The smoked salmon is an unstable product. It is necessary to constantly keep it refrigerated at temperatures between 0 and + 2 °C (Fasolato et al., 2008). The storage period can vary from 4-5 weeks to 3 months according to the health-hygienic measures taken during the processing phases (Fasolato et al., 2008).
H
YGIENICA
SPECTS ANDC
RITICALP
OINTSR
ELATED TO THEP
RESENCE OFL
ISTERIA MONOCYTOGENES INS
MOKEDS
ALMONListeria monocytogenes can contaminate smoked salmons at many levels of processing chain (Vogel et al., 2001b). Contamination of smoked salmon occurs mainly during processing rather than originating from raw materials, even if raw salmon can be a contamination source of the processing environment (Hoffman et al., 2003; Gudmundsdottir et al., 2005; Katzav et al., 2006).
Raw Material Arriving at a Processing Plant
Regarding the raw material quality, the best pre-slaughtering fast time should be two weeks exactly because a shorter time would cause the presence of a bigger quantity of water in the flesh and this would affect the whole production process (Fasolato et al., 2008).
Salmons should arrive at a processing plant stored under appropriate temperatures. Usually they are covered with ice flakes (2.5-3.0 Kg of ice for 10 kg of salmon) in perforated containers to allow the drainage of the water formed by the melted covering ice. Before processing, salmons have to be stored in a cell at a temperature of ≤ 3 °C (Fasolato et al., 2008). Defrosting should be carried out at refrigerating temperatures to avoid inappropriate multiplications of Listeria monocytogenes. As a matter of fact, the raw materials are often contaminated at negligible levels, from zero (Ben Embarek et al., 1997) to about 30%
(Hoffman et al., 2003; Miettinen and Wirtanen, 2005; Di Ciccio et al., 2012) while a massive contamination during processing due to contact with contaminated surfaces or during the storage of the finished products often occurs (Eklund et al., 1995).
Filleting
The filleting phase needs appropriate working conditions: all the cleaning and processing of the salmons should be done in places of work divided in departments and air-conditioned at 12 °C (Fasolato et al., 2008). The hygiene regime and the cleaning and sanitation practices applied during smoked salmon production represent key factors in reducing the Listeria
burden in smoked products: it will be imperative to set up an accurate washing ad disinfection plan for these areas (Rotariu et al., 2013). Several authors found evidence that the environment is the major source of smoked salmons contamination (Jorgensen and Huss, 1998; Autio et al., 1999; Rørvik, 2000) and that considerable contamination occurs during evisceration, handling and filleting of salmons as a result of inadequate hygiene (Katzav et al., 2006).It was shown (Johansson et al., 1999) that the same Listeria monocytogenes strains found in the smoked salmons were also isolated from the plant drains, the skinning and filleting equipment and conveyor belts. Another study (Autio et al., 1999) concluded that plant-resident strains of Listeria monocytogenes represented important sources of contamination for the smoked salmons and demonstrated that effective decontamination of the plant environment could be achieved using hot (80 °C) water, steam and hot (80 °C) air ovens. In a recent study, Di Ciccio et al., (2012) found an overall prevalence rate of 16%
among environmental samples from a salmon processing plant. The most contaminated niches of the plant were the working tables (43%) and the slicing machine (37%). Previous studies have shown that the main risk factor is represented by the rotation job that can be associated with the movement of smoking plant employees from one department to another of the processing plant without the adoption of appropriate precautionary measures (Rørvik et al., 1995). Smoking plant employees can act as fomites for Listeria monocytogenes (Tompkin et al., 1999).
Salting
It is important to use the right amount of salt or brine to avoid, in case of excessive quantities, compromising the final taste of the salmon or, in case of insufficient dosage, compromising the perfect preservation of the product (Fasolato et al., 2008). A light salting treatment can explicate most of all a firming action on the flesh, prevents their discoloration, gives the right flavour, but does not explicate an efficient and lasting Listeria monocytogenes inhibition. The risk of a contamination of the fillet can‘t be avoided when the process is continuous and with recycling of brine (Fasolato et al., 2008). The contamination level of brine containers is usually 17%, while brine is generally contaminated around at 36% (Rørvik et al., 1995).
