Study On Removal Technology Of Cadmium In Rice And Its Toxicity Evaluation

In recent years,the issue of food safety caused by cadmium pollution in rice has been paid more and more attention.According to statistics,from 2005 to2013,there have been five major domestic cadmium pollution incidents related to rice,and the annual output of cadmium-tainted rice is close to 20 million tons.Cadmium-tainted rice couldn't be edible,resulting in inventory backlog,which not only affected the normal development of the food economy,while affecting the safety of rice consumption,endangering the health of consumers.Therefore,how to remove the excess amounts of cadmium in cadmium-tainted rice,for the purpose of reaching or getting lower than the limited standard of the cadmium content in rice,is significant for rational utilization of food resources and ensuring the quality and safety of food.After removal of cadmium,the rice can be utilized as raw materials of feed,cosmetics,alcoholic fermentation,which can help to realize the safe conversion and utilization of cadmium-tainted rice.In this paper,contaminated rice as raw material,the main nutrients and cadmium content were analyzed and determined firstly to confirm the exceeding information of cadmium in rice;The removal efficiency of cadmium in rice by solvent complex extraction was studied and the best process of removing cadmium was optimized;Speciation of cadmium in rice was studied by the method of elemental speciation analysis;Finally,caenorhabditis elegan was selected as a model animal to evaluate the toxicity of different cadmium speciation,including the solution extracted by solvent complex extraction from original cadmium-contaminated rice,the extracted solution by solvent complex extraction from the treated rice which content of cadmium was below limited standard,cadmium protein?organic cadmium?,and CdSO₄?inorganic cadmium?.Specific research contents and results are as follows:?1?Determination of main nutrients and cadmium in raw materials.The main nutrients were analyzed according to the relevant national standards.The results were as follows:the contents of starch,water,crude protein,crude fat and ash were 76.79%,12.38%,5.87%,2.27%,and 1.16%respectively.The content of cadmium was determined by graphite furnace atomic absorption spectrometry with wet digestion pretreatment.Results of methodology validation of adopted method demonstrated that R² of the obtained standard curve was above 0.9990,and the recovery rate was between 107.1%and 111.0%,and the detection limit was 0.0573 g/L and the precision was less than 5%.Finally,the content of cadmium in sample rice was determined as 718.5 g/kg,which seriously exceeded the standard.Therefore,the removal experiment was carried out.?2?Study on removal of cadmium in rice by solvent complex extraction.The optimum conditions for the removal of cadmium by solvent complex extraction are as follows:the extraction solvent was X,the concentration of complex agent was 4%,the extraction temperature was 45?and the reaction time was 2.5 h.Under these conditions,the content of cadmium in rice decreased to 115.97 g/kg and the removal rate was up to 83.86%.The content of cadmium could be controlled in the standard range?less than 0.2 mg/kg?,the solvent polarity had greatest impact on the effect of extraction.At the same time,the single factor experiment showed that starch retention rate was above 90%.?3?Study on the speciation of cadmium in rice.Four kinds of proteins in rice were separated according to the method of osborne so that the distribution of cadmium in different proteins was investigated.The molecular weight of the protein with the highest cadmium content was analyzed by SDS-PAGE,and the cadmium-rich protein composition was analyzed by volume exclusion chromatography-inductivelycoupledplasmamassspectrometry?SEC-HPLC-UV-ICP-MS?.The results showed that cadmium was mainly distributed in glutenin and globulin,but less in albumin and gliadin;SDS-PAGE showed that the molecular weight of each subunit of gluten was 84.2,59.4,36.7,19.5,13.4 KDa;The analysis of speciation showed that there were 3 kinds of main organic cadmium in glutenin.?4?Study on toxicity evaluation in rice by C.elegans model.C aenorhabditis elegan was selected as a model animal to evaluate the toxicity of the solution A extracted from the rice which the content of cadmium was exceeded by solvent complex extraction,the solution B extracted from the rice which the content of cadmium was qualified by solvent complex extraction,cadmium protein?organic cadmium?,and CdSO₄?inorganic cadmium?.The toxicity of these four substances was investigated through median lethal time(LT₅₀),head swing frequency,body bend frequency and movement ability.The results showed that:compared with solution A,the LT50?p<0.05?,head swing frequency,body bend frequency and movement ability of C.elegans fed with solution B were improved to some extent,which indicated that the toxicity of rice was decreased after the removal of cadmium by solvent complex extraction.Compared with CdSO₄,the LT50?p<0.01?,head swing frequency?p<0.01?,body bend frequency?p<0.01?and movement ability?p<0.01?of C.elegans fed with glutelin were significantly improved,indicating that the toxicity of CdSO₄ is stronger than cadmium protein.However,compared with the blank control group,LT50?p<0.05?decreased significantly in the group of glutelin,and there was no significant difference in other indexes,which indicated that the gluten which are rich in cadmium was still toxic and could not be ignored.