Crab Apple (Malus sylvestris):

Crab apple, the remedy for feelings of self-disgust or uncleanness, is made by the boiling method.

Crab apple flowers; photo from pixabay.com

Related to domesticated apples, crab apple trees have a longer flowering period so are sometimes planted in commercial orchards as pollination partners. There are many varieties of crab apple but typically, crab apple fruits are smaller and more sour than domesticated apples. Fruit can be made into a jelly and crab apples are sometimes added during cider-making causing the resulting cider to be less sweet. Drinking or dry cider was thought to help rheumatism and gout and in regions where consumption of this type of cider is common, levels of calculus are reportedly very low.

Malic and tartaric acids in apple fruits were thought beneficial to the liver and not only make the apple digestible but also render other foods more easily digested – fatty foods such as pork and cheese are often paired with apple. Consumption of apples has been linked to a reduction in the occurrence of colorectal and lung cancer. The juice reduces acidity in the stomach. Ripe fruits can be eaten for constipation while the verjuice (from unripe fruits) was taken for diarrhoea.

Crab apples; image from pixabay.com

When the inside of a fruit is exposed to air, an enzyme, polyphenol oxidase, oxidises phenolic compounds to o-quinones which, in turn, produce brown pigments called melanins. These are responsible for the brown colouration of exposed apple flesh. The process can be avoided if the fruit is cooked, deactivating the enzyme. Alternatively, the apple pieces can be placed in water, limiting the amount of oxygen or  exposed to acid (e.g. citric acid from lemon juice) to keep the pH too low for the enzymatic reaction to occur.

Apple seeds (or pips) contain amygdalin, which can degrade to produce hydrogen cyanide (see Cherry plum blog for details).  Crab apple wood makes good quality timber and is also sometimes used for carving or turning. A yellow dye can be made using the bark.

Crab apples are a good source of pectin which can be used to help jams set (see Cherry plum blog for more details). However, some people are allergic to apples. In northern Europe, this often takes the form of the birch pollen-oral apple syndrome, which results from the  similarity of a protein found in apples with the allergen Bet v 1 from birch tree pollen. The Bet v 1 protein is the major source of hay-fever in northern latitudes and around 40% of birch pollen sensitive hay-fever sufferers become sensitised to the similar protein in apples. Symptoms are usually confined to the mouth and throat and occur within a few minutes of eating apples.

Chemical diagram of phloretin

Phloretin is found in the leaves and bark of crab apple trees and has antioxidant effects. It is sometimes used in anti-aging skin products as it helps protect against the effects of UV-radiation. Both phloretin and its 2’-glucoside, phlorizin, also found in apple trees, inhibit the transport of glucose in the body, reducing the amount of glucose in the blood. Phlorizin was at one time considered as a potential drug to treat type-II diabetes and also has antioxidant properties.

For an introduction and sources and more info., click the links.