Percorrer por autor "Hogg, T."
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- An overview of hazards and risks in food contact materialsPublication . Poças, M. F.; Hogg, T.
- Analyse du cis- et trans-resveratrol dans les vins produits au portugalPublication . Revel, G. de; Hogg, T.; Santos, CristinaNous mettons au point une méthode d'analyse du resveratrol (trallS-3,5,4'-trihydroxystilbene) à I'aide de Ia chromatographie en phase gazeuse et détection par ionisation de tlamme (FID), apres une extraction du vin par I'éther et sylilation par I'hexaméthyldisilazane (HMDS). Le seuil de détection est de 5 IIgII.Une séparation parfaite des différents isom"res tralls et eis du resveratrol est obtenue et permet leur détermination dans tous les vins étudiés. Ainsi nous montrons que I'isomere eis est toujours présent dans le vin et peut atteindre de 30 à 70 p. cent du resveratrol total. Nous présentons ici une premiere étude sur la composition en resveratrol des vins provenant de différentes régions du Portugal. Les vins analysés présentent des teneurs en isomeres trans de l'ordre de 120 à 500 Ilglldans les vins blancs, et de 400 à 4500 IIgIIdans les vins rouges. Une étude plus particuliere du Vinho Verde (vin du Nord dUPortugal) a été effectuée.
- Apiculate wine yeasts: growth kinetics and aroma compounds productionPublication . Moreira, N. E. O.; Silva, C. L. M.; Vasconcelos, I. M.; Mendes, F.; Hogg, T.
- Caracterização química e sensorial de vinhos provenientes de castas nobres da região do DãoPublication . Guedes, P.; Pina, C.; Santos, C.; Santos, S.; Vasconcelos, I.; Cabral, L.; Vieira, M.; Hogg, T.
- Caracterização química e sensorial de vinhos provenientes de castas nobres da região do DãoPublication . Guedes, P.; Pina, C.; Santos, C.; Santos, S.; Vasconcelos, I.; Cabral, L.; Vieira, M.; Hogg, T.
- Carotenoid compounds found in grapes and their relationship to plant water statusPublication . Oliveira, C.; Ferreira, A. C. Silva; Pinto, M. M. Mendes; Hogg, T.; Alves, F.; Pinho, P. Guedes de
- Carotenoid compounds in grapes and their relationship to plant water statusPublication . Oliveira, C.; Ferreira, A. C. Silva; Pinto, M. Mendes; Hogg, T.; Alves, F.; Pinho, Guedes deThe aim of this work was to study the relationship between carotenoid contents in grapevine berries and plant water status. For this purpose, a black grapevine variety, Vitis vinifera L. cv. Touriga Nacional, was studied. The experiments were carried out in the same Douro vineyards, with plants of the same age, in two different water retention soils. A higher water retention capacity soil, soil A, and a lower water retention capacity soil, soil B, were both in a 1.2 m deep silt-loam schist-derived soil. The training system was the double cordon trained and spur pruned. A first range was nonirrigated (NI) and a second one was irrigated (I), 60% of evapotranspiration (ET0). For soil B, a 30% of ET0 treatment was also applied. The plant water status was estimated by predawn leaf water potential. The effects of plant water status on berry growth were studied by measurement of the berry weight and total soluble solids (°Brix). The carotenoid profile was quantitatively determined by high-performance liquid chromatography/diode array. Carotenoids determined were â-carotene, lutein, neoxanthin, violaxanthin, and luteoxanthin. The comparison between irrigated and nonirrigated grapes was followed from 2 weeks before veraison until the ripe stage. Results showed that at harvest time, berries exposed to the NI had a lower weight than those exposed to the irrigated treatment (60% of ET0), 0.89 vs 1.36 g/berry and 0.94 vs 1.34 g/berry, for soils A and B, respectively. The irrigated treatment contributed to a higher sugar concentration in both soils. However, depending on the soil water retention capacity, the carotenoid contents were different in soils A and B. For soil A, the total carotenoid content was similar for both NI and I treatments. However, with regard to soil B, in irrigated treatment, levels of carotenoids were approximately 60% lower than those found for the NI. It seems to be possible to produce higher weight berries (with higher sugar levels) with similar carotenoid contents. On the other hand, soil characteristics had a larger influence than irrigation on the concentration of carotenoids in grapes, resulting in an important viticultural parameter to take into account in aroma precursor formation.
- Cellular death of two non-saccharomyces wine-related yeasts during mixed fermentations with saccharomyces cerevisiaePublication . Pérez-Nevado, F.; Albergaria, H.; Hogg, T.; Girio, F.The early death of two non-Saccharomyces wine strains (H. guilliermondii and H. uvarum) during mixed fermentations with S. cerevisiae was studied under enological growth conditions. Several microvinifications were performed in synthetic grape juice, either with single non- Saccharomyces or with mixed S. cerevisiae/non-Saccharomyces inocula. In all mixed cultures, non-Saccharomyces yeasts grew together with S. cerevisiae during the first 1–3 days (depending on the initial inoculum concentration) and then, suddenly, non-Saccharomyces cells began to die off, regardless of the ethanol concentrations present. Conversely, in both non-Saccharomyces single cultures the number of viable cells remained high (ranging 107–108 CFU ml− 1) even when cultures reached significant ethanol concentrations (up to 60–70 g l− 1). Thus, at least for these yeast strains, it seems that ethanol is not the main death-inducing factor. Furthermore, mixed cultures performed with different S. cerevisiae/ H. guilliermondii inoculum ratios (3 :1; 1:2; 1: 10; 1 : 100) revealed that H. guilliermondii death increases for higher inoculum ratios. In order to investigate if the nature of the yeast–yeast interaction was related or not with a cell–cell contact-mediated mechanism, cell-free supernatants obtained from 3 and 6 day-old mixed cultures were inoculated with H. guilliermondii pure cultures. Under these conditions, cells still died and much higher death rates were found for the 6 days than for the 3 day-old supernatants. This strongly indicates that one or more toxic compounds produced by S. cerevisiae triggers the early death of the H. guilliermondii cells in mixed cultures with S. cerevisiae. Finally, although it has not been yet possible to identify the nature of the toxic compounds involved in this phenomenon we must emphasise that the S. cerevisiae strain used in the present work is killer sensitive with respect to the classical killer toxins, K1, K2 and K28, whereas the H. guilliermondii and H. uvarum strains are killer neutral.
- Characterization of L. monocytogenes in a portuguese cheese production plantPublication . Almeida, G.; Carneiro, L.; Figueiredo, A.; Hogg, T.; Teixeira, P.
- Characterization of L. monocytogenes isolated from traditional portuguese cheesesPublication . Magalhães, R.; Almeida, G.; Leite, D.; Silva, J.; Hogg, T.; Teixeira, P.