1. Chemistry in the kitchen The kitchen is like a science laboratory. Don’t think that chemicals in the kitchen are only found in the sink. The ingredients you cook with are themselves made up of chemical compounds—some of them complex, and some of them quite simple. Why should we care about kitchen chemistry? Now that people's living standards have improved, they should pay attention to healthy and balanced diet. The body is the capital of revolution. In order to work and study better, we must pay more attention to our physical health and pay attention to the chemistry in the kitchen. In the process of this research study, our research group studied food cooking, food preservation, techniques for using condiments, precautions in the kitchen, ways to maintain the original nutrients of food, and techniques for handling ingredients. and so on have been explored. Based on the chemical knowledge we usually learn and the common sense of life we ??have accumulated, we combine theory with practice and further understand a lot of knowledge that we never knew before. Also realize how important chemistry is in the kitchen. We do this topic simply to hope that friends will pay attention to chemistry in the kitchen and chemistry in life, so that we can reduce harm, maintain nutrition, and improve health. 1. Chemistry in the Kitchen --- Condiments 1. When cooking, adding some salt when the oil is hot will cause a chemical reaction, which is harmful to the body. Research shows that traditional cooking methods have great damage to the nutrition of food: at high temperatures of 200°C, the unsaturated fatty acids contained in edible oil that are beneficial to the human body are oxidized, and "acrolein" is produced, which can cause cancer. The production of peroxides, 50% of the iodine in table salt will evaporate, and the oxidation of vitamins in food, etc. will cause a huge loss of nutrients in food. Experts point out that one of the nutritional damages caused by cooking methods such as frying and deep-frying is that the iodine in the salt volatilizes, making the amount of iodine in iodized salt different from the amount actually consumed by the human body. Because the oil temperature required for frying and deep-frying is very high, about 180°C. Iodine is a chemically active element that is easily volatile at high temperatures. Therefore, the loss rate of iodine in salt that has been fried at high temperatures can reach 40%-50%. Therefore, without changing cooking habits, even if iodized salt is vigorously promoted, people will still not be able to achieve adequate intake. Experts recommend not using iodized salt when cooking. Try to add salt when the dishes are about to come out of the pot. 2. Salt is used as a condiment in the food industry because humans have a strong physiological need for salty taste, and sodium chloride is also the main component that maintains the osmotic pressure balance in the human body. People can still live without sugar, but it is very difficult to live without salt. The limbs will be weak, indigestion, mental disorder, and even death. In addition, in food processing, salt can be used as a preservative. Pickled fish, pickled meat, and pickled vegetables are one of my country's traditional food processing methods, which not only prevents spoilage, but also produces delicious food. Because table salt has an osmotic effect, it can dehydrate meat and vegetables, and can also cause water in bacterial cells to leak out and die, thus acting as a preservative. Animal husbandry is also inseparable from salt. A cow needs 30-40g of salt a day and a horse needs 10-15g of salt a day. Livestock that eat salt can gain weight, become stronger, endure cold and hard work, and prevent diseases. 2. Salt is often used for salt precipitation in the soap making and dye industries, chlorination and roasting in the mining industry; surface treatment of steel; fur preservation in the leather industry; preparation of colored glazes in the kiln industry; acidic clay to become activated clay; or the use of quartz Salt is used to make emery from sand and coke. 2. Common sugars on the market are sucrose formed by two sugar rings bonded together. Sugar provides energy. Desserts are very important in our diet. In prehistoric times, people had to consume enough energy to hunt and feed their families, so we were quite adaptable and fond of sweet foods. Refined sugar was quite expensive when it first became available, but now sugar is very cheap. We even eat too much sugar – which is bad for our health. Sugar has many uses in the kitchen. In addition to making food taste sweet, we also add sugar to many Chinese dishes. Sugar molecules hold proteins together - making whipping them into meringue pies and making custards much easier. 2. Chemistry in the Kitchen - Fresh Preservation The development of industry and science and technology has enabled the processing of aquatic products to develop from simple primary processing products such as fresh, frozen, dried and salted in the past to a variety of products suitable for modern lifestyles. Various deep-processed products have more complex processes, more modern and complete equipment and packaging, and correspondingly higher requirements for product safety and hygiene. As a result, a new type of preservation technology - chemical preservation came into being.

