Effects of vegetable type, package atmosphere and storage temperature on growth and survival of Escherichia coli O157 : H7 and Listeria monocytogenes

The survival and growth of Escherichia coli O157:H7 (ATCC 43888 and NCTC 12 900) and Listeria monocytogenes (ATCC 19114 and NCTC 11994) during storage (4 and 8 degreesC) on ready-to-use (RTU) packaged vegetables (lettuce, swed es (rutabaga), dry coleslaw mix, soybean sprouts) were studied. The vegetab les were sealed within oriented polypropylene packaging film, and modified atmospheres developed in packs during storage due to produce respiration. S urvival and growth patterns were dependent on vegetable type, package atmos phere, storage temperature and bacterial strain. Populations of L. monocyto genes and E. coli O157:H7 increased (P < 0.05, by 1.5 to 2.5 log cycles, de pending on strain) during a 12-day storage period on shredded lettuce (8 de greesC). L. monocytogenes populations also increased (by similar to1 log cy cle) on packaged swedes, did not change significantly (P > 0.05) in package s of soybean sprouts and decreased by similar to1.5 log cycles (P < 0.05) o n coleslaw mix (8 degreesC). E. coli O157:H7 populations on packaged colesl aw and soybean sprouts increased (by 1.5 to 2.5 log cycles) up to day 5, bu t declined during subsequent storage (8 degreesC). On packaged swedes (8 de greesC), populations of E. coli O157:H7 strain ATCC 43888 increased (by sim ilar to1 log cycle) during storage, whereas populations of strain 12900 inc reased between days 2 and 5, and declined during subsequent storage. Reduci ng the storage temperature from 8 to 4 degreesC reduced the growth of L. mo nocytogenes and E. coli O157:H7 on packaged RTU vegetables. However, viable populations remained at the end of the storage period at 4 degreesC.