Malate, Tartrate, Potassium, and Sodium in Flesh and Skin of Shiraz Grapes During Ripening: Concentration and Compartmentation

Analysis of malate, tartrate, potassium, and sodium in Shiraz grape berries during ripening showed large and distinctive developmental differences between pericarp tissues. During ripening, tartrate per berry remained relatively constant in both flesh and skin, but malate per berry declined considerably in the flesh, while at the same time doubling in the skin. Potassium concentration increased in both flesh and skin, especially the latter — in some samples, 40% of the K of ripe berries was contained in the skin. Differential extraction with 80% ethanol showed that tartrate was converted to salt forms as ripening progressed, while malate existed entirely as the free acid in both flesh and skin at all stages. Efflux studies showed that the rate with which tartrate, malate, and K leached from flesh tissue increased as berries ripened, indicating a general increase in membrane permeability. However, efflux from skin was rapid at the initial stages of ripening but slow at midripening and showed differences between the behavior of the anions and K, suggesting compartmentation differences.