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Selenium Content of Foods 'V. C. M ORRIS AND O . A. LEVANDERH um an N utritio n R esea rch D ivisio n, A gricu ltu ra l R esea rch Service,U . S. D epartm ent of A griculture, B eltsville, M aryland 20705

ABSTRACT The selenium content of a wide variety of foods representing across section of the American diet was determined by fluorometry. M ost fruitsan d ve getables co ntain ed q uan tities o f se len ium less tha n 0.0 1 ig/g.E xcep tio nswere garlic, mushroom, and radish containing 0.25, 0.13 and 0.04 pg/g, respectively. G rain products varied w idely in their selenium content w ith cornflakescontaining as low as 0.025 M g/g and barley cereal as high as 0.66 /g/g.W holewheat flour, whole wheat bread and brown sugar contained two to four timesmore selenium than did white flour, white bread and white sugar. O f the milkproducts assayed, table cream was the lowest in selenium and skim milk thehighest (0.005 vs. 0.05 Mg/g). D ried skim milk powder samples ranged from0.095 to 0.24 ng/g. M eat sam ples ranged from about 0.1 jug/g for chicken m uscleto as high as 1.9 M g/g for pork kidney with most values between 0.2 and 0.5 ng/g.T he content of seafood w as generally higher, ranging from 0.4 to 0.7 g/g.T hesevalues suggest that a diet w ell balanced in other nutrients is probably also nutritionally adequate w ith regard to selenium , although possible effects of cooking,processing, geographical variation and biological availability rem ain to be investigated. J. Nutr. 200: 1383-1388, 1970.

Since the discovery by Schwarz andFoltz in 1957 that selenium prevents livernecrosis in rats (1), a wide variety of animal diseases has been found to respond toselenium (2-4). In spite of this overw helming body of evidence strongly im plicatingselenium as an essential trace elem ent forall species, there have been few data tosuggest the occurrence of a selenium deficiency in m an. Schwarz discussed the possible involvem ent of selenium in kw ashior-k or, a p ro te in c alo rie d efic ie ncy d is ea se , a searly as 1961 (5) and this has been confirmed by a prelim inary report (6). Burket al. found that the selenium level inwhole blood and plasma of Guatemalanchildren w as low er in those suffering fromkwashiorkor than in norm al controls (7).Dayton et al.* have reported lower valuesof selenium in the placentas of undernourished Guatemalan women as comparedwith women from the United States. A lthough the selenium content of a w ide variety of animal feeds has been surveyed inthe literature (8), there exist few dataconcerning amounts of selenium in foodsconsumed by humans. Hopkins and M ajaj(9) stated that the level of selenium in five

c ompo site samp le s o f ty pic al b ala nc ed d ie tsfor adolescent Am erican m ales was lowerthan their detection lim it for selenium byneutron activation analysis (< lO ppb).The present paper reports values for selenium in a variety of common food itemsassayed using a fluorom etric technique.This technique allows the precise and accurate determ ination of selenium in thenanogram range. The values found suggestthat, w ith certain qualifications, there exists an adequate level of selenium in thehum an dietary of the U nited States.

METHODSamples. Foods representing a crosssection of the American diet were chosenfor analysis. Samples were purchased inthe Beltsville, M aryland, area from localfood stores. Brand nam e products were sele cte d w he ne ve r p os sib le .Rec ei ve d f or p ub li ca ti on Ma y 2 9, 1 97 0.' A prelim inary report of this w ork w as given at theFifty-fourth A nnual M eeting of the Federation ofAme ri ca n So ci et ie s f or Expe rimen ta l B iol og y, A tl an ti cC it y, N . J ., A pr il 1 2- 17 , 1 97 0.2 Dayton, D . H., L . J. Filer and C. Canosa 1969C ellu la r ch ang es in th e p la ce nta s o f u nd erno uris he dm othe rs in G uatem ala. F ed era tio n P roc . 2 8: 4 88 (a b-str.).

