The extract from mangosteen pericarp was separated into eight fractions, four by solvent extraction (hexane, FH; petroleum ether, FP; ethyl acetate, FE; water, FW) and the other four by fractionation on Sephadex LH-20 column (fractions F1, F2, F3, and F4). Phenolic compounds were identified as the major antioxidant components in each fraction. UV–VIS spectrum, reversed-phase HPLC–ESI-MS coupled with thiolysis, normal-phase HPLC–ESI-MS and MALDI-TOF-MS analyses complementally showed that the phenolic-rich fractions were condensed tannins with structural heterogeneity in monomer units, degree of polymerization and interflavan linkages. Mangosteen condensed tannins predominately contained procyanidins with a significant amount of propelargonidin but much lower signals of prodelphinidin. Eicosapentamers of condensed tannins were detected by MALDI-TOF-MS. Both B-type and A-type linkages were present. Condensed tannins fractions from mangosteen pericarp, especially fractions F3 and FE, can be explored as beneficial food antioxidants because of their high yields and potent antioxidant activities.Graphical abstractHighlights► Tannin-rich fractions with potent antioxidant activity are obtained from mangosteen. ► Highly structural heterogeneity of mangosteen tannin is revealed by LC–MS and TOF-MS. ► Fractionation improves the detection of MALDI-TOF-MS for polymeric condensed tannin. ► Mangosteen condensed tannin with most potent antioxidant activity in 9.27 mDP.

Kandelia obovata, with abundant condensed tannins (CTs), is a typical mangrove species in China, but little is known about the chemical alterations and ecological roles of CTs during leaf litter decomposition. A litterbag experiment was conducted to investigate the changes of CTs in a subtropical mangrove swamp along Zhangjiang River Estuary, China, using the colorimetric assays, reversed/normal-phase HPLC–ESI-MS and MALDI–TOF-MS techniques. Total phenolics (TP), extractable CTs (ECT) and total CTs (TCT) decreased rapidly, while bound CTs (BCT), including protein- and fibre-bound CTs in leaves, increased during decomposition, and these temporal changes were well-expressed by exponential functions. Negative correlations between nitrogen (N) and TP, as well as N and ECT were found; however, a positive correlation between N and BCT was detected, suggesting that CTs played an important role in humification during N immobilization. The HPLC–ESI-MS analyses showed that the polymerization degree of CTs had an initial increase, due to leaching, followed by a decrease in the subsequent shift towards abiotic or/and biotic degradation. MALDI–TOF-MS confirmed the degradation processes for CTs. A decrease in the degree of hydroxylation, along with an increase in glycosylation-CTs, was obtained during litter decomposition. These chemical changes enhanced the current knowledge on the potential ecological role of N transformation in CTs in mangrove swamps.Highlights► Changes of condensed tannins (CT) during decay of Kandelia obovata leaves were studied. ► Structural changes of CT were analysed by MALDI–TOF-MS and HPLC–ESI-MS. ► Leaching, immobilization and degradation were the fate of CT during leaf decay. ► High CT levels provided a potential nutrient conservation strategy for K. obovata.