Relationship of Stage of Ripeness to Composition and Keeping Quality Highbush Blueberries1

Abstract ‘Wolcott’ blueberries were harvested at 8 stages of development (small, deep green to overripe) on 3 dates in 1963 and on 4 dates in 1964 from 2 plantings in eastern North Carolina. As the fruit developed, per cent acid decreased while pH, per cent soluble solids, sugar (per cent of fresh weight and mg/berry), soluble solids/acid ratio (SS/A), anthocyanin content and berry weight increased. Acid content (mg/berry) increased during early stages but decreased rapidly during later stages of development. Anthocyanin content (mg/cm 2 of berry surface) was significantly correlated with sugar/acid ratio and SS/A ratio. An increase in incidence of decay of 10 punctured or bisected fruit samples after 9 to 11 days at 70°F, or 21 days at 32° plus 6 days at 70°, was associated with an increase in ripeness. In culture solutions with acid and sugar levels paralleling those of fruit of various degrees of ripeness, growth of both Alternaria and Botrytis spp. decreased as the level of acid in culture solution increased. Thus, the acid composition of blueberry fruit appears to afford a mechanism of resistance to decay-producing organisms. This indicates a potential for selecting varieties with high-keeping quality through selection of clones high in acid. The increase in anthocyanin (Acy) content as berries develop indicates a potential means of sorting blueberries electronically, according to their Acy content.