Thesis
Control of Listeria monocytogenes in Berries and Postharvest Water: Effects of Cold Storage and UV-C Treatment
Master of Science (MS), Washington State University
2026
Abstract
Raw and minimally processed blueberries and raspberries do not undergo lethality treatments and are typically stored under refrigerated or frozen conditions to extend shelf life, creating potential risks if contamination occurs. Given these berry types are highly perishable, novel postharvest approaches are needed. Fresh blueberries and raspberries (10 g) were inoculated with a five-strain L. monocytogenes cocktail targeting high (5.5 log CFU/g) and low (2 log CFU/g) populations and stored at 4°C and −18 ± 2°C. Populations were enumerated for up to 14 days at 4°C and 168 days under frozen storage. Under refrigeration, L. monocytogenes populations remained largely stable over time, while frozen storage resulted in gradual but statistically significant reductions, particularly for high-inoculated berries. Differences in survival patterns between high and low-inoculum levels underscore the influence of initial contamination on die-off dynamics, with high-inoculation generally producing biphasic declines and low-inoculation resulting in more stable or minimally declining populations. To address contamination control, UV-C treatments were applied using a conveyor system equipped with integrated UV-C lamps at dosages of 232, 478, and 843 J/m². Experiments included dry inoculated berries, berries submerged in uninoculated postharvest water of varying turbidity (0, 150, 300, and 450 NTU), and uninoculated berries submerged in inoculated wash water to simulate cross-contamination. UV-C significantly reduced L. monocytogenes populations on both fruit and in wash water. Even under unrealistically high turbidity conditions (450 NTU), applying 232 J/m² achieved reductions in L. monocytogenes of over 1.5 log CFU/g on berries and 2.5 log CFU/mL in water, no different than increasing dosages. Results demonstrate that L. monocytogenes can persist on blueberries and raspberries during refrigerated and frozen storage, and that UV-C can be used as an added mitigation step that can strengthen safety outcomes.
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Details
- Title
- Control of Listeria monocytogenes in Berries and Postharvest Water: Effects of Cold Storage and UV-C Treatment
- Creators
- Miriam Paola Ruiz Cuadra
- Contributors
- Claire Murphy (Advisor)Meijun Zhu (Committee Member)Stephanie Smith (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- School of Food Science
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Number of pages
- 117
- Identifiers
- 99901393806101842
- Language
- English
- Resource Type
- Thesis