Most of us know eating fruit daily is a great way to try to stay healthy, with the Australian Guide to Healthy Eating encouraging us to eat two serves a day. This is because they are relatively low in energy content and rich in fibre, antioxidants and some phytochemicals that may have beneficial health effects.
Despite the benefits, less than half of Australians eat enough fruit. To try to make eating fruit easier, get the most nutritionally from what we eat and avoid wastage, it is important to consider the best stage to eat fruits from harvesting to over-ripening.
Fruits vary in nutritional quality
Fruits contain a range of nutrients essential for health, from energy-producing nutrients (mostly carbohydrates with some fat and protein) through to vitamins, minerals and fibre. The amounts of these nutrients vary, however, from one fruit to another.
Predominant sugars vary. In peaches, plums and apricots, there is more glucose than fructose. The opposite is the case in apples and pears. Fruits vary greatly in terms of their glycaemic index and the effect on our blood sugar (glucose).
If we look at vitamin C, relatively high amounts are found in strawberries and citrus fruits compared to bananas, apples, peaches or pears.
Passionfruit contains more phosphorus, an essential mineral used in releasing energy, than papaya. However, the opposite occurs in the case of calcium, the most common mineral in the human body.
According to a recent study, higher consumption of some whole fruits, especially blueberries, grapes and apples, significantly reduced the risk of developing type-2 diabetes. But eating oranges, peaches, plums and apricots had no significant effect. However, this does not mean the latter ones are bad fruits.
Sometimes, combinations of fruits work better than each individual fruit. Mixtures of orange and star fruit juices had higher antioxidant capacity than pure juices.
Even certain stages in fruit maturation showed better health effects. Bioactive compounds are chemicals that occur naturally in fruit and are not technically nutrients but appear to result in health benefits. These are found in higher levels in green (unripened) jujube fruit (red date) than in the ripe fruit.
Green or yellow bananas, does ripeness matter?
Fruit ripening involves a range of complex chemical processes. These cause changes in colour, taste, smell and texture. Generally fruits are more tasty when fully ripened, but this is not always the case. Guava, for example, tends to be more appealing when partially ripe.
Unripe fruits typically contain more complex carbohydrates, which can behave like dietary fibre and break down into sugars upon ripening. Unripe bananas contain higher levels of resistant starch (which we cannot digest, but can be a prebiotic acting as a food supply to the microbes in our gut), which is linked to lower risks of bowel cancer. This decreases during the ripening process.
With respect to vitamins and phytochemicals, researchers found the opposite is the case. The level of vitamin C decreases during the early stages of sweet cherry development but increases at the beginning of fruit darkening and accumulation of the pigment anthocyanin. Levels of glucose and fructose, the main sugars found in cherry fruit development, increase during ripening.
However, over-ripening leads to a loss of nutrients following harvest. It’s also linked to fruit darkening, softening and a general loss of sensory acceptability.
Impact of processing
Fruit can be processed by canning, freezing, drying, chopping, mashing, pureeing or juicing. Processing fruits can improve shelf life, but it can also lead to losses in nutrition due to physical damage, long storage, heating and chilling injury.
Usually, minimally processed fresh-cut fruits such as fresh fruit salad have the same nutritional qualities as the individual fruits. However, tinned fruit salad may contain added sugar as syrup and preservatives, which may be a less healthy option.
Eating whole fruit rather than drinking juice appears to be linked to better health. A study that gave participants whole fruit before a meal found it led to people eating less than if they drank juice. Additionally, those eating whole fruit appeared to have a lower risk of developing type 2 diabetes, although other studies suggest juices with added sugar may be the real problem.
It is also likely some processing such as juicing may help increase availability and quicker absorption of the beneficial nutrients in fruit. The benefits of this need to be weighed against the sugar being more available too.
So which to eat?
Nutritional qualities of fruits vary and it is hard to predict which fruit might be best. Generally, the more different types of fruits you can include in your diet, the better. For many fruits, eating fresh at its correct ripening stage may be more beneficial, perhaps more for taste than nutrition.
Overripe fruits may be still good to eat or easily convert into smoothie, juice or used as an ingredient such as in banana bread. Eating an over-ripe fruit such as a banana does not mean that you are putting more sugars into your body as the total amount of carbohydrates in the fruit does not increase after harvesting.
While fruit products (juice, dried or tinned products) that are higher in sugars and also preservatives in some cases are not as good as whole fruit, consuming fruit in this form is better than consuming no fruit at all.
But fruits alone cannot do all the work. It is important to choose foods from all the core food groups within the Australian Guide to Healthy Eating to reap the maximum health benefits of fruits.
Senaka Ranadheera, Early Career Research Fellow, Advanced Food Systems Research Unit, College of Health and Biomedicine, Victoria University; Duane Mellor, Associate Professor in Nutrition and Dietetics, University of Canberra, and Nenad Naumovski, Asistant Professor in Food Science and Human Nutrition, University of Canberra