Extractable and non-extractable bound phenolic compositions and their antioxidant properties in seed coat and cotyledon of black soybean (Glycinemax (L.) merr)

- Bound phenolics of black soybean were extracted by acid/alkali hydrolysis.
- Sixty extractable phenolics and 53 bound phenolics were qualified in black soybean.
- Twenty-eight extractable or bound phenolics were quantified in black soybean.
- The antioxidant activity results of all the extractions correlate well with TPC.

Both extractable (EPE) and non-extractable bound phenolic (BPE) in the seed coat and cotyledon of black bean were investigated in the present study. Their total phenolic contents (TPC) and antioxidant activities (DPPH, ABTS and FRAP) were evaluated, and the phytochemical compositions of EPE and BPE in both seed coat and cotyledon of black soybean were identified and quantified (Glycinemax(L.) merr) by UPLC-ESI-QTOF-MS/MS and UPLC-ESI-QqQ-MS/MS. In the present study, a total of 112 and 78 compounds were identified or tentatively characterized in the black soybean EPE and BPE, respectively, with the majority being phenolic acids and flavonoids. Seed coat contains more abundant phenolics than that of cotyledon in all fractions. In addition, our results indicated that acid hydrolysis is more thorough than alkaline hydrolysis in the extraction of bound phenolics of black soybean. Our study provides available information for non-extractable bound phenolic constituents and their distribution in the seed coat and cotyledon of black soybean.