Mineral content in legumes and nuts contribution to the Spanish dietary intake.pdf

the science of the total environment 308 2003 1 14 0048 9697 03 see front matter 2002 elsevier science b v all rights reserved pii s0048 9697 02 00611 3 mineral content in legumes and nuts contribution to the spanish dietary intake carmen cabrera fuensanta lloris rafael gimenez manuel olalla m carmen lopez department of nutrition and bromatology school of pharmacy university of granada campus de cartuja e 18071 granada spain received 2 july 2002 accepted 7 november 2002 abstract we evaluated the levels of essential elements as cu cr fe and zn and toxic elements as al ni pb and cd in a total of 40 samples of different legumes and 56 samples of different nuts that are widely consumed in spain these elements were determined in the samples mineralized with hno and v o using electrothermal atomic absorption 325 spectrometry etaas as the analytical technique reliability of the procedure was checked by analysis of a certified reference material no matrix effects were observed and aqueous standard solutions were used for calibration in legumes the levels ranged from 1 5 5 0 mg cuyg 0 05 0 60 mg cryg 18 8 82 4 mg feyg 32 6 70 2 mg znyg 2 7 45 8 mg alyg 0 02 0 35 mg niyg 0 32 0 70 mg pbyg and not detectable 0 018 mg cdyg in nuts the levels ranged from 4 0 25 6 mg cuyg 0 25 1 05 mg cryg 7 3 75 6 mg feyg 25 6 69 0 mg znyg 1 2 20 1 mg alyg 0 10 0 64 mg niyg 0 14 0 39 mg pbyg and not detectable 0 018 mg cdyg a direct statistical correlation between cu cr zn al and cr ni p 0 05 and al pb p 0 001 has been found the growing popularity of these products in recent years on the basis of its nutritional properties and beneficial effects requires additional data and a periodical control in addition the present findings are of potential use to food composition tables 2002 elsevier science b v all rights reserved keywords mineral content legumes nuts dietary intake etaas 1 introduction the determination of minerals and trace elem ents in foodstuffs is an important part of nutritional and toxicological analyses copper chromium iron and zinc are essential micronutrients for human health in addition these elements play an important role in human metabolism and interest corresponding author tel q34 958 243 863 fax q34 958 243 869 e mail address carmenc platon ugr es c cabrera in these elements is increasing together with reports of relationships between trace element status and oxidative diseases pelus et al 1994 fennema 2000 copper can be found in many enzymes some of which are essential for fe metabolism deficiencies of cu are infrequent however various studies have reported a direct correlation between the dietary znycu ratio and the incidence of cardiovascular disease because of the difficulties in establishing the recommended dietary intake of cu the national research coun 2c cabrera et al the science of the total environment 308 2003 1 14 cil 1989 has published a safe range in adults of 1 5 3 mgyday foods rich in cu include nuts and seeds chromium is involved in carbohydrate and lipid metabolism the most frequent sign of cr deficien cy is altered glucose tolerance this nutrient has also been associated with diabetes and cardiovas cular disease shils et al 1994 some authors have reported beneficial effects of dietary supple mentation with cr particularly in groups in which deficiencies are frequent van cauwenbergh et al 1996 provisionally a daily intake of 50 200 mg hasbeenrecommendedforadults national research council 1989 iron is an essential element although fe metabolism occurs in a close circuit there exist physiological losses which must be compensated three factors are important of iron needs the total amount in the diet the type of fe compound and the other diet compo nents hallberg et al 1998 when the fe amount supplied does not satisfy the requirement fe defi ciency ensues the recommended daily intake in adults is 10 15 mg national research council 1989 zinc enzymes participate in a wide variety of metabolic processes including carbohydrate lipid and protein synthesis or degradation the metal is required for deoxyribonucleic and ribon ucleic acid synthesis it may also play a role in stabilizing plasma membranes shils et al 1994 zinc has been recognized as a co factor of the superoxide dismutase enzyme which is involved in protection against oxidative processes shils et al 1994 the net delivery of zn to an organism is a function of the total amount of this element in