Comprehensive evaluation of fruit quality of six sweet cherry cultivars

【Objective】Sweet cherry (Prunus avium L.) is characterized by bright fruit skin, firm flesh texture, and high soluble solids content. It integrates the dual advantages of nutritional and commercial value, thereby securing a prominent position in the global fruit market. The fruit quality of sweet cherry primarily encompasses three dimensions: appearance quality, flavor quality, and nutritional quality. Appearance quality mainly includes fruit size, color, transverse and longitudinal diameters; Flavor quality is defined by fruit sweetness, acidity, aromatic substances, mouthfeel, and related traits; Nutritional quality primarily comprises vitamins, mineral elements, and other nutrients. Fruit quality is the core determinant of market competitiveness. Quality evaluation is regarded as a comprehensive assessment of external indicators (e.g., fruit size, shape and color) and internal quality traits (including texture, flavor, sweetness-acidity balance, and functional nutrients). It serves as a critical basis for elite cultivar selection and fruit quality optimization. This study presents a comprehensive evaluation of fruit quality across six sweet cherry varieties, with the goal to provide references for elite sweet cherry cultivar breeding, guide cultivation and management practices, and enhance market value.【Methods】Six sweet cherry cultivars (Hongdeng, Tieton, Summit, Zhukovskaya, Wanhongzhu, and Druzhba)served as the experimental materials for this study. The following analyses were conducted: Appearance quality, including fruit weight, transverse and longitudinal diameters, and color parameters, was determined using an electronic analytical balance, a vernier caliper, and a colorimeter. Soluble solids content (SSC) was determined with a handheld refractometer. Titratable acidity (TA) was determined by automatic potentiometric titration. Flesh firmness was determined using a TA-HD Plus dual-arm texture analyzer (Stable Micro Systems, UK) equipped with a 2 mm cylindrical probe (P/2). Fruit aromatic compounds were analyzed by gas chromatography-mass spectrometry (GC-MS, Thermo Fisher Scientific, USA). Sugar and organic acid compositions were quantified using ultra- performance liquid chromatography- tandem mass spectrometry (UPLC-MS/MS, Waters Corporation, USA). Total mineral elements (P, K, Ca, Mg, Fe, Mn, Zn, Cu, B and Mo) were measured by inductively coupled plasma optical emission spectrometry (ICP-OES, Thermo Fisher Scientific, USA). Total nitrogen (N) content was determined using a Kjeldahl nitrogen analyzer. Vitamin C content was determined by automatic potentiometric titration.【Results】Significant differences were observed in fruit quality attributes among the six sweet cherry cultivars. The single fruit weight ranged from 9.66 to 11.72 g, the fruit shape index varied between 1.08 and 1.32, and vitamin C content spanned 3.70-11.02 mg · 100 g- 1 . Sugar and acid composition analyses revealed that glucose was the predominant sugar, while malic acid was the dominant organic acid. A total of 32 aromatic compounds were identified, with 10 compounds—(+ )-limonene, (E)-2- hexen-1- ol, 1- penten-3-ol, benzaldehyde, hexanal, methyl heptenone, nonanal, n-hexanol, n-octanol, and n-octanal— common to all cultivars. Aldehydes were the core aroma contributors, accounting for 65.5%-75.1% of the total volatile content. Cluster analysis and principal component analysis (PCA) of the aroma profiles grouped the cultivars into three clusters: Hongdeng and Summit each formed a distinct group, while the remaining four cultivars clustered together. Correlation analysis demonstrated that single fruit weight exhibited a highly significant negative correlation with titratable acidity (TA) and quinic acid content (P＜0.01). Glucose showed a significant negative correlation with potassium (K) and zinc (Zn) levels (P＜0.01). Malic acid content correlated positively with sucrose (P＜0.01) and showed significant positive correlations with TA, quinic acid, and citric acid (P＜0.05). Nitrogen (N) and K were negatively correlated with soluble solids content (SSC), glucose, sorbitol, and fructose (P＜0.05), while vitamin C content exhibited a significant negative correlation with lightness (L) and yellowness (b) values (P＜ 0.01). Through classification and simplification of 35 measured indices, 21 key quality parameters were selected for further analysis. PCA of these parameters identified six critical evaluation criteria: (1) Fruit size and acid metabolism; (2) Sugar composition and the interaction between nitrogen (N) and potassium (K) metabolism; (3) Synergistic accumulation of calcium (Ca) and magnesium (Mg); (4) Sugar fractionation; (5) Color development and aroma profile; (6) Flesh firmness and zinc (Zn) content.【Conclusion】This study conducted a comprehensive evaluation of sweet cherry fruit quality based on external appearance, flavor compounds, and nutritional elements. Correlation and principal component analyses (PCA) were employed to investigate the quality characteristics of different cultivars. The results indicated that Zhukovskaya achieved the highest overall quality score, characterized by its large fruit size, low acidity, high sugar content, appealing color, and complex flavor profile. Druzhba ranked second, distinguished by elevated levels of mineral elements such as calcium (Ca) and magnesium (Mg), coupled with superior performance in both skin color and aromatic compound composition. Wanhongzhu secured the third position. Despite notable strengths in PC5 (fruit coloration and aroma), it was limited by its performance in PC1 (fruit size) and PC4 (total sugar content). Tieton placed fourth, with primary advantages in PC6 (flesh firmness and Zn content) and relatively large fruit size; however, it received low scores for PC4 (sugar composition). Ranking fifth, Hongdeng showed acceptable performance on PC4, indicating higher glucose and fructose concentrations, but its quality was compromised by smaller fruit size, higher acidity, and lower mineral element accumulation. In contrast, Summit performed poorly overall, with negative scores across all principal components, resulting in the lowest total score in the evaluation system.