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Unripe bananas are hard with thick skins and an unmistakeable raw flavour. As they ripen they shrink slightly, the skins become thinner, and the fruit becomes softer and sweeter; the raw flavour goes away.
How does the nutritional composition of the fruit change during the transformation?
Starch content and sweetness: Bananas become sweeter as they ripen because the starch is broken down. An unripe banana is full of complex carbohydrates, but as it ripens, these are broken down into simple sugars which is why riper bananas are sweeter. The lower starch content and higher sugar content also means that the banana is digested more quickly, so it becomes a slightly higher GI food as it ripens.
Antioxidant levels: Riper bananas also have higher levels of antioxidants. The brown spots on the skin are formed when the chlorophyll breaks down into antioxidants. These are very good for your body as they help prevent cell damage.
Calorie count: As the banana ripens, the calorie count stays the same. Even though the nutrients change, all carbohydrates contain 4 calories per gram so the total remains the same
Vitamins and minerals: As the fruit ripens, the micronutrients tend to decrease. Water soluble vitamins like vitamin C, folic acid and thiamin decrease. But the banana will still have a lot of potassium. You can store a ripe banana in the fridge to prevent some of these nutrients from being lost.
In unripe bananas a lot of the starch is made up of resistant starch. Green bananas may contain between 35.14 and 45.87% of resistant starch (in Thai bananas) which varies depending on the variety of banana.
Source: Chemical Compositions and Resistant Starch Content in Starchy Foods
