Antioxidant Activity and Profile of Phenolic Compounds in Selected Herbal Plants

Herbs are characterized by a high content of biologically active substances that positively affect human health. Phenolic compounds are one of the main bioactive compounds in these plants with highly beneficial properties (e.g., anti-carcinogenic, cardioprotective, immune system support and antibacterial). Therefore, this study aimed to determine the composition of free and bound phenolic compounds and antioxidant activity in 10 different herbs (bogbean leaves, sage leaves, whole Indian hemp, whole heartsease, whole horsetail, whole blessed thistle, whole thyme, chamomile flower, corn silk and pine buds). Phenolic compounds were analyzed using the HPLC-TOF-MS/MS method, total phenolic (TP) and flavonoid (TF) contents were measured using spectrophotometric methods, while antioxidant activity was determined by ABTS and DPPH assays. The highest content of free TP was found in thyme, while sage was characterized by the highest range of these compounds released from ester and glycosidic derivatives by hydrolysis. In turn, the highest values of TF in non-hydrolyzed extracts were found in Indian hemp. The highest values of TF, including bound phenols were observed in extracts obtained from sage leaves. In the analyzed herbs thirty-three phenolic compounds were found, constituting 16 phenolic acids, 9 flavonoids and eight stilbenes. Moreover, the analyzed compounds appeared in the bound form than in the free form. The antioxidant activity of herb extracts differed significantly across varieties (P < 0.05). The research showed that each tested herb possesses its own fingerprint of phenolic compounds and antioxidant properties.