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- Cardinal parameter meta-regression models describing Listeria monocytogenes growth in brothPublication . Silva, Beatriz Nunes; Cadavez, Vasco; Teixeira, José; Ellouze, Mariem; Gonzales-Barron, UrsulaListeria monocytogenes has a high case-fatality rate, substantial research has been devoted to estimate its growth rate under different conditions of temperature, pH and water activity (aw). In this study, published findings on L. monocytogenes growth in broth were extracted and unified by constructing meta-regression models based on cardinal models for (i) temperature (CM[T]), (ii) temperature and pH (CM[T][pH]), and (iii) temperature, pH and aw (CM[T][pH][aw]). After assessing all the sources retrieved between 1988 until 2017, forty-nine primary studies were considered appropriate for inclusion. Apart from the modelling variables, study characteristics such as: type of broth (BHI, TSB, TPB), reading method (colony-forming-units, CFU; or binary-dilution optical density methods, OD), inoculum concentration and strain serotype, were also extracted. Meta-regressions based on CM[T] and CM[T][pH] were fitted on subsets of the 2009 growth rate measures and revealed that type of broth and reading method significantly modulated the cardinal parameter estimates. In the most parsimonious CM[T][pH][aw] meta-regression model, whereby the variability due to type of broth was extracted in a nested random-effects structure, the optimum growth rate μopt of L. monocytogenes was found to be lower when measured as CFU (0.947 log CFU/h; SE = 0.094 log CFU/h) than when measured as OD (1.289 log CFU/h; SE = 0.092 log CFU/h). Such a model produced the following cardinal estimates: Tmin = -1.273 °C (SE = 0.179 °C), Topt = 37.26 °C (SE = 0.688 °C), Tmax = 45.12 °C (SE = 0.013 °C), pHmin = 4.303 (SE = 0.014), pHopt = 7.085 (SE = 0.080), pHmax = 9.483 (SE = 0.080), aw min = 0.894 (SE = 0.002) and awopt = 0.995 (SE = 0.001). Integrating the outcomes from numerous L. monocytogenes growth experiments, this meta-analysis has estimated pooled cardinal parameters that can be used as reference values in quantitative risk assessment studies.
- Dynamic modelling to describe the effect of plant extracts and customised starter culture on Staphylococcus aureus survival in goat's raw milk soft cheesePublication . Silva, Beatriz Nunes; Coelho-Fernandes, Sara; Teixeira, José António; Cadavez, Vasco; Gonzales-Barron, UrsulaThis study characterises the effect of a customised starter culture (CSC) and plant extracts (lemon balm, sage, and spearmint) on Staphylococcus aureus (SA) and lactic acid bacteria (LAB) kinetics in goat's raw milk soft cheeses. Raw milk cheeses were produced with and without the CSC and plant extracts, and analysed for pH, SA, and LAB counts throughout ripening. The pH change over maturation was described by an empirical decay function. To assess the effect of each bio-preservative on SA, dynamic Bigelow-type models were adjusted, while their effect on LAB was evaluated by classical Huang models and dynamic Huang-Cardinal models. The models showed that the bio-preservatives decreased the time necessary for a one-log reduction but generally affected the cheese pH drop and SA decay rates (logD(ref) = 0.621-1.190 days; controls: 0.796-0.996 days). Spearmint and sage extracts affected the LAB specific growth rate (0.503 and 1.749 ln CFU/g day(-1); corresponding controls: 1.421 and 0.806 ln CFU/g day(-1)), while lemon balm showed no impact (p > 0.05). The Huang-Cardinal models uncovered different optimum specific growth rates of indigenous LAB (1.560-1.705 ln CFU/g day(-1)) and LAB of cheeses with CSC (0.979-1.198 ln CFU/g day(-1)). The models produced validate the potential of the tested bio-preservatives to reduce SA, while identifying the impact of such strategies on the fermentation process.
