Browsing by Author "Miranda, Rebeca Becker"
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- Susceptibility of foodborne pathogens to lactic acid bacteria isolated from Portuguese ready-to-eat raw fermented meat productsPublication . Miranda, Rebeca Becker; Gonzales-Barron, Ursula; Cadavez, Vasco; Anschau, AndréiaFood safety is one of the main concerns of the food industry and regulatory bodies, due to the serious implications for public health that the consumption of contaminated food can cause. Foodborne pathogenic bacteria (FABBs) have a high morbidity and mortality rate, especially in susceptible individuals. Controlling these pathogens is crucial to ensuring food safety and reducing the risk of disease outbreaks. In order to improve food safety, there is growing interest in the use of so-called functional microorganisms, such as lactic acid bacteria (LAB), in the production of fermented foods. LAB are widely used throughout the world in food fermentation due to their potential to inhibit the growth of pathogens. Ready-to-eat fermented meat products (RTE) are an important food group in Portugal and are highly appreciated for their sensory characteristics. These products are produced through natural fermentation, but it is important to evaluate the ability of these LAB to inhibit food-borne pathogens under real production conditions in order to guarantee the microbiological safety of these products. For this reason, the aim of this thesis was to evaluate the ability of LAB, naturally present in raw fermented (RTE) sausages, such as chorizos and linguiças, to inhibit food-borne pathogens, in order to increase the safety of these foods. To this end, several LAB were isolated from these traditional Portuguese products and characterized in terms of their antimicrobial properties and metabolite production. To this end, seventy chorizos were purchased from fourteen artisan producers in the northeast region of Trás-os-Montes. Firstly, the lactic acid bacteria and relevant pathogens (Salmonella spp., Listeria monocytogenes and Staphylococcus aureus) present in the chorizo were isolated and confirmed. The LAB were tested for antagonism (antimicrobial properties), acidification, proteolytic activity and lactic acid production. The data was analyzed using principal component analysis (PCA) and factor analysis (FA), with the aim of synthesizing the information provided by the technological parameters, as well as their interrelationships. With the methodologies used, 207 LAB were isolated, and for subsequent tests 33 LAB were selected that showed the greatest diameter of inhibition against L. monocytogenes. The largest diameter of inhibition against L. monocytogenes was 37.29 mm, against S. aureus it was 16.9 mm and against Salmonella it was 24.3 mm. According to the inhibition results, the bacteria ML2CA (93), ML4CE (104), ML5CD (108) and AG3CC (18) showed excellent inhibition rays for the three pathogens tested. These LAB also showed a good acidification capacity, especially ML5CD, which reduced the pH from 7.000 to 5.665 (a reduction of 1.340) after 24 hours of incubation. However, in terms of proteolytic activity, the BAL mentioned above did not show large proteolysis radium, with AG3CD standing out with an average radius of 8.87 mm. The PCA and AF analyses showed that the inhibition of L. monocytogenes is closely related to the acidification capacity and the concentration of lactic acid. It was also observed that the inhibition of Salmonella and S. aureus was related to proteolytic activity and the concentration of lactic acid. It was also observed that the proteolytic activity of LAB is independent of the acidification capacity, the two being opposite in the correlation graph of the variables. By analyzing the correlation between the sites and the microbiological properties, it was possible to conclude that there is no trend or association between the producers and the technological properties of the LAB tested. The acidification potential does not seem to correlate with the acidification speed of the LAB. This suggests that initially slow-growing LAB are still capable of reaching low pH levels at the end of the process. The results of this work show that traditional fermented meat products are rich in naturally occurring LAB bacteria, which contribute to the microbiological safety of these foods. The LAB isolated and tested in this work have great technological potential, so it is important to study and understand their behavior and pathogen- inhibiting properties under real production conditions.