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Meta-analysis of antimicrobial activity of Allium, Ocimum, and Thymus spp. confirms their promising application for increasing food safety

Publication . Bonilla-Luque, Olga María; Silva, Beatriz Nunes; Ezzaky, Youssef; Possas, Arícia; Achemchem, Fouad; Cadavez, Vasco; Gonzales-Barron, Ursula; Valero, Antonio

Biopreservation strategies such as the use of Mediterranean plant extracts to ensure food safety are promising to deal with the emergence of antimicrobial resistances and the overreliance on food chemical additives. In the last few decades, antimicrobial susceptibility testing (AST) for evaluating the in vitro antibacterial potential of plant extracts against the most relevant foodborne pathogens has been widely reported in the literature. The current meta-analysis aimed to summarise and analyse the extensive evidence available in the literature regarding the in vitro antimicrobial capability of Allium, Ocimum and Thymus spp. extracts against foodborne pathogens. A systematic review was carried out to gather data on AST results of these extracts against Listeria monocytogenes, Staphylococcus aureus, Salmonella spp., Escherichia coli and Bacillus cereus, including inhibition diameters (ID) and minimum inhibitory concentrations (MIC). A total of 742 records were gathered from a raw collection of 2,065 articles. Weighted mixed-effect linear models were adjusted to data to obtain pooled ID, pooled MIC and the relationship between both model estimations and observations. The pooled results revealed B. cereus as the most susceptible bacteria to Allium sativum (pooled ID = 20.64 ± 0.61 mm) by diffusion methods and S. aureus (pooled MIC = 0.146 mg/mL) by dilution methods. Diffusion methods did not yield conclusive results for Ocimum spp. extracts; however, the lowest pooled MIC was obtained for S. aureus (0.263 mg/mL). Among the foodborne pathogens evaluated, B. cereus showed the highest sensitivity to Thymus spp. extracts by both diffusion and dilution methods (pooled ID = 28.90 ± 2.34 mm and MIC = 0.075 mg/mL). The methodology used for plant extraction was found to not significantly affect MIC values (p > 0.05). Overall, the antimicrobial effectiveness of the studied extracts against Gram-positive and Gram-negative bacteria was demonstrated. Finally, the robustness of the meta-regression model was confirmed, also revealing an inversely proportional correlation between the ID and MIC measurements (p < 0.0001). These results provide a robust scientific basis on the factors affecting the in vitro antimicrobial efficacy of extracts from Mediterranean plants. They also provide valuable information for stakeholders involved in their industrial application in food, including producers, regulatory agencies and consumers which demand green-labelled foods.

2024Journal article

Open access

Modelling the kinetics of Staphylococcus aureus in goat's raw milk under different sub-pasteurisation temperatures

Publication . Silva, Beatriz Nunes; Coelho-Fernandes, Sara; Teixeira, José António; Cadavez, Vasco; Gonzales-Barron, Ursula

In this study, the heat resistance of S. aureus in goats’ raw milk subjected to thermisation temperatures was characterised through tests at various temperatures and modelling the survival curves using the Weibull model, through a two-step and an omnibus approach, which can model a full dataset covering all experimental conditions in one step. The fitting capacity of the secondary models obtained from the two-step approach was reasonable (adj. R2 > 0.639) and both demonstrated the negative linear effects of temperature on ̅̅̅ χ √ (p = 0.0004) and ̅̅̅ β √ (p = 0.017). The fitting capacity of the omnibus model was more satisfactory (adj. R2 = 0.996) and also hinted at the negative linear effect of temperature on ̅̅̅ χ √ (p < 0.0001), with the added advantage that, in this model, random effects can be used to account for the variability in the parameters. Our study estimated the significant inactivation parameters and established a model capable of predicting S. aureus behaviour at various temperatures. This information is useful to create time-temperature tables to reach target log reductions of S. aureus in goats’ raw milk to be used by artisanal cheesemakers; hence providing an opportunity to increase the microbiological safety of cheeses made from unpasteurised milk.