- Mild heat treatment and biopreservatives for artisanal raw milk cheeses: reducing microbial spoilage and extending shelf-life through thermisation, plant extracts and lactic acid bacteriaPublication . Silva, Beatriz Nunes; Teixeira, José António; Cadavez, Vasco; Gonzales-Barron, UrsulaThe microbial quality of raw milk artisanal cheeses is not always guaranteed due to the possible presence of pathogens in raw milk that can survive during manufacture and maturation. In this work, an overview of the existing information concerning lactic acid bacteria and plant extracts as antimicrobial agents is provided, as well as thermisation as a strategy to avoid pasteurisation and its negative impact on the sensory characteristics of artisanal cheeses. The mechanisms of antimicrobial action, advantages, limitations and, when applicable, relevant commercial applications are discussed. Plant extracts and lactic acid bacteria appear to be effective approaches to reduce microbial contamination in artisanal raw milk cheeses as a result of their constituents (for example, phenolic compounds in plant extracts), production of antimicrobial substances (such as organic acids and bacteriocins, in the case of lactic acid bacteria), or other mechanisms and their combinations. Thermisation was also confirmed as an effective heat inactivation strategy, causing the impairment of cellular structures and functions. This review also provides insight into the potential constraints of each of the approaches, hence pointing towards the direction of future research.
- Meta-analysis of in vitro antimicrobial capacity of extracts and essential oils of Syzygium aromaticum, Citrus L. and Origanum L.: contrasting the results of different antimicrobial susceptibility methodsPublication . Silva, Beatriz Nunes; Bonilla-Luque, Olga María; Possas, Arícia; Ezzaky, Youssef; Elmoslih, Abdelkhaleq; Teixeira, José António; Achemchem, Fouad; Valero, Antonio; Cadavez, Vasco; Gonzales-Barron, UrsulaDiffusion methods, including agar disk-diffusion and agar well-diffusion, as well as dilution methods such as broth and agar dilution, are frequently employed to evaluate the antimicrobial capacity of extracts and essential oils (EOs) derived from Origanum L., Syzygium aromaticum, and Citrus L. The results are reported as inhibition diameters (IDs) and minimum inhibitory concentrations (MICs), respectively. In order to investigate potential sources of variability in antimicrobial susceptibility testing results and to assess whether a correlation exists between ID and MIC measurements, meta-analytical regression models were built using in vitro data obtained through a systematic literature search. The pooled ID models revealed varied bacterial susceptibilities to the extracts and in some cases, the plant species and methodology utilised impacted the measurements obtained (p < 0.05). Lemon and orange extracts were found to be most effective against E. coli (24.4 ± 1.21 and 16.5 ± 0.84 mm, respectively), while oregano extracts exhibited the highest level of effectiveness against B. cereus (22.3 ± 1.73 mm). Clove extracts were observed to be most effective against B. cereus and demonstrated the general trend that the well-diffusion method tends to produce higher ID (20.5 ± 1.36 mm) than the disk-diffusion method (16.3 ± 1.40 mm). Although the plant species had an impact on MIC, there is no evidence to suggest that the methodology employed had an effect on MIC (p > 0.05). The ID–MIC model revealed an inverse correlation (R2 = 47.7%) and highlighted the fact that the extract dose highly modulated the relationship (p < 0.0001). The findings of this study encourage the use of extracts and EOs derived from Origanum, Syzygium aromaticum, and Citrus to prevent bacterial growth. Additionally, this study underscores several variables that can impact ID and MIC measurements and expose the correlation between the two types of results.
