The skills of handling ingredients and the precautions in the kitchen should be related to chemistry.

I. Seasoning articles 1. When cooking, putting some salt in hot oil will cause a chemical reaction, which is harmful to health. Studies have shown that traditional cooking methods do great damage to the nutrition of food: at the high temperature of 200℃, unsaturated fatty acids beneficial to human body in edible oil are oxidized, and at the same time, the production of acrolein will lead to the formation of carcinogenic peroxides, 50% of iodine in salt will be volatilized, and vitamins in food will be oxidized, resulting in a large loss of nutrients in food. Experts pointed out that one of the nutritional damages to food by cooking methods such as frying and frying is to volatilize iodine in salt, so that the iodine content in iodized salt is different from the actual intake of human body. Because the oil temperature required for frying is very high, about 180℃. Iodine is a chemically active element and will volatilize at high temperature. Therefore, the loss rate of iodine in fried salt at high temperature can reach 40%-50%. Therefore, if we don't change our cooking habits, even if we vigorously promote iodized salt, people still can't get enough intake. Experts suggest not to use iodized salt to explode the pot when cooking, and try to add salt when the dish is ready to go out. 2. Salt is used as seasoning in food industry because human beings have a strong physiological demand for salty taste, and sodium chloride is also the main component to maintain osmotic pressure balance in human body. People can live without sugar, it is difficult to live without salt, limbs are weak, and there will be indigestion, mental disorder and even death. In addition, salt can be used as a preservative in food processing. Pickled fish, meat and vegetables are one of the traditional food processing methods in China, which can not only preserve corrosion, but also make delicious food. Because salt has osmotic effect, it can dehydrate meat and vegetables, and it can also make the water in bacterial cells seep out and die, thus playing an antiseptic role. Animal husbandry is also inseparable from salt. A cow needs 30 ~ 40g of salt every day, and a horse needs 10 ~ 15g of salt every day. Eating salt can make livestock gain weight, keep fit, resist cold and stand hard, and prevent diseases. Salt is often used for salting-out in soap making and dye industry, chlorination and roasting in mining industry; Surface treatment of steel; Fur preservation in leather industry: preparation of colored glaze in kiln industry: acid clay becomes active clay; Or emery made of quartz sand and coke. Use salt. 2. The common sugar in the market is sucrose formed by the combination of two sugar rings. Sugar can provide energy. Dessert is very important in our diet. In prehistoric times, people had to consume enough energy to hunt and support their families, so we were quite adapted to and liked sweets. Refined sugar was quite expensive when it first came into the market, but now sugar is very cheap. We even eat too much sugar, which is harmful to our health. Sugar has many uses in the kitchen. Besides making food taste sweet, we also add sugar to many Chinese dishes. Sugar molecules can connect protein together, so it is much easier to mix protein into the sweet egg pie and make milk egg paste. 2. With the development of fresh-keeping industry and technology, the processing of aquatic products has developed from simple primary processed products such as fresh, frozen, dried and salt to various deep-processed products suitable for modern lifestyles. The technology is more complex, the equipment and packaging are more modern and perfect, and the requirements for product safety and hygiene are correspondingly higher. Therefore, a new preservation technology-chemical preservation came into being. Chemical preservation is a fresh-keeping method by adding chemicals harmless to human body to aquatic products to prolong the fresh-keeping time and maintain the quality. Such as salting, sugar stains, acid bubbles, smoking, etc. Hygiene and safety are the most concerned issues in the use of chemical preservatives. There are also some sugar, salt, organic acids, alcohol and so on. It is harmless or less harmful to human body. These are all daily necessities. Smoking and adding nitrate, which used to be commonly used, are used less and less now because they are suspected of causing cancer. Some chemicals, such as benzoic acid, formaldehyde and boric acid, can also be used to keep aquatic products fresh, but they are toxic and harmful to people and cannot be thoroughly treated before eating, so they cannot be used now. There are many kinds of food additives used for preservation, and their physical and chemical properties and preservation principles are also different. Some of them inhibit bacteria, some change the environment, and some resist