J . NUTR IT ION ,OO:1383-1388. 1383

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1384 V. C. MORRIS AND O. A. LEVANDERPreparation of sam ples. A new container was opened for each analysis and duplicate aliquots taken for analysis. Freshvegetables and fruits w ere hom ogenized ina glass food blender to obtain homogeneous sam ples. O nly edible portions w ere usedwith the peeling being discarded in mostcases. Lean m uscle sam ples of m eats wereassayed and fat and connective tissue w ereavoided. All samples were assayed as received w ith no cooking or drying performed, since selenium might be lost as are su lt o f th ese p ro ce sse s.Procedure. Selenium content w as determ ined using the fluorom etric technique ofHoffm an et al. (10). This m ethod involvesdig esting the sam ple in a nitric-sulfuric-perchloric acid m ixture, masking potential interferences w ith disod ium e thylene-d iamin ete tra ac eta te , c omple xin g se le niumw ith fre sh ly p re pa re d 2 -3 ,d iam in on ap hth a-lene solution and determ ining seleniumflu orome tric ally a fte r e xtra ctio n o f th e c omplex into cyclohexane. Sam ples were activated in a spectrophotofluorometer3 at365 m/j. and fluorescence read at 525 m/j..S tandard curves were drawn with each setof analytical determ inations and reprodu-cibility w as fo und to be excellent. R ecoveryexperim ents show ed that selenium addedto food samples as selenite could be carried through the entire procedure essentially w ith out loss.O ne variation in the H offm an procedurewas necessary when the food sam ple beingassayed contained more than 0.05 ^g Se/gram . In such cases, 1-g samples were digested and then the acid digest was dilutedw ith glass-distilled w ater to a constant volume. Suitable aliquots of the diluted acidd ig est w ere ta ke n fo r a na ly sis. A pp ro pria teadjustments were made in the amounts ofammonium hydroxide that were added sothat a constant acid/base ratio was maintained. Sample volumes were equalizedw ith glass-distilled w ater prior to the addition of the diam inon aphthalene re agent.Selenium -free sulfuric acid was used inthe digestion mixture and in the prepara

tion of the diam inonaphthalene solution.It w as prepared by diluting concentratedsulfuric acid w ith an equal volume ofwater, adding 15 m l of reagent grade 48%hydrobrom ic acid per 200 ml of the m ixture, and heating strongly until the volum e

was the same as that of the original concentrated sulfuric acid (11).RESULTS

M ost fruits and vegetables were foundto contain less than 0.01 ^g Se/gram asshown in table 1. Some of the root vegeta ble s c on ta in ed c on sid era bly h ig he r v alu esranging from 0.015 /ig/g frwhite onionto 0.249 /ig/g for garlic. It is interestingthat garlic had the highest selenium content of the vegetables assayed since it hasbeen noted that certain selenium compounds have a garlic-like sm ell ( 1 ). M ushro om s c on ta in ed 0 .1 31 u g/g ;a dish , 0 .0 39/ g /g ;a nd c arro ts a nd c ab ba ge , 0 .0 22 ju g/g .Allaway (12) reported that a poisonousm ushroom , Am anita, took up significantamounts of selenium even when grown insoils containing low levels of selenium . N oconsistent relationship could be found betw een cann ed a nd fresh ve getables. C annedcarrots had half as much selenium asfresh, whereas canned tomatoes andcanned potatoes had about tw ice as muchselenium as fresh. Green beans, corn andmushroom s had about the same seleniumcontent in both the fresh and cannedstates. The selenium contents of all fruitsassayed w ere 0.013 / g/gor below . N o differences were found between canned andfresh sam ples of apples, peaches, pears orpineapples.The selenium values for grain productsassayed are given in table 2. A considerable difference between white bread andflour and whole wheat bread and flour wasfound (0.277 and 0.193 vs. 0.665 and0.636 Mg/g). White sugar (0.003 Mg/g)and brown sugar (0.011 ig/g) demonstrated the sam e relationship (see table 3).A lthough the difference betw een w hite andbrown rice was not as striking (0.318 vs.0 .3 88 / g /g ),th e p re vio us d ata su gg est th atthe refining process m ight be destroying orremoving some of the selenium present inthe raw products. Grain products variedgreatly in their selenium content. Processed breakfast cereals such as corn flakesand puffed rice had very low levels (0.026a nd 0 .0 28 / g /g ),w he re as o th er p ro ce sse dcereals such as prepared oat cereal hadcomparatively hig her values (0.4 28 / g/g ).