- Meta-regression models describing the effects of essential oils and added lactic acid bacteria on pathogen inactivation in cheesePublication . Silva, Beatriz Nunes; Cadavez, Vasco; Teixeira, José; Gonzales-Barron, UrsulaBiopreservatives such as plant-based antimicrobials and bacteriocinogenic starter cultures have been proposed as hurdles to increase microbiological safety of a variety of products, including cheese, and numerous studies have reported their pathogen inhibitory properties. For that reason, the objective of this meta-analysis was to summarise the inactivation of Listeria monocytogenes (LM), Staphylococcus aureus (SA) and Salmonella spp. (SS) in cheese attained by added lactic acid bacteria (LAB) and essential oils (EOs); and to compare the inhibitory effectiveness by application mode and specific antimicrobial. After systematic review, 1810 observations on log reduction data and study characteristics were extracted from 53 studies. Comparing among the factual methods of application of antimicrobials (in milk, cheese surface and incorporated in films), meta-regression models pointed out that addition of EOs to milk renders, as a whole, the lowest inhibitory effect against LM, SA and SS in the finished product; whereas for added LAB, incorporation in milk prompts a faster inactivation of LM than onto cheese surface. Lemon balm, sage and basil EOs showed the best inhibitory outcomes against LM and SA; whereas clove, oregano and bay EOs presented the highest bactericidal effect against SS. For a given increase in EO concentration, the application on cheese surface provides the greatest inhibitory effect against LM and SS, while EO-embedded films lead to a more rapid inactivation during maturation/storage. The experimental practice of inoculating the antimicrobial in cheese mixture should no longer be employed in challenge studies, since the meta-regression models have demonstrated that this application method biases the results, overestimating or underestimating the inhibitory effects of EOs or added LAB, respectively. This meta-analysis has also emphasised the need to further investigate the relationship between pathogen's inoculum size and their concentrations in time.
- In vitro antimicrobial activity of extracts and essential oils of Cinnamomum, Salvia, and Menthaspp. against foodborne pathogens: a meta‐analysis studyPublication . Ezzaky, Youssef; Elmoslih, Abdelkhaleq; Silva, Beatriz Nunes; Bonilla‐Luque, Olga M.; Possas, Arícia; Valero, Antonio; Cadavez, Vasco; Gonzales-Barron, Ursula; Achemchem, FouadGenetic analysis of the honey bee spermathecal content can be particularly useful to provide an estimate of the genetic diversity and purity of the surrounding populations. Here we compared the concentration and quality of DNA extracted from queen spermatheca using four commercial kits to determine the best method to obtain DNA suitable for single nucleotide polymorphism genotyping by next-generation sequencing. The four kits were tested with different adjustments in the lysis incubation time, use of RNA-carrier, elution conditions and number of re-elutions. Only the use of QIAamp DNA Microkit with 3 h of lysis incubation, the addition of RNA-carrier and multiple re-elutions produced a DNA concentration over the required threshold.
- A meta-regression model of the growth rate of Listeria monocytogenes as affected by temperaturePublication . Silva, Beatriz Nunes; Cadavez, Vasco; Ellouze, Mariem; Gonzales-Barron, UrsulaThe presence of L. monocytogenes in naturally-contaminated foods, its ability to endure various environmental stresses and grow at low temperatures and during the shelf life of some foods are great challenges for the food industry. To overcome this issue, predictive models can be used on the decision-making process in case of presumed contamination and possible growth of pathogens as they can assess bacterial levels before a control step is applied and evaluate if the process allows the pathogen’s inactivation or reduction to an acceptable level. In this sense, Cardinal Parameters Models (CPM) have been widely used to describe the effect of environmental factors on microbial growth rates. To be used, the determination of the parameters, known as cardinal values, is needed, but since experimental estimation is a laborious task, it is proposed here that meta-analysis of literature data could be useful to perform such assessments. This statistical analysis of results from published studies aims to integrate and interpret the findings to achieve an enlarged vision about the topic’s results. Suitable scientific articles were collected through search in several databases. Following study quality checking, 88 studies remained from which 3079 growth rates were extracted. To evaluate temperature’s effect on growth rates and estimate comprehensive cardinal values, meta-analysis was performed on a set of growth rates assessed at optimal conditions of pH (6.5-8) and aw (≥0.98). To appraise the share of the possible sources of variability, the CPM was also fitted on subsets of growth rates estimated using (i) distinct reading methods, (ii) distinct broth types and (iii) sub-optimal conditions of pH and aw. The pooled parameters from the optimal set were Tmin=-1.15±2.43 °C, Topt=37.42±2.00 °C, Tmax=45.20±0.37 °C and μopt=1.06±0.13 h-1. Regarding the possible sources of variability, it was concluded that the reading method (R2=24.8%) and the broth type (R2= 60.1%) used to estimate growth rates largely affect the estimation of cardinal values. Moreover, data at sub-optimal conditions, especially in food products, were found inadequate to assess cardinal values, unlike optimal conditions, as mean estimates changed and standard errors increased. The meta-analysis performed allowed the fitting of the CPM to growth rate data retrieved from scientific articles, showing that literature can be useful to assess cardinal values and to provide an insight on sources of variability.
