The effect of brine marination at chill temperatures on survival and growth of spoilage and pathogenic bacteria during processing and subsequent storage of ready-to-eat cold water shrimp was studied. Survival and growth of Lactobacillus sakei, Listeria monocytogenes, Salmonella, Staphylococcus aureus and Vibrio parahaemolyticus were examined. The effect of brine composition and pH was determined in 12 screening experiments without addition of shrimp. Sixteen challenge tests with shrimp were then carried out to examine the effect of brine composition and storage temperature on survival and growth during processing and subsequent storage of brined and drained shrimp in modified atmosphere packaging (MAP). Different brines with (i) acetic and lactic acids (AL) or (ii) benzoic, citric and sorbic acids (BCS) were studied. V. parahaemolyticus was inactivated in brine AL without shrimp whereas concentrations of all the examined microorganisms were reduced in brine BCS. A significant effect of brine pH on inactivation was observed and inactivation during chill marination of shrimp in brine was reduced compared to the effect of brine alone. This was explained by a relatively fast increase of pH in the brine during marination of shrimp. For shrimp in brine BCS, reductions were observed for V. parahaemolyticus and Salmonella, whereas inactivation in shrimp was only noticed for Salmonella in brine AL. The observed reductions were too small to be used in practise for decontamination of shellfish. None of the examined pathogens was able to grow at 7°C in brined and drained MAP shrimp that resembled commercial products. However, reducing the concentration of acetic and lactic acids by 50% resulted in relatively fast growth of L. monocytogenes in brined and drained MAP shrimp at 7°C. Growth of S. aureus and Salmonella was observed in similar products stored at 15°C. V. parahaemolyticus was reduced in brined and drained MAP shrimp stored at both 7 and 15°C. Based on the results of the present study, L. monocytogenes was identified as the greatest potential risk with respect to the safety of brined and drained MAP shrimp. The potential of L. sakei as spoilage bacterium in brined and drained MAP shrimp was confirmed. Importantly, growth rates of L. sakei and L. monocytogenes in brined and drained MAP shrimp were predicted accurately by available mathematical models. Thus, these models can be used for product development and establishment of shell-life for ready-to-eat shrimp taking into account both quality and safety aspects.
International Journal of Food Microbiology, 2012, Vol 157, Issue 1, p. 16-27