Any Listeria present in products of minced desalted cod, contaminating fish prior salting or during rehydratation, will survive during heat treatment if the fish cake is made sensory attractive (a light brown surface). To eliminate this risk completely, the temperature during frying has to be increased to about 65 ºC.
The maximum growth rate of Listeria monocytogenes is linearly proportional to the total phenolic content of different liquid smoke but minimum inhibitory concentration may vary indicating the presence of other inhibitory compounds in liquid smokes. The proteome of Listeria monocytogenes cytosoluble proteins is slightly modified after 2 h incubation with one of the liquid smoke at a final concentration of 30 ppm of phenol, but no protein already characterized in response to other known stresses is induced, except the protease ClpP. Liquid smoke inhibited the hemolytic potential without affecting hly gene expression, showing a potential inhibition of protein activity or stability.
Traditional drying has no effect on the level of different pathogenic and spoiling bacteria. Contrastingly, the electro-hydrodynamic drying (EHD) lowers the bacterial count up to approximately 2 log (ufc/plate) and this behaviour is not affected by the physiologic state or saline stress of bacteria. EHD is a promising technique for drying fish, being more rapid and economic than traditional one and also showing a bactericidal effect.
Lc. piscium strain EU2241 and in a lesser extend Le. gelidum EU2261 isolated during the first period of this project are very efficient to prevent cold smoked salmon (CSS) from spoilage. However, the mechanism of protective effect is unclear and not related to inhibition of specific bacterial group. Lc. piscium EU2241 also inhibits the growth of Listeria monocytogenes and Staphylococcus aureus in vacuum packed cooked shrimps by 2- 2.5 log at the end of the chilled storage period. In a lesser extend, similar results are also obtained with Le. gelidum EU2247. Those two PCs strains are well adapted to low temperatures: As an example, L. piscium EU2241 has on optimum growth rate at 26°C and does not grow at T° > 30°C whereas the reference strains grows only at temperature higher than 30°C. This is probably due to the overproduction at 5°C of a small peptide (around 7 kDa) highly similar to cold-shock protein D from Lactobacillus and Lactococcus species.
Coating CSS slices with a chitosan formulation does not induce any impact on fish sensory quality, colour, odour and global appearance after 25 days of storage at 4 ± 1 ºC. The antimicrobial efficacy of chitosan coatings are similar when applied on CSS and on desalted cod (about 1 log reduction during the first 7 days of storage at 4°C with 2% chitosan coating). The inhibitory activity is limited to the flora present on the surface of the product and that does not induced any effect against microorganisms inside the product. Compatibility between chitosan and Cd V41 strains was checked and conclusive results allow a larger scale trial where combination of hurdles will be tested.
The characterization of the chitosan films has been completed with the measurement of their light transmittance. The transparency was good for all the films even if they had a yellowish colour. The C4G formulation appeared to have the best mechanical properties and transmittance for application as an edible film in food.
The effect of environmental conditions (pH, NaCl, liquid smoke and bacteriocin concentration) on the antimicrobial effect of divercin (bacteriocin produced by Cd V41) against different target strains from HURDLETECH collection has been studied. Differences in sensitivity of the strains are observed, as well as some synergy between some environmental parameters and the bacteriocin.
Pulse light (PL) processing could improve the safety (Listeria hazard) of seafood products without any negative change in physico-chemical properties like a