| Areca taro is mainly produced in coastal areas such as Fujian and Guangxi,and has a high content of starch.Pickering emulsion stabilized by solid particles as emulsifiers instead of traditional surfactants,which not only retains the characteristics of traditional emulsions,but also has the advantages of less emulsifier dosage and strong interfacial stability.In this research,the esterified starch(ES),ball-milling starch(BMS)and compound modified starch(CS)were prepared from the areca taro native starch which was modified by different methods,respectively.Their basic physicochemical properties,structure and pasting characteristics were studied in detail,compared with the native starch(NS).ES,BMS and CS were respectively used as particulate emulsifiers to prepare Pickering emulsions,the emulsifying properties of emulsifiers and the stability of emulsions were studied,compared with the emulsions stabilized by NS particles.Further,the emulsion stabilized by CS particles was taken as an example,the stable mechanism and the effect of the preparation conditions on the stability of the emulsion were investigated.The main research contents and results were as follows:(1)The basic physicochemical properties of ES,BMS and CS were studied,such as solubility,swelling power,transparency,anticoagulation and freeze-thaw stability,compared with NS.The results indicated that the solubility,swelling power and transparency of BMS were significantly improved,especially the cold-water solubility,but the anticoagulation and freeze-thaw stability were reduced.The solubility,swelling power,transparency,anticoagulation and freeze-thaw stability of ES and CS were significantly improved.It can be seen that the quality of NS and BMS after esterification with OSA is significantly improved.(2)The structure,pasting and rheological properties of ES,BMS and CS were studied by microscopy,scanning electron microscopy,infrared spectroscopy,X-ray diffraction,differential scanning calorimetry,visco-analyser and rheometer when compared with NS.The results suggested that the granules and crystal structure of ES did not significantly changed,but the infrared spectroscopy showed new absorption peaks at 1725 cm-1 and 1572 cm-1.Furthermore,the gelatinization temperature decreased and the peak temperature decreased from 81.77℃ to 78.83℃,while paste viscosity increased and the peak viscosity increased from 597.67 mPa·s to 2066.33 mPa·s.BMS particles were broken obviously,and crystal structure was also severely damaged,gelatinization temperature decreased and the peak temperature was 72.14℃,paste viscosity decreased and the peak viscosity was 296.33 mPa·s.What is more,CS granules were liquated and seriously damaged,the degree of substitution was increased from 0.01756 to 0.01994 compared with ES,which suggested a higher degree of esterification.Its gelatinization temperature was the lowest and the peak temperature was 65.69℃,paste viscosity was the highest and the peak viscosity was 5063.67 mPa·s.So CS has better low-temperature gelatinization and thickening properties.Before and after modified areca taro starch were characterized by pseudoplastic fluid.The apparent viscosity of ES and CS were both significantly increased,the increase of CS was mostly significant which also showed its better thickening properties.(3)Taking refined soybean oil as the oil phase,Pickering emulsion was prepared by ES,BMS and CS particles under certain conditions,respectively.In order to evaluate the emulsifying properties of emulsifiers and the stability of emulsions,the appearance,emulsification index(EI),droplet size and microscopic morphology of emulsions were investigated,compared with the emulsion stabilized by NS particles.The results indicated that the viscosity,emulsion layer volume and EI value of emulsion respectively stabilized by NS,ES,BMS and CS all increased in turn and the droplet size decreased.It showed that the emulsifying properties of the above emulsifiers sequentially increased,and the emulsifying property of CS was the best.After standing for a long time,the increase range of the droplet size of the above emulsions all decreased in turn,indicating that the emulsion stability sequentially increased,and the stability of the emulsion stabilized by CS particles was also the best.It can be seen that CS particles were prepared by ball-milling combined with OSA esterification are more favorable for the preparation of stable emulsions.(4)The emulsion stabilized by CS particles was taken as an example,the stable mechanism of the emulsion was studied by the confocal laser scanning microscopy,meanwhile,the effect of preparation conditions(starch content,oil phase volume fraction)on the stability of the emulsion was also studied.The results indicated that it was clear that the apparent starch particles were adsorbed at the oil-water interface and formed a physical barrier.And the upper and middle emulsion layer were uniform and stable after standing for a long time.Because of the contact of the lower emulsion layer with the water phase,the droplet size became larger,the uniformity and stability became worse.With the increase of CS content,the viscosity,emulsion layer volume and EI value of the emulsion increased,the droplet size gradually decreased,and their increasing range decreased after standing for a long time.The dynamic viscoelasticity of the emulsion showed that the storage modulus(G’)and loss modulus(G")increased,and tanδ decreased as the CS content increased,which indicated that the stability of the emulsion enhanced.With the increase of oil phase volume fraction,the viscosity,emulsion layer volume and EI value of the emulsion increased,but the droplet size as well as their increasing range gradually increased after standing for a long time,which indicated that the emulsion delamination was slowed while the stability of the emulsion also diminished.The dynamic viscoelasticity of the emulsion showed that G’ and G" increased and tanδdecreased when the oil phase volume fraction was less than 30%,G’decreased and tanδ increased when the oil phase volume fraction was higher than 30%,which indicated that the stability of the emulsion was reduced.Therefore,the oil phase volume fraction was controlled within the range from 10%to 30%,and the stability of the emulsion was better. |
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