Comprehensive structural analysis of polyphenols and their enzymatic inhibition activities and antioxidant capacity of black mulberry (Morus nigra L.).

In this paper, the structures of polyphenols and their bioactivity of black mulberry (Morus nigra L.) cv. 'Heisang No. 1' were comprehensively analyzed. The 11 anthocyanins and 20 non-anthocyanin phenolic compounds were identified and quantified by liquid chromatography high-resolution time-of-flight mass spectrometry (LC-HR-TOF/MS2). The cyanidin-3-glucoside and cyanidin-3-rutinoside were the major anthocyanins in the black mulberry. In addition, the black mulberry showed potent antioxidant capacity as assessed by DPPH, ABTS, and FRAP assays. Black mulberry anthocyanins exhibited stronger inhibition activities against α-amylase, α-glucosidase, and lipase compared to non-anthocyanin polyphenols, with IC50 values of 1.10, 4.36, and 9.18 mg/mL, respectively. The total anthocyanin content of black mulberry crude extracts and anthocyanins was 570.10 ± 77.09 and 1278.23 ± 117.60 mg C3GE/100 g DW, respectively. Black mulberry may be a rich source of polyphenols, natural antioxidants, and effective antidiabetic substances with great potential in the food industry.

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 proanthocyanidins 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 proanthocyanidins had potent α-amylase and α-glucosidase inhibition activities with IC50 values of 0.19 ± 0.01 µg/mL and 0.18 ± 0.006 µg/mL, comparing favorably to commercial drug acarbose. Bird cherry oligomeric proanthocyanidins are a promising starch hydrolase inhibitor for the application of potential functional food components.