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Selenium Compounds in Milk. Studies of Selenoproteins, Selenium Enrichment and Oxidative Stability of Food

Hoac, Tien LU (2007)
Abstract (Swedish)
Popular Abstract in Swedish

Selen är ett essentiellt näringsämne som har många viktiga fysiologiska funktioner. Hos människor och djur utövar selen sin funktion bara om elementet är specifikt bundet i selenoproteiner som aminosyran selenocystein. Viktiga funktioner hos selenoproteiner är att verka som antioxidanter, upprätthålla redox-balansen i cellerna och reglera sköldkörtelhormonernas aktivitet. Förutom i selenoproteiner finns selen inbyggt ospecifikt i andra proteiner i form av selenometionin och det finns även i lågmolekylära substanser. Därför är det av intresse att inte bara studera totala selenkoncentrationer i livsmedel utan också få ny kunskap om förekomsten av olika selenoproteiner och andra... (More)
Popular Abstract in Swedish

Selen är ett essentiellt näringsämne som har många viktiga fysiologiska funktioner. Hos människor och djur utövar selen sin funktion bara om elementet är specifikt bundet i selenoproteiner som aminosyran selenocystein. Viktiga funktioner hos selenoproteiner är att verka som antioxidanter, upprätthålla redox-balansen i cellerna och reglera sköldkörtelhormonernas aktivitet. Förutom i selenoproteiner finns selen inbyggt ospecifikt i andra proteiner i form av selenometionin och det finns även i lågmolekylära substanser. Därför är det av intresse att inte bara studera totala selenkoncentrationer i livsmedel utan också få ny kunskap om förekomsten av olika selenoproteiner och andra selenformer.



Syftet med denna avhandling var att undersöka effekten av selentillskott till mjölkkor på selenhalter i mjölk, vassle och plasma och olika selenformer i vassle, att studera aktivitet och uttryck av selenoproteiner i juvervävnad och den antioxidativa rollen av selenföreningar i mjölk och andra animaliska livsmedel.



Supplementering med selen-berikad jäst (25 mg selen/dag) till mjölkkor medförde att selenhalten i mjölk, vassle och blodplasma ökade 10-, 10- och 2-faldigt. Fraktionering av vassle visade att en stor del av den ökade selenmängden var bundet till ?-laktoglobulin-?-laktalbumin-fraktionen. Däremot var selenökningen i plasma mer jämnt fördelad bland sex huvudfraktioner, till exempel albumin, selenoprotein P och lågmolekylära föreningar. Selensupplementeringen påverkade varken fördelning av zink i vassle eller i plasma, men proportionen av koppar i vassle tenderade att öka i den högmolekylära fraktionen.



I en delstudie jämfördes fördelningen av spårelement i vassle från kor som uppfötts med ekologisk resp. konventionell metod och andelen protein-bundet selen var lägre i ekologisk vassle än i den konventionella vasslen. Det fanns ingen skillnad i fördelning av zink och koppar mellan ekologisk och konventionell vassle, men selenhalten i den ekologiska vasslen och mjölken var signifikant lägre än i den konventionella.



För att få en uppfattning om eventuellt förekommande selenoproteiner i mjölk utsöndras från juvervävnad, studerades deras aktivitet och mRNA-uttryck. Enzymaktiviteten av glutationperoxidas (GSHPx) i juvervävnad från olika kor varierade 16-faldigt, och för tioredoxinreduktas (TR) och selenkoncentrationen var variationen 6-faldig. Korrelationsberäkningar visade parvis positiva samband mellan dessa tre variabler. Uttryck av mRNA av cellulär GSHPx, extracellulär GSHPx, fosfolipidhydroperoxid GSHPx, TR och selenoprotein P kunde också visas i kojuver och positiva samband mellan GSHPx aktivitet och cellulär GSHPx mRNA och mellan selen och selenoprotein P mRNA påvisades.



