Available at: https://digitalcommons.calpoly.edu/theses/3136
Date of Award
5-2022
Degree Name
MS in Agriculture - Food Science and Nutrition
College
College of Agriculture, Food, and Environmental Sciences
Advisor
Amanda Lathrop
Advisor Department
Food Science and Nutrition
Advisor College
College of Agriculture, Food, and Environmental Sciences
Abstract
The consumption of ready-to-eat (RTE) foods has increased with popular RTE salad blends including non-traditional ingredients such as shredded Brussels sprouts, kale, red and green cabbage, chicory, and broccoli stalk. Concurrently, there has been an increase in the number of foodborne illnesses and outbreaks associated with leafy greens. The potential risk associated with these ingredients must be addressed as they have not typically been consumed raw, especially since L. monocytogenes continues to be a leading cause of foodborne illnesses and outbreaks. This study evaluated the survival of L. monocytogenes on two RTE salad blends at refrigeration, mildly abusive, and abusive temperatures, and analyzed previous research to examine the growth on individual ingredients compared to growth experienced on a blend.
Two salad blends containing non-traditional inclusions were obtained from a local manufacturer, inoculated with L. monocytogenes, and incubated at 22℃, 8℃, or 4℃ for 12h, 10d, or 25d, respectively. Samples were enumerated for L. monocytogenes, aerobic mesophilic, psychrotrophic, and lactic acid bacteria. Headspace gas, water activity, and pH were measured at each sampling time. The results were modeled using the DMfit add-in provided by ComBase.
Growth of L. monocytogenes was observed with overall greater growth observed in Salad Blend A at 8℃ and 22℃ compared to Salad Blend B. In Salad Blend A, L. monocytogenes was able to achieve a 1 log CFU/g increase at 4℃, 8℃, and 22℃ by 600h (25d), 96h (4d), and 12h, respectively. In Salad Blend B, L. monocytogenes was able to achieve a 1 log CFU/g increase at 4℃ by 600h (25d) and at 8℃ by 144h (6d). Headspace and pH had no discernable effect on the growth of L. monocytogenes or background growth, but the data suggested a relationship between higher levels of background microflora and decreased growth of L. monocytogenes.