The effects of selected antimicrobials, applied singularly or in combination, and frozen or refrigerated storage conditions on the survival of Listeria spp. on inoculated shrimp was evaluated in this study. A combination of 0.5% CPC (Cetylpyridinium Chloride) with a water wash at room temperature and freezing of the shrimp at -22.3 degrees C was the only treatment that had a significant antimicrobial effect on the Listeria spp. Antimicrobial effects and the mode of action of PEF (Pulsed Electric Field) and CPC on Listeria cells were evaluated in detailed studies. PEF in 0.1% sodium chloride had a bacterostatic effect toward Listeria spp. during refrigerated storage, but no immediate or bacteriostatic effect was caused by freezing the samples. A concentration of 1% sodium chloride reduced the Listeria spp. population after freezing by 1.1 log; however, the pungent chlorine odor that was generated during treatment might cause discomfort for employees in shrimp processing facilities. Also, chlorine might cause corrosion of metal surfaces of processing equipment. There was no difference in the antimicrobial effects on the survival of Listeria spp. by PEF between the exposure times of 1 or 2 min, as well as in the sodium chloride concentrations of 0.1 and 0.5%. PEF treatment in the presence of 0.1% sodium chloride is recommended. A solution of 0.5% CPC effectively inhibited all of the strains of Listeria spp. in the cell suspensions. A treatment of 0.5% CPC combined with PEF treatment in a sodium chloride concentration of 0.1% caused a delayed effect on the Listeria spp. after 2 d of refrigerated storage. After 2 d of frozen storage, the formation of ice crystals was decreased in the number of Listeria spp. when contaminated samples were treated with water. The results indicated chemicals (e.g. CPC and NaCl) might protect Listeria spp. from the formation of ice crystals. TEM (Transmission Electron Microscopy) micrographs revealed that cell membranes were damaged by PEF treatment and that cells were ruptured by CPC treatment. A maximum reduction of 2.76 log10 CFU/g of Listeria spp. on shrimp was achieved by a combination of PEFCPC.

Master of Science / Food Science Institute / Randall Phebus / Shiga toxin-producing E. coli (STEC) are frequently associated with foodborne illness outbreaks, especially attributable to beef. Intervention methods, such as water washes and organic acid application, are widely implemented across the beef industry to combat this risk. This research evaluates the efficacy of intervention methods applied to chilled beef subprimal pieces and pre-rigor beef carcasses to reduce STEC contamination. Beef strip loins were inoculated (ca. 5 log CFU/cm²) with a 7-serotype STEC cocktail and sprayed with increasing concentrations of peracetic acid (200-1800 ppm; ambient temperature), lactic acid (3-10%; 55°C), or a water control before being vacuum-packaged and stored for 24 h at 4°C. Meat surface excision samples and color readings (L*, a*, and b*) were obtained from each subprimal at three sampling points: post-inoculation, 5 min post chemical spray, and post-24 h vacuum packaged chilling. Peracetic acid spray and lactic acid spray reduced STEC populations by 0.5 -1.3 log CFU/cm² and 0.2 – 0.7 log CFU/cm², respectively, across the incremental concentration increases. All concentrations of peracetic acid and lactic acid concentrations ≥3.5% reduced (P ≤ 0.05) STEC populations compared to their respective control. Application of higher concentrations of lactic acid (7-10%) decreased (P ≤ 0.05) L* and b* values compared to the control, indicating that quality attributes of the subprimals were negatively effected. Carcass intervention methods were evaluated using a three-stage commercial carcass washing cabinet (Chad Equipment). Four pre-rigor carcass sides were inoculated by electrostatically spraying with a 7-serogroup STEC cocktail (ca. 6.5 log CFU/100 cm²). Three treatments were applied, in order, to each side: ambient water wash, hot water wash (82-92°C at the nozzle head), and antimicrobial mist. Meat surface excision samples were taken from the bottom, middle, and top section of each carcass side at five sampling points: 30 min post-inoculation, post-ambient water wash, post-hot water wash, post-antimicrobial spray, and after 18 h spray chilling. The combination of the high-volume ambient water wash stage and subsequent hot water wash stage reduced STEC populations on sides by 3.5, 4.7, and 4.8 log CFU/100 cm² at the bottom, middle, and top of the carcass, respectively. Due to STEC populations declining to very low or undetectable levels after the hot water stage, minimal additional STEC reductions were observed after chemical spray application and chilling. Sequential antimicrobial treatments applied using a three-stage Chad carcass wash cabinet and a subsequent chill step reduced STEC populations on pre-rigor beef carcasses by 4.5 – 5.3 log CFU/100 cm².