foods and its bioavailability the recommended daily intake for adults is 12 15 mg national research council 1989 certain groups of people can be at risk with regard to zn nutrition it is not known if al is one of the trace elements essential for the human body because studies on its physiology and toxicity are made difficult by its ubiquity and because of contamination risks associated with it seiler et al 1994 aluminium is distributed in the whole food chain as result of its high presence in nature gerhardsson et al 1994 the possible connection between elevated tissue aluminium content and problems such as osteomalacia and neurodegenerative disorders e g encephalopathy dementia and alzheimer s dis ease has awakened interest in al intake via the diet massey and taylor 1991 normal intake ranges from 6 to 14 mgyday massey and taylor 1991 pennington and schoen 1995 estimated that al intake ranged from 0 7 and 11 5 mgyday and gramiccioni et al 1996 indicated that the mean dietary intake varied between 2 5 and 6 3 mgyday the functions of nickel are not complete ly understood and it has not been established as an essential element in man the principal route of ni exposure is dietary intake mcllveen and negusanti 1994 thecasesofnitoxicity described in man are work related skin and res piratory allergies are frequent and there is an increased risk of cancer of the nasal cavities lungs or larynx however available epidemiological data are limited alegr a et al 1988 teissedre et al 1998 environmental pollution is the main cause of heavy metal contamination in the food chain and lead and cadmium are two potentially harmful metals that have aroused considerable concern lead contamination of the environment is increas ing and the prolonged intake of even low concen trations of pb can cause serious toxic effects concon 1988 this has led to increased interest in determining pb levels in foodstuffs cabrera et al 1991 approximately 80 of the total human pb intake is supplied by the diet shils et al 1994 cadmium is a toxic element present in low concentrations in nature high levels are often associated with human activity and are found in urban and industrial waste disposal areas robards and worsfold 1991 cabrera et al 1994a its toxicity is manifested by kidney dysfunction hypertension hepatic injury reproductive toxicity lung damage bone effects etc robards and worsfold 1991 cabrera et al 1998 diet is the most important source of cd human intake of all foods legumes most adequately meet the recommended dietary guidelines for healthful eat ing they are high in carbohydrate and dietary fibre mostly low in fat supply adequate protein while being a good source of vitamins and min erals mann and truswell 1998 fennema 2000 nuts have been valued for their oils as much as a food and were an important source of nutrients 3c cabrera et al the science of the total environment 308 2003 1 14 and energy since the earliest civilizations hyson et al 2002 their high content of energy protein vitamins and minerals makes them a very nutri tious food mann and truswell 1998 the present study is focused on the mineral content in legumes and nuts analyzed in mineral ized samples with a previously validated etaas method under optimized conditions for each ele ment we also evaluated the contribution of these products to the total dietary intake of cu cr fe zn al ni pb and cd the growing popularity and consumption of legumes and nuts on the basis of its nutritional properties and beneficial effects requiresaperiodicalcontrolofthemineral presence 2 materials and methods 2 1 apparatus we used a perkin elmer 1100b double beam atomic absorption spectrometer equipped with deu terium arc background correction perkin elmer norwalk ct usa and a perkin elmer hga 700 graphite furnace atomizer pyrolytic graphite platforms ref b012 1092 and pyrolytically coat ed graphite tubes ref b013 5653 were obtained from perkin elmer argon of 99 999 purity sociedad espanola de ox geno barcelona spain at 300 mlymin flow was used as the internal gas during all the stages except atomization when the flow was stopped hollow cathode lamps of cu cr fe zn al ni pb and cd perkin elmer were used a selecta digestion block selecta sa barcelona spain and pyrex tubes were used for samplemineralization amoulinexfm 460 microwave oven with 600 w and 2450 mhz moulinex bangnolet france at 15 100 full power in 25 increments was used to dry the samples of fresh products a moulinex blender was used to homogenize the samples 