3. Chemical preservation is a preservation method that adds chemicals that are harmless to the human body to aquatic products to extend the preservation time and maintain quality. Such as salted, candied, pickled and smoked. The most concerning issue when using chemical preservatives is hygiene and safety. Chemical preservatives include sugar, salt, organic acids, alcohol, etc. that are harmless or less harmful to the human body. These are commonly used products in daily life. The fuming method and nitrate addition method that were commonly used in the past are now used less and less because they are suspected to be carcinogenic. There are also some chemicals such as benzoic acid, formaldehyde, boric acid, etc. that can also be used to preserve aquatic products, but they are toxic and harmful to people, and they cannot be completely processed before consumption, 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 inhibit bacteria, some change the environment, and some are antioxidants. Therefore, we must choose food additives that comply with national health standards to ensure the health of consumers.

4. 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 the development of microorganisms. Bactericides are chemical substances that can effectively kill microorganisms in food. They are divided into two categories: oxidizing type and reducing type. Antioxidants are substances that prevent or delay the oxidative deterioration of food. There are many types of antioxidants, and their mechanisms are also different. Some consume oxygen in the environment to protect its quality, and some act as hydrogen or electron donors to block the automatic oxidation of food. Chain reactions, and some inhibit oxidative activity to achieve antioxidant effects.

5. No matter what preservation method is used, a good preservative should have unique properties in maintaining moisture, freshness, color retention, quality improvement and safety. Specifically, the advantages and disadvantages of aquatic product preservatives can be tested from the following aspects.

See that preservatives with good foaming properties can significantly reduce the weight loss of products during processing, freezing, cooking, etc., maintain moisture, and prevent product moisture loss during shelf, freezing, and cooking processes.

Look at the freshness, elasticity and flavor of the fish. The preservatives can form an emulsification and chelation state between the product molecules, water molecules and meat molecules through emulsification and chelation, thereby improving the freshness and tenderness of the product. , elasticity and flavor.

Look at the good color of fish. Preservatives can form an antioxidant protective film on the surface of aquatic products, which can effectively maintain the freshness of frozen aquatic products, prevent the loss of water and nutrients during storage, and inhibit microorganisms. The growth makes the food stable in color, beautiful in appearance and delicious in taste. 3. Chemistry in the Kitchen - Cooking Skills 1. The order in which condiments are added is based on the strength of the penetration. Strong penetration. When cooking, sugar should be added first, followed by salt, vinegar, soy sauce, and finally MSG. If the order is reversed and the salt is put first, it will hinder the diffusion of sugar. Because salt has a dehydrating effect, it will cause the protein to coagulate, making the surface of the food hard and tough, making it difficult for the sweetness of the sugar to penetrate. There are also some general principles. Spices without fragrance (such as salt, sugar, etc.) can be heated for a long time during cooking, but spices with fragrance cannot be heated to prevent the fragrance from escaping. The main component of MSG is sodium glutamate, which cannot be tolerated. Cook at high heat and only add at the end.

6. When cooking food, the time of adding condiments is also related to the chemical changes that occur in the food. The protein in food itself has colloidal properties and will agglomerate when exposed to strong electrolytes such as sodium chloride. For example, if salt is added to soy milk, it will condense and become tofu curd. When cooking beans or roasting meat, if you add salt too early, on the one hand, there will be salt in the soup, and it will be difficult for the water to penetrate into the beans or meat; on the other hand, it will be difficult for the water to penetrate into the beans or meat; On the one hand, the salt causes the protein in the soybean meat to condense and harden. Both of these aspects make it difficult for beans or meat to be cooked, and are certainly not conducive to human digestion and absorption.

7. The heat of cooking food, that is, the temperature, has a great influence on food. Generally speaking, increasing the temperature can speed up the reaction speed. For example: the temperature of stewing food is about 100 degrees (the boiling point of water), the temperature of stir-frying is about 200 to 300 degrees (the boiling point of oil is higher than water), the temperature of stir-frying is slightly lower than that of frying, but it is better than stewing. The temperature is much higher. Therefore, the time required to cook and simmer the meat until tender is several times longer than that of stir-frying or deep-frying. The temperature in the pot is also related to the stir-frying. Stir-frying can heat the food evenly, but over-stirring will lower the temperature in the pot. If you stir-fry too much, the chances of the food coming into contact with oxygen in the air will increase, and the vitamin C in the food will be easily oxidized and destroyed. Therefore, it is necessary to add a lid to the pot after stir-frying. Firstly, it can prevent the pot temperature from lowering, and secondly, it can prevent vitamins from oxidizing and reducing the nutritional value.

