Foods are cooked to positively change some of their characteristics such as digestibility .
In fact, cooking determines processes similar to digestive ones, transforming complex chemicals into simpler ones. The starch contained in cereals, if subjected to a heat source, can for example partially transform into simpler sugars (the glycemic index increases with cooking).
Effects of cooking:
Edibility: nature is rich in products such as beans, peas, potatoes which, despite having a pleasant taste and a good nutritional value, contain anti-nutritional factors that would prevent their use in food. Many of these factors are rendered inactive with cooking.
Hygienicity A microbial load is always present in foods, which fortunately is mostly broken down by heat treatments. Keep in mind, however, that some microorganisms produce heat-stable toxic substances (toxins).
Enzymatic activity The enzymes contained in food provide for their natural degradation making them inedible. With cooking the enzymes are inactivated and the enzymatic processes blocked.
Changes in color - some vegetables turn yellow due to the action of acid substances present. To counteract this effect, there are those who add baking soda to the water. This practice negatively affects some vitamins. To reduce yellowing, just add a little cooking salt.
Changes in carbohydrates
Starch is the main food carbohydrate (cereals, legumes, potatoes, etc.). With heat, the starch granules pass into the cooking water, which takes on the characteristic sticky appearance. The presence of acid substances limits this phenomenon (if you want to obtain rice with well-separated grains, just add vinegar or lemon to the water). If the heating occurs at a very high and dry temperature, the starch turns into smaller molecules (dextrins), darkens and develops particularly pleasant smells (baked goods, such as bread, biscuits, etc.). The formation of dextrins makes the food more digestible.
Even the simplest sugars undergo transformations (sucrose is transformed into caramel). In the presence of proteins, simple sugars react with them to form brown products that can no longer be used by the body (decrease in nutritional value). A phenomenon of this type is the Maillard reaction (for example when baking bread) between glucose and lysine.
Lipid modifications
Responsible factors are temperature and oxygen in the air. The phenomena that occur affect both the lipids contained in the food and those added as a condiment.
Breaking of triglyceride molecules: free fatty acids and glycerine are formed; the glycerin, in part, turns into a toxic substance called acrolein: the fat becomes dark, foam and produces irritating fumes. The temperature at which the development of fumes begins is defined as a smoke point and corresponds to the onset of fat decomposition. Lard and butter have lower smoke points than those of many other condiments, so it is not advisable to use them as frying fats. It is not recommended to use the same oil for frying several times. The most suitable oil for frying is extra virgin olive oil, followed by peanut oil.
Polymerization phenomena: reactions in which many molecules join together to form macromolecules that determine an increase in fat viscosity and a decrease in digestibility.
Autoxidation and rancidity phenomena: due to the reaction between the unsaturated fatty acids present in the fat and the oxygen in the air (unpleasant and harmful odors and flavors).
Protein modifications
Cooking does not cause significant reductions in the nutritional value of proteins but leads to an increase in their digestibility. However, over-prolonged cooking can lead to less availability of some essential AAs such as cysteine, tryptophan, methionine, lysine.
If the cooking of protein-rich foods is carried out in an acidic environment (eg presence of vinegar, lemon and tomato sauce) there are similar changes to those obtained with digestion (formation of smaller molecules).
A transformation reaction that reduces the nutritional value of proteins is that between proteins and sugars (Maillard reaction). Negative phenomena occur when cooking, especially roasting, is prolonged so as to decrease the ability of proteins to bind water; it follows a more difficult action on the part of gastric juices (less digestibility).
Boiling determines the passage of soluble proteins in the water with loss of nutritional value if the broth is not used.
- if the protein food is introduced into the already boiling water, the high temp causes coagulation of the surface proteins with protection of the soluble ones that are inside the mass; it follows a good boiled meat and a poor broth;
- if the piece of meat is immersed in cold unsalted water, as the heating proceeds, the soluble proteins pass into the cooking liquid which becomes richer; so you have a good broth and a bad boiled.
Meat and fish contain a fair amount of creatine, but a good percentage is lost during cooking.
Changes in vitamins and mineral salts
If the cooking operations are not carried out properly, even considerable losses of vitamins can be registered due to their poor stability (in relation to heat, light, oxygen, acidifying or alkalizing substances).
Mineral salt losses are due to their high solubility in the cooking water.
When the foods are boiled, the loss of vitamins and mineral salts is greater if too much cooking liquid is used, if they are too chopped up and if the boiling lasts a long time; with the same cooking system, losses vary from one product to another depending on the acidity and presence of natural antioxidant substances.
To give an order of magnitude of the losses, referring to iron, we can say that in vegetable products the content of this element decreases by about 15% for cooking with a lot of water and about 10% for steaming (without water).
