Phenolic profile, antioxidant and enzyme inhibitory activities of Ottelia acuminata, an endemic plant from southwestern China

Abstract

Ottelia acuminata (O. acuminata) is an edible and medicinal aquatic plant endemic to southwestern China. In this work, for the first time, the phenolic composition and contents of different morphological parts of this plant were investigated by HPLC-PDA-ESI-MS2. Their potential antioxidant and enzyme inhibitory activities were also evaluated in vitro. A total of 44 compounds (38 in the inflorescences, 31 in the peduncles, 27 in the leaves), including 2 organic acids, 16 phenolic acids, and 26 flavonoids, were identified, and their levels were significantly different depending on the morphological part. Interestingly, a rarely reported isoflavone (tectorigenin -7-O-glucosyl-4’-O-acetylglucoside) was identified. Flavones (especially luteolin as well as its glycosides) and hydroxycinnamic acids (typically chlorogenic acid) were predominant in the inflorescences, while hydroxycinnamic acids, with a caffeoyl malic acid representative, and flavonols (in particular quercetin glycosides) were the main phenolics in the peduncles and leaves. The inflorescences showed the highest antioxidant activity, followed by the peduncles and leaves, which agreed with their phenolic contents. The phenolics displayed stronger inhibition of yeast α-glucosidase than acarbose with IC50 values in the range of 0.06-0.138 mg/mL in a mixed noncompetitive manner, whereas phenolics inhibit lipase activity by a competitive inhibition mechanism.