| Produce (lettuce, strawberries, apples, and cantaloupe) inoculated with E. coli O157:H7 and L. monocytogenes was exposed to several sanitizer treatments. Ozone (3 ppm) and chlorine dioxide (5 ppm) reduced populations of L. monocytogenes and E. coli O157:H7 by 5.5 and 5.7 logs, respectively. Chlorine dioxide (3 ppm) and sodium hypochlorite (200 ppm) resulted in maximum reductions of 4.8 logs for L. monocytogenes and 5.1 logs for E. coli O157:H7. Peracetic acid gave reductions of 4.3–4.5 logs for L. monocytogenes and E. coli O157:H7. Fruit and Vegetable Wash and SCJP 16-162 produced maximum log reductions of 3.3 and 3.4 logs for L. monocytogenes and E. coli O157:H7, respectively. In comparison, produce treatment with SCJ 16-172 and Viper™ yielded reductions of 3.0 and 2.5 logs for L. monocytogenes and E. coli O157:H7, respectively. Fit™ was the least effective, giving maximum reductions of only about 1 log for L. monocytogenes and E. coli O157:H7.; Storage of sanitized produce indicated that the most effective sanitizers for eliminating pathogens, facilitated growth of yeasts and molds and contributed to rapid spoilage of produce (3 ppm ozone and 3 and 5 ppm chlorine dioxide), while peracetic acid (80 ppm) and sodium hypochlorite (100 and 200 ppm) treatment did not adversely affect product shelf life. Sensory analysis using the non-extended triangle test, indicated that the only statistically significant differences between any of the treated and control samples occurred when whole apples were dipped in sodium hypochlorite (200 ppm) and when shredded lettuce was sprayed with peracetic acid (80 ppm).; The sequential use of copper ion (1 ppm), sodium hypochlorite (100 ppm) and sonication was assessed to decrease numbers of E. coli O157:H7 and L. monocytogenes during apple cider production. Using the hurdle approach, copper ion water did not significantly reduce populations of either pathogen; however, copper ion water/sodium hypochlorite (100 ppm) decreased populations of L. monocytogenes and E. coli O157:H7 by 2.3 and 2.2 log CFU/g, respectively. After juiceration, the pulp contained ∼1.1–1.3 log CFU/g of either pathogen with sonication decreasing the remaining pathogens in the expressed juice by ∼2 logs CFU/ml. Based on these findings, a 5-log reduction for both pathogens was achievable using 100 ppm sodium hypochlorite followed by juiceration and sonication.; Employing confocal scanning laser microscopy (CSLM) to visualize attachment, colonization, location, and viability of gfp-transformed E. coli O157:H7 on lettuce and strawberries revealed generalized non-specific attachment to surface structures with some penetration through intact surfaces up to approximately 20μm. E. coli O157:H7 attachment to both products was more strongly influenced by water deposition and pooling than by any affinity to stomata or other surface structures. Based on CSLM analysis, viable E. coli O157:H7 cells that survived sanitizer treatments did so by organizing into groups or clusters in areas of pooling rather than by penetrating through intact produce surfaces. |
