Multidimensional Evaluation of Fruit Color Differentiation in Rubus hirsutus Thunb.: Significant Differences in...

Rubus hirsutus Thunb., a typically red-fruited shrub in the Rosaceae family, was found to include a stable yellow-fruited variety at the Zhongshan Botanical Garden in Nanjing, China. This study provides the first comprehensive and multidimensional comparison of red (R) and yellow (Y) R. hirsutus fruits across three developmental stages (immature, color-turning, and mature), integrating morphological, sensory, nutritional, and antioxidant analyses. For the first time, we systematically characterized sugar composition, amino acid profiles, phenolic compounds, and multiple antioxidant parameters (including total phenols, anthocyanins, glutathione, and antioxidant enzymes) in both color variants. Results revealed that mature yellow fruits exhibited significantly larger size (diameter and weight) than red fruits. While red fruits showed brighter coloration, higher soluble solid-acid ratio, and superior flavor scores, they accumulated significantly more fructose, total phenols, anthocyanins, trace elements (Fe and Zn), glutathione, and peroxidase activity at maturity. Conversely, yellow fruits contained higher levels of titratable acid (0.89% vs. 0.73%), total amino acids (2263.52 vs. 1835.68 μg/g in red), specific essential amino acids (His, Trp, and Ile), potassium, and a higher K/Na ratio. The protein content did not differ significantly between the phenotypes. Correlation analysis revealed that morphological indices were closely associated with sugar accumulation, whereas antioxidant indicators showed limited correlation with other parameters. These novel findings not only fill a critical gap in the characterization of yellow-fruited Rubus germplasm but also provide a scientific foundation for targeted breeding and functional food development.