Comparison of three extraction methods used to evaluate phenolic ripening in red grapes.

ABSTRACT

Because there is not a single method for carrying out phenolic ripening analysis, it is very difficult to compare the results obtained by different researchers. In this study, the three most widely used extraction methods of polyphenols (Glories, AWRI, and ITV) have been analytically compared by evaluating two of the most important parameters for the wine industry total polyphenols and total anthocyanins. Samples from different grape varieties (Tempranillo, Garnacha, Carinena, Syrah, Merlot, and Cabernet Sauvignon), from three different vintages (2006, 2007, and 2008), and at different ripening states (from the beginning of ripeness until harvest) were analyzed to obtain a wide range of representative phenolic contents. To avoid external interferences on the comparisons, the same grape puree was used to make the maceration assays using the different solvents according to each extraction method. Although every extraction method exhibits a different extraction efficiency, the correlation between the results obtained with each one was very good both for total anthocyanins and for total polyphenols. Thus, after having determined a parameter value of the phenolic ripeness using a specific method, the relationship found can be used to predict the parameter value of the phenolic ripeness provided by the other two methods.