George-John E. Nychas

A study of the minimum inhibitory concentration and mode of action of oregano essential oil, thymol and carvacrol.

Aims: The minimum inhibitory concentration (MIC) of oregano essential oil (OEO) and two of its principle components, i.e. thymol and carvacrol, against Pseudomonas aeruginosa and Staphylococcus aureus was assessed by using an innovative technique. The mechanism of action of the above substances was also investigated.

Meat spoilage during distribution

Meat spoilage during distribution can be considered as an ecological phenomenon that encompasses the changes of the available substrata (e.g., low molecular compounds), during the prevailing of a particular microbial association, the so-called specific spoilage organisms (SSO). In fact, spoilage of meat depends on an even smaller fraction of SSO, called ephemeral spoilage organisms (ESO). These ESO are the consequence of factors that dynamically persist or imposed during, e.g., processing, transportation and storage in the market. Meanwhile spoilage is a subjective judgment by the consumer, which may be influenced by cultural and economic considerations and background as well as by the sensory acuity of the individual and the intensity of the change. Indeed, when spoilage progresses, most consumers would agree that gross discoloration, strong off-odors, and the development of slime would constitute the main qualitative criteria for meat rejection. On the other hand, meat industry needs rapid analytical methods or tools for quantification of these indicators to determine the type of processing needed for their raw material and to predict remaining shelf life of their products. The need of an objective evaluation of meat spoilage is of great importance. The use of metabolomics as a potential tool for the evaluation of meat spoilage can be of great importance. The microbial association of meat should be monitored in parallel with the estimation of changes occurring in the production and/or assimilation of certain compounds would allow us to evaluate spoilage found or produced during the storage of meat under different temperatures as well as packaging conditions.

Natural antimicrobials from plants

Food preservation is becoming more complex. New food products are being introduced onto the market. Generally these require longer shelf-lives and greater assurance of freedom from foodborne pathogenic organisms. The search for new substances to be used in food preservation is hampered by regulatory restrictions. Consequently a great deal of time and money may be required to develop a new chemical preservative and to get it approved especially in view of the public pressure against chemical additives in general. Such obstacles provide new opportunities for those seeking alternative routes in the search for new food preservatives. The excessive use of chemical preservatives, some of which are suspect because of their supposed or potential toxicity, has resulted in increasing pressure on food manufacturers to either completely remove chemical preservatives from their food products or to adopt more ‘natural’ alternatives for the maintenance or extension of a product’s shelf life. There is considerable interest in the possible use of such natural alternatives as food additives either to prevent the growth of foodborne pathogens or to delay the onset of food spoilage. Many naturally occurring compounds, such as phenols (phenolic acid, polyphenols, tannins), and organic acids (acetic, lactic, citric) have been considered in this context. Many spices and herbs and extracts possess antimicrobial activity, almost invariably due to the essential oil fraction (Deans and Ritchie, 1987). Thus the essential oils of citrus fruits exhibit antibacterial activity to foodborne bacteria (Dabbah et al., 1970) and moulds (Akgul and Kivanc, 1989) so too have the essential oils of many other plants such as oregano, thyme (Salmeron et al., 1990;Paster et al., 1990), sage, rosemary, clove, coriander etc. (Farag et al., 1989; Aureli et al., 1992; Stecchini et al., 1993). The antibacterial and antimycotic effects of garlic and onion have been well documented also (Mantis et al., 1978; Sharma et al., 1979; Saleem and Al-Delaimy, 1982; Conner and Beuchat, 1984a,b).

Effect of oregano essential oil on microbiological and physico‐chemical attributes of minced meat stored in air and modified atmospheres

Aims: This study aimed to determine the combined effect of packaging (air, modified atmosphere) with or without the addition of essential oil not only on the selection of microbial association of meat but also to determine any significant difference in microbial metabolites produced from the prevailing bacteria.

Inhibition of Salmonella enteritidis and Staphylococcus aureus in nutrient broth by mint essential oil

Abstract The effect of different concentrations (0–1.2% v/v) of mint (Mentha piperita) essential oil on the growth/survival of Salmonella enteritidis and Staphylococcus aureus was studied in nutrient broth, using the viable count method and conductance measurements. In particular the addition of mint essential oil reduced the total viable counts of St. aureus about 6–7 logs while this of S. enteritidis only ca. 3 logs. The detection time measurements showed also that the inhibitory effect of mint essential oil was affected by the incubation temperature as well as by the concentration of essential oil added in the growth medium. At low concentration of essential oil (

Development and Evaluation of a Model Predicting the Survival of Escherichia coli O157:H7 NCTC 12900 in Homemade Eggplant Salad at Various Temperatures, pHs, and Oregano Essential Oil Concentrations

