CONICET | Buscador de Institutos y Recursos Humanos

Foodborne illness outbreaks and ground beef recalls because of Escherichia coli O157:H7 contamination continue to be a mayor cause of concern to the public, regulatory authorities and food industry. E. coli O157:H7, which can have serious human health effects, particularly among children, is reported to have a very low infective dose. In the last years, there has been an increase in studies on the role of antimicrobial compounds produced by lactic acid bacteria (LAB) in the inhibition of pathogenic and contaminant microorganisms in food. Even when bacteriocins of LAB are effective against gram positive bacteria, by using a combination with a food-grade chelator, such as EDTA, theirs effectiveness can be extended to gram negative bacteria. This work aims to investigate the effect of the bioprotective cultures, Lactobacillus curvatus CRL705 and Lactococcus lactis CRL1109 combined with Na2EDTA on the growth of E. coli O157:H7 on frozen hamburgers (-12ºC), in a pilot plant scale and submitted to conditions of temperature abuse (5ºC during 6 days). Our data showed that the addition of bioprotective cultures with chelator was more effective against E. coli O157:H7 than was Na2EDTA alone, this effect being evident at 6 days of incubation at 5ºC. A similar effect on the indigenous coliforms present in the hamburgers with the treatment above mentioned was obtained. In the absence of Na2EDTA, the bacteriocinogenc strains did not affect E. coli O157:H7 growth, this reaching similar cell counts to the control samples (4.08 log ufc/g). L. curvatus CRL705 and Lc. lactis CRL1109 were able to growth increasing theirs population by 0.40 and 0.53 logs, respectively at the end of the assayed period. In the other hand, the pH value of hamburgers treated with bioprotective cultures and/or E. coli O157:H7 was not significantly different to the untreated control while that in the presence of chelator, a near-neutral pH value was obtained. The presence of inhibitory activity was detected after 48 h of incubation in the hamburgers inoculated with the bioprotective cultures remained stable throughout the storage period. The addition of both bacteriocinogenic strains had no substantial effect on objective colour (CIE L*,a*,b*), while the interaction E. coli O157:H7 with Na2EDTA significantly declined the colour units of the hamburgers. The results presented here validate the previously obtained at laboratory scale. It can be concluded that the effectiveness of L. curvatus CRL705 and Lc. lactis CRL1109 as bioprotective cultures in combination with Na2EDTA to inhibit the growth of E. coli O157:H7 contributes to the maintenance of the hygienic-sanitary quality of frozen hamburgers submitted to inadequate storage conditions

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