# Pairing Red Wine and Closure: New Achievements from Short-to-Medium Storage Time Assays
## 3 Results and Discussion
### Volatile Profile of Wines Sealed with Different Types of Closures
#### 3.4.1 Douro Red Wine  
The data set of 196 analytes includes compounds from a wide range of chemical families, namely, esters (51), acids (10), alcohols (28), aldehydes (8), aromatic hydrocarbons (10), dioxanes (2), ethers (5), furan derivatives (22), ketones (10), lactones (3), naphthalenes (5), norisoprenoids (3), phenol derivatives (7), sulfur compounds (6), terpenic compounds (17), and others (9). From this data set, 104 (ca. 53%) of the analytes exhibit significant differences among the wines bottled with the two types of closures. For rapid and visual access to the volatile pattern of the wines sealed with different closures, clustering analysis was performed, and the heatmap and dendrogram show two main clusters corresponding to the wines sealed with Natural Cork 1 and Micro A (Figure 4a). The content of each compound is illustrated through a chromatic scale (from dark blue to dark red, the minimum and the maximum, respectively), and unveiled that wine sealed with Natural Cork 1 exhibited, in general, higher amounts of volatile compounds. However, it is important to point out that, for analytes that present statistically significant differences among wines, on average, the variation magnitude is less than 0.25-fold. Similar clustering was observed (with similar Euclidean distance--70) by using all domains of information (sensory analysis, physicochemical parameters, phenolic compounds, and volatile organic compounds), which also revealed two main clusters corresponding to the wines sealed with Natural Cork 1 and Micro A (Figure 4b). This graphical representation reinforces the information that wines sealed with Natural Cork 1, in general, contain a slightly lower amount of phenolic compounds and a slightly higher quantity of volatile compounds. A closer look at the volatile composition (Supplementary Material Table S3) highlighted differences between the volatile profiles of wines sealed with different seals, which will be discussed below. Figure 3: Example of the analyte documentation procedure used to putatively identify the volatile compounds: \(\beta\)-damascenone, presented in wines sealed with different closures, detailing its retention times (on the first and second dimensions), linear retention index, and spectral identification through GC \(\times\) GC analysis (literature retention index (R\({}_{\text{lit}}\)) obtained from [53]). The esters that significantly contributed to the fruity and floral-like aromas of wines [15] exhibited higher content in the wine sealed with Natural Cork 1, as evidenced by the 31 compounds showing statistically significant differences (\(p<0.05\)). Among the ethyl esters (Figure 5a), ethyl 2-phenylacetate also showed slightly higher concentrations in the wine sealed with Natural Cork 1 (4.486 \(\pm\) 0.426 \(\mu\)g/L) compared to the wine sealed with Micro A (4.039 \(\pm\) 0.346 \(\mu\)g/L). The preservation of ethyl esters during bottle storage has been a challenge for winemakers, as ethyl esters tend to hydrolyze over time, mostly due to the low pH of wines [14]. As natural cork stoppers were able to better conserve the ethyl ester composition of red wines, it can improve their sensory attributes expected by consumers, as previously reported [13]. Building on the formation of Strecker aldehydes through the oxidation of amino acids, their presence in the volatile profile reflects the ongoing interaction between oxidative and reductive processes in wine. While these compounds are generally considered markers of oxidative conditions, with concentrations typically increasing under oxidative conditions [1], their accumulation patterns are influenced by various factors beyond oxidation alone. For a set of three compounds assigned as Strecker aldehydes (Figure 5b), only methional exhibited slight significant differences between the wines sealed with two closure types, and it was present in higher concentrations in wine sealed with Micro A (0.023 \(\pm\) 0.011 \(\mu\)g/L) compared with wine sealed with Natural Cork 1 (0.012 \(\pm\) 0.002 \(\mu\)g/L).