Antioxidant properties of polymeric proanthocyanidins from fruit stones and pericarps of Litchi chinensis Sonn

Fruit stones and pericarps of Litchi chinensis, waste products of the food, were studied as a source of polymeric proanthocyanidins. The structures of the polymeric proanthocyanidins isolated from Litchi chinensis were characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) coupled with high performance liquid chromatography electrospray ionization mass spectrometry (HPLC-ESI-MS) analysis. The spectra obtained through MALDI-TOF MS analysis revealed that the dominant A-type procyanidin polymers occurred in each polymer length with one or more A-type linkages. The polymeric proanthocyanidins of litchi fruit stones exhibited longer polymer length than those of fruit pericarps, with polymerization degrees up to 20 and 11 for fruit stones and pericarps, respectively. After depolymerization with toluene-α-thiol, HPLC-ESI-MS analysis showed that epicatechin and A-type dimer were the major constituent units, and the mean polymerization degrees were 15.4 and 5.8 for polymeric proanthocyanidins of fruit stones and pericarps, respectively. The antioxidant properties investigated using DPPH, ABTS and FRAP methods showed that the higher polymerization degree of polymeric proanthocyanidins from litchi fruit stones exhibited higher antioxidant activities than those from litchi pericarps.