För att studera den antioxidativa rollen av selen och selenföreningar i animaliska livsmedel, undersöktes fettoxidation i mjölk och kött. Fettoxidationen i selenberikad mjölk, mätt som hexanal, minskade jämfört med i kontrollmjölken. För köttexperimentet användes kyckling- och ankkött, och fettoxidation, mätt som tiobarbitursyra, ökade både vid värmebehandling och också med lagringstid i kyla. Fettoxidation i tillagat kycklingkött kunde förhindras genom tillsats av GSHPx i köttet. (Less)
Abstract
Selenium is an essential nutrient and in animals and humans it can either be specifically incorporated into proteins as selenocysteine or randomly as selenomethionine. It can also occur as low-molecular-weight compounds and the form of selenium in foods may also influence food quality. The aims of the present studies were: to study selenium and other trace element compounds in milk and whey; to elucidate the effect of dietary supplementation on selenium and other trace elements in cow's milk, whey and blood plasma; to study the expression and activity of selenoproteins in mammary tissue; and to investigate the antioxidant role of selenium compounds in animal foods.



Supplementation of the diet of cows with selenium caused... (More)
Selenium is an essential nutrient and in animals and humans it can either be specifically incorporated into proteins as selenocysteine or randomly as selenomethionine. It can also occur as low-molecular-weight compounds and the form of selenium in foods may also influence food quality. The aims of the present studies were: to study selenium and other trace element compounds in milk and whey; to elucidate the effect of dietary supplementation on selenium and other trace elements in cow's milk, whey and blood plasma; to study the expression and activity of selenoproteins in mammary tissue; and to investigate the antioxidant role of selenium compounds in animal foods.



Supplementation of the diet of cows with selenium caused an increase in selenium content in milk, whey and blood plasma of 10, 10 and 2 times, respectively, compared with control values. Most of the increase in whey occurred in the ?-lactoglobulin-?-lactalbumin fraction, while the increase in blood plasma was evenly distributed between six major fractions, including albumin, selenoprotein P and low-molecular-weight compounds. The distribution of copper in whey seemed to be shifted to the high-molecular-weight compounds, while the distribution of zinc was unaffected. The distributions of zinc and copper in plasma were unaffected by selenium supplements.



Milk and whey from cows reared on organic regimens were also compared with those from cows managed using conventional methods. Selenium contents in desalted milk and whey obtained using organic farming practices were significantly lower than those resulting from conventional farming, and the proportion of protein-bound selenium in ?organic? whey was lower than that in ?conventional? whey.



The activities of glutathione peroxidase (GSHPx) and thioredoxin reductase (TR), and the gene expression of five selenoproteins were also studied in mammary tissue. The GSHPx activity varied 16-fold among the investigated cows, and the TR activity and selenium content varied 6-fold. Pair-wise positive correlations were found between these three variables. Moreover, mRNA of cellular GSHPx, extracellular GSHPx, phospholipid



hydroperoxide GSHPx, TR and selenoprotein P (SelP) were also detected in mammary tissue, and the activity of GSHPx and the selenium content were found to be positively correlated to the mRNA of cellular GSHPx and SelP, respectively.



