Š. ZAMBERLIN et al.: Mineral elements in milk and dairy products, Mljekarstvo 62 (2), 111-125 111 Introduction On average, mineral elements account for 4 % of total body mass and part of every tissue, liquid, cell and organ in human body. There is a sufficient evidence that minerals, both independently or in proper balance with other minerals, have structural, biochemical and nutritional functions that are very important for overall human health, both mental and physical (Vahčić et al., 2010). Furthermore, they act as catalysts for many biological reactions in the body, including muscle contraction, transmission of nerve impulses and utilization of nutrients from food (Anonymous, 2010; Vahčić et al., 2010). Twenty mineral elements are assumed to be essen- tial in human nutrition: sodium, potassium, chloride, calcium, manganese, selenium, iodine, chromium, cobalt, molybdenum, fluorine, arsenic, nickel, silicon and boron (Cashman, 2002a). Essential minerals are occasionally classified into two groups: major ele- ments (macrominerals) and trace elements (or micro- minerals). The concentration of major elements (so- dium, potassium, chloride, calcium, magnesium and phosphorus) in the human body exceeds 0.01 % of to- *Corresponding author/Dopisni autor: E-mail: [email protected]Pregledni rad - Review UDK: 637.046 Mineral elements in milk and dairy products Šimun Zamberlin*, Neven Antunac, Jasmina Havranek, Dubravka Samaržija University of Zagreb, Faculty of Agriculture, Department of Dairy Science, Svetošimunska 25, 10000 Zagreb, Croatia Received - Prispjelo: 21.02.2012. Accepted - Prihvaćeno: 24.05.2012. Summary Mineral elements occur in milk and dairy products as inorganic ions and salts, as well as part of organic molecules, such as proteins, fats, carbohydrates and nucleic acids. The chemical form of mineral elements is important because it determines their absorption in the intestine and their bio- logical utilization. The mineral composition of milk is not constant because it depends on lactation phase, nutritional status of the animal, and environmental and genetic factors. The objective of this research is to point out the research results of chemical form, content and nutritional importance of individual mineral elements that are present in various milks and dairy products. Key words: milk, dairy products, mineral elements, nutritional significance tal body mass, whereas trace elements (remaining 14 elements) are present in much lower concentrations, and their dietary intake may be lower than 100 mg/ day. All essential mineral elements can be found in milk because by definition it contains the nutrients required for growth of the young (Bates and Pren- tice, 1996). Milk and dairy products are an impor- tant source of dietary minerals in many European countries, accounting for 10-20 % of daily dietary intake. However, the content of major and trace ele- ments in milk depends upon the content of these elements in soil and cattle feed, which varies con- siderably among and within countries (Dobrzański et. al., 2005; Malbe et al., 2010). Also, the thermal treatment of milk may have influence on mineral composition in the way that concentration of dietary minerals in consumer milk is lower than concentra- tion in raw milk, with the exception of iron, which is higher in consumer milk (M a l b e et al., 2010). On the other hand, in the study conducted by Zurera- Cosano et al. (1994) the existence of statistically significant differences were observed only for cop- per and iron with a tendency to decrease slightly
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Š. ZAMBERLIN et al.: Mineral elements in milk and dairy products, Mljekarstvo 62 (2), 111-125 111
Introduction
Onaverage,mineralelementsaccountfor4%oftotalbodymassandpartofeverytissue, liquid,cellandorganinhumanbody.Thereisasufficientevidence that minerals, both independently or inproperbalancewithotherminerals,havestructural,biochemicalandnutritionalfunctionsthatareveryimportant for overall human health, both mentaland physical (Vahčić et al., 2010). Furthermore,theyactascatalystsformanybiologicalreactionsinthebody,includingmusclecontraction,transmissionofnerve impulsesandutilizationofnutrientsfromfood (Anonymous, 2010; Vahčić et al., 2010).Twentymineralelementsareassumedtobeessen-tialinhumannutrition:sodium,potassium,chloride,calcium, manganese, selenium, iodine, chromium,cobalt,molybdenum,fluorine,arsenic,nickel,siliconand boron (Cashman, 2002a). Essential mineralsareoccasionallyclassifiedintotwogroups:majorele-ments(macrominerals)andtraceelements(ormicro-minerals).Theconcentrationofmajorelements(so-dium,potassium,chloride,calcium,magnesiumandphosphorus)inthehumanbodyexceeds0.01%ofto-
talbodymass,whereastraceelements(remaining14elements)arepresentinmuchlowerconcentrations,andtheirdietaryintakemaybelowerthan100mg/day.Allessentialmineralelementscanbefoundinmilkbecausebydefinitionitcontainsthenutrientsrequiredforgrowthoftheyoung(BatesandPren-tice,1996).Milkanddairyproductsareanimpor-tant source of dietaryminerals inmany Europeancountries, accounting for 10-20% of daily dietaryintake.However,thecontentofmajorandtraceele-ments inmilk depends upon the content of theseelements in soil andcattle feed,whichvariescon-siderablyamongandwithincountries(Dobrzańskiet.al.,2005;Malbeetal.,2010).Also,thethermaltreatment of milk may have influence onmineralcompositioninthewaythatconcentrationofdietarymineralsinconsumermilkislowerthanconcentra-tioninrawmilk,withtheexceptionofiron,whichishigherinconsumermilk(Malbeetal.,2010).Ontheotherhand,inthestudyconductedbyZurera-Cosanoetal. (1994)theexistenceof statisticallysignificantdifferenceswereobservedonlyforcop-per and iron with a tendency to decrease slightly
112 Š. ZAMBERLIN et al.: Mineral elements in milk and dairy products, Mljekarstvo 62 (2), 111-125 (2012)
duringpasteurizationandsterilization.Inmilk,min-eral elements occur in several chemical forms, in-cludinginorganicionsandsalts,oraspartsoforganicmoleculessuchasproteins,fats,carbohydratesandnucleicacids.
