**7.3 Irradiation**

The irradiation of fishery products is a physical treatment involving direct exposure to electron or electromagnetic rays, for their long time preservation and improvement of quality and safety (Oraei et al., 2011; Özden & Erkan, 2010). Irradiation of food has been legally allowed in many countries and the WHO has sanctioned radiation of up to 7.0 kilo Gray (kGy) as safe. This process is one of the most effective methods for decontaminating both the surface and deep muscle of fresh meat. There is substantial literature on the effects of irradiation in reducing *Salmonella* on some fishery product such as shrimp (Norhana et al., 2010). The alteration in pathogen population as a result of irradiation

Salmonella in Fish and Fishery Products 103

Chlorine is the decontaminating agent most widely used to kill pathogenic microorganisms in the seafood industry. It is used to disinfect water used in the process (such as thawing frozen products), washing raw materials and in making ice for chilling fishery products. Commonly used chlorine compounds are liquid chlorine solution (HOCl) and hypochlorite (OCl−). More recently chlorine dioxide (ClO2) and electrolyzed oxidizing (EO) water have also been used for this purpose. Specifically, ClO2 has been recognized as a bactericidal, viricidal and fungicidal agent and is widely used in Europe and US as an alternative to chlorine and hypochlorite. In addition, EO water has also been shown to possess strong

Both gaseous and dissolved forms of ozone are approved to be used as antimicrobial agents by the food industry, including the seafood industry. There are investigations on the effect of 2% ozonated saline (5.2 mg ozone/L, 5°C) on the inactivation of nine bacterial strains (including *S. typhimurium*) in shrimp meat. Findings showed that *S. typhimurium* was the most resistant of the species tested, with only 0.1 log cycle reductions (Norhana et al., 2010). Lactate is considered to be an effective additional hurdle against the growth of contamination flora and pathogens such as *Salmonella* and it is used in the further processed fish industry (fish cakes, smoked salmon, injected fillets, marinated fish). Studies on the specific action of lactates indicate they stimulate mechanisms that interfere with the metabolism of the bacteria, such as intercellular acidification and interfere with proton transfer across the cell membrane and feedback inhibition. Lactate also lowers water activity. Since lactate does not kill bacteria,

**10. Chemical approaches** 

**10.1 The use of antimicrobial agents** 

bactericidal activity against various foodborne pathogens.

it cannot be used to mask poor sanitation practices (Da Silva 2002).

**(ICMSF) recommended microbial limits** 

Fresh and frozen fish and cold-

1Number of representative sample units.

products

**11. Intermational commision on microbiological specification for food** 

smoked fish 5 0 0 - Frozen raw crustaceans 5 0 0 - Frozen cooked crustaceans 10 0 0 - Fresh and frozen bivalve molluscs 20 0 0 -

4Maximum recommended bacterial counts for marginally acceptable quality products. Plate counts below "m" are considered good quality. Plate counts between "m" and "M" are considered marginally acceptable quality, but can be accepted if the number of samples does not exceed "c." Plate counts at or

Table 5. Recommended microbiological limits for *Salmonella* spp. in fish and fishery

2Maximum number of acceptable sample units with bacterial counts between m and M.

3Maximum recommended bacterial counts for good quality products.

above "M" are considered unacceptable quality (SeafoodNIC; http://seafood.ucdavis.edu/haccp/compendium/chapt17.htm)

Product n1 c2 Bacteria/gram or cm2

m3 M4

depends on the dose of irradiation, storage temperature, packaging conditions and fish species (Özden et al., 2007). For example a study, showed complete elimination of *Salmonella* on frozen shrimp when irradiated at 4.0 kGy. Similarly it is also reported that doses of 4.0–5.0 kGy were required to reduce the numbers of *S. typhimurium* on shrimp by 6.0 log cycles. According to Oraei et al., (2011), low-dose gamma irradiation (especially 3 kGy) can be applied for microbial control and the safety of rainbow trout and shelf life extension in frozen state. Gamma irradiation at 3 kGy was more effective than irradiation at 1 and 5 kGy in eliminating microorganisms of rainbow trout fillets. The irridation doses are also reported in the range 1.5–2.0 kGy effectively control all pathogenic bacteria tested in shellfish except *Salmonella* spp., particularly, *S. enteritidis*, which requires 3.0 kGy (IAEA,2001). Similarly to achieve safety levels against *Salmonella* spp., particularly *S. enteritidis*, in raw oysters, a dose of 3.0 kGy is recommended by Gelli (2001). As a results although irradiation appears to be effective in eliminating pathogens in fishery product, there is an unsubstantiated view amongst the public that food irradiation is unsafe and undesirable. There is also evidence some that irradiation may reduce the nutritional value of some foods by the destruction of aromatic amino acids and producing rancidity and off-odours (Norhana et al., 2010).
