Generality
What is onion?
The onion, intended as a food, is the edible bulb produced by the homonymous herbaceous plant; strongly aromatic, this vegetable is botanically related to other spice-like vegetables with similar characteristics, such as garlic, leek, shallot and chives.
An inevitable ingredient of numerous recipes, the onion is distinguished by the abundant presence of trace elements, vitamins and enzymes that stimulate digestion and metabolism.
Botanical classification
The onion is a herbaceous plant belonging to the genus Allium, a cepa species. Traditionally inserted in the family of the Liliaceae, according to a more recent taxonomic classification, the lacipolla should be included in the family of the Amaryllidaceae.
Recall that the Allium botanical genus, in addition to the common onion, includes many other lesser known species and hybrids; for example: A. fistulosum (spring onion), A. xproliferum (in English, "tree onion") and A. canadense (Canadian onion).
There are also various types of "wild onion", which however are not the object of cultivation and do not constitute the ancestral form of the common one.
Description
The onion plant is characterized by long and thin hollow, bluish-green leaves, at the base of which, before the roots, the edible bulb develops. When fully ripe this bulb is wrapped in a drier outer layer of white, yellow or red. The pulp, typically stratified, is white-yellowish or red.
Property
Nutritional characteristics of the onion
The onion is a product of vegetable origin that can be placed in the group of vegetables; it does not easily contextualize in the VI and VII fundamental group of foods, since it contains uninteresting levels of vitamin C and carotenoids. Moreover, compared to other vegetables, it does not shine due to the high total fiber content.
The onion contains a lot of water and has a fair amount of fructose, a sugar that, in addition to giving it a certain sweetness, gives it a mild energy function. Proteins and lipids are irrelevant; cholesterol is absent.
With regard to mineral salts and vitamins, there are no concentrations worthy of particular note, so it is possible to say that the onion contains "a bit of everything".
The onion lends itself to most dietary regimens and, due to the content of some mildly spicy molecules, it can be contraindicated in case of hypersensitivity and / or gastro intestinal pathologies such as: stomach acid, gastritis, ulcer, irritable colon, haemorrhoids and fissures anal.
It has no contraindications for being overweight and for replacement pathologies; on the contrary, it seems to have a favorable impact on certain metabolic problems (hypertension, hypercholesterolemia, etc.). In fact, as we will see in the next section, the true "richness" of this vegetable does NOT lie in the energetic, plastic, vitaminic or saline nutrients, but in the PHYTO-THERAPY molecules (most of which have an antioxidant and beneficial function for the metabolism).
It does not contain gluten and lactose, and is permitted by vegetarian and vegan philosophies.
The average portion of onion can reach 200 g (80 kcal).
| Onion | |||
 | |||
| Nutritional values per 100 g | |||
| Power | 40 kcal | ||
| Total carbohydrates | 9.34 g | ||
| Starch | - g | ||
| Simple sugars | 4.24 g | ||
| fibers | 1.7 g | ||
| Grassi | 0.1 g | ||
| Saturated | - g | ||
| Monounsaturated | - g | ||
| polyunsaturated | - g | ||
| Protein | 1.1 g | ||
| water | 89.11 g | ||
| Vitamins | |||
| Vitamin A equivalent | - μg | -% | |
| Beta-carotene | - μg | -% | |
| Lutein Zexanthin | - μg | ||
| Vitamin A | - IU | ||
| Thiamine or B1 | 0.046 mg | 4% | |
| Riboflavin or B2 | 0.027 mg | 2 % | |
| Niacin or PP or B3 | 0.116 mg | 1% | |
| Pantothenic acid or B5 | 0.123 mg | 2 % | |
| Pyridoxine or B6 | 0.12 mg | 9% | |
| folate | 19.0 μg | 5% | |
| Choline | - mg | -% | |
| Ascorbic acid or C | 7.4 mg | 9% | |
| Vitamin D | - μg | -% | |
| Alpha-tocopherol or E | - mg | -% | |
| Vit. K | - μg | -% | |
| Minerals | |||
| Football | 23.0 mg | 2 % | |
| Iron | 0.21 mg | 2 % | |
| Magnesium | 10.0 mg | 3% | |
| Manganese | 0.129 mg | 6% | |
| Phosphorus | 29.0 mg | 4% | |
| Potassium | 146.0 mg | 3% | |
| Sodium | - mg | -% | |
| Zinc | 0.17 mg | 2 % | |
| Fluoride | 1.1 μg | -% | |
Benefits
Phytotherapy properties of the onion
The onion contains several substances that are well known and used in phytotherapy. Let us first of all remember sulfur compounds, the most important of which is allylpropyl disulfide . These substances, together with the flavonoid quercetin, give the onion a potential antitumor activity, especially with regard to colon, stomach and prostate cancer. Even if we are talking about a simple food, with all the limitations and caution of the case, it is true that there are scientific evidences that support this activity; Quercetin, for example, has been shown to be able to stop the development of colon tumors in the rat (induced by azroxymethane) and, to support this activity, there are also other clinical studies. Naturally, we must not let ourselves go to miraculous statements, but rather interpret everything with the utmost rationality and caution; an inveterate smoker, sedentary and obviously overweight, certainly cannot hope to prevent the negative repercussions of his lifestyle by eating some onions.
