No abstract

The oxidative degradation of white wines rapidly leads to a loss of their sensorial qualities. The identification of the most important descriptors related with oxidation-spoiled wine was performed by a trained sensory panel. The terms selected were "honey-like", "farm-feed", "hay", and "woody-like". By gas chromatography-olfactometry analysis three aromatic zones related to these descriptors in the oxidation-spoiled white wines could be determined. Comparison of the aroma extract dilution analysis aromagrams of oxidation-spoiled white wines and a nonspoiled wine showed the highest values of dilution factors were attributed to 3-(methylthio)propionaldehyde, phenylacetaldehyde, 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN), and 4,5-dimethyl-3-hydroxy-2(5H)-furanone (sotolon). A "forced aging" experiment was implemented to simulate the typical oxidation-spoiled aroma. Samples rated with the highest score in the ranking test were also those that presented the highest concentration of these four molecules. To test the sensory impact of these substances, a normal wine (unspoiled) was spiked with these molecules (with the exception of TDN) singly and in combination, and the similarity value (SV) between samples and the oxidation-spoiled white wines was then determined. The highest value from the similarity tests was 5.4 when the three compounds were added simultaneously; 3-(methylthio)propionaldehyde alone was found to be responsible for 3.6, suggesting that, among the molecules studied, it is the most important contributor to the typical aroma of an oxidation-spoiled white wine.

Application of aroma extract dilution analysis (AEDA) on organic extracts from Port wines barrel-aged over 40 years revealed 5 odor-active compounds corresponding to descriptors used to qualify the characteristic old wine aroma. One of the compounds, described as "nutty" and "spicy-like", and present in at least 9 dilutions above the others, was perceived as particularly important. The compound responsible for this flavor was identified as 3-hydroxy-4,5-dimethyl-2(5H)-furanone (sotolon). The levels ranged from 5 to 958 microg/L for wines between 1 and 60 years old. It was also observed that during oxidative aging the concentration of this compound increased with time according to a linear trend (r > 0.95). Although the presence of 2-ketobutyric acid was verified, the constant rate of formation of sotolon with aging and its high correlation with sugar derivates (HMF, furfural) suggests other mechanisms, different from those reported for other wines. The flavor threshold of sotolon was evaluated in Port wine at 19 microg/L. Sensorial tests provided valuable information concerning sotolon impact on Port wine aroma. Samples supplemented with this substance were consistently ranked as older. In view of these results it can be expected that sotolon plays a pre-eminent role in the characteristic old Port wine aroma.

The negative effects of oxygen on white wine quality and the various factors which influence it (including temperature, dissolved oxygen, pH, and free SO(2)) are well documented both at the sensory and compositional levels. What is less defined is the quantitative relationship between these parameters and the kinetics of the development of the negative effects of oxidation. The experiment presented here attempts to generate data which can be used to predictively model the oxidative degradation of white wines. Bottled wines were submitted to extreme conditions (45 degrees C temperature, O(2) saturation) during 3 months witth samples taken every 15 days for both sensorial and chemical analysis (GC-O/FPD/MS, 420 nm). The synergistic effects of increasing temperature and O(2) at lower pH are evident, both on the decrease in levels of terpene alcohols and norisoprenoids (which impart floral aromas), and on the development of off-flavors such as "honey-like", "boiled-potato", and "farm-feed" associated with the presence of phenylacetaldehyde, methional, and 1,1,6-trimethyl-1,2-dihydronaphthalene.