Abstract:

Four proanthocyanidin fractions (F1, F2, F3 and F4) from the red skin of lotus seed were measured for mean
degree of polymerization, and analyzed for chemical composition and structure by infrared spectroscopy, reversed phase
high performance liquid chromatography (RP-HPLC) and reversed phase high performance liquid chromatography coupled
with electrospray ionization mass spectrometry (RP-HPLC-ESI-MS). The results of measurement showed that the mean
degrees of polymerization of F1, F2, F3 and F4 were 2.12, 7.27, 7.85 and 8.16, respectively. Their infrared spectra exhibited
obviously the characteristic stretching vibration of proanthocyanidins, indicating that these proanthocyanidin fractions are
mainly composed of procyanidins. By RP-HPLC-ESI-MS, three types of monomers, four types of dimmers, and two types
of tetramers were tentatively identified in F1. The three types of monomers were catechin, epicatechin, and gallocatechin and
both the four types of dimmers and two types of tetramers were composed of catechin or epicatechin through polymerization.
In addition, the monomers of catechin and epicatechin were identified in F2, F3 and F4 by RP-HPLC. By comparing the HPLC
chromatogram of F1 with those of F2, F3 and F4, it can be speculated that F2, F3 and F4 contain three types of dimmers, and
the content for one of which was higher than those of the others. Meanwhile, an unknown component with relatively high
content existed in F2, F3 and F4.

Key words: red skin of lotus seed, proanthocyanidins, extraction, fractionation, degree of polymerization