Metabiosis of proteolytic moulds and Salmonella in raw, ripe tomatoes.

AIMS: The aim of this study was to determine the survival and growth characteristics of Salmonella enterica in sound and chill-injured tomatoes as influenced by co-infection with proteolytic moulds. METHODS AND RESULTS: Sound (not chill injured) raw, ripe tomatoes (Lycopersicon esculentum Mill. 'Roma') were inoculated with a five-serotype mixture of S. enterica and/or Alternata alternata (two strains), Cladosporium herbarum and C. cladosporioides. Simultaneous and delayed (3 days) inoculation of tomatoes with Salmonella and each mould was studied. Growth of moulds in sound tomatoes stored at 15 and 25 degrees C for up to 10 days was accompanied by increased pH of radial pericarp tissue (pulp), which enhanced the growth of Salmonella. Growth of moulds and Salmonella at 25 degrees C was enhanced in chill-injured tomatoes compared with sound tomatoes. CONCLUSIONS: Growth of proteolytic moulds in tomatoes stored at conditions simulating those commonly used in commercial postharvest storage and handling promotes the growth of Salmonella that may be an incidental contaminant. SIGNIFICANCE AND IMPACT OF THE STUDY: Discarding tomatoes that are infected by moulds is important in handling and minimal processing practices designed to minimize the risk of human salmonellosis.

Efficacy of ozone in killing Listeria monocytogenes on alfalfa seeds and sprouts and effects on sensory quality of sprouts.

A study was done to determine the efficacy of aqueous ozone treatment in killing Listeria monocytogenes on inoculated alfalfa seeds and sprouts. Reductions in populations of naturally occurring aerobic microorganisms on sprouts and changes in the sensory quality of sprouts were also determined. The treatment (10 or 20 min) of seeds in water (4 degrees C) containing an initial concentration of 21.8 +/- 0.1 microg/ml of ozone failed to cause a significant (P < or = 0.05) reduction in populations of L. monocytogenes. The continuous sparging of seeds with ozonated water (initial ozone concentration of 21.3 +/- 0.2 microg/ml) for 20 min significantly reduced the population by 1.48 log10 CFU/g. The treatment (2 min) of inoculated alfalfa sprouts with water containing 5.0 +/- 0.5, 9.0 +/- 0.5, or 23.2 +/- 1.6 microg/ml of ozone resulted in significant (P < or = 0.05) reductions of 0.78, 0.81, and 0.91 log10 CFU/g, respectively, compared to populations detected on sprouts treated with water. Treatments (2 min) with up to 23.3 +/- 1.6 microg/ml of ozone did not significantly (P > 0.05) reduce populations of aerobic naturally occurring microorganisms. The continuous sparging of sprouts with ozonated water for 5 to 20 min caused significant reductions in L. monocytogenes and natural microbiota compared to soaking in water (control) but did not enhance the lethality compared to the sprouts not treated with continuous sparging. The treatment of sprouts with ozonated water (20.0 microg/ml) for 5 or 10 min caused a significant deterioration in the sensory quality during subsequent storage at 4 degrees C for 7 to 11 days. Scanning electron microscopy of uninoculated alfalfa seeds and sprouts showed physical damage, fungal and bacterial growth, and biofilm formation that provide evidence of factors contributing to the difficulty of killing microorganisms by treatment with ozone and other sanitizers.