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- Pesquisa de Listeria monocytogenes em produtos cárneos fumados e de salsichariaPublication . Vaz-Velho, Manuela; Almeida, Gonçalo; Mena, Cristina; Carneiro, Luisa; Freitas, António
- Food safety and quality profile of Alheira de Vitela, Chouriço de Carne and Salpicão Serra D’Arga: traditional Portuguese sausages produced in the North of PortugalPublication . Noronha, Lúcia; Almeida, Ana Luísa; Freixo, Ricardo; Jácome, Samuel; Fonseca, Susana; Vaz-Velho, Manuela; Almeida, Gonçalo; Silva, Cristina L. M.; Morais, Alcina M. M. B.; Silva, Joana; Teixeira, Paula
- Comparison of antilisterial effects of two strains of lactic acid bacteria during processing and storage of a Portuguese Salami-like Product “Alheira”Publication . Vaz-Velho, Manuela; Jácome, Samuel; Noronha, Lúcia; Todorov, Svetoslav; Fonseca, Susana; Pinheiro, Rita; Morais, Alcina M. M. B.; Silva, Joana; Teixeira, PaulaTraditional smoked and/or cured salami-like products are much appreciated by Southwest European consumers. However modern consumers require products that not only have high appealing sensory attributes but are also safe. In this work the effect of the application of two bacteriocinogenic lactic acid bacteria (LAB) Lb. plantarum ST202 and Lb. sakei ST153 for controlling Listeria monocytogenes growth in "Alheira", a traditional salami-like product, was investigated. The paste of "Alheira',' produced by an industrial meat company, was sterilized by autoclaving before inoculation and L. monocytogenes growth was evaluated during 15 days of storage. Both LAB strains showed antilisterial activity in the inoculated paste, but as in preliminary experiments with sterilized minced pork meat only strain ST153 presented activity against L. monocytogenes. it was decided, for further industrial tests, to use only this strain. Therefore, the effect of Lb. sakei ST153 against L. monocytogenes in industrially processed "Alheira", packed under vacuum or under modified atmosphere (MA) (20 % CO2 and 80 % N-2), was evaluated during 7 days storage at 4 degrees C. The effect of the inoculation of the bacteriocinogenic culture in the organoleptic properties of "Alheira" was also investigated. A quantitative descriptive sensory test was performed by a semi-trained panel after 5 days storage. No significant differences were observed in the microbiological and sensory quality of "Alheira" packed under vacuum or MA. A significant reduction in the level of L. monocytogenes was observed in the presence of Lb. sakei ST153 (2 log cycles reduction during the first 7 days). Results showed that panellists did not find significant differences between "Alheira" with Lb. sakei ST153 addition and commercial control, except for mass connection, acid taste and atypical taste. Despite that, both samples were scored above conformity limit. Thus, the application of LAB is a very promising mean of preventing L. monocytogenes growth in "Alheira".
- Efficiency of four secondary enrichment protocols in differentiation and isolation of Listeria spp. and Listeria monocytogenes from smoked fish processing chainsPublication . Duarte, Gabriela; Vaz-Velho, Manuela; Capella, Christopher; Gibbs, PaulFour secondary enrichment protocols (conventional methods: UVM II, Fraser 24 h and Fraser 48 h: Impedimetric method: Listeria electrical detection medium) were studied for their ability to isolate Listeria spp. and Listeria monocytogenes from fish and environmental samples collected along the processing chain of cold-smoked fish. From all methods, Listeria spp. and L. monocytogenes were respectively present in 56 and 34 of 315 samples analysed. Fraser broth incubated for 48 h gave the fewest false negative Listeria spp. results [4/56; (7.1%)], but concurrently only 15/34 (44.1%) samples were correctly identified as containing L. monocytogenes. Listeria electrical detection (LED) medium detected only 36/56 (64.3%) Listeria spp. positive samples. Despite this lower isolation rate, LED identified 20/34 (58.8%) L. monocytogenes positive samples correctly and gave fewer false positive results. The overall conclusion was that more than one isolation method is needed to accurately estimate L. monocytogenes contamination rates.
