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Research on the Preparation and Characteristics of Nanoemulsions Using OSA Modified Starch as Emulsifier

Author: LiangRong
Tutor: MaJianGuo
School: Jiangnan University
Course: Of Food Science
Keywords: nanoemulsion modified starch peppermint oil β-carotene storage stability antimicrobial property bioaccessibility glass transition temperature
CLC: TS201.7
Type: PhD thesis
Year: 2013
Downloads: 377
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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.

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