The Mechanism Of Phloretin Inhibits Listeria Monocytogenes' Biofilm And The Study Of Sterilization Combining With Ultrasound Technique

Phloretin possesses dihydrochalcone structure,which is a kind of flavonoids.Phloretin has broad-spectrum antibacterial activity,and inhibits various food-borne pathogens.Biofilm is a typical group behavior associated with quorum sensing(QS).A suitable growth environment for microbes is provided by biofilm,and biofilm enhances the resistance to adverse environment.The extremely strict food sterilization should be achieved to reduce the harm.Thermal sterilization damages the food's nutrients and deteriorates the food quality.It is critical to develop an efficient non-thermal sterilization technique.In this study,we explored the effect of phloretin on Listeria monocytogenes biofilm and its mechanism.We combined phloretin and ultrasound and constructed the sterilization kinetic model to evaluate the sterilization efficacy.Moreover,we used the synergetic sterilization technique to cloudy apple juice.The main results of this study are as following:1.We used sub-MIC phloretin to treat L.monocytogenes at 37? and 4?.The results show that L.monocytogenes biofilm maximum inhibitory rate was up to 60%when 20 ?g/mL phloretin was used.The capacity of biofilm adhesion and aggregation of L.monocytogenes were declined.Meanwhile,biofilm protective capacity was impaired.The biofilm thickness of the treated group was decreased by 2 ?m approximately at 20 ?g/mL phloretin treatment.2.HPLC and RT-qPCR techniques were used to determinate the signal molecule concentration and the relative transcript level of genes related to QS.The concentration of autoinducer-2(AI-2),QS signal molecule,was decreased to 0.5?g/mL.The quorum sensing related genes were inhibited by phloretin.The relative transcript level of the Lux S system and agr system genes was reduced by 50%and 80%,respectively.3.Combined 700 W ultrasound and 300 ?g/mL phloretin ultrasound We found that synergistically treatment through 300 ?g/mL phloretin combining 700 W ultrasound caused 6.5 and 6.6 log CFU/mL reduction for E.coli and S.aureus,respectively.The experimental D-value of E.coli was 7 minutes,and S.aureus was 5.4 minutes,which is lower than the theoretical value.According to the Weibull sterilization model,the synergism efficiency was 11.4%for E.coli and 6.9%for S.aureus.4.Ultrasound combined with phloretin was used in apple juice sterilization.700 W ultrasound declined the browning index in apple juice.When synergistically treated with ultrasound and phloretin,no microbes grew in apple juice after 28 days at 37?.Moreover,apple juice had a high quality after storing.This study has shown that phloretin is effective to inhibit biofilm formation of L.monocytogenes,disrupting biofilm function and interfering the quorum sensing.Furthermore,the combination of phloretin and ultrasound synergistically inactivated E.coli and S.aureus.Ultrasound-phloretin treatment extended the shelf-life of apple juice.The study provides a theoretical significance to promote the application in food industry.