Not having access to fully ripe fruits is not only unsavory: underripe fruits do not provide the nutrition we expect and need. Moreover, unripe fruits still contain some level of plant defense compounds. This is the result of a myriad of potent chemical changes, such as sugars, acids, antioxidants alkaloids, and more.
Let’s explore why eating fruits in their fully ripe state is essential for health.
For quick readers:
Why is it important to eat fully ripe fruits and avoid underripe ones?
You should eat all of your fruits fully ripe! Fruits need to be eaten ripe for maximal health benefits and also safety. This has an interesting biological and even evolutionary reason: The plant only ripens its fruit when its seed has matured and is ready to be spread. That’s the point the fruits are ripe and palatable. Before this point, the consumer is not yet attracted by colors or flavors but rather put off by the highly acidic taste, lack of sweetness, and different unpalatable substances, like tannins, in the unripe fruit.
Fruits signal when they are ready – and healthy!
Fruits are the main food of specialized fruit-eating animals – frugivores. This includes humans! Taste and smell are two important adaptive instincts that indicate the nutritional value of the fruit to the animal while warning it of toxicity!
The importance of fruit ripening to human nutrition is reflected in the communication and interaction we have with our food source. Fruits unmistakable signal to our taste buds when they are ready… or not! Fruits are appealing and delicious at their nutritional peak, but off-putting with unpalatable flavors and weird textures when not ripe yet.
And those features are not a coincidence but clear communication: it is when fruits are ripe and ready that they are most nutritious, rich in antioxidants, and loaded with other beneficial metabolites. On the other hand, plants dissuade us from eating their unripe fruit with acidic flavors, toxic alkaloids, anti-nutrients, and other unfriendly compounds.
An example is the underripe banana: the fruit is a staple for primates; however, when underripe, it has an astringent, slightly bitter or hairy off-putting mouth-feel to it!
To understand this complex relationship, let’s look at the evolutionary background:
Seed dispersal and fruit ripeness: It’s all about the seed
The ripening process of fruits is highly coordinated and complex, by which a plethora of substances are increased, reduced, and transformed. But how does this affect our nutrition and health? How bad is it to eat unripe fruits? Let’s start by understanding the purpose of fruits from the plants’ perspective!
The plant give us tasty fruits in exchange of seed dispersion: The whole point of the delicious fruit surrounding the seed is to employ fruit-eating creatures (i.e., birds and primates – including humans) to disperse them. Plants ensure that the fruit is only eaten when the seed is ready! For this reason the symbiotic co-evolution of fruits and fruit-eater is not all just roses and sunshine:
Plants protect their fruit from being eaten before seed maturation with toxic and off-putting (warning) components that keep the fruit eater away until the seed has matured and is ready to germinate. This is vital for a plant’s reproductive success and fitness: if fruits are picked and dispersed with an immature seed, the embryo cannot sprout and grow. This scenario is a substantial reproductive disadvantage and energy loss for the “mother plant,” which has invested much of its energy into flowering and fruit building.
Fruits signal and communicate their ripeness with a change in color and appealing smell. Those changes attract the “right” fruit consumer and ultimately promote seed transportation. The animals gain the tasty, energy-rich fruit flesh in exchange.
Nutritional changes during fruit ripening
Why is the right timing of picking fruits such as big fuzz for our health? Ripe fruits are highly nutritious and very low in anti-nutrients – a perfect human food. However, the chemistry of unripe fruit is not as friendly!
More nutrients and energy, fewer anti-nutrients and toxins
To comprehend the implication of ripeness of a fruit on nutrition and health we can look at the chemical changes that take place within a fruit during ripening: Taste, smell and color molecules, which either attract or repel animals are mostly secondary metabolites, a powerful chemical family. Changes in acidity and sweetness are regulated by sugar assimilation and acid breakdown.
The ripening process begins once the fruit is fully mature and the process of cell division has stopped. It occurs as a result of hormones which activate the genes for the production of various enzymes that break down components in the mature fruit! During the ripening process fruits are transformed into the foods we know and love. They go from unpleasant, acidic and potentially toxic to juicy, attractive, sweet, and flavorful. Those are all chemical changes!
Typically, energy, vitamins, and flavorful molecules are increased (table 1), while unfavorable compounds such as anti-nutrients and defense toxins are decreased (table 2) in the process of ripening. Those components influence color, taste, pH, toxicity and energetic value of fruits.
|Sucrose||simple sugars (sweet)||Anthocyanin (blue, red, purple)||Vitamin C|
|Glucose||Flavonoids (flavors)||Carotenoids (yellow, orange, red, purple)||Beta Carotene|
|Defense Compounds (toxins)||Antinutrients||Taste||Color|
|Cyanogenic glycosides (cyanide)||Tannins||Malate (acidic)||Chlorophyll (green)|
Minerals: A study on ripening blackberries found that the mineral content (Potassium, Calcium, Zinc, Manganese and Copper) stays more or less the same. Only the magnesium contain lowers around one third because of the drop in green colored chlorophyll (which contains magnesium) and iron, which increases during ripening.
