【作者】 李文；

【导师】 许恒毅；

【作者基本信息】 南昌大学 ， 食品科学与工程， 2022， 硕士

【摘要】 新鲜果蔬含水量大、含糖量高,采后易产生脱水和微生物滋生等问题。另外,采后果蔬旺盛的生理代谢也会导致其发生不良品质变化,造成巨大的食品资源浪费和经济损失。因此,适当保鲜处理对采后果蔬具有重要意义。含纳米银(Ag nanoparticles,AgNPs)复合抗菌涂膜,综合了抗菌性、可降解性和屏障阻隔性等能力,是一种极具潜力的果蔬保鲜方式。AgNPs的合成方式按原理可分为物理法、化学法和生物法,由于物理法制备AgNPs能量消耗大、成本高,化学合成法涉及到对环境有毒害作用的试剂和反应副产物,故本研究采用生物合成方法制备AgNPs。本研究采用樟树叶提取物绿色合成AgNPs,探究了该AgNPs的理化性质及抑制微生物的效果,制备了载AgNPs天然生物大分子复合薄膜,并对该薄膜用于南丰蜜桔保鲜的效果及安全性进行了初步评估,以期为AgNPs在果蔬保鲜领域的应用提供依据。各章内容分述如下:第一章:综述了AgNPs的生物合成方法和AgNPs在果蔬保鲜中的应用研究进展。第二章:为解决物理法和化学法制备AgNPs的应用局限性问题,本研究设计了基于樟树叶绿色合成AgNPs的方案,并对合成后AgNPs的理化性质和抑菌性能进行了研究。以樟树叶提取物为还原剂和稳定剂,在常温下合成了均匀分散的,平均粒径为19.57 nm的球形或椭圆形AgNPs颗粒。该AgNPs呈面心立方晶格,稳定性较好,对革兰氏阳性菌[Gram-positive bacteria,Gram(+)]、革兰氏阴性菌[Gram-negative bacteria,Gram(-)]和真菌均具有较好的抑制作用。其中,AgNPs对Gram(-)的最低抑菌浓度(Minimum inhibitory concentration,MIC)可低至3μg/m L。并通过对细菌的形态、细菌内容物的泄露水平以及活性氧水平进行分析,初步探究了AgNPs对典型的Gram(+)和Gram(-)的抑菌机制。结果发现与空白对照组相比,经AgNPs处理的细菌菌体形态受损、细菌内蛋白质以及还原糖成分外泄、活性氧簇(Reactive oxygen species,ROS)水平增加。故推测该AgNPs对细菌的抑菌机制为:AgNPs作用于细菌表面后,造成菌体损伤,致使内容物流出;细菌受到来自AgNPs产生的银离子(Ag ion,Ag~+)的氧化压力,菌体内的ROS水平增加。当AgNPs的使用量超过细菌能承受的阈值,细菌菌体内的生理平衡被打破,菌体内产生不可逆的损伤,最终导致细菌死亡。第三章:为拓展天然大分子薄膜的应用范围,本研究以海藻酸钠(Sodium alginate,SA)和明胶(Gelatin,GL)为薄膜成型的主要材料,以甘油为增塑剂,AgNPs为抗菌剂,制备了载银复合抗菌薄膜。以薄膜的机械性能为主要指标,对薄膜各成分的配比进行了优化。其中,机械性能最佳的薄膜成分配比为SA:GL=1:1、5%的甘油、20%的100μg/m L AgNPs(v/v)。对薄膜进行表征发现,该载银复合抗菌薄膜各成分间的相互作用力以氢键(生物大分子间)和金属配位键(银原子与生物大分子间)为主,成分连接较紧密。在600℃的环境下,该载银复合抗菌薄膜的降解率可达70%;在干燥的土壤下掩埋该薄膜以模拟自然环境降解,15天(Day,d)后,其降解率达到40%。此外,由于AgNPs的添加,该薄膜对金黄色葡萄球菌(Staphylococcus aureu)和大肠杆菌(Escherichia coli)表现出较好的抑制效果。第四章:为探究可降解载银复合膜用于果蔬保鲜的可行性,本研究以载银复合抗菌薄膜形成液为涂膜材料,分析了该涂膜用于南丰蜜桔保鲜的效果,并对该涂膜中银元素向蜜桔内的迁移情况进行了评估。结果表明:与空白对照组相比,经载银复合涂膜处理的蜜桔其货架期得到了延长,且表面更具有光泽,水分散失情况得到了缓解,内部营养成分也更为稳定。此外,通过电感耦合等离子体原子发射光谱(inductively coupled plasma atomic emission spectrometry,ICP-AES)检测银元素迁移情况。实验结果表明,无论在短期(3 d)或长期(15 d)储藏期内,经该载银复合抗菌涂膜处理的蜜桔,其果实中银元素检出量均低于饮用水标准,即实验周期内银元素的迁移不会带来安全风险。第五章:概述了本研究的结论,并从载银复合薄膜的制备和应用范围等角度对其未来研究方向做了展望。综上所述,利用樟树叶提取物可合成抑制微生物效果良好的AgNPs,将该AgNPs负载于生物大分子薄膜中,可改善薄膜的性能。以载银复合抗菌薄膜形成液为涂膜材料用于南丰蜜桔的保鲜,可延长蜜桔的货架期。更多还原

