Composició fenòlica en varietats negres de Vitis vinifera. Estudi de la influència de diferents factors
Anthocyanic composition is a phenotypic characteristic that differs for each variety, which can be used to identify varieties. In this thesis 8 Vitis vinifera varieties (Cabernet sauvignon, Carinyena, Garnatxa, Merlot, Monastrell, Pinot noir, Syrah i Ull de llebre) have been characterized by their anthocyanic composition. But some other factors can modify this composition.
In vitro, those conditions that constitute a limitation for cellular growth, like depletion of nutrients (nitrogen stress) or water stress, lead generally to an increase in the anthocyans synthesis. In these conditions, even the composition of individual anthocyanins can be changed, with the promotion of the anthocyanin acylation.
In vivo, similar effects take place depending on the year, the climate, and the irrigation of vines. Those conditions limiting the plant vigor lead to higher accumulations of anthocyans, and also to a higher percentage of acylation. In this sense, it is a similar effect to that one described in vitro, although the variations are much lower and often there is no statistical difference.
Varieties have also been characterized by using the proanthocyanidin composition of seeds. Tannic composition is more complex than the anthocyanic one, because while there are only 5 anthocyanidin-monoglucosides and their correspondent acylated derivatives, there is a great number of proanthocyanidins (dimers, trimers, tetramers, polymers). In this thesis, we have also studied the evolution during maturation of the dimers, and it has been proved that the mean degree of polymerization increases towards the end of maturation.
Anthocyans (because of their chromatic properties) and proanthoyanidins (because of their tannicity) determine the quality of a red wine. For this reason, it is very important that satisfactory yields in these molecules are obtained during the maceration. In this thesis it has been observed that the extraction of anthocyans differs depending on the variety and on the anthocyan chemical structure. The efficient extraction of malvidine-3-glucoside, which is besides the main anthocyan in grape skin, implies that it is also normally the main anthocyanin in Vitis vinifera wines. On the contrary, musts obtained by traditional maceration have a lack of p-coumarylated anthocyans.
Red wine color also depends on the copigmentation phenomena and on the stabilization of color by formation of new structures. These aspects have been undertaken in this thesis by using model solutions. Some of these processes are promoted by acetaldehyde. In tests with young wines, acetaldehyde has given an evolution of color to similar tonalities to those of old wines. Acetaldehyde can also promote the formation of condensation pigments between anthocyanins and catechins, in a reaction that is faster at acidic pH. That leads to an evolution in wine phenolic composition and, consequently, to a color evolution.
Furthermore, it has been observed that some molecules (specially phenolic acids and lactic acid) promote hypercromic effects and have therefore an influence on red wine color.
In this thesis several studies have been performed with Vitis cellular suspensions, because they are a useful tool to investigate the factors that have an influence on phenolic composition. Cell cultures are isolated and controlled systems, and their manipulation is easy. But sometimes the results can differ from those of the plant, because of their different complexity. For example, in our experiments it has been observed that the expression levels of the phenylalanine ammonia lyase gene, which codifies for the key enzyme in the phenolic biosynthesis pathway, are relatively low in cell cultures.
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Advisor:Nadal Roquet-Jalmar, Montse
School:Universitat Rovira i Virgili
Source Type:Master's Thesis
Keywords:departament de bioquímica i biotecnologia
Date of Publication:05/27/2004