Sodium Bisulfite (Food) - India

Brief Overview

Sodium bisulfite, or sodium hydrogen sulfite, is a chemical compound denoted by the formula NaHSO₃. Designated as a food additive with the E number E222, it appears as a white crystalline solid and takes on a yellow color in solution. Because of its acidic properties, sodium bisulfite is corrosive. Upon contact with chlorine bleach (a sodium hypochlorite aqueous solution), it generates heat and undergoes a conversion to sodium bisulfate and sodium chloride.

Manufacturing Process

This salt of bisulfite can be produced by introducing sulfur dioxide into a sodium carbonate solution in water. Aqueous solutions of sodium hydroxide, sodium bicarbonate, sodium carbonate, or sodium sulfite can be subjected to treatment with sulfur dioxide to generate a sodium metabisulfite solution. In a single operation, the remaining solution from the previous batch is strengthened with additional sodium carbonate, which doesn't necessarily have to be completely dissolved, and is then exposed to sulfur dioxide. In some facilities, the reaction occurs in a series 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. Rapid drying, for example, in a stream-heated shelf dryer or a flash dryer, helps prevent excessive decomposition or oxidation, to which moist sodium metabisulfite is susceptible.

Food Industry

In the realm of fruit canning, sodium bisulfite serves a dual role of preventing oxidation-induced browning and eliminating microbes. In winemaking, its significance lies in releasing sulfur dioxide gas when introduced to water or water-containing products. This sulfur dioxide effectively eliminates yeasts, fungi, and bacteria present in grape juice before fermentation. Once sulfur dioxide levels decrease (typically within 24 hours), fresh yeast is introduced for the fermentation process. In bottled wine, sodium bisulfite is used to impede vinegar formation in the presence of bacteria, safeguarding the wine's color, aroma, and flavor from oxidative effects that lead to browning and other chemical changes. The swift reaction of sulfur dioxide with oxidation by-products prevents further deterioration. Additionally, sodium bisulfite is employed to maintain the visual freshness of leafy green vegetables, labeled as LeafGreen in salad bars and other settings. It is important to note that the concentration may sometimes be high enough to trigger severe allergic reactions.

Chemical Industry

Sodium bisulfite functions as a reducing agent in the synthesis of various organic compounds. It is utilized as a decolorizing agent in multiple purification processes, proficiently removing small amounts of chlorine, bromine, iodine, hypochlorite salts, chromium trioxide, and potassium permanganate.

Other Applications

Sodium bisulfite is utilized in large piping systems to prevent oxidative corrosion and maintain anaerobic conditions in biochemical reactors. In water treatment, it aids in removing residual chlorine after super chlorination. Its strong reducing capabilities are valuable in wastewater treatment, the formulation of textile dyes, and the production of photographic films. Moreover, sodium bisulfite is employed in the paper industry for bleaching pulp.