Evaluating the reliability of epicarp chromaticity as an independent indicator of maturity state during harvesting time for sweet cherry

Accurate maturity assessment is essential for sweet cherry quality, yet standardized indicators remain limited. This study characterized five maturity stages across a 12-day harvest for red ‘Tieton’ and yellow ‘Caiyu’ cultivars using integrated colorimetry, physicochemical analyses, and metabolomics. In ‘Tieton’, early stages showed rapid increases in redness ( a* from 26.1 to 34.8), sugar accumulation, flesh softening, and fruit enlargement. Later stages featured exponential anthocyanin accumulation (from 0.338 U to 2.500 U), which markedly decreased redness ( a* ), yellowness ( b* ), and chroma ( C* ), producing a darker appearance. Metabolomic profiling revealed that activation of the anthocyanin biosynthesis pathway closely paralleled visual color changes, confirming epicarp color as a reliable indicator of ripeness. Strong correlations between color indices and key quality parameters enabled highly accurate maturity prediction models using CIE L*a*b* ( R 2 = 0.915, MAE = 0.285) or L*C*h° ( R 2 = 0.909, MAE = 0.289). In contrast, ‘Caiyu’ exhibited weak associations between epicarp color and internal attributes, requiring a multi-parameter approach for maturity evaluation. Overall, this work establishes a theoretical and technical framework for maturity determination in red sweet cherries, supporting improved postharvest quality control and smart harvesting. • Color parameters were strongly correlated to physicochemical changes for red sweet cherry. • Parameters L * and h° could precisely differentiate each ripening state. • Anthocyanin metabolism dominates ripening, synchronized with color development. • Prediction models for ripening rating were established including color as independent variables.