effects of the domestic cooking on elemental chemical

Research ArticleEffects of the Domestic Cooking on Elemental ChemicalComposition of Beans Species (Phaseolus vulgaris L)

Alessandra S T Ferreira1 Juliana Naozuka1 Gislayne A R Kelmer2 and Pedro V Oliveira2

1 Universidade Federal de Sao Paulo 275 Prof Artur Riedel Street 09972270 Diadema SP Brazil2 Instituto de Quımica Universidade de Sao Paulo 748 Prof Lineu Prestes Avenue 05513-970 Sao Paulo SP Brazil

Correspondence should be addressed to Juliana Naozuka jnaozukagmailcom

Received 18 November 2013 Accepted 28 January 2014 Published 2 March 2014

Academic Editor Vassiliki Oreopoulou

Copyright copy 2014 Alessandra S T Ferreira et alThis is an open access article distributed under the Creative CommonsAttributionLicense which permits unrestricted use distribution and reproduction in anymedium provided the originalwork is properly cited

Cooking is imperative for beans owing to the presence of compounds that can negatively affect nutritional value Additionallythe heating of beans can increase protein digestibility and induce desirable sensory properties However cooking also causesconsiderable changes in the composition of numerous chemical constituents including amino acids vitamins and minerals Forthis effects of domestic cooking on the essential element concentrations in various beans species (Phaseolus vulgaris L) wereinvestigated using jalo fradinho rajado rosinha bolinha black and common species Elemental determination was made withflame atomic absorption spectrometry and inductively coupled plasma optical emission spectrometry after sample digestion in aclosed-vessel microwave oven using a diluted oxidant mixture Analytical methods were evaluated with an addition and recoverytest and analysis of certified reference materials (apple and citrus leaves) Ca Cu K and Mg were present mainly in rajado Cu injalo Fe in black S and Zn in fradinho and P in rosinha species Thermal treatment did not affect Cu Fe S and Zn concentrationsbut it increased Ca K Mg P and Zn concentrations in jalo and black species Ca concentration decreased in fradinho and rajadospecies as did Fe concentration in jalo and rajado species

1 Introduction

Brazil is the largest worldwide producer (22ndash25 milliontons on approximately 5 million hectares cultivated) andconsumer (around 16 kg per capita) of beans [1ndash3] TheBrazilian food pyramid shows beans in a group of their ownand the FoodGuide for theBrazilian Population recommendsthe consumption of at least one portion of beans per day [4]Beans are one of themain protein sources for Brazilians [1ndash3]

There are several typical Brazilian Phaseolus speciesincluding jalo rosinha fradinho rajado bolinha common(ldquocariocardquo) and black In general these species are goodsources of vitaminsminerals (K CaMg P and Fe salts) pro-tein (20ndash25) and complex carbohydrates (50ndash60) [2 5 6]Besides being nutritionally important beans serve as richsources of bioactive compounds such as enzyme inhibitorslectins phytates oligosaccharides and phenolic compoundswith potential health implications [7] Importantly the ele-mental chemical composition of beans varies with species

geographic origin (soil water pesticides insecticides andfertilizers) and climate [8]

Given the nutritional importance of beans differencesin the elemental chemical composition of Phaseolus speciesshould be evaluated in beans cooked for human consump-tion Cooking is imperative for beans owing to the presenceof compounds such as trypsin inhibitors lectins phytatespolyphenols (especially tannins) and oligosaccharides (raf-finose and stachyose) that can negatively affect nutritionalvalue Trypsin inhibitors and lectins are thermolabile dis-appearing after proper cooking Other compounds are ther-mostable but their concentrations are reduced by dissolutionin water [4]

The heating of beans can increase protein digestibilityfrom 25ndash60 (raw) to 85 (cooked) depending on thespecies and cooking method [9] Furthermore cookinginduces desirable sensory properties in beans such as sweettaste cooked bean flavour and soft and mushy textures [2]However cooking also causes considerable changes in the

Hindawi Publishing CorporationJournal of Food ProcessingVolume 2014 Article ID 972508 6 pageshttpdxdoiorg1011552014972508

2 Journal of Food Processing

composition of numerous chemical constituents includingamino acids vitamins and minerals [5]

