Why do fruit peels have oil

The oil on the surface of fruit peels is usually composed of natural wax or volatile oils secreted by plants themselves, which mainly have the functions of protecting fruits, reducing water evaporation, and resisting pests and diseases.

1. Natural Wax Layer

Citrus fruits are often covered with cuticle wax, which is composed of long-chain fatty acids and alcohol compounds. This type of wax can form a hydrophobic barrier, preventing rainwater erosion and microbial invasion. For example, the wax on the surface of an apple gradually thickens during the ripening process, helping the fruit maintain a plump shape.

2. Oil gland secretion

The oil cell layer of Rutaceae fruits such as oranges and lemons contains special glands that can secrete volatile oils with aroma. The main components of this type of oil are terpenoids such as limonene, which serve as both a plant defense mechanism and a source of fruit flavor. The liquid splashed out when peeling citrus fruits is the oil released by gland rupture.

III. Adhesion of environmental Pollutants

Some fruits may have oily skin due to post harvest preservation treatment. Edible grade mineral wax or insect glue coating agents can be used to delay decay, and these artificial coatings may appear oily and reflective under light. After ripening tropical fruits such as bananas with ethylene, the secretion of epidermal cells may also form a shiny appearance.

4. Differences in Variety characteristics

Varieties such as peaches undergo genetic mutations that significantly increase the secretion of oil from the skin, resulting in a smooth texture. This type of variation has been preserved in evolution and has become one of the distinguishing features of varieties. The white frost like substance on the skin of certain grape varieties is actually a metabolic product of yeast, unrelated to oil secretion but visually similar.

V. pathological reaction products

When the fruit is subjected to mechanical damage or fungal infection, oxidized phenolic substances may seep out from the wound site, forming an oily protective film. Mango and other tropical fruits may exhibit black oil stains in the early stages of anthracnose, which is a self-protection mechanism initiated by plants.

When consuming fruits with skin in daily life, it is recommended to gently scrub them with a soft bristled brush under running water to remove most of the surface attachments. The wax layer on the skin of fruits grown organically is usually thin, but it still needs to be thoroughly cleaned. For citrus fruits, contact between the skin oil and eyes or wounds may cause irritation, and hands should be washed promptly after peeling. People with special physical conditions who come into contact with mango peels may develop contact dermatitis, and it is recommended to peel and consume them.