Characterization of A-type Proanthocyanidins in Peanut Skins Using MALDI-TOF MS
Peanut skin, a low-value agriculture waste product, has drawn lots of research interest in recent years, due to its high content of A-type proanthocyanidins. A-type proanthocyanidins have been believed to contribute to cranberries' anti-UTI (urinary tract infection) effect. In this study, we compared the A-type proanthocyanidins in cranberry and peanut skin crude extracts using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). Many similarities were found in the proanthocyanidin composition of cranberries and peanut skins. New oligomeric and polymeric proanthocyanidins in peanut skins, including heteroproanthocyanidins and proanthocyanidins with sugar moieties or galloyl esters, were tentatively identified. Solid phase extraction (SPE) and HPLC fractionation largely improved MALDI-TOF's ability to detect proanthocyanidins with high degrees of polymerization (DP). By analyzing the identified compounds in each fraction, we were also able to find some interesting elution pattern of the proanthocyanidins on the SPE cartridges and on the HPLC column. For example, the elution order on both the SPE cartridges and the diol phase column generally followed the DP. A-type proanthocyanidins tended to elute earlier than the B-type. Prodelphinidins retained much longer than other proanthocyanidins with the same DP. These findings may help researcher to identify future research directions and develop new separation methods to facilitate the identification of bioactive components in proanthocyanidin-rich plant extracts.