitrogenous matters
Cellulose and kernel
Composition of Fruits (Yeo)
Other non-nitrogenous matters
Cellulose and seeds
Fruits arranged According to the Proportions between Acid, Sugar, Pectin,
Gum, etc. (Average). (Fresenius)
Pectin, gum, etc.