Sodium metabisulfite is a white or slightly yellow crystalline powder with a strong SO2 odor. Sodium metabisulfite has a stronger reducibility than sulfite, and its effect is similar to that of sodium sulfite.

Precautions for use in food

1) Sodium metabisulfite is a reducing bleaching agent, and its solution is unstable and prone to volatilization. Therefore, it should be prepared and used immediately to prevent the instability and volatilization of sulfites.

2) When metal ions are present in food, residual sulfite can be oxidized; It can also oxidize and discolor the reduced pigments, thereby reducing the effectiveness of the bleaching agent. So metal chelating agents are used simultaneously during production.

3) Substances bleached with sulfites are prone to discoloration due to the disappearance of sulfur dioxide, so excess sulfur dioxide is usually left in food, but the residual amount should not exceed the standard.

4) Sulfite cannot inhibit the activity of pectinase and can damage the cohesion of pectin. In addition, after the infiltration of sulfite into fruit tissue, the fruit can be crushed during processing to remove all sulfur dioxide. Therefore, fruits stored with sulfite are only suitable for making jam, dried fruits, fruit wine, preserves, etc., and cannot be used as raw materials for canned goods.

5) Sulfite can destroy thiamine, so it is not easy to use in fish food.

6) Sulfite easily reacts with aldehydes, ketones, proteins, etc.

The application of sodium metabisulfite in food

At present, in the processing and preservation of light colored vegetables in China, such as mushrooms, lotus root, horseshoe, white asparagus, yam and other products. Use sodium metabisulfite solution more often for color protection. Of course, there are some differences in the processes of different factories. For example, in the processing of canned mushrooms, soak fresh mushrooms in a water solution containing 0.03g/kg sodium metabisulfite twice, each time for 1-2 minutes.

Sodium metabisulfite is used as a dough improver in the biscuit industry. Before use, it is prepared into a 20% solution and added to the immature dough in stages during the dough preparation process. Due to the reducing effect of sulfur dioxide released by sodium metabisulfite during dough preparation, a small amount of it can be added when the gluten strength and toughness of the flour are high to prevent deformation of the biscuit product due to excessive gluten. Resilient dough can be added according to the strength of the flour, and should generally be avoided in crispy dough with a high proportion of oil and sugar. This is because the addition of oil and sugar itself has prevented the gluten protein from absorbing water and expanding, preventing the formation of a large amount of gluten, and there is no need to add sodium metabisulfite.