Anthocyanin profile and antioxidant activity from 24 grape varieties cultivated in two Portuguese wine regions

摘要

Aims: The purpose of this work was to evaluate the general phenolic composition and the anthocyanin profile of 24 grape varieties from two Portuguese wine regions as well as their antioxidant activity in the different grape berry fractions (skins, pulps and seeds).Methods and results: Individual anthocyanin composition of grape skin extracts was analyzed by HPLC, whereas total antioxidant activity was evaluated by two methods: DPPH and ABTS. In general, a high variability was found among the different autochthonous and non-autochthonous grape varieties in relation to the polyphenolic compounds analyzed, especially the individual anthocyanins. The individual anthocyanins in grape skin extracts were mainly malvidin (1.40-7.09 mg/g of skin), in particular malvidin-3-glucoside (0.62-6.09 mg/g of skin). The highest antioxidant activity was consistently detected in the seed extracts; however, it was not possible to establish a clear difference among the grape varieties analyzed.Conclusion: High variability in polyphenolic content, individual anthocyanin composition and antioxidant activity was found among the diverse autochthonous and non-autochthonous grape varieties studied. Seeds showed the highest antioxidant activity, followed by skin and pulp, irrespective of the grape variety.Significance and impact of the study: Most vineyards in Portugal grow Portuguese cultivars of Vitis Vinifera L. and other cultivars grown worldwide. The phenolic compounds and antioxidant activity of these grape cultivars have never been characterized under the environmental conditions of the Douro and D?o regions. The variability in phenolic content among the grape varieties studied confirms the hypothesis that genetic factors have an important role in the biosynthesis of these compounds and, consequently, in the antioxidant activity of grapes. IntroductionGrapes are the chief dietary sources of anthocyanins (Rechkemmer and Pool-Zobel, 1996). Anthocyanins are mainly localized in berry skin (Jord?o et al., 1998a), where they are found at concentrations of 200 to 5000 mg/Kg of fresh grapes (Ribéreau-Gayon, 1982). Anthocyanin pigments are of noticeable importance in grapes and wines because of their dual role: first, they constitute an essential part of the sensory attributes, as their concentration, different forms and derivatives directly affect the color of the final wine and second, they are considered to have diverse biological properties and therefore are regarded as secondary metabolites with potential nutritional value. Grape anthocyanins are the 3-O-monoglucosides of delphinidin, cyanidin, petunidin, peonidin, and malvidin. Glucosylated derivatives of these anthocyanins, esterified at the C6 position of glucose with acetyl or coumaroyl groups, have also been detected, yet generally at low concentrations. Malvidin is the predominant monomeric anthocyanin in grapes and is the reddest of all anthocyanins, providing the characteristic color of young red wines.Anthocyanin concentration and profile is influenced by several factors such as varietal diversity (Kallithraka et al., 2005), soil type (Yokotsuka et al., 1999), environmental conditions (Jackson and Lombard, 1993; Mateus et al., 2002), vineyard management (Jord?o et al., 1998b), and grape maturity (Jord?o et al., 1998a). Additionally, some grape varieties can have a high anthocyanin concentration but a low extractability index (Romero-Cascales et al., 2005).According to several studies, flavan-3-ols, flavonols and anthocyanins are the most important compounds that contribute to red grape and wine antioxidant proprieties (Beecher, 2003; Simonetti et al., 1997). For Rivero-Pérez et al. (2008), the free anthocyanin fraction is mainly responsible for the total antioxidant capacity and scavenger activity in red wines. However, other authors have reported that there is no correlation between antioxidant activity and spectral anthocyanin content in grapes and finished wines (Arnous et al., 2002; Kallithraka et al., 2005). For example, considering some individual anthocyanins (cyanidin-3-glucoside, peonidin-3-glucoside and malvidin-3-glucoside) from Italian wines, Di Majo et al. (2008) reported low correlations between these individual compounds and their antioxidant capacity (ranging from 0.29 to 0.54). In addition, Jord?o et al. (2012) reported differences in the correlation values between individual anthocyanins and antioxidant activity during the maceration process. Thus, there has been conflicting evidence regarding the contribution of anthocyanins to red grape and wine antioxidant properties.D?o and Douro are two important wine-producing regions in northeastern Portugal. The D?o region is sheltered on nearly all sides by high granite mountains and is situated in the transition zone between maritime and continental climate, with abundant rainfall in the winter months and long warm dry summers leading up to harvest. The Douro region, which is situated around the Douro River basi