Bioactive compounds from leaves of Taraxacum kok-saghyz

Taraxacum kok-saghyz L.E.Rodin (rubber or Russian dandelion, thereafter referred to as TKS) is a dandelion species native to Kazakhstan, Uzbekistan and north-west China, considered as a promising alternative source of natural rubber (NR) from its roots. It has been stated that, within the process for producing of an economic supply of NR from TKS roots, one of the major challenges is the exploitation of large quantity of byproducts that result from separating and purifying its NR. These include the non-rubber parts of roots and leaves, which must also be separated and converted into products and/or raw materials of value to different commercial sectors. A plenty of literature deals with the antioxidants from leaves in Taraxacum genus species except than in TKS. Thus, the specific aim of this study was to investigate the possible exploitation of TKS leaves, which represent a rubber byproduct, as a source of phenolic compounds with antioxidant properties for potential applications in forage, nutraceutical and pharmacological fields. Two accessions (TKS016, TKS018) grown in Sardinia (Italy) under Mediterranean conditions were investigated at vegetative and flowering stages, respectively. Leaf samples were kept on ice and stored at -80 °C, until lyophilisation. The procedures for sample preparation were according to (Re et al., 2019). Antioxidant capacity [ABTS ((2,2'-azinobis (3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt)) and by DPPH (1,1-diphenyl-2-picrylhydrazyl) assays], total phenolics and total flavonoids were quantified following procedures previously reported by Sulas et al., 2016. Analysis of phenolic compounds was performed on an HPLC instrument and the chromatographic separation was carried out according to Piluzza et al., 2019. The leaves of TKS018 had the highest antioxidant capacity values (19.6 mmol trolox equivalent antioxidant capacity 100 g -1 ), total phenolic (106.4 g gallic acid equivalent kg -1 ), and total flavonoid contents (22.9 g catechin equivalent kg -1 ). At both phenological stages, TKS016 showed significantly lower values than TKS018 in DPPH, and total phenolic. Among twentyone phenolic compounds screened, six individual molecules were identified, namely chlorogenic, cryptochlorogenic, caffeic, sinapic, chicoric and 3,4-dimethoxycinnamic acids. In particular, chicoric acid (8.53 - 10.68 mg g -1 DW) and chlorogenic acid (4.18 - 7.04 mg g -1 DW) were the most abundant identified in leaves of TKS. Chicoric acid has been already identified as the major compound occurring in T. officinalis aerial part as our results. A study on T. formosanum Kitam, a chinese medicinal herb, quantified chicoric acid as the predominant phenolic acid in its plant extracts. It has been reported that chicoric acid possesses various functional properties including antioxidant, antivirus and immunoregulation. Based on our results, T. kok-saghyz represents an important source of chicoric acid with potential application as antioxidant to be used as herbal medicine and nutrition for production of healthy food/feed. Additionally, leaves exploitation as an antioxidant source might contribute to an economic supply of TKS rubber chain.