* Am in co-B owman , American In str um en t C o., In c.,S ilv er S pr in g, M d.

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SELENIUM CONTENT OF FOODS 1385TA BL E HSelenium content of vegetables and fruits

P ro du ct 2 l ig Se/gramVegetablesCarrotsFreshCannedCabbage,freshCauliflower,freshCornFreshCannedGarlic,

freshGreenpepper,reshGreenbeansFreshCannedLettuce,freshMushroomFreshCannedOnion,

white,reshPotatoesSweet,freshWhite,freshWhite,cannedRadish,freshTomatoesFreshCannedTurnips,

fresh0.022,0.013,0.022,0.006,0.004,0.003,0.276,0.006,0.006,0.009,0.009,0.122,0.109,0.015,0.007,0.003,0.007,0.042,0.005,0.010,M ean excluding m ushroom and garlic 0.010

FruitsApple,fresh,eeledApplesauce,cannedBanana,fresh,eeledOrange,fresh,eeledPeachFresh,peeledCannedPearFresh,peeledCanned

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1386 V. C. MORRIS AND O. A. LEVANDERTABLE 3 i

S elen ium con ten t o f m iscella neo us p ro ductsProductEggYolk#lYolk#2White#1White#2SaccharinSugarBrownWhite/ig

Se /ram0.174,0.192,0.057,0.046,0.005,0.012,0.003,0.1930.1740.0570.0430.0050.0100.003

1 Se e fo otn ote 1 , ta ble 1 .TABLE 4 1Selen iu m co ntent o f d airy p ro du cts

ProductCheeseAmerican,processedCottageSwissCream,tableCreamsubstituteMilkEvaporated,cannedSkimSkim,

p owder ed , d ri ed1Skim,p owder ed , d ri ed2Wholehomogenized/ig

Se/gram0.090,0.054,0.101,0.005,0.034,0.012,0.045,0.098.0.243,0.013,0.0900.0500.1080.0060.0330.0

Mean 0.069i S ee f oo tn ote 1 , t ab le 1 .m ilk pow der. For exam ple, Fink " reportedthat the selenium content of skim milkpowder was variable according to themethod of drying. This is due to the volatilization of the selenium during the drying process. Therefore, both the effects ofp rocessing and geograph ical loca tion m ustb e cons id er ed .Of the cheeses assayed, cottage cheesew as th e lowe st w ith 0 .0 52 / g /g ,p ro ce sse dAm erican cheese interm ediate w ith 0.090fig/g and Swiss cheese the highest with0.104 /g/g(table 4). Egg yolk as shownin table 3 had selenium values threetimes higher than egg white (0.183 vs.0 .0 57 Mg /g ).Fresh m eats and seafoods (table 5) werefound to be very good sources of selenium .The average value for steak, ground beef,chicken, pork chops and lamb chops was0.22 / g/g.C hicken had the least selenium(0.134 /ig/g) and round steak the highest(0 .3 40 ig /g ). Howe ve r, b ee f liv er a t 0 .4 32was alm ost tw ice as high as the aver-

TABLE 5 1Selenium content of m eats and seafoods

Product gSe/g ramMeatsBeefRoundsteakGroundLiverKidneyPorkChopKidneyLambChopKidneyChickenBreastLeg

Mean ex clu din g k id ney s 0.224LobsterailShrimp,shelled,Cod,filletFlounder,filletOystersSeafoodsdeveined0.634,0.572,0.465,0.335,0.646,0.6810.6040.3900.