2 2 reagents bidistilled deionized water obtained with a mil li q system millipore milford ma was used exclusively standard solutions of cu cr fe zn al ni pb and cd 1 00 0 002 g tritisol merck darmstadt germany were used and dilut ed as necessary to obtain working standards high quality concentrated nitric acid 65 and vanadium pentaoxide analytical reagent merck were used for sample mineralization magnesium nitrate and ammonium dihydrogenphosphate reagent grade merck were used as chemical modifiers ammo nium molybdate reagent grade merck was used to precondition the furnace tubes 2 3 material to eliminate the risk of contamination all glass ware and polyethylene material was washed with tap water after each use soaked in a 6 n hno3 solution at least overnight and rinsed several times with bidistilled deionized water 2 4 samples a total of 40 samples of different legumes lentils haricot and kidney beans chickpeas broad beans and green peas and 56 samples of different nuts almonds cashew nuts hazelnuts peanuts pistachio roasted salted corn sunflower seeds walnuts chestnuts and pine nut kernel were analyzed several brand names of each product representing the most widely accepted and most frequently consumed in spain were selected for testing all samples were commercially available preliminary assays established the appropriate amount of sample for analysis to ensure homoge neity between samples and ensure they were rep resentative pomeranz and meloan 1994 prichard et al 1996 2 5 sample treatment different food items were sliced and inedible parts thrown away the remaining parts were homogenized in a blender and weighed for fresh products three aliquots of approximately 100 g were previously dried in a microwave oven under controlledtemperatureconditions driedand homogenized samples were mineralized in an acid digestion block a portion of 0 250 g of sample was treated with 5 ml of 65 hno and a few 3 micrograms of v o as a catalyst in pyrex tubes 25 4c cabrera et al the science of the total environment 308 2003 1 14 table 1 instrument parameters for cu cr fe zn al ni pb and cd determination in legumes and nuts by etaas elementwavelengthslit widthatomizationashingatomizationmatrix nm nm systemtemp 8ctemp 8cmodifier cu324 80 7platform12002300 cr357 90 7wall tube16502500mg no 3 2 fe248 30 2platform14002400mg no 3 2 zn213 90 7platform6001800mg no 3 2 al309 30 7platform17002500mg no 3 2 ni232 00 2wall tube9002500 pb283 30 7platform7001800nh h po mg no 4243 2 cd228 80 7platform4501600 table 2 analytical characteristics for cu cr fe zn al ni pb and cd determination in legumes and nuts by etaas elementdetectionsensitivitybaccuracycprecisiondslope ratio limit pg a pg r s d blankyadditione cu4 04 599 00 0 53 0 4 20 998 0 999 cr1 03 097 95 3 05 0 5 20 990 1 100 fe4 06 098 50 0 74 1 4 60 992 0 998 zn0 50 898 70 1 03 5 4 00 990 0 999 al4 010 099 00 1 03 2 4 50 997 1 100 ni10 013 098 85 0 24 8 5 60 998 1 040 pb0 414 099 00 0 12 7 2 80 995 1 050 cd0 161 398 70 1 02 2 3 40 995 1 100 calculated according to iupac rules and corresponding to 3 times the s d of the blank ns10 a expressed as characteristic mass in pgy0 0044 a s b results from recovery assays of 5 randomly chosen samples c relative standard deviation for 10 replicate determinations in each of 5 samples d application of the standard additions method in 5 randomly chosen samples e placed in the digestion block and heated at 60 8c for 30 min and at 120 8c for 60 min the solutions were cooled to room temperature transferred to a calibrated flask and diluted to a final volume of 25 ml with bidistilled deionized water all analyses were done in triplicate mineral content was deter mined in this solution by etaas 2 6 sample analysis copper cr fe zn al ni pb and cd were determined in the mineralized samples by etaas according to the optimized conditions shown in table 1 for all elements calibration was per formed using aqueous standards the heating pro gram used temperatures set on hga 700 power supplyandbackground correctedpeakareas caused by the analyte were obtained furnace conditions were optimized on the basis of time temperature assays the same procedure was used to run the blanks that were prepared fresh daily standard addition graphs were prepared for blanks and for samples and from these the blank to sample slope ratios were calculated to compare the selectivity of the method for all samples considered in this study the slope ratio values obtained were close to 1 table 2 the standard additions