Physicochemical Properties And Modification Of Okara Fiber And Protein

With the concept of green development deeply rooted in people's minds,the reuse of agricultural and sideline products has attracted more and more attention.As the main by-product in soybean production and processing,okara not only has a large yield but also contains rich dietary fiber and protein.It is a kind of agricultural processing waste with wide source,low price and excellent health effect.However,the current utilization of okara is mostly limited to feed.The exploitation and utilization of okara in food field is relatively shallow in breadth and depth,and the additional value of the product is low.This study is aimed at exploring the physical and chemical properties of okara fiber and okara protein,and improving its water holding capacity,oil holding capacity and solubility by means of ball milling,hydraulic cavitation and enzymatic hydrolysis,so as to expand the utilization of okara in food field.The main conclusions are as follows:(1)The effects of ball milling,hydraulic cavitation and enzymatic hydrolysis of plant hydrolase on the physicochemical properties of okara were studied.Ball milling can significantly reduce the particle size of okara,improve the color of okara and increase the content of soluble dietary fiber(SDF).The modification effect was positively correlated with the milling rate.The thermal energy and high mechanical strength released through cavitation collapse can make the structure of okara loose and expose more hydrophilic and lipophilic groups to improve its water and oil holding capacity significantly and reduce the viscosity of the solution.However,with the prolongation of hydraulic cavitation(>10min),the structure of okara may be further damaged,leading to a significant decrease in water and oil holding capacity.Plant hydrolases with cellulase,pectinase and lignase can also specifically break the glycosidic bonds in okara fibers to release more SDF and reduce the viscosity of okara.The enzymatic assisted cavitation treatment can further increase the SDF content,improve the water and oil holding capacity and significantly reduce apparent viscosity of okara on the basis of the single treatment of cavitation and enzymatic hydrolysis,which may be conducive to the application of okara in liquid food.(2)Okara protein(OP)was extracted under alkaline conditions(p H 12.0)and precipitated with hydrochloric acid,citric acid and phosphoric acid.Compared with soybean protein isolate(SPI),OP contained Bg7S and a small amount of oil body protein in addition to 7S and 11S.OP contained more disulfide bonds,and it was more hydrophobic and more digestible.Hydrophobic interaction,hydrogen bond and disulfide bond were all involved in the formation and stability of OP higher structure,and hydrophobic interaction played a dominant role.Different acid precipitation and high-pressure microfluidization treatments have important effects on the structure and functional properties of OP.Citric acid,as a strong ternary organic acid,can continuously ionize H⁺in the process of acid precipitation to recover higher purity OP.The SDS-PAGE spectrum showed that OP(HCl)was rich in macromolecular aggregates,and therefore showed worse solubility.In addition,the disulfide bond content of OP(H₃PO₄)was higher than that of OP(HCl)and OP(CA).The high-pressure microfluidization can effectively reduce the particle size and turbidity of OP,and made the protein structure fully unfold to show better solubility.The free sulfhydryl groups in OP can be induced to exchange sulfhydryl and disulfide bonds to form new disulfide bonds under high-pressure microfluidization treatment.(3)Okara protein-phytosterol nanoparticles(OP-PS)with stable properties were prepared by anti-solvent technology combined with high-pressure microfluidization treatment using OP.High-pressure microfluidization treatment can significantly reduce the particle size of OP-PS and improve the encapsulation rate of phytosterol(PS).The particle size of OP-PS can be reduced to 133.15 nm after three cycles of 120 MPa high-pressure microfluidization treatment.Meanwhile,the encapsulation rate of phytosterol was as high as 98.63%,and the water-soluble redispersibility of the nanoparticles was good.The stability of OP-PS particles was evaluated.It was found that after 50 days of storage at room temperature,the encapsulation rate of PS was still about 66.90%,and the thermal stability was significantly better than that of soybean protein isolate-phytosterol particles(SPI-PS)prepared under the same conditions.This may be attributed to the fact that OP had significantly higher free sulfhydryl groups and disulfide bonds than SPI.High-pressure microfluidization can induce the formation and cross-linking of intramolecular or intermolecular disulfide bonds of protein,which can effectively improve the stability of nanoparticles.