Abstract: The objectives of this study were (1) to analyze the main components of stevia residue extract and their antioxidant activities and (2) to elucidate their contributions to the total antioxidant capacity of stevia residue extract. Methods: The main components of stevia residue extract were qualitatively and quantitatively analyzed by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) and HPLC. The antioxidant activities were determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2’-azino-bis(3-ethylbenzthiozoline-6)-sulphonic acid (ABTS) and ferric reducing/antioxidant power (FRAP) methods, and comparatively evaluated using antioxidant potency composite (APC) index. The eight main components of stevia residue extract were 5-CQA, 4-CQA, caffeic acid, 3,4-diCQA, 3,5-diCQA, 4,5-diCQA, quercetin-3-rhamnoside and quercetin, among which, 4,5-diCQA was the most abundant, whose content was (126.7 ± 1.27) mg/g, followed by caffeic acid ((97.2 ± 0.36) mg/g) and 5-CQA ((46.5 ± 0.29) mg/g). The results of APC indexes showed that the antioxidant activities of the main components declined in the following order: caffeic acid (92.56%) > quercetin (78.31%) > 3,4-diCQA (62.09%) > 5-CQA (58.92%) > 3,5-diCQA (48.15%) > 4,5-diCQA (36.55%) > 4-CQA (35.5%) > quercetin-3-rhamnoside (34.24%). At concentrations of 50–400 μg/mL, the antioxidant activity of stevia residue extract was stronger than that of its simulant. Stevia residue extract contained high contents of chlorogenic acids and flavonoids and exhibited strong antioxidant activity, and caffeic acid contributed the most to its antioxidant. In addition to the eight main components, other components with antioxidant activities may also exist in stevia residue extract.

Key words: stevia residue extract; antioxidant activity; antioxidant potency composite index; contribution rate