Freezing Technology

2.5.2.1.Concentration of chlorine used in Fish processing

It has been established in the fish processing industry that the injection of chlorine into a supply cold water used for general wash-up helps to control microbial contamination. Chlorine dosage should be around 10 ppm during the normal use and 100 ppm of residual concentration during the clean – up.

Codex recognize that up to 10 mg/l active chlorine in fish processing water and ice that contacts seafood to be generally recognized as safe (GRAS).

An on-line hypochlorite injection system recommended for seawater treatment is a dosage of 20ppm. This system, together with improved handling and storage of cooked shrimp, has been found to double the chilled storage life while improving both the eating and microbiological quality of products. Concentrations of 20-30 mg/L in running water have been used to reduce the number of Listeria monocytogenes, while thawing frozen salmon. The removal of this pathogen from the surface of fish destined for cold smoking is a major health gain for the industry as the temperature of the cold smoking process are insufficient to kill L monocytogenes. Chlorine at levels of 20-25 mg/L were shown to be effective in killing strains of both Escherichia coli and L monocytogenes in a fish model system under laboratory conditions.