Cooking decreases carbohydrate content and increasesthe protein content of kidney beans A significant decreasein the content of all amino acids especially methionine tyro-sine and threonine has also been observed for this species[10] Studies with other types of beans and legumes havealso revealed changing mineral content Essential elementslost during cooking lixiviate to the cooking water and beanpreparations consumed with their cooking water can retainthose minerals [4 11] However heating can alter elementalchemical species and consequently their bioavailability

The aim of this study was to evaluate the effects ofdomestic cooking on the essential elements (Ca Cu Fe KMg P S and Zn) compositions of seven Phaseolus speciesElemental determination was carried out with inductivelycoupled plasma optical emission atomic spectrometry (ICPOES) and flame atomic absorption spectrometry (F AAS)after acid digestion of raw and cooked beans using a dilutedoxidant mixture and a closed-vessel microwave oven

2 Materials and Methods

21 Reagents and Samples Seven Phaseolus species (com-mon black rajado rosinha bolinha fradinho and jalo) werepurchased at a local market in Sao Paulo Two brands wereselected with mass of 500 g of beans Six species (commonblack jalo rosinha rajado and bolinha) were of the samebrand The geographic origin of the species are Sao Paulo(rosinha rajado and bolinha) and Minas Gerais (commonblack fradinho and jalo) according to the producers Apple(SRM1515) and citrus (SRM1572) leaves as standard referencematerials from the National Institute of Standards and Tech-nology (Gaithersburg MD) were used to check the accuracyof the analytical methods

All solutions were prepared from analytical reagent gradechemicals using high-purity deionised water obtained from aMilli-Q water purification system (Millipore Belford MA)Analytical grade 65 (wv) HNO

3distilled in a quartz

subboiling still (Marconi Piracicaba Brazil) and 30 (wv)H2O2(Merck Darmstadt Germany) were used for sample

digestion Titrisol standard solutions of 1000mgL of allelements (Merck Darmstadt Germany) were used to pre-pare the reference analytical solutions in 014molL HNO

3

Analytical curves were prepared with the following referencesolutions 10ndash200mgL of Ca K Mg P and S 15ndash60mgLof Cu 10ndash30mgL of Fe and 020ndash080mgL of Zn Allsolutions were prepared in 014molL HNO

3

22 Preliminary Sample Preparation Rawbeanswere cleanedwith deionized water and dried in an oven (model 515FANEM Sao Paulo Brazil) at 60∘C to constant mass Thenone part of the raw beans was ground using a cryogenicgrinder (MA 775 model Marconi Brazil) with 5min offreezing followed by three cycles of 2min of grinding with1min of freezing between each cycle [12 13] The rest of theraw beans were cooked

Table 1 Instrumental parameters for elemental and residual carbondeterminations using axially viewed ICP OES

Pump rotational speed 25 rpmPressure of nebulizer gas 01MPaIntermediate gas flow 10mLminPower (W) 1250WVazao do gas do plasma gas flow 12 Lmin

Analytical wavelength (nm)mdashaxial viewCa 3968 K 7664 Mg 2795P 1859 S 1807

23 Cooking Procedure To apply cooking techniques similarto those used in homes [3 14] we soaked raw beans (approx-imately 20 g) in tap water at room temperature for 24 h Thesoaking water was discarded a volume of deionized water(approximately 200mL) was added to the soaked beans andthe beans were cooked on an electric hotplate until they weresoft and 90 of water had evaporatedThe total cooking timeranged from 45 (bolinha) to 60 (rosinha) min depending onthe Phaseolus species Cooked beans and water were mixedand dried in an oven at 60∘Cuntil constantmass was reachedThe mixture was then ground using a cutting mill (GM 200model Retsch Germany) for 3min at 1800timesg

24 Sample Digestion Raw and cooked beans (and certifiedmaterial of apple leaves) were submitted to acid digestion ina closed-vessel microwave system (Multiwave 3000 AntonPaar Austria) equipped with 16 fluoropolymer vessels anda ceramic vessel jacket These components supported amaximum temperature and pressure of 240∘C and 4MParespectively Sample masses ranging from 150 to 250mg weredigested using a diluted oxidant mixture (2mLHNO

3+ 1mL

H2O2+ 3mLH

2O) [15]The heating programwas performed

in three steps (temperature∘C rampmin holdmin) (1)(140 5 1) (2) (180 4 5) and (3) (220 4 10) A fourth stepfor cooling the system through forced ventilation was carriedout for 20min After digestion samples and blank solutionswere transferred to plastic flasks and made up to 10mL withdeionized water The digestion procedure was carried out intriplicate for each sample

