Abstract: 【Objective】In order to characterize the flavor quality of Xinjiang red-flesh apple, the composition and content of flavor compounds were analyzed and a preliminary evaluation on nutritional quality of these fruits was made, which will provide useful information for exploitation and utilization of these apple fruits.【Method】High performance liquid chromatography (HPLC) and gas chromatography-mass spectrometer (GC-MS) were employed to detect and analyze sugars, organic acids and volatile compounds in the peels and pulps of three Xinjiang red-flesh apple lines, and compared with the control Fuji apple ‘Changfu 2’. The contents of total phenols (TP), total flavonoids (TF) and antioxidant activity were also measured and evaluated. 【Result】The titratable acid (TA) of apple tested were 21.01-27.71 mg·mL^-1, which were 3.68-4.85 times of the control. The pH values were 3.12-3.19, which was significantly lower than the control (P<0.05). Fructose, glucose and sucrose were identified in these fruits, fructose was the dominant sugar (56.71%-64.07%), while sucrose content was the least and it only accounted for 8.89%-31.12% of total sugar. The contents of soluble sugars in three Xinjiang red-flesh apple were significantly lower than those in the control. Fructose in pulps was higher than those in peels, while no significant differences of glucose and sucrose were found between them (P<0.05). Five organic acids, including oxalic acid, tartaric acid, malic acid, citric acid, and quinic acid, were identified from the lines tested. Malic acid (56.51%-95.11%) was the richest component, followed by citric acid (2.07%-40.72%). The contents of other acids were less than 0.6 mg·g^-1 fresh weight (FW). Quinic acid was only detected in ‘13-3’. The content of malic acid in peels and pulps was 6.56-8.99 times and 5.58-6.61 times as much as that in control, and the content of citric acid was 16.80-117 times and 4.50-16.17 times of that in control, respectively. The content of malic acid in pulps was significantly higher than that in peels, while citric acid in pulps is significantly lower than that of peels (P<0.05). Totally, 85 volatile compounds were identified from the fruits tested. Aldehydes, esters and terpenes were the most abundant components, accounting for 92.32%-97.84% of the total volatile compounds. Similar with the control, ‘13-3’ was characterized by esters and terpenes. Ethyl butyrate, ethyl 2-methylbutyrate, methyl hexanoate and hexyl acetate were the main esters, while styrene, D-limonene and α-farnesene were the dominant terpenes. ‘P3’ and ‘Xinnong’ were mainly characterized by aldehydes and terpenes, hexanal and (E)-2-hexenal were the main aldehydes. The content of volatile components in peels were significantly higher than those in pulps (P<0.05). The contents of TP and TF in peels and pulps of three Xinjiang red-flesh apple lines were 2.31-2.65 times and 1.23-1.61 times as that of the control, and as 5.53-16 times and 1.43-3.49 times as that of the control, respectively. Free radical scavenging ability of extraction from these fruits were also significantly higher than the control. The contents of TP and TF in peels were higher than those in pulps, and its antioxidant capacity were significantly higher than those in pulps. Among the tested lines, ‘13-3’ presented the highest TP and TF contents and antioxidant capacity. 【Conclusion】 The apple lines tested belong to the high-acid type of Xinjiang red-flesh apple. Low soluble sugar, high malic acid and citric acid, low ratio of total sugar to malic acid and the characteristic aroma components, such as hexanal, (E)-2-hexenal, ethyl butyrate, ethyl hexanoate, hexyl acetate and ethyl 2-methylbutyrate, play an important role in flavor quality decision. ‘13-3’ belongs to “fruity odor” fruit, while ‘P3’ and ‘Xinnong’ are the “grassy odor” type. The three lines tested presented characteristic flavor and high nutritional quality, which could be good materials for studying flavor quality and breeding functional processing apple, and ‘13-3’ is the optimal.

Key words: Xinjiang red-flesh apple, sugar, acid, aroma volatiles, antioxidant activity