Construction Of OSA-modified Tartary Buckwheat Starch-based Pickering Emulsion And Its Application In Transporting Rutin

With good biocompatibility and stability of starch,protein and other solid particle sources of Pickering emulsions have become a hot research topic in recent years.Tartary buckwheat is a class of small grains widely grown in the southwest of China for medicinal and food purposes,and has good nutritional value.The starch of Tartary buckwheat（TBS）is the most important source of carbohydrates,with small particles,low allergenicity,high peak viscosity,hot paste stability and cold paste stability and other characteristics,but also has poor hydrophobicity,poor emulsion stability and other limitations.Rutin,also of Tartary buckwheat origin,has a variety of biological activities such as antioxidant,anti-inflammatory and hypoglycemic effects,but the low solubility of the corresponding product limits the further development of applications.To improve these deficiencies and increase the versatility of TBS and rutin applications,this paper presents a study of octenyl succinic anhydride（OSA）modified Tartary buckwheat starch（OS-TBS）,the preparation of OS-TBSs based Pickering emulsions and further analysis to study their transport properties.The main research methods and conclusions of this paper are as follows:（1）Tartary buckwheat starch was extracted by soaking in alkaline solution and modified with OSA（OSA added at 3%,5%and 7%of starch mass）to obtain OS-TBSs（OS-3%,OS-5%and OS-7%）.The degrees of substitution（DS）of the OS-TBSs were 0.0184,0.0251and 0.0312,respectively,as determined by titration.The successful substitution of starch hydroxyl groups by OSA modification was further verified by the discovery of a characteristic carbonyl peak at 1726 cm^-1 and a carboxyl stretching vibration peak at 1573 cm^-1 of the starch molecule as measured by FT-IR spectroscopy.A series of physical and chemical indexes such as scanning electron microscopy,particle size determination,X-ray diffraction spectroscopy and differential scanning calorimetry showed that the OSA modification did not change the original morphological structure and"A"crystalline structure of TBS,the esterification reaction mainly occurred in the amorphous region of starch,and the straight chain starch content and crystallinity of starch were reduced.The thermal properties analysis indicated a significant decrease（p<0.05）in T_o,T_p and T_c of OS-TBSs,resulting in a decrease in the energy required for starch pasting.（2）OS-TBSs-based Pickering emulsions were prepared by high-pressure homogenization method,and the stability of the emulsions was investigated at different particle concentrations,different oil phase ratios（Φ）,different p H and different Na Cl concentrations.It was found that the particle size of OS-TBSs-based Pickering emulsions were smaller than that of TBS-based Pickering emulsions,and decreased gradually with the increase of OS-TBSs DS in the emulsions.The particle adsorption at the oil-water interface of the emulsion is saturated at 4%（w/w）particle concentration and the Pickering emulsion has a small particle size and uniform particle size distribution.Pickering emulsions prepared with an oil phase ratio of 30%（v/v）are more homogeneous and stable,and the oil droplets are stably coated by the starch granules.At alkaline conditions（p H=11）Pickering emulsions become less stable,the emulsifier flocculates and the emulsion delaminates.An increase in the concentration of Na Cl in the emulsion（100 m M）leads to a decrease in electrostatic repulsion between particles at the emulsion interface,a gradual decrease in surface charge triggering aggregation of particles,an increase in particle size and a decrease in emulsion stability.Further analysis of OS-TBSs based Pickering emulsions prepared at 4%（w/w）particle concentration,Φ=30%,neutral and free of salt ions,revealed that the emulsion system was an elastic dominated pseudoplastic fluid showing shear thinning.The emulsion droplet distribution was dense and homogeneous,and remained uniform and stable during 30days of storage at room temperature without significant delamination,showing excellent storage stability.（3）OS-TBSs-based rutin Pickering emulsions were prepared,and the emulsions droplet size were less than 300 nm.After 30 d of storage at room temperature the particle size of the emulsion changed by<100 nm and the stability remained good.The rheological tests show that the pseudoplastic fluid characteristics of the emulsion were not altered.Subsequently,in vitro simulated gastrointestinal digestion was performed to investigate the release of rutin from the emulsions,using oil-water mixtures of rutin（OS-3+R and OS-5+R）as controls.It was found that rutin was better released in the intestinal tract in both the OS-3-R_（L/H）and OS-5-R_（L/H）groups of the emulsions at different rutin concentrations（1.5～3.0 mg/m L）,with the final cumulative release rates reaching 98.47%,98.36%and 79.36%,76.94%,significantly higher（P<0.05）than the release of free rutin in the oil-water mixture OS-3+R and OS-5+R（62.21%and 60.80%）.Finally,an ulcerative colitis model mouse was established and the effect of OS-TBSs based rutin Pickering emulsion on the symptoms of colitis in model mice was further investigated in in vivo experiments.It was found that the rutin Pickering emulsion group better alleviated and improved the symptoms of colitis in mice compared to the rutin oil-water mixture group,further improved the bioavailability of rutin.