Lactic acid bacteria (LAB) are responsible for spoiling vacuum-packed meat products, such as ham. Since the temperature is the main factor affecting the microbial dynamic, the use of mathematical ...models describing the microbial behavior into a non-isothermal environment can be very useful for predicting food shelf life. In this study, the growth of Lactobacillus viridescens was measured in vacuum-packed sliced ham under non-isothermal conditions, and the predictive ability of primary (Baranyi and Roberts, 1994) and secondary (Square Root) models were assessed using parameters estimated in MRS culture medium under isothermal conditions (between 4 and 30°C). Fresh ham piece was sterilized, sliced, inoculated, vacuum-packed, and stored in a temperature-controlled incubator at five different non-isothermal conditions (between 4 and 25°C) and one isothermal condition (8°C). The mathematical models obtained in MRS medium were assessed by comparing predicted values with L. viridescens growth data in vacuum-packed ham. Its predictive ability was assessed through statistical indexes, with good results (bias factor between 0.95 and 1.03; accuracy factor between 1.04 and 1.07, and RMSE between 0.76 and 1.33), especially in increasing temperature, which predictions were safe. The model parameters obtained from isothermal growth data in MRS medium enabled to estimate the shelf life of a commercial ham under non-isothermal conditions in the temperature range analyzed.
This study aimed to assess the effects of ripening at refrigeration and ambient temperatures on physic-chemical and microbiological parameters of artisanal Minas cheeses (made from raw milk) and to ...model the kinetics of lactic acid bacteria – LAB, Escherichia coli – Ec, and coagulase-positive staphylococci – Sa along the ripening. Cheese pH, acidity, and moisture, fat, and protein contents were quantified, as well as LAB, Ec, and Sa concentrations. Richards and simplified Lotka-Volterra models were used to describe the microbial kinetic data. The fits were assessed by statistical indices, and the Monte-Carlo method was applied to identifiability analysis. Cheese moisture was reduced along the ripening, increasing protein concentration and acidity values. Cheese pH showed a reduction followed by an increase. LAB concentration increased to the stationary phase after a few days; Ec and Sa concentrations increased and then decreased due to interactions with LAB and low moisture content. Mathematical models successfully described the kinetics of LAB, Ec, and Sa in cheese throughout ripening. Most parameters were not correlated to each other and were estimated with narrow confidence intervals.
ABSTRACT Mathematical models are widely used to predict the shelf life of foods. Lactic acid bacteria (LAB), particularly Lactobacillus plantarum, Weissella viridescens and Lactobacillus sakei, are ...the main spoilage bacteria of refrigerated, vacuum-packed meat products, stored in modified atmosphere, and their growth determines the shelf life length of these products. The objective of this study was to model the growth of L. plantarum, W. viridescens and L. sakei under different isothermal cultivation conditions and establish secondary models to describe the effect of temperature on the growth parameters of these bacteria. The LAB growth was evaluated in culture medium at temperatures of 4, 8, 12, 16, 20 and 30 ºC. The fit of Baranyi and Roberts (BAR) and Gompertz (GO) primary models to the growth curves of LAB was compared by statistical indices, in which the BAR model showed slightly better fits to the experimental data. The BAR growth parameters were used to establish the secondary models, µmax and Nmax were established for the three LAB. The power model described the influence of temperature on the parameter λ for L. plantarum, and other bacteria showed no lag phase. The growth of LAB was strongly influenced by storage temperature and the obtained models allow predicting the growth of these bacteria within the temperature range from 4 to 30 ºC.
The current study was conducted to statistically compare the SYBR® Green quantitative polymerase chain reaction (qPCR) assay and the conventional plate counting (PC) method to construct growth curves ...of a cocktail of Weissella viridescens in pure culture under different isothermal storage conditions (4, 8, 14, and 30 °C) and in mixed culture with Leuconostoc mesenteroides at 8 °C. The efficiency and specificity of the qPCR standard curves were confirmed, and both methods were adequate to quantify the growth kinetics of W. viridescens at all isothermal temperatures, demonstrating a good correlation and agreement. The efficiencies of the standard curves varied between 98% and 102%. The SYBR® Green qPCR assay was also able to differentiate the growth curves of W. viridescens and L. mesenteroides in the mixed culture at 8 °C. Additionally, the SYBR® Green qPCR method was considered a faster and more sensitive alternative to construct growth curves under different isothermal conditions and differentiate morphologically similar lactic acid bacteria. Overall, the results suggest that the SYBR® Green qPCR method is a reliable and efficient tool to study microbial growth kinetics in pure and mixed cultures.
