WINETECH Technical Yearbook 2019

As expected, glutathione levels decreased with time and temperature. After nine months, the wines stored at 15°C retained the highest level of GSH (Figure 4 and 5).

affect the volatile composition of all the wines similarly, possibly due to the different initial compositions. ANTIOXIDANTS AND RELATED MEASUREMENTS The wines were bottled between a month and a few days before the start of the experiment. Therefore, at the time of initial storage, the wines had very different levels of dissolved O 2 , ranging from 0.04 to 1.23 mg/L. As expected, glutathione levels decreased with time and temperature. After nine months, the wines stored at 15°C retained the highest level of GSH (Figure 4 and 5). There was an increase in absorbance at 420 nm with temperature and time, indicating browning of the wines with storage temperature and duration. Also considering the transformation of the UV- Vis measurements into CIE Lab parameters, wines stored at higher temperature for longer corresponded to higher b* (increase in yellow colour), while wines stored at lower temperature and with shorter storage time corresponded to higher a* and L* (higher green and clarity). In most cases, the differences in colour components given by the CIELab parameters were below perception threshold by the human eye. In other words, the changes were too subtle to be perceived using sensory evaluation of the colour. There were some exceptions, all of

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FIGURE 4. CB GSH concentration (mg/L) during storage for one of the wineries participating in the study. Samples are colour-coded according to storage time. FIGURE 4. CB GSH concentration (mg/L) during storage for one of the wineries participating in the study. Samples are colour-coded according to storage time.

FIGURE 5. SB GSH concentration (mg/L) during storage for one of the wineries participating in the study. Samples are colour-coded according to storage time. FIGURE 5. SB GSH concentration (mg/L) during storage for ne of the wineries participating in the study. Samples are colour-coded according to storage time. There was an increase in absorbance at 420 nm with temperature and time, indicating browning of the wines with storage temperature and duration. Also considering the transformation of the UV-Vis measurements into CIE Lab parameters, wines stored at higher temperature for longer corresponded to higher b* (increase in yellow colour), while wines stored at lower temperature and with shorter storage time corresponded to higher a* and L* (higher green and clarity). In most cases, the differences in colour components given by the CIELab parameters were below perception threshold by the human eye. In other words, the changes were too subtle to be perceived using sensory evaluation of the colour. There were some exceptions, all of them for SB wines, which saw a substantial increase in the green colour ( a* ) with temperature vs time. Take home message For the first time, a parallel study was done for Sauvignon blanc and Chenin blanc, with a focus on whether these two cultivars go through similar changes during storage. The changes reported in this study were over a nine month period of storage in conditions that varied from controlled to normal room temperature fluctuations that can be expected when a wine is on a shelf or at home. The results of the chemical evaluation of aroma and antioxidant-related parameters showed that the duration of storage has a great influence on a wine’s profile. The storage of wine at higher temperatures creates less change in the wine when stored for shorter periods. The evolution of the chemical composition of the wines was clear for most of the parameters considered (thiols and antioxidants), with time being the most was observed from T0 to T3 and T9 samples. Among the volatile compounds measured, the varietal thiol concentrations were associated with storage time/temperature combination for both SB and CB. The controls had high r 3MHA concentrations compared to the xtr m treatment (T9/25). Wines stor d at high temp ratures for longer (T9/25 as the extrem ) had higher 3MH and 4MMP, which in previous studies on New Zealand Sauvignon blanc was found not to have changed throughout storage (Makhotkina et al ., 2012). Major volatile composition was different between wineries and cultivars, in both levels and profile. The changes in the major volatile composition were not as marked as for thiols. This type of results is similar to findings on Spanish white wines (Pérez- Coello et al ., 2003), where the researchers found differences only after more than one year of storage; this may explain the results found in urrent study, since the storage was only over ine months. Taking into account all the aroma compounds analysed, the pattern of evolution was different between the wines tested. This can be due simply to the limited number of compounds easur d ( 34 aroma compounds) or to the differences in the T0 wine profiles. In other words, the storage conditions (time and temperature) did not

Sauvignon blanc (SB) wines had more 4MMP than Chenin blanc (CB), a result we have noticed before (Figure 2-4) (Coetzee et al ., 2018). SB samples stored at higher temperature for longer had more 3MH, whilst those at lower temperature for shorter had more 3MHA. This corresponds to the findings from New Zealand and to the hypothesis that 3MHA hydrolyses and produces 3MH. This did not, however, correspond to an increase in the 3MH- associated attributes in the sensory results, most probably because of other oxidation reactions that masked the increase in 3MH. T0 samples were consistently different from the other treatments and a gradual trend