Effect Of External Factors On Antimicrobial Activity Of Cinnamon Oil

Food safety problems and economic losses caused by food-related microorganisms have drawn more and more attentions. Spice oil, regarded as one of most potential natural preservative agents, has showed broad-spectrum antimicrobial activity against food-borne pathogenic bacteria and spoilage bacteria, and ability in extending the food shelf-life. However, antimicrobial activity of spice oil may be effect by abiotic factors (such as food ingredients and food processing conditions) and biotic factor (strss reponse of adapted bacteria).Cinnamon oil (CO) was elected from nine spice oils by minimum inhibitory/bactericidal concentration (MIC/MBC) and diameter of inhibition zone (DIZ) tests against Escherichia coli and Staohylococcus aureus. The composition of CO was analyzed by GC-MS. In order to study the effect of food ingredients and food processing conditions on antimicrobial activity of CO, time-kill curves test was conducted and kinetic curves observed by OD600 were fitted by Modified Gompertz. Furthermore, effect of strss reponse on CO antimicrobial activity were studied after exposing bacteria to sublethal amount of CO.(1) All nine spice oils revealed the antimicrobial activity against tested bacteria and CO showed the minimum MIC/MBC and the maximum DIZ against E. coli (250?L/L,500?L/L. 31.8±1.7mm) and S. aureus (500?L/L,2000?L/L,30.5±0.5mm). E. coli and S. aureus cells were killed rapidly by MIC CO. However,1/4 MIC and 1/2 MIC CO showed inhibition against tested bacteria, instead of lethal. Main compositions of CO were found to cinnamyl aldehyde (87%) and cinnamyl acid (11.04%).(2) Antimicrobial activity of CO was effected differently by three food ingredients. Antimicrobial activity of CO was enhanced by protein and carbohydrate. With the presence of 1/4 MIC CO, the lag phases of E. coli were prolonged in both beef broth and potato broth, compared to Luria-Bertani broth. For S. aureus, the lag phases were prolonged to more than 24h in two food media. Conversely, antimicrobial activity of CO was impaired by sunflower oil. DIZs of E. coli and S. aureus were reduced with the increasing of sunflower oil content.(3) Antimicrobial activity of CO against S. aureus and E. coli was damaged after treating under 121? for 1 h. CO treated under 4?,25?,60? did not effect CO antimicrobial activity. With the presence of MIC CO, survival rate of S. aureus cultured in 4? was higher than 37 ?, and cultured in acid condition (pH=4) was higher than alkaline and neutral condition (pH=10).(4) Survival profile of E. coli, overnight pre-adapted by 1/4MIC and 1/2 MIC CO, was related to may factors, like exposing concentration of CO, exposure time and stress agents. Successive CO-adaptation of E. coli reduced CO inhibitory concentration to 1/2MIC. Conversely, stress response of pre-adapted S. aureus showed no effect on antimicrobial activity of CO and stress conditions.