Food Additives & Contaminants
ISSN: 0265-203X (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/tfac19
Investigation of trace element content of cheese L. Gabrielli Favretto To cite this article: L. Gabrielli Favretto (1990) Investigation of trace element content of cheese, Food Additives & Contaminants, 7:3, 425-432, DOI: 10.1080/02652039009373905 To link to this article: http://dx.doi.org/10.1080/02652039009373905
Published online: 10 Jan 2009.
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Citing articles: 1 View citing articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=tfac20 Download by: [Universite Laval]
Date: 06 November 2015, At: 19:30
FOOD ADDITIVES AND CONTAMINANTS, 1990, VOL. 7, NO. 3, 4 2 5 - 4 3 2
Investigation of trace element content of cheese L. GABRIELLI FAVRETTO Dipartimento di Economia e Merceologia delle Risorse Naturali e della Produzione, Università di Trieste, 1-34100 Trieste, Italy
Downloaded by [Universite Laval] at 19:30 06 November 2015
(Received 4 March 1989; revised 8 September 1989; accepted 17 September 1989) Nine trace elements (Al, Cr, Mn, Fe, Ni, Cu, Zn, Cd, Pb) were determined in cheese by atomic absorption spectrophotometry with electrothermal atomization in a graphite tube, using the ashing procedure. Associations among mineral constituents were studied by means of principal component analysis, which allows determination of interdependences among trace elements in foods. A test for normality was used to investigate monovariate distributions, in order to estimate the symmetry of data vector. The correlation matrix was used as a starting matrix for principal component analysis; nine variables were reduced to four principal components. The clusters of elements appear to be determined by their origin. Keywords: Cheese, trace elements, atomic absorption spectrophotometry, principal component analysis
Introduction
The composition of the mineral fraction of cheese has been frequently considered (Aitzemiiller and Wirotama 1974, Basile et al. 1978, Coppini et al. 1979, Wong et al. 1978), but only a few of the published papers deal with minor and trace elements (Koops and Westerbeek 1983, Losi and Ferri 1988), despite their importance in nutrition or in food contamination. The aim of this paper is to consider the concentration of some trace elements (Al, Cr, Mn, Fe, Ni, Cu, Zn, Cd, Pb) in a cheese from a single origin of the type Latteria, and to evaluate the associations existing among these metals by means of principal component analysis (PCA). This multivariate method allows study of the interdependences among the components of foods, and allows identification of clusters of these components according to their origin. In the present research PCA was applied to the cheese, in order to clarify the origin of the clusters of trace elements, and to identify possible contributions from external sources. Multivariate methods were widely used to analyse data collected on foods (Martens and Russwurm 1983). PCA was already being applied to establish any associations existing among some minor and trace elements in pasteurized cow milk (Gabrielli Favretto et al. 1987, Favretto etal. 1987, Gabrielli Favretto et al. 1989) and in Parmesan cheese (Favretto et al. 1985). The trace elements were determined by atomic absorption spectrophotometry with electrothermal atomization (AAS-EA) in 38 cheese samples collected over the period of a year. 0265-203X/90 $3.00© 1990 Taylor & Francis Ltd.
