Residual Levels of Sulfite in Raw and Boiled Frozen Shrimp: Variability, Distribution and Losses

The contents of free and total SO₂ were determined in the edible and inedible parts of different samples of four batches of raw and boiled frozen shrimp. The variability observed in the residual levels of SO₂ between batches was always clearly higher than the variability inherent in the analytical method. The use of sulfites can be said to be abusive since the residuals in the edible parts of raw shrimp are higher than 100 mg total SO₂ per kg. Much higher concentrations are found in the inedible parts. The process of boiling causes a mean reduction of 53.5 + 8.5% in the case of free sulfite and 33.0 ± 4.3% for total sulfite in the edible parts. Boiling the shrimp does not cause important modifications in the distribution of sulfites between the edible and inedible parts, although it does affect the ratio between free and bound forms in the edible parts. The presence of elevated amounts of sulfite in the boiling water is reported. The retention of the additive is variable and independent of the content and the amount of loss from the shrimp.