THE INFLUENCE OF OXYGEN AND CARBON-DIOXIDE ON THE GROWTH OF PREVALENTENTEROBACTERIACEAE AND PSEUDOMONAS SPECIES ISOLATED FROM FRESH AND CONTROLLED-ATMOSPHERE-STORED VEGETABLES

To obtain more insight into the specific impact of modified gas condit ions on the composition of microflora of minimally processed vegetable s, the prevalent bacteria on mungbean sprouts and cut chicory endive w ere determined during storage under controlled atmospheric (CA) condit ions at 8 degrees C. Enumeration of the total mesophilic counts, Enter obacteriaceae, Pseudomonas species, and lactic acid bacteria indicated that Enterobacteriaceae and Pseudomonas species constituted the major populations found on these products before and after CA storage. iden tification of the predominant species within these populations reveale d that on fresh and CA-stored mungbean sprouts, Enterobacter cloacae, Pantoea agglomerans, Pseudomonas fluorescens, Ps, viridilivida and Ps. corrugate were the prevalent species. On chicory endive, Rahnella aqu atilis and several Pseudomonas species were found on the fresh product , while after CA storage, Escherichia vulneris and Ps, fluorescens wer e the main species. Growth of the predominant epiphytes was subsequent ly quantified in pure culture, using an agar model system at 8 degrees C under 1.5 or 21% O-2 with 0, 5, 20, or 50% CO2. In general, these C A conditions did not strongly influence maximum population densities a nd lag rimes were not detected. For each of the strains, however, maxi mum specific growth rates were reduced at increased CO, concentrations , independent of the 0, concentration applied. This effect was more pr onounced for Pseudomonas species than for Enterobacteriaceae. Notably, the agar model study showed that individual species of Enterobacteria ceae or Pseudomonas responded similarly to the specific CA conditions applied. This did not correlate with the shift in predominant species observed on chicory endive. Our data underline the complexity of the e cological conditions to which micro-organisms on vegetables are subjec ted during storage under modified gas conditions. (C) 1998 Academic Pr ess.