Preparation And Antimicrobial Activities Of Clove Oil Emulsion Systems

Clove oil extracted from the flower buds of clove, which major component is consideredto be eugenol, shows strong antimicrobial activities. However, some special properties ofclove oil limit its application in food industry, such as volatile, insoluble, sensitive to light andheat and so on. Nano-scale emulsion systems can improve the solubility, stability andavailability of fat-soluble bioactive substance, thus they can be used for embedding systems.Firstly, clove oil was taken as the research object and different types and differentparticle sizes of emulsion systems were prepared. The formula of clove oil microemulsionswas optimized by appointing the area of microemulsion region in pseudo-ternary phasediagram and the minimum dilution ratio as the primary criterions in this study. The resultsshowed that Cremophor EL30was the best surfactant for preparing microemulsions and thebest weight ratio of surfactant to cosurfactant (Km value) was2. The results of conductivityand rheology indicated that W/O region ranged up to a water content of51%~54%and O/Wregion was achieved when the water content was greater than64%~67%. On this basis,Cremophor EL30and Tween60, which showed better emulsifying abilities amongCremophor and Tween series surfactants, were used to prepare nanoemulsions byhigh-pressure homogenization. The results showed that ostwald ripening was delayed whensoybean oil was added. Nanoemulsions (110.30nm and208.10nm) were prepared by8%clove oil,2%soybean oil and2%Tween60. In addition, nanoemulsions (104.35nm and217.00nm) were prepared by6%Cremophor EL30at the same oil phase. Moreover,microemulsions and nanoemulsions with smaller particle size could be stored for at least120days and one month, respectively. However, creaming was observed when nanoemulsionswith larger particle size were stored after15days.Secondly, antimicrobial activities of microemulsions and nanoemulsions were studied.The minimum inhibition concentrations (MIC) of clove oil against E. coli and S. aureus were0.625μl/ml and1.250μl/ml. MICs of nanoemulsions were the same with clove oil, but lowerthan that of clove oil microemulsions, which indicated that microemulsions systems with highconcentrations of surfactants could reduce the antimicrobial activities of clove oil.Microemulsions formulated by Triton X-100were also prepared in order to verify thisphenomenon, which MIC was higher than clove oil. Among the three microemulsions, theantimicrobial activities of microemulsions formulated by Triton X-100were the strongest andindependent surfactant in microemulsions showed15~35%inhibition against test bacteria,indicating that antimicrobial activity of surfactant itself influenced little on the antimicrobialactivities of emulsion systems. Moreover, mode of action studies comfirmed that interactionbetween cell membrane and microemulsions caused change in membrane structure andfunction, lead to loss of bacterial viability, which indicated that antimicrobial activities ofmicroemulsions were related to the structures of surfactants. In addition, the growth curves oftest bacteria showed that antimicrobial activities of emulsion systems were independent oftheir particle sizes.Finally, the preservation effects of clove oil emulsion systems in chilled meat were compared. The results demonstrated that the increasing of total volatile basic nitrogen(TVB-N), pH value, aerobic plate count (APC) and coliforms were reduced by the addition ofclove oil microemulsions and nanoemulsions. No obvious preservation effect was observedwhen chilled meat was treated with MIC concentration of microemulsions and nanoemulsions.However,2MIC concentration of them extended the shelf life to6and10days, respectively.Clove oil microemulsions and nanoemulsions showed prolonged antimicrobial activities.