Estabilização tartárica de vinhos com resinas de troca catiónica: avaliação da eficiência das resinas e alteração das características físico-químicas e composição volátil dos vinhos

Mestrado em Química - Química Analítica e QualidadeO uso de resinas de troca iónica para a estabilização tartárica foi permitido em 2009, através do Regulamento (CE) Nº 606/2009, que permite a estabilização tartárica com resinas poliméricas de estireno e divinilbenzeno funcionalizadas com grupos sulfónicos (fortemente ácidos), regeneradas em solução ácida. A sua aplicação baseia-se no facto de as resinas trocarem iões hidrogénio por catiões presentes no vinho, essencialmente potássio, fazendo diminuir a sua concentração e impedindo assim a precipitação dos respectivos sais tartáricos. Neste trabalho, foram estudados os efeitos da estabilização com uma resina de troca catiónica, na composição e propriedades de diversos tipos de vinho. Os resultados evidenciaram variações significativas das suas características, nomeadamente aumento da acidez, diminuição do pH, diminuição no teor de catiões metálicos e alteração da cor, sendo essas variações proporcionais ao volume de vinho permutado. Relativamente à matriz volátil, de um modo geral e salvo um número reduzido de exceções, não se observaram variações significativas do teor dos ésteres e terpenos analisados por GCxGC-TOF-MS, num total de 59 compostos.The use of ion exchange resins for tartaric stabilization was accepted in 2009 by Regulation (CE) Number 606/2009, which allows the tartaric stabilization with styrene and divinylbenzene polymeric resins functionalized with sulfonic groups (strongly acidic), regenerated in acid solution. Their application is based on the fact that resins are able to exchange hydrogen cations by metal cations present in wine, essentially potassium, decreasing its concentration and hence the precipitation of tartaric salts. In this work, the effects of stabilization with a cation exchange resin, on the composition of different types of wine were studied. The results showed significant variations of the wine characteristics, including increased acidity, decreased pH, decreased content of metal cations and changes in colour. These variations were proportional to the volume of wine exchanged. For the volatile matrix, with only a few exceptions, no significant changes were in the contents of the esters and terpenes analyzed by GCxGC-TOF-MS, in a total of 59 compounds

Bottom-up and top-down controls on sedimentary ecosystem functioning in a seagrass habitat

Coastal seagrass ecosystems are complex habitats that are increasingly influenced by human perturbations. Disturbances that affect the strength of bottom-up (i.e. resource availability) and top-down (i.e. consumer) controls may also influence biomass distribution between trophic levels, sediment biogeochemistry, and seagrass ecosystem metabolism. Here, I experimentally tested how top-down and bottom-up perturbations interact with community structure (diversity, food chain length of epibenthic consumers) to alter sediment biogeochemistry and ecosystem metabolism in an experimental eelgrass (Zostera marina ) system. My data indicated that resource availability influenced SOM composition and ecosystem metabolism. Light availability tended to be a stronger determinant of SOM composition while nutrient enrichment affected secondary production of invertebrate grazers more strongly than primary producers or SOM. Top-down predator effects on SOM composition and ecosystem flux rates tended to be weak. However, the strength of the trophic cascade may partly be a function of grazer community composition and grazer susceptibility to predation. Finally, my results indicated that grazer species identity and community composition strongly influenced SOM composition. In addition to the main effects of light, nutrients, predators, and grazers there were a variety of interactive effects between resources and food web composition. Consequently, the effects of resource availability and food web composition on seagrass ecosystem functioning should not be considered in isolation