•The recN primer pair demonstrated selective detection of W. viridescens.•Standard curves of W. viridescens cocktail had adequate efficiency values.•LoD values were suitable for W. viridescens quantification at 4, 8, 14, and 30 °C.•SYBR® Green qPCR and PC methods showed good correlation and agreement.•SYBR® Green qPCR method distinguished the growth curves of LAB in mixed culture.
The physical and thermophysical properties (density, freezing temperature, specific heat, enthalpy, and thermal conductivity) of coffee extract were experimentally determined as a function of ...concentration (10–52 °Brix) and temperature (20 to −40 °C). Some models from the literature were also evaluated for predicting the behavior of these properties. Results indicated that all properties were influenced by the temperature and concentration of the solution due to their relationship with the amount of water/ice in the coffee extract. In general, the evaluated models described well the behavior of the coffee extract properties for a temperature range from −40 °C to 20°C, except for the specific heat. Thus, a model for predicting specific heat was obtained using the experimental data through a non-linear regression (R2 > 0.95). These models can be used to solve heat transfer problems involved in the cooling and freezing process of coffee extract.
•Thermophysical properties of coffee extract were determined.•The properties were influenced by temperature and concentration.•Models for the prediction of the thermophysical properties were proposed.•The proposed models can be used to solve heat transfer problems.
Salmonella genus has foodborne pathogen species commonly involved in many outbreaks related to the consumption of chicken meat. Many studies have aimed to model bacterial inactivation as a function ...of the temperature. Due to the large heterogeneity of the results, a unified description of Salmonella spp. inactivation behavior is hard to establish. In the current study, by evaluating the root mean square errors, mean absolute deviation, and Akaike and Bayesian information criteria, the double Weibull model was considered the most accurate primary model to fit 61 datasets of Salmonella inactivation in chicken meat. Results can be interpreted as if the bacterial population is divided into two subpopulations consisting of one more resistant (2.3% of the total population) and one more sensitive to thermal stress (97.7% of the total population). The thermal sensitivity of the bacteria depends on the fat content of the chicken meat. From an adapted version of the Bigelow secondary model including both temperature and fat content, 90% of the Salmonella population can be inactivated after heating at 60 °C of chicken breast, thigh muscles, wings, and skin during approximately 2.5, 5.0, 9.5, and 57.4 min, respectively. The resulting model was applied to four different non-isothermal temperature profiles regarding Salmonella growth in chicken meat. Model performance for the non-isothermal profiles was evaluated by the acceptable prediction zone concept. Results showed that >80% of the predictions fell in the acceptable prediction zone when the temperature changes smoothly at temperature rates lower than 20 °C/min. Results obtained can be used in risk assessment models regarding contamination with Salmonella spp. in chicken parts with different fat contents.
•Inactivation curves show biphasic behavior related to inactivation phase.•Temperature affects decimal reduction more significantly than fat content.•Most promising model combines double Weibull and Bigelow models.•Model predicts acceptably non-isothermal inactivation at rates up to 20 °C/min.
The TaqMan-based quantitative Polymerase Chain Reaction (qPCR) method and the Plate Count (PC) method are both used in combination with primary and secondary mathematical modeling, to describe the ...growth curves of Leuconostoc mesenteroides and Weissella viridescens in vacuum-packaged meat products during storage under different isothermal conditions. Vacuum-Packaged Morcilla (VPM), a typical cooked blood sausage, is used as a representative meat product, with the aim of improving shelf-life prediction methods for those sorts of meat products. The standard curves constructed by qPCR showed good linearity between the cycle threshold (CT) and log10 CFU/g, demonstrating the high precision and the reproducible results of the qPCR method. The curves were used for the quantification of L. mesenteroides and W. viridescens in artificially inoculated VPM samples under isothermal storage (5, 8, 13 and 18 °C). Primally, both the qPCR and the PC methods were compared, and a linear regression analysis demonstrated a statistically significant linear correlation between the methods. Secondly, the Baranyi and Roberts model was fitted to the growth curve data to estimate the kinetic parameters of L. mesenteroides and W. viridescens under isothermal conditions, and secondary models were used to establish the dependence of the maximum specific growth rate on the temperature. The results proved that primary and secondary models were adequate for describing the growth curves of both methods in relation to both bacteria. In conclusion, the results of all the experiments proved that the qPCR method in combination with the PC method can be used to construct microbial growth kinetics and that primary and secondary mathematical modeling can be successfully applied to describe the growth of L. mesenteroides and W. viridescens in vacuum-packaged morcilla and, by extension, other cooked meat products with similar characteristics.
