The Weibull Model for Microbial Inactivation

Modeling of mold inactivation via cold atmospheric plasma (CAP)

During their reproduction cycles, the omnipresent pathogens produce a broad class of mycotoxins responsible for serious health problems in living organisms. To reduce (or even to eradicate) the microorganisms from the invaded system, various conventional methods are applied in practice, sometimes with counterproductive effects. To overcome these challenges, the cold atmospheric plasma (CAP) is applied to terminate mold proliferation within the system. The paper presents a mathematical model for the elimination of microscopic filamentous types of fungi, specifically molds, by using the CAP. The evolution of mold population is described by a nonlinear logistic equation with a density-dependent inactivation rate. Exactly calculated growth curves are compared with experimental data for Aspergillus brasiliensis obtained for two plasma operating times. The results show that if the plasma inactivation rate is comparable to the maximum natural growth rate of the mycelium, the mold colony becomes extinct after a finite time. Otherwise, the mycelium may survive the plasma intervention. The model presented in the paper can be applied to other classes of microorganisms (e.g., bacteria and viruses), using different inactivation techniques (e.g., heating or high pressures with properly defined inactivation rates).

IMPORTANCE

The novelty of this study is to model the extinction process of molds from an invaded system by using a nonlinear logistic equation with a density-dependent inactivation rate. The resulting analytical solution allows us to determine the coverage of the surface by mycelium at arbitrary times. The calculated growth curves are compared with data sets for Aspergillus brasiliensis. An advantage of this model is the possibility to obtain relevant information in a matter of minutes, compared to the highly time-consuming real experiments that can take weeks.

A farm-to-consumption quantitative microbiological risk assessment for hepatitis E in pigs

Foodborne transmission appears to be a significant route for human hepatitis E virus (HEV) infection in Europe. We have developed a quantitative microbiological risk assessment (QMRA) for HEV infection due to consumption of three selected pork products (liver pâté, minced meat, and sliced liver), which models the steps from farm to human consumption in high detail, including within-farm transmission dynamics and microbiological processes such as cross contamination and thermal inactivation. Our model is unique in that it considers prevalence and viral load of two microbiological variables, HEV RNA and infectious HEV, expressing the latter in terms of the former through so-called "adjustment factors" where data are lacking. When the QMRA was parameterized for France and using infectious HEV, we found that sliced liver posed by far the highest risk of infection, with mean probability per portion3.35 × 10 - 4 [ 95 % CI ( 3.28 - 3.42 ) × 10 - 4 ] $3.35\times 10^{-4}\,[95\%\ \text{CI}\ (3.28-3.42)\times 10^{-4}]$ , corresponding to3447 ( 95 % CI 3372 - 3522 ) $3447\,(95\%\ \text{CI}\ 3372-3522)$ human cases annually. For minced meat, the probability of infection was3.68 × 10 - 8 [ 95 % CI ( 3.56 - 3.80 ) × 10 - 8 ] $3.68\times 10^{-8}\,[95\%\ \text{CI}\ (3.56-3.80)\times 10^{-8}]$ , with only21 ( 95 % CI 20 - 21 ) $21\,(95\%\ \text{CI}\ 20-21)$ human cases. While our model predicted appreciable levels of HEV RNA remaining in liver pâté at the point of consumption, the amount of infectious HEV and hence risk of infection was zero, emphasizing the importance of using the correct microbiological variable when assessing the risk to consumers. Owing to its highly mechanistic nature, our QMRA can be used in future work to assess the impact of control measures along the pork-supply chain at high resolution.

Improving ready-to-eat meat safety: Evaluating the bacterial-inactivation efficacy of microplasma-based far-UVC light treatment of food-contact surfaces and deli turkey breast

The safety of ready-to-eat (RTE) deli meats, especially those sliced in retail establishments, may be improved by light-based surface decontamination. Conventional 254 nm ultraviolet-C (UVC) systems have strong germicidal effects but pose human-health hazards that make them unsuitable for retail use. This study therefore explores the efficacy of microplasma-based 222 nm far-UVC lamps as a safer alternative for decontaminating liquid buffer, two common food-contact surfaces (polyethylene terephthalate and stainless steel), and RTE turkey breast. In all three non-meat cases, the system achieved approximately 5-log reductions of both Listeria monocytogenes and Salmonella Typhimurium. The system also caused a 1.3-log reduction of L. monocytogenes and a 1-log reduction of S. Typhimurium on turkey breast at the highest tested dose of 786.3 mJ/cm2. Color is a key quality indicator for RTE meat consumers, and treatment caused no significant change in L∗, a∗, or b∗ color values (p > 0.05) until doses reached 224.7 mJ/cm2. However, higher doses could lead to statistically significant color changes. Given that far-UVC light has been deemed human-safe by other studies, the proposed system has considerable potential to improve RTE food-related safety in retail establishments, even when consumers and workers are present.