25 Ca K Mg P and S Determinations An iCAP 6300Duo ICP optical emission spectrometer (Thermo FisherScientific Cambridge England) equipped with axially andradially viewed plasma was used throughout the studyThe spectrometer was equipped with a simultaneous chargeinjection device detector allowingmeasurements from 16625to 84700 nm The Echelle polychromator was purged withargon The introduction system was composed of a cyclonicspray chamber and a Meinhard nebulizer The injector tubediameter of the torch was 20mm The instrumental condi-tions for ICP analysis are given in Table 1

Limit of detection (LOD) was calculated using thebackground equivalent concentration (BEC) and signal-to-background ratio (SBR) according to IUPAC recommenda-tions [15 16] BEC = 119862rsSBR SBR = (119868rs minus 119868blank)119868blank

Journal of Food Processing 3

50 55 60 65 70 75 800020

0025

0030

0035

006

008

010

012

014

016

4 6 8 10 12 14 16

Abso

rban

ce

Acethylene flow (lh) Observation height (mm)

Figure 1 Optimization of flame chemical composition (acetyleneflow) and observation height using analytical solutions of 10mg Lminus1Cu (◼) 10mg Lminus1 Fe (∙) and 02mg Lminus1 Zn (998771)

LOD = 3 times BEC times RSD100 where 119862rs is the concentrationof multielemental reference solution (10mgL) 119868rs and 119868blankare the emission intensities for the multielemental reference(10mgL) and blank solutions respectively and RSD is therelative standard deviation for 10 consecutive measurementsof blank solution The limit of quantification (LOQ) wascalculated as 10timesLOD LOQwas equal to 3timesLODThevalueswere given in 120583g gminus1 considering a sample mass of 250mgand a final volume of 10mL Citrus leaves (SRM 1572) weresubmitted to acid digestion and used to check the accuracy ofthe analytical method

26 Cu Fe and Zn Determination An atomic absorptionspectrometer (Model AAS Vario 6 Analytik Jena AG JenaGermany) equipped with a hollow cathode lamp of Cu(324 nm 4mA and slit 08 nm) Fe (259 nm 4mA and08 nm) and Zn (213 nm 4mA and 05 nm) and a deuteriumlamp for background correction were used For elementaldetermination with F AAS acetylene flow was optimizedranging from 50 to 80 L hminus1 in increments of 5 L hminus1 withconstant air flow (430 L hminus1) and observation height (6mm)The observation height was evaluated (5 8 10 12 and 15mm)in the best acetylene flow for each element of interest Undereach condition absorbance signals were obtained in triplicateusing analytical solutions of 10 10 and 02mg Lminus1 of Cu Feand Zn respectively

LOD was calculated using the standard deviation of 10measurements of analytical blank (LOD = 3 times 120590blank where120590 is the standard deviation) LOQ was equal to 3 times LODThevalues were obtained in 120583g gminus1 considering a sample mass of250mg and a final volume of 10mL

Addition of 1mg Lminus1 of Cu2+ 1 mg Lminus1 Fe3+ and05mg Lminus1 Zn2+ and recovery tests were used to verify thereliability of the procedure Additions of analytical solutionsof Cu Fe and Zn in raw and cooked beans were made beforeacid digestion in the microwave oven Apple leaves (SRM1515) were submitted to acid digestion and used to check theaccuracy of the analytical method

3 Results and Discussion

31 Optimization of Flame Conditions The appropriatedchemical environment of the air-acetylene flame is suitablefor breaking downmost compounds to atomswith reasonableefficiency The flame conditions can alter the atomic precur-sors or form refractory species of the element of interest orboth [17] As shown in Figure 1 the variation of fuel flowhad no effect on the atomization of Cu and Fe HoweverZn showed significant increase in absorbance signal from70 L hminus1 In a poor flame it can form a refractory Zn oxidebecause above 70 L hminus1 the analytical signal was increasedTherefore the fuel flow for the three elements was 70 L hminus1taking into consideration the profile and standard deviationof the absorbance signal After the optimization of the fuelflow the observation height was studied (see Figure 1) Thebest height was chosen considering the profile and standarddeviation of the absorbance signal 8mm was applied in theCu Fe and Zn determination in the samples The evaluationof this parameter is important because high absorbancesignal represents the interaction of the radiation from thehollow cathode lamp with gaseous atoms in the fundamentalstate

