Relationship between quality characteristics and skin color of 'Fuji' Apples (Malus domestica Borkh.)

We investigated the relationship between apple skin color and internal quality characteristics, such as the concentration of functional compounds, physicochemical and textural properties. The skin color of 'Fuji' apples (N = 420) was determined and the apples were categorized into three classes (class A, N = 231; class B, N = 130; class C, N = 59). The apple skin color values correlated significantly with flesh color intensity. For sensory attributes, the yellow color intensity of apple flesh had a positive correlation with redness (a*, r = 0.781) and Delta E(r = 0.787) of apple flesh color (r = 0.787). There was strong correlation between a*, and the chemical properties of apple flesh. Apple skin color (a*) was positively correlated with total juice content (r = 0.784), soluble solid contents (r = 0.626), soluble solid contents/total acidity (r = 0.697), fructose (r = 0.444), sorbitol (r = 0.476), and sucrose concentrations (r = 0.823), respectively. However, malic acid (r = - 0.525), shikimic acid (r = - 0.443), and total organic acid concentrations (r = - 0.519) correlated negatively with a*. The a* value also showed positive correlations with phenol and anthocyanidine concentrations, but a negative correlation with DPPH, FRAP, and ABTS concentrations. A principal component analysis was performed to analyze functional compounds, sensory attributes, and physicochemical properties of apple skin and flesh; the total variance was 91.31% (F1; 58.92%, F2: 32.39%), 84.55% (F1;50.86%, F2;33.69%), 90.37% (F1;75.74%, F2; 14.63%) and 57.20% (F1;41.92%, F2;15.28%), respectively. Our results confirmed a strong correlation between the Delta E and a*, which are indicative of the skin color and the internal quality measures of the Fuji apple. Thus, the skin color of Fuji apples seems to be a reliable index of internal fruit quality.