【Abstract】 Fresh fruits and vegetables have high water content and high sugar content,which are prone to problems such as dehydration and microbial growth after harvesting.And the vigorous physiological metabolism of harvested vegetables will also lead to poor quality changes,resulting in huge waste of food resources and economic losses.Therefore,it is of great significance to properly preserve the fruits and vegetables after harvest.The composite antibacterial coating containing Ag nanoparticles(AgNPs)combines antibacterial,degradable and barrier properties,and is a promising way to preserve fruits and vegetables.The synthesis methods of AgNPs can be divided into physical method,chemical method and biological method according to the principle.Due to the high energy consumption and high cost of preparing AgNPs by physical methods,and the chemical synthesis methods involve reagents and reaction by-products that are toxic to the environment,a green synthesis method was explored to prepare AgNPs.In this study,the green synthesis of AgNPs was carried out by using the extract of Cinnamomum camphora leaves,and the physical and chemical properties of the AgNPs and their inhibitory effects on microorganisms were investigated.The natural biomacromolecule composite film loaded with AgNPs was prepared,and the preservation effect and safety of the film on Nanfeng tangerine were preliminarily evaluated,to provide a basis for the application of Ag NP in the field of food preservation.The contents of each chapter are as follows:In the first chapter,the biosynthesis of AgNPs and the application research progress of AgNPs in the preservation of fruits and vegetables were reviewed.In the second chapter,in order to solve the application limitation of AgNPs prepared by physical and chemical methods,a scheme for green synthesis of AgNPs based on Cinnamomum camphora leaves was designed,and the physicochemical properties and antibacterial properties of AgNPs were studied.Using the extract of Cinnamomum camphora leaves as reductant and stabilizer,the spherical or elliptical AgNPs particles with an average particle size of 19.57 nm were synthesized at room temperature.The AgNPs have a face-centered cubic lattice,good stability,and good antibacterial activity against Gram-positive bacteria[Gram(+)],Gram-negative bacteria[Gram(-)]and fungi.The Minimum inhibitory concentration(MIC)against Gram(-)was 3μg/m L.Through the analysis of the apparent morphology of bacterial,the leakage level of bacterial contents and the level of reactive oxygen species,the antibacterial mechanism of AgNPs on typical Gram(+)and Gram(-)was preliminarily explored.the results showed that:compared with the blank control group,the bacteria treated with AgNPs showed the following phenomena:The morphology of bacterial cells was damaged;Leakage of proteins and reducing sugars from bacteria;Increased levels of Reactive oxygen species(ROS).It was speculated that the antibacterial mechanism of the synthesized AgNPs on bacteria was that AgNPs acted on the surface of bacteria,causing damage to the bacteria and causing the contents to flow out;in addition,the bacteria were subjected to oxidative pressure from silver ions(Ag ion,Ag~+)produced by AgNPs,which increased the level of ROS in the bacteria.When the amount of AgNPs used exceeds the threshold that the bacteria can bear,the physiological balance in the bacteria will be broken,resulting in irreversible damage to the bacteria,or even death.In the third chapter,in order to expand the application range of natural macromolecular films,the silver-loaded composite antibacterial film was prepared by using Sodium alginate(SA)and Gelatin(GL)as the main materials,glycerol as the plasticizer and AgNPs as the antibacterial agent.With the mechanical property of the film as the main index,the ratio of each component of the film was optimized,and the best film ratio of the mechanical property was SA:GL=1:1,5%glycerol,20%100μg/m L AgNPs(v/v).The analysis of the film showed that the interaction between the components of the silver-loaded composite antibacterial film was dominated by hydrogen bonds(between biomacromolecules)and metal coordination bonds(between silver atoms and biomacromolecules),and the components were closely connected.The degradation rate of the silver-loaded composite antibacterial film can reach 70%at the temperature of 600℃,and the degradation rate of the silver-loaded composite antibacterial film can reach 40%after being buried under dry soil to simulate natural environment degradation for 15 days(d).In addition,due to the addition of AgNPs,the film showed a good inhibitory effect on Staphylococcus aureus(S.aureus)and Escherichia coli(E.coli).In the fourth chapter,in order to explore the feasibility of the degradable silver-loaded composite film for the preservation of fruits and vegetables,this study used the silver-loaded composite antibacterial film-forming liquid as the coating material,and analyzed the effect of the coating film on the preservation of Nanfeng tangerines.The migration of silver elements in the film into the tangerine was evaluated.The results showed that compared with the blank control group,the tangerines treated with the silver-loaded composite coating film had a longer shelf life,more glossy surfaces,less water loss,and more stable internal nutrients.In addition,the migration of silver elements was detected by inductively coupled plasma atomic emission spectrometry(ICP-AES).The experimental results show that no matter in the short-term(3 d)or long-term(15 d)storage period,the detected amount of silver elements in the tangerines treated with the silver-loaded composite antibacterial coating film is lower than the drinking water standard.The migration of silver elements during the period will not bring security risks.In the fifth chapter:the conclusions of this study are summarized,and its future research directions are prospected from the perspectives of the preparation and application scope of silver-loaded composite films.In conclusion,AgNPs with good microbial inhibitory effect can be synthesized by using the extract of camphor leaves,and the AgNPs can be loaded into the biomacromolecular film,which can improve the performance of the film.The silver-loaded composite antibacterial film-forming liquid is used as the coating material for the preservation of Nanfeng tangerines,which can prolong the shelf life of the tangerines.更多还原