Edible coatings to control the growth of Listeria monocytogenes on poached and deli turkey products and the effect of growth conditions on the pressure resistance, inactivation, and recovery of pathogens
Date
2011
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Publisher
University of Delaware
Abstract
The relatively high prevalence of Listeria monocytogenes, E. coli O157:H7, and S. Typhimurium in various ready-to-eat (RTE) food products is of great concern to the food industry. The overall objective of this project was to assess the efficacy of edible coating and high hydrostatic pressure (HHP) processing technologies to enhance the safety of RTE turkey products. In the first phase of the study, we compared the antimicrobial efficacy of polysaccharide-based edible coatings (alginate, carrageenan, pectin, xanthan gum, and starch) incorporating nisin (500 IU/g), sodium lactate (SL, 2.4%), sodium diacetate (SD, 0.25%), and potassium sorbate (PS, 0.3%) and the commercial products, Novagard™ CB1 (0.25%) and Guardian™ NR100 (500 ppm) to inhibit L. monocytogenes on deli turkey. The coatings were applied onto the surface of deli turkey discs inoculated with ~ 3 log CFU/g of L. monocytogenes and stored at 4̊C for 30 days. The most effective treatments were alginate-based coatings supplemented with SL (2.4%)/PS (0.3%) which delayed growth of the pathogen with final counts reaching 1.2-5.6 log CFU/g lower than the control untreated samples. In the second part of the project, the influence of growth and recovery temperatures (15, 25, 35, and 40̊C), pressure levels (400 and 600 MPa), treatment temperatures (4, 20, and 40̊C) and recovery gaseous conditions (aerobic and anaerobic) on pressure resistance of Salmonella, E. coli O157:H7 and L. monocytogenes was investigated. Pressure inactivation of the bacterial pathogens was shown to increase as a function of the pressure levels and treatment temperatures. The temperature history and physiological age of the bacterial culture also influenced their pressure resistances. In general, early stage cells (representative of exponential phase) were more baro-resistant than late stage cells (representative of stationary phase) (P < 0.05). Aerobic and anaerobic recovery conditions were not found to have any appreciable effect on bacterial recovery (P > 0.05). In addition, recovery temperatures ≤ 35̊C promoted greater recovery of injured stationary phase cells than higher temperatures (P < 0.05). Overall, HHP treatments at the 40 ̊C recovery temperature, 15 ̊C growth temperature, 600 MPa, 40 ̊C treatment temperature, and stationary phase were the most promising, delivering 5.3 to 7.7 log CFU/g reduction of Salmonella, E. coli, and L. monocytogenes. This study thus highlights the effectiveness of two intervention technologies that can be applied to foods such as RTE turkey that are susceptible to post-processing recontamination.