Modeling the influence of propionic acid concentration and pH on the kinetics of Salmonella Typhimurium.

Salmonella Typhimurium is a foodborne pathogen often found in the poultry production chain. Antibiotics have been used to reduce S. Typhimurium contamination in poultry aviaries and improve chicken growth. However, antibiotics were banned in several countries. Alternatively, organic acids, such as propionic acid (PA), can control pathogens. This study determined the PA minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and mathematically modeled S. Typhimurium growth/inactivation kinetics under the influence of PA at different pH values (4.5, 5.5, and 6.5) which are within the pH range of the chicken gastrointestinal tract. The PA MIC against S. Typhimurium was pH-dependent, resulting in 5.0, 3.5 and 9.0 mM undissociated PA at pH 4.5, 5.5, and 6.5, respectively. The Baranyi and Roberts and the Weibull model fit growth and inactivation data well, respectively. Secondary models were proposed. The validated model predicted 3-log reduction of S. Typhimurium in 3 h at 68.2 mM of undissociated PA and pH 4.5. The models presented a good capacity to describe the kinetics of S. Typhimurium subjected to PA, representing a useful tool to predict PA antibacterial action depending on the pH.

Predicting Bacillus coagulans spores inactivation in tomato pulp under nonisothermal heat treatments.

UNLABELLED: The knowledge and understanding of Bacillus coagulans inactivation during a thermal treatment in tomato pulp, as well as the influence of temperature variation during thermal processes are essential for design, calculation, and optimization of the process. The aims of this work were to predict B. coagulans spores inactivation in tomato pulp under varying time-temperature profiles with Gompertz-inspired inactivation model and to validate the model's predictions by comparing the predicted values with experimental data. B. coagulans spores in pH 4.3 tomato pulp at 4 °Brix were sealed in capillary glass tubes and heated in thermostatically controlled circulating oil baths. Seven different nonisothermal profiles in the range from 95 to 105 °C were studied. Predicted inactivation kinetics showed similar behavior to experimentally observed inactivation curves when the samples were exposed to temperatures in the upper range of this study (99 to 105 °C). Profiles that resulted in less accurate predictions were those where the range of temperatures analyzed were comparatively lower (inactivation profiles starting at 95 °C). The link between fail prediction and both lower starting temperature and magnitude of the temperature shift suggests some chemical or biological mechanism at work. Statistical analysis showed that overall model predictions were acceptable, with bias factors from 0.781 to 1.012, and accuracy factors from 1.049 to 1.351, and confirm that the models used were adequate to estimate B. coagulans spores inactivation under fluctuating temperature conditions in the range from 95 to 105 °C. PRACTICAL APPLICATION: How can we estimate Bacillus coagulans inactivation during sudden temperature shifts in heat processing? This article provides a validated model that can be used to predict B. coagulans under changing temperature conditions. B. coagulans is a spore-forming bacillus that spoils acidified food products. The mathematical model developed here can be used to predict the spoilage risk following thermal process deviations for tomato products.

Modeling Penicillium expansum resistance to thermal and chlorine treatments.

Apples and apple products are excellent substrates for Penicillium expansum to produce patulin. In an attempt to avoid excessive levels of patulin, limiting or reducing P. expansum contamination levels on apples designated for storage in packinghouses and/or during apple juice processing is critical. The aim of this work was (i) to determine the thermal resistance of P. expansum spores in apple juice, comparing the abilities of the Bigelow and Weibull models to describe the survival curves and (ii) to determine the inactivation of P. expansum spores in aqueous chlorine solutions at varying concentrations of chlorine solutions, comparing the abilities of the biphasic and Weibull models to fit the survival curves. The results showed that the Bigelow and Weibull models were similar for describing the heat inactivation data, because the survival curves were almost linear. In this case, the concept of D- and z-values could be used, and the D-values obtained were 10.68, 6.64, 3.32, 1.14, and 0.61 min at 50, 52, 54, 56, and 60 degrees C, respectively, while the z-value was determined to be 7.57 degrees C. For the chlorine treatments, although the biphasic model gave a slightly superior performance, the Weibull model was selected, considering the parsimony principle, because it has fewer parameters than the biphasic model has. In conclusion, the typical pasteurization regimen used for refrigerated apple juice (71 degrees C for 6 s) is capable of achieving a 6-log reduction of P. expansum spores.