32 Figures of Merit Characteristic parameters of the ana-lytical calibration curve such as linear range correlationcoefficient (1198772) average RSD for repeatability of calibrationsolution measurements (119899 = 5) and LOD and LOQ (in120583g gminus1) are presented in Table 2 The quality of the resultsobtained with F AAS and ICP OES was checked by analysingSRM 1515 and SRM 1572 respectively which were submittedto the same experimental procedures adopted for the samplesThe comparison between experimental and certified valuesfor all analytes is presented in Table 3The results showed thatthemethods were selective and accurate and they are in goodagreement with Studentrsquos t-test at a 95 confidence limit

Analytical solutions of Cu Fe and Zn were added to asample mass (raw and cooked beans) before acid digestion inthemicrowave ovenThe influence of concomitants in Cu Feand Zn determinations with F AAS and analyte losses duringthe sample preparation (digestion) were investigated throughan addition and recovery test (see Table 3) The recoveries(see Table 3) showed an absence of chemical interference inthe elemental determination and no losses or contaminationin the sample pretreatment step According to NBR ISOIEC17025 [18] the recovery tolerance ranged from 70 to 120

33 Cooking Effects on Essential Element Concentrations inBeans The elemental concentrations of cooked and rawPhaseolus species are shown in Table 4 Between the speciesthese concentrations were different due to genetic environ-mental and processing factors However the influence ofgrowing location seasonal variation cultivation practicesand between-plant variation can be determined only throughan analysis of chemical composition [8] In raw Brazilianbeans Ca Cu K and Mg were present mainly in the rajadospecies Cu in jalo Fe in black S and Zn in fradinho andP in rosinha After cooking the highest Cu Fe and Zn


Table 2 Parameters of the analytical calibration curves linearrange correlation coefficient (1198772) average (RSD) for repeatability ofcalibration solutions measurements and limits of detection (LOD)and quantification (LOQ) for the studied elements

Element Linear range(mgL) 119877

2 RSD()

LOD(120583g gminus1)

LOQ(120583g gminus1)

F AASCu 010ndash40 09908 52 14 46Fe 025ndash30 09954 54 19 62Zn 015ndash080 09846 63 27 91

ICP OESCa 10ndash200 09910 10 15 50K 10ndash200 09995 14 67 22Mg 10ndash200 09931 15 11 36P 10ndash200 09983 24 19 62S 10ndash200 09981 23 094 31

Table 3 Recovery values and concentrations of Cu Fe and Zn inthe certified reference material (SRM 1515mdashapple leaves)

(a) F AAS

Element Recovery test () Concentration (120583g gminus1)plusmn standard deviation (119899 = 3)

Raw Cooked Certified value Found valueCu 112 81 546 plusmn 024 547 plusmn 027

Fe 84 108 83 plusmn 5 79 plusmn 1

Zn 90 94 125 plusmn 03 125 plusmn 23

(b) ICP OES

Element Concentration (120583g gminus1) plusmn standard deviation (119899 = 3)Certified value Found value

Ca 315 plusmn 010a

313 plusmn 088a

K 182 plusmn 006a

164 plusmn 036a

Mg 058 plusmn 003a

053 plusmn 012a

P 013 plusmn 002a

011 plusmn 003a

S 0407 plusmn 0009 0402 plusmn 0007

a ww

concentrations were found in the same raw species HoweverCa Mg and S were present in the black species whereas Kand P were present in the jalo species

Studies of the chemical composition of food are criticalfrom the nutritional and toxicological points of view Theamount of an essential nutrient considered adequate forhuman requirements is called the dietary reference intake USFood and Drug Administration regulations require nutritionlabelling for most foods Reference daily intakes for someessential elements of human nutrition and daily referencevalues have been established namely Ca (1000mg) Cl(3400mg) Cu (2mg) Fe (18mg) K (3500mg)Mg (400mg)Mn (2mg) P (1000mg) and Zn (15mg) [19] Consideringthe concentrations of these elements (see Table 4) and theconsumed amount (approximately 170 g) of the differentspecies of the cooked beans the masses of these ingested

elements ranged from 107 (fradinho) to 281 (black)mg for Ca10 (fradinho) to 17 (jalo)mg for Fe 06 (bolinha) to 24 (black)for Cu 1423 (fradinho) to 2125 (jalo) mg for K 114 (bolinha)to 167 (black) mg for Mg 583 (rosinha) to 889 (jalo) mg for P275 (rosinha) to 386 (preto)mg for S and 6 (rajado and black)to 9 (fradinho) for Zn Daily reference values can be achieveddepending on the bean species and consumed amount

