Browsing by Author "Silva, Manuela V. da"
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- Emerging risks and strategies for environment and health protectionPublication . Silva, Manuela V. da; Teixeira, João P.; Rodrigues, Matilde; Oliveira, Rui S.
- Production of histamine and tyramine by bacteria isolated from Portuguese vacuum-packed cold-smoked fishPublication . Silva, Manuela V. da; Pinho, Olívia; Ferreira, Isabel; Plestilov, LindaAn agar medium containing histidine or tyrosine incubated anaerobically was used for detecting the decarboxylating activity of bacteria isolated from Portuguese vacuum-packed cold-smoked fish during chilled storage. The capacity of each bacterial isolate to produce histamine and tyramine was studied at 25 and 5 C incubated for 48 h and 10 days, respectively. More strains produced histamine and tyramine at 25 C compared with 5 C although lactic acid bacteria (LAB) strains exhibited similar results at the two different temperatures. Tyramine was produced by majority of the isolates tested although very low concentrations were produced at 5 C as confirmed by high-pressure liquid chromatography (HPLC). Tyrosine-agar was shown to be a good indicator medium for detection of bacteria that produced high levels of tyramine, since typical colonies surrounded by a translucent halo were easily recognised. LAB identified as Lc. Lactis lactis 1 and Carnobacterium divergens were detected as tyramine-producing bacteria. Acinetobacter spp. and Pseudomonas spp., isolated from all Portuguese smoked fish products, were negative on histidine-agar, but HPLC identified considerable quantities of histamine produced in a broth medium.
- Significance of biogenic amines in cold-smoked fish and their relation to microbiological characteristics of products available in Portuguese retail marketsPublication . Silva, Manuela V. da; Gibbs, PaulStudies on microbial characterization of cold-smoked salmon and salmon trout during cold storage were performed on samples available in the Portuguese market. Samples were also classified microbiologically according to guidelines for ready-to-eat (RTE) products. Further investigations on sample variability and microbial abilities to produce tyramine and histamine were also performed. The coefficient of variation for viable counts of different groups of microorganisms of samples collected at retail market point was high in the first 2 wk of storage, mainly in the Enterobacteriaceae group and aerobic plate count (APC), suggesting that microbiological characteristics of samples were different in numbers, even within the same batch from the same producer. This variation seemed to be decreased when storage and temperature were controlled under lab conditions. The numbers of Enterobacteriaceae were influenced by storage temperature, as indicated by low microbial numbers in samples from controlled refrigeration. Lactic acid bacteria (LAB) and Enterobacteriaceae were predominant in commercial products, a significant percentage of which were tyramine and less histamine producers. These results might be influenced by (1) the technological processes in the early stages of production, (2) contamination during the smoking process, and (3) conditions and temperature fluctuations during cold storage at retail market point of sale.