Display omitted
•Lactic acid bacteria quantification in meat products by qPCR•Correlation of plate count and qPCR methods, both were adequate for evaluating the growth curves.•Primary and secondary models were successfully applied for fitting of molecular data.•qPCR combined with mathematical models estimated growth kinetics of lactic acid bacteria in cooked meat product.
The aim of this study was to establish primary and secondary models to describe the growth kinetics of Byssochlamys fulva on solidified apple juice at different temperatures. B. fulva was inoculated ...on solidified apple juice at 10, 15, 20, 25 and 30 °C. Linear-with-breakpoint, Baranyi and Roberts, and Huang primary models (without upper asymptote) were fitted to the data, and they showed good ability to describe the growth kinetics. B. fulva showed longer adaptation time on apple juice than on culture medium, but growth rates were similar as reported in the literature. The dependence of µmax and λ parameters on temperature was described with Square Root and Arrhenius-Davey secondary models, respectively. These models were important to establish process/storage conditions and apple juice shelf life.
The present study modeled the effect of oregano essential oil, as an antimicrobial agent, on the shelf-life of vacuum-packed cooked sliced ham, based on the growth of lactic acid bacteria natural ...microbiota under isothermal conditions. The bacterial growth in ham without oregano essential oil (control) and with 0.4% oregano essential oil (v/w) was evaluated at five different temperatures (6, 12, 15, 20 and 25°C). Baranyi and Roberts, and modified Gompertz primary models were fitted to microbial growth curves. Square Root and Exponential secondary models were fitted to μmax parameter data. The addition of oregano essential oil increased lag phase, decreased growth rates and extended shelf-life of ham for all temperatures (at 6°C extended for, at least, 30days when compared to control). Statistical indexes showed that Baranyi and Roberts, and Exponential were the primary and secondary models, respectively, that better fit to the data. Thus, oregano essential oil showed a good antimicrobial effect and extended the ham shelf-life.
The present work aimed to evaluate and to model the influence of UV-C light treatments with different irradiances (6.5, 13, 21, and 36 W/m2) on Aspergillus fischeri and Paecilomyces niveus ascospores ...inactivation in clarified apple juice. Approximately 5.0 and 6.0 log CFU/mL spores of P. niveus and A. fischeri, respectively, were suspended in 30 mL of clarified apple juice (pH 3.8, 12 ± 0.1°Brix) and exposed to UV-C light at different irradiances (as above) and exposure times (0 to 30 min). The first-order biphasic model was able to describe the experimental data with good statistical indices (RMSE = 0.296 and 0.308, R2 = 0.96 and 0.98, for P. niveus and A. fischeri respectively). At the highest irradiance level tested (36 W/m2), the UV-C light allowed the reduction of 5.7 and 4.2 log-cycles of A. fischeri and P. niveus ascospores, respectively, in approximately 10 min. P. niveus was the most UV-C resistant mould. The results showed that, to a defined UV-C fluence, a change in the level of either time or UV-C irradiance did not affect the effectiveness of UV-C light for A. fischeri and P. niveus inactivation. Thus, the modeling of the inactivation as a function of the UV-C fluence allowed the estimation of the primary model parameters with all experimental data and, consequently, no secondary models were needed. The model parameters were validated with experiments of variable UV-C fluences. Accordingly, experimental results allowed to conclude that UV-C treatment at the irradiances tested is a promising application for preventing A. fischeri and P. niveus spoilage of juices.
•UV-C treatment was able to inactivate A. fischeri and P. niveus in apple juice.•36 W/m2 for 8 min reduced 5 and 4 log cycles of A. fischeri and P. niveus, respectively.•P. niveus was more UV-C resistant than A. fischeri in apple juice.•P. niveus and A. fischeri exhibited first-order biphasic inactivation in apple juices.•The model parameters were validated with experiments of variable UV-C fluences.
PDF