Integrated Quality Prediction Model for Food Quality Management Based on E. coli in Shared Kitchens

Shared kitchens have a lower entry barrier than traditional kitchens, which generally require a significant initial investment, and have thus attracted attention as the most realistic new business model for restaurants in the sharing economy. The restaurant industry is founded on ensuring the safety of the food it serves in order to prevent the spread of foodborne diseases within the community, so strict quality control is essential. Existing food quality management typically employs continuous quality assistance, which is difficult to apply to the highly volatile shared kitchen environment and its various stakeholders. Therefore, in this study, a predictive model for managing food quality that can monitor volatility using quantitative indicators, especially microbial counts, is proposed. Stakeholder- and quality-related factors associated with shared kitchens are first defined, then a modified Gompertz growth curve and the transfer rate equation are used to quantify them. The proposed model, utilizing E. coli as a practical indicator for easily measuring changes in general environments, can be used to systematically manage food quality within the shared kitchen industry, thus supporting the establishment of this new business model.

Improving Cleaning Efficiency through the Measurement of Food Fouling Adhesive Strength

This study aims to investigate the impacts of factors, including textural properties, surface roughness, and contact angle, on the cleaning performance of food soils and develop a preliminary mathematical model to predict the cleaning score, depending on the soil-surface properties. The force required to remove soil from the surface was determined by a texture analyzer equipped with a newly designed probe. Potato puree and egg yolk soils showed high adhesive forces compared to other deposits. Margarine required the lowest force to detach from the surfaces. A soil-surface characteristic number (SSCN) was constructed from the results of contact angle, roughness, and textural analysis to predict the cleaning score depending on the soil-surface properties. The experimental work presented indicates that a higher SSCN was associated with lower cleaning scores for soil-surface combinations. Furthermore, a predictive model was developed to define the relationship between cleaning scores and SSCN. The applicability of the model was validated by measuring the cleaning performance of caramel and pudding soils on glass, porcelain, and stainless-steel household surfaces by using an automatic method. Therefore, it can be concluded that the SSCN approach can be improved in further studies to predict cleaning scores of soil-surface combinations in the experimental rig or automatic dishwasher.

Predictive modeling of molds effective elimination by external inactivation sources

Presented paper deals with a novel application of the (nonlinear) logistic equation to model an elimination of microscopic filaments types of fungi-molds from affected materials via different external inactivation techniques. It is shown that if the inactivation rate of the external source is greater than the maximum natural growth rate of mycelium, the mold colony becomes destroyed after a finite time. Otherwise, the mycelium may survive the external attack only at a sufficiently large initial concentration of the inoculum. Theoretically determined growth curves are compared with the experimental data for Aspergillus brasiliensis mold inactivated by using both cold atmospheric plasma (CAP) and UV-germicidal lamp. Model presented in the article may be applied also to other classes of microorganisms (e.g. bacteria).

Water disinfection using hydrogen peroxide with fixed bed hematite catalyst - kinetic and activity studies

A lab-scale reactor with a fixed-bed hematite catalyst for the effective decomposition of H2O2 and bacteria inactivation was designed. The bactericidal effect is the largest at a low initial bacterial count of 2·103 CFU/L, which is typical for natural surface waters. When using a 5 mM H2O2 solution and a residence time of 104 min, the reduction in the number of E. coli bacteria is about 3.5-log. At a higher initial bacterial count of 1-2·104 CFU/L, a 5 mM H2O2 solution reduces the bacteria number by about 4-log. The H2O2 decomposition follows the log-linear kinetics of a first-order reaction while the bacterial inactivation does not. The kinetics of bacterial inactivation was described using the Weibull model in the modified form: log10(N0/N) = b · tn. The values of the non-linearity parameter n were found to be lower than 1, indicating that bacterial inactivation slows down over time. With increasing initial H2O2 concentration, the rate parameter b increases while the non-linearity parameter n decreases. With increasing temperature, both parameters increase. The stability of the catalyst has been proved by XRD, FTIR, SEM, and ICP-OES. The concentration of iron leaching into water during disinfection is much lower than the limit declared by WHO for iron in drinking water. The results show that technical-grade hematite is a promising Fenton-like catalyst for water disinfection. The fixed-bed reactor can be the basis of the mobile installations for water purification in emergencies.

