Adsorption Of Cadmium In Rice Flour By Chitosan/EDTA/Rhamnolipid Composite And Its Application

With the rapid development of modern industry and agriculture,heavy metal pollution of farmland in China is widespread.The heavy metal cadmium(Cd)cannot be degraded by microorganisms and accumulates in the soil.Compared with other cereal crops,rice is more likely to accumulate Cd from the soil.Cadmium can lead to anemia,heart failure,liver and lung damage with long-term intake.It is urgent to solve the problem of quality and safety of rice with excessive cadmium.At present,a variety of rice cadmium reduction techniques have been put into use,but these methods still have certain limitations in practical application,such as the loss of nutrients and deterioration of functional properties of rice.Therefore,based on the existing cadmium reduction methods,it is necessary to combine the advantages of each method for cadmium reduction of rice with excessive cadmium.In this paper,a novel chitosan/EDTA/rhamnolipid composite,namely CTS/EDTA/RL micro-nanoparticles,was successfully synthesized by acylation and ionic cross-linking reactions using chitosan(CTS),ethylenediaminetetraacetic acid(EDTA)and rhamnolipid(RL)as raw materials.The preparation conditions of the composites were optimized by single-factor tests,and characterized by particle size analysis,transmission electron microscopy analysis and Fourier infrared spectroscopy analysis.The composite material was used for cadmium reduction of rice flour with excessive cadmium standard,and the parameters of cadmium reduction process were optimized by single-factor test and response surface test.The changes of main chemical composition,microstructure,crystal structure,thermodynamic properties,pasting properties,infrared spectrogram,rheological properties and chromaticity of rice flour before and after cadmium reduction were analyzed and compared,providing technical basis and theoretical reference for the removal of cadmium from rice flour,which has certain practical application value.(1)The best preparation process of CTS/EDTA/RL composite was studied by singlefactor test,and the best preparation process was obtained:EDTA:CTS was 3:1(w/w);reaction pH was 5.0;1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride(EDAC·HCl)concentration was 20 mmol/L;rhamnolipid concentration was 40%(v/v);Sodium tripolyphosphate(TPP)addition was 25%(v/v),at which the Cd2+ adsorption rate was 82.71%.The results of transmission electron microscopy,FTIR spectra and particle size distribution showed that the CTS/EDTA/RL micro-nanoparticles were dispersed nearly spherical with an average particle size of 141.8 nm.(2)CTS/EDTA/RL was used for the adsorption of cadmium in rice flour with cadmium content of 0.5007 mg/kg as raw material.The optimal levels of each factor in the cadmium reduction process of rice flour were initially determined by the single-factor test:the adsorption time was 120 min,the adsorption temperature was 45℃,the liquid to material ratio was 10 mL/g,and the addition of CTS/EDTA/RL was 50%(v/v).Based on the singlefactor test,a response surface optimization test was conducted to obtain the best cadmium reduction process:adsorption time of 123 min,adsorption temperature of 48℃,liquid-tomaterial ratio of 10 mL/g,and CTS/EDTA/RL addition of 45%(v/v),at which the cadmium removal rate in rice flour could reach 72.93%.Different reagents were selected for cadmium adsorption in rice flour,in which the cadmium reduction rate of rice flour by ultrapure water treatment was 2.44%,CTS was 19.12%,EDTA was 35.77%,RL was 5.09%,and CTS/EDTA was 61.85%,indicating that the cadmium reduction rate of rice flour by CTS/EDTA/RL micro-nanoparticles was significantly higher than other reagents.(3)After cadmium reduction by CTS/EDTA/RL,the moisture content of rice flour decreased from 13.09%to 9.64%,the protein content decreased from 8.86%to 8.52%,the rice starch was relatively enriched,the content increased from 75.29%to 80.15%,the straight chain starch content increased from 22.49%to 23.10%,while the fat content of rice flour did not change significantly.Microstructural analysis showed that the structure of rice flour was looser after cadmium reduction,some depressions and cracks appeared on the surface of rice flour,and more voids were generated in the structure of rice flour particles.Crystal structure analysis showed that rice starch still showed A-type crystalline structure after cadmium reduction,and the crystallinity increased.The results of thermal characteristics and pasting characteristics showed that the pasting temperature of rice flour decreased and the peak viscosity and attenuation values increased after Cd reduction treatment,indicating that CTS/EDTA/RL treatment was beneficial to improve the taste quality of rice flour.The results of FTIR spectra showed that the cadmium reduction treatment did not cause the rice flour to produce new chemical bonds and moieties.Rheological analysis showed that the rice starch gel was not easily destroyed after cadmium reduction,and the rice flour paste viscoelasticity increased and showed stronger solid characteristics.The colorimetric analysis showed that the whiteness value of rice flour increased after cadmium reduction.