Influence of grapevine flower treatment with gibberellic acid (GA3) on polyphenol content of Vitis vinifera L. wine

Four Vitis vinifera L. cultivars (Riesling, Sauvignon blanc, Kadarka, and Lemberger) were treated at full bloom with 20 ppm gibberellic acid (GA3). Depending on variety, the respective wines showed different polyphenol contents and profiles. While GA3 seemed to have a small impact on polyphenols in Riesling (−5%), treatment of Sauvignon blanc led to significantly higher polyphenol content (+19%). Principal component analysis revealed that mainly caftaric acid and GRP account for the difference between treatments and varieties. In red varieties, GA3 generally led to a delay in ripening. In Kadarka, GA3 led to significantly higher polyphenol (+52%) and anthocyanin (+229%) content. The much higher anthocyanin content was referred to the lower Botrytis infection grade in GA3 treated grapes. Lemberger showed much lower polyphenol (−38%) but slightly higher anthocyanin (+11%) content. Principal component analysis showed that mainly caffeic acid and epicatechin as well as p-coumaric acid and rutin, respectively, are responsible for the differences between treatments and varieties. Since no uniform impact of GA3 treatment on wine composition was observed during the scope of this study and did not only occur in polyphenolic composition but also, e.g. in mineral content, it is concluded that the hormone-like influence of GA3 on the chemical composition of grapes is extremely complex and has to be studied in more detail in further research trials.