method was therefore unnecessary and consequently the analysis was much simplified to evaluate the analytical characteristics of the meth od for each element the detection limits were calculated according to iupac rules long and winefordner 1983 and the sensitivity expressed as characteristics mass mass of analyte that pro duced 0 0044 absorbance units was evaluated accuracy was checked with recovery assays by 5c cabrera et al the science of the total environment 308 2003 1 14 table 3 accuracy and precision of the method against a certified reference material citrus leaves srm 1572 nbs elementcontent mgyg a accuracy precision r s d measuredbcertifiedb cu16 30 0 8016 50 1 0098 794 90 cr0 79 0 080 80 0 2098 7510 12 fe89 90 0 9890 00 10 0099 891 09 zn28 70 1 0029 00 2 0098 963 48 al91 75 5 0092 00 15 0099 735 40 ni0 59 0 050 60 0 3098 338 62 pb13 10 0 8613 30 2 4098 496 56 cd0 028 0 0040 03 0 0193 3314 20 dry weight a mean s d at 95 ci interval about the mean ns10 b table 4 copper chromium iron and zinc content in legumes range and mean expressed as mgyg of the edible portion sample scientific name ncopperchromiumironzinc lentil lens esculenta 62 00 3 300 12 0 6064 60 74 7045 10 70 20 2 50 0 31 71 00 56 50 bean phaseolus multiflorus haricot bean52 40 3 700 09 0 2160 30 66 7035 40 45 00 2 80 0 15 62 50 39 70 kidney bean52 60 3 500 08 0 2262 00 66 6638 80 50 20 3 00 0 17 64 40 46 90 chickpea cicer arietinum 73 20 4 900 09 0 2565 00 70 2037 40 42 80 3 50 0 12 68 80 39 20 broad bean vicia faba 53 90 5 000 10 0 3077 80 82 4042 80 50 00 4 30 0 28 80 00 41 20 green peas pisun sativum l fresh61 50 1 900 05 0 1018 80 25 5032 60 40 30 1 70 0 08 20 20 38 90 canned61 70 2 200 06 0 1220 60 29 6050 00 61 90 1 80 0 09 24 60 58 80 adding known amounts of analyte to five different randomly chosen samples and processing the mixtures as described above for experimental sam ples precision was checked in ten replicate deter minations on each of five different randomly chosen samples and relative standard deviation r s d was calculated for each element the results are summarized in table 2 the detection limits and sensitivity were suitable for the range concentrations of each analyte encountered in the samples we analyzed and are compatible with estimates given by other authors moreover the analytical precision and accuracy are acceptable horwitz et al 1990 pomeranz and meloan 1994 the reliability of the method was further corroborated by using a certified reference material table 3 the paired t test showed good agree ment level of significance 0 05 between the certified values and the results we obtained the statistical treatment was performed with the stat graphic statistical software 6 0 package stsg inc rockville md 1991 3 results and discussion the methods described above were used to determine the concentrations of cu cr fe zn al ni pb and cd in different legumes and nuts 6c cabrera et al the science of the total environment 308 2003 1 14 table 5 aluminium nickel lead and cadmium content in legumes range and mean expressed as mgyg of the edible portion sample scientific name naluminiumnickelleadcadmium lentil lens esculenta 68 30 45 800 10 0 330 40 0 610 008 0 010 30 20 0 24 0 51 0 009 bean phaseolus multiflorus haricot bean55 00 18 100 12 0 290 58 0 65n d 0 009 a 13 40 0 15 0 62 0 005 kidney bean56 60 20 200 10 0 200 50 0 70n d 0 011 19 00 0 17 0 69 0 007 chickpea cicer arietinum 72 70 18 000 20 0 350 40 0 690 004 0 015 10 20 0 26 0 48 0 010 broad bean vicia faba 53 90 9 900 12 0 190 36 0 480 007 0 016 6 70 0 17 0 40 0 012 green peas pisun sativum l fresh64 00 7 700 02 0 090 32 0 43n d 6 50 0 05 0 37 canned610 80 20 300 03 0 100 40 0 570 007 0 018 15 50 0 07 0 45 0 015 not detectable a table 6 copper chromium iron and zinc content in nuts range and mean expressed as mgyg of the edible portion sample scientific name ncopperchromiumironzinc almond prunus amygdalus 610 50 12 600 39 0 4940 30 48 7027 90 50 00 11 10 0 40 45 00 38 80 cashew nut36 60 8 500 25 0 3110 30 15 6037 50 49 60 anacardium occidentale 7 80 0 29 14 20 40 00 hazelnut corylus avellana l 514 00 17 200 36 0 3813 30 19 9038 00 45 60 16 60 0 37 17 30 42 50 peanut arachis hypogea 56 00 7 100 35 0 4220 00 26 6029 90 37 80 6 90 0 38 22 80 31 90 pistachio pistacia vera 85 60 10 300 37 0 4170 00 75 6030 20 36 70 9 20 0 39 73 50 33 40 roasted salted corn65 00 9 300 30 0 4142 80 55 4037 90 45 20 zea mays 6 60 0 38 50 30 40 50 sunflower seed510 00 15 700 41 1 0538 80 43 3050 60 69 00 helianthus annuus l 13