Issue link: http://winesandvines.uberflip.com/i/754815
60 WINES&VINES December 2016 WINEMAKING PRACTICAL WINERY & VINEYARD minimized. 22,46 Our results suggest that, with time, this trend is enhanced to such an extent as to cancel the differences. A decrease of native monomeric anthocya- nins with MOx was detected in agreement with reported results 18,22,47 and can be related to the involvement of these molecules in the oxygen- activated reactions between anthocyanins and flavanols. These reactions determine the for- mation of anthocyanin-ethyl flavanol com- pounds, which are unstable and may undergo cleavage of the ethyl bridge with consequent liberation of monomeric anthocyanins. 14 This latter phenomenon could explain the increase of several monomeric anthocyanins observed in previous studies. 17 In agreement with litera- ture, the content of total monomeric anthocya- nins in bottle decreased over time. 49,50 Three months after the treatments, the content of total phenolics increased with MOx treatment for both wines. Since different phe- nolic classes possess slightly different chemical properties, the data observed may be due to the formation of phenolics with a higher reac- tivity toward the Folin-Ciocalteu reagent used for the analysis. 51 In contrast, the aged MOx wines showed a lower content of total pheno- lics conpared to control wines, indicating that phenolic compounds changed or rearranged over time, giving less reactive compounds. In Wine A, no statistically significant differ- ence in PAs was detected at both dates of sampling. According to U. Vrhovsek et al., 52 the Bate-Smith reaction used to determine the tannins provides an estimation of high proan- thocyanidins corresponding to more than five units, therefore no variation in this kind of molecule was observed. In spite of the same initial content of PAs of the two wines, Wine B showed a decrease of PAs when the higher level of micro-oxygenation was applied. This might be due to the fact that PAs can have different reactivity toward oxygen and oxygen-derived compounds, depending on the monomers constituting the polymers as well as the polymerization degree. 53 Variations in the degree of polymerization of tannic molecules are also suggested by the finding that changes in VRFs (corresponding to phenolic polymers of two to four units) are detected with MOx and time for both wines. For Wine A, a decrease was always observed when MO2 level was applied; for Wine B, a decrease of VRF always occurred when the MO1 level was applied. Because vanillin reacts only with terminal units of tannic molecules, its decrease may be caused either by precipitation of tannins or by an increase of their polymerization degree. Concerning the degree of polymerization, dif- ferent behaviors were reported. For some re- searchers it was thought that MOx induced the polymerization of PAs, 19 but recently no varia- tion of degree of polymerization of proantho- cyanidins was detected. 22 It is not very clear if the changes of the polymerization degree of proanthocyani- dins 1,9 —or the combination of proanthocyani- dins and anthocyanidins—are responsible for the decrease of astringency of wine. Therefore, only on the basis of these analyses, the effect of micro-oxygenation and bottle aging on wine astringency is not predictable. In this study concerning sensory analysis, the variation occurring in phenolic composition three months after MOx is not enough to cause a significant variation of the astringency (see "Evolution of Astringency of Wine A" and "Evo- lution of Astringency of Wine B" on this page). For both wines, a decrease of astringency was detected after 42 months of aging in bottle. No effect of MOx was observed in Wine A while, for Wine B, a significant decrease of astringency was detected with increasing MOx levels. This result is confirmed by data on SPI (see "Impact of Micro-Oxygenation on SPI" on page 57), which gives a direct measure of the reactivity of whole wine phenolics with salivary proteins. In the literature, both a significant de- crease 17 and no effect 21 on the astringency with micro-oxygenation of wines have been re- ported. This is the first time that a significant effect was observed with time, and it occurs only in the lower pH wine. Therefore, in agree- ment with recent findings 22 showing that pH exerts a major effect on the evolution of phe- nolic compounds during aging, our data seem to show that this effect can result in a variation of wine reactivity toward salivary proteins and, then, in wine astringency. However, this result can be also due to: a) differences in phenolic composition between the two wines; b) the direct effect of wine pH on astringency perception 34 and, c) the lower content of molecular SO 2 protecting wine components from oxidation. Effect of OTR on changes in phenolic composition, color, SPI and astringency To evaluate the effect of nano-oxygenation, two red wines with a different level of TPO at bottling (9.8 mg/L = W1, and 6.5 mg/L = W2) were sealed with different closures and analyzed after 10 months of storage in bottle. Three increasing OTR conditions (W low , W medium and W high ), ensured by using synthetic closures with controlled oxy- gen permeability, were compared. Color intensity of W1 low did not differ be- tween W1 high and W1 medium , while W1 medium showed slightly higher color intensity than W1 high . This result contrasts with data reported by S. Caillé et al., 21 which showed a positive correlation between color intensity of red Gr- enache wine and OTR. The different trend may depend on the differences in TPO of closures used in the two studies. However, wine type can also affect the evolution of color intensity during bottle aging. For W1, a significant loss of total mono- meric anthocyanins of W1 medium and W1 high with respect to W1 low was observed. The last two samples were similar to each other. The highest percentage of loss of monomeric an- thocyanins (comprised between 38% and 44% of total monomeric anthocyanins) with re- spect to that observed in literature 26,27 can be related to the highest oxygen exposure of W1. Further studies aimed to determine the rela- The mean sensory rating of astringency for experi- mental Wine B is evaluated over time. Different letters indicate statistical differences (p<0.05). Capital letters (A, B) are used to compare wines of the same micro-oxygenation level over time. Small letters (a, b) are used to compare control and micro-oxygenation samples at the same time. EVOLUTION OF ASTRINGENCY FOR WINE B Mean Sensory Rating 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 n 42 months n Three months Micro 0 Micro 1 Micro 2 cB bB aB aA aA aA The mean sensory rating of astringency for experi- mental Wine A is evaluated over time. Different let- ters indicate statistical differences (p<0.05). Capital letters (A, B) are used to compare the wines of the same micro-oxygenation level throughout the time. Small letters (a, b) are used to compare control and micro-oxygenation samples at the same time. EVOLUTION OF ASTRINGENCY FOR WINE A Mean Sensory Rating 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 Micro 0 Micro 1 Micro 2 n 42 months n Three months aA aB aB aB aA aA