Anthocyanin Composition and pH Correlate with Berry Skin Color Across Diverse Grape Germplasm

Berry skin color CIE parameters, pH and anthocyanidin profiling of 46 grape accessions were investigated using CIE Lab system, pH measurement and anthocyanidin profiling. CIE parameters separated the samples into three groups: yellowish-green, pinkish-red, and purplish-black, and principal component analysis confirmed clear clustering, with the first two components explaining 99.1% of the variance. After anthocyanidin analysis, cyanidin was detected in all samples, whereas trace-level pelargonidin derivatives were identified by UPLC-MS/MS. Total anthocyanidin content was insufficient to evaluate the quality of berry color, but anthocyanidin composition and relative proportions showed a stronger association with color classification. Yellowish-green berries were enriched in cyanidin, while purplish berries contained more malvidin- and cyanidin. Multivariate analysis identified cyanidin, malvidin, and peonidin derivatives as the main drivers of berry skin color variations. Skin homogenate pH ranged from 3.36 to 4.63 and it was lower in wild grape relatives. Correlation analysis indicated that pH was associated with color parameters. Species-related differences in anthocyanidin glycosylation and acylation were evident, and mono/diglucosides may have potential effects on skin color. Overall, skin color appears to depend on anthocyanidin composition, relative proportions, and pH, offering a chemical basis for grape breeding and fruit quality evaluation.