Phenolic Ketone Contents and Antioxidant, Antibacterial Properties and Inhibitory Tyrosinase Activity of the Ethyl Acetate Extracted from Calendula officinalis L.

In this paper, the total phenolic and total flavonoid content, in vitro antioxidant and antibacterial activities of ethyl acetate extraction (EA phase) and its related extracted phases of Calendula officinalis L were studied. The content of five phenolic ketones, namely gallic acid, chlorogenic acid, caffeic acid, rutin and ferulic acid was analyzed by high performance liquid chromatography (HPLC). The results showed that the total phenolic ketone content, antioxidant and antibacterial activities of EA phase were higher than other extracted phases, the total phenolic ketone content of EA phase was 330.760±4.640 mg/g, rutin and gallic acid were the highest in EA phase, which were 0.978±0.203 and 0.230±0.301 mg/g, respectively. The antioxidant activity of EA phase was close to that of the positive control V_C, and moderately sensitive to Staphylococcus aureus. The enzyme kinetic experiment showed that EA phase had a good inhibiting effect on tyrosinase activity with an IC₅₀ of 0.965±0.001 mg/mL, which was better than that of the positive control arbutin. The results demonstrated that EA phase suppressed the activity of tyrosinase in a reversible mixed-inhibition, and the inhibition constants K_I and K_IS were 0.254 and 5.577 mg/mL, respectively. The best antioxidant, antibacterial and tyrosinase inhibiting effects of EA phase were correlated with the high content of total phenols and total flavonoids and their richness in functional components, which were more easily extracted by ethyl acetate solvent.