【作者】 章敏；

【导师】 胡秋辉；

【作者基本信息】 南京农业大学 ， 食品科学， 2009， 硕士

【摘要】 由于绿茶生产的时效性和季节性很强,难以确保一年四季都新鲜如初,若包装不当,则香气消散,色泽变黄,陈化劣变。目前国内外最常用干燥、低温、除氧和抽气冲氮等保鲜技术都存在局限性,迫切需要一套科学完整的绿茶保鲜工艺技术体系来促进我国的绿茶保鲜事业。近几年来,因纳米复合材料具有可塑性、阻隔性、稳定性、抗菌性、保鲜性等某些物理化学以及生物性能,从而在食品包装业得到大规模的应用。因此,本课题研制一种新型的纳米材料,以提高绿茶保鲜品质。主要研究结果如下：纳米材料的制备：选择纳米粉体D（凹凸棒土）、纳米粉体HTB （Ag₃PO₄银系抗菌材料）、纳米粉体TiO2R（金红石型）、；纳米粉体TiO2A（锐钛型）,各按照质量比取纳米粉体30%,聚乙烯塑料56%,硅烷偶联剂10%、石蜡2%、抗氧化剂2%,经高速混匀0.5小时后在起塑机中捏合随后挤出切粒分别获得4种母粒D、HTB、TiO₂R, TiO₂A。纳米母粒D, HTB、TiO₂R、TiO₂A按质量比5：2：4：1的比例混合,再与聚乙烯塑料粒子按质量比1：6的比例充分混合吹成薄膜,然后镀铝膜制成纳米保鲜包装材料。将上述制备的纳米材料进行扫描电镜观察；测定其透湿率、透氧率、纵向拉伸强度；并测试其抗菌性。结果表明,各种不同的纳米粒子在膜中均匀分布且直径都在纳米范围内；纳米包装的透湿量和透氧量比普通包装分别降低44.3%和44.6%,纵向拉伸强度则增加了24.14%；而纳米材料处理的黑曲霉孢子液,孢子萌发率仅为20.2%,比普通包装处理的孢子萌发率低45.4%。这说明该纳米包装在具有良好的机械性能的同时具有良好的阻透性,能降低防止02、水气等小分子物质的渗透,同时,该纳米材料还具有有效的抗菌抑菌性能,对黑曲霉的抑制率显著高于普通包装材料。使用本研究制备的纳米包装材料对碧螺春和青峰两种绿茶进行1年的保鲜研究,分别对其理化品质和感官品质进行测定。碧螺春在常温条件下贮藏360天后,纳米包装材料组的水分比普通包装低10.1%,对游离氨基酸、茶多酚、叶绿素、维生素C保留量比普通包装分别高25.3%、9.2%、36.9%、40.0%,感官评定结果也明显优于普通组；青峰在常温条件下贮藏360天后,纳米包装材料组的水分比普通包装低6.7%,对游离氨基酸、茶多酚、叶绿素、维生素C保留量比普通包装分别高21.1%、8.8%、34.2%、22.9%,感官评定结果也明显优于普通组；结果表明,纳米包装材料碧螺春和青峰两种不同品种的绿茶的研究结果相一致,即纳米材料能显著提高绿茶的保鲜品质。更多还原

【Abstract】 Quality of tea especially high-grade green tea deteriorated easily during storage and transportation, which will lower merchandise and economy value of the tea. Much attention has been paid to the storage techniques of green tea, such as cold storage, deoxidizer packaging, nitrogen packaging and vacuum packing. However, most of these strategies are expensive and time-consuming. Thus, there is an urgent need to have alternative technologies to inhibit the undesirable physicochemical and biochemical changes during storage.In recent years, nano-materials have attracted increasing attention because of their unique advantages. Compared with the traditional materials, nano-phase materials exhibit unusual chemical, mechanical, optical, electrical and magnetic properties. The objective of this work was to prepare a novel nano-packing material and investigate its effect on perseveration quality of green tea during room temperature storage. The main results were as follows:Nano-powder (attapulgite:Ag3PO4:anatase TiO2:rutile TiO2= 5:2:4:1,30%), polyethylene (56%) and cross-link reagent KH-570 (14%) were immingled to uniformity for 0.5 h through a high-speed mixer, extruded out by a twin screw extruder, and then cut to nano-granules after cooling for 2 min. Subsequently,30 kg polyethylene granule and 5 kg mixed nano-granule were immingled for 0.5 h, and then blown into films of 80μm thickness. After cooling, another aluminium film in the same thickness was stuck on the NCP film. Finally, the combined film was made into bags of 30×20 cm using a bag-making machine (FBD-300W, JiaQi Packaging Machiner Co., Zhejiang). The polyethylene bags of the same size and thickness without nano-powder served as control.According to China National Analysis Standards, the microstructure, antibacterial activity and physical property of nanocomposite, including water vapor transmission rate and oxygen transmission rate. The relative humidity (RH) and oxygen transmission rate of nano-packing material were 1.03 g/m2·24 h and 0.29 cm3/m2·24h·0.1 MPa, respectively, and decreased by 44.3% and 44.6% compared with the normal packing material. These results indicated the novel nano-packing material had higher barrier property to H2O and O2. From the microstructure observation, we could get that the nano-particles (attapulgite, Ag3PO4, anatase-TiO2 and rutile-TiO2) uniformly distributed in the nano-packing film with irregular shape. The dimension of most of these nano-particles was in the range of 100 nm. Meanwhile, few particles were found in normal packing material.Its effect on preservation quality of green tea (Biluochun and Qingfeng) during ambient storage was investigated. Results showed that nanocomposite-based packing (NCP) had quite beneficial effect on physicochemical and sensory quality compared with normal packing (polyethylene bags). After one-year ambient storage, the moisture of Biluochun and Qingfeng with NCP was decreased by 10.3% and 6.1% compared with the normal packing. Meanwhile, the contents of amino acid, tea polyphenols, chlorophyll and ascorbic acid were increased by 22.8%,9.4%,30.4%,9.5% for Biluochun and 19.2%,9.3%,27.3%, 21.6% for Qingfeng, respectively. Moreover, the sensory quality of NCP was also superior to that with normal packing. Therefore, the novel NCP material may provide an attractive alternative to maintain the preservation quality of green tea at a high level during a long-term storage.更多还原