| In recent years,food grade Pickering emulsifiers constructed by biomass-based edible solid particles have attracted increasing interests in the food industry,due to their great stability against coalescence and their compatibility with food.Taro starch,as the ultra-small granule starch(1?3 ?m)existing in nature,has the advantages of low allergenicity and easy digestion,which is the ideal precursor to construct the food grade Pickering emulsifier,and has the important potential uses in the fields of functional food and biomedical formula.In this study,taro starch(NTS)with high-purity was used as raw material to construct food-grade Pickering emulsifier-OSA modified taro starch(OSTS)through octenyl succinic acid(OSA)modification.The physicochemical properties,emulsifying properties,stability mechanism and application of OSTS in functional emulsion-based delievery system were systematically studied.The research results provide theoretical guidance and technical support for the creation of n ovel starch-based emulsifiers in the field of food industry and the construction of functional starch-stabilized emulsion delivery systems.The main research methods and conclusions of this paper were as follows:(1)NTS was extracted by alkaline protease method and it was used as raw material to prepare OSTS through wet process;Taking the degree of substitution(DS)as an indicator,the optimal process parameters were obtained through response surface test: Starch concentration 37%,reaction temperature 36 °C,reaction time 5 h,p H value 8.4;The OSTS sample(DS=0.0188)prepared under this condition has high purity,good quality,white color,fineness and smoothness,and can be used as food-grade OSTS in the food field.FTIR,SEM,XRD and DSC were used to analyze and characterize the samples.It was confirmed that there wer e ester carbonyl groups(1724 cm-1)and carboxyl groups(1572 cm-1)on starch molecules.At the same time,it was found that OSA modification did not change the particle size(1?3 ?m)and crystal structure(type A)of NTS,but could significantly reduce the T0?TP?TC and ?H of NTS.(2)OSTS with different DS(0.009?0.032)were prepared by adjusting the amount of OSA,and used as particle emulsifier to prepare O/W Pickering emulsion.By characterizing and analyzing the structure characteristics of OSTS and t he physicochemical properties of the OSTS-emulsions,the influence path and mechanisms of DS on the stability of OSTS-emulsions were explored.OSA modification significantly enhances the wettability of OSTS particles,thus effectively improving their emulsifying properties.With the increase of DS,the emulsification activity of OSTS gradually increased,the droplet size of Pickering emulsion formed by OSTS gradually decreased,and the viscoelasticity,centrifugal and storage stability of the OSTS-emulsion gradually increased.The increase of DS can enhance the hydrophobic interaction between OSTS particles,and further enhance the interfacial interaction between droplets,thus contributing to the formation of gel network structures between droplets,droplet s-particles,and particles,and achieving strong interfacial stability of OSTS Pickering emulsion.(3)OSTS Pickering emulsion was prepared by combining high-speed shearing and high-pressure homogenization process.The influence of emulsion formula factors(emulsifier concentration,oil-water volume ratio)and homogenization process conditions on the stability of OSTS-emulsion was explored.The results showed that with the increase of emulsifier concentration,the droplet size of emulsion gradually decreased,the ?a and centrifugal stability of emulsion gradually increased.With the increase of oil volume fraction(?: 16.7%?33.3%),the droplet size of emulsion gradually increased,the ?a and centrifugal stability of emulsion gradually increased as well.When ? was at 50.0%?67.7%,the concentration of emulsifier in the emulsion was relatively low,which was not enough to form a compact and stable droplet interfacial film,thus the centrifugal stability of the emulsion was poor.With the increase of homogenization pre ssure(homogenization cycle),the size of emulsion droplets gradually decrease d,the dispersion stability of droplets gradually increased,and the centrifugal stability of the emulsion also gradually increased.In addition,the application of high-pressure homogenization process had achieved a significant change in the droplet size of OSTS Pickering emulsion from micron to nano-scale.(4)Amorphous taro starch-based emulsifier(GOSTS)was prepared through the gelatinization treatment of OSTS and it was then used as emulsifier to construct O/W emulsion.By characterizing and analyzing the particle size,rheological and physicochemical properties of GOSTS-emulsions(0.009?0.032),the influence path and mechanism of DS on the emulsion stability were explored.With the increase of DS,the emulsification activity of GOSTS gradually increases,the particle size of emulsified emulsion droplets gradually decreases,and the viscoelasticity,centrifugal and storage stability of emulsion system gradually increase.Starc h molecular chains in GOSTS(DS?0.018)aqueous dispersion system can self-assemble to form a weak gel network structure driven by hydrophobic interaction and hydrogen bonds,thus endowing it with multi-scale particle size distribution and enhanced viscoelastic properties.Meanwhile,these gel matrices can act as dispersed phases to enhance the viscoelasticity of the emulsion system,thus improving the physical stability of the emulsion.With the increase of DS,the viscoelasticity of GOSTS gradually increases,and the viscoelasticity of the formed GOSTS-emulsion system gradually increases as well.(5)Using OSTS and GOSTS(DS=0.0188)as starch-based emulsifiers,MCT as oil phase carrier and curcumin as lipophilic functional factor model,food-grade curcumin-loaded emulsion delivery system was constructed.Through the analysis of curcumin loading rate,physicochemical properties and in vitro digestion characteristics of the OSTS-and GOSTS-based emulsion delivery systems,the ways and mechanisms of improving curcumin bioavailability by the two emulsion delivery systems were preliminarily explored and compared.The results show that compared with curcumin-lodaded OSTS Pickering emulsion,GOSTS emulsion has smaller droplet size,stronger viscoelasticity and higher curcumin loading rate.At the same time,the analysis of CLSM and FFA release during in vitro digestion of the emulsions showed that due to its smaller droplet size,GOSTS emulsion has a faster oil hydrolysis rate in the simulated small intestine digestion stage,which helps to accelerate the release of curcumin in the oil phase and its transport in the mixed micelle phase,and finally further improves the bioaccessibility of curcumin.(6)OSTS and GOSTS(DS=0.0188)curcumin emulsions were used as templates to investigate whether OSTS and GOSTS have the function of emulsifying wall materials through spray drying process.The results show that both emulsions have the characteristics of direct spray drying and curing to form microencapsulated powder,that is,OSTS and GOSTS have the function of emulsifier and emulsified wall material.In addition,the redissolution experiment and morphology observation of OSTS and GOSTS curcumin emulsion microcapsule powder show that the GOSTS powder samples has more uniform particle size and better redissolution effect than OSTS powder samples.SEM analysis shows that the film-forming properities of GOSTS as emulsified wall material was more stable. |
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