ABSTRACT Homemade eggplant salad, a traditional Greek appetizer, was inoculated with Escherichia coli O157:H7 NCTC 12900 supplemented with different concentrations of oregano essential oil (0.0, 0.7, 1.4, and 2.1% [vol/wt]) and stored at different temperatures (0, 5, 10, and 15°C). The products pH was adjusted to 4.0, 4.5, or 5.0 with lemon juice. For each combination of the environmental factors, the bacterial counts were modeled, using the Baranyi model, as a function of time to estimate the kinetic parameters of the pathogen. A reduction of more than 1 log unit in E. coli O157:H7 counts was observed in all cases, and the death rate depended on the pH, the storage temperature, and the essential oil concentration. Separate quadratic models were developed with natural logarithms of the shoulder period and death rate as estimated by the growth model, as a function of temperature, pH, and oregano essential oil concentrations. These were further used to predict the population of E. coli O157:H7 NCTC 12900 from other inoculated eggplant salads at random conditions of temperature, pH, and oregano oil concentration. The predicted values were compared with viable-count measurements for validation.

Application of a systematic experimental procedure to develop a microbial model for rapid fish shelf life predictions.

A systematic experimental procedure for fish shelf-life modelling was used to develop a model for predicting the quality of fish in the chill chain. For this, the growth of the naturally occurring bacteria pseudomonads, Shewanella putrefaciens, Enterobacteriaceae, lactic acid bacteria and yeasts, on gilt-head seabream (Sparus aurata), was studied at temperatures from 0 to 15 degrees C. The results from the microbiological, organoleptical and chemical analysis conducted on naturally contaminated fish as well as on inoculated sterile fish blocks identified pseudomonads as a good spoilage index. Growth of pseudomonads was modelled as a function of storage temperature and correlated to organoleptical shelf life. To reduce the time required for the enumeration of the initial pseudomonads number, which is crucial information for shelf life prediction, a conductance assay was established. Compared with the conventional microbiological tests, this method gave results in one-fourth of the time.

Spoilage microbiota associated to the storage of raw meat in different conditions

The spoilage of raw meat is mainly due to undesired microbial development in meat during storage. The type of bacteria and their loads depend on the initial meat contamination and on the specific storage conditions that can influence the development of different spoilage-related microbial populations thus affecting the type and rate of the spoilage process. This review focuses on the composition of raw meat spoilage microbiota and the influence of storage conditions such as temperature, packaging atmosphere and use of different preservatives on the bacterial diversity developing in raw meat. In addition, the most recent tools used for the detection and identification of meat microbiota are also reviewed.

Use of time–temperature integrators and predictive modelling for shelf life control of chilled fish under dynamic storage conditions

A systematic approach for fish shelf life modelling and Time Temperature Integrator (TTI) selection in order to plan and apply an effective quality monitoring scheme for the fish chill chain was developed. The temperature behaviour of the natural microflora of the Mediterranean fish boque (Boops boops) was studied and growth of the specific spoilage bacteria Pseudomonas spp. and Shewanella putrefaciens was modelled and correlated to organoleptic shelf life. Arrhenius and square root functions were used to model temperature dependence of maximum growth rates. Bacterial growth and shelf life models were validated under dynamic storage conditions with independent variable temperature experiments. The response of several TTIs from similar storage experiments was also modelled. The reliability of the TTI monitoring was cumulatively expressed by the error in the TTI derived effective temperature (Teff) for different variable temperature distributions. Teff was directly translated to shelf life of the fish.

Development of a Microbial Model for the Combined Effect of Temperature and pH on Spoilage of Ground Meat, and Validation of the Model under Dynamic Temperature Conditions

ABSTRACT The changes in microbial flora and sensory characteristics of fresh ground meat (beef and pork) with pH values ranging from 5.34 to 6.13 were monitored at different isothermal storage temperatures (0 to 20°C) under aerobic conditions. At all conditions tested, pseudomonads were the predominant bacteria, followed by Brochothrix thermosphacta, while the other members of the microbial association (e.g., lactic acid bacteria and Enterobacteriaceae) remained at lower levels. The results from microbiological and sensory analysis showed that changes in pseudomonad populations followed closely sensory changes during storage and could be used as a good index for spoilage of aerobically stored ground meat. The kinetic parameters (maximum specific growth rate [μmax] and the duration of lag phase [λ]) of the spoilage bacteria were modeled by using a modified Arrhenius equation for the combined effect of temperature and pH. Meat pH affected growth of all spoilage bacteria except that of lactic acid bacteria. The “adaptation work,” characterized by the product of μmax and λ(μmax × λ) was found to be unaffected by temperature for all tested bacteria but was affected by pH for pseudomonads and B. thermosphacta. For the latter bacteria, a negative linear correlation between ln(μmax × λ) and meat pH was observed. The developed models were further validated under dynamic temperature conditions using different fluctuating temperatures. Graphical comparison between predicted and observed growth and the examination of the relative errors of predictions showed that the model predicted satisfactorily growth under dynamic conditions. Predicted shelf life based on pseudomonads growth was slightly shorter than shelf life observed by sensory analysis with a mean difference of 13.1%. The present study provides a “ready-to-use,” well-validated model for predicting spoilage of aerobically stored ground meat. The use of the model by the meat industry can lead to effective management systems for the optimization of meat quality.