Assessment of the microbiological quality of ready-to-use vegetables for health-care food services

Abstract

The microbiological quality of ready-to-use (RTU) vegetables, including chopped lettuce, salad mix, carrot sticks, cauliflower florets, sliced celery, coleslaw mix, broccoli florets, and sliced green peppers was determined before and after processing. Microbial profiles were obtained 24 h after processing and on days 4, 7, and 11 after storage at 4 and 10°C to simulate temperature abuse. In addition, the microbial profiles of four RTU vegetables, coleslaw mix, salad mix, cauliflower florets, and sliced green peppers were determined 7 days after distribution to a select group of Ontario hospitals. RTU vegetables, with the exception of green peppers, showed up to a 1-log decrease in aerobic colony counts after processing. These counts increased to preprocessing levels after 4 days of storage at both 4 and 10°C. RTU vegetables stored at temperature abuse conditions (10°C) had significantly higher counts (P < 0.001) on days 4 to 11 as compared to those stored at 4°C. Green peppers had the highest bacterial counts while cauliflower and chopped lettuce had the lowest counts at both storage temperatures (P < 0.05). Increased levels of Listeria monocytogenes in RTU vegetables were associated with temperature abuse. Levels of >100 MPN/g for L. monocytogenes were detected in 8 of 120 (6.7%) samples stored at 10°C but not in 175 samples stored at 4°C after 7 days (P <0.05). Overall, L. monocytogenes was detected in 13 of 120 (10.8%) RTU vegetables stored for up to 11 days at 10°C and 5 of 176 (2.8%) samples stored at 4°C (P < 0.05). E. coli was detected in 2 of the 120 (1.7%) processed RTU vegetables after day 7 of storage at 10°C and l of the 65 (1.5%) unprocessed vegetables from the same batches of vegetables used for processing. This indicator organism was not detected in RTU vegetable samples stored at 4°C or in any of the RTU vegetable samples obtained from hospital coolers. Other pathogenic bacteria, such as Salmonella spp., Campylobacter spp., Yersinia enterocolitica (serotype O:3) and verocytotoxigenic E. coli (VTEC) were not detected in any of the RTU vegetables tested. Recommendations regarding processing, distribution, and storage of these products are presented.