The starch in green banana is very indigestible, but as the banana ripens, the starch is converted to digestible sugars. Unripe bananas contain mostly starch, which makes up 70–80% of their dry weight. Much of that starch is resistant starch, which is not digested in the small intestine. It is absorbed slowly and does not cause sharp rises in blood sugar. The starch acts as food for the growth of beneficial microbes in the digestive tract.
As the banana fruit ripens, the starches (which are found in organelles called amyloplasts) break down. The breaking down of the starch into simpler sugars will make the fruits taste a little sweeter and be softer.
When the skin is yellow green, 40 percent of its carbohydrates are starch; when the skin is fully yellow and the banana is ripe, only 8 percent of the carbohydrates are still starch.
The starch content of bananas (Musa acuminata, “Cavendish”) has been reported to change from approximately 21 g/100g in unripe fruit to approximately 1 g/100g in fully ripe fruit. During ripening there is a decrease in enzyme-resistant starch and an increase in water-soluble pectin.
Ripe bananas have a low GI of 51, due to the higher carbohydrate content of bananas. The type of carbohydrate in bananas is classified as resistant starch, which functions similarly to dietary fiber. Resistant starch is not broken down in the small intestine so it causes less glucose to be released into the bloodstream.
Starch in banana
