Sulfur in daily life


Eggs will smell bad if left for a long time. This is because hydrogen sulfide is produced in the eggs. Hydrogen sulfide is an inorganic compound that is highly toxic. It is a flammable acidic gas under standard conditions and has a sulfur smell at low concentrations. Hydrogen sulfide is the result of a chemical reaction between sulfur-containing organic matter, which means there is sulfur in the egg. So, where is the sulfur in eggs?

Besides water, the most abundant substance in eggs is protein. Proteins are biological macromolecules, composed of thousands of amino acids. There are generally only more than 20 types of amino acids, including methionine and cysteine. Methionine is also called methionine or methionine, that is, there is an amino group and a methylthio group on butyric acid, that is to say, there is a sulfur atom in methionine. Cysteine is also an important sulfur-containing amino acid. Since the chemical substances that make up higher animals are basically similar, methionine and cysteine are also important components of human protein.

Among the more than 20 amino acids that make up proteins, 9 cannot be synthesized by the human body and must be obtained from food. We call them essential amino acids. Methionine is an essential amino acid for the human body, and cysteine can be converted from methionine in the human body. The methionine content in meat, eggs, and milk is relatively rich, and the ratio of various amino acids required by the human body is consistent, so we should consume a certain amount of meat, eggs, and milk every day.

Protein is the essential material basis of human life. It is composed of a variety of different amino acids. These amino acids have a certain spatial structure. They must be "folded" into a certain shape at a certain position and in a certain method. During folding, groups on different amino acids also interact, and when the sulfhydryl groups on two amino acids are close to each other, a disulfide bond may be formed. Disulfide bonds are relatively stable covalent bonds that play a role in stabilizing the spatial structure of the peptide chain in protein molecules. The greater the number of disulfide bonds, the greater the stability of the protein molecule against the influence of external factors. Disulfide bonds cause the peptide chain to fold into structures and shapes that are not easy to spread out. Therefore, sulfur plays a very important role in the process of forming proteins, which also makes every cell in our body contain sulfur.

There is also an important sulfur-containing amino acid in the human body - taurine. Although taurine is not a component of protein, it is free in certain organs of the human body, such as the brain, liver, and eyes. Taurine has a very wide range of physiological functions, and it plays a particularly important role in the growth of the baby's brain and nervous tissue.

Thiamine, or vitamin B1, is a sulfur-containing water-soluble vitamin that actively participates in the body's sugar metabolism process. Animal muscle tissue, eggs, and the outer skin and germ of plant seeds (such as rice bran and bran) are rich in vitamin B1. In addition, yeast is also rich in vitamin B1.

Sulfur plays an indispensable role in the human body. It is one of the most important elements in living organisms. The main way we obtain sulfur is through protein in food. In addition to animal-source foods, many plant-source foods are also rich in protein, such as soybeans, rice, and wheat.

According to the protein content in flour, people divide flour into high-gluten flour, medium-gluten flour and low-gluten flour. Among them, bread flour has the highest protein content (usually over 11%). It has strong gluten and is often used to make elastic and chewy foods.

When water is added to knead the dough, different protein molecules in the flour will "hold hands" (that is, the disulfide bonds between different molecules are cross-linked). Together with starch and fat molecules, they form a "protein-starch- Fat” is a big network. The amino acids in the protein in flour contain a small amount of sulfhydryl groups. During the process of adding water and kneading the dough, some sulfhydryl groups are oxidized to form intermolecular disulfide bonds; during the process of the mixed noodles standing (i.e., dough), they will More sulfhydryl groups are oxidized and more disulfide bonds are formed. As a result, the mesh becomes "tighter" and the dough becomes chewier, making the pasta smoother and chewier. In addition, some people will add eggs when kneading the dough. The protein in the eggs can work with the protein in the flour through disulfide bonds to form the above-mentioned network, which will also make the dough better.

Although food contains sulfur, some sulfur must be excreted or excreted after digestion by the human body. After the carbohydrates and fats in food are digested by the human body, their metabolites are carbon dioxide and water, which have no bad smell; and after the proteins containing nitrogen and sulfur are digested by the human body, their metabolites are often excreted with It has an unpleasant taste, so eating too much nitrogen- and sulfur-containing food will cause odor. The reason why humans feel strong discomfort with the smell of these compounds is because it reminds us that the things with this smell have been digested by us and are not nutritious to us.

The active ingredient of wine is ethanol. If one of the oxygen atoms in ethanol is replaced by a sulfur atom, it will be ethyl mercaptan. Ethyl mercaptan is one of the smelliest gases in the world. The air contains only one part per 50 billion of ethyl mercaptan, and its odor can be smelled by people.

No one likes to smell bad, but those smelly gases have their uses. For example, the main component of natural gas is methane, which is colorless and odorless. Once leaked in large quantities, it can easily cause poisoning and explosion. Therefore, people added odorants to natural gas, such as sulfur-containing ethyl mercaptan, tetrahydrothiophene, etc. Once the gas leaks, people will smell the odor of the odorant and can take protective measures immediately. Since these odorants are released in very small quantities, they will not cause serious pollution to the atmosphere.

Coal also has high sulfur content. When burned, the carbon in coal produces carbon dioxide, the hydrogen produces water vapor, and the sulfur produces sulfur dioxide. Sulfur dioxide is one of the major atmospheric pollutants. When it comes into contact with water molecules, it will also generate sulfurous acid, and some of it can be further oxidized into sulfuric acid, thus harming people's respiratory system.

During the formation and fall of rain and snow, they absorb and dissolve sulfur dioxide, nitrogen oxides, etc. in the air, forming acidic precipitation with a pH value less than 5.6, that is, acid rain. Acid rain is one of the three major environmental hazards in the world. Since the 1970s, large-scale acid rain has occurred in various countries around the world, mainly due to the burning of large amounts of coal with high sulfur content. Acid rain can cause the loss of nutrients in the soil, thereby affecting the growth of crops; acid rain can also damage buildings and other facilities, and is a disaster involving human factors. In order to reduce sulfur dioxide emissions, we should improve coal-burning technology, give priority to the use of low-sulfur fuels, carry out flue gas desulfurization, and actively develop and utilize environmentally friendly new energy sources.