Mean 0.532i S ee fo otn ote 1 , t able 1 .TABLE 6 1

Selenium content of strained baby foodsProduct l ig Se/gram

Beef 0.118, 0.113Chicken 0.112, 0.101Lamb 0.123, 0.138Liver 0.247, 0.269Pork 0.114, 0.133Carrots 0.002, 0.002Green beans 0.005, 0.004Peaches 0.003, 0.004Pears 0.002, 0.005O atm ea l c er ea l w ith a pp le sa uc eand bananas 0.026, 0.033R ic e c er ea l w it h a pp le sa uc eand bananas 0.019, 0.023Vanilla custard pudding 0.016, 0.015

Mean 0 .068i S ee footnote 1, table 1.

age. B eef, pork and lam b k idneys containe d1.55, 1.90 and 1.43 /g/g, r espectively.Sheep kidney is known to be an excellentsource of Factor 3, the biologically activeform of selenium (5). The average con-ink, H . 1960 Selenium content of skim milkp ow ders a nd th eir in clin atio n fo r p ro du cin g d ieteticliver necrosis. A bstracts of the F ifth InternationalC on gress o n N utritio n, S ep t. 1 -7, W ash in gto n, D . C .,p . 1 9 ( ab st r. ).

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SELENIUM CONTENT OF FOODS 1387tent of seafoods (0.53 / g/g)w as considerably higher than that of m eats (0.22 / g/g).Shellfish such as oysters, shrimp and lobsters had an average selenium content of0.63 /ig/g w hereas cod and flounder filletsa ve ra ge d o nly 0 .3 8 /x g/g se le nium.A few commercial baby foods were analyzed to obtain some indication of the effects of processing (table 6). The averagevalue for chicken, beef, lam b and pork wasonly 0.12 /g/gwhereas for the fresh rawsam ples it was 0.22 /*g/g. Baby food livercontained 0.258 /xg/g whereas the freshliver sam ple tested contained 0.432 ftg/g.The baby food fruits, cereals and vegetables w ere also low er than the fresh sam plesanalyzed. T hese resu lts co uld in dicate thatsome selenium might be lost as a result ofp ro ce ssin g a lth ou gh , o f c ou rse , th e o rig in almaterials used in the baby food manufacture could have contained lower levels ofselenium.While this work was in progress, a report concerning the levels of selenium infoods appeared in Germany (15): the results generally agree well w ith our dataw hen expressed on an equivalent basis.

DISCUSSIONThe present results suggest that the levels of selenium in the American diet ares uffic ie nt fo r g oo d n utritio n. T homp so n a ndScott (16) have shown that 0.04 to 0.10ppm selenium are needed in the diet toprevent selenium deficiency in chickensdepending on the vitam in E content of thediet. Assum ing a reasonable intake of animal protein and grain products, mostA mericans should receive at least these levels in their dietary. However, three im portant qualifications should be consideredbefore it is flatly assumed that persons inthe U .S. need not worry about their selenium intake. First of all, there may be certain local pockets of low selenium soilwhich could contribute to a possible deficiency just as there are known to be highselenium areas that are hazardous for agricultural p urposes (13). T hese low seleniumareas are w ell delineated geographically(17) and the use of interregional food shipm ents should m inim ize any geographicalcontribution to selenium deficiency. Secondly, little is known regarding the availability and biopotency of selenium as it

occurs naturally in foods. There is a widevariation in the ab ility of various seleniumcom pounds to prevent liver necrosis in rats(18). Many of the most active form s of selenium (such as sodium selenite) are alsothe least stable chemically, whereas there la tiv ely in ert e leme nta l se le nium is e sse ntia lly w ith ou t v alu e in a lle via tin g se le niumdeficiency diseases. A lso, it has recentlybeen stated 5 that the selenium in fish m eal(which contains m oderate levels of selenium) is much less active than inorganicse le nite in a lle via tin g n utritio na l m us cu la rdystroph y in chic kens. T herefore, the totalselenium content of foods may not be avalid indicator of their nutritional valu e.Finally, it m ust be recognized that m anyselenium com pounds are quite volatile andcould thus be lost as a result of food cooking or processing. Although the experim ents w ere adm ittedly not controlled, theresults obtained for the baby foods in thisstudy suggest that selenium losses as a result of cooking or processing could be am ajor factor in determ ining the seleniumcontent of an individual's diet. There is anobvious ne ed for m ore research conce rningthe chem ical form s of selenium that occurin foods, the biological effectiveness ofthese various forms, and the possible effects of cooking and processing on theseforms.L IT ERATURE C IT ED

