As a kind of food additive, sodium metabisulfite is mainly used as bleaching agent, preservative, loosening agent, antioxidant, color-protecting agent and preservative in the food industry due to its special physical and chemical properties. Sodium metabisulfite is used  in different foods The functions they play are also different, and in summary, the main functions can be divided into these three types.

1. The role of antiseptic and preservative

The internal tissue of the fruit or vegetable after picking does not stop moving immediately, but can usually carry out normal activities and decompose the oxygen in the tissue. There will be a large number of multiplied microorganisms in the injured part, and these microorganisms can decompose the nutrients in the tissue produce harmful substances, which in turn leads to the rot of fruits and vegetables.

Therefore, the use of food-grade sodium metabisulfite can play a good role in slowing down the rot of fruits and vegetables. After picking the grapes are fumigated with sulfur dioxide, the respiration of the grapes will be reduced, reducing the respiration substrate, thereby reducing the activity of oxidase, so that during the entire storage period, the respiration of the grapes has been at a low level. Obviously, ethylene release is also less. Its action process is: when sulfur dioxide meets water, it undergoes a combination reaction to generate sulfurous acid. The substance has a strong anti-oxidation property, can consume oxygen in tissues well, and hinder normal processes such as the reproduction, respiration and fermentation of microorganisms. Sodium metabisulfite undergoes a decomposition reaction under this condition, and the reaction produces hydrogen ions, which can hydrolyze proteins and nucleic acids on the surface of bacteria, thereby eliminating a large number of microorganisms. There are a lot of oxidase in the grape tissue, this enzyme destroys nutrients and changes the color of the tissue, and the role of sodium metabisulfite in decomposing oxygen can just slow down the effect of this enzyme, thus playing a role in keeping fresh.

2. Antioxidant and bleaching effect

In food processing, it is often used as a food bleaching agent. The reason why sodium sulfite has strong anti-oxidation is that in sodium sulfite, the valence of sulfur is +4, which is reducing and can react with oxygen or oxidizing agents to form sulfate, so it has anti-oxidation effect. Sodium sulfite can bleach the color of anthocyanins. The principle of bleaching is: an addition reaction between sodium sulfite and anthocyanin molecules causes damage to the conjugated system in the anthocyanin molecules, forcing the color of the product to disappear, resulting in bleaching Effect. When sodium metabisulfite reacts with colored substances, the stability of the product is weak and it is easy to decompose. The substances produced after decomposition lose their function due to oxidation, which will cause discoloration of food. Therefore, sodium metabisulfite often remains in food processing.

3. Inhibitors to reduce food browning

Enzymatic browning is generally found in fresh plant foods, such as fresh fruits and vegetables. Sodium metabisulfite can inhibit the activity of phenolase, and can undergo addition reaction with carbonyl, thereby reducing the polymerization reaction of carbonyl compounds. Sodium metabisulfite can inhibit enzymatic browning in an acidic environment. In the process of food storage, sodium metabisulfite is usually mixed with citric acid and ascorbic acid, which can maintain the color of the original substance for a long time.

Sodium Metabisulfite has a stronger reducing property than bisulfite, and its effect is similar to that of sodium sulfite. my country stipulates that it can be used in candied fruit, biscuits, sugar, rock sugar, maltose, candy, glucose, liquid glucose, bamboo shoots, mushrooms and canned mushrooms, with a maximum usage of 0.45g/kg. The residues of candied fruit, bamboo shoots, mushrooms and canned mushrooms, grapes and black currant juice concentrate (calculated as SO2) are less than 0.05g/kg; the residues of biscuits, sugar, vermicelli and other varieties are less than 0.1g/kg; the residues of liquid glucose The amount shall not exceed 0.2g/kg. In the food industry, it is used as bleaching agent, preservative, loosening agent, antioxidant, color-protecting agent and fresh-keeping agent.

Safety and Environmental Impact of Sodium Metabisulfite

As a widely used chemical, sodium metabisulfite has attracted much attention for its impact on human health and environmental safety. Generally speaking, sodium metabisulfite is safe to use within the specified dosage range. However, if it is used excessively or exposed to high concentrations of sodium metabisulfite for a long time, it will have a certain impact on human health, such as skin irritation, breathing difficulties, and allergies. In addition, sodium metabisulfite may also produce pollutants such as SOx (sulfur oxides) during the process of decomposition to generate sulfur dioxide, which will have a certain negative impact on the environment. Therefore, when using sodium metabisulfite, control and safety considerations should be taken to avoid possible hazards and environmental impacts.