Research On Effect Of Aicd-Precipitation Condition On Cadmium Content,Structure,and Functional Properties Of Rice Bran Protein

Cadmium pollution in rice was more serious in China in recent years.Cadmium was mainly distributed in rice bran layer in the form of protein complexes.Therefore,there was a safety hazard in the development and utilization of rice bran protein.In this thesis,defatted rice bran which polluted by cadmium was used raw material,and effects of acid-precipitation condition on cadmium content as well as functional properties and structural characteristics of rice bran protein were studied by using a variety of organic acids which replacing hydrochloric acid in the process of conventional preparation of rice bran protein by alkali-extraction and acid-precipitation method.Firstly,based on the investigation of the effect of acid-precipitation on the cadmium content of rice bran protein with mixed-acids under different pH,effects of mixed-acids composition,acid-precipitation time,and acid-precipitation pretreatment(magnetic stirring,high-speed shearing,colloid grinding)on cadmium content by acid-precipitation were studied,and effects of acid-precipitation on the composition of rice bran protein were also analyzed.The results showed that when the same acid was used to precipitate rice bran protein,the cadmium content of rice bran protein gradually decreased as the pH value of acid-precipitation decreased.Acid-precipitation by tartaric acid,malic acid,and citric acid could effectively removed cadmium.As acid-precipitate time increased,cadmium content of rice bran protein firstly increased,and then decreased.Precipitation mixed-acids and Acid-precipitation pretreatment(magnetic stirring,high-speed shear,colloid mill processing)had insignificant effect on cadmium content of rice bran protein.Acid precipitation with organic acid can effectively remove cadmium from rice bran albumin and globulin.Secondly,effects of acid-precipitation on functional properties of rice bran protein were studied.The results indicated that as the same acid was used to precipitate rice bran protein and pH value of acid-precipitation decreased,solubility,water holding capacity,foam stability,and emulsion stability of rice bran protein gradually decreased;oil holding capacity,foamability,and emulsifying activity firstly increased,and then decreased,which reached the maximum value at pH 3.0.Compared with hydrochloric acid which used in traditional alkaline-extraction and acid-precipitation method,acid-precipitation by tartaric acid,malic acid,and citric acid at pH3.0 could effectively improved functional properties of rice bran protein.Thirdly,effects of acid-precipitation on structural characteristics of rice bran protein were investigated.The results indicated that when the same acid was used to precipitate rice bran protein,free sulphydryl and random coil content gradually increased,P-sheet and P-tum content decreased,total sulphydryl content,α-helix,andβ-sheet content had insignificant changes as acid-precipitation pH decreased;intrinsic fluorescence intensity,surface hydrophobicity,and absolute value of zeta potential value firstly increased,then decreased,and reached the maximum value at pH 3.0,which indicated that the structure of rice bran protein was gradually unfolded,and the internal group gradually exposed.The results of molecular weight distribution,particle size distribution,and electrophoresis analysis of rice bran protein indicated that rice bran protein does not form aggregates and new subunits.When the pH value of acid-precipitation was the same,structural characteristics of rice bran protein could not affected by acid-precipitation with different acid.Finally,emulsion stability of rice bran protein which removal of cadmium removing by hydrochloric acid,tartaric acid,malic acid,and citric acid precipitation at pH 3.0 was studied.The results showed that as rice bran protein concentration was 0.5%,there were insignificant differences(P>0.05)in the emulsion stability of rice bran protein among the four kinds of acids precipitation,and the emulsion stability was poor.When the rice bran protein concentration was 1.0%or 2.0%,the emulsion of rice bran protein after cadmium removing by tartaric acid,malic acid,and citric acid-precipitation had smaller particle size,less flocculation,and lower creaming index,which exhibited better emulsion stability.Preheat treatment of rice bran protein which removed cadmium by acid-precipitation resulted in decreasing of size of emulsion particle,promotion of emulsion stability,and there is insignificant difference(P>0.05)in emulsion stability of rice bran protein after cadmium removing by four kinds acid precipitation.