Diss. Clemson University, 2015

Abstract:

Three experiments were performed to enumerate the natural microflora on unwashed peaches, known as “field” peaches, and to determine the efficacy of using acidified electrolyzed water as a topical antimicrobial to remove or reduce the number of the natural microflora or inoculated Listeria innocua from to peach surfaces. During the first experiment, field peaches were divided into four treatment groups: no wash (NW), tap water wash (TW), acidified electrolyzed water wash (AEW), and chlorinated water wash (CL). Peaches were dipped into each of the treatment solutions at ambient temperature and immediately removed (approximately 5 seconds). Peaches were then rinsed in 100 mL of 0.1% peptone and rinsates were plated on aerobic plate count agar for enumeration. For the second experiment, exposure time to the treatment solutions and the temperature of the same treatment solutions were studied. Field peaches were again divided into NW, TW, AEW, and CL but treatments were applied using two exposure times of 5 seconds and 40 minutes at a temperature of 2°C (samples were given either a “0” or “40” in their labels to denote exposure time in minutes where 5 second exposures = 0 minutes e.g. TW-0, TW-40, AEW-0, etc.). Rinsing and plating was conducted as mentioned above. Experiment three investigated the efficacy of NW, TW, AEW, and Cl, in reducing numbers of Listeria innocua on peaches that were previously inoculated and held at 4°C for 24 hours. Inoculated peaches were dipped in treatment solutions for 5 second- and 40-minute times at 2°C. Results showed that exposure time had a significant effect on bacterial reduction for both AEW and Cl treatments. Average aerobic counts from all NW peaches were 4.2 log10 CFU/g peach for natural microflora and 4.3 log10 CFU/g peach for samples inoculated with Listeria. The following results show the number of bacteria recovered (log10 CFU/g peach) from natural microflora samples and Listeria inoculated samples, respectively: NW = 4.2 and 4.9, TW-0 = 3.8 and 4.3, TW-40 = 3.2 and 4.7, AEW-0 = 3.6 and 3.7, AEW-40 = 2.6 and 1.6, CL=0 = 3.7 and 3.7, and CL-40 = 2.3 and 1.9. Greatest reductions were found with AEW-40 and CL-40 at refrigerated temperatures against both aerobic microorganisms and Listeria innocua. They reduced natural microflora counts by approximately 1.6 and 1.9 log10 CFU/g peach, respectively and they also reduced Listeria innocua counts by 3.3 and 3.0 log10 CFU/g peach, respectively. Listeria innocua, like monocytogenes, thrives in cold environments and the analysis of this study’s results suggest that Listeria in TW-40 may have reattached to peaches during exposure. Color studies were also performed on the peaches from the preliminary experiment and Experiment 2 to determine the effects of exposing the peaches to low pH environment such as that of the AEW used in this study. Peaches were analyzed for L*a*b* color data prior to their exposure to treatment solutions then they were analyzed again after their treatment concluded and they had air dried until no visible moisture remained. There was no significant color difference shown in any of the peaches when the pre- and post-treatment data was compared. Results from these studies demonstrate that total aerobic microorganisms and Listeria spp. may be reduced, but not eliminated, during washing (by dipping) with AEW or CL with similar reductions for both antimicrobial treatments.

Report:

https://tigerprints.clemson.edu/cgi