- Extracts from red eggplant: impact of ohmic heating and different extraction solvents on the chemical profile and bioactivityPublication . Ferreira-Santos, Pedro; Duca, Anna Barbara; Genisheva, Zlatina; Silva, Beatriz Nunes; Biasio, Filomena de; Botelho, Cláudia; Rocha, Cristina M.R.; Gorgoglione, Domenico; Teixeira, José AntónioEggplants contain a multitude of biocompounds with nutritional and/or biological activities. The objective of this work was to study the nutritional, chemical and bioactive value of red eggplant from Rotonda, Italy. Ohmic heating (OH) was compared to conventional heating, as different solvents were used (water, ethanol 30, 50, and 90%and methanol) for biocompounds extraction. Extracts were evaluated for their total phenolic compounds, antioxidant and antibacterial activities, and its toxicity was assessed in cells, L929 and Caco-2. The nutritional characterization of Rotonda’s eggplant demonstrated that it is rich in carbohydrates (65%), fiber (12.5%), proteins (13%), lipids (7.6%) and minerals. Potassium is the mineral with the highest concentration in the red eggplant (27.24 mg/g). Phenolic composition of the obtained extracts was dependent on the extraction method, as well as on the solvent. The use of OH method increased the extraction of biocompounds, especially when using 50% of ethanol as solvent. The main phenolic compounds found in the extracts of this eggplant variety were ellagic acid, p-coumaricic acid, epicatechin, narginin, taxifolin and kaempferol. Antioxidant activity was positively correlated with the total amounts of phenolics. Red Eggplant extracts showed activity against Gram-negative bacteria (E. coli and S. enterica), however, they did not demonstrate activity against Gram-positive bacteria. The extracts obtained did not show cytotoxic effects in fibroblast and colorectal studied cells. Ohmic heating is a sustainable technology that increases the extraction yield of biocompounds, with reduced energy consumption and the resulting extracts show low toxicity and high biological activity.
- Correction: Silva et al. Chemical Profile and Bioactivities of Extracts from Edible Plants Readily Available in Portugal. Foods 2021, 10, 673Publication . Silva, Beatriz Nunes; Cadavez, Vasco; Ferreira-Santos, Pedro; Alves, Maria José; Ferreira, Isabel C.F.R.; Barros, Lillian; Teixeira, José António; Gonzales-Barron, UrsulaThe authors found a mistake in the original paper [1]. Throughout the article, French lavender was wrongfully named rosemary. Rosemary was not used in the original study. Below are provided the full details of the changes in the Figures, Tables, and text. The authors sincerely apologise for any inconvenience caused and state that the scientific conclusions are unaffected. The original publication has been updated.
- Meta-analysis of the incidence of foodborne pathogens in vegetables from retail establishments in EuropePublication . Silva, Beatriz Nunes; Cadavez, Vasco; Teixeira, José; Gonzales-Barron, UrsulaOver the last years, concerns regarding the effect of a healthy diet on one’s quality of life have promoted the increase of vegetable consumption. However, these products can be contaminated by pathogens such as Escherichia coli , Salmonella spp. and Listeria monocytogenes. Thus, this work aims to summarise the incidence of foodborne pathogens in vegetables sold at European retail stores.
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