Smoking
Both hot and cold smoking are usually not capable of preventing the growth of Listeria monocytogenes to high numbers, posing an increased risk of causing listeriosis has a high lipid content which may protect microorganisms from a possible thermal treatment or from freezing and cold-smoking below 20°C, cannot be considered a listericidal treatment (Serio et al., 2011). Cold smoking processing does not eliminate the possibility of contamination of raw materials and refrigeration or vacuum storage are not able to prevent the growth of Listeria monocytogenes (Duffes, 1999). In a recent study, Listeria monocytogenes has been isolated from raw salmon samples and final products highlighting that the pathogen can be reduced during cold smoking, although this process does not include a listericidal heat treatment (Di Ciccio et al., 2012). The temperatures and conditions required to denature
salmon protein during hot smoking are generally sufficient to cause the complete kill of Listeria monocytogenes present on the surface of the salmon (Poysky et al., 1997). In a 1992 survey, Jemmi and Keush have shown that after experimental inoculation of Listeria monocytogenes in fresh salmon that had to be hot-smoked, the microorganism would not survive the process with applied temperatures of >70°C. This led to thinking that hot smoked salmon contamination might be mainly post-process. This treatment alone cannot guarantee the total safety of the product during marketing or a satisfactory shelf life. Therefore, a preliminary salting treatment and a strictly controlled refrigeration when the product is marketed are both necessary. In hot-smoked salmons, the prevalence of Listeria monocytogenes never exceed 9.12% (Jemmi and Keush, 1992; Ben Embarek, 1994, Jorgensen et al. 1998; Rørvik, 2000).
Cutting and Reconstruction of the Smoked Fillet
The cutting and reconstruction of the fillet requires a very high attention towards the compliance to the hygienic regulations by the smoking plant employers. The hygiene regime and the cleaning and sanitation practices applied to surfaces and work equipment during smoked salmon production represent key factors in reducing the Listeria monocytogenes contamination (Fasolato et al., 2008; Rotariu et al., 2013).
Bagging and Packaging
Vacuum packed smoked salmons are ready to eat products mostly eaten without any further cooking (Eklund et al., 1995; Gudmundsdóttir et al., 2005). Their recontamination with Listeria monocytogenes at packaging stage represents a health hazard, although the presence of salt and the refrigeration can limit the risk of development of the microorganism.
Marketing
For smoked salmons, the need to meet the consumers taste forces the producers to limit salt use (Fasolato et al., 2008). Moreover, physical and chemical parameters of smoked salmon are usually within values permitting the growth of Listeria monocytogenes, obtaining in this way, preparations that have to be kept compulsorily in strictly controlled refrigerating conditions during their life on the market (T < 3.0 °C). The growth of Listeria monocytogenes in vacuum packaged smoked salmon stored at T <5 °C can be inhibited by the use of a competitive lactic acid bacteria flora (Nilsson et al., 1999). Again, the development of Listeria monocytogenes during storage is definitely inhibited by the use of bacteriocins: nisin in combination with modified atmosphere packaging seems to have a decisive role on the control of Listeria monocytogenes in smoked salmon (Szabo and Cahill, 1999). Other studies have shown that the presence of bacteriocins producing strains can inhibit the growth of Listeria monocytogenes (Duffes et al., 1999). Nevertheless, Listeria monocytogenes is often isolated from smoked salmon, albeit in low numbers (Katzav et al., 2006) and the prevalence has been documented repeatedly varying between 10% and 40% (Jemmi and Keusch, 1992;
Hudson et al., 1992; Rørvik et al., 2000; Vogel et al., 2001a; Dauphin et al., 2001; Aguado et al., 2001; Autio et al., 2003; Nakamura et al., 2004; Azevedo et al., 2005; Miettinen and Wirtanen, 2005). In recent studies performed in Italy, Di Pinto et al. (2010) reported a prevalence of 34%, Mureddu et al., (2011) and Di Ciccio et al., (2012) 12% while Gambarin et al., (2011) of 16%. The high prevalence of Listeria monocytogenes in these products could be due to the low smoking temperature (20 °C) applied during the cold-salmon processing, as this condition would be ideal for the proliferation of Listeria monocytogenes. As reported above, the characteristics of the product should allow the growth of the pathogen at levels dangerous to humans (Gombas et al., 2003, Cornu et al., 2006). When the refrigeration temperatures are observed throughout the storage period, the development of Listeria monocytogenes is generally moderate (<100 cfu / g), however the long period of shelf life may allow a significant increase in the level of contamination, because of the absence of competitive microflora (Johansson et al., 1999; Little et al., 2007). Temperature abuse may be a factor in growth to high numbers unless prolonged storage has occurred (ILSI, 2005).
Although it is rather uncommon, contamination levels up to 104cfu/g have been reported in samples stored at temperatures of thermal abuse between 8 and 10°C (Loncarevic et al., 1996, Cortesi et al., 1997, Jorgensen et al. 1998). For these reasons, consumer education to keep cold chain management during the shelf life becomes very important to minimize the growth of the pathogen. Shortening of the best-before date is sometimes useful to reduce the risk of causing food-borne listeriosis (Marklinder et al. 2004; ILSI, 2005; Garrido, 2008) and to respect the food safety criteria provided by the Commission Regulation (EC) N° 2073/2005 on microbiological criteria for foodstuffs.
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Editor: Edmund C. Hambrick © 2014 Nova Science Publishers, Inc.
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