Effect Of Selenium Treatment On Glucosinolate Synthesis And Metabolism In Broccoli

Broccoli(Brassica oleracea.var.italic)are consumed globally because they contain large amounts of anticarcinogenic,antioxidant and health-promoting compounds,such as sulforapHane.SulforapHane,a type of isothiocyanate hydrolysed from glucosinolate,was reported has the strongest anti-cancer activity in vegetables.Selenium is essential trace element for humans and mammals because it ensures the activation of key metabolic enzymes,while methylated compounds have been shown to be effective forms of proventing tumor.Based on the characteristic of accumulating lots of glucosinolates and selenium,more and more people are intrestied in it.In this study,broccoli sprouts were first used as research material to evaluate the nutritional value and then designed four-factor three-level response surface experiment to determine the best enzymolysis condition of sulforapHane.Based on the best enzymolysis condition,we detected the highest sulforapHane content during different growth and storage days.Then we used selenium to treat broccoli sprout,seedling and floret for understanding how selenium affect the synthesis of glucosinolate.Finally,this study found adding appropriate amount of sulpHate can protecte selenium toxicity.The specific results are as follows:1.The broccoli contains abundant of nutritious and every 100 g fresh broccoli sprout contains about water 90 g,protein 4.3-7.6 g and fat 1.3-3.1 g.Every 1 g of freeze dried sprouts containing potassium 17.0-30.0 mg,calcium 6.0-10.0 mg,sodium 1.5-2.6mg,zinc 0.2-0.3 mg,magnesium 4.0-6.6 mg,iron 0.6-2.0 mg.The broccoli sprouts are also rich in amino acids involved in protein synthesis.Depend on the four-factor threelevel response surface experiment,the optimal enzymolysis conditions for sulforapHane production are as follows: solid-liquid ratio of 1: 30,hydrolysis time of 1.5 h,ascorbic acid content of 4 mg/g DW,and temperature of 65 °C.Based on the optimal enzymolysis conditions,we found fresh broccoli sprouts possess high sulforapHane contents during early germination and maintain high levels of the compound when stored at-20 °C no more than one week.2.Se treatment significantly affected the contents of health-promoting compounds in broccoli sprouts among different cultivars.Anthocyanin,ascorbic acid and flavonoid contents significantly increased,whereas total pHenolics content decreased.Theglucosinolate-myrosinase system in broccoli sprouts was also affected by Se treatment.The most important effect during metabolism was observed in myrosinase,whose activity slightly increased during the early growth days.Hence,sulforapHane content also increased as myrosinase activity.However,the GSL content was not significantly affected under the same condition.3.An unbiased metabolomics approach was developed and applied to determine the metabolic pHenotypes of broccoli sprouts treated with 100 ?mol/L selenate in comparison with blank.The results indicated that selenium treatment had a certain effect on the primary metabolites in broccoli sprouts.More than 500 different compounds were obtained by univariate statistical analysis and multivariate statistical analysis.Finally,about 50 compounds with VIP>1 and P<0.05 were shown.The contents of serine,Derythro-lactone,Melezitose,tyrosine,threo-beta-hydroxyaspartate,isomaltose,ribulose-5-pHospHate and some other amino acids were significantly increased after treatment.Meanwhile,3-(1-pyrazolyl)-L-alanine,glutaric acid,galacturonic acid and 5,6-dihydrouracil were significantly decreased after treatment.In this study,beta-alanine and glutathione metabolic pathways are affected by selenium treatment,which suggests selenium treatment may affect the synthesis of amino acids that are involved in the synthesis of glucosinolates while broccoli may need to absorb lots of sulfur to resist the toxicity of selenium.4.The total glucosinolate and individual glucosinolates were reduced by selenium treatment in broccoli young leaves and floret except sprouts.Total sulfur content was invested in broccoli in these three different periods and it shown there was no difference.Based on the results from last chapter,we focused the change on the amino acid and the genes involved in glucosinolate synthesis.The results shown both the amino acid and the genes involved in glucosinolate synthesis were affected by selenium treatment.To prove the results,mature broccoli was choosed as a sample of TMT markers for proteomics analysis.The results shown that the expression of 384 proteins was reduced after selenium treatment,and most of which were enzymes involved in synthetic of amino acid.5.When broccoli sprouts,seedling and floret were treated with selenium,excessive selenium will inhibit the growth of plants.However,adding sulfur in the growth solution could protect the plants from selenium toxicit.The pHenotype of plants was not significant affected when treated with both sulfur and selenium,but the the plants justtreated with selenium shown weak pHenotype.Meanwhile,the level of total selenium,extractable selenium and non-extractable selenium also reduced when adding sulfur in the growth solution.In addition,Selenium treatment could accumulate selenium in plant tissue leading to generate ROS production to damage the cell structure.In this study,sulfur could enhance the antioxidant enzymatic activity which can remove the ROS production and reduce toxic from some selenium compounds in broccoli.