oxidation. Therefore, we must choose food additives that meet the national hygiene standards to ensure the health of consumers. At present, the chemical preservation methods used in aquatic products processing industry in China include food additives (preservatives, fungicides and antioxidants), antibiotics, wine storage, salt storage and smoking, among which food additives are particularly common. Broadly speaking, chemicals that can inhibit or kill microorganisms can be called preservatives. Their principle of action is to control the physiological activities of microorganisms and slow down or stop their development. Bactericide is a chemical substance that can effectively kill microorganisms in food, which can be divided into two categories: oxidation type and reduction type. Antioxidants are substances that can prevent or delay the oxidative deterioration of food. There are many kinds of antioxidants with different mechanisms of action. Some of them consume oxygen in the environment to preserve quality, some act as hydrogen or electron donors to block the chain reaction of automatic oxidation of food, and some inhibit oxidation activity to achieve antioxidant effect. No matter what kind of preservation method is adopted, a good preservative should have unique properties in moisturizing, preservation, color retention, quality improvement and safety. Specifically, the advantages and disadvantages of aquatic products preservatives can be tested from the following aspects. A good foaming preservative can significantly reduce the weight loss of products during processing, freezing and cooking, keep moisture and prevent products from losing water during shelf, freezing and cooking. Secondly, it is a preservative with good freshness, elasticity and flavor of fish products. Through emulsification and chelation, emulsified chelation state can be formed between product molecules, water molecules and meat molecules, thus improving the freshness, elasticity and flavor of products. 3. The antistaling agent with good fish color can form an antioxidant protective film on the surface of aquatic products, effectively maintain the freshness of frozen aquatic products, prevent the loss of water and nutrients during storage, inhibit the growth of microorganisms, and make the food stable in color, beautiful in appearance and delicious in taste. Third, cooking 1. The order of adding condiments is based on the strength of penetration. Strong permeability is strong after. When cooking, put sugar first, then add salt, vinegar, soy sauce and monosodium glutamate. If the order is reversed, put salt first, which will hinder the diffusion of sugar. Because salt has dehydration effect, it will promote protein solidification, make the surface of food hard and tough, and the sweetness of sugar is difficult to penetrate. There are also individual principles, that is, odorless spices (such as salt and sugar) can be heated for a long time when cooking, while scented spices can't, so as to avoid the fragrance escaping. The main component of monosodium glutamate is sodium glutamate, which can't stand the high temperature of cooking and can only be added at the end. When cooking food, the time of adding seasoning is also related to the chemical changes in food. Protein in food itself has the nature of colloid, which will condense when it meets strong electrolytes such as sodium chloride. For example, soy milk with salt will condense into tofu brain. If salt is added too early when cooking beans and burning meat, there is salt in the noodle soup, so it is difficult for water to penetrate into beans or meat; On the other hand, salt makes protein in bean meat coagulate and harden. These two aspects make it difficult to cook beans or meat, and of course it is not conducive to human digestion and absorption. Cooking time, that is, temperature, has a great influence on food. Generally speaking, increasing the temperature can speed up the reaction. For example, the temperature of stewing food is about 100 degrees (boiling point of water), and the temperature of frying is about 200 to 300 degrees (boiling point of oil is higher than water). The temperature of frying oil is slightly lower than that of frying, but much higher than that of stewing. Therefore, it takes several times more time to cook and simmer the meat than to fry it, and the temperature in the pot is also related to mixing and frying. Stir-frying can make food heated evenly, but excessive stir-frying will reduce the temperature in the pot, increase the chance of food contacting with oxygen in the air, and make vitamin C in food easy to be destroyed by oxidation. Therefore, the pot cover must be added after cooking. First, it can prevent the pot temperature from decreasing. Second, it can prevent vitamin oxidation and reduce nutritional value. Many families like to add some wine when cooking fish. What do you think this is? There is more trimethylamine in dead fish, so the