Research On The Characteristics Of Translocation And Accumulation Of Selenium In Rice

Selenium(Se)is an essential trace element for human health.Since the human body cannot synthesize the required organic selenium,it is necessary to maintain selenium levels of human body through dietary intake.Selenium deficiency can cause diseases,while excessive selenium supplement also have toxic effects on human body,and the threshold between deficiency and toxicity is relatively narrow.As a staple food for more than half of Chinese population,rice(Oryza sativa L.)is an important source of selenium intake.Therefore,Se-enriched rice,as a functional food,provides selenium to human from dietary source,and has been increasingly recognized by selenium deficiency populations in China.It has been confirmed that the application of selenium can effectively increase the selenium content in rice and has been widely used.Rice absorbs selenium through roots or leaves and accumulates in the edible part by its own transport ability.Therefore,the study on the translocation,accumulation characteristics and speciation transformation of rice provides a scientific basis for the production of Se-enriched rice.Since the biological functions of selenium are closely related to its chemical forms,the establishment of selenium speciation analysis method for Se-enriched rice and the evaluation of dietary exposure risk are essential to ensure the food safety.1.A method for the determination of five selenium species in Se-enriched rice was established.Selenium species in Se-enriched rice were extracted by enzyme extraction method.The effects of enzyme selection,extraction time and enzyme dosage on extraction efficiency were investigated to determine the optimal enzymatic hydrolysis method.The HPLC-ICP-MS/MS method was applied to the quantitative analysis of selenium in selenium-enriched rice,and the method was verified.The results showed that the established method has high separation efficiency and good resolution.The linearity and precision of the method were excellent,and the recovery was 86.4%-113.0%.The limits of quantitation of SeCys(selenocystine),SeMeCys(methylselenocysteine)and SeMet(selenomethionine)were 0.10 ?g/kg,while Se(VI)and Se(IV)were 0.20 ?g/kg.The method can fully meet the need of selenium speciation analysis of Se-enriched rice samples,and provide a practical and feasible method for objectively and comprehensively evaluating the quality of Se-enriched rice and further evaluation of dietary exposure of Se-enriched rice.2.The translocation and accumulation characteristics of selenium in rice were studied.The methods of hydroponic and soil culture were used to study the characteristics of root uptake,upward translocation and grain accumulation under selenium treatment,and the speciation transformation of selenium in rice were investigated.The results showed that when selenite was applied to the roots,the absorbed Se(IV)was converted into organic forms of SeMet,SeMeCys and SeCys in the root system,and then transported upwards and stored in the shoots with SeMet as the main form,accompanied by the transformation process of SeCys to SeMeCys and Se(IV)to Se(VI);when SeMet was applied,part of selenium maintained the form of SeMet,and some of the SeMet were converted into SeMeCys in roots,and the two forms were transported upward.In the shoots,SeMet was the dominant species,followed by SeMeCys;the foliar sprayed Se(IV)was mostly converted into SeMet and SeCys in the leaf.In addition,there were slight speciation transformations during the process of translocation,and selenium was accumulated in the grain in the form of SeMet and SeCys.3.Selenium content of Se-enriched rice was analyzed and dietary exposure assessement was conducted.To evaluate the selenium content and dietary exposure risk of selenium-enriched rice in China,selenium-enriched rice samples were collected from supermarkets to determine the selenium content and its risk to dietary safety so as to provide reference for production and consumption.The non-parametric probabilistic assessment method was used to estimate the selenium intake of Se-enriched rice,and the selenium dietary exposure risk index from Se-enriched rice was calculated to assess its risk level to consumers.The results showed that the selenium content in regular Se-enriched rice and Se-enriched baby rice were 0.022-0.880 mg/kg and 0.029-0.668 mg/kg,with an average of 0.160 mg/kg and 0.284 mg/kg,of which only 48.7% and 50.0% of the samples met the national standard for selenium-enriched rice,respectively.The exposure of selenium from Se-enriched rice showed certain age and gender differences.Took the selenium tolerance upper limit(UL)as the evaluation criterion,the samples were safe with no negative effects on the consumers' health;but when taking selenium appropriate intake(AI)as the evaluation criterion,the exposure risk was very low for the population aged 0-7 years,while for the population over 7 years was relatively high,which indicated that the selenium content of Se-enriched rice had exceeded the appropriate dietary intake standard.Therefore,the consumption of Se-enriched rice for the target population in this age group had certain unsafe risk and should be properly monitored.The results provided a scientific basis for understanding and mastering the selenium levels in commercial Se-enriched rice and its safety risk.