Theobjectiveofthisresearchistopresenttheresearch results that have been conducted on thechemicalforms,contentandnutritionalimportanceofindividualmineralelementsfoundinvarioustypesofmilkanddairyproducts.However, it shouldbeemphasizedthatthereareinsufficientresearchesonthecontentandchemicalformofminerals inmilkanddairyproducts.
Chemical form and distribution of mineral ele-ments in the soluble and colloidal milk phase
Thechemicalformofmineralelementsfoundinmilkanddairyproductsisveryimportantduetotheirabsorptionintheintestineandbiologicalutili-zation(transport,assimilationincellsandconversionintobiologicallyactiveform).Ofthetotalcalciumincowmilk,99%ispresentintheskimmilkfrac-tion.Two-thirdsofthetotalcalciumcanbefoundascalciumphosphateinthecolloidalphasee.g.caseinmicellesorascalciumionsboundtophosphoserine(approximatelyone-sixthoftotalcalcium).There-mainingone-ofcalciuminmilkcanbefoundinthesolublephase.Ioniccalciuminthesolublephaseac-countsforapproximately10%oftotalcalciumandtheremainingpartofsolublecalciumascalciumci-trate.Inaddition,asmallquantityofcalcium(0.15%) is bound toα-lactalbumin (Cashman,2002a).Ofthetotalphosphorusfoundincowmilk,20%oc-cursasorganicphosphateboundtocasein,and80%asinorganicphosphate.Ofthetotalcontentofinor-ganicphosphate,44%isboundtocaseinmicellesascalciumphosphateand56%ispresentinthesolublephase,mostlyasfreephosphateions.Incowmilk,98-100%ofmagnesiumisfoundintheskimmilkfraction,65%ofwhichinthesolublephase(40%asmagnesiumcitrate,7%asmagnesium-phosphateand16%asfreeions).Theremainingpartinthecol-loidalphaseisboundtocaseinmicelles(50%tocol-loidalcalciumphosphateand50%tophosphoserineincasein).Thebalanceofsaltsbetweenthesolubleandthecolloidalphaseincow,goatandsheepmilkis important for definition of their inherent nutri-tionalproperties.Also,thebalanceisimportantfor
maintainingmineralelementsincheesecurdduringcheeseproduction(Cashman,2002a).Insamplesofgoatmilk,takenfromdifferentherdsinthemid-dleof lactation,thecontentofcalcium,magnesiumandphosphorusinthesolublephasewas33%,66%and39%,respectively(Fuenteetal.,1997).Also,research results of themineral elements content inEuropeangoatbreedsshowthatthecontentofsolu-blecalciumrangesfrom30%to38%(O’ConnorandFox,1977;Remeuf,1993).Furthermore, re-search shows that the contents of magnesium andphosphorus in the soluble phase of goat milk are66%and39%, respectively,while thecontentsofcalcium,magnesium and phosphorus in sheepmilkin the soluble phase amounts to 21 %, 56 % and35%(Pellegrinietal.,1994).Mostzincingoatandsheepmilk(93%insheepand89%ingoatmilk)andmanganese(93%insheepand89%ingoatmilk)ispresentinthecolloidalphase(Fuenteetal.,1997).Thedistributionofironandcopperbetweenthetwophasesofgoatandsheepmilkshowsgreaterdiffer-ences thanother researchedmineralelements.Forexample, the solublephaseof sheepmilkcontains29%ironandgoatmilk44%.Incomparison,sheepmilkcontainsahigherlevelofsolublecopper(33%)thangoatmilk(18%)(Fuenteetal.,1997).