Lactiplantibacillus plantarum MIUG BL21 paraprobiotics: Evidences on inactivation kinetics and their potential as cytocompatible and antitumor alternatives

Two new -biotics concepts, such as paraprobiotics and postbiotics were introduced, with beneficial effects beyond the viability of probiotic. In this study, the effect of individual (thermal, ohmic heating, high pressure, and ultrasound) and combined (ohmic, high pressure and ultrasound in combination with heating) treatments on the inactivation kinetics of Lactiplantibacillus plantarum was investigated. Different inactivation rates were obtained, up to 8.18 after 10 min at 90 °C, 2.07 after 15 min at a voltage gradient of 20 V/cm, 6.62 after 10 min at 600 MPa and 3.6 after ultrasound treatment for 10 min at 100 % amplitude. The experimental data were fitted to Weibullian model proposed by Peleg, allowing to estimate the inactivation rate coefficient (b) and the shape of the inactivation curves (n). At lower concentration, the samples showed both cytocompatibility and antiproliferative effect, stimulating the cell proliferation on both murine fibroblast and human colorectal adenocarcinoma cell lines.

Modeling the γ-irradiation inactivation kinetics of foodborne pathogens Escherichia coli O157:H7, Salmonella, Staphylococcus aureus and Bacillus cereus in instant soup

The objective of the present study was to assess the inactivation kinetics of γ-irradiation of selected foodborne pathogens in instant soup. Escherichia coli O157:H7 (ATCC 25922), Salmonella enterica subsp. enterica serovar Enteritidis (ATCC 13076), Staphylococcus aureus (ATCC 2592), and Bacillus cereus (ATCC 11778) were inoculated into instant soup and irradiated at various doses of 0 (control), 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, and 10.0 kGy using 60Co source. The radiation response of these four major foodborne disease pathogens in instant soup was tested. As expected, the pathogen population decreased with increasing irradiation dose. By comparing bacterial resistance in instant soups according to D10 values, E coli O157: H7 was the most radio-resistant bacteria (D10 of 1.580 kGy), followed by Salmonella (D10 of 1.160 kGy), S aureus (D10 of 0.775 kGy), B cereus (D10 of 0.462 kGy). For modeling of inactivation kinetics, both, the conventional first-order linear model and Weibull model were compared and the goodness of fit of these models was investigated. Weibull model produced a better fit to the data. This research has shown that γ-irradiation was effective to eliminate pathogens in instant soup and it can be a great way to assure the microbiological safety of the instant soup.

The probability of bacterial spores surviving a thermal process: The 12D myth and other issues with its quantitative assessment

The concepts of "D-value," "thermal death time" and "commercial sterility," innovative and useful at their inception, are based on untenable assumptions, notably that the log-linear isothermal inactivation model has universal applicability, that extrapolation over several orders of magnitude below the detection level is permissible, and that total microbial inactivation is theoretically impossible. Almost all commonly observed inactivation patterns, the log-linear is just a special case, can be described by both deterministic and fully stochastic models, examples of which are given. Unlike the deterministic, the stochastic models predict either complete elimination of the targeted cells or spores in realistic finite time, or residual survival. In most cases, the published survival data do not contain enough information to establish which actually happens. The microbial safety of thermally processed foods can be compromised not only by under-processing but also by a variety of mishaps whose occurrence probabilities are unrelated to the inactivation kinetics. Moreover, the available sampling plans to detect microbial contamination in sterilized containers through incubation alone are insensitive to levels of potential safety concerns. In principle, many of these issues could be resolved by developing new dramatically improved detection methods and/or verifiable methods to predict very low levels of microbial survival.

Salmonella spp. in low water activity food: Occurrence, survival mechanisms, and thermoresistance

The occurrence of disease outbreaks involving low-water-activity (a_w ) foods has gained increased prominence due in part to the fact that reducing free water in these foods is normally a measure that controls the growth and multiplication of pathogenic microorganisms. Salmonella, one of the main bacteria involved in these outbreaks, represents a major public health problem worldwide and in Brazil, which highlights the importance of good manufacturing and handling practices for food quality. The virulence of this pathogen, associated with its high ability to persist in the environment, makes Salmonella one of the main challenges for the food industry. The objectives of this article are to present the general characteristics, virulence, thermoresistance, control, and relevance of Salmonella in foodborne diseases, and describe the so-called low-water-activity foods and the salmonellosis outbreaks involving them.