Browsing by Author "Hogg, Tim A."
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- Ability of lactic acid bacteria to produce volatile phenolsPublication . Couto, José A.; Campos, Francisco M.; Figueiredo, Ana R.; Hogg, Tim A.Thirty-live strains of lactic acid bacteria (20 species) were screened for the ability to produce volatile phenols from the corresponding phenolic acids, p-coumaric and ferulic, in culture medium. The concentration of vinylphertols and ethylphenols in the growth mediuro was analyzed by gas chromatography. Results showed that 13 strains t3?%) were able to produce volatile phenols from p-coumaric acid, although only three (9%) produced 4-ethylphcnnl. the final product of the p-coumnric acid metabolic pathway. The reduction step of this pathway was only l`ound in the Lactobacillus genus: L brevis, L. cotlinoider, and L plnntnrttrrt. Seven of the eight pediococci strains studied were able to produce 4-vinylphenol but not 6-ethylphenol from p-coumaric acid. The two Oenococcus nent strains und the strain of Leuconostoc rneseitterriirler studied did ROI produce either of the two p-coumaric acid derivatives. Strains that produced volatile phenols were used in subsequent studies at lower phenolic acid con-centrations. Experiments with added 5 mgfL oi`p-cottniaric acid showed that some strains can still produce re1atively high (up to S00 ugiL) concentrations of 4-ethylphenol. The capacity of lactic acid bacteria to produce volatile phenols from l`crulic acid was much lower than its capacity to produce volatile phcrtols from pecouniaric acid.
- Plant aqueous extracts: antioxidant capacity via haemolysis and bacteriophage P22 protectionPublication . Gião, Maria S.; Leitão, Isabel; Pereira, Ana; Borges, André B.; Guedes, Catarina J.; Fernandes, João C.; Belo, Luís; Santos-Silva, Alice; Hogg, Tim A.; Pintado, Manuela E.; Malcata, F. XavierThe bacteriophage P22/Salmonella Typhimurium system, as well as human erythrocytes have been used to assay for protection, against forced oxidation caused by hydrogen peroxide, brought about by several aqueous extracts of selected adventitious plants grown in Portugal. This study proved, for the first time, that the aforementioned bacteriophage-based system is a suitable method to assess the antioxidant activity of plant extracts; among the 12 plants tested, raspberry (Rubus idaeus), sage (Salvia sp.), savory (Satureja montana) and yarrow (Achillea millefolium) were found to effectively protect against oxidative damage caused by H2O2. Haemolysis was inhibited via pre-treatment with every plant extract tested, except heath at 0.1% (w/v). The two analytical methods produced different results – and for some plants, there was a dependence (either direct or inverse) of the quantitative protection effect on extract concentration, whereas for others no significant dependence was found at all. Savory yielded the most promising results, using either method. Therefore, the P22/Salmonella system can be used as a suitable in vivo assay, and human erythrocytes as a suitable in vitro assay to confirm (or not) the antioxidant capacity of plant extracts in biological matrices.