【作者】 梁蓉；

【导师】 麻建国；

【作者基本信息】 江南大学 ， 食品科学， 2013， 博士

【摘要】 纳米乳液，是指粒径在10~200nm之间的一种乳化运输体系，与一般乳液相比，纳米级的粒径赋予体系特殊的小尺寸、高表面活性和强吸附等特性，进而对体系的物理化学稳定性和所运载营养物质的体内吸收起到增强效果。本课题以纳米乳液为研究对象，以食品生物大分子——辛烯基琥珀酸酯化淀粉（OSA变性淀粉）为乳化剂，针对脂溶性功能成分中易挥发且不易被乳化的精油类（EO）和不易溶解且易结晶的营养素类，构建稳定、高效、生物兼容性强的水包油（O/W）型纳米乳液，并对体系的物理化学特性、生物学效应和生物安全性等重要应用品质进行检测，最终建立乳化剂的特性与乳液特性之间的相关性。首先，对应用广泛、但技术参数缺乏的五种OSA变性淀粉的分子特性、溶液特性和乳化特性进行了测定。由高效液相排阻色谱-多角度激光散射-示差折光仪串联系统得出，五种OSA变性淀粉的重均分子量和平均旋转半径值均小于原淀粉，且淀粉分子在水溶液中均为球形或近球形构象，分子分散密度表现为Purity Gum2000> Purity Gum Be>HI-CAP> CAPSUL TA> CAPSUL。淀粉溶液表现为近牛顿流体性状，且溶液黏度随淀粉质量浓度的增加而增大。在乳化特性方面，淀粉分子能显著降低体系的表/界面张力，并能在高速分散和高压均质条件下乳化中链甘油三酸酯（MCT），制备得到纳米乳液，为后续构建脂溶性营养成分的纳米乳液提供了实验依据。针对EO普遍存在的易挥发、不易形成稳定乳液的现象，选择我国分布及应用广泛的薄荷油（PO）作为代表，研究OSA变性淀粉在EO纳米乳液制备中的特性。结果显示，使用MCT与PO作为混合油相，以Purity Gum2000为乳化剂，能有效抑制乳液因奥氏熟化引起的失稳，并在均质压力为100MPa，均值次数为10次，芯壁比为1:1时，制备得到粒径在180nm左右的薄荷油纳米乳液。且在此条件下，不同PO载量的乳液乳化产率均高于97%，在室温下储藏30天后，乳液的粒径增加20~30nm，PO保留率高于95%，乳液均无明显分层现象发生。气质联用结果显示乳化过程能有效抑制PO中主要抗菌成分——薄荷醇和薄荷酮的损失，且乳化前后PO对两种革兰氏阳性菌显示相同的最小抑菌浓度（0.5%，v/v），但从微生物的生长曲线显示，PO纳米乳液显示出更为持久的抑制菌落生长的特性。因此，通过纳米乳液包埋不仅能提高EO的稳定性，还能作为一种长效抗菌剂应用于食品及其它体系中。针对溶解度低且不易被人体吸收的营养素类物质，选择β-胡萝卜素作为代表，构建以OSA变性淀粉为乳化剂的纳米乳液。首先，通过对不同β-胡萝卜素载量乳液的粒径和核磁共振测定结果显示，在乳液中β-胡萝卜素处于表面活性剂和油相的界面，且与OSA淀粉分子之间存在相互作用。进一步通过比较五种OSA变性淀粉制备β-胡萝卜素乳液的乳化产率和芯材保留率得出，淀粉分子的取代度、界面特性对乳液的乳化产率影响显著，而淀粉分子的表面吸附量和分子分散密度对芯材的保留率影响显著，并最终确定使用HI-CAP、CAPSUL和CAPSUL TA三种淀粉制备β-胡萝卜素纳米乳液（乳化产率、保留率均高于90%）。与未包埋的β-胡萝卜素相比，乳化体系中β-胡萝卜素的储藏稳定性和体外生物利用率均显著提高，但这三种变性淀粉乳化配方之间的差异，同样与变性淀粉的表面吸附量和分子分散密度相关。进一步对这三种乳液的潜在生物毒性进行了检测，结果显示，乳液不存在潜在细胞毒性（HepG2），对于HI-CAP稳定的乳液不存在溶血性，对于CAPSUL和CAPSUL TA稳定的乳液，当其与血液直接接触浓度小于0.4%时，溶血性可忽略不计。因此，通过OSA变性淀粉的使用，可以制备得到稳定、有效且安全的营养素纳米乳液运输体系。高浓度OSA变性淀粉（HI-CAP、CAPSUL和CAPSULTA）在β-胡萝卜素纳米乳液配方中的使用，同时兼具了乳化剂和乳化壁材的作用，赋予了纳米乳液可直接喷雾干燥的特性。因此，为了克服乳液水相基质的不稳定性和应用缺陷，实验中将高压均质后的稳定乳液，直接采用喷雾干燥法制备β-胡萝卜素的乳化粉末。通过对粉末的溶解特性研究显示，复原乳液保持了与初始乳液相同的纳米级粒径，且粉末中β-胡萝卜素的乳化效率和产率均高于90%。粉末的X-射线衍射和红外光谱测定结果均表明，OSA变性淀粉与油相和β-胡萝卜素之间存在相互作用，有利于芯材的包埋和稳定。与β-胡萝卜素纳米乳液相比，喷雾干燥粉末的储藏稳定性显著提高，进一步验证了该方法的可行性。进一步将纳米乳液粉末在不同水分湿度（RH）条件下进行储藏，结果显示OSA变性淀粉制备膜的透氧系数（OP）和透水系数（WVP）与粉末在储藏过程中的吸水性和保留率密切相关，表现为OP值越大，芯材的保留率越低，WVP值越大，粉末的吸水性越强。并且，在不同RH条件下β-胡萝卜素的降解速率与样品的玻璃化转变温度Tg相关。在样品发生玻璃化转变前，β-胡萝卜素的降解速率随RH增加而增加，但当样品发生玻璃化转变后，β-胡萝卜素与壁材之间发生“二次包埋”，降解速率反而下降。因此，可通过选择具有不同特性的乳化剂分子，制备得到不同储藏特性的营养成分包埋系统。更多还原

【Abstract】 Nanoemulsions are colloidal systems usually with the droplet sizes around10to200nm.The very small droplet size offers nanoemulsions various advantages over conventionalemulsions for their applications, including high physical and chemical stability, high surfaceactivity and strong adsorption characteristic, which further increase the bioavailability oflipophilic functional ingredients. In this research, biopolymer emulsifier-octenyl succinateanhydride modified starch (OSA starch) general recognized as safe (GRAS) was chosen asemulsifier to incorporate lipophlic functional compounds (essential oils which are volatile andnot easily to emulsification and nutraceuticals with low