Identification of bioactive composition and antioxidant activity in young mandarin fruits

The naturally dropped fruits of nine mandarin cultivars were collected and evaluated for their potential use in traditional Chinese medicine (TCM) or as nutraceutical materials. The main bioactive substances were analysed, including four flavanone glycosides (narirutin, naringin, hesperidin, and neohesperidin), two polymethoxlated flavones (nobiletin and tangeretin), and another two compounds of limonoid, and synephrine. The total phenolic content (TPC) and antioxidant capacity were determined by Folin–Ciocalteu, FRAP, DPPH, and ABTS assays. Hesperidin and narirutin were the main flavanones in all tested cultivars. Naringin and neohesperidin were not detected in any of the mandarin cultivars except for Ougan, which contained 10.6 ± 0.6 mg/g naringin. The highest contents of nobiletin and tangeretin were found in Zhuhong (13.7 ± 0.4 and 12 ± 0.2 mg/g, respectively), and in Ougan (11.6 ± 0.1, 10.3 ± 0.1 mg/g, respectively). High synephrine levels were found in Zhuhong (22.5 ± 1.4 mg/g) and Manju (17.6 ± 0.3 mg/g). The limonoid content varied from 104.54 to 1128.13 μg/g with the highest amounts in Manju. The extractable phenolic acids (free and ester form) were more prevalent than the bound forms. Ferulic and caffeic acids were predominate in both the extractable and bound phenolics. The TPC were in order from high to low: Zhuhong > Bendizao Wenzhang Satuma > Ponkan > Manju > Ougan > Shantian Satuma > Gongchuan Satuma > Rinan No. 1 Satuma. The antioxidant capacity followed a very similar trend when assayed by the FRAP, DPPH, and ABTS procedures. The results showed that the dropped fruit from super early to medium mature Satsuma, a world famous mandarin variety, contained relatively lower bioactive substances than the other local varieties. The results also suggest that the dropped mandarin fruit, especially the local varieties such as Zhuhong, Bendizao, Ougan, Manju, and Ponkan, could serve as a good source of extractable nutraceuticals and to serve as a raw material source for crude TCM.