In this food we also find flavonoids with diuretic action and glucokinin, a plant hormone with antidiabetic activity (action assisted by sulfur and chromium compounds).
Numerous other virtues are attributed to the onion; it is in fact considered an antihypertensive plant (due to the presence of the aforementioned flavonoids, but also of alliin and derivatives), vermifuge, expectorant, antibiotic (especially at the intestinal level, thanks to the prebiotic action of inulin), normolipidemizzazione (prevents atherosclerosis and the damage of hypercholesterolemia), antithrombotic (reduces platelet aggregation and prevents the formation of thrombi), mildly laxative (due to its content in pectin and inulin), purifying (onion favors diuresis) and anti-gout (promotes elimination of nitrogenous waste and uric acid).
We must also remember that the onions are not all the same. The many varieties contain very different levels of nutritional factors. For example, yellow onions have the highest level of total flavonoids (11 times more than white ones), while red ones contain the highest amount of anthocyanins (25 different types, which make up 10% of the total flavonoid content ). The shallot, although not properly an onion, contains up to 6 times more polyphenols than the Vidalia onion.
Many of these therapeutic activities have been known since the time of the ancient Egyptians, so much so that references to its healing properties can be found a little in all medical publications of every age. It should be noted, however, that most of the substances endowed with these important activities, together with the precious vitamin content, undergo irreversible alterations when the onion is left too long in boiling oil.
The best cooking, therefore, is the sober one, limited to a simple burn or a very short browning; only in this way can the onion transfer all its precious therapeutic virtues to our body.
Contraindications
Does onion consumption have contraindications?
If from an alimentary-culinary point of view the onion is well a little everywhere, from the phytotherapic one it does a little good for everything; remember that its use should still be contained in the presence of meteorism, flatulence, stomach pain (hyperacidity, peptic ulcer) and hiatal hernia. Finally, during lactation, the onion tends to give the milk a particular, sometimes unpleasant taste for the infant. It was once believed that for this reason it should be removed from the nurse's diet; today, on the other hand, it has been concluded that aromatic compounds are fundamental for the development of taste in infants which, little by little, is perfectly capable of tolerating all aromatic factors in reasonable quantities.
Allergy to Onions
After handling the onions, some people suffer from allergic symptoms such as contact dermatitis, intense itching, rhinoconjunctivitis, blurred vision, bronchial asthma, sweating and anaphylaxis. Allergic reactions do not seem to occur when cooked onions are consumed, perhaps due to the denaturation of the proteins involved in cooking.
Kitchen
Recipes and culinary applications
The onion is a food that, in general, is incorporated into the culinary preparations to flavor the recipe that contains it; its presence is therefore supplementary, or rather supplementary.
Together with oil, carrots and celery, the onion forms the basis of the so-called "fried", a fundamental element to favor the "taking of body" of many preparations.
Although less known, there are plenty of recipes that use onion as the main element. Some examples are: sweet and sour onions, baked au gratin onion, baked onion, red onion supplì with balsamic vinegar and cane sugar, onion soup, etc.