solubility and crystallization) intonanoemulsion system. The physicochemical properties, biological properties and potentialtoxicity of nanoemulsions would be evaluated. Thereafter, the correlative relationshipbetween various properties of emulsifiers and their influence on the characteristics ofnanoemulsions would be established.At first, the molecule and solution characteristics of OSA starches related to theemulsification properties were measured. According to the HPSEC-MALLS-RI system, theweight-average molecular weight and radius of gyration of OSA starches are both smallerthan the original starches. The conformations for all the OSA molecules are spherical. Thedispersed molecular density decreased in the order Purity Gum2000> Purity Gum Be>HI-CAP> CAPSUL TA> CAPSUL. The OSA starch solutions showed Newtonian fluidproperties, and with the increase of OSA concentration, the viscosities of solutions wereincreased. As an effective emulsifier, OSA starch can significantly reduce the surface andinterfacial tensions of solutions and incorporate medium chain triglycerides (MCT) tonanoemulsions by using high speed and high pressure homogenization, which provide anbasis formulation for the subsequent research.The research was carried out by choosing peppermint oil (PO) as a model of essential oilto prepare nanoemulsions stabilized by OSA starch. The mixture of PO with MCT beforehigh-pressure homogenization was a useful method to inhibit the Ostwald ripening.Nanoemulsion with particle size about180nm were prepared by using Purity Gum2000asemulsifier, core to wall at1:1, with pressure at100MPa and10cycles. The formulated POnanoemulsions with different PO concentration showed high emulsification efficiency around97%and high stability over storage time. After30days storage at room temperature, theparticle size of emulsions was increased from20to30nm and PO retention was remainedhigher than95%. And there was no obvious phase separation or creaming observed for any ofthe samples. From GC-MS results, the concentration of the main components in PO and POemulsion, menthol and menthone, were close. Their antimicrobial properties related to POhave also been evaluated by two assays, the minimum inhibitory concentration (MIC) andtime-kill dynamic processes against two Gram-positive bacterial strains. With the same MICvaules at0.5%(v/v), PO nanoemulsions showed a prolonged antibacterial activity comparedto bulk PO. Our results suggest that the nanoemulsion technology can provide novelapplications of essential oils in extending the shelf-life of aqueous food products. As a model of bioactive labile lipophilic compound, β-carotene was insoluble in waterand only slightly soluble in oil at room temperature. Oil-in-water nanoemulsions stabilized byOSA were fabricated to improve the stability and bioaccessibility of β-carotene. The NMRtest showed that β-carotene in emulsions was