The Analysis of the Behaviour of Listeria Monocytogenes in Fresh Cheeses with Various Spices During Storage

The occurrence, growth, and biocontrol of Listeria monocytogenes in fresh and surface-ripened soft and semisoft cheeses

Listeria monocytogenes continues to pose a food safety risk in ready-to-eat foods, including fresh and soft/semisoft cheeses. Despite L. monocytogenes being detected regularly along the cheese production continuum, variations in cheese style and intrinsic/extrinsic factors throughout the production process (e.g., pH, water activity, and temperature) affect the potential for L. monocytogenes survival and growth. As novel preservation strategies against the growth of L. monocytogenes in susceptible cheeses, researchers have investigated the use of various biocontrol strategies, including bacteriocins and bacteriocin-producing cultures, bacteriophages, and competition with native microbiota. Bacteriocins produced by lactic acid bacteria (LAB) are of particular interest to the dairy industry since they are often effective against Gram-positive organisms such as L. monocytogenes, and because many LAB are granted Generally Regarded as Safe (GRAS) status by global food safety authorities. Similarly, bacteriophages are also considered a safe form of biocontrol since they have high specificity for their target bacterium. Both bacteriocins and bacteriophages have shown success in reducing L. monocytogenes populations in cheeses in the short term, but regrowth of surviving cells can commonly occur in the finished cheeses. Competition with native microbiota, not mediated by bacteriocin production, has also shown potential to inhibit the growth of L. monocytogenes in cheeses, but the mechanisms are still unclear. Here, we have reviewed the current knowledge on the growth of L. monocytogenes in fresh and surface-ripened soft and semisoft cheeses, as well as the various methods used for biocontrol of this common foodborne pathogen.

Modelling viability of Listeria monocytogenes in paneer

Paneer is a fresh, soft ready-to-eat cheese that is susceptible to Listeria monocytogenes contamination, exemplified by product recalls in Australia, Canada, and the USA. Previous research demonstrates that L. monocytogenes grows in paneer, however there are no paneer-specific predictive models that quantify the effect of environmental conditions on L. monocytogenes viability. This study measured the viability of a five-strain cocktail of L. monocytogenes in freshly prepared paneer incubated at 4-40 °C. Growth rates were fitted with the extended Ratkowsky square root model, with growth rates ranging from 0.014 to 0.352 log₁₀ CFU/h. In comparison with published models, only the ComBase L. monocytogenes broth model acceptably predicted growth (B_f = 1.01, A_f = 1.12) versus the developed model. The influence of paneer pH (5.0-6.0) and storage temperature (41-45 °C) on L. monocytogenes growth at the upper temperature growth boundary was described using a logistic model. These models provide quantitative tools to improve the safety of paneer processing conditions, shelf-life estimation, food safety management plans, and risk assessment.

Chemical Composition and Antimicrobial Potential of Satureja hortensis L. in Fresh Cow Cheese

This study presents data about the chemical composition and antimicrobial effect of Satureja hortensis L. used as both dry plant and essential oil, on fresh cow’s cheese, in order to extend its shelf-life. The proximate and elemental composition of dry plant of Satureja hortensis L. highlights important level of microelements. The content of microelements increases even when small amounts of Satureja hortensis in fresh cheese were added. The addition of Satureja hortensis dry plant leads to an increase in Fe (13.46–65.54%) and Mn (8.33–88.33%) content of fresh cheese, depending on the amount of plant added. The composition of essential oil isolated from Satureja hortensis L. was analyzed by GC-MS and the main compounds found were carvacrol (19.68%), o-cymene (30.86%), and p-cymene (28.07%). In order to use Satureja hortensis L. as natural preservative in food industry, in vitro effect of plant extract and essential oil against Staphylococcus aureus Gram-positive bacteria was tested. The oil of Satureja hortensis L. showed antimicrobial activity at 0.50–1.5%, while the alcoholic extract does not inhibit Staphylococcus aureus mycelial growth. The antimicrobial effect of Satureja hortensis L. dry plant in various proportions (0.5–1.5%) and essential oil (0.1%; 0.25%; 0.5%), on fresh cow’s cheese, was assessed after 3 and 7 days by counting colonies obtained at 30°C. Results have shown that the addition of Satureja hortensis L. dry plant and essential oil led to a reduction in the total number of germs, this reduction being more significant when the essential oil was used. Regarding the effect of Satureja hortensis L. essential oil against Staphylococcus aureus inoculated in fresh cow’s cheese, the results highlight that the essential oil of Satureja hortensis L. may be a natural solution to prevent the development of this bacteria, while the ethanol extract does not prove to be effective.