426
L. Gabrielit Faretto
Experimental
Downloaded by [Universite Laval] at 19:30 06 November 2015
Sampling, apparatus and reagents The same cheese was considered over the period March 1987-February 1988. Sampling was performed on cheese aged 30 days, from a dairy factory (Latterie Carsiche, Duino, Trieste). A Perkin Elmer HGA-500 graphite furnace mounted on a Perkin Elmer model 1100 atomic absorption spectrophotometer was used with a Perkin Elmer AS-40 autosampler. Pyrolitically coated graphite tubes and background correction (D2 lamp) were utilized. Working solutions were prepared by diluting immediately before use standard solutions for atomic absorption spectroscopy (1 mg/ml Spectrosol, BDH) with 0· 1 M nitric acid (AristaR, BDH). Water was doubly distilled in pure silica apparatus. Sample, preparation The sampling procedure of the Italian Official Analytical Methods for Cheese (Gazzetta Ufficiale Rep. Ital., Gen. Ser. 229, 2 October 1986) was adopted. A slice of 0-5 kg from a whole cheese of about 5 kg was divided into small pieces, which were randomly distributed in five subsamples; two subsamples were chosen at random and used for weighing the aliquots to be analysed. Cheese weighing 5 · 00 g was first charred under an infrared lamp and then ashed at 450°C in a platinum dish. The ash was dissolved in 1 -00 ml of 2-0 M nitric acid at 95°C and then mixed with 1 ml of 0·1 Μ nitric acid. The solution was filtered through a 5-cm diameter filter paper (Schleicher and Schiill 589') into a polyethylene 20 ml calibrated flask. The filter was washed with 1 ml of 0· 1 M nitric acid and then transferred into the platinum dish, charred and ashed again. The dish was treated with 0·1 Μ nitric acid as previously indicated, and the solution was filtered in the same calibrated flask, washing the filter up to the mark. AAS determination Instrumental conditions are summarized in table 1. For each element, calibration graphs were obtained by plotting the total integrated absorbance corrected for integrated absorbance of background (A) versus q, at the analytical wavelength, where q is the mass (ng) of the element injected in 20 μΐ of 0-1 M nitric acid. All signals were recorded in the time range 0-5 s. The calibration graphs of the elements of table 1 were linear only at q -* 0 and deviated from linearity as q was increased. Since, as q -* 0, the repeatability decreases, a working range was selected with an upper and lower limiting value. When the sample solutions exceeded the selected upper limiting value, dilutions were carried out systematically. Each element was determined on two independent samples of the cheese, taking the mean as a final value. A total reagent blank was run in parallel, and its integrated absorbance was subtracted from the sample. Total reagent blanks were < 5 % of q. Accuracy and precision of the analytical procedure It was shown that 20 μ\ of 0· 1 M nitric acid gave a blank absorbance < 0-003; the frequency of blank determinations was about one blank every ten samples. Procedures for testing the percentage recovery and possible matrix effects have been already reported (Pertoldi Marietta and Gabrielli Favretto 1983, Gabrielli Favretto and Pertoldi Marietta 1984). After addition of known amounts of the
427
Trace element content of cheese Table 1. Experimental conditions for determination of some trace elements with electrothermal atomization" (qm, minimum amount of standard injected). Element
Al Cr
Mn Fe Ni Cu
Zn
Downloaded by [Universite Laval] at 19:30 06 November 2015
Cd Pb
Wavelength (nm)
Slit width
309-2 357-9 279-3 248-3 232-0 324-7 307-6 228-8 283-3
0-7 0-7 0-2 0-2 0-2 0-7 0-7 0-7 0-7
Charring
b
0
Atomization
(nm)
(ng) 1100°C/20s/20s 1000°C/20 s/30 s 1000°C/20 s/20 s 1000°C/20 s/20 s 1000°C/20 s/30 s 900°C/20 s/20 s 500°C/20 s/30 s 250° C/15 s/25 s 5OO°C/15 s/15 s
d
2400°C/0 s/5 s d 2300°C/0 s/5 s 2600°C/l s/5 s 250O°C/l s/5 s d 2300°C/0 s/5 s 2600°C/l s/5 s 2100°C/l s/5 s 2100°C/l s/5 s 1800°C/0 s/5 s
0-25 0-25 0-10 0-30 1-00 1-50 75-0 0-10 1-00
a For all the elements the drying step was the same: 120°C with 20 s ramp, 30 s hold and a nitrogen flow of 250 ml/min. Charring and atomization are given as temperature/ramp time/hold. b 200 ml/min nitrogen. c 20 ml/min nitrogen. d 50 ml/min nitrogen (for aluminium, argon was used as purging gas). For all the elements, background correction (except chromium) and pyrolytically coated graphite tube (except cadmium and lead) were used.
