Application of abscisic acid (S-ABA) to cv. Isabel grapes (Vitis vinifera × Vitis labrusca) for color improvement: Effects on color, phenolic composition and antioxidant capacity of their grape juice

• S-ABA applied to grapes increased color intensity and total anthocyanins in juices.
• S-ABA also increased the proportion of B-ring trisubstituted anthocyanidins.
• S-ABA applied before or at the onset of véraison of grapes led to better results.
• Among other phenolic compounds, only flavonols were increased in 2012 juice.
• The low antioxidant capacity of juices did not change by S-ABA treatment of grapes.

Hybrid grape Isabel (Vitis vinifera × Vitis labrusca) is the main cultivar used to produce grape juice in Brazil. However Isabel grape is deficient in anthocyanins. Application of abscisic acid (S-ABA), which is responsible for promoting the anthocyanin synthesis, offers a way for color improvement. This study evaluates the changes on the phenolic composition of Isabel grape juice produced from grapes treated with S-ABA, over two consecutive harvest seasons. Application of S-ABA to grapes increased the content of total anthocyanins in the corresponding juices and also the proportion of anthocyanins based on B-ring tri-substituted anthocyanidins. Regarding non-anthocyanin phenolic compounds, total flavonol content was only significantly higher in juices produced from grapes treated in the 2012 season, whereas the treatment did not significantly affect the content of hydroxycinnamic acid derivatives, flavan-3-ols, resveratrol and even the antioxidant capacity of juices. Juice from Isabel grapes treated with S-ABA provides an enhancement of total anthocyanin concentration, mainly when grapes are treated before or at the onset of véraison. As a consequence, the color intensity increased in all the juices obtained from treated grapes.