Application of ethephon induces an increase in berry flavonols leading to an increase in wine blueish hue through copigmentation

Abstract

Exogenous applications of plant growth regulators are valuable tools to modulate berry ripening and to explore the roles of phytohormones in controlling plant developmental processes. In this study, berries of ‘Tempranillo’ fruit-bearing cuttings were sprayed with either abscisic acid (ABA) or ethephon (ETE, an ethylene-releasing compound). Berries were periodically sampled to track ripening progress and phenolic accumulation. After harvest, nano-vinifications were performed to assess the effects of ABA and ETE on wine composition. ETE accelerated sugar accumulation and organic acid degradation and enhanced phenolic content in the berry skins. Must from ETE-treated berries showed lower concentrations of total amino acids, aroma-precursor amino acids, and yeast-assimilable nitrogen (YAN). ETE markedly altered the anthocyanin profile, increasing the relative abundance of cyanidin and peonidin derivatives while reducing malvidins. The amino-acid profile was also modified, with lower relative glutamine and higher levels of glutamic acid and several terminal amino acids. ETE improved several wine color attributes, including color intensity (CI), total polyphenol index (TPI; Abs 280 nm) and blue hue (Abs 620 nm/Abs 520 nm). Changes in flavonol concentrations in wine were strongly associated by partial least squares regression to the induction of blue hue. Although both ABA and ETE applications showed beneficial effects, their impacts are complex and may influence wine characteristics in ways that extend beyond color intensity.