Application And Preparation Of Octenyl Succinic Anhydride Starch As The Wall Material Of Microcapsule

Microencapsulation has been becoming a hotspot in research field about the stabilization of food sensitive ingredients, especially the bioactive ingredients, by the reason that it could protect the original structure, characteristics, and functionalities of bioactive food materials. The wall material plays a critical role in the preparation of microcapsules as it determines the embedding and releasing properties of the microcapsules. Octenyl succinate starch, an amphiphilic polymer as one of the microencapsulation wall materials, has been drawn great attention for its higher safety, better emulsifying properties and viscosity properties. Therefore, a series of octenyl succinate starches have been produced to adapt to different embedded requirements in foreign countries. However, the domestic products are lacking and their embedding performance is poor compared with the imported products. Furthermore, the price of the imported products is much higher than that of the domestic products. Therefore, the application of the octenyl succinate starch is very limited.In consideration of the problems which restrict the preparation of octenyl succinate starch and its application as microencapsulation wall material, the method of octenyl succinate starch synthesis and degradation was developed and the chain structure, crystal structure and morphology were also characterized. Meanwhile, the influence of molecular structure on the embedding properties of the octenyl succinate starch was indicated. On these bases, different kinds of bioactive food ingredients were microencapsulated with the prepared octenyl succinate starches as microcapsule wall materials and their microencapsulation performance was compared with that of the imported and domestic octenyl succinate starches purchased from market. Furthermore, the microencapsulation performance of octenyl succinate starches prepared from different kinds of native starch was investigated. From which, the microcapsule wall materials, octenyl succinate starches which could meet different application requirements were obtained by adjusting their microencapsulation performance. The main results were summarized as follows:The optimal synthesis process for octenyl succinate starches by the experiments of single factors and response surface analysis was obtained. The results showed that the octenyl succinate starch with largest degree of substitution (DS) was prepared by the esterification between waxy corn starch and octenyl succinic anhydride(OSA) (6.5% OSA based on dry starch solids) at 35℃and pH 9.0 for 4.2h. The effects of varied factors such as added amount of OSA, reaction time, reaction temperature and pH value on the esterification were studied. The results showed the esterification extent was mostly affected by the added amount OSA, the second was pH value, the third was reaction time and then was reaction temperature.The molecular weight of octenyl succinate starches with different DS greatly reduced after high-temperature degradation process and the molecular weight distribution was mostly below 100,000 Dalton. The results showed that the reaction temperature, reaction time and the starch amount all affected the molecular weight distribution and molecular size and the reaction temperature affected mostly.Fourier transform infrared spectroscopy analysis showed that octenyl succinate group introduced to the waxy corn starch molecule after OSA esterification and this group could not be degraded or changed during the heat treatment. Polarizing microscopy, X-ray diffraction and small angle X-ray scattering analysis showed that the crystalline morphology of octenyl succinate starches with different DS was still A type crystalline structure which did not change after esterification and heat treatment, the esterification occurred mainly in the amorphous regions of the starch granules and the order of the crystalline layer and amorphous layer reduced as the DS increased. Scanning electron microscopy showed morphology of the starch granules was destroyed on different degree after esterification, but the starch granules become slightly larger and still were round in high-temperature degradation which only affected the free volume of the starch molecular.Further, the emulsifying properties of OSA modified waxy corn starch were greatly improved and the viscosity of their pastes was greatly reduced after high-temperature degradation and esterification processes, while the viscosity and emulsifying properties were sensitively affected by the molecular size and molecular weight distribution compared with the effect of the degree of substitution.Wheat germ oil was microencapsulated with OSA modified waxy corn starch as microcapsule wall material by using spray-drying method. The microencapsulation performance of the prepared OSA modified waxy corn starch was better than that of the domestic products and was close to that of the imported products through the analysis of the results of surface oil, extraction oil by solvent, embedded oil, encapsulated capacity, release properties, particle size and morphology. As a results, the encapsulated capacity of the prepared OSA modified waxy corn starch can reach 98.5% and had a good adaptability to different core materials because of its excellent emulsifying properties and suitable viscosity resulted in a much thicker and denser layer in the microencapsulation process.The octenyl succinate starches prepared by the method of water dispersion and high temperature degradation have a good potential industrial application for their equivalent microencapsulation performance to the imported products and lower price than the domestic products. After indicating that the sensitivity factors affected the DS and the molecular size and molecular weight distribution were the amount of octenyl succinic anhydride and the degradation temperature, the controlled method of adjusting the emulsifying properties and viscosity properties of wall material was developed by controlling the DS and the molecular size and molecular weight distribution. All the results provide theoretical foundation and basic data for the design of octenyl succinate starches embedded wall material with excellent performance to meet different requirements and their industrial applications.