Digestibility and halitosis
Many believe that the onion is basically a LITTLE digestible product, as the smell tends to "reappear" insistently in the breath for several hours after the meal. In reality, the onion is a TUTT'ALTRO food that "heavy"; it is a vegetable that quickly passes into the stomach and intestines. What determines the aforementioned drawback is the relative aromatic component, which struggles to fade from both oral and gastric mucosa. If the meal, besides being rich in onions, has also been rather full-bodied (therefore difficult to digest and permanent in the stomach), the undesired effect will certainly be amplified. Some useful systems to moderate the "alitosic" effect of the onion are: the elimination of the so-called soul, or the internal bud (especially if already greenish), and the soaking of the onion already cut into the milk (in the latter case it is not clear what the mechanism is, but it seems to work empirically).
Cooking
Let us remember again that the onion tends to lose much of its nutritional content with cooking; moreover, if it is true that it gives an excellent taste to the recipes, it is equally true that, once "burned", it completely TAPS the preparation in question. The most suitable cooking level is called "imbiondire" and provides a very slight chromatic alteration of the bulb which, from white, acquires a yellowish tinge.
To obtain a properly golden onion (Maillard reaction) it is possible to add a little water to the oil inside the still cold pan; in this way, during cooking, the liquid does not reach "dangerous" temperatures and the onion remains well hydrated. It is however a good idea not to overdo it because, once dried, it must be dried with caution and at low heat; too much water would cause a "boiled" effect or total loss of consistency. To speed up the process of "maillardisation" of the onion it is possible to increase the pH (making it basic) with a pinch of sodium bicarbonate.
Eye Irritation
Freshly cut onions often cause burning eyes, tearing and a runny nose in people nearby. This is caused by the release of a volatile gas called in English syn-propanethial-S-oxide, which stimulates the nerves in the eye creating a pungent sensation. This gas is produced by a chain of reactions that act as a defense mechanism for the plant: cutting the onion causes cell damage with release of alliinase enzymes.
These reduce the sulfoxides of amino acids and generate sulfonic acids. One in particular, 1-propensulfene acid, is rapidly converted by a second enzyme called lachrymatory factor synthase, producing syn-propanethial-S-oxide . This volatile gas diffuses into the air reaching the eyes, where it activates the sensory neurons. As a result, the lacrimal glands begin to secrete tears to dilute and rinse the irritant.
Prevention
Irritation can be avoided by cutting onions immersed in water, in a container, or under the tap. Leaving the root end of the bulb intact helps to reduce this effect because at this point there is a greater concentration of sulfur-based compounds than the rest of the bulb.
Refrigerating onions before use reduces the reaction rate of the enzyme. Using a fan can speed up the expulsion of gases from the eyes. The tolerance to this element increases with the frequency of exposure.
In 2008, the "New Zealand Institute of Crop and Food Research" created a variety of onions lacking the lacrimation factor, which therefore do not burn in the eyes.
storage
Store onions: how to prevent them from sprouting?
The onions must be stored at room temperature, in a single layer, in knitted bags (for example of jute), placed in a dark, cool, dry and well-ventilated place. With this system the onions can reach a shelf life of three or four weeks.
It is recommended to be careful not to stack them with fruit, as they can absorb the odor (for example from apples and pears). Furthermore, by easily retaining moisture from other plant-based foods, they can decompose more quickly.
The peeled and cut onion must be used within two or three days, beyond which it tends to dry out and develop mold.
Cultivation
Notes on onion cultivation
Onion is the most cultivated botanical species of the entire genus Allium .
Despite being a two-year vegetable, the onion is treated as an annual crop. It can be grown starting from the seed, from the plants obtained after the seedbed and from the bulbs.
The cultivation soil for the onion must be fertile, light, loose and draining. Compact (clay and hard) soils are not suitable and a correct milling of the previously broken soil (depth about 25-30cm), combined with fertilization with mature manure is essential.
The harvest of the onion must be done at 1 year of maturity, then in the middle of the life cycle.
The crop is subject to a number of pests and diseases, in particular the onion fly, Ditylenchus dipsaci and various fungi that cause it to rot.
