【作者】 刘鹏；

【导师】 余龙；

【作者基本信息】 华南理工大学 ， 淀粉资源科学与工程， 2010， 博士

【摘要】 抗菌活性包装是上世纪90年代提出的一种新型包装理念,它是将抗菌剂混入一种或几种高聚物包装材料中,通过抗菌剂的缓慢溶出释放产生抗菌活性,逐渐减少或代替向食品中加入盐、糖或防腐剂等,在包装内部维持长期稳定的抗菌剂浓度而达到抗菌防腐的目的,使食品能够较长时间保存。抗菌活性包装材料具有传统包装材料不可比拟的优势,应用和发展前景十分广阔,是目前食品及材料领域研究的一个前沿和热点。本论文是在高水分活度食品抗菌的需求下,在抗菌活性包装材料发展趋势的基础上,选择环境友好型的淀粉/聚乳酸共混材料作为基材,选择水溶性壳聚糖作为抗菌剂,深入研究淀粉在甘油/水混合溶液中的相变、直链/支链淀粉对热塑性淀粉玻璃化转变的影响、以及抗菌材料的抗菌活性等基础理论问题,为制备出环境友好的、能够用于高水分活度食品的淀粉/聚乳酸/壳聚糖共混抗菌活性包装材料提供理论和工艺支持。本论文在制备热塑性淀粉时,选用甘油/水混合溶液作为增塑剂,深入研究了淀粉在甘油/水混合溶液中的相变,发现甘油/水混合溶液是作为一个整体来影响淀粉的相变,甘油不是“反增塑剂”,只要混合溶液中有“足量的”自由羟基存在,淀粉相变的发生就只受温度的影响,与甘油含量无关,且相变吸热焓值不会随混合溶液中甘油比例的不同发生变化。另一方面,在富甘油相混合液(甘油摩尔分数高于0.8)增塑时,由直链淀粉分子和脂类所形成的络合物吸热熔融产生的M2峰消失,这是由于甘油会抽提淀粉中的脂类物质,破坏直链淀粉分子和脂类所形成的络合物。这些研究结果,尤其是不同甘油含量的甘油/水混合溶液对高直链含量的淀粉在高温下(~180°C)多重相变的影响尚未见报道,且这些研究结果可以用来指导甘油/水混合溶液增塑条件下的热塑性淀粉的制备。对热塑性淀粉玻璃化转变温度(T_g)的准确测定,以及直链/支链淀粉对T_g的影响,这些是热塑性淀粉材料领域里尚未解决的问题。本论文针对这些问题,首先建立了合适的方法测量热塑性淀粉的玻璃化转变温度,发现高速升温DSC通过提高升温速率,能将玻璃化转变和结晶熔融两个热事件分离开,能够消除水分蒸发对T_g的影响,并且能够放大热信号,提高仪器灵敏度,避免基线噪音的干扰,而通过一定的校正方法,又可以消除升温速率过快带来的温度滞后效应,因此最适用于测量热塑性淀粉的T_g;然后在此基础上研究了直链/支链淀粉对热塑性淀粉玻璃化转变温度的影响,发现相同水分含量的热塑性玉米淀粉,其T_g随着直链淀粉含量的增大而升高,并从重结晶、热塑性淀粉的相变模型等角度进行了解释。上述研究成果有助于丰富和充实淀粉科学理论,并且由于T_g是高分子材料加工的重要参数,决定了材料的加工温度,因此这些结果也可以用来指导热塑性淀粉的制备。对不同直链/支链淀粉含量的热塑性淀粉T_g的研究,尚未见报道。本论文选用淀粉/聚乳酸共混材料为基材制备抗菌材料。在制备过程中,利用配有密炼机的Haake转矩流变仪研究甘油/水混合溶液增塑时,不同甘油比例对热塑性淀粉流变性质的影响,发现富甘油相混合液增塑时,样品的喂料峰很微弱,相变峰很明显;富水相混合液增塑时情况相反,喂料峰很大,相变峰很微弱;而当混合溶液中甘油和水的比例达到一定时(70:30和80:20,甘油/水),由于甘油和水的相互作用降低了混合溶液的润滑效果和增塑活性,使得样品的喂料峰和相变峰都很明显。此外还利用接触角评价了共混材料的亲疏水性,发现聚乳酸的亲水性差,水对聚乳酸的浸润速度很缓慢;而加入淀粉后,材料的亲水性增强,且水对材料的润湿速度随着淀粉含量的增加而增大,这就为壳聚糖的溶出迁移提供了依据。本论文将壳聚糖与淀粉/聚乳酸共混粒料一同挤出,制备抗菌材料。通过测定壳聚糖从抗菌材料中的溶出迁移,发现壳聚糖的溶出分为快速溶出阶段和缓慢溶出阶段,前者是分散于材料表面的壳聚糖遇水后的溶出迁移,后者是分散在共混材料内部的壳聚糖在水分子的渗透下,逐渐从材料内部迁移溶出。通过定性、定量考察不同壳聚糖含量的抗菌材料的抗菌活性发现,当壳聚糖在材料中的含量达到10%后,材料具有显著的抗菌实效性;并且由于壳聚糖的溶出是一个缓慢的过程,能够使抗菌活性在一定时间内维持。综上,本论文深入探讨了淀粉/聚乳酸/壳聚糖共混抗菌材料制备中的若干基础科学问题。通过对这些问题的深入研究,为制备出环境友好的、能够用于高水分活度食品的抗菌活性包装材料提供理论和工艺支持,将淀粉和淀粉基材料在包装材料领域中的应用推进更深层次。更多还原

