Abstract: Ultrasonic-assisted organic solvent extraction was used to obtain soluble anthocyanins from black soybean seed coat, and bound anthocyanins from the extraction residue were obtained by treatment with acid, alkaline, sequential acid/ alkali hydrolysis or the reverse sequence. By ultra-high performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry (UPLC-ESI-QTOF-MS), a total of 17 anthocyanin components, including 11 anthocyanin glycosides: delphinidin-3-O-glucoside, delphinidin-3-O-galactoside, petunidin-3-O-glucoside, petunidin-3-O-galactoside, pelargonidin-3-O-rutinoside, cyanidin-3-O-glucoside, cyanidin-3-O-galactoside, pelargonidin-3- O-hexoside, peonidin-3-O-hexoside, pelargonidin-3-O-(6”-malonyl glucoside) and apigeninidin-3-O-(6”-malonyl glucoside); and 6 anthocyanin aglycones: delphinidin, cyanidin, petunidin, pelargonidin, apigeninidin, and peonidin, were identified from these extracts. High performance liquid chromatography coupled with electrospray ionization triple quadrupole mass spectrometry (HPLC-ESI-QQQ-MS) was used to accurately quantify the content of anthocyanins. The total content of bound anthocyanins in the acid extract was the highest. In addition, in the soluble anthocyanin extract, anthocyanins were present mainly in the form of anthocyanin glycoside with lesser amounts of aglycons, whereas in the bound anthocyanin extract, anthocyanin aglycons were the main components but glycosides were rare.

Key words: ultra-high performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry, high performance liquid chromatography coupled with electrospray ionization triple quadrupole mass spectrometry, black soybean seed coat, soluble anthocyanin, bound anthocyanin