| During the processing and storage of food,the growth and reproduction of microorganisms often affect its properties such as appearance,flavor,nutritional content,shelf life which may cause many negative effects.It is critical to use preservatives,bacteriostatic agents to make food better preserved.However,most of the currently used preservatives in the food industry are artificially synthesized products,while their safety has been disputed.Therefore,it is particularly important to develop natural and safe bacteriostatic agents to replace the chemically synthesized preservatives,to further improve food quality,and to protect consumer health.Antibacterial emulsions are emulsions prepared using surfactants,antibacterial agents,and fat-soluble carriers.They have many advantages such as embedding,control-release,and protection of bioactive ingredients,which have greatly improved the antibacterial activity of natural antibacterial agents such as plant essential oils.In recent years,it has become a research hotspot and focus in this field.In the present work,tea saponin(TS),carvacrol and MCT oil are respectively used as surfactant,bacteriostatic agent and mature inhibitor to construct an antibacterial emulsion delivery system.And its stability,antibacterial activity,antibacterial mechanism and application on chilled beef preservation are investigated in depth.On the other hand,Tween 80-stabilized(Tw80)emulsion served as a control to compare the properties of different surfactant stabilized antibacterial emulsion systems.The results can provide the new technical and theoretical insight into the development of novel natural antibacterial emulsions.The main research contents and results are as follows:Firstly,the formula of the tea saponin-based carvacrol antibacterial emulsion is determined by exploring the impacts of surfactant content and oil phase composition on the stability and bacteriostatic properties of emulsion.It consists of 1%tea saponin and 10%oil phase(60%carvacrol+40%MCT Oil),On the contrary,TW80 system needs a higher proportion of surfactant(5%Tween80)and maturation inhibitor(40%carvacrol+60%MCT oil)in order to fabrictethe similar small average droplet diameters stable nanoemulsion(d<190 nm);It was found that the inhibition zone diameter of the TS carvacrol emulsion against S.aureus was 3.57 cm,while the TW80 emulsion against S.aureus was only 1.70 cm;The MIC value of the TS carvacrol emulsion are 3.91 mL/L against S.aureus and 7.81 mL/L against E.colis,while that of Tw80 emulsion are 15.63 mL/L and 31.25 mL/L respectively.The results showed that the antibacterial activity of the TS emulsion is much higher than that of the system stabilized with Tween80,and the TS carvacrol emulsion have a stronger inhibitory effect on S.aureus than on E.coli.Also,the antibacterial emulsion system has an outstanding storage stability since it still remains stable after a storage of 30 days(d<250 nm).Secondly,through observation of cell morphology and the simulation of carvacrol partitioning rate,cell membrane permeability,cell protein leakage and cell membrane potential,the mechanism of action of the delivery system on inhibiting E.coli and S.aureus was explored.The results showed that the conductivity of the bacteria solution of E.coli increased from 126.1?s/cm to 137.7 ?s/cm,and the amount of protein leakage increased from 37.5 ?g/mL to 47.9 ?g/mL without antibacterial emulsion treatment,while,for S.aureus,increased from 133.4 ?s/cm to 137.8 ?s/cm,and 37.8 ?g/mL to 59.2?g/mL respectively.The conductivity of the bacteria solution of E.coli treated with TS carvacrol emulsion increased from 143.8 ?s/cm to 154.8?s/cm,and the amount of protein leakage increased from 82.0 ?g/mL to 104.4 ?g/mL.The electrical conductivity of the bacteria solution of S.aureus increased from 143.2 ?s/cm to 161.2 ?s/cm,and the amount of protein leakage increased from 79.2 ?g/mL to 109.6 ?g/mL;Treated with the TS carvacrol emulsion,the membrane potential of E.coli cells decreased from 409 AU to 234 AU,and the cell membrane potential of S.aureus decreased from 358 AU to 193 AU;Compared to Tween80,the TS carvacrol emulsion makes the bacteriostatic agent(carvacrol)to be transferred to bacterial cells faster and more quickly,which destroys the integrity of cell membrane,leads to the leakage of cell electrolyte and proteins,changes the permeability of cell membrane,and finally leads to cell death.Sum up the aboving results,it was found that the TS carvacrol emulsion has better antibacterial effect than Tw80 antibacterial emulsion,and the delivery system is more destructive to S.aureus than E.coli,which provides theoretical support for the research results of antibacterial activity of the emulsion.Finally,the chilled beef was treated by the antibacterial emulsion delivery system and stored at 4?.The total colony,pH,TVB-N content of beef,and sensory evaluation were measured regularly to envaluate its freshness.The results found that the tea saponin-stabilized delivery system can extend the shelf life of chilled beef to more than 20 days,and the Tween80-stabilized system extends the shelf life of chilled beef to 10?15 days,And the shelf life of the blank group is only about 5 days.The results showed that the system had better preservation effect on chilled beef,and the tea saponin-stabilized system is better than the Tw80 system.In conclusion,natural tea saponin and a major component of plant essential oils(carvacrol)has a synergistic antibacterial effect.By constructing an antibacterial emulsion delivery system,the antibacterial activity of carvacrol is significantly improved.Overall,the formula of the tea saponin-based carvacrol antibacterial emulsion is 1%tea saponin and 10%oil phase(60%carvacrol+40%MCT Oil).Because of the delivery system can make antibacterial agents(carvacrol)to be transferred to bacterial cells faster and more quickly,changing the permeability of the cell membrane,destroying the integrity of the cell membrane,causing leakage of cell electrolytes and proteins,and ultimately leading to bacterial death,Therefore,its antibacterial activity against E.coli and S.aureus are better,and the antibacterial activity against S.aureus is better than that of E.coli.At the same time,Its storage stability is better,can extend the shelf life of chilled beef to more than 20 days effectively. |
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