Structure, degree of polymerization, and starch hydrolase inhibition activities of bird cherry (Prunus padus) proanthocyanidins

The structure of proanthocyanidins extracted from bird cherry fruits was characterized by HPLC-ESI/MS2 and MALDI-TOF/MS analyses, and their subunits and mean degree of polymerization (mDP) were investigated by thiolysis reaction, and the inhibition activity against starch hydrolases measured using the high-throughput turbidity assay. This is the first mass spectrometric analysis to thoroughly investigate the structure and mDP of proanthocyanidins in bird cherry fruits. Bird cherry proanthocyanidins were categorized as oligomeric proanthocyanidins (mDP = 5.6), which constituted of (epi)gallocatechins and (epi)catechins. The proanthocya-nidins increased from a (epi)gallocatechin-[(epi)catechin]3 tetramer to a (epi)gallocatechin-[(epi)catechin]11 dodecamer through the addition of one (epi)catechin with both A-type and B-type linkages. The proanthocya-nidins had potent alpha-amylase and alpha-glucosidase inhibition activities with IC50 values of 0.19 +/- 0.01 mu g/mL and 0.18 +/- 0.006 mu g/mL, comparing favorably to commercial drug acarbose. Bird cherry oligomeric proanthocya-nidins are a promising starch hydrolase inhibitor for the application of potential functional food components.

Automated summary

The structure and mean degree of polymerization (mDP) of proanthocyanidins in bird cherry fruits were thoroughly investigated for the first time using HPLC-ESI/MS2 and MALDI-TOF/MS analyses. The proanthocyanidins in bird cherry fruits were identified as oligomeric proanthocyanidins (mDP = 5.6) composed of (epi)gallocatechins and (epi)catechins. These proanthocyanidins showed significant inhibition activity against starch hydrolases, indicating their potential as functional food components.