Control of Listeria monocytogenes on berries and in postharvest water by ultraviolet (UV-C) light

The persistence of Listeria monocytogenes on fresh and frozen berries presents a major food safety concern, necessitating interventions to reduce contamination while preserving quality. This study evaluated the reduction of L . monocytogenes on inoculated blueberries and raspberries in postharvest water treated with UV-C light (254 nm). Fresh berries were inoculated with a five-strain L. monocytogenes cocktail at 5.5 log CFU/g. A conveyor belt operated with integrated UV-C bulbs system was used to irradiate berries at dosages of 232, 478 and 843 J/m 2 . Trials included dry inoculated berries, inoculated berries submerged in uninoculated postharvest water at varying turbidities (0, 150, 300, and 450 NTU), and uninoculated berries submerged in inoculated postharvest water at varying turbidities. UV-C treatment significantly reduced L. monocytogenes on inoculated blueberries and raspberries, in postharvest wash water, and under cross-contamination scenarios, with reductions generally increasing with UV-C dosage. UV-C achieved approximately 2–3 log CFU/g reductions on blueberries and from 1. 5 - 4.2 log CFU/g on raspberries, while in wash water reductions ranged from ∼2 to 3.6 log CFU/mL across turbidity levels, with higher dosages (478and 843 J/m 2 ) consistently providing greater inactivation. Although increasing turbidity reduced UV-C efficacy in some scenarios, substantial pathogen reductions and mitigation of cross-contamination were still achieved, and modeling confirmed a significant dose–response relationship and interactive effects among turbidity, dosage, and contamination source. These findings support optimizing postharvest UV-C protocols to enhance the microbial safety of berries while maintaining quality to limit contamination. • UV-C reduced L. monocytogenes by 2 - 4 log CFU/g on both inoculated berry types and ∼3 log CFU/mL in water • UV-C reduced cross-contamination from water to fruit by ∼1.9 log CFU/g and from fruit to wash water by ∼2.4 log CFU/mL • UV-C remains effective despite increasing water turbidity, making it a practical multi-barrier intervention