Riyadh: Dr. Hassan Muhammad Sandakji
Clinical Nutrition sources report that one of the key elements in healthy eating is the method of cooking food with heat. And if one can choose healthy food products to eat, then it may become unhealthy as a result of the way he cooks. Doctors from the Mayo Clinic say: “Healthy cooking methods make food taste better and preserve the nutrients in foods without adding any excessive amounts of fat or salt. Healthy cooking does not mean that you have to become a good cook or cook in expensive cookware. You can use basic cooking techniques to prepare food in healthy ways. ”
The basis for this shift from healthy food to unhealthy cooking is the type of chemical reactions that took place during that process. This is because during the cooking process, many types of chemical reactions take place, which differ according to the quality and components of the food product and according to the method of cooking. One of them is the Maillard reaction, which Dr. Jean-Marie Lynn, Nobel Prize winner for chemistry in 1987 says: “The Maillard reaction (the reaction of food proteins and sugars by heat) is the most widespread chemical reaction in the world, because it is a reaction that occurs daily in homes, restaurants and bakeries. Around the world whenever food is cooked. ”
The British Royal Society of Chemistry says: “There are many reasons for cooking, including killing microbes in food to make it safe to eat, and a number of other reasons related to increasing food acceptability. This includes: improving the texture (by softening hard meats), improving color (for meat or toast) and improving flavor and aroma (such as developing the flavor and aroma of cooked meat). It is important to use the appropriate cooking conditions, such as temperature and cooking time. ” Also, as a result of the cooking process, the food becomes more suitable for the digestive system to carry out the processes of digestion and absorption of nutrients, especially the main components such as proteins, carbohydrates, fats, minerals, vitamins and other chemical compounds such as antioxidants and materials with aromatic and distinctive aromas and flavors.
Two main interactions
Since carbohydrates, sugars and proteins are present in most food products, there are two main types of chemical reactions during the thermal cooking process. These are: Caramelization reaction between types of sugars, and Maillard reaction between proteins and sugars. Both rely on heat (not enzymes) and produce many chemical compounds and volatile chemicals that give the characteristic shape, color and smell.
Caramel reactions are the basic process in cooking many plant foodstuffs, such as vegetables cooked on high heat, baked goods of all kinds, roasting coffee or nuts, or frying or many others. When the sugars are heated, the color changes to brown due to the polymerization processes in which several compounds combine with each other, then they turn into a liquid, and then bubbles appear. The bubble occurs due to the refraction of hydrogen and oxygen in the sugars, the formation of water molecules and their evaporation. During this the unique caramel aroma is shown by the volatiles that are released during pyrolysis, such as diacetyl.
In addition to the caramel reaction causing the golden brown color to appear when baking in the oven, the baked goods acquire that color and another distinct flavor, as a result of Maillard reactions between the proteins and starches of the flour dough. Maillard reactions begin to occur at low temperatures, that is, between 140 and 160 degrees Celsius, while caramel reactions require high temperatures to start. And the occurrence of these reactions in bread, for example, to release more antioxidants, and make it easier for the intestine to absorb them and increase the benefit of the body from them.
Vegetable discoloration. In raw vegetables, there is a large amount of gases confined in the small spaces between cells, which enables us to see the green chlorophyll compounds in the plant cell. In the beginning of the cooking process, the heat breaks down the cell membranes, which leads to gas leakage, and the flow of fluids from the plant cell into these spaces, giving us a clearer view of the shiny chlorophyll in the vegetables.
But as the cooking process continues, the excess heat causes the magnesium atom to separate from the center of the chlorophyll molecule, and to replace the hydrogen atoms with it. What changes the color of vegetables from light green to pale grayish green.
High temperatures also break down most of the vitamins and antioxidants in vegetables and excrete them into boiling liquid, which weakens their nutritional value.
But in return, heat can make some other food ingredients more easily absorbable, especially starch and plant proteins with tough molecules that our digestive system cannot break down raw so that they can be absorbed.
Pink shrimp and lobster. When shrimp and other marine crustaceans are cooked, three chemical processes occur: the appearance of pink, the change of the color of the meat from translucent to white, and the curl of the shrimp.
Shrimp and other crustaceans contain a pink pigment called astaxanthin, which is in the carotenoid class of antioxidants. And in raw shrimp, astaxanthin binds to a blue-gray crusty protein. No pink color. Upon heat cooking, astaxanthin is released from the crusty proteins and appears naturally in color, making the cooked shrimp pink.
“This change in color has been a mystery for a long time,” comments the Swiss researcher at the University of Basel, Dr. Thomas Sholomik. And raw shrimp meat is semi-transparent. When cooked, it changes color to white, as is the case with many other (white) fish and egg whites. This happens through “protein denaturation” reactions, because proteins are sensitive to heat, and they originally take on complex three-dimensional shapes, such as bending, screwing and wrinkling. But when it is heated to a sufficiently high temperature, reactions take place in which the complexities are dissolved and the color changes to white. The shrimp changed shape towards turning as small balls, as a result of the contraction of the muscles inside the shrimp due to the heat and the removal of their water content.
