"Rognoni" is the term commonly used to indicate the renal apparatus of the slaughtered animal (the most widespread are bovine); the kidneys are therefore offal, or a fraction of the beast grouped in the "fifth quarter".
The kidneys have a characteristic and proportional flavor to the old age of the animal of origin. The veal kidneys, for example, are those with the most delicate taste, while the beef or horse kidneys have a particularly strong taste.
This distinction originates from the fact that the kidneys are organs deputed to the filtration of the blood and to the concentration of the urine, therefore, the level of urea and other nitrogenous groups contained in them results extremely elevated but variable with the feeding; a young animal that feeds mainly on milk has a greater renal filtering than that of an adult beast, which results in a lower concentration of urine and urea contained in them.
|Nutritional composition of bovine kidney - Reference values of the INRAN Food Composition Tables|
Nutritional values (per 100 g of edible portion)
Kidneys are foods with excellent nutritional value, but it is also necessary to specify immediately that their use almost always leads to an excessive intake of cholesterol. Obviously, for those who suffer from diseases linked to the metabolism of this steroid lipid, eating kidneys systematically but periodically would not involve any blood decompensation; on the other hand, in the event that an excess of total cholesterol or LDL is present in the blood, the kidneys do not constitute an advisable food.
Kidneys are offal that contain few fatty acids (although mostly saturated), many proteins with high biological value and traces of sugars; the result is an extremely limited energy supply comparable to that of lean meats.
The kidneys bring almost all the mineral salts in quantities to say the least excellent; we particularly appreciate iron (lacking in anemic people), selenium and zinc (the latter have a high antioxidant power). Kidneys do NOT contain good doses of calcium, while phosphorus is appreciable; this is not a positive aspect since a chronic alteration of the relationship between calcium and phosphorus in the diet could lead to a worsening of bone metabolism.
From a vitamin point of view, kidneys are rich in water-soluble and fat-soluble molecules; among the fat-soluble, vitamin A (retinol) and vitamin D (calciferol, very rare) stand out, while among the water-soluble, excellent quantities of thiamine, riboflavin, niacin, biotin, etc. (or almost all the molecules belonging to group B) are highlighted.
Kidneys are foods with a medium purine content and therefore must be introduced in moderation in the diet against hyperuricemia.