The thermal treatment applied to beans improves proteinand starch digestibility and raises nutritive value by reducingantinutrients such as phytic acid and tannins [2] Howeverinformation regarding the effect of thermal treatment onessential element concentrations in beans remains limitedComparing the results of the raw and cooked beans (seeTable 4) and applying Studentrsquos t-test at a 95 confidencelimit the Cu Fe S and Zn concentrations were unalteredby cooking In jalo and black species the heating increasedCa K Mg P and Zn concentrations Contamination mayhave occurred during acid digestion cooking or bothContaminations of the deionized water used in the cookingwere discarded due to production of analytical blank Addi-tionally cooking decreased Ca concentration in the fradinhoand rajado species and Fe concentration in the jalo and rajadospecies Reduction in essential element concentrations maybe the result of the discarding of the soaking water Studieshave shown that soaking beans in water and discarding thewater may eliminate a percentage of tannins phytates andoligosaccharides [4]

The effects of cooking on soluble iron distribution havebeen evaluated in legumes beans chickpeas and lentils [12]Cooking reportedly increases soluble iron content in thecooking water Additionally thermal treatment can promotethe interaction of accessible species with other components ofthe human diet altering bioavailability An increase in non-heme iron absorption is observed in the presence of ascorbicacid and amino acids and decreased absorption occursduring interactions with antinutrients such as phytatespolyphenols and calcium which are part of the food andhaving a varied nature exert toxic or antinutritional actionwhen ingested in the native form (uncooked or insufficientlycooked foods) [1] In white beans traditional cooking has apositive effect on the bioavailability of Ca Zn and Fe Studieshave shown that the digestibility and hence absorption ofFe can be improved by heat processing owing to break ofprotein-iron bonds [7] Notably the total concentrationsof these essential elements were not modified by cookingbut chemical speciation and bioavailability studies must beundertaken to draw conclusions about thermal effects onchemical species These studies are important for improvingmineral content in cultivated bean species through breedingprograms [6]

4 Conclusion

Essential element determination with F AAS and ICP OESafter acid digestion in a closed microwave oven using dilutedoxidantmixture was carried out to evaluate the effect of cook-ing on various Phaseolus species The total concentrations ofessential elements in raw beans of seven Phaseolus species


Table 4 Mineral characterization of beans and the effect of domestic cooking

Species Concentration plusmn standard deviationc

Caa Cub Feb Ka Mga Pa Sa Znb

JaloRaw 093 plusmn 012 14 plusmn 2 84 plusmn 2 89 plusmn 03 061 plusmn 007 34 plusmn 01 18 plusmn 01 35 plusmn 3

Cooked 096 plusmn 015 14 plusmn 1 79 plusmn 2 13 plusmn 1 096 plusmn 011 52 plusmn 01 21 plusmn 01 48 plusmn 3

FradinhoRaw 084 plusmn 016 31 plusmn 18 61 plusmn 5 81 plusmn 04 057 plusmn 009 35 plusmn 01 20 plusmn 01 58 plusmn 4


RajadoRaw 096 plusmn 017 14 plusmn 3 75 plusmn 9 97 plusmn 05 070 plusmn 013 34 plusmn 01 17 plusmn 01 35 plusmn 5


BolinhaRaw 072 plusmn 015 97 plusmn 29 61 plusmn 4 74 plusmn 03 053 plusmn 010 31 plusmn 01 17 plusmn 01 36 plusmn 4


RosinhaRaw 061 plusmn 013 13 plusmn 5 56 plusmn 3 81 plusmn 04 067 plusmn 009 37 plusmn 01 19 plusmn 01 35 plusmn 4


BlackRaw 076 plusmn 019 12 plusmn 6 94 plusmn 3 88 plusmn 05 060 plusmn 012 36 plusmn 01 18 plusmn 01 33 plusmn 4


CommonRaw 086 plusmn 020 96 plusmn 26 87 plusmn 9 75 plusmn 05 055 plusmn 015 33 plusmn 01 17 plusmn 01 33 plusmn 8


aConcentration in mg gminus1bConcentration in 120583g gminus1c119899 = 3

displayed the potentialities of each species related to theseelements The differences are related to plant physiologygrowing location and environmental conditions Concen-trations of Cu Fe S and Zn were unaltered by cookingIncreases in Ca K Mg P and Zn concentrations wereobserved for jalo and black species Conversely a decrease inCa concentration in the fradinho and rajado species and inFe concentration in the jalo and rajado species was observed

