Screening for Antioxidant Effects and Chemical Profiles of Different Extracts of Rheum ribes Parts

Rheum ribes L. (rhubarb) is a valuable plant that is consumed raw and cooked and contains important secondary metabolites. This study aimed to investigate the chemical profile and biological activities of different extracts (ethyl acetate, methanol, and water) of aerial parts and roots of R. ribes. Antioxidant and enzyme inhibitory properties were examined for biological activities. The antioxidant properties were examined by various chemical tests, including free radical scavenging (2,2'-azino-bis[3-ethylbenzothiazoline-6-sulfonic acid] and 2,2-diphenyl-1-picrylhydrazyl), reducing the ability (cupric reducing antioxidant capacity and ferric reducing antioxidant power), metal chelation and phosphomolybdenum. The inhibitory effect of the extracts was investigated against cholinesterase, amylase, glucosidase, and tyrosinase. In addition, the total amounts of phenolics and flavonoids in each extract were detected by spectrophotometric methods. The chemical compounds of the extracts were identified using liquid chromatography-electrospray ionization tandem mass spectrometry technique. The extraction solvents changed the total phenolics and flavonoids content, and the highest total phenolics contents of both parts were found in the methanol extract (root: 140.97 mg gallic acid equivalent (GAE)/g; aerial parts: 74.56 mg GAE/g). In the chemical profile, it was found that hesperidin is the main component in the extracts of the aerial part (613.48–12194.83 µg/g of extract), while in the root extracts, the dominant components are catechin (799.11–3230.44 µg/g extract) and gallic acid was (184.03–960.58 µg/g extract). The methanol extract of the roots provided the best radical scavenging and reducing ability. In contrast, the methanol extract of the aerial parts had the greatest metal chelating ability (62.05 mg ethylenediaminetetraacetate equivalent/g). The best acetylcholinesterase and butrylcholinesterase abilities were determined in the methanol extracts of both parts. However, the ethyl acetate extracts were the most active on amylase. Our results suggest that R. ribes can be considered a valuable source of bioactive compounds for developing health-promoting applications.