elements before charring, percentage recoveries in a sample having an average concentration of the analyte, were as follows: Al 96-8, Cr 98-9, Mn 102, Fe 100-6, Ni 98-5, Cu 99-6, Zn 97-8, Cd 95-0, Pb 97-3%. No appreciable matrix effect was observed when background is corrected with a D 2 lamp at the dilutions used in the analytical procedure. The absence of matrix effect was also checked by comparison of the curve obtained with some standard additions to the solution of the sample, with the calibration graph, both in a linearized form. The calibration graphs used for all elements have the general formula A = abql(l + aq), where a and b are parameters. The linearized equation \\A = l/b + \\abq was used as a working calibration graph, by plotting \\A versus \\q. The quality of fit was estimated by the index ratio F, obtained from the analysis of the variance for the linear regression. As an example, figure 1 shows the linearized calibration line for Mn: the observations tend to fit the regression line well, and this is shown by the value of F. The same figure also shows the line obtained by addition of five aliquots of the standard solution to a diluted solution of a sample, having 206-2 μΒ/kg of Mn. The calibration and the standard addition graphs appear to be overimposed and the calibration graph can be directly used for analyte determination. Ni is determined at 232-0 nm, and a spectral interference was attributed to calcium phosphate matrix in the analysis of milk (Koops et al. 1982). In order to confirm the amount of the element found in cheese by AAS-EA, a solution of sample (10-0 ml) was extracted three times with ammonium pyrrolidine-carbodithioate in heptan-2-one (3-0 ml) at pH 2-0. The organic extracts were ashed and the ash was dissolved in 10-0 ml of 0-1 M nitric acid; a corresponding blank was prepared. Testing of this solution gave a Ni recovery of 98%, in a sample of cheese containing 49-6 iig/kg of Ni. No absorbance was detected in the aqueous extracted phase.
Downloaded by [Universite Laval] at 19:30 06 November 2015
428
L. Gabrielli Favretto
Figure 1. Linearized plot (continuous line) of the standard additions of Mn (five additions, open circles) to an aliquot of a diluted solution of a cheese sample (solid circle); the regression line corresponds to the following equation: \\A =0-8893+ 1-3359 (1/?), with F=5943. The dotted line corresponds to the linearized calibration graph of Mn (11 observations, crosses); the regression line corresponds to the equation: \\A =0-6796+ 1-3592 (l/
ISSN: 0265-203X (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/tfac19
Investigation of trace element content of cheese L. Gabrielli Favretto To cite this article: L. Gabrielli Favretto (1990) Investigation of trace element content of cheese, Food Additives & Contaminants, 7:3, 425-432, DOI: 10.1080/02652039009373905 To link to this article: http://dx.doi.org/10.1080/02652039009373905
Published online: 10 Jan 2009.
Submit your article to this journal
Article views: 7
View related articles
Citing articles: 1 View citing articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=tfac20 Download by: [Universite Laval]
Date: 06 November 2015, At: 19:30
FOOD ADDITIVES AND CONTAMINANTS, 1990, VOL. 7, NO. 3, 4 2 5 - 4 3 2
Investigation of trace element content of cheese L. GABRIELLI FAVRETTO Dipartimento di Economia e Merceologia delle Risorse Naturali e della Produzione, Università di Trieste, 1-34100 Trieste, Italy
Downloaded by [Universite Laval] at 19:30 06 November 2015
(Received 4 March 1989; revised 8 September 1989; accepted 17 September 1989) Nine trace elements (Al, Cr, Mn, Fe, Ni, Cu, Zn, Cd, Pb) were determined in cheese by atomic absorption spectrophotometry with electrothermal atomization in a graphite tube, using the ashing procedure. Associations among mineral constituents were studied by means of principal component analysis, which allows determination of interdependences among trace elements in foods. A test for normality was used to investigate monovariate distributions, in order to estimate the symmetry of data vector. The correlation matrix was used as a starting matrix for principal component analysis; nine variables were reduced to four principal components. The clusters of elements appear to be determined by their origin. Keywords: Cheese, trace elements, atomic absorption spectrophotometry, principal component analysis
Introduction
The composition of the mineral fraction of cheese has been frequently considered (Aitzemiiller and Wirotama 1974, Basile et al. 1978, Coppini et al. 1979, Wong et al. 1978), but only a few of the published papers deal with minor and trace elements (Koops and Westerbeek 1983, Losi and Ferri 1988), despite their importance in nutrition or in food contamination. The aim of this paper is to consider the concentration of some trace elements (Al, Cr, Mn, Fe, Ni, Cu, Zn, Cd, Pb) in a cheese from a single origin of the type Latteria, and to evaluate the associations existing among these metals by means of principal component analysis (PCA). This multivariate method allows study of the interdependences among the components of foods, and allows identification of clusters of these components according to their origin. In the present research PCA was applied to the cheese, in order to clarify the origin of the clusters of trace elements, and to identify possible contributions from external sources. Multivariate methods were widely used to analyse data collected on foods (Martens and Russwurm 1983). PCA was already being applied to establish any associations existing among some minor and trace elements in pasteurized cow milk (Gabrielli Favretto et al. 1987, Favretto etal. 1987, Gabrielli Favretto et al. 1989) and in Parmesan cheese (Favretto et al. 1985). The trace elements were determined by atomic absorption spectrophotometry with electrothermal atomization (AAS-EA) in 38 cheese samples collected over the period of a year. 0265-203X/90 $3.00© 1990 Taylor & Francis Ltd.