【Abstract】 The notion of antimicrobial active packaging has been put forward in 1990s. The antimicrobial active packaging is prepared by adding antimicrobial agents into packaging materials. Through the release of antimicrobial agents from packaging material, it can change the condition of the packed food to extend shelf-life and to improve safety, without the change of taste quality of food. Furthermore, using antimicrobial active packaging, the antimicrobial additives in food can be reduced gradually or instead thoroughly. The antimicrobial active packaging is superior to traditional packaging, and has brilliant application and development foreground. Consequently, it attracts researchers’attentions.In this thesis, with the maintenance requirement of high-water-activity food, and based on the development direction of packaging materials, it chose water-soluble chitosan as antimicrobial agents and starch/PLA blends as substrate materials to prepare antimicrobial active packaging material. Furthermore, it studied the basic scientific problems in the preparation, which include the influence of glycerol/water mixture on the phase transition and rheological property of starch, the influence of amylose/amylopectin on the glass transition of thermoplastic starch, and the antimicrobial and releasing property of chitiosan from substrate.In this thesis, it chose glycerol as plasticizer to prepare thermoplastic starch. Former researchers have studied the effect of glycerol concentration on the gelatinisation parameters of starch before; but the results were not consistent with each other. Consequently, it studied the influence of glycerol/water mixture on the phase transition of starch with different amylose/amylopectin ratio. It found that glycerol–water solution as a whole affected the gelatinisation behaviour, and glycerol was not“anti-plasticiser”. When solution has“abundant”free hydroxy, the phase transition and the enthalpy of phase transition of starch can only be affected by temperature, and is independent with glycerol content. On the other hand, when plasticized by glycerol-rich solution, the M2 phase transition peak, which was caused by the phase transition within amylose–lipid complex, disappeared. The reason for this is that glycerol can extract lipid in starch and destroy amylose-lipid complex, so M2 disappeared. These results, especially the phase transition of amylose-rich starch in glycerol/water solution with different glycerol content in high temperature (~180°C), have not been reported before, and these results can be used to guide the preparation of thermoplastic starch under the plasticization of glycerol.Glass transition temperature is the key parameter for polymer materials, and determines the application of materials. But former researchers’results about the glass transition temperature for thermoplastic starch contradicted with each other. In this thesis, it set up a new method to detect glass transition temperature of thermoplastic starch. Specifically, using high-speed DSC, which the linearity heating rate can reach 500°C/min, the signal of glass transition can be separated from crystalline melting, and the influence of water evaporation on glass transition can also be eliminated. Furthermore, the high heating rate can also enlarge thermal signal, increase sensitivity, and avoid the disturbance of baseline noise. Moreover, through an adjusting method, the temperature-lag effect that is caused by high heating rate can be solved. Consequently, high-speed DSC is the most suitable method to detect glass temperature of thermoplastic starch. After that, it also studied the influence of amlylose/amylopectin ratio on T_g, and found that T_g became higher with the increasing of amylose content. This has been explained by re-crystallization, and the phase transition model of thermoplastic starch. This is the first time to detect T_g from natural thermoplastic starch, and proofs former researcher’s deduction from acetate starch material.In this thesis, it used Haake Rheometer with Mixer to study the rheological property of starch under the plasticization of glycerol/water mixture. It found that under the plasticization of glycerol-rich mixture, the loading peak was weak, but the phase transition peak was obvious. Under the plasticization of water-rich mixture, the situation was on the opposite, namely loading peak was obvious, and phase transition peak was weak. Besides, when glycerol and water ratio reached 7:3 or 8:2 in mixture, because of the interaction between glycerol and water, both the lubrication and plasticization effect of solution were impaired, so both loading peak and phase transition peak were strong. On the other hand, it also evaluated the hydrophilic property of starch/PLA blends by contact angle. It found that the hydrophilic property of PLA material was poor and the soaking rate of water into material was very slow. When added with thermoplastic starch, the hydrophilic property of blends was improved and the soaking rate of water increased with more starch content.In this thesis, the chitosan was extruded with starch/PLA blend pellets to prepare antimicrobial materials. By detecting the releasing rate of chitosan from substrate materials, it found that the releasing rate was high at the beginning, which was caused by the releasing of chitosan from the surface of materials, and then the rate became slow, which was cause by the embedded chitosan in materials. On the other, from the qualitative and quantitative detection, it found that when the concentration of chitosan in materials reached 10%, the materials can have notable antimicrobial activity, and the antimicrobial activity can last for a peirod.All in all, through studying on the basic scientific problems in the preparation of starch/PLA blend antimicrobial materials, which include the influence of glycerol/water mixture on the phase transition and rheological properties of starch, the influence of amylose/amylopectin on the glass transition of thermoplastic starch, and the antimicrobial and releasing property of chitiosan from substrate, it prepared the environment friendly antimicrobial packaging materials , which can be used for the maintenance of high-water-active food. It improves the application range of starch based and starch/PLA material.更多还原