Taste and color compounds
Humans have taste receptors to detect and love sweetness for a good reason! The sweet taste in fruits is attributed to simple sugars, which are mobilized from the plant to the fruit. This valuable energy reward is exchanged for seed-dispersing by the animal. Sweet tastes so good for frugivores like humans because it nourishes us.
Fruit go from acidic to sweet: Complex sugars found within the fruit are broken down by enzymes into simple sugars like glucose and fructose. This transforms these otherwise bland complex sugars into the sweet simple sugars our taste buds love. This process also makes the fruit soft as the complex sugars are no longer playing their role as structural components in the cell wall. The insides of the plant cells also become released making the fruit juicy and its nutrition more bioavailable. Concurrently, fruit acidity is decreasing, because the concentration of organic acids such as malate and citrate drops.
From green to colorful: Color is an important feature of signaling ripeness in fruit. The change in color typically occurs as chlorophyll, which is responsible for the green color, breaks down and other pigments are produced. Pigments produced in ripe fruit include carotenoids, flavonoids, and betalains. Many of these, such as the flavonoid called anthocyanin, are renowned antioxidants. Color in fruit also serves to get the fruit eaters attention, as it is easier detectable between green leaves. To be able to do the best job possible in spotting tasty, ripe fruits, frugivore species have evolved specialized color vision!
More sweetness means more simple carbs and energy in ripe fruits
Fruit development precedes the ripening process. This begins after pollination and involves the physiological development of a fruit from a flower. Most fleshy fruits originate from tissues that originally composed the female reproductive organs of the flower. Fertilized ovules develop into seeds and in most fruit it is the ovary walls that become the fleshy parts we consume. During this process, plants sink all of their energy into the development of the fruit: they move sugars produced via photosynthesis through their vascular system and finally into the fruit.
Some plants may even mobilize sugars stored in their roots and other plant tissues. These sugars will later on provide the energetic nutrition for its consumer (read here, why simple sugars in fruits are good for us). Once they reach the developing fruit, the sugars are incorporated into the rapidly dividing cells. Here simple sugars (which taste sweet) like sucrose and glucose are transformed into complex sugars like cellulose and hemicellulose (which do not taste sweet). These compose various cellular components such as the cell walls.
The complex sugars in unripe fruit are technically full of energy, but we are incapable of breaking them down. This means if we eat them, they simply act as a dietary fiber and don’t contribute any calories to our diet. Our taste buds know this, and despite them technically being sugars, they are bland and without a hint of sweetness. Only simple sugars taste sweet.
Decreased toxicity of ripe fruits
During fruit development, plants often synthesize many different types of alkaloids, anti-nutrients, acids, and other distasteful compounds within the fruit. The latter is why many immature and unripe fruits have bitter and astringent flavors. These compounds may actually be toxic and have various health consequences if consumed in excess. Plants purposefully incorporate these into their immature fruit to prevent you from eating their fruits before they are ready.
Bananas, plums, citrus, and countless other fruits contain harmful compounds before they are fully ripe. Some of these may cause negligible to minor symptoms, while some can be more serious. Due to co-evolution, humans have developed a higher tolerance to the “unfriendly” compounds (and developed more effective warning signals) of fruits they have consumed regularly during evolutionary timelines.
However, once ripe, fruits are among the foods with the least anti-nutrients and toxins!
Be aware though of fruits, which are relatively new in our diet, which can be more toxic to humans! They can have more severe effects, which we sometimes only feel when it is already too late: For example, green tomatoes (a fruit of the toxin-rich nightshade family) contain various toxic compounds. The most notorious of these are the alkaloids Tomatine and Solanine. Poisoning by these compounds can cause headaches, diarrhea, cramping, dizziness, eczema, and countless other health issues. And even worse, the Ackee fruit, which is famous in Jamaican cuisine, is deadly toxic until ripe and results in deaths every year.
Eating fruit fully ripe is crucial for health!
Fruits are an integral part of the human diet. There is nothing more delicious than a perfectly ripe fruit: only fully ripe fruits unfold their appealing color, smell, and taste, signaling that they are ready to be eaten. But, eating fruits when fully ripe is not only about taste but also about health! Only ripened fruits provide the essential nutritional value we need: Fruits are far less nutritious and often contain toxic compounds when picked before the plant’s seed is mature and ready to be distributed!
Sadly, as it is becoming more and more difficult to access ripe fruits straight from nature, at least know which ones ripen after being picked (see list of fruits that ripen or don’t ripen after harvest). I hope you live in a tropical place with loads of colorful, divine-smelling, and sweet tasty fruits, though… In the meantime, we can integrate frozen fruits in smoothies and juices as a second choice, because frozen fruits are the ones that were too ripe to make it to the shelves.
If you take away only one message here: eat at your fruits perfectly ripe whenever possible – because a perfect fruit has enormous, near-magic health benefits!
This article was written in conjunction with another biologist and botany expert.
What’s healthier, simple carbs from fruits or complex carbs from grains?
Read more here
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