Mathematical modeling and growth kinetics of Clostridium sporogenes in cooked beef

Characterisation of the surface growth of Mucor circinelloides in cheese agar media using predictive mathematical models

The main objective of this work was to characterise the mycelial growth of Mucor circinelloides, one of the fungal contaminants that appear frequently in the artisan cheese production environment. The study uses primary Baranyi and Huang models to compare their parameters and predict M. circinelloides on cheese-based medium (CBA) under diverse environmental conditions (temperature range from 6 to 37 °C and 0 and 1 % NaCl concentration). However, the Baranyi model consistently estimated longer lag phases and higher surface growth rates (sgr) than the Huang model; both models showed adequate best-fit performance (exactly with the mean coefficient of determination R2 = (0.993 ± 0.020 × 10-1). The groups of primary growth parameters were analysed against temperature using the cardinal model (CM) with the following main outputs. The optimal surface growth rates (sgropt) on CBA were 6.8 and 6.5 mm/d calculated with the Baranyi and Huang models, respectively. They were reduced by approximately 46 % on the surface of the agar medium when 1 % NaCl was added. Topt was estimated in a very narrow range of 32.1-32.5 °C from both primary sgr data sets (0 % and 1 % NaCl). Similarly, Tmax values of 37.2 °C and 37.3 °C were estimated for the Baranyi and Huang models, respectively; however, they decreased at 2 °C in CBA with 1 % NaCl (Tmax = 35.1 °C). The application of CM for sgr provided an estimation of the parameter Tmin with negative values that are considered only as a theoretical output. The results provide insight into the modelling and prediction of fungi growth as a function of time and salt concentration, including the times to detect visible mycelial growth of Mucor circinelloides. The mere quantification of this phenomenon can be useful for practice. Adjusting the frequency of the cheese surface washing step with a salt solution at the early stage of ripening properly can prevent the growth of not only fast fungal growers.

Comparison of Sodium Nitrite and ‘Natural’ Nitrite on the Inhibition of Spore Germination and Outgrowth of Clostridium sporogenes in Low- and High-Fat Frankfurters

In the US, sodium and potassium nitrite are regulated food preservatives that prevent the germination of Clostridium spores in cured and processed meats. In recent years, the use of vegetable-derived nitrite (i.e., vegetable nitrate fermented to nitrite) has been designated as ‘natural nitrite’ to accommodate natural meats that cannot use artificial ingredients, and such meat products can be labelled as having ‘no added preservatives’. This new status and labelling allowance for microbially-modified nitrite provides for a ‘clean label’ application of nitrite against the stigma of chemical ingredients and has found increased use within the processed meat industry. The objectives of this study were to examine Clostridium sporogenes as a pathogen-surrogate challenge organism and the use of vegetable (celery) nitrite to prevent spore germination in cooked meat products. A three-strain spore crop of C. sporogenes ATCC 3584, ATCC 19404 and ATCC BAA-2695 was applied during ingredient formulation of low and high-fat hotdogs that were divided into three sub-batches (control without nitrite, hotdogs with sodium nitrite, hotdogs with celery nitrite). In both low and high-fat processes, sodium nitrite was compared to hotdogs made with comparable levels of celery nitrite (156 ppm). All treatments were performed with duplicate trial replication and triplicate sample testing within each trial. Comparisons were analyzed by repeated measures analysis of variance to determine significant difference (p < 0.05) of time course treatments. In shelf-life assays, growth was inhibited at both 5 °C and 15 °C, even if nitrite was absent; however, spore germination and growth readily occurred at 35 °C. Comparison of nitrite effects was best evaluated at 35 °C as a permissive condition to examine the effects of nitrite treatments. Celery nitrite showed no significant difference from sodium nitrite when used in both low and high-fat hotdogs, and spore outgrowth was only observed after 2–3 days at 35 °C compared to hotdogs without nitrite. Application of bacteriocin preparations in the formulation that were effective against Listeria monocytogenes, and moderately inhibitory towards the 3-strain spore mixture of C. sporogenes, were not effective in spore control in manufactured hotdogs. The nitrite validation hotdog trials described herein demonstrates that (celery or sodium) nitrite may prevent Clostridium spore germination for 24–48 h even under permissive conditions to help keep processed meat safe.

