Antihyperglycemic, antioxidant activities of two Acer palmatum cultivars, and identification of phenolics profile by UPLC-QTOF-MS/MS: New natural sources of functional constituents

This research aimed to compare the antihyperglycemic and antioxidant abilities, and to characterize the bioactive constituents of two Acer palmatum cultivars, Acer palmatum 'Atropurpureum' (APA) and Acer palmatum Thunb (APT). Dry materials were respectively extracted with 70% and 90% methanol, followed by sequentially fractionation with ethyl acetate and n-butanol. The phytochemical profile of selected fraction was determined by using UPLC-QTOF-MS/MS. APT is a better source of natural antioxidants and α-glucosidase inhibitors than APA due to its higher total phenolic content (TPC), and stronger antioxidant and α-glucosidase inhibitory activities. The highest total phenolic and total flavonoid content were found in the ethyl acetate fraction (EAF) of 90% methanol extract of APT (468.49 mg GAE/g Extract) and 70% methanol extract of APA (142.60 mg QuE/g Extract), respectively. The EAF of 70% methanol extract of APT gave the strongest DPPH· scavenging ability, ABTS+· scavenging ability and α-glucosidase inhibitory, with the IC50 values of 7.06, 4.18 and 1.99 μg/mL, respectively. The latter two were much higher than that of individual positive control. HPLC analysis revealed similar phytochemical profiles of all EAFs. Twenty-five compounds, including 3 organic acids, 5 phenolic acids, 8 tannins, 7 flavonoids and 2 proanthocyanidins, were identified or tentatively identified from APT, with tannins and flavonoid glucosides as the major active compounds. The results indicated a strong potential of Acer palmatum as a natural source of excellent antioxidants and antihyperglycemic compounds in the prevention and treatment of type II diabetes and its complication.