Types of frying
During the frying process, three main types of reactions take place: the Maillard reaction, the reactions of “denaturation” of protein to maturation, and the breakdown of cell walls. In addition to other chemical reactions, such as oxidation and polymerization, which take place in both: fried pieces and the oil used for frying. Frying depends on the use of fats, either from animal sources (margarine) or vegetable (oil), to cook foods of all kinds, because the oil reaches much higher temperatures than boiling water, which allows for a rapid number of reactions that cause foods to mature. As a result of the caramel and Maillard reactions, a crunchy layer is formed, and the penetration of heat leads to the exudation of cooking proteins.
And in deep frying, using a large amount of hot oil and immersing foods in it, a rapid and massive penetration of fats into the fried food pieces before the formation of chemical reactions that create a crunchy protective layer as a coating. This leads to two things; Decreased nutrients such as vitamins and minerals as a result of their leakage into the oil, and the amount of fat in fried pieces is about five times higher than what is already in them. Shallow frying uses a small amount of oil, which reduces the possibility of penetration. With rapid stirring, the food preserves many of its nutritional components, especially with the use of olive oil.
In addition to the sizzling sounds of frying, as a result of the rapid evaporation of water on the surface of the oil, the Royal British Council of Chemistry reports that protein-containing foods are particularly susceptible to sticking to metal pans, as a result of the formation of chemical bonds between food proteins and materials in the pan, especially strong bonds. The van der Waals Forces or Covalent Bonds. The powers of Van der Walls and the covalent bonds are both essential in the formation of proteins and the bonding of their parts, amino acids and peptide bonds with each other in order to be able to maintain their shape and function, and arise from the mutual effects between those parts as a result of electrical force interactions in them. .
With heat and a different metal, such as iron, the chance of instantaneous electrical polarization increases, which causes adhesion. This adhesion is followed by the loosening of the protein and collagen composition and the speed of Maillard reactions by increasing the effect of heat on the proteins, which leads to the formation of a layer of crunchy, brown, and relatively solid proteins. As adhesion continues and the Maillard reactions increase, a burning layer forms in the pan. This crunchy protein layer differs from the Patina layer. (The layer that sticks and colors the pan inside or outside it black) that occurs as a result of the reactions of fats with the very hot metal of the pan, the breaking of chains of hydrocarbons in long chain fatty acids, and the polymerization process to form a new solid and sticky substance And heat resistance, as a result of creating a longer chain of compounds compared to that of the original oil.
– Chemical reactions in cooking meat ingredients
> Meat is cooked in multiple ways; Including grilling in the oven or on hot coals, boiling either with hot water directly or on steam, and frying. The key to understanding the interactions of cooking meat and the occurrence of physical and chemical changes is to know the basic structures of meat.
Meat is muscle, and muscles are made up of muscle cells, connective tissue, fat and water.
And muscle cells contain proteins, including the pink protein myoglobin that gives red meat its color. The greater the movement of a muscle, the darker it becomes due to the accumulation of more myoglobin in it.
Connective tissue is strong, like the tendons and the thin shiny covering between the folds of meat. It consists of the protein elastin that contracts rapidly on rapid heating, and becomes non-chewable. There is a soft type of connective tissue that permeates meat structures called collagen. Upon cooking, it turns into gelatin and the composition of meat cuts loose. The longer and slowly cooked portions of meat rich in fiber and collagen, those fibers and meats become softer and more relaxed, and thus easier to chew and swallow.
Fats provide a lot of flavor in red meat, because they absorb and store many of the aromatic compounds found in animal food, especially when feeding the wild pastures. As animals age, muscle and connective tissue fibers become stiffer, and the fat accumulates a strong, unpalatable flavor.
Most of the liquid in the meat is water, and the red color in the meat and its juices is not due to blood, but is the protein myoglobin dissolved in the water, because most of the blood is discharged to a large extent in the slaughterhouse. If there is blood left, it will be a dark color and a clotted appearance.
While the meat is cooked, several chemical reactions take place, with the muscle proteins themselves and the connective tissues. With a temperature of 140 degrees Celsius when grilling, Maillard reactions between proteins and sugars are produced, and hundreds of new chemical compounds are produced that give the meat a brown color and give it the distinct flavor and flavor. The important thing is not to reach the state of carbon burn. Reactions of “protein denaturation” also take place for the maturation of proteins.
In smoked meats, the pink color appears just below the surface, caused by the effects of gases in the smoke that maintain the color of myoglobin. This pink color differs from the pink color in the inside and the middle of the grilled meat cuts due to the incomplete cooking of it.
It should be noted that the meat is a poor conductor of heat, so the shell of a piece of meat can be cooked, while the inside or the parts attached to the bone remain raw. Therefore, the best way to cook meat is with low heat and slow for a long time. This greatly reduces the formation of harmful chemicals, including carcinogens.
The muscle meat of fish differs because it lives in a practically weightless environment. Specifically, fish muscles contain very little connective tissue, there is not much collagen to hydrate the muscle fibers, and the amount of myoglobin is low. Therefore, the color of fish is mostly white, while the color of fish that swim long distances is darker and sometimes red.