Università degli Studi di Milano, 2015-12-15
Phenolics derived from grape are essential components of wine quality, contributing to its taste, aroma, color, bitterness, and mouth feel properties. Anthocyanins are responsible for the color of red wine, various interactions occur among the three flavonoid classes in wine resulting in a complex matrix of pigmented polymers. Proanthocyanidins (PAs) or condensed tannins are composed of flavan-3-ol subunits, and are primarily responsible for the astringency of wine and contribute to its bitterness. They possess a high antioxidant capacity and contribute to protection against cardiovascular diseases and cancer (reviewed by Lin and Weng, 2006) when consumed as part of a Mediterranean diet. Berry growth follows a double sigmoid habit that can be divided into two growth phases (Stage I and III) separated by a lag phase (Stage II) (Coombe 1976). The transition from Stage II to Stage III is named veraison and is considered to be the onset of ripening, as at this time sugars and anthocyanins begin to accumulate in red grapes. Tannins are synthesized before veraison, while anthocyanins are synthesized after veraison. The genotype is primary factor to the content of phenolic compounds. Concentration changes due to seasonal weather conditions are far less than those due to genotype. Then the cultivars variations prevail than those due to vintage. There are many environments and field practices factors reputed to affect flavonoid biosynthesis in plants. For example, vine vigor has also been reported to impact upon the tannin content and composition of grape skins in Pinot noir. In the berry skin, proanthocyanidins were higher in low-vigor vines, with an increase in the proportion of epigallocatechin subunits in proanthocyanidin polymers and an increase in the average size of polymers observed with decreasing vine vigor (Cortell et al. 2005). It is uncertain whether this change is due to the difference in vine vigor or is an indirect effect of changes in canopy architecture resulting in differential bunch exposure effects. Some researches suggest that while excessive water application decreased tannin content (Kennedy et al. 2000), water deficit had little or no effect on tannin or anthocyanin accumulation in the grape berry. Rather, the primary effect of water deficit was to decrease berry size and thus change the ratio of skin weight to total berry weight and therefore anthocyanin and tannin concentration in the berry. In a three-year study published by Cohen (2012) was showed that total PA content per berry varied only in one year, when PA content was highest in heated berries (1.46 mg berry) and lowest in cooled berries (0.97 mg berry). In two years, cooling berries resulted in a significant increase in the proportion of (–)-epigallocatechin as an extension subunit. In the third year, rates of berry development, PA accumulation, and the expression levels of several genes involved in flavonoid biosynthesis were assessed. Heating and cooling berries altered the initial rates of PA accumulation, which was correlated strongly with the expression of core genes in the flavonoid pathway. However, the study examined proanthocyanidins content and composition throughout berry development in both shaded and exposed fruit, revealing significant differences in both content and composition throughout the intermediate stages of berry development, with shaded fruit reaching a much lower maximum in proanthocyanidin content than exposed fruit. The peak in proanthocyanidin accumulation in winegrapes occurred around time of veraison and then decreased toward harvest in what is generally considered to be a decrease in tannin extractability rather than degradation or turnover. This decrease in tannin extractability was observed in both shaded and exposed fruit; however, the decrease was greater in exposed fruit such that the levels were virtually the same in shaded and exposed fruit at harvest. The effects of shading on tannin accumulation in grape berries have only been examined in Shiraz, although this is an active area of research in the Australian wine industry (Downey et al. 2006). Goal of this research is the study of some Sicilian native cultivars grown in different areas of Sicily to assess the evolution of proanthocyanidins during ripening. Cultivars considered in this study are Nero d’Avola (biotype A, B and C) and Frappato (biotype A and B). Experimental fields are located in Marsala (TP) and Sambuca (AG). In these vineyards, various agronomic aspects were considered: meteorological data, leaf relative water content (Marchesi, 2004) and pruning wood weight. Experimental grapes samples were analyzed in the laboratory of the Viticulture and Enology Research Center of the Sicilian Region Extension Service located in Marsala (Sicily). Sampling were carried out in pre-veraison, mid-ripening and harvesting. Skins extract were subjected to analysis proanthocyanidins index (PI), flavans reactive to vanillin (FRV) and HPLC analysis (by phloroglucinolysis). The wines were analyzed in the Viticulture and Oenology Department of Fresno State University (California), for the study of proanthocyanidins, through the use of various chromatographic techniques: phloroglucinolysis, molecular mass, and hydrophobic interactions Observed results have confirmed that proanthocyanidins were been synthesized before the veraison; while during ripening they have decreased, in the degree of polymerization they have increased. Environment conditions of Sambuca site have led to increased synthesis of proanthocyanidins, a more severe decreased than Marsala site during ripening. At harvest time, the greater degree of polymerization was found in the grapes of Sambuca site. This result was also confirmed by the analysis results made on wines. At the biotype level, observing the information acquired, to Nero d'Avola, the biotype B presents more and more proanthocyanidins polymerization than other biotype in both sites. For what concerns Frappato, in both sites, no significant differences were found between the two biotypes, both at the level of accumulation of proanthocyanidins both at the level of polymerization..
diritti: info:eu-repo/semantics/openAccess
supervisor: O. Failla ; coordinator: R. Di Stefano
Settore AGR/03 - - Arboricoltura Generale e Coltivazioni Arboree

Tesi di dottorato. | Lingua: Inglese. | Paese: | BID: TD16002180