Extracts of Southern African aquatic and wetland plant species as effective tyrosinase inhibitors

South Africa harvests approximately 19 500 tonnes of medicinal plants annually for the treatment of various ailments and an additional 6000 tonnes is exported globally for the development and design of cosmetic and medicinal products. South Africa is home to 30 freshwater and marine ecological regions, however, medicinal plant species from these semi-aquatic and aquatic habitats are largely understudied in comparison to other biomes. The lack of knowledge and reported pharmacological activity of these species may be hindering the potential contribution to the herbal medicine and personal care markets. South Africa is Africa's largest market for cosmetic and personal care products and in 2018 this sector reported 3.2 billion US dollars in revenue. Eighteen (18) Southern African freshwater aquatic and wetland plant species were selected and screened for their potential as cosmeceutical ingredients by investigating their antibacterial, anti-tyrosinase and cytotoxicity. The extracts of Erythrina zeyheri and Plantago longissima exhibited antimycobaterial activity with MIC values of 125 µg/mL. Two extracts of the genus Cyperus, C. marginatus and C. sexangularis showed tyrosinase inhibition with IC₅₀ values of 75.03 and 64.26 µg/mL, respectively. Carex rhodesiaca and Gunnera perpensa both exhibited dual antimicrobial activity against Cutibacterium acnes with MIC values of 250 and 125 µg/mL, respectively and anti-tyrosinase activity with IC₅₀ values of 64.71 and 70.43 µg/mL. Persicaria senegalensis exhibited anti-tyrosinase activity with an IC₅₀ of 71.59 µg/mL. Fractionation of P. senegalensis yielded F14 with an IC₅₀ of 68.77 µg/mL against tyrosinase enzyme activity. Purification of F3 yielded (24S)-Stigmast-5,22(E)-dien-3-β-ol which is the first report of this compound from this species. This study provides scientific validation of the traditional use of the selected species and provides proof of concept for further investigations of these extracts as potential active ingredients in the personal care sector.