Concentration of major mineral elements in various milk types and dairy products
MaravalandVignon(1982)observedsignifi-cant changes in the concentration of mineral ele-mentsingoatmilkinthefirst7weeksoflactation.Furthermore,Khanetal.(2006)foundsignificantinfluenceofseasonandbreedontheconcentrationofmostmineralelements in sheepmilk.Thecon-tentofmajorelements inmilkdiffers significantlyfromthecontentinblood.Comparedtoblood,milkcontainsmorepotassium,calciumandphosphorus,andlesssodiumandchloride.Thisisduetothesodi-um-potassiumpumpthatregulatesosmoticpressure
Š. ZAMBERLIN et al.: Mineral elements in milk and dairy products, Mljekarstvo 62 (2), 111-125 113
betweenthecytoplasmofbloodcellsandmilk.Atthesametime,calciumistransportedfromtheba-salmembranetocytosolandonwardintotheGolgiapparatusofthealveolarcellsofthemammaryglandstobeincorporatedintocaseinmicelles(PaulinaandBencini,2004).Thetransportofions,lactoseandwateramongblood,intercellularalveolarliquidsandmilkisveryimportantforosmoticbalanceinhealthyudder,and itshowsapositivecorrelationwiththequantityofmilkproduced(PaulinaandBencini,2004).Thereisaveryhighinverselevelofcorrela-tion between the lactose content and the concen-trationof sodiumandpotassium ingoatandothermilktypes(Konaretal.,1971;ParkandChukwu,1988).Particularlyhighlevelofsodiumwasdeter-minedincowcolostrum.However,thesodiumcon-centrationinmilkdecreasestoaveragelevelsafewdays later. Sodium concentration inmilk does notdependonitsdietaryintake.Itishigherattheendofthelactationperiod,whenthequantityofmilkisreduced.Also,milkskimminghasnoeffectonthesodium content (Cashman, 2002a).Unlike othermineral elements, the potassium concentration in
cowcolostrumislowerthaninmilk,butitincreasesoverthenexttwotothreedaysofthelactationperioduntilanormalvalueisreached.Itdependsondietarypotassiumintake.Researchresultshaveshownthatchlorideconcentrationisinpositivecorrelationwithpotassium concentration and negative correlationwith lactosecontent.Thepotassiumconcentrationingoatmilkdoesnotdependonthelactationphase(Konaretal.,1971).Thechlorideconcentrationincolostrum is increased.However, it decreases to anormallevelwithintwotothreedays.Towardsendoflactation,chlorideconcentrationincreasesnotde-pendingonfoodintake.Ingeneral,asfatcontentinmilkincreases,thecontentofthemajormineralsinmilkanddairyproductsdecreases.
Ofthe20essentialmineralelements,calciumisthemostcommoninmilk(Table1).Thecalciumcon-centrationofcowmilkisslightlyhigherincolostrumandat theendof the lactation.Removing fat frommilkdoesnotaffectthemagnesiumcontent.Itscon-tentistwotothreetimeshigherincolostrumthaninmilk,butdecreasesfromthefirsttothethirddayoflactationtoreachitsnormallevel(Table1).
114 Š. ZAMBERLIN et al.: Mineral elements in milk and dairy products, Mljekarstvo 62 (2), 111-125 (2012)
Themagnesiumcontentinmilkisnotdepend-ing on its dietary intake (Cashman, 2002a). Thecontentof calcium,phosphorus andmagnesium indairyproductsisshowninTables2to5.Ingeneral,thehighestquantitiesofcalciumandphosphorusarefound in hard cheeses (Parmigiano,Gouda, EdamandCheddar - a level up to 10 times higher thaninmilk).Thelowestcontentoftheseelementswasrecorded increamandcottagecheese.Magnesiumcontent in cheese changes in the sameway as thecalciumcontent(Table5).
Nutritional importance of major mineral elements present in milk and dairy products
The recommended daily allowance (RDA) ofsomemajor elements is shown in Tables 6 and 7.RDA values present the average daily calorie andnutrientintakethatisconsideredsufficienttomeettheneedsofhealthyinfants,childrenandadults.
Sodium is themajor cation in the extracellu-lar fluids and is an important regulator of osmoticpressure, acid-basebalance and cellularmembranepotential.Itisalsoimportantfortheactivetranspor-tationofsubstancesthroughthecellularmembrane.The contribution of cowmilk to daily sodium in-takeinhumannutritionislow,butcheeseandsomecreamproductswhich contain addedquantities ofsalt,canprovidesignificantsourcesofsodium.
