Changes in Fruit Characteristics of Various Blueberry Cultivars During Ripening Stages

The quality of fresh blueberries is determined by physicochemical properties and sugar-acid composition, which exhibit significant variations across different cultivars and ripening stages. This study investigated two rabbiteye blueberry cultivars ('Brightwell', 'Homebell') and three highbush blueberry cultivars ('Bluegold', 'Emerald', 'Legacy'), measuring basic physicochemical indices, soluble sugar and organic acid profiles at six ripening stages. HPLC analysis revealed that soluble sugars in blueberries are primarily composed of fructose and glucose. The organic acids in highbush blueberries are dominated by malic and citric acids, while rabbiteye blueberries contain higher levels of quinic acid in addition to malic and citric acids. Correlation analysis demonstrated that glucose and fructose contents were significantly positively correlated (p ≤ 0.01) with average fruit weight, soluble pectin to total pectin ratio (SP/TP), and total soluble solids to titratable acidity ratio (TSS/TA), but showed a highly significant negative correlation with malic acid. In contrast, malic acid exhibited a significant positive correlation (p ≤ 0.05) with firmness and moisture content. Cluster analysis divided the measured parameters into two groups: Class 1 includes average fruit weight, SP/TP, TSS/TA, and soluble sugars. Class 2 comprises fruit shape index, firmness, moisture content, and organic acids. Quality variation patterns among blueberry cultivars clustered according to cultivated type (rabbiteye and highbush), with differences within the same type being smaller than those between the two types. Rabbiteye blueberries exhibited a higher TSS/TA and a sweeter taste, whereas highbush varieties displayed softer texture, higher moisture content, and a balanced sweet-sour juiciness. This study clarified the dynamics of sugar and acid metabolism during blueberry ripening, providing a theoretical basis for quality evaluation, harvest timing, and breeding.