WINETECH Technical Yearbook 2019

the wineries participating in the study. Storage time is colour-coded on the outline (green – control, blue – T3 and red – T9).

1200

250

14

12

1000

200

10

800

150

8

600

6

100

400

4

50

200

2

0

0

0

Control

T3/RT

T3/15

T3/25

T9/RT

T9/15

T9/25

Control

T3/RT

T3/15

T3/25

T9/RT

T9/15

T9/25 FIGURE 3. Concentrations of 4MMP (ng/L) for SB (orange) and CB (green) for one of the wineries participating in the study. Storage time is colour-coded on the outline (green – control, blue – T3 and red – T9). 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. Control T3/RT T3/15 T3/25 T9/RT T9/15 T9/25 FIGURE 3. Concentrations of 4MMP (ng/L) for SB (orange) and CB (green) for one of the wineries participating in the study. Storage time is colour-coded on the outline (green – control, blue – T3 and red – T9).

FIGURE 1. Concentrations of 3MH (ng/L) for SB (orange) and CB (green) for one of the wineries participating in the study. Storage time is colour-coded on the outline (green – control, blue – T3 and red – T9). FIGURE 1. Concentrations of 3MH (ng/L) for SB (orange) and CB (green) for one of the wineries participating in the study. Storage time is colour-coded on the outline (green – control, blue – T3 and red – T9).

FIGURE 2. Concentrations of 3MHA (ng/L) for SB (orange) and CB (green) for one of the wineries participating in the study. Storage time is colour-coded on the outline (green – control, blue – T3 and red – T9). FIGURE 2. Concentrations of 3MHA (ng/L) for SB (orange) and CB (green) for one of the wineries participating in the study. Storage time is colour-coded on the outline (green – control, blue – T3 and red – T9).

250

0 both sensory and chemical approaches. The results of studies focused on this type of evaluation can help the industry by looking at the positive and negative aspects resulting from storage, thus indicating what to be avoided and what to be optimised. On the academic side, efforts are aimed at better analysis methods, more efficient and robust sensory techniques, and generally more knowledge related to wine and the transformations it goes through as time passes. 50 100 150 200 Control T3/RT T3/15 T3/25 T9/RT

T9/25 at the moment that elucidates the fate of various compounds of interest present in Chenin blanc wines for example. Thiols in particular are sensitive to oxidation and it can be hypothesised that the matrix effects will play a role in the degradation (or stability) of these compounds. The phenolic composition of a wine can play a role in the protection against oxidation, to give only one example. The evaluation was done in parallel for Chenin blanc and Sauvignon blanc, since there is some chemical data available for the stability of thiols in Sauvignon blanc (from New Zealand), but the findings were not correlated with sensory assessment.

Vis was used for the evaluation of ph nolics (total phenolics at 280 nm, phenolic acids at 320 nm and browning at 420 nm). Additionally, the colour of the wines and the changes in colour were evaluated using CIE Lab, a system that decomposes the UV-Vis measurements into colour-related characteristics similar to the perception of the human eye. CIE Lab Colour Space system expresses colour as three numerical values, L* for the lightness, 0 = black, 100 = diffuse white, a* and b* for the green-red and blue- yellow colour components. THIOLS AND MAJOR VOLATILES Even though generally 3MH and 3MHA levels were comparable between cultivars,

10 12 14 16 18 20 EXPERIMENTAL LAYOUT We have se l ected Chen i n b l anc and Sauvignon blanc wines from six wineries. The wines were stored for three and nine months in various conditions – 15°C and 25°C (temperature controlled environment), and room conditions (temperature not controlled). A control set was also included (time 0/T0 and no storage). Once the wines reached the designated storage time, they were moved to -4°C until further evaluation. The chemical analyses were focused on thiols (3MH, 3MHA and 4MMP) (Mafata et al ., 2018), major volatiles (esters, higher alcohols and acids), and general antioxidants (glutathione and phenolic compounds). UV-

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).

T9/15

FIGURE 2. Concentrations of 3MHA (ng/L) for SB (orange) and CB (green) for one of the wineries participating in the study. Storage time is colour-coded on the outline (green – control, blue – T3 and red – T9). One of the aspects relevant to wine aroma is its stability during storage. Even though some extrapolations can possibly be made from other white cultivars, there is no data

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