2023Journal article

Restricted access

Exploring the role of Autochthonous lactic acid Bacteria in enhancing quality and safety of Alheira

Publication . Fernandes, Nathália; Cadavez, Vasco; Gonzales-Barron, Ursula

The alheira is a traditional meat sausage produced in the Portuguese region of Trás-os-Montes. Lactic Acid Bacteria (LAB) are the dominant microorganisms in alheira and can endow it with various technological properties. This study aimed: 1) Isolate and identify LAB from artisanally produced alheiras from the Trás-os-Montes region; 2) Study their phenotypic characteristics and in vitro antimicrobial activity; and 3) Differentiate and associate the phenotypic characteristics of the LAB with 16S ribosomal gene sequencing data. Sixty-two LAB isolates were identified and Enterococcus (E.) faecium corresponded to 32.3% of isolates, followed by Leuconostoc (L.) mesenteroides (19.4%) and Latilactobacillus (Lb.) sakei (17.7%), aligning with previous research on traditional Portuguese fermented meat sausages. The phenotypic analysis of LAB isolates indicated diverse acidification capacities, proteolytic activities, and inhibitory effects against foodborne pathogens Listeria (L.) monocytogenes, Salmonella (S.) Typhimurium and Staphylococcus (S.) aureus. LAB play an essential role as biological control agents, generating metabolites with antimicrobial properties, including organic acids, proteases, peptidases and bacteriocins. Overall, lactobacilli displayed high inhibition activity ((inhibition zone radius higher than 10 mm) against the pathogens S. aureus, L. monocytogenes and S. Typhimurium. The mechanisms of pathogenic microorganism inhibition remain to be clarified and will be the subject of future studies. However, these results reveal the significant diversity of LAB found in artisanally produced alheiras, as well as their contribution to the microbiological safety and organoleptic characteristics of alheiras.

2024Master thesis

Open access

Chemical profiles and bioactivities of polyphenolic extracts of Lavandula stoechas L., Artemisia dracunculus L. and Ocimum basilicum L

Publication . Silva, Beatriz Nunes; Cadavez, Vasco; Caleja, Cristina; Pereira, Eliana; Calhelha, Ricardo C.; Molina, Adriana K.; Finimundy, Tiane C.; Kostić, Marina; Soković, Marina; Teixeira, José António; Barros, Lillian; Gonzales-Barron, Ursula

This study assessed the chemical profiles and bioactivities of the infusions, decoctions and hydroethanolic extracts of tarragon, basil and French lavender. The extracts were chemically characterised (HPLC-DAD-ESI/MS) and their bioactivities were evaluated in vitro. All extracts revealed antimicrobial, antifungal and antioxidant properties. French lavender extracts showed higher total phenolic content, regardless of the extraction method used, and antioxidant and antitumour capacities, but no anti-inflammatory action. All basil and two of the tarragon extracts revealed anti-inflammatory power. Thus, tarragon, basil and French lavender extracts may be considered for inclusion in foods, as preservatives or functional ingredients. Nonetheless, further studies must be conducted to evaluate the pharmacokinetic parameters of the bioactive compounds.

2024Journal article

Open access

In vitro antimicrobial activity of extracts and essential oils of Cinnamomum, Salvia, and Menthaspp. against foodborne pathogens: a meta‐analysis study

Publication . Ezzaky, Youssef; Elmoslih, Abdelkhaleq; Silva, Beatriz Nunes; Bonilla‐Luque, Olga María; Possas, Arícia; Valero, Antonio; Cadavez, Vasco; Gonzales-Barron, Ursula; Achemchem, Fouad

Essential oils (EOs) are a class of natural products that exhibit potent antimicrobial properties against a broad spectrum of bacteria. Inhibition diameters (IDs) and minimum inhibitory concentrations (MICs) are the typical measures of antimicrobial activity for extracts and EOs obtained from Cinnamomum, Salvia, and Mentha species. This study used a meta-analytical regression analysis to investigate the correlation between ID and MIC measurements and the variability in antimicrobial susceptibility tests. By utilizing pooled ID models, this study revealed significant differences in foodborne pathogens’ susceptibility to extracts, which were dependent on both the plant species and the methodology employed (p < .05). Cassia showed the highest efficacy against Salmonella spp., exhibiting a pooled ID of 26.24 mm, while cinnamon demonstrated the highest efficacy against Bacillus cereus, with a pooled ID of 23.35 mm. Mint extract showed the greatest efficacy against Escherichia coli and Staphylococcus aureus. Interestingly, cinnamon extract demonstrated the lowest effect against Shiga toxin-producing E. coli, with a pooled ID of only 8.07 mm, whereas its EOs were the most effective against this bacterial strain. The study found that plant species influenced the MIC, while the methodology did not affect MIC measurements (p > .05). An inverse correlation between ID and MIC measurements was identified (p < .0001). These findings suggest that extracts and EOs obtained from Cinnamomum, Salvia, and Mentha spp. have the potential to inhibit bacterial growth. The study highlights the importance of considering various factors that may influence ID and MIC measurements when assessing the effectiveness of antimicrobial agents.

2023Journal article

Open access