SURVIVAL OF ESCHERICHIA COLI O157:H7 DURING THE STORAGE OF GREEN TABLE OLIVES CV. HALKIDIKI IN BRINE

摘要

The survival of the pathogen Escherichia coli O157:H7 during the storage of green table olives cv. Halkidiki in brine was studied in parallel with the evolution of lactic acid bacteria, yeasts and pH. A strain of Lactobacillus pentosus was used as starter culture in the Spanish style fermentation that was conducted prior to packaging. After the end of the fermentation, olives were packaged in brine (NaCI 6% w/v) and inoculated with E. coli O157:H7 (co-culture of 5 strains) in initial concentration of 6.9 log cfu/ mL. The corresponding concentration of the pathogen on the olive fruits was 4.8 log cfu/ g, whilst lactic acid bacteria and yeasts were found to be 6.2 and 2.2 log cfu/ g, respectively. The population of E. coli O157:H7 reduced gradually reaching the detection limit of the enumeration method after 8 and 5 days in the brine and olive fruits, respectively. On the contrary, using the enrichment method, the pathogen was detected even on the 27th and 19th day of storage in the brine and olive fruits respectively. At the same time the population of lactic acid bacteria was similar with the initial levels (with a minor increase), whereas yeasts population showed an increase of 3 log cycles. The pH values in the olives fruits remained stable during storage at 4.2 approximately, with the brine pH reaching the same value after the 6th day. These results demonstrate that the pathogen E.coli O157:H7 retains the ability of surviving for a long period (27 days) in a stressful environment of a fermented product with low pH value (4.2), a fact that enhances the need of applying strictly good manufacturing practices to reduce the possibility of cross contamination.