Purpose: Antimicrobial coatings alone, or in combination with cryogenic freezing, were evaluated for their ability to inhibit the growth of Listeria innocua, a surrogate for Listeria monocytogenes, on whole raw and ready-to-eat (RTE) shrimp.
Methods: Shrimp were inoculated with L. innocua and treated with antimicrobial coatings and cryogenic freezing (-75°C, 2 min), used alone or in combination. The coating solutions contained chitosan (20 mg/ml), allyl isothiocyanate (AIT, 60 µl/ml), or lauric arginate ester (LAE, 50 µl/ml. The treated shrimp were stored at -18°C for 6 days before being thawed at 4, 10 or 22°C for either 24 or 48 h and the survival of inoculated L. innocua and natural bacteria on shrimp was investigated.
Results: Results revealed that antimicrobial coating treatments or cryogenic freezing used alone reduced the natural bacteria or L. innocua on raw shrimp by less than 2 log CFU/g, while antimicrobial coatings achieved ca. 5.5 to 1 log CFU/g reduction of L. innocua on RTE shrimp, depending on inoculated population levels. Chitosan+AIT coating in combination with cryogenic freezing achieved more than 5-log reduction of L. innocua and natural bacteria on raw shrimp. The coating-treated RTE shrimp had significantly (P < 0.05) less L. innocua than controls at each thawing temperature and time.
Significance: This study demonstrates that the hurdle technology is an effective approach to reducing microbial loads on shrimp surfaces, which may provide processors or distributors with viable options for designing non-thermal interventions to improve the microbiological safety and shelf life of shrimp.