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Does fruit lose fibre as it ripens?

If you’re looking for a fruit-fibre hit, fear not that the benefits disappear with ripening.

QUESTION: I read that as bananas ripen, starch is converted to sugar. However, the article also stated that the fibre content declines as that process takes place. Does this reduction in fibre happen with all fruit?

ANSWER: The short answer is yes, there is a reduction in fibre as fruit ripens. But the reduction in fibre that occurs during the edible phase of fruit ripening is very small.

Fruit plays an important role in our health, by supplying crucial nutrients such as vitamin C, a variety of B vitamins, beta-carotene, vitamin K (in some cases) and a range of antioxidants, as well as energy, minerals and dietary fibre. Of course, to impart all those nutritional goodies, we need it to be edible and, therefore, ripe.

Fruit ripening is a highly complex and co-ordinated transformation process into a soft, appetising form. Aside from the colour changes that occur with ripening, taste and texture are also significantly altered.

For a start, there are increases in flavour and aroma compounds. But the biggest change is the increase in sweetness, along with a slight decrease in acidity, resulting in an enjoyable blend of sugar and tartness.

Major textural changes during ripening also lead to the fruit’s softening, as the structure and composition of the cell wall changes and the stored starch granules inside the fruit cells break down into sugar.

The taste and texture changes result in a food that is more desirable and more likely to be eaten by animals, which will then disperse the fruit’s seeds.

To take the banana example, as it develops, 15-35% of its wet weight is starch. Starch is resistant to digestion, so it counts as part of the total dietary fibre of the banana. However, as the banana ripens, the starch breaks down into sugars, giving it its characteristic sweetness and smooth texture.

The cell walls of fruit also contain another important source of fibre – a mixture of polysaccharides, including pectins, which are digested by gut bacteria.

During ripening, much of the insoluble form of pectin in the cell walls changes into a soluble form of fibre. There is also a slight decrease in the total amount of pectin and, therefore, the total amount of fibre in the cell walls.

So, yes, as a general rule, there is a slight reduction in fibre as most fruit ripens. But aside from the pectins in the cell walls, it’s worth noting that not all fruit contains starch and not all starch in fruit is resistant starch (the form that qualifies as dietary fibre). Apples, for example, turn their starch into sugar and sweeten as they ripen. However, peaches and citrus don’t have any starch to start with.

Overall, then, how ripe the fruit is makes very little difference to the non-starch portion of dietary fibre in the fruit. The biggest change in fibre occurs as a result of resistant starches in some fruit, such as bananas, transforming into sugars. However, by the time a banana or other fruit reaches the edible part of its ripening phase, most of that decrease in resistant starch and increase in sugar content has already occurred.

If you want to eat a lot of fibre with less sugar, then choose vegetables. Because that’s exactly what they offer – plenty of fibre, with less sugar. It certainly beats trying to eat an unripe piece of fruit.

This article was first published in the September 28, 2019 issue of the New Zealand Listener.