Studies On Effects Of Citral,Cinnamaldehyde And Tea Polyphenols On Mixed Biofilm Formation By Food-borne Pathogens

In the food industry, due to the unique microstructure and resistant ability of biofilm. prevention and elimination of bacteria biofilm formation have always been major difficulty in food processing. In recent years, some studies suggest that natural products can effectively decrease the biofilm formation, and avoid the residual of disinfectant, which present desired prospects to prevent biofilm formation effectively in food processing. There are no studies on effects of citral. cinnamaldehyde and tea polyphenols about mixed biofilm formation by food-borne pathogens. Therefore, this study would give further understand natural products on the regulation mechanism of biofilm. and find effective means to prevent biofilm infections of foodborne pathogens. There are a certain scientific significance and realistic significance.In this study, foodborne mixed (S.aureus20and S. enteritidis07mixed culture) biofilm model to study on the biofilm formation was established a and quorum-sensing signal molecules of AI-2were analyzed in sub-MIC of citral. cinnamaldehyde and tea polyphenols..And what is more, after treated with the natural products, the changes of sensitivity of the mixed biofilm to common disinfectants were demonstrated. The main results were as follows:1. Minimum inhibitory concentration (MIC) of S.aureus20and S. enteritidis07for citral. cinnamaldehyde. and tea polyphenols were determined by a microtitre broth dilution method, found that the MIC value of citral was0.8μg/ml and the MIC value of cinnamaldehyde was0.4μg/ml for both microbes. The MIC value of tea polyphenols against the S. aureus20and S. enteritidis07was300and600μg/ml respectively.2. According to the MIC value, concentration of natural products added were designed to1/8MIC.1/4MIC.1/2MIC, MIC. The adhesion rates of mixed strains in different concentration of additives were determined by a microtitre plate assay. The results showed that citral inhibited the formation of the mixed biofilm at sub-inhibition concentrations (p <0.05). Cinnamaldehyde at the concentration of0.05μg/ml did not inhibit the mixed bacteria adhesion rate (p<0.05). However, when its concentration was0.1μg/ml, the mixed biofilm formation ability was reduced (p＜0.05). Tea polyphenols with concentration of＞75μg/ml inhibited the mixed biofilm formation (p<0.05). with increasing concentration decreasing the film formin aability. 3. The microbial community structure and distribution on the surface of stainless steel was observed and analyzed by SEM and plate colony counting. The results indicated that food additive-treated mixed biofilm had a structure with sparse colonies, less extra cellular material and the viable cells on the stainless steel was significantly less than the control group. This results proves three natural food additives could reduce the mixed-species biofilm on stainless steel.4. Activity of AI-2was measured by V. harveyi BB170bioluminescence. showed that sub-MIC citral could reduce the synthesis of AI-2in mixed bacteria. However. AI-2was induced by cinnamaldehyde. Tea polyphenols also induced AI-2excretion from mixed bacteria when the concentration was between75μg/ml and150μg/ml, but AI-2decreased significantly when the concentration>300μg/ml. The differences were statistically significant.5. After added1/4MIC natural products, sensitivity for disinfectant (hydrogen peroxide, sodium hypochlorite. peracetic acid) of mixed biofilm were determined by a microplate method. The results showed that all three natural products significantly increased the sensitivity of mixed biofilm to disinfectants. The resistance of mixed-species biofilm to hydrogen peroxide disinfectant was reduced by2-10fold, sodium hypochlorite2-4fold and peracetic acid4-8fold.