the delight of fruit

Although it hides many wonders, that of maturation is remarkable because we witness it frequently: a hard, green, bitter and unappetizing product turns in an amazing way into an appetizing delicacy, offering us the richness of its flavour, its sweetness, its juiciness and aromas. Citrus fruits that make you think of Andalusian patios populated with orange trees, smooth skins that inspire poets and striking and varied colors.

But before unraveling the ripening, what is a fruit?

Botanically, a fruit is the matured ovary of a flowering plant that houses the seed or seeds with which the plant will reproduce. The ovary can be hard and dry, as in the case of walnuts, peanuts and other products that we call dried fruit, or it can be fleshy and succulent, as is the case with apples, tomatoes, bananas or avocados. These last examples also tell us that fruits can be sweet or not.

Once fertilized, the ovary of a plant undergoes a series of transformations to protect the ovules it contains, the same ones that when they mature are the seeds that will give rise to new plants. Thus, a small yellow flower the size of a thumb can develop into a huge, juicy watermelon. It is reasonable to ask, then, what are the reasons why plants have evolved in such a way that they dedicate such an enormous amount of resources (water, photosynthesis, nutrients, chemical processes) to create that fruit.

The answer is twofold. The fruit is a strategy for protecting and dispersing the seeds so that as many of them as possible germinate and flourish, perpetuating the species.

It should be made clear that when we speak of 'strategy' we are using a human metaphor to explain a natural evolutionary process which, unlike the strategies of our species, is neither voluntary nor conscious. Over millions of years, plants that by natural variation or mutations have better fruits (i.e., ovaries that protect and disperse seeds better when they mature) have reproduced a little more successfully... and those accumulated successes go giving rise to the results we see today, as if they were a conscious goal.

Clarified that, and speaking only of non-dried fruits, this strategy consists of having certain nutrients or being tasty or sweet, attracting animals with various colors that indicate their maturity and with seductive aromas that tell different species, such as the Alice in Wonderland cake: "Eat me." The 'trade deal' that is inadvertently made between plant and animal could be summed up like this (only as a metaphor): I give you a tasty and nutritious food and you, in return, take my seeds away from here and throw them away or, better , you deposit it with your feces as food so that they can germinate and develop.

Animals, whether birds or mammals, are thus the vehicles for the seeds to take them further and further, with a passage paid for by the flesh of the fruit. This result, evolutionarily useful for the survival of the species, makes the energy cost of fruit production a 'good deal' for the plant that produces it.

Caring for the coral to care for the oceans

Fruits as such were the logical result of the evolution of a type of plant, the angiosperms, which appeared on our planet in the late Cretaceous period, between 100 and 125 million years ago, and fruits probably began to evolve at the same time. : better protected seeds were less likely to be digested by animals that ate them, so dry fruits with hard protection appeared first, and then fruits that surrounded hard-to-digest seeds, to disperse the seeds without They were part of the food.

Transformation

Every fruit, then, is originally a flower or, more exactly, the ovary at the center of the flower. The different layers of the ovary (which is a structure made up of modified leaves called carpels) give rise to the tissues of the fruit: the epicarp, which is the peel or skin, the mesocarp, which is the flesh of the fruit itself, and the endocarp, that protects the seeds.

As it is not good for survival that the seeds or embryos of the plant are eaten in their early stages of development, the developing mesocarp that forms the fruit is not at first attractive to predators, as anyone who has sunk a tooth knows. in an unripe fruit. It is only when the seeds are ready to germinate that the fruit takes on its desirable characteristics for those of us who eat them. When it matures.

And the ripening process is a complex series of coordinated events that profoundly transform the fruit in all its sensory and nutritional aspects.

Let's start with the softness of the fruit. An unequivocal sign of an unripe fruit is precisely that it is hard, a characteristic that we frequently use to tactilely assess whether the avocado we are buying is ready to be part of our meal. The hardness of the fruit is given by the thickness of the walls of its cells, walls formed mainly by layers of polysaccharides, especially pectin. For ripening, enzymes come into action that allow the pectin to dissolve in water.

fruit sugar

Nutrients in fruits accumulate primarily in the form of starch, another polysaccharide that, when affected by enzymes during ripening, breaks down into shorter, water-soluble molecules such as fructose, glucose, and sucrose, giving the fruit its sweetness or flavor. characteristic flavor. At the same time, its acid content drops.

The enzyme-mediated process also causes the fruit to produce essential oils in well-defined mixtures that give each fruit its characteristic flavor. At the same time, its generally green color due to chlorophyll changes as it is replaced by pigments called carotenoids, which range from yellow to red and are also precursors of vitamin A.

A complex succession of phenomena developed over more than 100 million years that result in our enjoyment... a word that means, precisely, 'reap the fruit' or 'obtain the benefit' of something.

Your plastic and your fruit

The enzyme that triggers fruit ripening is ethylene, a colorless, odorless gas from which polyethylene, a common plastic, is made. As the seeds ripen, the plants produce ethylene, but it can also be applied externally, as is done with many fruits that are picked green and ripened 'in chamber' with ethylene. We can do the same at home by placing unripe fruits next to other ripe ones such as bananas, which therefore emit ethylene.

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