Chloride is the most important extracellularanion. It is responsible formaintaining electrolytebalance.Excessiveintakeoftablesalt(sodiumchlo-ride) increases urinary calcium excretion, whichnegatively affects bone condition (Massey andWhiting,1996;CashmanandFlynn,2003).TheRDAofchlorideisshownintheTable7.
Potassium isoneof themost important intra-cellularcations.Itoccurs incells inconcentrations30timesgreaterthaninextracellularfluids.Extra-cellular potassium is important for the transmis-sionofnerveimpulses,musclecontractionsandthemaintenance of blood pressure. In addition, it hasbeendeterminedthatpotassiumintakehasaposi-tiveeffectonhumanbones.Forexample,theintakeofalkalinepotassiumsalts(potassiumbicarbonate)by healthy adults significantly reduces urinary cal-ciumexcretion,evenwithexcessivetablesaltintake(Morrisetal.,1999).AnadequatedailypotassiumintakeforpeopleisshowninTable7.Thecontentofsodium,potassiumandchlorideinmilkhasaphysi-ologicalsignificanceininfantnutrition.Conversely,excessive intake of these three mineral elementsmaycauseclinicalproblemsbecausetheycanstartaccumulating, limitingtherenalcapacityof infants(Cashman,2002a).
Calciumaccountsfor1.5-2%ofthetotalbodymassofanadult.Ofthisamount,99%isfoundinbones and teeth as calciumphosphate and the re-maining1%inextracellularfluidsandintracellularstructuresaswellasincellularmembranes.
Calcium is responsible for many regulatoryfunctions, such as normal cardiac rhythmmainte-nance, blood clotting, hormone secretion, musclecontraction and enzyme activation (Cashman,2002a).Milkanddairyproducts(cheeseandyogurt)areveryrichsourceofcalcium(Tables1,3and4).ThemajorityofdietaryCa(70%)comesfromdairyproductsbecauseinmilk,caseinmicellesconstitutethe natural vector of Ca (Canabady-RochelleaandMellemab,2010).TheRDAforcalcium(Ta-ble6)isdifficulttoreachwithoutconsumingmilkand dairy products. In the past, special attention
Š. ZAMBERLIN et al.: Mineral elements in milk and dairy products, Mljekarstvo 62 (2), 111-125 115
wasdevoted to thebioavailabilityof calciumfrommilk.Theaveragecalciumabsorptionfromcowmilkvariesbetween21%and45%.Also, thebioavail-abilityofcalciumfromcheeseandyogurtequalstothosefrommilk.
CalciumabsorptiondependsonthevitaminDlevelandageofaperson.Atthesametime,ithasbeenproventhatcalciumabsorptioninthestomachis also affected by lactose. Furthermore, the dairyproductscalciumbioavailabilityisbetterthanoftheothersources,suchasvegetables.Thiscouldpartlybe due to their contents in highly phosphorylatedfragments of caseins, named caseinophosphopep-tides(CPPs).Thesepeptidesappearmainlyduringtheelaborationofmilkproductssuchascheeseoryoghurt, under the action on caseins of milk-en-dogenous,milk-clotting and/ormicrobial enzymes.TheymayalsoarisefromαS1-,αS2-andβ-kazeinadi-gestioninthegut(FitzGerald,1998;Dupasetal.,2009).OneuniquefeatureofCPPsistheirabilitytoformCPP-metalioncomplexes,whichwouldpoten-tiallyincreasethebioavailabilityofcalciumandiron,
notablybymaintainingmetals ina soluble form inthedistalsmallintestine(Peresetal.,1999;Dupasetal.,2009).Osteoporosisisaverycommondiseaseinwesterncountriesandmostlyaffectswomen.Oneofitscausesinoldageisinsufficientcalciumintakewhen young. Maximum bone mass is achieved inthethirddecadeoflifebyprovidingsufficientcal-cium intake at young age. It has also been proventhatbonemassisanimportantfactorinosteoporosisprevention (Prentice, 1997; Cashman, 2002a).Despitethedatafromthevariouscalciuminterven-tionstudies,thereisstillconsiderabledebateonthemeaningoftheseeffectsofcalciumonbone(Cash-man,2006).
Phosphorusisamajorelementwithmanyim-portant biological functions in the human body. Itoccursasorganicorinorganicphosphateinallbodytissues and fluids, and is the main component ofmany biological compounds, including lipids, pro-teins, carbohydrates andnucleic acids (Cashman,2002a).
