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Escherichia coli O157:H7 has become a concern within the apple cider industry. The purpose of this study was to screen several essential oils and isolated components for antimicrobial activity against E. coli O157:H7 in tryptic soy broth at neutral and acidic pH and to assess the effect of these additives on the D-value of E. coli O157:H7 in apple cider in combination with mild heat treatments. Cinnamon oil and clove oil strongly inhibited the growth of E. coli O157:H7 at neutral and acidic pH, (R)-(--)-carvone and (S)-(--)-perillaldehyde were moderately inhibitory at both pH 7.2 and pH 4.5, and citral and geraniol, displayed moderate activity at pH 4.5 only. Lemon oil, methyl jasmonate, and p-anisaldehyde displayed little or no antibacterial activity. A synergistic effect between the essential oils and the lower pH of the growth medium was evident by consistently lower MICs at pH 4.5. Cinnamon and clove oils (0.01%, vol/vol) were further tested in apple cider in combination with mild heat treatments for the practical control of E. coli O157:H7 in apple cider. The addition of either essential oil resulted in lower D-values than those for cider alone, suggesting a synergistic effect and the potential efficacy of a mild heat treatment for apple cider. [ABSTRACT FROM AUTHOR]

Competition between spoilage microorganisms and foodborne pathogens provides a potentially simple approach to limiting the growth of pathogens. A strain of Pseudomonas fluorescens isolated from raw milk repressed growth of Escherichia coli O157:H7 at 22°C in nutrient broth once the maximum population density of the pseudomonad had been reached (9.6 log CFU ml-1). The presence of iron in the growth medium and the parallel inhibitory effect of a siderophore-deficient mutant of P. fluorescens precluded iron limitation as the mechanism of action. Medium depleted by prior growth of P. fluorescens prevented the growth of E. coli, and this effect was reversed by the replenishment of the nutrient broth, its component fractions, or the addition of soy peptones but not peptones derived from milk protein. This is the first report of competition between spoilage microflora and foodborne pathogens in which the mechanism was clearly shown to be nutrient limitation. These results suggest possible improvements in biocontrol systems to prevent pathogen growth on foods. [ABSTRACT FROM AUTHOR]

A probability model was developed to describe the influence of temperature (10–30°C) and factors characterizing the composition of mayonnaise (salt [0·5–16·5%], pH [3·5–6·0], acetic acid [0–4%] and sucrose [0–8%]) on the survival of Escherichia coli O157:H7 in tryptic soy broth. pH was adjusted independently by the use of HCl or NaOH. Logistic polynomial regression with a total of 1820 factor combinations was used to describe the influence of main, quadratic, and cross-product effects of the environmental factors. The model successfully predicted survival or death in 1772 (97·4%) of the samples; of those incorrectly predicted, 28 were false-positive (survival predicted where death occurred) and 20 were false-negative (death predicted where survival occurred). The concordance index was 99·4% and the disconcordance index was 0·6%, indicating a good fit of the model to the observed data. The model was validated using survival data from experimental mayonnaise inoculated with E. coli O157:H7. Of 30 combinations of acetic acid, salt and sucrose tested, survival/death was incorrectly predicted by the model in only six cases and, of these, only one prediction was not ‘fail-safe’. This prediction was attributed to the influence of quadratic effects in the model, and to attempts to make predictions outside the boundary of experimental conditions. The results suggest that the probability model developed here can be usefully applied to predictions of E. coli O157:H7 survival in mayonnaise. [Copyright &y& Elsevier]

Any theory constructed out of the metric tensor and its derivatives can also be regarded as a theory constructed out of a frame field and its derivatives. In general, the converse is not true. It is shown that with the additional assumption that the theories are Lorentz invariant the converse is true. Theories involving the metric spinor and its derivatives are then included in this equivalence and the various interrelationships are studied. [ABSTRACT FROM AUTHOR]