Study of survival characteristics of Listeria monocytogenes on edible vegetables

ObjectiveTo investigate the impact of edible vegetable varieties， temperatures， and inoculation sites on the survival of Listeria monocytogenes （L. monocytogenes）， providing a theoretical foundation for risk assessment and key control measures of L. monocytogenes in edible vegetables.MethodsFreeze-dried quantitative L. monocytogenes served as the strain source， with the surfaces and sections of five edible vegetables （colored pepper， onion， cucumber， virgin fruit and lettuce） used as inoculation sites. The strain was cultured at both 4 ℃ and 25 ℃ for 7 days. Regular monitoring of the L. monocytogenes quantity in each sample was conducted， and growth was analyzed.ResultsThe quantity of L. monocytogenes freeze-dried in different bottles was uniform （F=1.923， P<0.05）， with a 93.3%±4.2% recovery rate after 28 days of storage at -20 ℃. At 4 ℃， L. monocytogenes did not show significant growth on vegetables， except for the surface of colored pepper， cucumber slices， the surface and cut side of lettuce after 7 days on other vegetables （δ<0.5 log10 CFU/mL）. At 25 ℃， L. monocytogenes exhibited supportive growth on colored pepper， onion， virgin fruit， lettuce and cucumber slices ［δ=（1.16±0.35）~（2.68±0.18）log10 CFU/mL］. The quantity of L. monocytogenes on the cut of cucumber， the surface of lettuce and the cut of lettuce continued to increase after 7 days of storage， with a consistent growth trend and concentration on the surface and cut side of lettuce.ConclusionThe survival of L. monocytogenes on edible vegetables is closely linked to vegetable species， surface and section， storage temperature and other conditions. Temperature control is essential to mitigate the risk in edible vegetables. Lettuce and cut cucumbers are high risk foods for L. monocytogenes and should be of particular concern for risk assessment.