Effect of the addition of peptidic hydrolysates from grape pomace by-products to red wines in warm regions

Abstract

High temperatures typical of warm climates cause the colour of red wines to become increasingly unstable over time. This is due to the fact that phenolic and technological maturities do not coincide at the time of harvest in these climates, in contrast to colder viniculture zones. As a consequence, the colour of wines decreases after months of storage within bottles or barrels due to copigmentation processes being hampered by a shortage of pigments and copigments.
This study has focused on improving the colour stability of red wines elaborated in warm climates by adding an enzymatic hydrolysate of defatted grape seed meal six months after fermentation of Syrah grapes cultivated in “Condado de Huelva” Designation of Origin (Spain). This defatted meal comes from the industrial processing of grape pomace, contributing to the reuse of this residue as a by-product. Two different types of defatted grape seed meal were used (from red and white grapes), which protein fraction was extracted and further submitted to enzymatic hydrolysis with Alcalase under alkaline conditions. Hydrolysis was carried out at two different times, 1 and 4 h, to obtain peptides of high and low molecular weight, which were added to the wine at two different concentrations: 1 g/L and 3 g/L, in triplicate. Differential tristimulus colorimetry (L*, C*ab, hab, ΔE*ab), copigmentation, molecular weight distribution, and polyphenolic content (HPLC-DAD) were studied in wines every month along six months of time evolution.
The addition of 3 g/L peptides from 1-hour hydrolysis showed a colour stabilization effect on red wines regardless of the grape variety, in the light of the higher values of chroma (C*ab) and copigmentation, even though the total anthocyanin content decreased, which tends to occur naturally during the evolution of any wine. However, the addition of peptides from 4-hour hydrolysis of the red variety, regardless of their concentration, provoked a lightening effect of red wines, evidenced by higher values of L* and lower of C*ab. In contrast, these wines had visually perceptible colour differences (ΔE*ab > 3), mainly qualitative due to the higher values of hue (hab), but sensorially acceptable. In conclusion, the implementation of wines with peptidic hydrolysates from grape seed meal residue could be a promising technique for oenological industry.

 Acknowledgments:

We thank FEDER/Ministerio de Ciencia e Innovación – Agencia Estatal de Investigación (Project AGL2017-84793-C2) for financial support.