- Effects of lactobacillus plantarum bacteriocinogenic culture on physicochemical, microbiological, and sensorial characteristics of "Chouriço Vinha d'Alhos", a traditional Portuguese sausagePublication . Macieira, A.; Barros, D.; Vaz Velho, Manuela; Pinheiro, R.; Fonseca, S.; Albano, H.; Teixeira, P.Background: “Chouriço Vinha d’Alhos” is a traditional fermented dry meat sausage from North of Portugal. The aim of this work was to evaluate the effects of a fresh and a lyophilized bioprotective Lactobacillus plantarum ST153Ch culture, on an industrial scale, on the physicochemical, microbiological, and sensorial characteristics of “Chouriço Vinha d’Alhos”. Methods: “Chouriço Vinha d’Alhos” added with Lb. plantarum ST153Ch (fresh or lyophilized) were analyzed for the physicochemical, microbiological, and sensorial characteristics, over 90 days of storage at 4 ºC. All data were statistically analyzed using an ANOVA procedure by IBM SPSS Statistics v. 25. Results: The results showed that there was no difference in the reduction of L. monocytogenes, without or with the addition of Lb. plantarum either fresh or lyophilized. There were no significant differences (p>0.05) in some analyzed physicochemical parameters of products added with fresh or lyophilized Lb. plantarum cultures over the 90 days of storage; but both, fresh and lyophilized cultures, influenced some of the tested physicochemical parameters. Conclusion: Considering no significant differences between application methodologies (fresh or lyophilized Lb. plantarum), industry might be able to choose the most suitable method according to their manufacturing process.
- Characterization of Listeria monocytogenes isolated from production lines of fresh and cold-smoked fishPublication . Vaz-Velho, M.; Duarte, G.; McLauchlin, J.; Gibbs, P.Aims: The aims of this study were to characterize strains of Listeria monocytogenes isolated from cold-smoking fish plants to establish possible routes of contamination through the processing chain. Methods and Results: Listeria monocytogenes from fresh fish suppliers, raw materials, factory sites and finished products isolated in Portugal (162 isolates) and England (28 isolates) were characterized by serotyping, phage typing, tetracycline, cadmium and arsenic resistance, and plasmid profiling. On the basis of serotyping and phage typing, the isolates were categorized into eight groups. Although cultures within some of the groups could be further differentiated on the basis of plasmid profiling and cadmium and arsenite typing, consideration of all typing data predominantly clustered together isolates from a single location. L. monocytogenes strains: from fresh salmon suppliers were not found in the processing lines; from fresh salmon from different locations differed; and from the water where salmon trout were farmed differed from those isolated from the fish samples. Significance and Impact of the Study: No clear source or route of contamination in the cold-smoked processing chain could be established; however, these results highlight the complexity in tracking this bacterium through food chains.
- Evaluation of enhanced haemolysis agar for detection of Listeria spp. and L. monocytogenes from production lines of fresh to cold-smoked fishPublication . Vaz-Velho, Manuela; Duarte, Gabriela; Gibbs, PaulEnhanced haemolysis agar (EHA) was compared to the two conventional Listeria isolation agars Oxford and PALCAM for its ability to detect Listeria spp. from production lines of fresh to cold-smoked fish. The ability of EHA for distinguishing L. monocytogenes colonies from other Listeria spp. was also evaluated. A total of 243 fish and environmental samples were analysed. Overall, 42 samples were found to contain Listeria spp. Only 34 samples were positive simultaneously by the three plating media. Two samples considered to be negative by the two conventional agars were found to be positive after isolation on EHA. All three selective agars were shown to be less effective in recovering Listeria spp. after primary enrichment in half-Fraser broth, compared to secondary enrichment in Fraser broth after 24 and 48 h. From 79 Listeria but presumptive negative L. monocytogenes colonies, EHA identified correctly 76 Listeria spp. and presented three false-negative results_three colonies further identified as L. monocytogenes but showing no noticeable haemolysis on EHA. Twenty-three of the thirty-three L. monocytogenes presumptive positive colonies, were confirmed positive and ten were identified as L. seeligeri. Despite its ability of distinguishing L. monocytogenes from the other Listeria spp., unless it is produced as a commercial medium, EHA cannot be an alternative to time-consuming classical identification because the preparation of this medium is both time and labour intensive.