loaded in the interface between surfactant andoil and had a strong interaction with OSA molecules. Thus, the DS, amount of surfaceadsorbed and dispersed molecular density of OSA would affect the emulsification yield andretention of β-carotene. The stable β-carotene nanoemulsion could be stabilized by HI-CAP,CAPSUL and CAPSUL TA with emulsification yield higher than90%. Compared to theβ-carotene dispersed in bulk oil, the retention and bioaccessibility of β-carotene innanoemulsions were significant increased. At last, the β-carotene nanoemulsions were testedfor hemolysis and cytotoxicity tests. The results showed that all emulsions showed nocytotoxicity for HepG2. And emulsions stabilized by HI-CAP did not show any hemolysis.For the emulsions stabilized by CAPSUL and CAPSUL TA, the hemolysis results werenegligible when the concentrations were less than0.4%. This result provides usefulinformation for developing protection and delivery systems for nutraceuticals.The high concentration of modified starches in formulations (HI-CAP, CAPSUL andCAPSUL TA) made it possible for the further spray drying process for the emulsions. And inorder to overcome the limitations of liquid-base emulsion system, β-carotene nanoemulsionsstabilized by modified starch were spray-dried to powders after the emulsification process.The powders showed a good dissolution in water and the reconstituted emulsions had similarparticle sizes with the fresh nanoemulsions which suggested that the spray drying process didnot affect the characteristics of nanoemulsions. The emulsification efficiency and yield forβ-carotene nanoemulsion powders are both higher than90%. By X-ray diffraction and IRmeasurement, the results indicated that there was an interaction between OSA modifiedstarches and β-carotene. And compared to the stability of nanoemulsions, a significantincrease was showed for the spray-dried powder under the same storage conditions. Theseresults indicated that it was a useful method to prepare nutraceutical emulsion powders toimprove stability.A further storage test was carried out to investigate the effect of relative humility (RH)on the storage stability of β-carotene powders. The results showed that modified starches withlower film oxygen permeability had a higher retention of β-carotene during storage. And themodified starches with higher film water permeability showed a stronger hygroscopicity. Theglass transition temperature of powder in different RH also affected the rate of β-carotenedegradation. The degradation of β-carotene increased at a higher RH before Tg. As thetemperature approached to Tg, the transformation from glassy to rubbery state occurs and there-encapsulation process would benefit for the decrease of degradation. Overall these resultsprovide useful information for choosing wall materials and storage conditions to protectnutraceuticals in delivery systems.更多还原