Changes in the principal phenolic compounds during the vinification process and storage under modified atmosphere of Greek wines have been investigated. HPLC-DAD-ESI-MS/MS was used for the identification and quantification of more than 30 principal phenolic compounds, namely anthocyanins (malvidin, etc.), flavonols (quercetin, myricetin, etc.,), flavan-3-ols (catechin) and hydroxycinnamates (caftaric and coutaric acid). The existence of some of these molecules (laricitrin, syringetin and isoramnetin), was confirmed for the first time in Greek wines.
During maceration, the most polar molecules, like anthocyanins, were extracted imminently, while the flavan-3-ols followed at a lower rate after a lag phase. In all varieties, the total phenol content reached a maximum within 2-8 days. The effect of vinification processes, like cold maceration and addition of pectolytic enzymes, has been studied. Both processes enhanced the extraction of grape polyphenols during the vinification. Moreover, during cold maceration, due to the low ethanol content and the obstruction of the fermentation, the more polar and water soluble constituents presented increased extraction rates, whereas the extraction of flavan-3-ols was suspended. On the other hand, the use of pectolytic enzymes did not appear to affect the extraction rates of phenolic compounds. Comparing the variation of metals at maceration process, with the variation of monomeric anthocyanins and flavonols, an inverse relationship was noticed that can be attributed to complexing reactions of polyphenols with particular trace elements.
During one year storage, the concentration of total phenols remained practically constant and even samples stored under a thin atmospheric air layer, retained up to 80% of their initial phenolic content. On the contrary, free anthocyanins, participated in polymerization reactions with flavan-3-ols and their concentration declined almost tenfold during a few months, following 1st order kinetics. Also, enzymatic hydrolysis of other phenolic compounds like flavonol glycosides and tartaric esters that lead to the respective aglycones and hydroxycinnamic acids was observed.
The modified atmosphere had little effect on the observed changes of phenolic constituents, except for the decrease of monomeric anthocyanins. The rate constants of the reactions presented a significant difference (p<0.05) between the MAP stored samples and the blind samples that were packaged with atmospheric air.
Considering the evolution of color during storage, the indexes of color intensity (CI) and brilliance (dA%) declined, while the hue index (T) followed an increasing trend during storage of red wines. The statistical evaluation of the results did not detect significant differences on color parameters due to storage under different modified atmosphere.
Copigmentation of anthocyanins accounts for over 30% of the fresh red wine color, while during storage, the color of polymeric pigments formed between anthocyanins and proanthocyanidins predominates. Rosmarinic acid and natural extracts rich in hydroxycinnamic acids, obtained from aromatic plants (Origanum vulgare and Satureja thymbra), were examined as cofactors to fresh Merlot wine and the effect on anthocyanin copigmentation and wine color was studied during storage for 6 months. An increase of the copigmented anthocyanins that enhanced color intensity by 15–50% was observed, confirming the ability of complex hydroxycinnamates to form copigments. The samples with added cofactors retained higher percentages of copigmented anthocyanins and higher color intensity, compared to the control wine, up to 3 months. However, the change in the equilibrium between monomeric and copigmented anthocyanins that was induced by added cofactors, did not affect the rate of polymerization reactions during storage.