Š. ZAMBERLIN et al.: Mineral elements in milk and dairy products, Mljekarstvo 62 (2), 111-125 117
Ascalciumphosphate,phosphorusisthemostimportantstructuralcomponentofbonesandteeth.However,excessiveintakeofphosphoruscombinedwithreducedcalciumintakemayhavenegativeef-fectsonbones(Cashman,2006).TheRDAofphos-phorusisshowninTable6.Milkanddairyproductsarerichsourceofphosphorusandinwesterncoun-tries account for 30-45%of the total phosphorusintake(InstituteofMedicine,2004).
Magnesium plays an important role in manyphysiologicalprocesses,suchasmetabolismofpro-teinsandnucleicacids,neuromusculartransmissionand muscle contraction, bone growth and bloodpressureregulation.Magnesiumisalsoaco-factorofmanyenzymes.Ontheotherhand,magnesiumdefi-ciencymayalsocauseosteoporosis(Rude,1998).
Therehasnotbeenmuchresearchonthebio-availabilityofmagnesiumfrommilkforthehumanbodyinhumannutrition.Studiesofmetabolicbal-ance have shown that 16-43 % of magnesium isabsorbedfrominfantformulasbasedoncowmilk,and that lactose facilitates magnesium absorption.Inwesterncountries16-21%oftotalmagnesiumisconsumedthroughmilkanddairyproducts(Cash-man,2002a).
Concentration of trace elements in milk and dairy products
Unlikethemajorelements,traceelementsarepresent in the human body in the concentrationslower than0.01%of the totalbodymass.Of the20 essentialminerals, 14 are trace elements: iron,copper,zinc,manganese,selenium,iodine,chromi-um, cobalt,molybdenum, fluorine, arsenic, nickel,siliconandboron.Scientificresearchesontestani-malshaveproventhatsomeoftheaboveelements(arsenic, nickel, silicon and boron) are essential.Therefore,itisassumedthattheyarealsoessentialforhumans(Cashman,2002b).Manyothertraceelementsalsooccurinmilk.However,theyarenotnutritionallyimportant.Theseincludelithium,bro-mine,aluminium,strontium,silver, lead, tin,vana-dium,mercury,cadmium,rubidiumandcaesium.
Manyofthetracemineralelementsaretoxic.However, their concentrations inmilk are too lowtopose a threat tohumanhealth. Like contentofothermineralspresentinmilk,theconcentrationoftrace elements (Table 1 and 8) is not constant. Itdependsonthelactationstage,nutritionalstatusofthe animal, and environmental and genetic factors(Cashman,2002b).Thecontentoftraceelements
Table 8.Concentrations of trace elements in goat, sheep and cowmilk compared to humanmilk (Po-sati and Orr, 1976; Jenness, 1980; Park and Chukwu, 1988; Park and Chukwu, 1989;FlynnandCashman,1997;Conietal.,1999;Park,2006;DeutchenForschungsanstaltfürLebensmittelchemie,2012)
118 Š. ZAMBERLIN et al.: Mineral elements in milk and dairy products, Mljekarstvo 62 (2), 111-125 (2012)
ingoatandothermilktypesalsodependsonthespe-cies, its individual characteristics, feedingmethod,lactationstage,andhealthconditionofudder(ParkandChukwu,1989).Sheepmilkcontainsapproxi-mately0.9%ash,comparedto0.7% incowmilk(Parketal.,2007).Aconclusionmaybe that thecontentofminerals insheepmilkishigherthanincowmilk,primarilyduetodifferences innutritionand metabolism (Rincon et al., 1994). To date,therehasbeen little researchon traceelements insheepmilk,althoughtheycouldplayan importantroleduetotheirpossiblypositiveinfluenceonhu-manhealth.Bycarryingoutdiscriminatoryanalysisofthemineralcompositionin360samplesofrawmilk,(120samplesofcow,goatandsheep)statisticaldis-tanceandsignificantdifferenceswereestablishedin120samplesofcowmilkcomparedto120samplesofgoatmilk,while in10%ofthecasestherewasacorrespondencebetweenthesamplesofgoatandsheepmilk(Jay,2000).Theseresultsclearlyshowaseparationofelementsintermsofthemilk(Jay,2000;HaenleinandWendorff,2006).
