Pre-fermentative addition of an enzymatic grape seed hydrolysate in warm climate winemaking. Effect on the differential colorimetry, copigmentation and polyphenolic profiles
Introduction
In warm climates, high temperatures increase the difficulty of obtaining high quality red wines because of colour instability over time. Unlike in colder viniculture zones, the phenolic and technologic maturities do not coincide at the time of harvesting in warm climates (López, Sánchez, Díaz, Ramírez, & Morales, 2007). Thus, the seeds do not unripen and copigmentation phenomena (which contribute to colour stabilization) are hampered by the shortage of pigments and copigments (Boulton, 2001). Therefore, the colour decreases after months in storage within either bottles or barrels.
Numerous studies about infusing wines with tannins from natural sources have been developed to counteract wine’s natural shortfall and avoid colour losses (Vivas & Glories, 2003). In this way, grape seeds and pomace, notwithstanding being a by-product, are rich in tannins and other polyphenolic compounds (González-Centeno et al., 2010, Jara-Palacios et al., 2014). These compounds could participate in the colour stabilization of red wines. Thus, several studies have reported the addition of seeds or pomace from white grape varieties to red wine for the purpose of colour stabilization (Canals et al., 2008, Cliff et al., 2012, Gao et al., 2013, Revilla et al., 1998). That approach could be viable because red and white grape varieties are harvested at the same time in warm climates, allowing white grape pomace and seeds to be added to red winemaking. Concretely, our research group has focused on improving the colour stability of red wines elaborated in warm climates to counteract the tannin deficit. One example is the pre-fermentative addition of American oak chips to Tempranillo fermentation material (Gordillo, Cejudo-Bastante, Rodríguez-Pulido, González-Miret, & Heredia, 2013); another is the addition of Pedro Ximenez white grape pomace to Syrah red grapes (Gordillo et al., 2014).
Furthermore, another new approach is the addition of commercial, ready-to-use oenological tannin preparations extracted from natural sources. Chamorro, Viveros, Alvarez, Vega, and Brenes (2012) characterized grape skin and seed extracts after the addition of different enzymes, such as carbohydrase, tannase, pectinase, and cellulose (Fernández, Vega, & Aspé, 2015). Enzymes were also added to the winemaking process, demonstrating improvement in the colour extraction and stability of Sangiovese red wines (Canuti et al., 2012) as well as higher flavonol and caftaric acid levels in Monastrell wines (Bautista-Ortín, Martínez-Cutillas, Ros-García, López-Roca, & Gómez-Plaza, 2005). An increase in the procyanidin level was observed when polygalacturonase and cellulase were added to Tannat, Monastrell and Cabernet Sauvignon wines (Favre et al., 2014).
However, the disadvantage of using commercial tannins is that they are often extracted with organic solvents that pose environmental and health risks. Although several authors have studied how to minimize the use of organic solvents (Guerrero et al., 2006, Xia et al., 2010), there are eco-friendly and solvent-free alternative procedures for achieving optimal extraction of compounds. Rodriguez-Rodriguez et al. (2012) developed and patented an enzymatic method for extracting phenolic compounds from grape pomace using an endoprotease mixture (trypsin- and chymotrypsin-like mixture) (Parrado Rubio, Romero Ramírez, & Bautista Palomas, 2006). These authors demonstrated its higher stability, antioxidant properties and bioactivity as well as phenol release compared with those that are traditionally extracted. On the one hand, this technique could resolve the problems with the low extractability of polyphenolic compounds from seeds to wine (because the hydrolysate is completely soluble in water). On the other hand, this technique could avoid the use of organic solvents for extracting polyphenolic compounds. Moreover, to the best of our knowledge, the effect of adding this enzymatic hydrolysate to the process of winemaking has not previously been studied.
As part of the objective of stabilizing the colour of red wines, the main goal of this work was to study the effect of adding a soluble enzymatic hydrolysate of grape seeds during the fermentation of Syrah grapes cultivated in “Condado de Huelva” Designation of Origin (Spain). Grape seeds were chosen as natural material for reinforcing wines with tannins, compounds that are normally present at low quantities because of the immaturity of seeds at the time of harvest for warm climate winemaking. We focused on studying the chromatic characteristics by applying differential colorimetry and polyphenolic composition to influence the colour. This is the first attempt to use this product type in winemaking and scrutinize its efficiency in stabilizing the colour of wines elaborated in a warm climate.
Section snippets
Chemicals and solvents
HPLC-grade methanol was purchased from J. T. Baker (Baker Mallinckrodt, Mexico), and formic acid and Folin-Ciocalteau reagents were supplied by Sigma-Aldrich (St. Louis, MO, USA); they were converted into HPLC grade using a Milli-Q plus water purification system (Millipore Corp., Bedford, MA, USA). Malvidin-3-glucoside, (+)-catechin, (−)-epicatechin, gallic acid, caffeic acid, and quercetin were supplied by Sigma-Aldrich (St. Louis, MO, USA).
Enzymatic hydrolysis of grape seeds
The product was prepared according to an enzymatic
Results and discussion
The effect of the pre-fermentative addition of an enzymatic hydrolysate of grape seed to red wines was scrutinized. Follow-up at different vinification stages (day 0, initial point; and skin-maceration of 2, 4 and 7 days) and stabilization times (15, 22, 30, 37, 45, 60, 75, 90, 105, 120 and 150 days) was conducted. An in-depth study of polyphenolic compounds, copigmentation and polymerization, CIELAB parameters and differential tristimulus colorimetry was performed.
Conclusions
This study demonstrated that the addition of a grape seed enzymatic hydrolysate offers a promising technique for achieving colour stability in red wines, which is lacking in wines developed in warm climates. Treated wines had higher chroma values and lower lightness values, without a significant change in tonality, which is probably due to the high level of colourless polyphenols that could act as copigments. However, higher enzymatic hydrolysate levels did not improve the purported colour
Acknowledgments
We are indebted to Consejería de Ciencia, Innovación y Empresa, Junta de Andalucía, Spain (Project P10-AGR06331), the Ministerio de Economía y Competitividad, Spain (Project AGL2014-58486-C2) and V Plan Propio de investigación de la Universidad de Sevilla, Spain for financial support. Also, authors are grateful to Cooperativa Vitivinícola Nuestra Señora del Socorro (Rociana del Condado, Huelva, Spain) for collaborating with the experiments and Viñaoliva Sociedad Cooperativa (Almendralejo,
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