To study the antioxidant role of selenium and selenoprotein in foods, selenium-enriched milk was exposed to light, and lipid oxidation was assessed by hexanal formation. Selenium-enriched milk resisted light-induced lipid oxidation better than control milk. In a tissue model, GSHPx activity in chicken and duck meat decreased to below 20% of the control values after being heated to 80ºC, whereas cold storage did not affect GSHPx activity. Lipid oxidation, measured as thiobarbituric acid reactive substances (TBARS) increased after heat treatment and cold storage. In cooked chicken meat, but not duck meat, adding GSHPx reduced the TBARS formation to approx. 55% of the control value. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Docent Alfthan, Georg, Biomarkörlaboratoriet, Folkhälsoinstitutet, Helsingfors, Finland
organization
publishing date
type
Thesis
publication status
published
subject
keywords
metabolism, Biokemi, Metabolism, Biochemistry, Naturvetenskap, Natural science, Copper, Zinc, Oxidative stability, Thioredoxin reductase, Glutathione peroxidase, Selenoproteins, Milk, Selenium supplementation, Technological sciences, Teknik
pages
146 pages
publisher
Pure and Applied Biochemistry, Lund University
defense location
Hörsal B, Kemicentrum, Getingevägen 60
defense date
2007-03-09 13:15
ISBN
978-91-7422-150-3
language
English
LU publication?
yes
id
a1a8e275-1b33-4c95-aa5b-e8860512b2f6 (old id 548103)
date added to LUP
2007-10-09 10:56:57
date last changed
2016-09-19 08:45:09
@misc{a1a8e275-1b33-4c95-aa5b-e8860512b2f6,
  abstract     = {Selenium is an essential nutrient and in animals and humans it can either be specifically incorporated into proteins as selenocysteine or randomly as selenomethionine. It can also occur as low-molecular-weight compounds and the form of selenium in foods may also influence food quality. The aims of the present studies were: to study selenium and other trace element compounds in milk and whey; to elucidate the effect of dietary supplementation on selenium and other trace elements in cow's milk, whey and blood plasma; to study the expression and activity of selenoproteins in mammary tissue; and to investigate the antioxidant role of selenium compounds in animal foods.<br/><br>
<br/><br>
Supplementation of the diet of cows with selenium caused an increase in selenium content in milk, whey and blood plasma of 10, 10 and 2 times, respectively, compared with control values. Most of the increase in whey occurred in the ?-lactoglobulin-?-lactalbumin fraction, while the increase in blood plasma was evenly distributed between six major fractions, including albumin, selenoprotein P and low-molecular-weight compounds. The distribution of copper in whey seemed to be shifted to the high-molecular-weight compounds, while the distribution of zinc was unaffected. The distributions of zinc and copper in plasma were unaffected by selenium supplements.<br/><br>
<br/><br>
Milk and whey from cows reared on organic regimens were also compared with those from cows managed using conventional methods. Selenium contents in desalted milk and whey obtained using organic farming practices were significantly lower than those resulting from conventional farming, and the proportion of protein-bound selenium in ?organic? whey was lower than that in ?conventional? whey.<br/><br>
<br/><br>
The activities of glutathione peroxidase (GSHPx) and thioredoxin reductase (TR), and the gene expression of five selenoproteins were also studied in mammary tissue. The GSHPx activity varied 16-fold among the investigated cows, and the TR activity and selenium content varied 6-fold. Pair-wise positive correlations were found between these three variables. Moreover, mRNA of cellular GSHPx, extracellular GSHPx, phospholipid<br/><br>
<br/><br>
hydroperoxide GSHPx, TR and selenoprotein P (SelP) were also detected in mammary tissue, and the activity of GSHPx and the selenium content were found to be positively correlated to the mRNA of cellular GSHPx and SelP, respectively.<br/><br>
<br/><br>
To study the antioxidant role of selenium and selenoprotein in foods, selenium-enriched milk was exposed to light, and lipid oxidation was assessed by hexanal formation. Selenium-enriched milk resisted light-induced lipid oxidation better than control milk. In a tissue model, GSHPx activity in chicken and duck meat decreased to below 20% of the control values after being heated to 80ºC, whereas cold storage did not affect GSHPx activity. Lipid oxidation, measured as thiobarbituric acid reactive substances (TBARS) increased after heat treatment and cold storage. In cooked chicken meat, but not duck meat, adding GSHPx reduced the TBARS formation to approx. 55% of the control value.},
  author       = {Hoac, Tien},
  isbn         = {978-91-7422-150-3},
  keyword      = {metabolism,Biokemi,Metabolism,Biochemistry,Naturvetenskap,Natural science,Copper,Zinc,Oxidative stability,Thioredoxin reductase,Glutathione peroxidase,Selenoproteins,Milk,Selenium supplementation,Technological sciences,Teknik},
  language     = {eng},
  pages        = {146},
  publisher    = {ARRAY(0x99bac28)},
  title        = {Selenium Compounds in Milk. Studies of Selenoproteins, Selenium Enrichment and Oxidative Stability of Food},
  year         = {2007},
}