SANITATION OF PROCESS WATER FROM FRESH-CUT LETTUCE PRODUCTION BY MEANS OF UV-C

During fresh-cut production, the process water represents a major source of cross-contamination, facilitating foodborne pathogen transfer. Therefore, the efficacy of UV-C disinfection to reduce the microbiological load of lettuce wash waters was investigated. Wash water of iceberg and oak leaf lettuce was subjected to different doses of UV-C ranging from 34.8-174.2 J L^-1. As shown by the inactivation kinetics of total mesophilic viable counts, UV-C was highly efficient in reducing the microbial load of both lettuce wash waters. At 174.2 J L^-1, the initial viable counts were reduced by 3.2 and 2.1 log₁₀ cfu ml^-1 in iceberg and oak leaf lettuce process water, respectively. At this highest UV-C dose, members of the Enterobacteriaceae family were even reduced by 3.5 log₁₀ cfu ml^-1 in oak leaf lettuce wash water, while they were not detected in washing water of iceberg lettuce processing. Microbial loads in oak leaf lettuce wash water were higher than in that of iceberg lettuce processing, which was also reflected by a higher chemical oxygen demand (COD), higher absorption and turbidity. In the second experiment, conducted with iceberg lettuce and endive, UV-C lamps were installed in an industrial tubular washing system. Highly contaminated shredded lettuce was circulated six times in the tubes. Water and lettuce samples were analysed throughout processing. Despite high turbidities of up to 34.5±0.7 NTU, UV-C illumination reduced the viable counts in the water by 2.0 (endive) and 1.9 log₁₀ cfu ml^-1 (iceberg lettuce) after the sixth cycle compared to untreated process water. Both experiments proved UV-C treatment to be a promising option for product quality enhancement and sanitation of water during fresh-cut lettuce production, thus reducing the consumption of fresh water and microbial hazards. However, the efficacy of UV-C disinfection was shown to depend on physicochemical parameters, e.g., absorption, turbidity and COD of the water.