Increased exposure of dairy animals to grow-ing environmental pollution has also increased theneed for more research regarding the content ofheavymetalsinmilk.Heavymetals,suchasleadandplatinum,whichcanbefoundinexhaustgases,canbe absorbedwhen animals graze nearmajor trans-portationroutes(Ikedaetal.,1996;Raghunathetal.,1997).Inaddition,negativeeffectsofleadandcadmiumonhumanhealthweredetected.Traceele-mentslikecopperandzincareessentialandhavearole inmany biological functions (Tripathi et al.,1999).However,ifpresentathigherlevels,theycanhave negative effects on human health (Brewer,2010).Researchresultsshowthattheconsumptionof sheepmilk products in Italy leads to an intakeof 15%of thepermissible content of heavymet-als (Coni et al., 1999).The content of cadmium,whichisalsoaheavymetal,issignificantlyhigherinsheepmilkthanincowmilk,probablyduetodiffer-encesinnutritionandmetabolismbetweentwospe-cies(Conietal.,1999;HaenleinandWendorff,2006;Herwigetal.,2011).
Research on other trace elements shows that,for example, the iron concentration inmilk is re-ducedby35to50%inthefirstthreedaysoflacta-tion;afterthatitremainsataconstantlevel,anditdoesnotdependonnutrition.Furthermore,14%of
thetotalironcontentinmilkcanbefoundinmilkfatboundtothemembraneoffatglobules;24%isboundtocasein(probablytophosphoserine);29%islinkedtowheyproteins,while32%isboundtolowmolecularmasscompounds(Cashman,2002b).Bi-oavailabilityofironfromhumanmilkrangesfrom49to70%,whichissignificantlyhigherthanfromcowmilk(10to34%).Thereisnoclearexplanationforthisdifference.However, itmightbeexplainedbythehighleveloflactoferrin(glycoproteinthatbindsironions)presentinhumanmilk.Anotherpossibleexplanation may be found in the high content oflactose and ascorbate inhumanmilk,which facili-tatesironabsorption,andinlowcontentofproteins,calcium and phosphorus, which inhibit absorption(Cashman,2002b).
The average zinc concentration inmilk is 3.9mg/L (Flynn andCashman, 1997).However, itshouldbenotedthattherearegreatvariationsincon-centration(2.0to6.0mg/L).Zincincowcolostrumisreducedby50%inthefirstthreedaysoflactationafter that further change is negligible.Hard sheepcheeses are rich source of zinc (Samaržija et al.,2005)duetoinherenthighconcentrationinsheep’smilk(Table1).Zinc in nutritionalso increases itscontentinmilk.Inaddition,itwasdeterminedthatadditionofzinctomilkresults inreducedsomaticcellcount(Pechovà etal.,2006).Only1to3%ofzincinmilkisrelatedtothelipidfraction,whiletheremainingpartcanbefoundintheskimmilkfrac-tion.Also,outof the total zinccontentpresent intheskimmilkfraction,95%isboundtophosphoser-inebycaseinmicellesand5%tocitrate.Thebioa-vailabilityofzincinhumanmilkismuchhigherthanincowmilk,becauseinhumanmilkit isboundtoligandsoflowmolecularmass(forexample,citrate),which facilitatesabsorption.Also, thebindingofalargeproportionof zinc to casein in cowmilk (10timeshigherthaninhumanmilk),maycause ittobeblockedwithinthecaseincurdthatisproducedintheabdomen,makingitunavailableforabsorption(PabόnandLönnerdal,2000).Contrary,researchconducted on rats established a high capacity forzincabsorption(85to95%)fromhumanandcowmilk,anddairyinfantformula.Itispossiblethatthelowconcentrationofzincinhumanmilkcontributesto better absorption because it is homeostaticallycontrolled,andsmallquantitiesarebetterabsorbedthanlarge(Cashman,2002b).
Š. ZAMBERLIN et al.: Mineral elements in milk and dairy products, Mljekarstvo 62 (2), 111-125 119
Theconcentrationofcopperinmilkisalsore-ducedby50% inthefirst threedaysof lactation,butunlikeironandzinc,additionofcoppertoani-malfeedincreasesitscontentinmilk.Thereislittleinformation on the content of absorbed copper inthehumanbody.Experimentsonratsshowed83%absorptionfromhumanmilk,76%fromcowmilk,and86 to87%fromdairy infant formula (Cash-man,2002b).
Manganesecontentishigherincolostrum(100to160µg/L)thaninmilk(20to50µg/L),reducedbymorethen50%inthefirstthreedaysoflacta-tion.Incowmilk67%ofthemanganeseisboundtocasein,1%toglobularfatmembranes,14%towheyproteins, and18% to lowmolecularweightfraction. Research results show that manganeseabsorption from human milk in healthy adultsamounts to 8.2±2.9 % and is significantly higherthanfromcowmilk(2.4±1.7%),whilemanganeseabsorption fromdairy infant formula amounted to1.7±5.9 %. Nevertheless, the absolute content oftheabsorbedmanganesefromdairy infantformulaandcowmilkwashigherthanfromhumanmilkbe-causeof itshigher inherentconcentration in thosetypesofmilk.Ontheotherhand,studiesconductedon ratsdidnot showany significantdifferences inabsorbedmanganesefromhumanandcowmilkand,alsodairyinfantformula(Cashman,2002b).