426
L. Gabrielit Faretto
Experimental
Downloaded by [Universite Laval] at 19:30 06 November 2015
Sampling, apparatus and reagents The same cheese was considered over the period March 1987-February 1988. Sampling was performed on cheese aged 30 days, from a dairy factory (Latterie Carsiche, Duino, Trieste). A Perkin Elmer HGA-500 graphite furnace mounted on a Perkin Elmer model 1100 atomic absorption spectrophotometer was used with a Perkin Elmer AS-40 autosampler. Pyrolitically coated graphite tubes and background correction (D2 lamp) were utilized. Working solutions were prepared by diluting immediately before use standard solutions for atomic absorption spectroscopy (1 mg/ml Spectrosol, BDH) with 0· 1 M nitric acid (AristaR, BDH). Water was doubly distilled in pure silica apparatus. Sample, preparation The sampling procedure of the Italian Official Analytical Methods for Cheese (Gazzetta Ufficiale Rep. Ital., Gen. Ser. 229, 2 October 1986) was adopted. A slice of 0-5 kg from a whole cheese of about 5 kg was divided into small pieces, which were randomly distributed in five subsamples; two subsamples were chosen at random and used for weighing the aliquots to be analysed. Cheese weighing 5 · 00 g was first charred under an infrared lamp and then ashed at 450°C in a platinum dish. The ash was dissolved in 1 -00 ml of 2-0 M nitric acid at 95°C and then mixed with 1 ml of 0·1 Μ nitric acid. The solution was filtered through a 5-cm diameter filter paper (Schleicher and Schiill 589') into a polyethylene 20 ml calibrated flask. The filter was washed with 1 ml of 0· 1 M nitric acid and then transferred into the platinum dish, charred and ashed again. The dish was treated with 0·1 Μ nitric acid as previously indicated, and the solution was filtered in the same calibrated flask, washing the filter up to the mark. AAS determination Instrumental conditions are summarized in table 1. For each element, calibration graphs were obtained by plotting the total integrated absorbance corrected for integrated absorbance of background (A) versus q, at the analytical wavelength, where q is the mass (ng) of the element injected in 20 μΐ of 0-1 M nitric acid. All signals were recorded in the time range 0-5 s. The calibration graphs of the elements of table 1 were linear only at q -* 0 and deviated from linearity as q was increased. Since, as q -* 0, the repeatability decreases, a working range was selected with an upper and lower limiting value. When the sample solutions exceeded the selected upper limiting value, dilutions were carried out systematically. Each element was determined on two independent samples of the cheese, taking the mean as a final value. A total reagent blank was run in parallel, and its integrated absorbance was subtracted from the sample. Total reagent blanks were < 5 % of q. Accuracy and precision of the analytical procedure It was shown that 20 μ\ of 0· 1 M nitric acid gave a blank absorbance < 0-003; the frequency of blank determinations was about one blank every ten samples. Procedures for testing the percentage recovery and possible matrix effects have been already reported (Pertoldi Marietta and Gabrielli Favretto 1983, Gabrielli Favretto and Pertoldi Marietta 1984). After addition of known amounts of the
427
Trace element content of cheese Table 1. Experimental conditions for determination of some trace elements with electrothermal atomization" (qm, minimum amount of standard injected). Element
Al Cr
Mn Fe Ni Cu
Zn