- Effect of lactic acid bacteria on quality and safety of ready-to-eat sliced cured/smoked meat productPublication . Jácome, Samuel; Fonseca, Susana; Pinheiro, Rita; Toorov, Svetoslav Dimitrov; Noronha, Lucia; Silva, Joana; Gomes, Ana; Pintado, Manuela; Morais, Alcina M. M. B.; Teixeira, Paula; Vaz-Velho, ManuelaThe bioprotective properties of native lactic acid cultures and their bacteriocins may be used for increasing the microbiological safety and stability of traditional sliced smoked pork products. It is expected that this addition would not affect consumer’s perception and, consequently, the acceptability of these traditional smoked meat products. The effect of two different LAB cultures, two different application methods and two different modified atmosphere packaging conditions (MAP) on growth control of Listeria monocytogenes and on sensory properties of “Chouriço”, a sliced cured/smoked pork product, were studied. Lactobacillus sakei ST153 (autochthonous bacteria) and BLC35 (commercial mixed starter culture including strains of Lactobacillus curvatus, Staphylococcus xylosus and Pediococcus acidilactici; CHR Hansen) both with bacteriocinogenic activity against Listeria monocytogenes, were applied by immersion or spray on smoked pork slices that were produced at industrial scale and packed under MAP (8 % or 12 % v/v CO2) and stored at 5 ⁰C. Previously to the incorporation of LAB cultures, L. monocytogenes was gently spread with a sterile cotton swab into the slices. The enumeration of LAB and L. monocytogenes was performed during the storage at 5 ºC. A quantitative descriptive sensory test was performed by a sensory trained panel at 30, 90 and 120 days, involving previous sessions for main descriptors definition, their scale limits as well as verbal anchors by panel consensus. A final sheet with nine descriptors (meat colour, greasiness, characteristic odour, offodour, hardness, succulence, characteristic taste, acid taste, bitter taste), each one with a 13-point scale, was validated. Listeria monocytogenes decreased to values <100 CFU/g in smoked pork slices of both application techniques. Meat colour, succulence and characteristic taste were the common attributes for both LAB cultures that varied over the shelf life. The application method had no significant effect on any of the sensorial attributes analyzed. MAP influence was only noticed in terms of greasiness and hardness. The samples containing BLC35 addition were categorized as harder and as less succulent than the ones containing L. sakei ST153.
- Note. Occurrence of Listeria spp. in salmon-trout (Onchorhyncus mykiss) and salmon (Salmo salar)Publication . Vaz-Velho, M.; Duarte, G.; Gibbs, P.Salmon-trout (Onchorhyncus mykiss) and salmon (Salmo salar) are the main raw materiaIs in the cold-smoked fish industry. It is important to prevent the contamination of these ready-to-eat products with Listeria monocytogenes and other (Listeria spp.) because the temperature used in the cold-smoking process is not sufficient to inactivate these organisms. The presence of Listeria spp. and L. monocytogenes in the cold-smoked salmon and salmon-trout processing chains of three Portuguese factories examined was already confirmed in previous studies. Thus, it was important to ascertain the possible sources of contamination, the raw material being the most important one. AlI the Portuguese cold-smoking fish factories use fresh salmon-trout from two trout farms in the north of Portugal and Norwegian salmon which arrives by lorry every week under refrigeration, imported always by the same company; 88 samples of salmon and salmon-trout were analysed; 67 environrnental samples from the two trout farms were also examined. The overalI frequency (n =40) of Listeria spp. and L. monocytogenes in salmon was 12 and 0% respectively. The overalI frequency (n =48) of Listeria spp. and L. monocytogenes in salmon-trout was 6.3 and 2.1% respectively. Listeria was not found in the environmental samples.
- Comparison of two pre-enrichments broths for recovering Listeria spp. from salmon (Salmo salar) and salmon-trout (Oncorhynchus mykiss)Publication . Vaz-Velho, Manuela; Duarte, Gabriela; Gibbs, PaulLow levels of occurrence of Listeria spp. in fresh salmon (Salmo_salar ) and salmon-trout (Oncorhynchus mykiss), may be related to the selectivity of the pre-enrichment broth recommended by ISO 11290-1. The purpose of this study was to compare the abilities of Fraser base (without supplements) and 0.1% (w/v) peptone water for recovering Listeria spp. from the fresh fish samples. Fifty-six fish were swabbed and the swabs placed in Fraser base and in 0.1% (w/v) peptone water. Samples were analysed 4–6 h later following the ISO 11290-1 protocol. A total of fifteen Listeria spp. positive samples were found. Three and twelve samples were found to contain respectively, L. monocytogenes and L. innocua. The Fraser base did not detect any of the three L. monocytogenes positive samples. Only two Listeria spp. positive samples were simultaneously recovered by the two broths.