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- The protective effect of food matrices on Listeria lytic bacteriophage P100 application towards high pressure processingPublication . Komora, Norton; Bruschi, Carolina; Ferreira, Vânia; Maciel, Cláudia; Brandão, Teresa R. S.; Fernandes, Rui; Saraiva, Jorge A.; Castro, Sónia Marília; Teixeira, PaulaThe application of lytic phages as biocontrol agents is emerging as a promising strategy towards elimination or reduction of foodborne pathogens in a variety of food products. This technology is particularly advantageous for minimally processed and ready-to-eat (RTE) foods. In this study, the potential use of Listex™ P100 combined with high hydrostatic pressure (HPP), to enhance the control of Listeria monocytogenes in food was evaluated. For that, the effect of three pressures (200, 300 or 400 MPa; 5 min, 10 °C) on phage P100 stability was tested when inoculated in six different matrices: phosphate buffered saline (PBS, pH 7.4); apple juice (pH 3.41); orange/carrot nectar (pH 3.54); UHT whole milk (pH 6.73); and, two traditional Portuguese fermented products, “Serra da Estrela” cheese (pH 5.66) and “Alheira”, a meat sausage (pH 6.07). The results showed that treatment at 400 MPa reduced phage titres to below the detection level in all matrices, whereas at milder pressures the survival of the phage was matrix dependent. “Alheira”, “Serra da Estrela” cheese and UHT whole milk were shown to be baroprotective matrices that support phage P100 application in HHP up to 300 MPa; however, an accentuated phage inactivation was observed in apple and orange/carrot nectar, which may be related to the acidic pH values of these matrices. The initial phage load did not affect the inactivation rate during HHP processing (300 MPa, 5 min, 10 °C) in PBS, cheese, sausage or milk matrices, and the phage titres were stable in these matrices during storage at 4 °C for 28 days for milk and 60 days for “Alheira” and “Serra da Estrela” cheese. In addition, a baroprotective effect on phage stability was observed when PBS was supplemented with reducing sugars, dextrin, casein, and tween 80. In conclusion, at mild HHP treatment, phage P100 remained active in specific matrices and seems to present potential to be added in non-thermal inactivation of L. monocytogenes.
- Antimicrobial activity of ethanolic extract of propolis in "Alheira", a fermented meat sausagePublication . Casquete, Rocío; Castro, Sónia Marília; Jácome, Samuel; Teixeira, PaulaThe objective of this study was to evaluate the efficacy of an ethanolic extract of propolis (EEP) in the control of Listeria innocua PHLS 2030c (as a surrogate for Listeria monocytogenes) during storage of Alheira at 4°C. Total phenolic content was evaluated to determine the minimal inhibitory concentration of EEP against the growth of L. innocua by the agar dilution method. Alheiras were manufactured by incorporating EEP (0.28 mg/mL) and pathogenic bacteria and storage during 62 days at 4°C. Growth of L. innocua was determined during storage. The behaviour of L. innocua in the food matrix was significantly affected (p < 0.01) by the addition of EEP. The ethanolic extract of propolis reduced the Listeria population to below the detection limit of the technique after 8 days of storage. These results suggest that incorporation of EEP in a food susceptible to Listeria contamination may be an interesting alternative to existing chemical preservatives and can extend the shelf life of these products.
- Non-thermal approach to Listeria monocytogenes inactivation in milk: the combined effect of high pressure, pediocin PA-1 and bacteriophage P100Publication . Komora, Norton; Maciel, Cláudia; Pinto, Carlos A.; Ferreira, Vânia; Brandão, Teresa R. S.; Saraiva, Jorge M. A.; Castro, Sónia Marilia; Teixeira, PaulaNon-thermal food processing and replacement of chemical additives by natural antimicrobials are promising trends in the food industry. The objective of the present work was to evaluate the effect of a process which combines mild high hydrostatic pressure – HHP (200 and 300 MPa, 5 min, 10 °C), phage Listex™ P100 and the bacteriocin pediocin PA-1 as a new non-thermal process for destruction of Listeria monocytogenes (104 CFU mL−1 or 107 CFU mL−1) in milk. For inoculum levels of 104 CFU mL−1, HHP combined with phage P100 eliminated L. monocytogenes immediately after pressurization. When L. monocytogenes was inoculated at levels of 107 CFU mL−1, a synergistic effect between phage P100, pediocin PA-1 and HHP (300 MPa) on the inactivation of L. monocytogenes was observed during storage of milk at 4 °C. For non-pressure treated samples inoculated with phage or pediocin or both, L. monocytogenes counts decreased immediately after biocontrol application, but regrowth was observed in a few samples during storage. Phage particles were stable during refrigerated storage for seven days while pediocin PA-1 remained stable only during three days. Further studies will have to be performed to validate the findings of this work in specific applications (e.g. production of raw milk cheese).
