1. University of Agronomic Sciences and Veterinary Medicine of Bucharest
Faculty of Horticulture
International Student Symposium “Hortus Academicus”
March 29, 2019, Bucharest, Romania
THE EFFECT OF THE PRE-FERMENTATIVE SKIN CONTACT CONDITIONS ON THE CIELab PARAMETERS AND TOTAL PHENOL EXTRACTION ON WHITE WINES
Author,
MSc. student eng. Ilie Bogdan
Coordinator Professors:
Professor PhD. Arina Oana ANTOCE
Lecturer PhD George Adrian COJOCARU
International Student Symposium "Hortus Academicus“ March 29, Bucharest, Romania

2. INTRODUCTION
The pre-fermentative skin contact on white grapes is performed in order to extract certain primary aroma compounds, along with certain phenolic compounds important for wine texture, but during this phase and later on during winemaking, it is desired to better preserve these constituents in their native form and to protect them from oxidation
With controlled temperature during skin contact and modern equipment, lower concentrations of sulphur dioxide to be used during this phase is also possible. In many situations during pre-fermentative phase even inert gases with carbonic ice are used to counteract the negative effects of oxygen during grapes processing
International Student Symposium "Hortus Academicus“ March 29, Bucharest, Romania

3. MATERIALS AND METHODS
This study was carried out on a blend of grapes varieties consisting of 80% Fetească albă and 20% Muscat Ottonel, harvested in 10th of September 2018 from a vineyard located in Dealul Mare - DOC Boldesti Scaeni.
Table 1. Technological steps and controlled parameters
applied during the skin contact experiment
Pre-fermentative technological steps and parameters
Experimental variants codification M0 M6
M12
I. Grape mash, kg
5 kg
II. Treatment with SO2 on grape mash, mg/kg 50
III. Skin contact, hours
Direct pressing
6 hours
12 hours
IV. Temperature during skin contact, °C
8-10
V. Reserved grape must after pressing, liters 3
VI. Clarification time by settling at 10°C, hours
VII. Reserved clarified grape must, liters 2
International Student Symposium "Hortus Academicus“ March 29, Bucharest, Romania

4. MATERIALS AND METHODS
The CIELab parameters and Total Polyphenolic Index (TPI) were conducted on an UV-VIS spectrophotometer Analytik Jena AG Specord 250 equipped with Chroma software Ver. 2.0.
The CIELab parameters were measured in glass cuvettes of 10 mm optical thickness.
The Total Polyphenolic Index was measured in a quartz cuvettes of 10 mm optical thickness at a wavelength of 280 nm on a 10% diluted samples. The results were multiplied with 10.
International Student Symposium "Hortus Academicus“ March 29, Bucharest, Romania

5. RESULTS AND DISCUSSIONS
Table 1. Physico-chemical analyses of variants at different stages
Stage
Variants
Sugars, g/l
Total acidity, g/l tartaric acid pH
Grape must after pressing M0
205 ± 0.39
5.30 ± 0.03
3.01 ± 0.03 M6
215 ± 2.36
4.70 ± 0.13
3.32 ± 0.02
M12
208 ± 3.14
4.40 ± 0.29
3.41 ± 0.02
Grape must after settling
205 ± 1.36
5.39 ± 0.09
3.10 ± 0.01
4.67 ± 0.04
3.34 ± 0.03
208 ± 3.21
4.76 ± 0.24
3.38 ± 0.06
Wine after cold treatment
0.84 ± 0.39
5.73 ± 0.12
3.23 ± 0.02
0.57 ± 0.11
5.17 ± 0.40
3.33 ± 0.01
0.76 ± 0.09
5.16 ± 0.35
3.32 ± 0.03
Results showed an increasing pH and a decreasing total acidity with an increase of skin contact time.
However, this phenomenon is well explained by the extraction of potassium cations from skins, while the pH and total acidity of resulted wines is altered by yeast metabolism and by tartaric acid salts precipitation during cold treatment.
International Student Symposium "Hortus Academicus“ March 29, Bucharest, Romania

6. RESULTS AND DISCUSSIONS
L- Clarity show the tendency to decrease with the skin contact, statistically significant decrease being recorded after 12 hours skin contact.
CIELab parameter L (clarity)
International Student Symposium "Hortus Academicus“ March 29, Bucharest, Romania

7. RESULTS AND DISCUSSIONS
The a/b parameters of CIELab of the wines resulted from direct pressing showed that the colour is the least intense yellow and almost imperceptible by naked eye on the green side, while the 6 hours macerated wine showed a slightly increase in yellow, but noticeable moved on the green side.
On the other hand, 12 hours macerated wine also showed an increased yellow colour, but this time, moved on the red side, which suggest an increased oxidation compared with the other variants.
CIELab parameters a (green/red) and b (yellow/blue)
International Student Symposium "Hortus Academicus“ March 29, Bucharest, Romania

8. RESULTS AND DISCUSSIONS
Results showed a statistically significant decrease in TPI in skin-macerated wines. This effect could be a result of certain polyphenols condensation with extracted proteins.
Total Polyphenol Index
International Student Symposium "Hortus Academicus“ March 29, Bucharest, Romania

9. CONCLUSIONS AND RECOMMENDATIONS
The influence of skin contact time on physico-chemical analyses
Emphasizes that the longer the time of contact, the more it is noticed an increase in pH and a decrease in total acidity in the resulted musts.
On the other hand, the pH and total acidity of wines are unpredictable because of yeast metabolism and tartaric salts precipitation during cold treatment.
International Student Symposium "Hortus Academicus“ March 29, Bucharest, Romania

10. CONCLUSIONS AND RECOMMENDATIONS
The influence of skin contact time on Total Polyphenol Index
Showed a statistically significant decrease of polyphenol concentration in longer skin-macerated wines, probably because of:
oxidation during skin contact;
or condensation of certain polyphenols with extracted proteins and subsequent precipitation.
International Student Symposium "Hortus Academicus“ March 29, Bucharest, Romania

11. CONCLUSIONS AND RECOMMENDATIONS
The influence of skin contact time on CIELab parameters
Clarity (L) showed:
increased values in wines with no skin contact or macerated up to 6 hours;
increasing the maceration time up to 12 hours decreases statistically significant this parameter.
Parameters a and b showed:
no skin contact (M0) result in pale-yellow colour;
maceration of 6 hours (M6) results a slightly more intense yellow-green colour, desired by most winemakers;
maceration of 12 hours (M12) results a larger yellow component with a sensitive and pale reddish component, possibly due to an increased oxidation compared to the rest of the variants.
International Student Symposium "Hortus Academicus“ March 29, Bucharest, Romania