Browsing by Author "Hogg, Tim"
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- Activity of lysozyme on Lactobacillus hilgardii strains isolated from Port winePublication . Dias, Rita; Vilas-Boas, Eduardo; Campos, Francisco M.; Hogg, Tim; Couto, José AntónioThis work evaluated the effect of lysozyme on lactobacilli isolated from Port wine. Bacterial growth experiments were conducted in MRS/TJ medium and inactivation studies were performed in phosphate buffer (KH2PO4), distilled water and wine supplemented with different concentrations of lysozyme. The response of bacteria to lysozyme was found to be highly strain dependent. Some strains of Lactobacillus hilgardii together with Lactobacillus collinoides and Lactobacillus fructivorans were found to be resistant to concentrations of lysozyme as high as 2000 mg/L. It was observed that among the L. hilgardii taxon the resistant strains possess an S-layer coat. Apparently, the strains of L. collinoides and L. fructivorans studied are also S-layer producers as suggested by the total protein profile obtained by SDS-PAGE. Thus, the hypothetical protective role of the S-layer against the action of lysozyme was investigated. From the various treatments used to remove the protein from the surface of the cells, the one employing LiCl (5 M) was the most effective. LiCl pre-treated cells exposed to lysozyme (2000 mg/L) in KH2PO4 buffer maintained its resistance. However, when cells were suspended in distilled water an increased sensitivity to lysozyme was observed. Moreover, it was found that the addition of ethanol (20% v/v) to the suspension medium (distilled water) triggered a strong inactivation effect especially on cells previously treated with LiCl (reduction of >6 CFU log cycles). The results suggest that the S-layer exerts a protective effect against lysozyme and that the cell suspension medium influences the bacteriolysis efficiency. It was also noted that ethanol enhances the inactivation effect of lysozyme.
- Activity of wine against campylobacter jejuniPublication . Carneiro, Anabela; Couto, José António; Mena, Cristina; Queiroz, Jorge; Hogg, TimThis study focuses on the activity of wine against the important food-borne pathogen Campylobacter jejuni. The kinetics of inactivation of two strains of C. jejuni (one food-borne and one clinical) were characterised in various scenarios of exposure to wine and wine components. Undiluted wine was found to rapidly inactivate C. jejuni (>6D inactivation within 30 s); further inactivation data were obtained from experiments performed in wine diluted with water (1:2 and 1:4). Experiments with isolated antimicrobial fractions of wine (ethanol and certain organic acids) suggest that these two components act synergistically, demonstrating an inactivation capacity similar to wine itself. The results indicate that the exposure of contaminated food to wine, as in marinade conditions, Significantly reduces the number of viable cells of C. jejuni. A model stomach, containing a food matrix and a synthetic gastric fluid, was used to infer the effect of wine against C. jejuni in a consumption-like scenario. Wine was found to potentiate the anti-Campylobacter effect of gastric fluid. The results strongly suggest that the ingestion of wine during a meal may greatly diminish the quantity of C. jejuni persisting further in the alimentary tract, thus lowering the risk of infection
- Alcohols, esters and heavy sulphur compounds production by pure and mixed cultures of apiculate wine yeastsPublication . Moreira, Nathalie; Mendes, Filipa; Hogg, Tim; Vasconcelos, IsabelStrains of Hanseniaspora uvarum, Hanseniaspora guilliermondii and Saccharomyces cerevisiae were used as pure or mixed starter cultures in commercial medium, in order to compare their kinetic parameters and fermentation patterns. In pure and mixed cultures, yeasts presented similar ethanol yield and productivity. Pure cultures of H. uvarum and S. cerevisiae showed a specific growth rate of 0.38 h⁻¹; however, this value decreased when these yeasts were grown in mixed cultures with H. guilliermondii. The specific growth rate of pure cultures of H. guilliermondii was 0.41 h⁻⁻¹ and was not affected by growth of other yeasts. H. guilliermondii was found to be the best producer of 2-phenylethyl acetate and 2-phenylethanol in both pure and mixed cultures. In pure cultures, H. uvarum led to the highest contents of heavy sulphur compounds, but H. guilliermondii and S. cerevisiae produced similar levels of methionol and 2-methyltetrahydrothiophen-3-one. Growth of apiculate yeasts in mixed cultures with S. cerevisiae led to amounts of 3-methylthiopropionic acid, acetic acid-3-(methylthio)propyl ester and 2- methyltetrahydrothiophen-3-one similar to those obtained in a pure culture of S. cerevisiae; however, growth of apiculate yeasts increased methionol contents of fermented media.
- Antilisterial activity of lactic acid bacteria isolated from "Alheiras" (traditional Portuguese fermented sausages)Publication . Albano, Helena; Oliveira, Márcia; Aroso, Ricardo; Cubero, Núria; Hogg, Tim; Teixeira, PaulaA total of 226 lactic acid bacteria (LAB) isolated from ‘‘Alheira’’, a traditional Portuguese fermented sausage, were screened for antagonistic activity against some pathogenic microorganisms, including Listeria monocytogenes. The objective was to isolate LAB with antibacterial activity from ‘‘Alheiras’’ and to select strains that could be used in ‘‘Alheira’’ production. Isolates displaying antibacterial activity against Listeria innocua and L. monocytogenes were investigated for the nature of the antibacterial compounds active against these microorganisms. Results showed that two LAB cultures retained activity in the supernatants after neutralization and catalase treatment. These two strains were both identified as Pediococcus pentosaceus. The final aim of this work was to test the antilisterial activity of these two strains during storage of ‘‘Alheira mass’’ (sterilized), at 4 C. The growth of L. innocua population was significantly suppressed in the paste of ‘‘Alheira’’ when the samples were co-inoculated with the LAB strains, in comparison with the paste only inoculated with L. innocua or co-inoculated with a bacteriocin negative strain of Ped. pentosaceus (ca. 1 · 107 CFU/g after 28 days of incubation).
