Fate of Microbial Contaminants in Lettuce Juice ¹

Lettuce is a common menu item that may involve bacteria of public health significance. The most favorable environment for bacterial growth is the exudate (juice) from cut or broken leaves. Bacteria from growing lettuce and those added during harvesting, transportation and storage are able to grow in the exudate. At 10 C gram-negative, psychrotrophic bacteria become the predominant elements of the microflora, while at 20 C the microflora resemble those commonly associated with lactic fermentation of vegetables. Increasing the concentration of solids in lettuce juice to simulate evaporation from droplets of exudate suppressed growth of some members of the natural flora but had little effect on added bacteria of public health significance. Vacuum packaging only decreased slightly the rate of growth of the normal flora in droplets of lettuce juice. All the results indicated lettuce juice may be important as a harborage for bacteria of public health significance.