Foodborne outbreaks and recalls associated with fresh-cut produce are currently on the rise due to increased consumption. Using cucumbers and zucchini squash as model products based on their inherent compositional differences, the objective of this dissertation was to assess the transfer of L. monocytogenes from inoculated cucumbers and zucchini to various surfaces of rotating and stationary slicers. After slicing one inoculated sample followed by fifteen uninoculated samples, Listeria populations on different parts of the stationary slicer decreased significantly (P ≤ 0.05). When the spread of Listeria was assessed during slicing of zucchini and cucumbers at different slicing speeds, the decay rates after slicing at high speed were -0.01 ± 0.005 and -0.02 ± 0.002, respectively, which were statistically similar (P > 0.05). Another objective of this study was to evaluate the effect of water content on transfer of Listeria during slicing. Floral foam, to which different amounts of water were added, was used as a model system in order to obtain different water saturation levels (75, 85 and 100%) under the same conditions. The decay rate observed at the 100% water saturation level (-0.23 ± 0.04) was significantly (P ≤ 0.05) less than low water saturation level (-0.72 ± 0.17) which indicate that moisture content affected bacterial transfer during slicing. The next study focused on quantifying the impact of various physicochemical parameters (water content, pH, texture, soluble solids content, surface hydrophobicity, and surface roughness) of produce (pears, onions, radishes, tomatoes, potatoes, carrots, zucchini, cantaloupe, apple, cucumber, gray zucchini and, sweet potatoes) on L. monocytogenes transfer during slicing. To evaluate the effect of pear firmness on bacterial transfer, three pear firmness categories were determined; firm (10-15 N), medium (6 - 9 N), and soft (< 6 N). For pear slicing, one pear was dip-inoculated with an avirulent L. monocytogenes cocktail (M3, J22F and J29H) as well as a 3-strain Salmonella cocktail (Montevideo, Poona, Newport) at ~5.5 log CFU/cm2 and air-dried in a bio-safety cabinet for 1 h before slicing. The inoculated product was sliced using a NEMCO slicer # 59155491 (Nemco Food Equipment Inc., Hicksville, OH), followed by 15 uninoculated pears, all of which yielded quantifiable numbers of bacteria after slicing. Statistically similar (P > 0.05) decay rates of -0.026, -0.039, and -0.032 were observed for firm, medium, and soft pears, respectively. Finally, onions, radishes, tomatoes, potatoes, carrots, zucchini, cantaloupe, apple, sweet potato, grey zucchini, and cucumber were assessed for Listeria transfer, after which a two-parameter exponential decay model was fit to the Listeria populations obtained during subsequent slicing of 15 uninoculated samples of the same product type. The decay rate (parameter B) ranged from 0.008 ± 0.002 for cucumber to 0.095± 0.41 for radish. The root mean square error (RMSE) ranged from 0.25 to 0.68 log CFU/product across the different types of produce, indicating a relatively good fit. When the inherent characteristics of these products were fit into a multiple linear model to describe the Listeria decay rate, produce surface roughness, soluble solids content, water content and surface hydrophobicity had a significant (P ≤ 0.05) effect on decay rate with parameter estimates of 0.00007±0.00002, -0.02±0.006, -0.008±0.002 and -0.0008±0.0002, respectively, with an intercept estimate of 0.955±0.28. Although the secondary model showed that surface roughness, soluble solids content, water content and surface hydrophobicity affected the bacterial decay rate during slicing, bacterial transfer could not be adequality explained based on the inherent produce factors that were studied.
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