Citric Acid Modified Soybean Residue Insoluble Dietary Fiber And Pickering Emulsion Application Study

Okara is a waste generated during the processing of traditional soy products and is often used in low-cost feed and fuel applications.However,okara is rich in nutrients,especially the dietary fiber can account for 50%～60%of the dry matter of okara,of which insoluble dietary fiber（IDF）accounts for more than 90%of the total dietary fiber.Therefore,in order to improve the functional activity of the dregs IDF,citric acid is used to modify it,so that the insoluble dietary fiber is nanomorphized and the emulsification is improved,which provides theoretical and practical guiding significance for the development and application of okara fiber products and Pickering emulsion.As a weak tricarboxylic acid,citric acid（C6H8O7）is widely used to modify insoluble dietary fiber due to its non-toxic and easily recyclable properties.In addition,the citric acid modified IDF exhibits excellent dispersibility in the aqueous phase.And citric acid is easy to recover after hydrolysis,and the hydrolyzed sugar can be used as a precursor for the production of platform chemicals such as lactic acid and furfural,so as to achieve the purpose of green environmental protection.Therefore,this study provides a green and sustainable way for the efficient production of IDF with high dispersion and high emulsion stability,while exploring the optimal preparation conditions and tolerance to environmental factors of Pickering emulsion,and further exploring the interface composition and structure of Pickering emulsion.The main findings are as follows:1.Study on the emulsification stability of citric acid modified insoluble dietary fiber（OIDF,C₆H₈O₇-IDF）emulsion stability（ESI,Emulsion stability）:Taking the emulsification stability as the index,IDF was modified by citric acid,and the effects of citric acid concentration,hydrolysis temperature and hydrolysis time on the emulsification stability of IDF were explored.Through the single factor test and Box-Behnken test to obtain the best preparation conditions:the acid concentration is 70%,the hydrolysis temperature is 70°C,the hydrolysis time is 4h,under this optimal condition,after three parallel tests,the emulsification stability is obtained as 195.64±1.16%,with the continuous increase of acid concentration,the emulsification stability of IDF first increases and then decreases.Response surface analysis showed that IDF with the best emulsification stability under this process condition was a solid emulsifier for the preparation of highly stable Pickering emulsion in the later stage.2.The composition determination and physical and chemical properties（water-holding property,oil-holding and swelling）of IDF and OIDF were analyzed,and the physical and chemical structure analysis of IDF and OIDF was carried out by scanning electron microscopy（SEM）,Fourier transform infrared（FTIR）,X-ray diffraction（XRD）,atomic force microscopy（AFM）,differential calorimetry scanning（DSC）,thermogravimetric analysis（TG）,etc.,and it was found that the size of OIDF modified by citric acid was reduced from 200μm to 293 nm.And after citric acid modification,the water holding capacity of OIDF increased by 30.4%,the oil holding capacity increased from 4.31 g/g before treatment to 4.78 g/g,the swelling capacity increased by 27.5%,and the soluble dietary fiber content increased significantly.3.The emulsifying activity index and emulsification stability index of Pickering emulsion were used as the indicators of univariate test,and the optimal preparation conditions were obtained by comprehensive analysis:solid emulsifier concentration of 2.0%,oil phase ratio of15%,p H of 7,and the ESI of Pickering emulsion（OIDF-Pickering）prepared by OIDF was963.28%,and the average particle size was 2.30μm.After 30 days of storage at 4°C,no stratification occurred in the OIDF-Pickering emulsion.Pickerine emulsions prepared by OIDF as a solid emulsifier have high stability compared to IDF.The effects of IDF and OIDF on the emulsification characteristics and interfacial stability of Pickering emulsions and the tolerance to environmental factors were compared.The analysis showed that OIDF had good suspension stability and dispersibility,which indicated that OIDF was adsorbed at the oil-water interface to form a complete interface barrier,while IDF was not closely connected to the oil-water interface.Pickerine emulsion stabilized by OIDF presents a denser and stronger bridge network structure and gel-like characteristics,and the surface tension is significantly reduced（p<0.05）,and the Pickering emulsion system constructed by OIDF has a high degree of homogeneity and stability.In summary,OIDF can be used as an efficient natural food-grade solid emulsifier because the size of the nanometer level is much smaller than the droplet size of the target emulsion（at least one order of magnitude smaller）,and Pickering emulsion stabilized by OIDF as a solid emulsifier shows stronger emulsifying ability.It also shows significant advantages in storage,which provides a theoretical basis for the development and application of IDF.