Unveiling quality links: External predictors of internal quality in Guanxi honey pomelo (Citrus maxima (Burm.) Merr.) mutants

Abstract

Guanxi honey pomelo is highly valued for its distinctive flavor and nutritional profile. This study evaluated ∼1700 fruits from core orchards in Pinghe, Fujian, China, to investigate the relationships between external appearance and internal quality across two major mutants, Hongrou and Sanhong. Twenty-six key indicators were assessed, encompassing external traits (e.g., fruit shape, peel color, firmness) and internal attributes (e.g., flavor, antioxidants, and minerals). Hongrou and Sanhong pomelos exhibited comparable average fruit weight (∼1300 g), volume (∼2.0 L), density, and shape index, but differed in peel coloration and texture - Hongrou showed higher yellowness (b*), while Sanhong displayed greater redness (a*) and lower firmness. Internally, Sanhong demonstrated enhanced flavor characteristics (TSS: 11.57 %; TSS/TA: 18.2) and higher antioxidant contents (total phenolics: 6.09 g/kg; total flavonoids: 2.56 g/kg; vitamin C: 36.4 mg/100 g), whereas Hongrou had higher mineral concentrations, including Ca, Mg, Zn, and Fe. Canonical correlation analysis (CCA) revealed strong and significant associations between external and internal quality traits (canonical r = 0.70 in Hongrou; 0.66 in Sanhong; P < 0.05). In Hongrou, color b* emerged as the strongest external predictor (loading: 0.777), while in Sanhong, shape index (0.726), peel saturation (0.463), density (-0.648), and weight (-0.525) were key external predictors. These traits were primarily linked to internal indicators such as juice pH, reducing sugars, and TSS/TA ratio. In summary, yellow peel with moderate saturation predicted superior internal quality in Hongrou, while in Sanhong, higher shape index, greater peel saturation, and moderate weight were indicative of enhanced internal quality. Among internal quality dimensions, flavor quality showed the strongest and most consistent correlation with external traits (r = 0.62 in Hongrou; r = 0.59 in Sanhong). Fruit bagging experiments further validated these external-internal correlations. These findings serve as a valuable reference for advancing pomelo quality grading and breeding strategies.