1. Schwarz, K ., and C. M . Foltz 1957 Selenium as an integral part of Factor 3 againstdietary necrotic liver degeneration. J. A mer.Chem . Soc. 79: 3292.2. Hartley, W . J., and A. B. Grant 1961 Areview of selenium -responsive diseases ofN ew Zealand livestock. Federation P roc. 20:679.3. Nesheim, M . C., and M . L. Scott 1961 Nutritional effects of selenium compounds inchicks and turkeys. F ederation Proc. 20: 674.4. Schubert, J. R ., O . H. Muth, J. E . Oldfieldand L. F. Remmert 1961 Experimental results with selenium in white m uscle diseaseof lambs and calves. Federation Proc. 20:689.5. Schwarz, K . 1961 Development and statusof experimental work on Factor 3 selenium .F ederation P roc. 20: 665.6. Schwarz, K . 1965 Selenium and kwashior-kor. Lancet 1: 1335.7. Burk, R . F ., Jr., W . N. Pearson, R . P. Wood,II and F. Viteri 1967 Blood selenium levelss S co tt, M . L ., C orn ell U niv er sit y, I th ac a, N . Y ., p ersonal communication .

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1388 V. C. M ORRIS A ND O. A. LEVA NDERand in vitro uptake of "Se in kwashiorkor.A mer. J. C lin. N utr. 20: 723.8. A llaway, W . H ., and E. E . Cary 1966 Theenv ir onmen ta l b ac kg round o f s ele nium -def ic ie ncy d is ea se s. F eeds tu ff * 38: 62.9. Hopkins, L . L ., Jr., and A . S. Majaj 1967S elenium in hum an nutrition. In: Seleniumin Biom edicine, ed., O . H. M uth. AVI Publish in g C o., We stp ort, C on n., p p. 2 03 -2 14 .10. H offm an, I., R. J. W esterby and M . Hidiro-g lo u 1 96 8 P rec ise flu orometric d eterm in ation of selenium in agricultural m aterials.J . A ss. O ffic . A na l. C hem. S 3: 1 03 9.11. Ewan, R. C., C . A . Baumann and A . L. Pope19 68 D eterm in ation o f selen ium in biolog ical m aterials. J. A gr. Food C hem . 16: 212.12. A llaway, W . H. 1969 Control of the environm ental levels of selenium . In: TraceS ub stan ces in E nv iro nm ental H ealth , v ol. 2,ed ., D . D . H em ph ill. U niv ersity o f M issou riP re ss , C olumb ia , Mo ., p p. 1 81 -2 06 .13. Rosenfeld, I., and O. Beath 1964 Seleniumcontent of soils. In: S elenium : G eobotany,

B ioc hem istry , T ox icity and N utritio n. A cad em ic P ress, N ew Y ork, p p. 4 1-51 .14. Hadjimarkos, D. M . 1965 Effect of selenium o n den tal caries. A rch . E nv iro n. H ea lth1 0: 8 93 .15. Oelschlager, W ., and K. H. Menke 1969berSelengehalte pf lanzlicher, t ie r ischer undanderer Stoffe. 2. M itteilung Selen- undS chwe fe lg eh alte in N ah ru ng sm itte ln . Z . E r-n ae hru ng sw iss . 9 : 2 16 .16. Thompson, J. N., and M . L. Scott 1969R ole o f se le nium in th e n utritio n o f th e c hic k.J. N utr. 97: 335.17. Allaway, W . H., E . E . Cary and C. F. Ehlig1967 T he cycling of low levels of seleniumin so ils, plants a nd anim als. In : S elen ium inB iomed icine, ed ., O . H . M uth . AVI P ub lishin g C o., In c., W estpo rt, C on n., p p. 27 3-2 96 .18. Schw arz, K., and A. J. Fredga 1969 Biologic al p ote nc y o f o rg an ic s ele nium c ompo un ds .J. B io l. C hem . 24 4: 2 103 .