Conflict of Interests

The authors declare that there is no conflict of interests regar-ding the publication of this paper

Acknowledgments

The authors are grateful to professors Pedro Vitoriano deOliveira and Cassiana Seimi Nomura both of the ChemistryInstitute of the Sao Paulo University for laboratory infras-tructure support Juliana Naozuka thanks the Fundacao deAmparo a Pesquisa do Estado de Sao Paulo (201211517-1)for financial support Gislayne A R Kelmer has receivedscholarship from Fundacao de Amparo a Pesquisa do Estadode Sao Paulo (201200133-8)

References

[1] P Brigide and S G Canniatti-Brazaca ldquoAntinutrients andldquoin vitrordquo availability of iron in irradiated common beans

(Phaseolus vulgaris)rdquo Food Chemistry vol 98 no 1 pp 85ndash892006

[2] L G Ranilla M I Genovese and F M Lajolo ldquoEffect ofdifferent cooking conditions on phenolic compounds andantioxidant capacity of some selected Brazilian bean (Phaseolusvulgaris L) cultivarsrdquo Journal of Agricultural and Food Chem-istry vol 57 no 13 pp 5734ndash5742 2009

[3] J Naozuka and P V Oliveirab ldquoCooking effects on iron andproteins content of beans (Phaseolus vulgaris L) byGFAAS andMALDI-TOFMSrdquo Journal of the BrazilianChemical Society vol23 no 1 pp 156ndash162 2012

[4] A C Fernandes W Nishida and R P da Costa ProencaldquoInfluence of soaking on the nutritional quality of commonbeans (Phaseolus vulgaris L) cooked with or without thesoaking water a reviewrdquo International Journal of Food Scienceamp Technology vol 45 no 11 pp 2209ndash2218 2010

[5] J Słupski ldquoEffect of cooking and sterilisation on the com-position of amino acids in immature seeds of flageolet bean(Phaseolus vulgaris L) cultivarsrdquo Food Chemistry vol 121 no4 pp 1171ndash1176 2010

[6] S Saha G Singh V Mahajan and H S Gupta ldquoVariability ofnutritional and cooking quality in bean (Phaseolus vulgaris L) asa function of genotyperdquo Plant Foods for Human Nutrition vol64 no 2 pp 174ndash180 2009

[7] NWangDWHatcher R T Tyler R Toews and E J GawalkoldquoEffect of cooking on the composition of beans (Phaseolusvulgaris L) and chickpeas (Cicer arietinum L)rdquo Food ResearchInternational vol 43 no 2 pp 589ndash594 2010

[8] JMHarnlyMA Pastor-Corrales andD L Luthria ldquoVariancein the chemical composition of dry beans determined from


UV spectral fingerprintsrdquo Journal of Agricultural and FoodChemistry vol 57 no 19 pp 8705ndash8710 2009

[9] R Bressani ldquoGrain quality of commonbeansrdquo FoodReviews Int-ernational vol 9 no 2 pp 237ndash297 1993

[10] MCandela I Astiasaran and J Bello ldquoCooking andwarm-hol-ding effect on general composition and amino acids of kidneybeans (Phaseolus vulgaris) chickpeas (Cicer arietinum) andlentils (Lens culinaris)rdquo Journal of Agricultural and Food Chem-istry vol 45 no 12 pp 4763ndash4767 1997

[11] C RMeiners N L Derise H C LauMG Crews S J Ritcheyand EWMurphy ldquoThe content of ninemineral elements in rawand cooked mature dry legumesrdquo Journal of Agricultural andFood Chemistry vol 24 no 6 pp 1126ndash1130 1976

[12] V M O Carioni R Chelegao J Naozuka and C S NomuraldquoFeasibility study for the preparation of a tuna fish candidatereferencematerial for total As determinationrdquoAccreditation andQuality Assurance vol 16 no 8 pp 453ndash458 2011

[13] J Naozuka and C S Nomura ldquoTotal determination and directchemical speciation of Hg in fish by solid sampling GF AASrdquoJournal of Analytical Atomic Spectrometry vol 26 no 11 pp2257ndash2262 2011

