Factors influencing use of sulphite for prevention of black spot in prawns

Abstract

Sodium metabisulphite is used to prevent melanosis (black spot) on prawns. Health concerns restrict the amount of residual sulphite, measured as sulphur dioxide, allowable in prawn meat. The effects on residual sulphite levels in prawns of spp., size, standing time after dipping, dipping alive or dead, method of thawing during processing of frozen prawns, and boiling were investigated. Size and spp. of prawns had no influence on sulphite residue levels after dipping for 30 s in 1% sodium metabisulphite. Sulphite retained in prawns decreased rapidly after dipping, indicating the need to minimize delays to ensure an adequate retention. On thawing after frozen storage a second application of sodium metabisulphite was necessary. Dipping prawns live caused significant reduction in uptake of sulphite. Boiling prawns for 2 min only slightly reduced sulphite levels.