Effects Of Ultrasonic Treatment On Chemical Structure And Functional Properties Of Chickpea Protein Isolate

In recent years,ultrasonic technology has been widely used in the food industry due to its green,efficient and pollution-free advantages.The functional properties of chickpea protein are limited in practical production and application due to the influence of its original protein composition and chemical structure.Therefore,it is necessary to find a suitable modification method to change its protein composition and chemical structure,so as to improve its functional properties.This study took chickpea protein(CPI)as the research object to analyze the chemical structure,functional properties and in vitro digestibility of ultrasonically modified chickpea protein.Combined with the addition of pectin,the stability of chickpea protein emulsion was explored.The results are as follows:1.The effect of ultrasonic treatment on the chemical structure of chickpea protein.Chickpea protein(CPI)extracted by alkali solution and acid precipitation was treated with ultrasound for different time(10 min,15 min,30 min)and different power(200 W,400 W,600 W).The solubility,zeta potential and chemical structure of CPI before and after ultrasonic treatment were measured.The results showed:The extracted CPI protein content was 91.66%,the moisture content was 4.50%,the fat content was0.99%,and the ash content was 2.31%;ultrasonic treatment enhanced the solubility of CPI;the absolute value of zeta potential of CPI solution after ultrasonic treatment are higher than those before treatment,indicating that the ionization degree of CPI group is enhanced after ultrasonic treatment;ultrasonic treatment changed the sulfhydryl content and surface hydrophobicity of CPI,exposing more free sulfhydryl groups and hydrophobic binding sites;after ultrasonication,the hydrophobic amino acid content of CPI increased,and the subunit distribution remained basically unchanged.The FT-IR spectrum data showed that the random coil structure was transformed into aβ-sheet structure under 30 min of sonication,and the endogenous fluorescence spectrum showed that the fluorescence intensity of the sonicated CPI decreased.This indicates that ultrasonic treatment can change the secondary and tertiary structure of CPI,but has no effect on the primary structure.2.The effect of ultrasonic treatment on the functional properties and in vitro digestibility of chickpea proteinThe sonicated chickpea protein was mixed with sunflower oil,and a crude emulsion was prepared by high-speed homogenization,and its emulsifying activity index(EAI)and emulsifying stability index(ESI)were determined,and the foaming ability and in vitro digestibility of the samples were also determined.The results showed that ultrasonic treatment significantly increased the EAI and ESI of CPI,and decreased the particle size of CPI emulsion.The minimum emulsion particle size was observed at 15 min/600 W.The ultrasonic cavitation effect induces the aggregation and unfolding of CPI molecular structure,improves the adsorption capacity of proteins at the water-oil interface,and promotes the improvement of protein emulsification.The emulsion exhibited the smallest particle size and the largest absolute value of Zeta potential at p H 12.0 and Na~+concentration of 0.8 mol/L and 0.1 mol/L,respectively,that is,the best emulsifying activity and emulsifying stability.The foaming capacity of CPI was the largest at 15 min/200 W(114.44%),and the foaming stability of CPI was significantly enhanced.Sonication enhances the in vitro digestibility of CPI due to altered protein conformation and exposure of cleavage sites,promoting protein accessibility by digestive enzymes,and increasing digestibility.3.Effect of pectin addition combined with ultrasonic treatment on the stability of chickpea protein emulsionSelect the CPI with the best emulsification characteristics of ultrasonic treatment,that is,15 min/600 W,and different concentrations(0.1%,0.5%,1%)of citrus pectin,according to different protein:pectin ratios(1:1,2:1,5:1,10:1,20:1),the preparation of chickpea protein-citrus pectin complex(CPI-CP)was carried out at p H 3.5,and the turbidity and Zeta potential of the complex solution were measured.The emulsion was prepared by high-pressure homogenization,and the particle size and microscopic observation of the emulsion were carried out during the storage period of 12 days.The results showed that after ultrasonic treatment of CPI,the addition of pectin could significantly improve the physical stability of the composite system even if the pectin content was low.The particle size of the CPI-CP composite emulsion showed a smaller particle size increase during storage of the sonicated CPI-CP emulsion,as evidenced by the microscopic images.Compared with the CPI-CP composite emulsion without ultrasonic treatment,the composite emulsion after ultrasonic treatment is more stable,and the emulsion has a relatively longer shelf life.