| Industry has widely used freezing as a strategy to halt pathogen growth and more recently, crust freezing has been suggested as a means to improve mechanical operations, quality, and safety of poultry products. Two separate studies were conducted to evaluate the effect of crust freezing (20 min, -85°C) on the survival of Escherichia coli and Salmonella Typhimurium and on quality and shelf life of raw chicken breasts, with or without skin. For the first study, ampicillin-resistant E. coli JM 109 and nalidixic acid-resistant S. Typhimurium were used in the experiments. A set of cultures was subjected to cold-shock stress by storage at 4°C for 10 days. Commercial chicken breasts without skin and chicken thighs with skin were inoculated with each bacterium in separate experiments after being either cold-shocked or non-cold-shocked prior to inoculation. Samples were crust frozen at -85°C for 20 min or completely frozen at -85°C for 60 min. E. coli and S. Typhimurium were recovered on appropriate selective and non selective media containing the corresponding antibiotic. Log reductions and injury extent were calculated and treatments were compared using ANOVA. For the second study, quality of fresh chicken breasts during aerobic, refrigerated storage for up to 18 days was assessed by means of International Commission on Illumination (CIE) color parameters L*, a* and b*; tenderness; and total aerobic (APC) and yeasts and molds counts (YMC). Skin-on breasts had significantly higher L* values compared to skinless units (average 75 vs. 55), whereas a* and b* remained relatively constant no matter the presence of skin, freezing or time. Values oscillated between -2.10 to 0.78 and 1.38 to 3.77, respectively. Shear energy varied erratically for skinless samples but tended to remain constant throughout time for skin-on units. Microbial load increased over time and was considered unacceptable over 8.0 log10CFU/ml, which occurred before 12 days of storage. Under the experimental conditions used, crust freezing did not show practical significance for initial reduction of E. coli or S. Typhimurium in raw poultry products and was not useful in extending shelf life of raw chicken breasts, with or without skin. |
