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J. Agric. Food Chem. 2005, 53, 4696−4700
Rapid Multimineral Determination in Infant Cereal Matrices Using Wavelength Dispersive X-ray Fluorescence L. PERRING,* D. ANDREY, M. BASIC-DVORZAK,
AND
J. BLANC
Department of Quality and Safety Assurance, Nestle´ Research Centre, Vers-Chez-les Blanc, CH-1000 Lausanne 26, Switzerland
A rapid and simple method for the determination of a series of macroelements (sodium, magnesium, phosphorus, chlorine, potassium, and calcium) and trace elements (manganese, iron, and zinc) by wavelength dispersive X-ray fluorescence has been developed and validated for infant cereal matrices. Reference values were obtained by inductively coupled plasma optical emission spectroscopy and by potentiometry. The 88 investigated samples were commercially available products. Pellets of 4 g were prepared under 10 tonnes of pressure. For each sample, 3 pellets were prepared and analyzed. Limits of quantification and repeatabilities were evaluated. Calibrations were established with 43 samples, and method validation was made using a second set of 45 samples. An evaluation of this alternative method was done by comparison with data obtained from the reference methods. The results show the good performances of the alternative method to routine infant cereals analysis. KEYWORDS: WDXRF; infant cereals; food; ICP-AES; potentiometry; mineral; sodium; magnesium; phosphorus; chloride; potassium; calcium; manganese; iron; zinc
INTRODUCTION
The addition of minerals (and/or vitamins), also called fortification, is a common way (1, 2) to allow the standardization of the nutrient content in foods (that naturally show variable concentrations) and thus to ensure the consistency of the product quality, to restore those nutrients lost during processing and then to maintain the nutritional quality of foods, to provide correction and prevention of nutritional deficiencies in the population, and to add value to finished products. To ensure correct addition of premixes during infant formula or infant cereal production, analytes such as calcium, iron, or zinc may be used as tracers and thus can be determined in final products. Data obtained with accurate and rapid analyses can be used to adapt the process parameters and thus to ensure target concentration of added premixes is achieved. When target concentrations are obtained in compliance with the declaration, the production can be released. In this connection, since the advent of greater control of starting raw materials as well as finished food products, the development of rapid, robust, multielemental, and accurate techniques to obtain data about the origin, identity, nutrition, or processing has become a priority. The major advantage of the X-ray fluorescence (XRF) technique compared to wet chemical analysis is that the measurements can be carried out directly on solid samples (powder in a sample cup or pressed into pellets). This avoids lengthy and laborious sample preparation steps, using corrosive and toxic reagents, which in turn * Corresponding author (e-mail
[email protected]; fax 41 21 78 52 553).
lead to contamination risks. Less manipulation and fewer timeconsuming digestions mean cost and time savings. Further advantages of XRF include simplicity of use, short analysis time, and simultaneous analysis of elements, leading to a high throughput. The XRF technique possesses the main characteristics of an analytical tool to be used near the food production lines (3). For milk powders and infant formulas, the use of the X-ray fluorescence technique shows successful results (4, 5), thus minimizing risks of recall or rework. In the present study, a wavelength dispersive (WDXRF) method is proposed for the rapid checking of major minerals in finished infant cereals. Calibrations were established using a suitable range of products