Sodium metabisulphite is a white powder that releases sulphur dioxide when it meets water or acid. It is INS 223 and E223, and Codex lists it as an antioxidant, bleaching agent, flour treatment agent and preservative. In fruit products the sulphur dioxide it releases stops browning, keeps colours bright and holds back moulds, yeasts and bacteria.
It has long been used in dried and preserved fruit. On SeekSnack it is listed as an antioxidant on Doi Kham Savoury Guava Chinese Apricot Flavor, a seasoned guava snack, and among the preservatives of Denma filled cookie with fruits.
Sulphites are a recognised sensitivity: they can trigger breathing symptoms in some people with asthma. For this reason the Codex labelling standard, the EU and many other jurisdictions require sulphites to be declared when they are present at 10 mg/kg or more.
