Studies on structures and activities of initial Maillard reaction products by electrospray ionisation mass spectrometry combined with liquid chromatography in processing of red ginseng

► Four initial Maillard reaction products (MRPs) were identified from red ginseng (RG). ► They showed good α-glucosidase inhibition and antioxidant activities. ► Initial MRPs are new active ingredients of red ginseng. ► Effective improvement on the preparation of RG was implemented. Electrospray ionisation-mass spectrometry (ESI-MS) was applied to analyse the water-soluble extract of red ginseng (RG). Several new compounds were produced from the Maillard reaction during the steaming and drying process for preparing RG. Both the tandem electrospray ionisation (ESI-MSn) and Fourier transform ion cyclotron resonant mass spectrometric (FT-ICR-MS) data of these products proved that they were the initial Maillard reaction products (MRPs) of maltose with glutamic acid/aspartic acid, which were specific components in RG. In addition, their anti-diabetic and antioxidant activities were examined in vitro. The anti-diabetic activities were evaluated by studying the α-glucosidase inhibition using ultrafiltration LC–MS/MS techniques, while the antioxidant activities were investigated by UPLC–ESI-MS method. The results demonstrated that four initial MRPs in RG were identified as α-glucosidase inhibitors, and showed marked scavenging effect on the hydroxyl radical (OH). Based on these studies, the processing method of RG was improved to generate more active compounds.