Dried, smoked or salted fish has a low aw, which limits the growth of microorganisms. Therefore, for these products, the main risk is oxidation. Therefore, N2 can be used alone, sometimes added with up to 30% CO2, with an expected shelf life ranging from one month (smoked) to six months (dry). The same solution is used for marinated fish, since the growth of bacteria is inhibited by the acidity of the marinade. For fish preparations (surimi, cooked or fried shrimp, tamara), heat treatment and / or preservatives stabilize the products, which are less sensitive to microbial development. Generally a CO2 concentration of 30% to 50% is used, depending on the expected useful life, the quality of the product and the risk of acidity due to the dissolution of CO2 in water and grease. In addition, whatever the product, the percentage of CO2 can be reduced to the benefit of N2 in case of collapse of the container. It should be noted that botulism is not a risk for heat-treated fishery products, since Clostridium botulinum toxin is heat labile.
The listeriosis outbreaks have involved smoked seafood. Two smoking methods are generally employed: a cold smoking process at 18–28 ° C and a hot smoking process at> 68 ° C. The ability to achieve reductions in L. monocytogenes contamination differs clearly between the two, and the last process essentially represents a stage of pasteurization. Cold smoking takes place for c. 18 hours and in theory represents a significant opportunity for the growth of polluting species of Listeria. The organism commonly contaminates fish during slaughter and further processing in the gutting, filleting and salting stages. Reducing contamination by operating good hygiene practices at these stages is essential for the safety of this production process.
Smoking processes involve burning wet wood chips or wood shavings. Although there are reports of the antimicrobial effects of smoke on Listeria spp., It is clear that the nature of the smoke and the site of contamination are important in the survival and growth potential of Listeria spp. Eklund et al. (1995) showed that the organism did not grow or decrease in number if it was inoculated outside the fish. However, levels increased by several orders of magnitude during the smoking process when inoculated into meat.
Fish processing is mainly carried out by artisanal fish processors. The main products are dried, salted, fermented and smoked fish. Table 5 is a summary of the unit operations that can be applied in fish processing.
The perishable high of the fish requires that it be handled properly immediately after capture and until it is preserved for human consumption. Traditional technologies available for fish processing contribute to reducing post-harvest losses.
Important operations in fish processing are washing, de-stemming, salting, fermentation, drying and smoking. These operations contribute to the development of flavor, texture, color and improved storage characteristics of the products. Different salting systems are used in traditional fish processing, for example, dry salting and salting with brine.
Salting serves to impart flavor and color to fish and has a profound effect on texture. Salted, fermented or fresh fish can be sun dried to reduce the moisture content. Also, fish can be dried without salt; Examples are triggerfish (Balistes forcipatus), anchovy (Engraulis encrasicolus) and herring (Sardinella aurita). Drying the fish in the open sun (Figure 3) can introduce various contaminants into the product.