Profiles and α-Amylase Inhibition Activity of Proanthocyanidins in Unripe Manilkara zapota (Chiku)

Proanthocyanidins in unripe Manilkara zapota (chiku) were isolated using solvent extraction followed by Sephadex LH-20 fractionation with a yield of 0.9%. HPLC analysis using a diol column revealed well-resolved oligomers ranging from dimer to hexamer. The majority of the proanthocyanidins are composed of higher-degree oligomers appearing as one large peak in the chromatogram. Analysis of the proanthocyanidins using LC/MS showed that (epi)­gallocatechins were the dominant extension unit in the proanthocyanidins. In agreement with this result, thiolysis treatment of the proanthocyanidins using mercaptoacetic acid produced thioether derivatives of (epi)­gallocatechins as the major product and (epi)­gallocatechin gallate derivatives as the minor product. The mean of the degree of polymerization was estimated to be 9.0. From MALDI-TOF MS, B-type gallocatechin oligomers up to decamer could be detected. The unripe chiku proanthocyanidins are thus good starting material for preparation of (epi)­gallocatechin derivatives. The proanthocyanidins was shown to inhibit α-amylase with an IC₅₀ value of 4.2 ± 0.2 μg/mL and inhibit α-glucosidase with an IC₅₀ of 16.6 ± 0.3 μg/mL