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Synergistic effect of ulleungdo stonecrop with licorice-rosemary extract emulsion on antibacterial activity
Licorice and rosemary contain a number of natural phenolic compounds which have a strong antibacterial and antioxidant activity. Ulleungdo stonecrop (US, scientific name: Sedum takesimense Nakai), indigenous island, is also known as a good antibiotic agent and skin whitening agent and is regarded as a promising materials in cosmetics field. Although the antibacterial activity of each material have been reported, little is known about the effect of using them together. Therefore, the purpose of this study was to investigate the synergistic effect on antibacterial activity when licorice and rosemary extract and US were used together. Since licorice and rosemary are lipid soluble materials and US is water soluble material, oil in water (O/W) emulsion system was used for this study. To manufacture O/W emulsions containing three kinds materials, first licorice and rosemary extracts and US was dispersed in soy bean oil and phosphate buffer (pH7) respectively. Decaglyceryl laurate was used as an emulsifier. There was slight decrease (-0.09~-0.46 Δlog) in the number of bacteria when O/W emulsion containing 300ppm of each licorice and rosemary extracts was mixed into B.subtilis. However, adding US (2,700ppm) into aqueous phase caused the rapid decrease in the amount of bacteria to -1.71 ~ -2.96 Δlog which were much higher decrement than US only in normal emulsion (-1.64 Δlog). In particular, there was a noticeable synergistic effect when rosemary extract and US was used together. The results obtained from this study could provide useful information for utilizing licorice and rosemary extracts and US as functional materials in the food and cosmetic areas.
