Banana peels generally contain 6 to 9 percent protein, 20 to 30 percent fiber and other components such as starch, sugars, lignin, tannins and minerals in varying amounts. The exact quantity of these components depends on the banana cultivar and its maturity.
For example, plantain peels have less fiber than dessert banana peels. Plantain peels also have more starch at 40 percent, than banana peels, which have 15 percent, while still green or immature. When the peels ripen, all the starches of the plantain peels are converted to sugars so that sugar content is at approximately 30 percent. Lignin content also increases as the peels ripen, from 7 percent to 15 percent. Minerals such as calcium, phosphorus, potassium, sodium, magnesium and iron do not change significantly in quantity with peel maturity or cultivar.
Two substances sometimes found in banana peels that have a non-nutritional effect are tannins and pesticide residue. Tannins are responsible for the astringent or less palatable taste of immature fruit, but this substance reduces with ripening. With the application of heavy pesticides on the banana plants, the banana peels may contain pesticides residue, which affects the meat and certain tissues of animals that are fed with banana peels.