Downloaded by [Universite Laval] at 19:30 06 November 2015
Cd Pb
Wavelength (nm)
Slit width
309-2 357-9 279-3 248-3 232-0 324-7 307-6 228-8 283-3
0-7 0-7 0-2 0-2 0-2 0-7 0-7 0-7 0-7
Charring
b
0
Atomization
(nm)
(ng) 1100°C/20s/20s 1000°C/20 s/30 s 1000°C/20 s/20 s 1000°C/20 s/20 s 1000°C/20 s/30 s 900°C/20 s/20 s 500°C/20 s/30 s 250° C/15 s/25 s 5OO°C/15 s/15 s
d
2400°C/0 s/5 s d 2300°C/0 s/5 s 2600°C/l s/5 s 250O°C/l s/5 s d 2300°C/0 s/5 s 2600°C/l s/5 s 2100°C/l s/5 s 2100°C/l s/5 s 1800°C/0 s/5 s
0-25 0-25 0-10 0-30 1-00 1-50 75-0 0-10 1-00
a For all the elements the drying step was the same: 120°C with 20 s ramp, 30 s hold and a nitrogen flow of 250 ml/min. Charring and atomization are given as temperature/ramp time/hold. b 200 ml/min nitrogen. c 20 ml/min nitrogen. d 50 ml/min nitrogen (for aluminium, argon was used as purging gas). For all the elements, background correction (except chromium) and pyrolytically coated graphite tube (except cadmium and lead) were used.
elements before charring, percentage recoveries in a sample having an average concentration of the analyte, were as follows: Al 96-8, Cr 98-9, Mn 102, Fe 100-6, Ni 98-5, Cu 99-6, Zn 97-8, Cd 95-0, Pb 97-3%. No appreciable matrix effect was observed when background is corrected with a D 2 lamp at the dilutions used in the analytical procedure. The absence of matrix effect was also checked by comparison of the curve obtained with some standard additions to the solution of the sample, with the calibration graph, both in a linearized form. The calibration graphs used for all elements have the general formula A = abql(l + aq), where a and b are parameters. The linearized equation \\A = l/b + \\abq was used as a working calibration graph, by plotting \\A versus \\q. The quality of fit was estimated by the index ratio F, obtained from the analysis of the variance for the linear regression. As an example, figure 1 shows the linearized calibration line for Mn: the observations tend to fit the regression line well, and this is shown by the value of F. The same figure also shows the line obtained by addition of five aliquots of the standard solution to a diluted solution of a sample, having 206-2 μΒ/kg of Mn. The calibration and the standard addition graphs appear to be overimposed and the calibration graph can be directly used for analyte determination. Ni is determined at 232-0 nm, and a spectral interference was attributed to calcium phosphate matrix in the analysis of milk (Koops et al. 1982). In order to confirm the amount of the element found in cheese by AAS-EA, a solution of sample (10-0 ml) was extracted three times with ammonium pyrrolidine-carbodithioate in heptan-2-one (3-0 ml) at pH 2-0. The organic extracts were ashed and the ash was dissolved in 10-0 ml of 0-1 M nitric acid; a corresponding blank was prepared. Testing of this solution gave a Ni recovery of 98%, in a sample of cheese containing 49-6 iig/kg of Ni. No absorbance was detected in the aqueous extracted phase.
Downloaded by [Universite Laval] at 19:30 06 November 2015
428
L. Gabrielli Favretto
Figure 1. Linearized plot (continuous line) of the standard additions of Mn (five additions, open circles) to an aliquot of a diluted solution of a cheese sample (solid circle); the regression line corresponds to the following equation: \\A =0-8893+ 1-3359 (1/?), with F=5943. The dotted line corresponds to the linearized calibration graph of Mn (11 observations, crosses); the regression line corresponds to the equation: \\A =0-6796+ 1-3592 (l/
