Antioxidant Activities of Sonchus oleraceus L.
Authors:   , Mawalagedera Sundara Mudiyanselage Maheshini Rangika 
Published: November 2021

<p>Supernumerary free radicals and other reactive species can cause oxidative damage in animal cells, potentially leading to non-infectious diseases. Diets rich in low molecular weight antioxidants (LMWAs) may prevent or arrest the pathogenesis of these diseases. Leaves of Sonchus oleraceus L. may be an excellent dietary LMWA source for humans given their apparent strong antioxidant activities in vitro. However, different S. oleraceus plants vary in their antioxidant capacity. Nothing is known of possible environmental effects on antioxidant potential. Equally, the effects of cooking and gastrointestinal digestion are unknown. The goals of this research were: (i) to study the effects of plant age, locality, and abiotic stressors on antioxidant potential; (ii) to study the effects of cooking and in vitro gastrointestinal digestion on antioxidant activity and uptake in human cells; and (iii) to study extractable antioxidant activities of S. oleraceus cell suspension cultures in relation to abiotic stressors.   Antioxidant activities and levels of total phenolics, hydroxycinnamic acids and ascorbate increased as plants aged. An ecotype from Acacia Bay had a higher phenolic content and antioxidant activities than one from Oamaru; these differences were maintained across generations as well as in calli from in vitro cultures. This indicates heritability and genetic fidelity of antioxidant potential.   Chilling and salinity had variable effects on concentrations of phenolics and antioxidant activities in plants, and the combination of the two stressors was not synergistic. This indicates that these two stressors share signalling and response pathways. Stressor-induced increases in antioxidant activities of leaf extracts correlated with improved cellular antioxidant activities (CAA) inside HepG2 cells. Antioxidants were released from leaves following in vitro gastrointestinal digestion, which were then subsequently uptaken by Caco2 and HepG2 cells wherein they displayed CAAs. Thus, elevated levels of antioxidants in stressor-imposed plants provide potentially more antioxidant protection to live human cells.  Caftaric, chlorogenic and chicoric acids accounted for 92% of the phenolic compounds in S. oleraceus leaves. Of these, only chlorogenic acid was inducible by stressors, both in intact plants and in calli. In young stressor-applied plants, chlorogenic acid was enhanced to the levels achievable with plant ageing.   Boiling leaves prior to digestion did not diminish the caftaric and chlorogenic acid levels released through digestion, but chicoric acid levels were. Out of the nine phenolic compounds in leaves, only chicoric, chlorogenic and caftaric acids were released into the medium during in vitro gastrointestinal digestion. Digestion of leaves resulted in effective release of caftaric and chlorogenic acids from leaves but the levels of released chicoric acid were diminished by digestion.  This study offers insights into the factors that influence the antioxidant potential of S. oleraceus L. in vivo, in vitro, during cooking and in vitro gastrointestinal digestion. These results provide the foundation for: (1) encouraging the consumption of its fresh shoots as an antioxidant rich food; (2) further improving its antioxidant activities through manipulation of agronomy, ecotype and breeding; (3) developing its cell cultures as a commercial platform for phyto-antioxidant production aimed at formulating dietary supplements or food additives in biopharmaceutical industry.</p>