Sodium Bisulfite (Food) - Thailand

Brief Overview

Sodium bisulfite, also known as sodium hydrogen sulfite, is a chemical compound represented by the formula NaHSO₃. Classified as a food additive with the E number E222, it exists as a white crystalline solid that assumes a yellow hue in solution. Due to its acidic nature, sodium bisulfite is corrosive. When in contact with chlorine bleach (an aqueous solution of sodium hypochlorite), it produces heat and transforms into sodium bisulfate and sodium chloride.

Manufacturing Process

This bisulfite salt can be synthesized by introducing sulfur dioxide into a sodium carbonate solution in water. Aqueous solutions of sodium hydroxide, sodium bicarbonate, sodium carbonate, or sodium sulfite can undergo treatment with sulfur dioxide to yield a solution of sodium metabisulfite. In a single process, the residual solution from the previous batch is fortified with additional sodium carbonate, which doesn't necessarily need to be completely dissolved, and is then exposed to sulfur dioxide. In certain facilities, the reaction takes place in a sequence of two or more stainless steel vessels or columns, where sulfur dioxide is passed countercurrent to the alkali. After cooling, the sodium metabisulfite is separated through centrifugation or filtration. Swift drying, for instance, in a stream-heated shelf dryer or a flash dryer, helps prevent excessive decomposition or oxidation, which moist sodium metabisulfite is prone to.

Food Industry

In the context of fruit canning, sodium bisulfite serves the dual purpose of preventing oxidation-induced browning and eliminating microbes. In winemaking, sodium bisulfite plays a crucial role by releasing sulfur dioxide gas upon introduction to water or water-containing products. This sulfur dioxide effectively eradicates yeasts, fungi, and bacteria present in grape juice prior to fermentation. After the sulfur dioxide levels diminish (typically within 24 hours), fresh yeast is introduced for the fermentation process. Sodium bisulfite is subsequently employed in bottled wine to hinder vinegar formation in the presence of bacteria and safeguard the wine's color, aroma, and flavor from oxidative effects that lead to browning and other chemical alterations. The rapid reaction of sulfur dioxide with oxidation by-products prevents further degradation. Additionally, sodium bisulfite finds use in preserving the apparent freshness of leafy green vegetables, labeled as LeafGreen in salad bars and other settings. It's worth noting that the concentration at times may be high enough to elicit severe allergic reactions.

Chemical Industry

Sodium bisulfite serves as a reducing agent in the production of various organic compounds. It is employed as a decolorization agent in numerous purification procedures, effectively eliminating trace quantities of chlorine, bromine, iodine, hypochlorite salts, chromium trioxide, and potassium permanganate.

Other Applications

Sodium bisulfite finds application in extensive piping systems to inhibit oxidative corrosion and ensures anaerobic conditions within biochemical reactors. In water treatment, it plays a role in eliminating residual chlorine following super chlorination. Its potent reducing properties make it valuable in wastewater treatment, the preparation of textile dyes, and the development of photographic films. Additionally, sodium bisulfite is utilized in the paper industry for pulp bleaching.