Effects of leaf removal on phenolic compounds in wine grape Cabernet Franc from Eastern foothills of Helan Mountains

In order to enhance the color of grape fruits, increase the content of phenols (such as anthocyanins), and improve the quality of wine, using Cabernet Franc (Vitis vinifera) from Hejinzun Chateau located in the Eastern foothills of Helan Mountains, Ningxia as the test material, two leaves, four leaves and six leaves were removed from the base of the new shoots at the beginning of veraison, finishing of veraison, and two weeks after veraison, and the difference of phenolic substances in ripe grape fruits with different treatments was compared. The results showed that the most leaf removal treatments could improve the soluble solid contents of grape berries (P<0.05). Leaf removal treatments at different stages and intensity of new shoots base significantly increased total anthocyanins contents in grape berries (P<0.05), and most treatments greatly enhanced the contents of total phenols, tannins, flavanols, and flavonoids (P<0.05). Leaf removal treatments significantly increased the total contents of nine main monomeric anthocyanins in the grape pericarp (P<0.05). Meanwhile, most treatments improved the proportion of coumaroylated and glycosylated anthocyanins of pericarp in the total monomeric anthocyanins. However, the leaf removal treatments of new shoots base significantly increased the contents of anthocyanins and other phenols in Cabernet Franc fruits at the Eastern foothills of Helan Mountains (P<0.05). The effects of removing 6 leaves at finishing of veraison and 4 leaves at beginning of veraison were the optimal.