Inhibition of enzymatic browning and antioxidant activities of Marrubium vulgare L extracts: A promising natural solution

Marrubium vulgare L. (苦薄荷或) has been traditionally utilized in Traditional Chinese Medicine (TCM) for its cooling, detoxifying, and phlegm-resolving properties. Despite its historical use, limited pharmacological evidence exists regarding its phytochemical profile and antioxidant mechanisms in relation to enzymatic browning. Methanolic and aqueous extracts from the leaves and stems of M. vulgare were assessed for total phenolic, flavonoid, and condensed tannin content. Antioxidant activities were evaluated using DPPH, ABTS, and β-carotene bleaching assays. Inhibitory effects against peroxidase (POD) and polyphenol oxidase (PPO) were examined through enzyme kinetics. Methanolic leaf extracts exhibited the highest phenolic (35.36 ± 0.42 mg GAE/g DW) and flavonoid content (20.56 ± 0.35 mg QE/g DW), correlating with superior antioxidant activity (IC 50 = 20.83 ± 0.62 μg/mL in DPPH assay). Condensed tannins were most abundant in aqueous stem extracts. Enzyme inhibition studies revealed mixed-type inhibition for POD and competitive inhibition for PPO, with methanolic leaf extracts being the most potent (51.40% PPO inhibition; Km = 0.810 mM, Vmax = 0.595 ΔA/min). These results highlight the pharmacological relevance of M. vulgare , particularly its leaf extracts, as natural antioxidants and anti-browning agents. The variation in inhibition mechanisms suggests differential interaction of bioactive compounds with enzyme targets, aligning with their traditional TCM usage for internal heat and inflammation. M. vulgare exhibits significant antioxidant and enzymatic inhibitory properties, supporting its development as a multifunctional ingredient in food, cosmetic, and medicinal applications.