Influence of storage temperature and apple variety on patulin production by Penicillium expansum.

This study examined the potential for patulin production in six different varieties of apples (Red Delicious, Golden Supreme, Gala, Fuji, Empire, and McIntosh) inoculated with Penicillium expansum spores and stored at two different temperatures (11 and 20.5 degrees C). Samples for patulin analysis were randomly taken from apples stored at different times, ranging from 21 to 93 days. While patulin was produced at both storage temperatures, apples incubated at 20.5 degrees C yielded significantly higher patulin concentrations than did those incubated at 11 degrees C. All apple varieties showed mold spoilage at both temperatures, except Red Delicious and Empire. A total of 44% of the samples analyzed showed patulin concentrations above the U.S. Food and Drug Administration regulatory limit (50 ppb). The highest patulin productions occurred in Golden Supreme (54,221 ppb) and McIntosh (52,131 and 48,457 ppb) varieties. Our results showed that careful culling of apples is essential for high juice quality, since high patulin levels in some apples varieties could result in a level greater than 50 ppb of this mycotoxin in the finished juice or cider, even when only one contaminated apple occurs in 1,000 apples.

Efficacy of sanitizing treatments against Penicillium expansum inoculated on six varieties of apples.

The effectiveness of several wash treatments was evaluated against spores of Penicillium expansum inoculated on six varieties of apples (Red Delicious, Golden Supreme, Empire, Macintosh, Fuji, and Gala). The wash treatments were water, acidified water (pH 6.5), acidified sodium hypochlorite (pH 6.5), nonacidified sodium hypochlorite (pH 8.8, 9.3, and 9.7; 50, 100, and 200 ppm, respectively), and peracetic acid (50 and 80 ppm). Spores of P. expansum were dried on the surface of the apples for 2 h before exposure to the different sanitizer solutions. Each apple was submerged in 100 ml of each treatment solution for 30 s, and the number of spores remaining were recovered and enumerated. The efficacy of chlorine solutions was enhanced by decreasing the pH to 6.5 (up to 5-log reduction, depending on apple variety). Peracetic acid solutions (50 and 80 ppm) resulted in a reduction of less than 2 log spores per g and had the same efficacy (P < or = 0.05) as nonacidified chlorine solutions (50, 100, and 200 ppm). Control water solutions produced a reduction of 1.34 log spores per g. Chlorine solutions at pH 6.5 resulted in the largest reduction of P. expansum spores for all apple varieties tested.

Evaluation of the Weibull and log normal distribution functions as survival models of Escherichia coli under isothermal and non isothermal conditions.

Published survival curves of Escherichia coli in two growth media, with and without the presence of salt, at various temperatures and in a Greek eggplant salad having various levels of essential oil, all had a characteristic downward concavity when plotted on semi logarithmic coordinates. Some also exhibited what appeared as a 'shoulder' of considerable length. Regardless of whether a shoulder was noticed, the survival pattern could be considered as a manifestation of an underlying unimodal distribution of the cells' death times. Mathematically, the data could be described equally well by the Weibull and log normal distribution functions, which had similar modes, means, standard deviations and coefficients of skewness. When plotted in their probability density function (PDF) form, the curves also appeared very similar visually. This enabled us to quantify and compare the effect of temperature or essential oil concentration on the organism's survival in terms of these temporal distributions' characteristics. Increased lethality was generally expressed in a shorter mean and mode, a smaller standard deviation and increased overall symmetry as judged by the distributions' degree of skewness. The 'shoulder', as expected, simply indicated that the distribution's standard deviation was much smaller than its mode. Rate models based on the two distribution functions could be used to predict non isothermal survival patterns. They were derived on the assumption that the momentary inactivation rate is the isothermal rate at the momentary temperature at a time that corresponds to the momentary survival ratio. In this application, however, the Weibullian model with a fixed power was not only simpler and more convenient mathematically than the one based on the log normal distribution, but it also provided more accurate estimates of the dynamic inactivation patterns.