- Application of a liquid chromatographic method for the determination of phenolic compounds and furans in fortified winesPublication . Ho, P.; Hogg, Tim; Silva, M.C.M.Fortified wines which suffer extended periods of wood ageing develop characteristics which in many cases define the product. An important component of this style is contributed by the specific phenolic compounds and furans which are either extracted from the wood or formed during the barrel ageing process. An HPLC method is presented here for the determination of phenolic compounds and furans in wood aged fortified wines. The method employed involved direct injection with no sample pre-treatment, separation on a RP C18 column in a single run and detection with a diode array detector. In this way up to 28 compounds from various phenolic groups (hydroxybenzoic acids, hydroxycinnamic acids, phenolic aldehydes, coumarins, ¯avan-3-ols, ¯avonol aglycones and other compounds involved in browning reactions in food systems (furans and pyranones) could be separated and determined. Of these, 10 phenolic compounds, gallic acid, protocatechuic acid, p-coumaric acid, ca eic acid, chlorogenic acid, ellagic acid, vanillic acid, syringic acid, p-hydroxybenzaldehyde, myricetin, and two furans; furfural, 5-hydroxymethyl-2-furaldehyde, were determined in forti®ed and similar wood aged wines. Three other compounds, a chlorogenic acid isomer, vanillin and resorcinol, were also tentatively identified in these wine types
- Building on scientific excellence via sharing of scientific expertise - The case study of food safetyPublication . Hogg, Tim; Couto, José A.; Teixeira, Paula; Malcata, F. XavierMany of the difficulties faced nowadays by society at large in maintaining a safe food supply can be effectively addressed by more and (preferably) better science. However, excellence in science will become more and more dependent on sharing of data and expertise - the nuclear idea emphasized in this viewpoint article, which conveys the major points presented and discussed by the senior author in the (invited) opening plenary lecture delivered at EFSA 5th anniversary scientific forum. Data and knowledge are usually shared within the scientific community itself - and are typically aimed at peers; however, the associated citing metrics do not often correlate with their applicability and usefulness. Funding bodies have for long recognized the value of networking and crossbreeding among scientists - in reinforcing complementarities and promoting synergies. Furthermore, these bodies have had a major effect in driving food scientists reach out of their cocooned, narrow communities toward embracing a wider spectrum of disciplines (e.g. in social and economic sciences). Web-supported databases of e.g. risk data and pathogen sequences have also revolutionized access to, and use of knowledge. Finally, a number of formal trans-European platforms have been launched by private stakeholders to promote sharing. In all cases, the thrust is to be put on trust - that what is shared is genuine and valid, and will not be subsequently adulterated or used inappropriately. Willingness to engage in free circulation of information and expertise will determine the extent of effective sharing on the long run, and of excellence of science derived therefrom - which is ultimately developed for the well-being and safety of the citizen, seen first of all as a food consumer.
- Cell membrane damage induced by phenolic acids on wine lactic acid bacteriaPublication . Campos, Francisco M.; Couto, José A.; Figueiredo, Ana R.; Tóth, Ildikó V.; Rangel, António O. S. S.; Hogg, Tim
- Cell membrane damage induced by phenolic acids on wine lactic acid bacteriaPublication . Campos, F.M.; Couto, J.A.; Figueiredo, A.R.; Tóth, I.V.; Rangel, António O. S. S.; Hogg, TimThe aim of this work was to investigate the effect of phenolic acids on cell membrane permeability of lactic acid bacteria from wine. Several phenolic acids were tested for their effects on the cell membrane of Oenococcus oeni and Lactobacillus hilgardii by measuring potassium and phosphate efflux, proton influx and by assessing culture viability employing a fluorescence technique based on membrane integrity. The experimental results indicate that hydroxycinnamic acids (p-coumaric, caffeic and ferulic acids) induce greater ion leakages and higher proton influx than hydroxybenzoic acids (p-hydroxibenzoic, protocatechuic, gallic, vanillic, and syringic acids). Among the hydroxycinnamic acids, p-coumaric acid showed the strongest effect. Moreover, the exposure of cells to phenolic acids caused a significant decrease in cell culture viability, as measured by the fluorescence assay, in both tested strains. The results agree with previous results obtained in growth experiments with the same strains. Generally, phenolic acids increased the cell membrane permeability in lactic acid bacteria from wine. The different effects of phenolic acids on membrane permeability could be related to differences in their structure and lipophilic character.
- Challenge testing and shelf life studiesPublication . Hogg, Tim; Almeida, Gonçalo
- Changes in colour and phenolic composition during the early stages of maturation of port in wood, stainless steel and glassPublication . Ho, Peter; Silva, Maria da Conceição M.; Hogg, TimDifferences in colour and phenolic composition during the maturation of port in oak wood, stainless steel and glass were examined for a period of 311 days at 18 °C. Principal component analysis (PCA) was used in variable selection, data reduction and data analysis. Nine out of 13 colour and phenolic variables were heavily loaded on PC1 (76.1% of explained variance), and a plot of PC1 scores versus maturation time showed differences in colour and anthocyanins between ports matured in different containers. Ports matured in oak casks developed at a faster rate than the other ports. Total phenolics remained fairly constant in all ports, as monomeric anthocyanins were rapidly depleted during the time of maturation. Polymeric pigments formed during maturation contributed to increases in colour density, hue and the rate of browning. Differences in redox potential between wood matured ports and non-wood matured ports indicated that there were differences in dissolved oxygen which could have affected the maturation rate of these wines.