Physicochemical Properties and Phytochemical Composition of ‘French’ Plums at Different Maturities

Plums are primarily sold fresh, but post-harvest softening and rotting can cause significant economic losses. Understanding quality changes across different maturity stages is crucial for meeting consumer demand for high-quality fruit. This study systematically analyzed the dynamic changes in the physicochemical properties, phenolic content, and cellular structure of ‘French’ plums during six growth and development stages (D1–D6), and comprehensively evaluated fruit quality using correlation analysis and principal component analysis (PCA). The results showed that firmness declined considerably with maturity, whereas the soluble solids content (SSC) increased and titratable acidity (TA) decreased. The peel color progressed from green to a purplish-red. The levels of sugars, such as glucose and fructose, increased, whereas those of major organic acids decreased. Phenolic content varied with developmental stage, with catechin and epicatechin peaking at the D3 stage (pre-color green stage), demonstrating exceptional antioxidant potential. At the D5 stage (purple stage), the fruit exhibits an ideal balance of sweetness, acidity and moderate firmness. Although at the D6 stage (full purple ripe stage), SSC reached its highest levels, fruit cell walls were compromised, vesicles ruptured, and firmness significantly decreased. At this stage, phenolic content declined, indicating that the fruit had attained full maturity. At this maturity level, the fruit should be promptly consumed or processed.