Generality
Oysters are fishery products of animal origin, belonging to the Phylum dei Molluschi, the Classe dei Bivalvi and the Ostreidae family. There are therefore different types of oysters, belonging to different genera and species; among all, the most widely used and known ones undoubtedly belong to the Genres Ostrea (common oyster - Ostrea edulis) And Crassostrea (oyster of the Pacific or Japanese oyster - Crassostrea gigas).
Oysters have a very low energy intake and mainly contain proteins; lipids are scarce but the cholesterol content requires moderate consumption. The health and hygiene risk associated with the consumption of raw oysters from wild or unsecured origin is not negligible.
Some oysters (not those mentioned above) produce pearls and are widely exploited in the jewelry industry.
Description
As anticipated, oysters are molluscs belonging to the Bivalve Class; the common ones have an external shell (valve) that protects the soft part. Externally, this sort of shell is wrinkled, lamellar, irregular, of a gray-white color; internally it appears smooth and mother of pearl color. The shell of the oysters, in addition to shielding the animal, is essential for anchoring it on the rocks. The lower segment is larger and concave, while the upper one is flat. THE
The internal body of common oysters is discoid, gray-beige and greenish in color, delimited by small cilia and attached to the inside of the flat valve. Outside, the shell acts as an adhesive on solid bodies (rocks, poles, wrecks, etc.). ). The common oysters are medium in size, just over 10cm, while the C. gigas it reaches much larger dimensions and has a very strong polymorphism, that is a considerable irregularity of the overall shape; however, the anatomical organization is comparable to that of common oysters.
Basics of biology
Oysters live in salty or brackish waters, possibly rich in organic residues and small organisms, which they feed on by filtering the water (similar to mussels). They colonize bathymetric ranges from 0 to tens of meters deep (some remain uncovered with low tide) and are present in the seas all over the world.
At the European level, the Specie edulis it is grown / bred mainly in Italy, France and Croatia. In addition to the Mediterranean basin, common oysters are also present in the Atlantic Ocean, in the North Sea.
At the same time, Pacific oysters (which, as the term suggests, are typical of that area) have reached and colonized both the Atlantic Ocean and the Mediterranean Sea. They have a proliferation and a higher yield than common oysters and this is determining commercial taxation with respect to European cousins.
Oysters in the kitchen
Oysters owe their fame to the unmistakable taste perceived in "raw" recipes. In reality, oysters are not the only bivalve molluscs that lend themselves to such consumption; also mussels, scallops, cockles, clams, etc. represent real delicacies.
As far as oysters are concerned, probably, the only useful observation is that concerning the cleanliness of the raw food. Farmed oysters are already sufficiently clean; however, sometimes it is still necessary to apply an energetic brushing to the shell to eliminate sand residues and any algae. This is a particularly important procedure because, both in raw consumption (where it is still served in the shell), and in which involves cooking (sautéed, gratinated, etc.), the presence of impurities can compromise their pleasantness. Furthermore, for raw oysters, it is also essential to have a good technique for opening the valves; this process is carried out using a special tool consisting of a drop-shaped steel blade (not sharpened) with a handle. Holding the oysters with one hand suitably protected by the characteristic metal glove, we proceed with the identification of the point where the two shells join. Right there, with energy, it will be necessary to insert the blade and force the opening of the valves using the lever of the instrument. ATTENTION! For the more inexperienced it is advisable to check that, during the opening phase, the shell splinters do not fall inside the mollusk . Once the oysters have been opened, it is then sufficient to season them with black pepper (or white, according to taste) and lemon juice; for some, a little caviar and / or a drop of extra virgin olive oil are also appreciated. olive oil; ABSOLUTELY avoid adding salt! The sea water contained inside the oysters, in fact, is already sufficient to give flavor to the dish.
Obviously, for raw consumption, the choice of a good and safe source of supply is crucial which, in addition to ensuring the freshness and organoleptic quality of the oysters, will guarantee the complete healthiness of the molluscs, protecting the consumer from food poisoning. Some examples of diseases that can be contracted by consuming contaminated raw oysters are: HAV viral hepatitis, cholera, fecal coliform gastroenteritis etc. Obviously, at the time of purchase, the oysters must be alive, therefore sealed, and give off a pleasant scent of the sea and fresh seaweed. If there is any doubt about the state of conservation, it is better to avoid them.
Sautéed oysters is an almost banal preparation; after having brushed them, fry them with oil and garlic, blending with white wine as soon as the shells start to open. From there, wait for it to completely hatch (less evident than that of clams or mussels) and add ground pepper and fresh parsley.
Nutritional values (per 100 g of edible portion)
Edible part
12.0%
Waterfall
85.7g
Proteins
10.2g
Prevailing amino acids
-
Limiting amino acid
-
Lipids TOT
0.9g
Saturated fatty acids
-mg
Monounsaturated fatty acids
-mg
Polyunsaturated fatty acids
-mg
Cholesterol
150.0mg
TOT Carbohydrates
5.4g
Glycogen
4.5g
Soluble sugars
0.9g
Dietary fiber
0.0g
Soluble fiber
0.0g
Insoluble fiber
0.0g
Power
69.0kcal
Sodium
510.0mg
Potassium
260.0mg
Iron
6.0mg
Football
186.0mg
Phosphorus
267.0mg
Thiamine
0.10mg
Riboflavin
0.20mg
Niacin
1.5mg
Vitamin A
75.0 µg
C vitamin
tr
Vitamin E
- mg
The au gratin oysters are prepared by opening the shellfish (as described above) and dirtying it on the surface with a "panure" flavored with extra virgin olive oil, pepper, fresh parsley and garlic. The addition of a little bottarga, capers, anchovies and cubes of fresh tomato is very pleasant. For some, a pinch of grated aged pecorino is not bad. It should be cooked in the oven (or salamander) at very high temperatures (> 200 ° C) to a few minutes (from 5 to 10).
Nutritional characteristics
Oysters are definable foods with low energy intake. Suitable for diet against overweight, however, they have a large limit to portions; this is due to the reduced digestibility of the food which, in case of excess, could be a reason for annoying adverse reactions (gastric cramps and vomiting, not to be confused with symptoms of a possible food poisoning). Oysters are therefore not suitable for feeding those suffering from digestive difficulties (eg hypo and hyperchlorhydria).
We also remind you that oysters are potentially allergenic foods and that their consumption is not recommended in: pregnancy, breastfeeding and early childhood.
It should also be remembered that oysters are molluscs capable of retaining high concentrations of sea water; this characteristic gives it a very high sodium content, an element potentially responsible for the onset or aggravation of arterial hypertension. Oysters are not suitable for a low-sodium diet, so they should be excluded from the diet for hypertension, which can only include them occasionally.
From the point of view of energy nutrients, oysters are distinguished by the prevalence of proteins (with a high biological value) compared to sugars (the latter present in a few grams of glycogen) and fats (of the three, the most deficient element).
Oysters are also high in cholesterol; this aspect occasionally contextualizes them in the diet of the healthy subject but precludes their use in the diet of those suffering from hypercholesterolemia.
As far as mineral salts are concerned, as well as sodium, oysters are very rich in iron (important for avoiding iron deficiency anemia especially in fertile women) and calcium (useful for bone metabolism especially in growing subjects and in the elderly).
From a vitamin point of view, oysters contain good concentrations of retinol equivalent (vitamin A). It is interesting to learn that in some types of oysters (eg Olimpia) good amounts of vitamin C have been found (38mg / 100g - not mentioned in the table).
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