Selenium in plants is affected by the contentandavailabilityoftheelementinsoilwhileseleniumcontentofmilkisaffectedbytheseleniumcontentinfeedsanditsavailability(Reykdaletal.,2011).Also, processing of milk can diminish seleniumconcentration (Navarro-Alarcon and Cabrera-
Vique, 2008). Selenium is linked to the enzymeglutathioneperoxidase(12%ofthetotalcontent).Lessthan0.1%oftotalseleniumcontentisboundtofat(Cashman,2002b).
Theiodinecontentdependsontheseasonanddietaryintake;itvariesfrom20to>4000µg/L.Themostofiodineinmilk(80to90%)isfoundinin-organic form; another 5 to 13% is bound to pro-teinsbycovalentbondorweakintermolecularbonds(Cashman,2002b).
Thechemicalformofchromiuminmilkisnotknown, although it mostly occurs in triple bondform.Theaveragecontentofchromiumandcobaltinmilkdependsontheirdietaryintake.
Molybdenumcontentinmilkisboundtoxan-thine oxidase and is dependent on feed. Averagefluorinecontentinmilkis20µg/L(rangingfrom10to140µg/L).Approximately46to64%offluorinecontentinmilkispresentasfreeion,theremainingis bound to proteins (Cashman, 2002b).Little isknownaboutthechemicalformsofcobalt,arsenic,nickel, silicon and boron inmilk. The amounts oftheseelementsinmilkanddairyproductsareshowninTables8to12.
Iron as an essential trace elementparticipatesascatalystinseveralmetabolicreactions.Asacom-ponentofhemoglobin,myoglobin, citochromeandotherproteins, ironplays an important role in thetransport,storageandutilisationofoxygen.Itisalsoaco-factorofmanyenzymes(BatesandPrentice,1996).Milkanddairyproductsarepoorsourceofiron.Irondeficiencyinthehumanbodyisoneofthemostcommonhealthissues,occurringininfantsandchildrenbecauseoffastgrowthandlowdietaryin-take.Thisproblemcanbepreventedbyadditionofirontodairyinfantformulassinceadditionalascor-bate in infant formulas improves iron absorption(Bermejoetal.,2002).
Zincisveryimportantforgrowth,sexualdevel-opment,thehealingofwoundsaswellasnormalfunc-tioningoftheimmunesystemandotherphysiologi-calprocesses.Zincisacomponentofthehormoneinsulin.Itassistsinthefunctioningofseveralotherhormones thatare important for reproductionandsynthesisofDNA,RNAandproteins(Salgueiroetal., 2002). It is also a co-factor ofmany enzymesthat are included in most of metabolic processes.Dairyproductssuchasmilk,cheeseandyoghurtarevery important inhumannutrition, but an insuffi-cientsourceofzinc.Itisestimatedthatinwesterncountriesthecontributionofdairyproductstothetotalzincintakerangesfrom19to31%(Cashman,2002b).
Copper isessentialelement important for theabsorptionofironandascofactorofenzymesinglu-cosemetabolismandsynthesisofhemoglobin,con-nectivetissuesandphospholipids(Solaimanetal.,2001).Copperdeficiencyinthehumanbodyisveryrare,occurringonlyincasesoflong-termstarvation.Milkanddairyproductsareapoorsourceofcopper(DavisandMertz,1987)(Tablica9).
Manganese is a specific enzyme co-factor in-volvedinthesynthesisofmucopolysaccharides,anda non-specific co-factor for many other enzymes.Thereareseveralknownmanganesemetaloenzymeslike arginase, glutamine synthetase, phosphoen-lopyruvatedecarboxilaseandmanganesesuperoxidedismutase (Aschner and Aschner, 1991). Man-ganese can be found in significant quantities in allfoodstuffs.Itsdeficiencyhasnotbeenrecordedasacauseofdisturbanceordisease.Cowmilkisapoorsource ofmanganese. Its contribution to the totalmanganeseintakeinwesterncountriesislow(1to3%).Ofthetotaldietaryintakeofmanganeseonly3 to5%are successfullyabsorbed.The remainingquantitiesareeliminatedfromthebodythroughfae-ces(Auetal.,2008).
