Comprehensive screening and characterization of polyphenol compounds from pasture grasses used for livestock production under temperate region

Pasture grasses and legumes have a wide range of polyphenol compounds of which have potential antioxidant capacity. In recent years, polyphenol compounds from forages have gained attention due to their health-promoting abilities, but comprehensive profiling of these forages is still in shadow. Therefore, the purpose of this study was to comprehensively profile the polyphenol compounds in pasture grasses, legumes and novel forages collected during successive seasons of winter, spring, and summer. A total of 31 compounds were tentatively identified in which 11 compounds are phenolic acid, 10 were flavonoids, and 10 were other polyphenols. Among all forages collected, chicory and perennial ryegrass contained higher phenolic acid concentrations, while plantain, brassica and lucerne contained higher concentrations of flavonoids. Forages harvested during the winter and spring seasons have higher polyphenol concentrations and antioxidant potential than those samples collected in summer. The ethanolic extracts of plantain harvested during winter contained the highest concentration of total phenolic content (16.83 ± 0.95 mg GAE/g DW) and chicory showed total flavonoids content (1.51 ± 0.12 mg QE/g DW) in winter. Plantain harvested during spring showed the highest concentration of total condensed tannins (18.81 ± 0.36 mg CE/g DW). Spring- chicory (21.30 ± 1.42 mg Trolox/g DW), winter- plantain (25.71 ± 0.26 mg AAE/g DW), winter-plantain (0.5 ± 0.07 mg AAE/g DW), spring- plantain (5.33 ± 0.07 mg AAE/g DW), winter-lucerne (4.77 ± 0.12 mg EDTA/g DW), summer-plantain (27.83 ± 0.83 mg AAE/g DW), and winter- plantain (57.87 ± 3.67 mg/Trolox/g DW) showed highest concentration of antioxidant potential in DPPH, ABTS, FRAP, RPA, FICA, •OH-RSA, and TAC assays, respectively. This study suggests that as the season moves from winter to spring to summer, the polyphenol concentrations in the forages decline, probably due to pasture maturity or dry climatic conditions, or a combination of both.