[14] A Quinteros R Farre andM J Lagarda ldquoOptimization of ironspeciation (soluble ferrous and ferric) in beans chickpeas andlentilsrdquo Food Chemistry vol 75 no 3 pp 365ndash370 2001

[15] J Naozuka E Carvalho Vieira A N Nascimento and P VOliveira ldquoElemental analysis of nuts and seeds by axially viewedICP OESrdquo Food Chemistry vol 124 no 4 pp 1667ndash1672 2011

[16] IUPAC ldquoNomenclature symbols units and their usage inspectrochemical analysismdashII Data interpretation analyticalchemistry divisionrdquo Spectrochimica Acta vol 33 no 6 pp 241ndash245 1978

[17] D J Halls ldquoThe role of various flame constituents in the pro-duction of atoms in the air-acetylene flamerdquo Analytica ChimicaActa vol 88 no 1 pp 69ndash77 1977

[18] R Burin V M Burin P Taha and M T Bordignon-LuizldquoValidacao de umametodologia analıtica para determinacao decalcio em produtos carneosrdquo Ciencia e Tecnologia de Alimentosvol 28 no 4 pp 973ndash978 2008

[19] S P Dolan and S G Capar ldquoMulti-element analysis of foodbymicrowave digestion and inductively coupled plasma-atomicemission spectrometryrdquo Journal of Food Composition and Anal-ysis vol 15 no 5 pp 593ndash615 2002

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composition of numerous chemical constituents includingamino acids vitamins and minerals [5]

Cooking decreases carbohydrate content and increasesthe protein content of kidney beans A significant decreasein the content of all amino acids especially methionine tyro-sine and threonine has also been observed for this species[10] Studies with other types of beans and legumes havealso revealed changing mineral content Essential elementslost during cooking lixiviate to the cooking water and beanpreparations consumed with their cooking water can retainthose minerals [4 11] However heating can alter elementalchemical species and consequently their bioavailability

The aim of this study was to evaluate the effects ofdomestic cooking on the essential elements (Ca Cu Fe KMg P S and Zn) compositions of seven Phaseolus speciesElemental determination was carried out with inductivelycoupled plasma optical emission atomic spectrometry (ICPOES) and flame atomic absorption spectrometry (F AAS)after acid digestion of raw and cooked beans using a dilutedoxidant mixture and a closed-vessel microwave oven

2 Materials and Methods

21 Reagents and Samples Seven Phaseolus species (com-mon black rajado rosinha bolinha fradinho and jalo) werepurchased at a local market in Sao Paulo Two brands wereselected with mass of 500 g of beans Six species (commonblack jalo rosinha rajado and bolinha) were of the samebrand The geographic origin of the species are Sao Paulo(rosinha rajado and bolinha) and Minas Gerais (commonblack fradinho and jalo) according to the producers Apple(SRM1515) and citrus (SRM1572) leaves as standard referencematerials from the National Institute of Standards and Tech-nology (Gaithersburg MD) were used to check the accuracyof the analytical methods

All solutions were prepared from analytical reagent gradechemicals using high-purity deionised water obtained from aMilli-Q water purification system (Millipore Belford MA)Analytical grade 65 (wv) HNO

3distilled in a quartz

subboiling still (Marconi Piracicaba Brazil) and 30 (wv)H2O2(Merck Darmstadt Germany) were used for sample

digestion Titrisol standard solutions of 1000mgL of allelements (Merck Darmstadt Germany) were used to pre-pare the reference analytical solutions in 014molL HNO

3

Analytical curves were prepared with the following referencesolutions 10ndash200mgL of Ca K Mg P and S 15ndash60mgLof Cu 10ndash30mgL of Fe and 020ndash080mgL of Zn Allsolutions were prepared in 014molL HNO

3

22 Preliminary Sample Preparation Rawbeanswere cleanedwith deionized water and dried in an oven (model 515FANEM Sao Paulo Brazil) at 60∘C to constant mass Thenone part of the raw beans was ground using a cryogenicgrinder (MA 775 model Marconi Brazil) with 5min offreezing followed by three cycles of 2min of grinding with1min of freezing between each cycle [12 13] The rest of theraw beans were cooked

Table 1 Instrumental parameters for elemental and residual carbondeterminations using axially viewed ICP OES

Pump rotational speed 25 rpmPressure of nebulizer gas 01MPaIntermediate gas flow 10mLminPower (W) 1250WVazao do gas do plasma gas flow 12 Lmin

