Introduction: How can we cook food to be not only beautiful in color, aroma, taste, shape, and texture, and harmless, but also easily absorbed, beneficial to health, and strengthening to the body? First, we should understand at least the following changes that occur in food during the heating process:
Dispersion In raw vegetables, there is a large amount of pectin between cells. When heated, the pectin dissolves, and the cytoplasm and cell membrane denature due to heat, increasing the cell's permeability. Water and inorganic salts inside the cells seep out, and the connections between cells are destroyed. We can see that the vegetables change from being crisp to wilted, and the water inside the vegetables turns into soup. When starchy foods like potatoes and sweet potatoes are heated in water for a long time, the starch grains absorb water and swell, becoming soft, and even undergoing gelatinization.
Hydrolysis When food is heated with water, the large molecular structures in the food are broken down into smaller molecular structures by water, which are more easily absorbed and digested by the human digestive tract. For example, when fish, meat, and poultry are heated in water, some of the protein is broken down into peptides and then further hydrolyzed into various amino acids. The reason broth becomes savory is due to the appearance of free amino acids. Different foods have different umami and flavors, mainly because they break down into different amino acids.
Coagulation Any animal or plant cell is composed with the participation of protein. When heated, protein denatures and coagulates, and the coagulated protein is easily digested and absorbed. The most obvious example is a cooked egg.
Esterification When cooking animal fats, adding alcohol quickly produces some ester substances with special aromas. Lard, tallow, mutton fat, and chicken fat have different aromas. Using different wines will also produce different aromas, which is also one of the reasons for the formation of different flavors.
Oxidation-Reduction The rapid change in the color of food after heating is a manifestation of an oxidation-reduction reaction. For example, the muscle tissue of animals contains myoglobin, which is blood-red when raw. When heated to 56°C, the myoglobin denatures and coagulates, and the heme is simultaneously oxidized into denatured myoglobin, appearing light gray or brownish-gray. The longer the cooking time, the more obvious the denaturation, and finally it is hydrolyzed into broth. As free amino acids increase, the broth becomes more savory. Some vitamins in food, such as vitamin C, are easily destroyed when heated, especially with the intervention of salt and alkali, which accelerates the oxidation-reduction reaction.
Relatively speaking, the loss of fat-soluble vitamins is slightly less than that of water-soluble vitamins. Most of the chlorophyll in vegetables is also destroyed by high temperatures, so the heating time of food should not be too long, and it is not advisable to add alkali. Adding seasonings too early should also be avoided to reduce the loss of certain vitamins.
Destruction of Activity Generally, enzymes can only exert their optimal activity at a suitable temperature (30°C to 40°C). When the temperature reaches 40°C, their activity is inhibited, and at 60°C, it will cause enzyme inactivation. When protein is heated with sugar, it can produce some amino acids, aldehydes, and other compounds, thus generating some aroma, and its color can also be visually appealing. These carbonized sugars can also absorb some toxic gases in the intestines.
Other Effects The physicochemical reactions that occur during the heating of food are very complex. Today's research often lags behind practical needs, and many cooking and processing techniques are harmful and must be improved in a timely manner.
From a health perspective, we recommend choosing more raw food, cold salads, steaming, stewing, and simmering cooking methods, provided the food is not contaminated, to ensure basic nutrient absorption and improve physical health.