Relationship between Phenolic Compounds, Antioxidant Activity and Color Parameters of Red Table Grape Skins Using Linear Ordering Analysis

Color, being one of the most important sensory characteristics, could be associated to the phenolic compound content and/or the antioxidant activity of fruits and vegetables. In this study, linear ordering was used to build quality rankings of red table grapes based on color parameters or phenolic compounds. First, the principle component analysis (PCA) was used to show the association between color of red grape skins (evaluated in CIE L*a*b* and L*C*h systems) and their individual phenolic compounds (investigated by the HPLC), total polyphenol content (TPC), total anthocyanins (ACNs), as well as the antioxidant activity (DPPH) of five table grape varieties. It could be observed that the lightness (L*) and hue angle (h) are the color coordinates strongly related to some phenolic compounds and ACN, whereas a* was related to DPPH and TPC. Five distinct clusters could be observed from PCA analysis with dark-colored grape varieties showing high levels of ACN (3.48–5.83 mg/g), low lightness (47.8–53.0), and high h values (353.7–359.8°). L*, a*, and h color coordinates were used to build table grape ranking. The second ranking was built based on phenolic compound content. Results of the two rankings were correlated. High Tau Kendall correlation coefficient (0.51, p = 0.000) indicated that linear ordering analysis, based on the simple color measurements, could be a useful tool for rapid screening of the quality of grapes. This could be valuable information for producers and consumers of the fruit making decision on the market.