Changes in Anthocyanins in Berry Skins of Merlot and Cabernet Sauvignon Grapes Grown in Two Soils Modified With Limestone or Oyster Shell Versus a Native Soil Over Two Years

Abstract

Two cultivars, Merlot and Cabernet Sauvignon, were grown in vineyard plots in which the soil was modified by treatment with either limestone or oyster shells, as well as in untreated native soil. In the limestone-treated plot, graded limestone particles or small pebbles were mixed at 20% with the top 70 cm of the native soil and the subsoil was replaced with limestone pebbles and small rocks to a depth of 1 m. In the oyster shell-treated plot, shells were mixed with the top 20 cm of the native soil at 6 t/0.1 ha. The native soil was weakly acidic (pH 6.1), the limestone soil weakly alkaline (pH 8.0), and the oyster shell soil neutral (pH 7.0). The exchangeable calcium content was highest in the limestone soil and lowest in the native soil. The soil moisture content was higher in 1992 than in 1993 (p < 0.01), and was greatest in the oyster shell soil (p < 0.001) and least in the limestone soil (p < 0.05 or < 0.001). During ripening in 1992 and 1993, which were respectively warmer and drier, and cooler and wetter years than average, grape berries were periodically sampled and the chemical components of the berry juices and skins were analyzed. The amounts of three phenolic components — total phenols, total red pigments, and total anthocyanins — increased with increasing sugar content in the berry juices of both cultivars, and when compared at the same °Brix, the amounts were higher in cool 1993 than in warm 1992. In terms of soil type, in 1993 the amounts of these three phenolic components were significantly higher (p < 0.05 or < 0.001) in the juices of berries grown in the limestone soil than in the other two soils. HPLC analysis showed that the contents of individual anthocyanins per berry increased as ripening proceeded, and that amounts were maximal at 18° to 20° Brix. Changes in the individual anthocyanin contents above these °Brix values varied with the variety, season, soil type, and anthocyanin. Addition of limestone or oyster shells to the native soil significantly influenced the anthocyanin composition in Cabernet Sauvignon berry skins in both years (p < 0.01 or < 0.001) but had little influence on that in Merlot berry skins. There were no significant anthocyanin composition differences in skins of berries from the same cultivar and grown in the same soil type harvested at different times during the ripening season in either year.