- Evaluation of the effect of high pressure on total phenolic content, antioxidant and antimicrobial activity of citrus peelsPublication . Casquete, Rocío; Castro, Sónia Marilia; Martín, Alberto; Ruiz-Moyano, Santiago; Saraiva, Jorge A.; Córdoba, María G.; Teixeira, PaulaThis study aimed to assess the effect of high pressure at 300 and 500 MPa for 3 and 10 min on the phenolic compounds, antioxidant capacity and antimicrobial activity of citrus peel extracts. Total phenolic contents (TPC) and antioxidant properties of extracts were determined as free radical-scavenging ability of DPPH and using the ABTS radical cation decolorization assay. Additionally, extracts were tested for antimicrobial activity against twenty different strains of bacteria representing both Gram-positive and Gram-negative types. Citrus peel extracts demonstrated antimicrobial activity against a wide range of bacteria. The maximum level of TPC as well as antioxidant capacity were observed at 300 MPa for 3 min. Citrus peels extracts demonstrated antimicrobial activity against a wide range of microorganisms. The antimicrobial activity of orange peel extract was the highest among the four citrus peels studied. Generally, bacteria Acinetobacter and the strain Listeria innocua were more sensitive to the peel extracts.
- Evaluation of the microbiological safety and sensory quality of a sliced cured-smoked pork product with protective cultures addition and modified atmosphere packagingPublication . Casquete, Rocío; Fonseca, Susana C.; Pinto, Ricardo; Castro, Sónia M.; Todorov, Svetoslav; Teixeira, Paula; Vaz-Velho, ManuelaThe aim of this study was to evaluate the effect of two protective lactic acid bacteria cultures combined with modified atmosphere packaging on the survival/growth of Listeria innocua 2030c (as a surrogate for Listeria monocytogenes) and on sensory attributes of ready-to-eat ‘lombo’ over storage time. Sliced ‘lombo’, a traditional cured-smoked pork loin, was inoculated with L. innocua 2030c, Lactobacillus sakei ST153 (isolated from ‘salpicão’) and BLC35 culture (with Lactobacillus curvatus, Staphylococcus xylosus and Pediococcus acidilactici; CHR Hansen) as protective cultures. Samples were packed in two modified atmosphere packaging conditions (20% CO2/80% N2 and 40% CO2/60% N2) and stored at 5 ℃ for 124 days. Both cultures led to a reduction of 1–2 log CFU/g of L. innocua 2030c after 12 h; however, at the end of storage only Lb. sakei ST153 maintained this antilisterial effect, which was more evident at 40% CO2/60% N2. The influence of cultures addition and modified atmosphere packaging conditions on the sensory characteristics of the product were not significant. Thus, Lb. sakei ST153 combined with modified atmosphere packaging is a strong candidate to be used in a biopreservation strategy maintaining the traditional sensory quality of cured-smoked pork products and increasing their safety with respect to Listeria spp.
- Processing slime from snail (Helix aspersa maxima): a preliminary study on the effect on microbial loadPublication . Teixeira, Raquel; Barbosa, Joana; Albano, Helena; Maciel, Cláudia; Silva, Joana; Saraiva, Jorge A.; Castro, Sónia M.; Teixeira, PaulaSlime from earth snails (Helix aspersa maxima) is a sub-product often used in the cosmetic industry. Due to its origin, a decontamination process ought to be considered. After exposure to UV radiation, no significant (P > 0.05) reduction of the initial microbial load of slime was observed, while treated at 60 °C, a decrease of 4.0 log CFU∙mL-1 was obtained (when compared to non-treated slime). A similar reduction was attained for pressurized (500 MPa) slime. The sequential combination of temperature and pressure treatment had a similar effect (P > 0.05) on the microbial load when compared to 400 MPa (30 min), but the reduction was higher when compared to the less intense treatments (60 °C, 15 min; 400 MPa, 15 min). Overall, the results suggest that pressure ( 400 MPa) is a promising technology for processing snail slime, which can have positive effects on its microbial load, for further use in the cosmetic industry
- Combined effect of pediocin bacHA-6111-2 and high hydrostatic pressure to control listeria innocua in fermented meat sausagePublication . Castro, S. M.; Silva, J.; Casquete, R.; Queirós, Rui; Saraiva, J. A.; Teixeira, P.In and ex situ production of bacteriocin (bacHA-6111-2) combined with high hydrostatic pressure (300 MPa, 5 min, 10ºC) were assessed on the survival of Listeria innocua reviously inoculated in Alheira, a traditional Portuguese fermented meat product. The effect was evaluated immediately after each treatment, alone and combined, and during 60 days of storage (4ºC). For higher concentrations of L. innocua, a bacteriostatic effect was verified: i) during the first days of storage for the pressure treatment alone and in combination with ex situ production of bacteriocin; and ii) for longer periods, when pressure was combined with in situ production of bacteriocin. After this effect, the first treatments revealed rapid growth up to the initial values; while the latest treatment, and for lower initial cells, resulted in a decrease > 2 log CFU g-1, from day 3 of storage until the end of the study. A similar result was obtained for analogous pressurized L. innocua samples with ex situ production of bacteriocin. The developed work has demonstrated the potential of using the combination of natural antimicrobial compounds (pediocin bacHA-6111-2, produced either in or ex situ) with mild pressure (300 MPa, 5 min) treatments to control effectively L. innocua in fermented meat products such as Alheiras, when contaminated with values closed to the ones that might potentially arise by natural postcontamination.