of infant cereals. These “calibration products” contain a wide range of mineral values, which have been analyzed using reference methods. MATERIALS AND METHODS Trial Samples. Infant cereal samples were worldwide commercially available. Two groups of samples were used during this study: the calibration set including 43 samples and the validation set including 45 samples. References values of all samples are compiled in Table 1. Prior to all analyses, infant cereal samples were homogenized using a coffee grinder. No synthetic sample was produced by spiking. Reference Methods. Reference values of all samples were determined using in-house-validated procedures by ICP-AES for Na, Mg, P, K, Ca, Mn, Fe, and Zn and by potentiometry for chloride. Analyses were systematically made in duplicate. A Varian Vista-AX Axial ICP-AES instrument (Varian, Mulgrave, Australia) equipped with a charge-coupled device (CCD) detector was
10.1021/jf047895+ CCC: $30.25 © 2005 American Chemical Society Published on Web 05/14/2005
J. Agric. Food Chem., Vol. 53, No. 12, 2005
Mineral Determination in Infant Cereals
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Table 1. Reference Values (Milligrams per Kilogram) of the Samples and Identification of the Calibration Samples sample
Na
Mg
P
Cl
K
Ca
Mn
Fe
Zn
caliba
sample
Na
Mg
P
Cl
K
Ca
Mn
Fe
Zn
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44
2717 2666 962 1155 921 1319 1261 135 125 217 210 1238 1039 135 121 1172 1349 1300 160 1219 227 1646 1732 1871 1443 235 1610 1411 1380 1993 1098 119 412 359 1340 1258 1248 1275 79 201 207 67 119 1521
724 774 542 425 494 494 463 753 329 593 547 1037 399 405 303 543 492 468 429 504 396 743 620 1393 1260 318 753 528 537 693 978 271 262 272 580 463 649 505 204 212 503 1199 1096 526
3640 3693 3249 3354 3122 4224 3685 1748 1261 2051 2211 3764 3083 2105 2320 3352 3644 3476 1459 3375 1260 3742 3920 2253 1943 1755 4135 3263 3426 3815 4003 1341 1428 1440 3719 3359 3254 3430 789 1021 1338 3380 3307 4200
2231 2192 3144 3126 2865 3605 3331 549 714 712 918 2500 3251 839 653 3808 3767 3606 574 3545 526 2818 3684 817 353 416 4234 3812 3653 3380 2796 810 1146 1068 3832 3419 3386 2871 254 861 1156 729 544 4103
5502 5777 6731 5374 6318 6316 5817 4687 1752 3560 2979 6543 5027 6106 3953 7147 5787 6593 2978 6668 1561 5709 6103 1473 1209 2373 6498 6428 5517 6824 5028 2200 2054 2094 7529 5874 5634 6675 658 1522 6632 5556 3906 6915
5564 5472 5070 4069 4729 5858 4563 366 274 4818 4246 5757 3936 2637 3192 4085 4543 4516 1766 4334 1109 4891 4919 424 457 1566 5685 4331 4298 4462 2543 2535 2461 2984 4432 3999 4026 4413 197 309 1214 449 372 4678
9.3 10.0 4.0 3.3 3.7 2.8 3.9 9.3 7.5 9.0 8.0 23.9 4.1 11.7 9.1 4.0 7.7 3.2 6.9 6.7 5.3 3.6 2.7 12.5 10.5 10.1 2.6 2.9 5.8 3.9 16.3 6.5 6.0 6.4 3.8 4.2 4.5 5.2 4.8 6.9 10.9 23.9 28.3 4.3
89.7 88.4 87.5 76.5 77.5 84.9 82.3 166.0 9.5 202.5 166.2 98.6 85.2 129.7 220.6 82.7 69.4 84.3 209.7 78.8 125.0 69.3 68.6 110.4 117.5 100.4 89.4 73.8 79.6 81.7 160.1 153.6 173.2 110.8 76.7 75.5 83.6 75.7 83.4 98.5 86.5 31.9 32.4 43.2
76.8 75.6 14.3 14.1 13.1 17.7 24.0 12.9 8.9 9.1 6.2 40.8 13.7 8.8 9.8 14.5 18.0 14.8 8.9 14.2 8.1 20.1 18.9 13.7 11.5 14.3 21.2 16.3 17.3 19.1 25.2 7.0 8.6 7.4 16.5 14.4 15.7 13.3 8.1 5.2 10.9 23.3 26.6 17.3
X
45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88
62 62 848 398 163 109 43 88 71 68 478 394 906 398 415 1082 1594 2024 45 50 56 45 96 125 46 93 97 106 99 158 103 60 124 2240 100 97 99 171 128 146 162 96 102 97
179 398 336 178 244 250 393 225 736 547 667 446 330 584 512 676 745 908 178 150 934 960 853 815 934 362 335 527 463 310 304 188 462 246 335 311 348 396 303 413 382 385 442 392
839 1073 2512 973 1106 874 554 1819 1779 1603 2896 2691 2371 1965 1945 2161 2422 3022 830 792 2965 3053 2397 2509 2844 3309 3493 3561 3475 1443 1254 793 1073 1845 1158 1126 1214 1384 1095 1286 1234 1368 1397 1356
478 460 1830 893 776 389 29 695
