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Antilisterial active compound from lactic acid bacteria present on fresh iceberg lettuce

Publication . Ramos, Bárbara; Ferreira, Vânia; Brandão, Teresa R. S.; Teixeira, Paula; Silva, Cristina L. M.

Pediococcus pentosaceus DT016, a bacteriocin producing strain, was isolated from fresh lettuce. A protein with antilisterial activity (bacDT016), between 11 to 17 kDa, was identifi ed and characterized as the bioactive substance from the LAB culture. Highest bacteriocin production was noted after 15 h of growth. Antibacterial activity was affected by some enzymes and detergents, as well as by temperatures equal or above 80 ºC. DT016 strain contains an 1110 bp DNA fragment with homology to pediocin AcH/PA-1.

2016Journal article

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Biopreservation approaches to reduce Listeria monocytogenes in fresh vegetables

Publication . Ramos, Bárbara; Brandão, Teresa R. S.; Teixeira, Paula; Silva, Cristina L. M.

Two biopreservation approaches for fresh lettuce, rocket salad, parsley and spinach were studied. The potential of Pediococcus pentosaceus DT016, as a protective culture, to suppress Listeria monocytogenes in vegetables during storage was evaluated. The pathogen numbers in the vegetables inoculated with P. pentosaceus DT016 were significantly (p < 0.01) lower throughout the storage period and, at the last storage day, a minimum difference of 1.4 log CFU/g was reported when compared with the vegetables without the protective culture. Moreover, by using two levels of L. monocytogenes (about 6 and 4 log CFU/g), it was observed that the antagonist effect of P. pentosaceus was higher for the lower pathogen numbers. The second approach evaluated a pediocin DT016 solution to inactivate and control L. monocytogenes proliferation. The pathogen load was studied after washing with: water, chlorine and the pediocin solution and along storage at 4  °C. Comparing the various washing solutions, the vegetables washed with pediocin presented significantly (p < 0.01) lower pathogen numbers throughout storage, by a minimum of 3.2 and 2.7 log CFU/g, than in vegetables washed with water and chlorine, respectively. The proposed methodologies are promising alternatives to maintain the safety of fresh vegetables during extended storage at refrigeration temperature.

2020Journal article

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Balsamic vinegar from Modena: an easy effective approach to reduce Listeria monocytogenes from lettuce

Publication . Ramos, Bárbara; Brandão, Teresa R. S.; Teixeira, Paula; Silva, Cristina L.M.

The microbiological safety of fresh produce is a significant concern of consumers and industry. After applying at an inoculated level (6e7 log CFU/mL) of Listeria monocytogenes on Iceberg lettuce, the antilisterial properties of balsamic vinegar from Modena, white wine vinegar and acetic acid solutions were investigated. Different proportions of the vinegars, acetic acid (58.7 g/L), and deionized water were evaluated to determine the role of those solutions at the stage of washing Iceberg lettuce to remove L. monocytogenes. The maximum observed log reduction of L. monocytogenes was 2.15 0.04 for balsamic vinegar (50% (v/ v)), 1.18 0.06 for white wine vinegar ((50% (v/v)) and 1.13 0.06 for acetic acid ((50% (v/v)). Washing with water only reduces 0.05 0.04 log CFU/mL of L. monocytogenes numbers. Listeria reductions observed for balsamic vinegar are similar or higher than those of chlorine-based sanitizers evaluated in other studies with lettuce. In the case of balsamic vinegar solutions, Listeria inhibition followed a linear reduction according to the model: Log (N/N0) ¼ 4.09 balsamic vinegar proportion % (v/v) 0.13; R2 ¼ 0.95. Balsamic vinegar washings may be a promising method for reducing other foodborne pathogens present in produce or other foods, at home and retail environments.

2014Journal article

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Fresh fruits and vegetables – An overview on applied methodologies to improve its quality and safety

Publication . Ramos, B.; Miller, F. A.; Brandão, T. R. S.; Teixeira, P.; Silva, C. L. M.

The consumers' demand for fresh fruits and vegetables has increased in recent years. These foods may be consumed raw or minimally processed, and therefore can be a vehicle of several pathogens. The microorganisms most frequently linked to produce-related outbreaks include bacteria (Salmonella spp., Listeria monocytogenes, Escherichia coli, and Shigella spp.), viruses and parasites. There are many traditional technologies to reduce/eliminate the microorganisms present in food products. However, further research on this topic is still required, since none of the methods reported can control all the parameters necessary to achieve produce with an extending shelf-life, without compromising its quality. In this paper, an analysis of the alternative and traditional methodologies is made, pointing out the significant advantage and limitations of each technique. Industrial relevance: The significant increase in the incidence of foodborne outbreaks caused by contaminated minimally processed produce in recent years has become of extreme importance. The extensive knowledge of gentle (non-thermal) processes to enhance safety, preservation and shelf-life of these products is crucial for the food industry. This manuscript presents non-thermal processes that have shown efficient microbial reductions on fresh produce and highlights some of their challenges and limitations.

2013Journal article

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