Selenium is the main component of the en-zyme glutathione peroxidase, which is present inmanytypesoftissues.IncombinationwithvitaminE, catalase and superoxidedismutase, it acts as anantioxidant (Somer and Ínam, 2000). After die-taryintake,seleniumisconvertedintoorganicform,mostlyasseleno-methionine,whichisthenincorpo-ratedintoproteins(Petreraetal.,2009).Insome
Low selenium concentrations in the humanbodyhavealsobeenobservedinNewZealandandFinland,countrieswithlowseleniumconcentrationsin the soil. TheRDAof selenium is shown in theTable13.
Iodineisanessentialcomponentofthyroidhor-mones that are important for the control of basalmetabolismand reproduction. Iodinedeficiency inthehumanorganismcanresultinenlargementofthethyroid gland.On the other hand, a high concen-trationofdietaryiodinecanleadtoaslowdowninthyroidglandfunction(Reidetal.,2008;Sorigueretal.,2010).Iodineistheonlytraceelementthatisconsideredtobeexcessivelypresentinmilk,dueinpart to the excessiveuseof organic iodide saltsandiodophorfordisinfection.TheRDAfor iodineisshowninTable13.Thecontributionofmilkanddairyproductstototaliodineintakerangesfrom6to7%inGermanyto37%inGreatBritain(Schöneetal.,2009).
Molybdenum is also an essential component ofseveralenzymes,includingxanthineoxidereductase,aldehydeoxidaseandsulphiteoxidase,whereitoc-cursasprostheticgroupofmolybdopterin(Hilleetal.,2010).Itisnotknownwhetherthehumanbodyneedsmolybdenumassuchorasmolybdopterin.
The RDA of molybdenum is shown in Table13.Milkcontributessignificantlytototalmolybde-numintake-asmuchas36%inwesterncountries(Cashman,2002b;Yoshidaetal.,2006.).
It is assumed that chromium is an essentialnutrientinhumannutrition.Lackofchromiumcancauseproblemswithlactosetolerance.CobaltisthecomponentofvitaminB12,whichisitsonlyknownfunction. Fluorine is accumulated in hard tissues,such asbones and teeth, and although it is not anessentialelement,itisconsideredimportantbecauseitpreventstoothdecay.TherearenoRDAsbecauselimiting factorhasnotbeendetermined. Itsnutri-tional function is not yet known. Arsenic, nickel,silicon,andboronareessentialelementsinanimals,soitcanbeassumedthatthisisalsothecasewiththe humanbody (Casey et al., 1995).Thenutri-
ingwithmineralsinmilkanddairyproducts.Essen-tialmineralelements,includingsodium,potassium,chloride, calcium, manganese, selenium, iodine,chromium, cobalt, molybdenum, fluorine, arsenic,nickel, silicon andboron, canbe found in allmilktypes and dairy products.They are present in theformofinorganicionsandsalts,orarepartoforgan-icmolecules like proteins, fats, carbohydrates andnucleicacid.Sodium,potassium,chlorideandiodinecanbefoundinmilkandinfantformulasinachemi-
Š. ZAMBERLIN et al.: Mineral elements in milk and dairy products, Mljekarstvo 62 (2), 111-125 123
calformwhichallowsanalmostentireabsorptioninthehumanbody.Thebioavailabilityofcalciumandmagnesiumhasnotyetbeensufficientlyresearched.Amongsheep,goatandcowmilkthebioavailabilityofironandzincfromcowmilkisthehighest,how-ever, significantly lower than in humanmilk.Verylittle information is available on the bioavailabilityofcopper,manganese,selenium,fluorineandothertraceelementspresent inmilkanddairyproducts.However,itisassumedthatlactose,ascorbate,cit-rate,phosphopeptidesandlactoferrinhaveasignifi-cantimpactontheabsorptionofmineralelements.Furthermore,milkdoesnotcontainsubstancessuchasphitatesandpolyphenols,whichstrongly inhibittheabsorptionofmineralsinhumanbody.
Mineralni sastav mlijeka i mliječnih proizvoda
Sažetak
Mineralni elementi se u mlijeku i mliječnimproizvodimanalazeuoblikuanorganskihionaisoli,ilikaodioorganskihmolekulakao što subjelanče-vine,masti,ugljikohidratiinukleinskekiseline.Ke-mijska formaukojoj sumineralni elementiprisut-nijevrlovažnajeronjojovisiapsorpcijauželucuitimenjihovobiološko iskorištenje.Mineralnisastavmlijeka nije konstantan i ovisi o stadiju laktacije,hranidbenom statusu životinje, okolišnim uvjetimai genetskim čimbenicima. Cilj ovog rada je prika-zati dosadašnje rezultate istraživanja koncentracija,kemijske forme i prehrambene važnosti pojedinihmineralnihelemenatakojisuprisutniurazličitimvr-stamamlijekaimliječnihproizvoda.
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