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- Fresh fruits and vegetables – An overview on applied methodologies to improve its quality and safetyPublication . 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.
- Antilisterial active compound from lactic acid bacteria present on fresh iceberg lettucePublication . 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.
- Heat inactivation of Listeria innocua in broth and parsley under non-isothermal conditionsPublication . Miller, Fátima A.; Ramos, Bárbara F.; Brandão, Teresa R. S.; Teixeira, Paula; Silva, Cristina L. M.
- Antilisterial effect of vinegar solutions in fresh salads preparationPublication . Ramos, Bárbara F.; Silva, Joana; Brandão, Teresa R. S.; Teixeira, Paula; Silva, Cristina L. M.
- Heat inactivation of Listeria innocua in broth and parsley under non-isothermal conditionsPublication . Miller, Fátima A.; Ramos, Bárbara F.; Brandão, Teresa R. S.; Teixeira, Paula; Silva, Cristina L. M.
- Influences of physicochemical stresses on injury and inactivation behaviour of Listeria innocuaPublication . Miller, Fátima A.; Ramos, Bárbara; Gil, Maria M.; Brandão, Teresa R. S.; Teixeira, Paula; Silva, Cristina L. M.Many minimally processed foods depend on a combination of inhibitory factors to reduce the hazard of foodborne illness. Therefore, inactivation of Listeria innocua was studied according to a 24 factorial experiment designed to draw conclusions about temperature (52.5 °C and 65.0 °C), pH (4.5 and 7.5), water activity (aw=0.95 and 0.99) and solute type (NaCl and glycerol) effects. Three different recovery media were used to assess injured cells. Survival data were fitted with a Gompertz-based model and kinetic parameters (shoulder, maximum inactivation rate – kmax, and tail) were estimated. Results showed that shoulder was affected by temperature, pH and combined effects; kmax was influenced by all factors and their combinations; and tail was affected by aw, temperature and aw/pH combination. Results demonstrated the potential occurrence of microbial cross-protection survival techniques between the various stresses, e.g. heat and osmolarity. Indeed, this work clearly established that, to avoid hazards, Listeria inactivation must be evaluated with a maximum of environmental factors that undergo alterations. Only thus, appropriate food preservation treatments can be developed and consequently, the safety of food products can be assured.
- Comparison of recovery methods for the enumeration of injured Listeria innocua cells under isothermal and non-isothermal treatmentsPublication . Miller, Fátima A.; Ramos, Bárbara; Brandão, Teresa R.S.; Teixeira, Paula; Silva, Cristina L.M.This study compares the feature of different media with the combination of selective with non-selective media in a TAL method for recovery of Listeria innocua cells exposed to thermal treatments. Experiments were conducted in broth at constant temperature (52.5 and 65.0 ºC) and pH (4.5 and 7.5) conditions, using NaCl or glycerol to adjust water activity to 0.95. Four different media were used in bacterial cell enumeration: (i) a non-selective medium e TSAYE, (ii) two selective media e TSAYE þ 5%NaCl and Palcam Agar and (iii) TAL medium (consisting of a layer of Palcam Agar overlaid with one of TSAYE). Two food products were used as case studies aiming at comparison of results obtained on selective and TAL media enumeration. Parsley samples were inoculated with L. innocua and subjected to posterior thermal treatments both under isothermal (52.5, 60.0 and 65.0 ºC) and non-isothermal (heating rate of 1.8 ºC/min from 20.0 to 65.0 ºC) conditions. The recovery capability of TAL method was also studied when a pre-cooked frozen food (i.e. meat pockets) was fried (oil temperature of w180 ºC). TAL method proved to be better than Palcam Agar in terms of capability to recover injured cells and was effective in L. innocua enumeration when non-sterile samples were analysed.
- Biopreservation approaches to reduce Listeria monocytogenes in fresh vegetablesPublication . 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.
- On the assessment of an agar overlay method for the recovery of heat-injured Listeria innocua in parsleyPublication . Miller, Fátima A.; Ramos, Bárbara F.; Brandão, Teresa R. S.; Teixeira, Paula; Silva, Cristina L. M.
- An overview concerning methodologies applied to guarantee fruits and vegetables safetyPublication . Ramos, Bárbara F.; Brandão, Teresa R. S.; Teixeira, Paula; Silva, Cristina L. M.
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