longer the fish dies, the stronger the smell. Trimethylamine is insoluble in water and soluble in alcohol, so adding wine when cooking fish can remove the fishy smell and make the fish taste better. Wine can remove the fishy smell of fish and meat; The role of wine is not limited to this. When cooking, the fat in food will be partially hydrolyzed to produce acid and alcohol. When wine (containing ethanol), vinegar (containing acetic acid) and other seasoning accessories are added, acid and alcohol undergo esterification reaction to form aromatic esters. Maybe mom once told you not to put the salt too early when cooking beans, otherwise the beans won't go bad. This sentence is of great chemical significance. Don't soybeans get "fat" when they are soaked in clear water? This is actually a kind of infiltration phenomenon. Because there is little water in dried soybean, we can regard it as a concentrated solution, and the skin of soybean is equivalent to a semi-permeable membrane. When soybeans are soaked in clean water and cooked, infiltration will occur. Therefore, water molecules in clean water enter soybeans through the skin, making soybeans obese. Only when soybeans are fully soaked and cooked for a period of time will the cells of soybeans be broken and the beans be cooked. If you add salt too early when cooking beans, soybeans will be soaked in salt water, because the concentration of salt water is much stronger than that of clear water, so it is difficult for water to penetrate into soybeans again. If more salt is added, the concentration of brine may even exceed that in soybeans. In this way, water not only can't get in, but may even "drill out" from slightly fat soybeans. There is not enough moisture in soybeans, so it is no wonder that soybeans should be cooked thoroughly. Similarly, when cooking mung bean soup and red bean soup, don't put sugar too early; When cooking pork and beef, don't add salt too early to avoid easy boiling. 3. There are several simple methods to remove pesticide residues in vegetables and fruits at home: soaking and washing: the main pollutants in vegetables are organophosphorus pesticides, which are insoluble in water. This method can only remove some contaminated pesticides. But water washing is the basic method to remove other pollutants and residual pesticides in vegetables and fruits. Mainly used in leafy vegetables, such as spinach, day lily, leek flower, lettuce, Chinese cabbage and so on. Generally, the dirt on the surface should be washed off with water first, and then soaked in clear water for not less than 10 minute. Fruit and vegetable cleaning agent can increase the dissolution of pesticides, so a small amount of fruit and vegetable cleaning agent can be added during soaking. Rinse with running water for 2-3 times after soaking. Peeling method: There are relatively many pesticides on the surface of vegetables and fruits, so peeling is a good way to remove residual pesticides. Can be used for apples, pears, kiwis, cucumbers, carrots, white gourd, pumpkins, zucchini, eggplant, radishes, etc. When processing, it is necessary to prevent mixed pollution of peeled vegetables and fruits again. Storage method: pesticides will slowly decompose into harmless substances in the environment over time. Therefore, fruits and vegetables that are easy to preserve can be preserved for a certain period of time with less pesticide residues. Suitable for apple, kiwi, wax gourd and other non-perishable varieties. Generally stored 15 days or more. At the same time, it is suggested that the newly picked fruits should not be peeled and eaten immediately. Heating method: the decomposition of carbamate pesticides is accelerated with the increase of temperature. Therefore, some vegetables and fruits that are difficult to treat by other methods can be heated to remove some pesticides. Commonly used in celery, spinach, Chinese cabbage, cabbage, green pepper, cauliflower, beans and so on. Clean the dirt on the surface with clear water, put it in boiling water for 2-5 minutes, and then rinse it with clear water 1-2 times. The significance of this research-based learning lies in: ① getting the experience of participating in the exploration and research in person; ② Cultivate the ability to find and solve problems; ③ Cultivate the ability of collecting, analyzing and utilizing information; ④ Learn to share and cooperate; ⑤ Cultivate scientific attitude and morality :⑤Stimulate our initiative and innovative consciousness, and urge us to take the initiative to learn, so that the process of acquiring chemical knowledge and skills becomes a process of understanding chemistry, conducting scientific inquiry, connecting with social life reality and forming scientific values. "Research-based learning" is like a spring breeze, which brings vitality and vigor to the boring traditional teaching, so that we can be close to life in learning and understand knowledge in life. I hope I can help you!