Impact of maceration enzymes on skin softening and relationship with anthocyanin extraction in wine grapes with different anthocyanin profiles
Introduction
Color is one of the most important attributes in the initial assessment of the red wine. High-colored wines are usually associated with high perceived quality scores (Parpinello, Versari, Chinnici, & Galassi, 2009). Anthocyanins contribute strongly to the sensory quality of red wines because these compounds, and their interactions with other phenolic compounds are responsible for the color and its stability during aging (Boulton, 2001, Fulcrand et al., 2006, Monagas et al., 2006).
Anthocyanins are mainly located inside the skin cell vacuoles and are partially extracted from the berry skin into the must/wine during winemaking (González-Neves, Gil, & Barreiro, 2008). The anthocyanin content and composition of red wines depend on the amount of pigments in the berry skin at harvest and on the easiness of their extraction. Although the qualitative and quantitative composition of anthocyanins in the wine is directly related to the wine grape variety, ripening stage, culture practices, growing season and environmental conditions, the oenological practices also play an important role (González-Neves et al., 2012, González-Neves et al., 2008, Sacchi et al., 2005).
Exogenous enzymes are widely used in red winemaking, attempting to accelerate the extraction of anthocyanins from the berry skin and thus increasing the color intensity of the resulting wine (Bautista-Ortín et al., 2005, Gil-Muñoz et al., 2009, Ortega-Heras et al., 2012, Romero-Cascales et al., 2012, Soto Vázquez et al., 2010). The commercial enzyme preparations mainly show pectolytic (polygalacturonase, pectin methyl esterase and pectin lyase), cellulase, hemicellulase and acid protease activities (Romero-Cascales, Fernández-Fernández, Ros-García, López-Roca, & Gómez-Plaza, 2008). Maceration enzymes degrade the berry skin pecto-cellulosic cell walls by partial hydrolysis of structural polysaccharides. Therefore, the permeability of the cell wall is increased facilitating the diffusion process of anthocyanins from the vacuoles into the must during fermentation (Romero-Cascales et al., 2008, Romero-Cascales et al., 2012).
Contradictory results have been reported about the impact of maceration enzymes on the anthocyanin content and color intensity in red wines (Sacchi et al., 2005). The discrepancies are probably due to the different nature and activities of the commercial enzyme preparations (Bautista-Ortín et al., 2005, Romero-Cascales et al., 2008), as well as to varietal and vintage effects on the grape anthocyanin content and composition or on the skin cell wall morphology and composition (Bautista-Ortín et al., 2007, Ducasse et al., 2010, Ortega-Heras et al., 2012).
The differences in the mechanical properties of the berry skin are also linked to variations in the chemical composition of the cell walls, which determines the resistance of the skin to the anthocyanin release (Hernández-Hierro et al., 2014). In fact, the berry skin hardness and berry skin thickness influence the rate and extent of the anthocyanin extractability (Río Segade et al., 2011, Rolle et al., 2012a). Although it is well known that the degradation of the cell walls causes the skin softening (Ortega-Regules, Ros-García, Bautista-Ortín, López-Roca, & Gómez-Plaza, 2008), the effect of maceration enzymes on the skin mechanical properties has not been quantified to date.
The maceration time also affects the anthocyanin release, chromatic characteristics and color stability in the red wine. A longer maceration time usually contributes to a greater anthocyanin extraction from the skins and improves the color stability of the wine (González-Neves et al., 2008, Kelebek et al., 2009, Romero-Cascales et al., 2005, Romero-Cascales et al., 2012, Sacchi et al., 2005). Nevertheless, this relationship may be affected by the participation of extracted anthocyanins in oxidation and polymerization reactions occurring during the maceration process, their partial adsorption by the yeasts and their fixation onto the grape solid parts (Bautista-Ortín et al., 2007, González-Neves et al., 2008, Romero-Cascales et al., 2005, Romero-Cascales et al., 2012).
Given that the production of high quality red wines demands the exploitation of the intrinsic chromatic characteristics of the grapes and their preservation in the final product, the aim of this work was to evaluate the effect of an enzyme preparation used at two different doses on the kinetics and extent of the anthocyanin extraction during maceration and to relate this effect with the skin softening of two red wine grape cultivars. In particular, Vitis vinifera L. cv. Cabernet Sauvignon and Nebbiolo were selected on the basis of their different anthocyanin content and profile mainly composed of tri- and disubstituted anthocyanins, respectively. The two varieties are widely used to produce high quality red wines that are commercialized in worldwide.
Section snippets
Grape samples
In this study, whole bunches of red grape V. vinifera L. cv. Cabernet Sauvignon and Nebbiolo were harvested from various vines in commercial vineyards located in the same growing zone (Piedmont, Cuneo province, north-west Italy) in 2013. Once in the laboratory, for each variety, a subsample consisting of approximately 1.5 kg of grapes (1000–1200 berries) was randomly selected by picking berries with attached short pedicels from different positions in the cluster (shoulders, middle and bottom).
Technological ripeness parameters
As a consequence of the selection of the berries belonging to the most representative density class for each wine grape variety, Cabernet Sauvignon (1094 kg/m3) and Nebbiolo (1100 kg/m3) berries showed different technological ripeness parameters. Sugars and organic acids are primary metabolites directly influenced by the grape berry density (Rolle et al., 2012a). Nebbiolo grapes were richer in reducing sugars (257 g/L) than Cabernet Sauvignon (230 g/L). However, the parameters related to the
Conclusions
The enzyme preparation used in this work influenced the mechanical properties of the berry skin, increasing the softening that naturally occurs during maceration as a result of the degradation process. This effect of enzymes on the skin hardness was instrumentally quantified for the first time, and the mechanical properties of the skin may be considered predictors of the extraction yield of anthocyanins during maceration. Furthermore, the use of enzymes permitted to increase the extraction
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These authors contributed equally to the study.