FACTORS AFFECTING THE GROWTH OF LISTERIA-MONOCYTOGENES ON MINIMALLY PROCESSED FRESH ENDIVE

The influence of various factors on the fate of Listeria monocytogenes on cut leaves of broad-leaved endive has been studied. Factors consid ered were temperature, characteristics of the leaves (age, quantity an d quality of the epiphytic microflora) and characteristics of the L. m onocytogenes inoculum (concentration, strain). The increases in number s oft. monocytogenes were lower than those of the aerobic mesophilic m icroflora at 3 degrees, 6 degrees, 10 degrees and 20 degrees C. Doubli ng times of the populations of L. monocytogenes were in the same order of magnitude as those of aerobic bacteria at 10 degrees and 20 degree s C, but longer at 3 degrees and 6 degrees C. There were positive sign ificant correlations between growth of L. monocytogenes and population s of aerobic bacteria, and between growth of L. monocytogenes and exte nt of spoilage on the leaves. Of 225 bacteria isolated from the leaves , 84% were identified as fluorescent pseudomonads; there was no differ ence in the species isolated from leaves that showed a low growth of L . monocytogenes and leaves that showed a high growth of L. monocytogen es. Populations of L. monocytogenes increased faster during the first 2 and 4 d of storage at 10 degrees C on leaves inoculated with 10-10(3 ) cfu g(-1) than on leaves inoculated with about 10(5) cfu g(-1), but the population reached after 7 d was lower. The behaviour of L. monocy togenes was similar among the three strains tested.