【作者】 张珊珊；

【导师】 冯武；

【作者基本信息】 华中农业大学 ， 农产品加工及贮藏工程， 2018， 硕士

【摘要】 百里香精油(Thyme oil)富含百里香酚和香芹酚等酚类物质,具有很强的抗菌和抗氧化活性。但由于精油中的这些活性酚类物质对光、热、氧气等极为敏感,特别是在复杂的食品体系中,容易和食品成分发生反应,从而减低其抗菌和抗氧化活性。而微胶囊技术可通过壁材的物理屏障作用,减少活性成分的损失,掩盖不愉快的气味,同时实现精油的可控释放,从而解决了精油在食品领域中的应用难题。本论文通过乳液模板-层层自组装法制备百里香精油微胶囊,并对其形貌和性能进行了表征,同时研究了其释放动力学和抑菌性能。具体研究内容和结果如下:1.以壳聚糖和海藻酸钠为壁材,百里香精油为芯材,采用乳液模板-层层自组装法制备微胶囊。首先以粒径和Zeta电位作为乳液模板的评价指标,以包埋率作为微胶囊的评价指标,通过单因素和正交试验得到的最佳制备条件:微射流均质压力62MPa下循环6次,NaCl添加量为0.3%,pH为8的条件下获得乳液模板,制备得到的微胶囊平均包埋率为71.13%。研究发现微胶囊的包埋率和乳液模板的粒径在一定范围内呈正相关,和Zeta电位绝对值呈负相关。2.微胶囊表面的电位显示壳聚糖和海藻酸钠在乳液模板上基于静电作用成功进行交替自组装。微胶囊的尺寸会随着组装层数的增加而线性增长,大约为10 nm/层。由红外图谱分析可知,自组装过程中壁材的结构未发生明显变化,且壳聚糖和海藻酸钠通过静电作用结合形成微胶囊。通过粒径分析显示4层的微胶囊平均粒径为140 nm,粒径较均匀。通过扫描电镜和透射电镜可知,微胶囊分散性良好,表面光滑平整,孔隙不明显。通过荧光显微镜观察表明精油被较好的包埋在微胶囊内部,且微胶囊球形规整。通过气质联用分析可知,采用乳液模板-层层自组装法制备所得的微胶囊能有效的保留百里香精油的主要成分。3.温度越高,百里香精油和百里香精油微胶囊的释放速率越大,百里香精油的释放速率大于微胶囊,表明微胶囊化可降低精油的释放速率,且百里香精油微胶囊在4℃和25℃下的释放遵循一级释放动力学规律。组装层数越多,百里香精油微胶囊的缓释性能越好,且不同组装层数的百里香精油微胶囊在100℃下的释放均符合零级动力学方程。百里香精油微胶囊具有良好的pH敏感性和可控释放性;当释放介质的pH值由低变高时,百里香精油微胶囊的释放速率逐渐增加,其释放曲线符合一级释放动力学规律。百里香精油微胶囊溶液具有良好的贮藏稳定性,其最佳存储温度是4℃。4.百里香精油对金黄色葡萄球菌、大肠杆菌和枯草芽孢杆菌均具有较强的抑菌效果,且对G~+抑制作用强于G~-,百里香精油微胶囊与百里香精油的抑菌效果一致。随着温度的升高,百里香精油的抑菌效果逐渐减弱,而百里香精油微胶囊的抑菌效果逐渐增强。百里香精油的抑菌效果随着pH的升高而减弱,而百里香精油微胶囊在酸性或碱性条件下的抑菌效果均比中性条件下有所增强。微胶囊化可显著提高百里香精油的抑菌效果及抑菌的持久性。百里香精油微胶囊可抑制牛奶中微生物的生长,延长其保质期。更多还原

【Abstract】 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.更多还原