Inactivation of Listeria spp. in high value aquatic food products

Listeria monocytogenes is a psychrotrophic pathogen, posing a food safety threat in refrigerated foods. High value aquatic food products such as salmon and sturgeon caviars may be vulnerable to colonization by L. monocytogenes. Therefore, the main objective of this research was to develop a methodology to accurately determine the thermal inactivation parameters for Listeria in the caviar products as a prerequisite to developing pasteurization procedures based on conventional or dielectric heating processes. Considering the heat liability of the caviar products, combination of thermal and non-thermal (chemical) antimicrobial treatments were studied to maximize the antimicrobial effect and to lessen the heat-induced quality deterioration.;Thermal inactivation kinetics equivalent to those found in the literature were obtained for L. innocua in salmon and sturgeon caviars. These values were used to develop conventional water bath or radio frequency (RF) dielectric heating pasteurization protocols. Also, the effects of chemical antimicrobial treatments such as nisin, lactic acid, sodium hypochlorite and chlorous acid were studied. High concentration of CA (268 ppm) was distinctively effective in inhibiting L. monocytogenes in sturgeon caviar. Nisin (500--1000 IU/ml) resulted in a sharp initial reduction of L. monocytogenes cells. Nisin (500 IU/ml or 750 IU/ml) in combination with heating in a water bath at 60°C for 3 min resulted in a complete reduction of total mesophilic microorganisms and L. monocytogenes . No change in the visual quality of the product was observed. Radio frequency pasteurization of salmon and sturgeon caviar at three different temperatures (60, 63, and 65°C) resulted in a significantly shorter come up time compared to water bath pasteurization. A short process time pasteurization of salmon and sturgeon caviar in combination with nisin (500 IU/ml) eliminated >7 log units of L. innocua. The overall quality of the products was retained.