8. Many families like to add some wine when cooking fish. Do you know what this means? There is more trimethylamine in dead fish, so the longer the fish is dead, the stronger the fishy smell. Trimethylamine is not easily soluble in water, but is easily soluble in alcohol, so adding some wine when cooking fish can remove the fishy smell and make the fish more delicious. Wine can remove the fishy smell of fish and meat; the function of wine is not limited to this. When the fat in food is cooked, it will be partially hydrolyzed to generate acid and alcohol. When seasoning excipients such as wine (containing ethanol) and vinegar (containing acetic acid) are added, the acid and alcohol undergo an esterification reaction with each other to form an aromatic ester. 2. Maybe your mother once told you that when cooking beans, don’t put the salt too early, otherwise the beans will not be cooked properly. This sentence makes a lot of sense in chemistry. When soybeans are soaked in clear water, don't they slowly become "fat"? This is actually a penetration phenomenon. Because there is very little water in dry soybeans, we can think of it as a concentrated solution, and the skin on the outside of the soybeans is equivalent to a semipermeable membrane. When the soybeans are immersed in water and boiled, it will The result of osmosis phenomenon is that the water molecules in the clear water pass through the soybean skin and enter the soybeans, making the soybeans fatter. Only after the soybeans are fully soaked and cooked for a period of time will the cells of the soybeans burst, causing the beans to become rotten. If the salt is added too early when cooking beans, the soybeans will be immersed in salt water. Since the concentration of salt water is much thicker than that of clean water, it will be difficult for the water to penetrate into the soybeans.

If more salt is added, the concentration of salt water may even exceed the concentration in the soybeans. In this way, water will not only be unable to enter, but may even "drill" out of the slightly fatter soybeans. There will not be enough water in the soybeans. , no wonder the soybeans are boiled over and over again. In the same way, when cooking mung bean soup and adzuki bean soup, do not add sugar too early; when cooking pork or beef, do not add salt too early to avoid overcooking. 3. Simple methods for removing pesticide residues on vegetables and fruits at home include the following: Soaking and washing method: The main types of pesticides contaminated by vegetables are organophosphorus pesticides. Organophosphorus pesticides are difficult to dissolve in water. This method Only partially contaminated pesticides can be removed. But washing is the basic method for removing other dirt and residual pesticides on fruits and vegetables. Mainly used for leafy vegetables, such as spinach, daylily, leek flowers, lettuce, Chinese cabbage, etc. Generally, rinse the surface dirt with water first, and then soak it in clean water for no less than 10 minutes. Fruit and vegetable cleaning agents can increase the dissolution of pesticides, so a small amount of fruit and vegetable cleaning agents can be added during soaking. After soaking, rinse with running water 2-3 times. Peeling method: There are relatively large amounts of pesticides on the surface of vegetables and fruits, so peeling is a better method to remove residual pesticides. Can be used on apples, pears, kiwis, cucumbers, carrots, winter melons, pumpkins, zucchini, eggplants, radishes, etc. When handling, prevent peeled vegetables and fruits from being mixed together and causing contamination again. Storage method: Pesticides can slowly decompose into substances harmless to the human body over time in the environment. Therefore, fruits and vegetables that are easy to preserve can be stored for a certain period of time with less pesticide residue. Suitable for apples, kiwis, winter melons and other non-perishable varieties. Generally stored for more than 15 days. It is also recommended not to eat freshly picked unpeeled fruits immediately. Heating method: Carbamate pesticides decompose faster as the temperature increases. Therefore, some pesticides can be removed by heating some vegetables and fruits that are difficult to treat with other methods. Commonly used in celery, spinach, bok choy, cabbage, green peppers, cauliflower, beans, etc. First, wash the surface dirt with clean water, put it in boiling water for 2-5 minutes, remove it, and then rinse it with clean water 1-2 times. The significance of this research study is: ① Gain the experience of personally participating in exploratory research; ② Cultivate the ability to discover and solve problems; ③ Cultivate the ability to collect, analyze and utilize information; ④ Learn to share and cooperate; ⑤ Cultivate a scientific attitude and ethics: ⑥ Stimulate our initiative and sense of innovation, prompt us to take the initiative to learn, so that the process of acquiring chemical knowledge and skills also becomes a process of understanding chemistry, conducting scientific inquiry, connecting with the reality of social life, and forming scientific values. "Research-based learning" is like a ray of spring breeze, bringing vitality and vitality to the dull traditional teaching, allowing us to get closer to life in learning and understand knowledge in life.