Phenolic Profiles, Antioxidant, and Inhibitory Activities of Kadsura heteroclita (Roxb.) Craib and Kadsura coccinea (Lem.) A.C. Sm.

Kadsura spp. in the Schisandraceae family are woody vine plants, which produce edible red fruits that are rich in nutrients and antioxidant activities. Despite their valuable food applications, Kadsura spp. are only able to grow naturally in the forest, and reproduction handled by botanists is still in progress with a very low growth rate. Subsequently, Kadsura spp. were listed as endangered species by the International Union for Conservation of Nature and Natural Resources (IUCN) in 2011. Two different Kadsura spp., including Kadsura coccinea (Lem.) A.C. Sm. and Kadsura heteroclita (Roxb.) Craib, are mostly found in northern Thailand. These rare, wild fruits are unrecognizable to outsiders, and there have only been limited investigations into its biological properties. This study, therefore, aimed to comparatively investigate the phenolic profiles, antioxidant activities, and inhibitory activities against the key enzymes involved in diabetes (α-glucosidase and α-amylase) and Alzheimer's disease (acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and beta-secretase 1 (BACE-1)) in different fruit parts (exocarp, mesocarp (edible part), seed, and core) of Kadsura coccinea (Lem.) A.C. Sm. and Kadsura heteroclita (Roxb.) Craib. The results suggested that Kadsura spp. extracts were rich in flavonol (quercetin), flavanone (naringenin), anthocyanidins (cyanidin and delphinidin), and anthocyanins (cyanidin 3-O-glucoside (kuromanin), cyanidin 3-O-galactoside (ideain), cyanidin 3-O-rutinoside (keracyanin), and cyanidin 3,5-di-O-glucoside (cyanin)). These flavonoids were found to be responsible for the high antioxidant activities and key enzyme inhibitions detected in Kadsura spp. extracts. The findings of the present study can support further development of Kadsura spp. as a potential source of phenolics and anti-oxidative agents with health benefits against diabetes and Alzheimer's disease. Besides, exocarp and the core of Kadsura spp. exhibited higher phenolic contents, antioxidant activities, and key enzyme inhibitory activities compared to the mesocarp and seeds, respectively. This information can promote the use of fruit parts other than the edible mesocarp for future food applications using Kadsura spp. rather than these being wasted.