Total Phenolic Compounds, Carotenoids and <i>In Vitro</i> Antioxidant Activity of Three Traditional Indigenous Medicinal Plants of Saskatchewan, Canada

Abstract

Medicinal plants are an important component in Indigenous cultures. Aralia nudicaulis L., Rubus idaeus L., and Rosa arkansana Porter were analyzed for total phenolic compounds, carotenoids and antioxidant activity by DPPH (2,2-diphenyl-1-picrylhydrazyl), FRAP (ferric-reducing antioxidant power), and ABTS (2,2-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid). The samples were harvested in Saskatchewan, Canada, with the help of an Indigenous Traditional Knowledge Keeper and the analyses were performed by spectrophotometry. The results showed that total phenolic compounds amount ranged from 0.08 to 0.88 mg GAE/mg d.w. and the total carotenoid contents ranged from 0.03 to 1.26 mg/g d.w. The in vitro antioxidant activity ranged from 0.02 to 0.71 μmol TE/mg d.w. by DPPH, from 0.05 to 2.53 μmol TE/mg d.w. by FRAP, and from 0.04 to 1.06 μmol TE/mg d.w. by ABTS. Rosa arkansana leaves stood out with higher amounts of total phenolic compounds (TPC) (0.88 ± 0.02 mg GAE/g d.w.), carotenoids (TC) (1.26 ± 0.03 mg/g d.w.) and antioxidant activity (TAA) by DPPH (0.71 ± 0.01 μmol TE/mg d.w.), ABTS (1.06 ± 0.01 μmol TE/mg d.w.) and FRAP (2.32 ± 0.01 μmol TE/mg d.w.), with the same amount of Rubus idaeus belowground (2.53 ± 0.01 μmol TE/mg d.w.) in last technique (2.32 ± 0.01 μmol TE/mg d.w.). The first principal component describes 83.88% of the total variance and all the variables have high influence on this component (factor loadings: T = 0.976, TC = 0.735, TAA by DPPH = 0.955, FRAP = 0.894 and ABTS = 0.996), demonstrating that these samples do not have large dissimilarity. The second principal component represents 13.64% of the total variance, and the TC is the dominant variable on the second principal component (0.658). Aralia nudicaulis, Rubus idaeus, and Rosa arkansana had interesting amounts of total phenolic compounds, total carotenoids and in vitro antioxidant activity. Rosa arkansana leaves and Rubus idaeus have the highest amount of total phenolic compounds and antioxidant activity in this study. Rosa arkansana leaves are also a good source of carotenoids, and so, they have great potential health benefits and use in industry as a source of bioactive compounds with high antioxidant activity. This study enriches the literature on medicinal plants used by Indigenous people of Saskatchewan and surrounding Canada. More studies are necessary to identify its applications, security and to assess which compounds generate the benefits reported by Traditional Knowledge Keepers.