Analytical wavelength (nm)mdashaxial viewCa 3968 K 7664 Mg 2795P 1859 S 1807

23 Cooking Procedure To apply cooking techniques similarto those used in homes [3 14] we soaked raw beans (approx-imately 20 g) in tap water at room temperature for 24 h Thesoaking water was discarded a volume of deionized water(approximately 200mL) was added to the soaked beans andthe beans were cooked on an electric hotplate until they weresoft and 90 of water had evaporatedThe total cooking timeranged from 45 (bolinha) to 60 (rosinha) min depending onthe Phaseolus species Cooked beans and water were mixedand dried in an oven at 60∘Cuntil constantmass was reachedThe mixture was then ground using a cutting mill (GM 200model Retsch Germany) for 3min at 1800timesg

24 Sample Digestion Raw and cooked beans (and certifiedmaterial of apple leaves) were submitted to acid digestion ina closed-vessel microwave system (Multiwave 3000 AntonPaar Austria) equipped with 16 fluoropolymer vessels anda ceramic vessel jacket These components supported amaximum temperature and pressure of 240∘C and 4MParespectively Sample masses ranging from 150 to 250mg weredigested using a diluted oxidant mixture (2mLHNO

3+ 1mL

H2O2+ 3mLH

2O) [15]The heating programwas performed

in three steps (temperature∘C rampmin holdmin) (1)(140 5 1) (2) (180 4 5) and (3) (220 4 10) A fourth stepfor cooling the system through forced ventilation was carriedout for 20min After digestion samples and blank solutionswere transferred to plastic flasks and made up to 10mL withdeionized water The digestion procedure was carried out intriplicate for each sample

25 Ca K Mg P and S Determinations An iCAP 6300Duo ICP optical emission spectrometer (Thermo FisherScientific Cambridge England) equipped with axially andradially viewed plasma was used throughout the studyThe spectrometer was equipped with a simultaneous chargeinjection device detector allowingmeasurements from 16625to 84700 nm The Echelle polychromator was purged withargon The introduction system was composed of a cyclonicspray chamber and a Meinhard nebulizer The injector tubediameter of the torch was 20mm The instrumental condi-tions for ICP analysis are given in Table 1

Limit of detection (LOD) was calculated using thebackground equivalent concentration (BEC) and signal-to-background ratio (SBR) according to IUPAC recommenda-tions [15 16] BEC = 119862rsSBR SBR = (119868rs minus 119868blank)119868blank


50 55 60 65 70 75 800020

0025

0030

0035

006

008

010

012

014

016

4 6 8 10 12 14 16

Abso

rban

ce















2 RSD()






(a) F AAS




Zn 90 94 125 plusmn 03 125 plusmn 23

(b) ICP OES


Ca 315 plusmn 010a

313 plusmn 088a

K 182 plusmn 006a

164 plusmn 036a

Mg 058 plusmn 003a

053 plusmn 012a

P 013 plusmn 002a

011 plusmn 003a

S 0407 plusmn 0009 0402 plusmn 0007

a ww






4 Conclusion
























Acknowledgments


References






























Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology


50 55 60 65 70 75 800020

0025

0030

0035

006

008

010

012

014

016

4 6 8 10 12 14 16

Abso

rban

ce















2 RSD()






(a) F AAS




Zn 90 94 125 plusmn 03 125 plusmn 23

(b) ICP OES


Ca 315 plusmn 010a

313 plusmn 088a

K 182 plusmn 006a

164 plusmn 036a

Mg 058 plusmn 003a

053 plusmn 012a

P 013 plusmn 002a

011 plusmn 003a

S 0407 plusmn 0009 0402 plusmn 0007

a ww






4 Conclusion
























Acknowledgments


References






























Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology




2 RSD()






(a) F AAS




Zn 90 94 125 plusmn 03 125 plusmn 23

(b) ICP OES


Ca 315 plusmn 010a

313 plusmn 088a

K 182 plusmn 006a

164 plusmn 036a

Mg 058 plusmn 003a

053 plusmn 012a

P 013 plusmn 002a

011 plusmn 003a

S 0407 plusmn 0009 0402 plusmn 0007

a ww






4 Conclusion
























Acknowledgments


References






























Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology























Acknowledgments


References






























Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology





















Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology

effects of the domestic cooking on elemental chemical

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