Survival of Salmonella in Processed Chicken Products during Frozen Storage

Abstract

Frozen chicken products have been identified recently as a cause of salmonellosis. At least eight salmonellosis outbreaks from 1998 to 2008 have implicated undercooked frozen chicken nuggets, strips, and entrees as infection vehicles. Thus, the presence of Salmonella in frozen products may pose an infection risk if the product is improperly cooked. The objective of this study was to assess the survivability of Salmonella during frozen storage (−20°C) when inoculated in processed chicken products. Four Salmonella strains originally isolated from poultry were inoculated into frozen chicken nuggets (fully cooked) and frozen chicken strips (containing raw poultry) at initial populations of 104 to 105 CFU/g. Survival was assessed during storage at −20°C for 16 weeks by measuring bacterial growth on minimal, selective, and nonselective agars. Results indicate that cell populations measured in nonselective agars (plate count agar and plate count agar supplemented with tetracycline) and minimal (M9) agar remained relatively constant during the entire −20°C storage period studied (16 weeks) for both chicken nuggets and strips. However, cell populations were significantly (P < 0.05) lower when measured in selective agar (XLT4) during the 16 weeks of frozen storage for both chicken nuggets and strips, suggesting that these cells were structurally injured. The data presented in this study indicate that Salmonella can survive frozen storage when inoculated in frozen, processed chicken products and confirm that microbial counts on selective agar are not representative of the total population of samples subject to freezing.