Preparation Of Thyme Microcapsule With Emulsion Templates By Layer-by-layer Self-assembly Method And Its Controlled Release And Antibacterial Effect Research

Thyme oil is rich in thymol and carvacrol,phenolic compounds which are the main components responsible for the antimicrobial and antioxidant activity of thyme oil.All these bioactive components consisting in essential oils are extremely sensitive when it exposureed to light,heat or oxygen or interact with other compounds in complex food formulations will lower its antibacterial and antioxidant activity.Microcapsule technology could not only keep active ingredients,cover unpleasant odors because of the physical barrier of wall materials,but also realize the essential oil of controlled release,so as to solve the application of essential oil in the food field.In this study,thyme oil microcapsules were prepared with emulsion templates by layer-by-layer self-assembly method,the morphology and properties,release kinetics,antibacterial activity were evaluated,respectively.The results were as follows:1.Using chitosan and sodium alginate as wall materials,thyme oil as core material,the microcapsules were prepared with emulsion templates by LBL self-assembly method.The particle size and Zeta potential were used as evaluation indexes of the emulsion templates,taking the embedding rate as the evaluation index of microcapsules.The optimal preparation conditions obtained by single factor and orthogonal experiments were as follows: homogenization pressure of the microfluidics,62 MPa;homogenization cycles,six;the addition of NaCl,0.3%;and pH,8.Under this condition,the emulsion template was obtained,and the average embedding rate of microcapsules was 71.13%.The study found that the embedding rate of microcapsules was positively correlated with the size of the emulsion template in a certain range,and negatively correlated with the absolute value of the Zeta potential.2.The surface potential of microcapsule were positive and negative alternately changed.Chitosan and sodium alginate were successfully self assembled on the emulsion template through the electrostatic interaction.The size of microcapsules increased with the increase of assembled layers.The thickness of every layer is about 10 nm.According to the infrared spectrum analysis,the wall material has not changed significantly during the self-assembly process,chitosan and sodium alginate are combined to form microcapsules through electrostatic interaction.According to the particle size analysis,the average size of the microcapsules with 4 layers was 140 nm,and the size was uniform.The results of scanning electron microscopy and transmission electron microscopy showed that the microcapsules with good dispersion,smooth surface and no apparentporosity.By fluorescence microscopy,it was found that the thyme oil was well embedded in the microcapsules,and the configuration of microcapsules was same.The microcapsules prepared with emulsion template by self-assembly method can retain the main components of thyme oil effectively with GC-MS analysis.3.The release rate of thyme oil and thyme oil microcapsules increased when the temperature increased,and the release rate of thyme oil is higher than that of microcapsule,indicating that microencapsulation can reduce the release rate of essential oil.The release of the thyme oil microcapsule obeyed the first order release kinetics at4? and 25?.The more assembled layers,the better sustained-release performance of thyme oil microcapsule was,and the release of thyme oil microcapsules with different layers obeyed the zero order release kinetics at 100?.The microcapsule has good pH sensitivity and controllable release.When the pH value of the release medium changed from low to high,the release rate of thyme oil microcapsule gradually increased,and the release of thyme oil microcapsule obeyed the first order release kinetics.The thyme oil microcapsule solution has good storage stability and the best storage temperature is 4?.4.Thyme oil showed strong antimicrobial activity on Staphylococcus aureus,Escherichia coli and Bacillus subtilis.And the inhibitory effect on Gram-positive bacteria was stronger than that of Gram-negative bacteria.However,there was no significant differences of the antibacterial activity between thyme oil microcapsule and thyme oil.The bacteriostasis effect of thyme oil gradually weakened with the temperature increase,while the antibacterial effect of thyme oil microcapsules gradually increased with the temperature increase.The antibacterial effect of thyme oil decreased with the pH increase,while the antibacterial effect of thyme oil microcapsule under acid or alkaline conditions was enhanced compared with neutral conditions.Microencapsulation can significantly improve the antibacterial effect and antibacterial persistency of thyme oil.Thyme oil microcapsules can inhibit the growth of microorganism in milk,extend the shelf life of milk.