Influence of Acid Adaptation on the Probability of Germination of Clostridium sporogenes Spores Against pH, NaCl and Time

The Clostridium sp. is a large group of spore-forming, facultative or strictly anaerobic, Gram-positive bacteria that can produce food poisoning. The table olive industry is demanding alternative formulations to respond to market demand for the reduction of acidity and salt contents in final products. while maintaining the appearance of freshness of fruits. In this work, logistic regression models for non-adapted and acid-adapted Clostridium sp. strains were developed in laboratory medium to study the influence of pH, NaCl (%) and time on the probability of germination of their spores. A Clostridium sporogenes cocktail was not able to germinate at pH < 5.0, although the adaptation of the strains produced an increase in the probability of germination at 5.0-5.5 pH levels and 6% NaCl concentration. At acidic pH values (5.0), the adapted strains germinated after 10 days of incubation, while those which were non-adapted required 15 days. At pH 5.75 and with 4% NaCl, germination of the adapted strains took place before 7 days, while several replicates of the non-adapted strains did not germinate after 42 days of storage. The model was validated in natural green olive brines with good results (>81.7% correct prediction cases). The information will be useful for the industry and administration to assess the safety risk in the formulation of new processing conditions in table olives and other fermented vegetables.

A Systematic Review of Beef Meat Quantitative Microbial Risk Assessment Models

Each year in Europe, meat is associated with 2.3 million foodborne illnesses, with a high contribution from beef meat. Many of these illnesses are attributed to pathogenic bacterial contamination and inadequate operations leading to growth and/or insufficient inactivation occurring along the whole farm-to-fork chain. To ensure consumer health, decision-making processes in food safety rely on Quantitative Microbiological Risk Assessment (QMRA) with many applications in recent decades. The present study aims to conduct a critical analysis of beef QMRAs and to identify future challenges. A systematic approach, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, was used to collate beef QMRA models, identify steps of the farm-to-fork chain considered, and analyze inputs and outputs included as well as modelling methods. A total of 2343 articles were collected and 67 were selected. These studies focused mainly on western countries and considered Escherichia coli (EHEC) and Salmonella spp. pathogens. Future challenges were identified and included the need of whole-chain assessments, centralization of data collection processes, and improvement of model interoperability through harmonization. The present analysis can serve as a source of data and information to inform QMRA framework for beef meat and will help the scientific community and food safety authorities to identify specific monitoring and research needs.

Selection of Surrogate Bacteria for Use in Food Safety Challenge Studies: A Review

Nonpathogenic surrogate bacteria are prevalently used in a variety of food challenge studies in place of foodborne pathogens such as Listeria monocytogenes, Salmonella, Escherichia coli O157:H7, and Clostridium botulinum because of safety and sanitary concerns. Surrogate bacteria should have growth characteristics and/or inactivation kinetics similar to those of target pathogens under given conditions in challenge studies. It is of great importance to carefully select and validate potential surrogate bacteria when verifying microbial inactivation processes. A validated surrogate responds similar to the targeted pathogen when tested for inactivation kinetics, growth parameters, or survivability under given conditions in agreement with appropriate statistical analyses. However, a considerable number of food studies involving putative surrogate bacteria lack convincing validation sources or adequate validation processes. Most of the validation information for surrogates in these studies is anecdotal and has been collected from previous publications but may not be sufficient for given conditions in the study at hand. This review is limited to an overview of select studies and discussion of the general criteria and approaches for selecting potential surrogate bacteria under given conditions. The review also includes a list of documented bacterial pathogen surrogates and their corresponding food products and treatments to provide guidance for future studies.