Influence of Spraying Various Agricultural Compounds Containing Bioactive Substances on the Skin Color and Wine Hue of ‘Muscat Bailey A’ Grapes

Abstract

The cultivation of ‘Muscat Bailey A’ for fresh consumption is popular in western Japan, but growers are facing issues with poor coloration of grape berries partly due to insufficient cooling of nighttime temperatures. To ameliorate the coloration defects in ‘Muscat Bailey A’ grapes grown with gibberellin treatment for seedlessness under high nighttime temperatures, and to improve the color characteristics of red wine made from these grapes, the effectiveness of agricultural materials aimed at correcting poor coloration was tested on grape berries intentionally subjected to conditions that induce poor coloration in 2017 and 2018. Inactivated yeast derivatives, shochu lees filtrate, and proteolytic enzymes were sprayed on leaves, and fertilizer containing optically active abscisic acid (S-ABA) was sprayed on clusters during veraison as agricultural materials that could potentially improve fruit characteristics such as grape skin color and the hue of wine. After veraison, the grapes were grown under conditions in which the nighttime temperature was kept above 25°C. The L*, a*, and b* values of these grape skins were determined using colorimetry. Low L* values, indicating darker berry coloration, and notable decreases in hue angle, suggesting a shift towards red and purple hues, were observed after treatment with S-ABA-containing fertilizer. The absorbance of wine made from the grapes described above was measured spectrophotometrically. A significant difference in the color characteristics of the wine was observed for various absorbance indices (A₄₂₀ representing yellow, A₅₂₀ representing red-purple, and A₅₂₀, at pH 1.0 as an indicator of total anthocyanins). The tannin content in the wine from S-ABA-treated grapes was significantly higher compared to the control. However, no differences were observed in taste among these wines. Comprehensive analysis by LC-MS confirmed that mainly levels of malvidin, petunidin (both purple-colored anthocyanins), and peonidin (a red-colored anthocyanin) compounds had increased. These results suggest that S-ABA-containing fertilizer works effectively in alleviating the poor coloration of ‘Muscat Bailey A’ clusters grown under high nighttime temperature conditions and in improving coloration of the wine made from these grapes.