Comprehensive Assessment of Pomological, Colorimetric, and Nutraceutical Quality Dynamics in Nine Sweet Cherry Cultivars (Prunus avium L.) Harvested at Two Ripening Stages Under Mediterranean Conditions

Sweet cherry (Prunus avium L.) is a non-climacteric fruit that reaches its optimal organoleptic and nutraceutical quality only when fully ripened on the tree. However, growers often harvest prematurely to avoid weather-related losses or to capture early-market premiums. This study evaluated the impact of harvest timing on the pomological and nutraceutical profiles of nine red-skinned sweet cherry cultivars (Black Star, Burlat, Cashmere, Ferrovia, Giorgia, Grace Star, Lapins, Regina, Sandra Rose) grown in the Puglia region of Southeastern Italy, a major Mediterranean production area. Fruits were collected at two maturity stages: light-red skin (Stage 1) and dark-red skin (Stage 2). Pomological parameters, i.e., fruit weight, equatorial diameter, CIELAB color parameters, soluble solids content (SSC), titratable acidity (TA) and nutraceutical metrics (total polyphenols, total anthocyanins, FRAP antioxidant activity) were measured. Delaying harvest significantly increased fruit weight (5.7–24.5%), equatorial diameter (up to 9.8%), and SSC (14.0% average, up to 26.4% in early ripening cultivars), while decreasing TA in most cultivars (non-significant in some). The SSC/TA ratio, a key driver of consumer preference, improved substantially across all genotypes. CIELAB parameters h° and C* decreased sharply, and L* generally decreased, reflecting intense anthocyanin accumulation. Total polyphenols increased by 20.7–68.8%, total anthocyanin content (TAC) by 203–1053% and FRAP antioxidant capacity by 20.7–111.7%. Two-way ANOVA revealed significant (p < 0.01), cultivar × stage, interactions for all parameters, confirming genotype-dependent ripening kinetics. Principal component analysis using all quality parameters clearly separated Stage 1 from Stage 2 fruits, with SSC, TAC, and FRAP as primary discriminators. These results demonstrate that delaying harvest until a uniform dark-red skin consistently enhanced fruit size, SSC, and health-promoting bioactive compounds across all evaluated genotypes. We provide cultivar-specific harvest calendars, colorimetric targets (hue angle ≤ 10° for optimal maturity), and a quantitative framework to help growers balance quality improvement against agronomic risks.