Abstract: This study aimed to understand the changes in the contents of bioactive substances and their contributions to the antioxidant properties in the fruits of Rosa roxburghii (Guinong 5 cultivar). The contents of total phenolics, total flavonoids, total triterpenes and vitamin C and superoxide dismutase (SOD) at different developmental stages were determined. The antioxidant activity in vitro was evaluated by measuring scavenging capacities against 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2’-amino-di(2-ethyl-benzothiazoline sulphonic acid-6)ammonium salt (ABTS) radicals and ferric reducing antioxidant power (FRAP). We also investigated the correlation between the bioactive substance contents and antioxidant activity. The results showed that different bioactive substances in the fruits of Rosa roxburghii changed differently with developmental stage. The VC content increased to reach the maximum at 100 d after anthesis. The contents of total phenolics, total flavonoids and total triterpenes consistently decreased firstly and then increased; higher levels were observed in the young (20–40 d after anthesis) and ripe fruits. However, higher SOD activity was recorded at 40–60 d after anthesis. Overall, three antioxidant properties changed consistently with total phenolic content, showing a significantly positive correlation (P < 0.01). Principal component analysis (PCA) showed the contribution of five bioactive substances to antioxidant capacity was in the decreasing order of total phenolics, total flavonoids > VC > total triterpenes > SOD, and the cumulative contribution rate of the first three substances to the total variance was over 80%. All of the above results showed that the antioxidant capacity of the fruit was ascribed to the synergistic effects of several bioactive substances, and the total phenolics, total flavonoids and ascorbate played a decisive role.

Key words: Rosa roxburghii Tratt., fruit development, bioactive substance, antioxidant capacity