International Journal of Analytical Chemistry

International Journal of Analytical Chemistry / 2010 / Article

Research Article | Open Access

Volume 2010 |Article ID 149895 | 9 pages | https://doi.org/10.1155/2010/149895

Discriminant Analysis of Undaria pinnatifida Production Areas Using Trace Elemental Analysis

Academic Editor: Richard G. Brereton
Received08 Jun 2009
Revised02 Nov 2009
Accepted13 Feb 2010
Published12 May 2010

Abstract

Increasingly, attention is being paid to declaring the origin of agricultural and marine products after the advent of the bovine spongiform encephalopathy (BSE; commonly known as mad-cow disease). The display of the production centers on U. pinnatifida has been required in Japan since 2006. As an example of testing in another marine product, near-infrared spectra (NIR) and trace elemental analysis of U. pinnatifida are proven effective methods for discriminating production centers by us and Food and Agricultural Materials Inspection Center (FAMIC). In the present study, we found that X-ray fluorescence analysis of Br was also effective for the discrimination of production centers. The results of our study suggest that a combination of NIR and X-ray fluorescence analysis is a convenient and efficient method for determination due simple sampling procedures and increased effectiveness.

1. Introduction

Issues related to the safety of foods have gathered the attention of consumers following the advent of bovine spongiform encephalopathy (BSE). There have also been improper displays of production centers on some marine products such as clams (Undaria pinnatifida). Hence, there is an urgent need for establishment of convenient and efficient scientific methods for discriminating the production centers.

In our earlier studies [1, 2], we reported that near-infrared spectroscopy is a useful method for discriminating production areas [3]. In addition, Food and Agricultural Materials Inspection Center (FAMIC) reported that the inorganic elemental analysis results were valid markers for discriminating the production areas between China, Korea, and Japan (Sanriku and Naruto) of U. pinnatifida by ICP-MS spectroscopy [47]. Analysis results of these studies showed that the error rates were 0%, 26%, and 6% for samples from China, Korea, and Japan, respectively. In our present study, we hypothesize that additional accuracy can be achieved by classification and regression trees (CART [8, 9]) as a discriminant method.

In addition we explored the possibility of a more convenient discrimination method using elemental analysis of Br. The main purpose of this paper is reporting the possibility of the screening test, which would be conveniently applicable without using expensive and large equipments like an ICP-MS and so on, for discriminating production areas. Some NIR or X-ray fluorescence equipments are portable and the usages are not so complicated.

2. Materials and Methods

Results from the study in [5] involving ICP-MS analysis for 22 elements, namely, Al, Ba, Ca, Fe, K, Mg, Mn, Sr, Li, Co, Ni, Cu, Zn, Rb, Y, Mo, Cd, La, Nd, Sm, Gd, and W in 95 U. pinnatifida samples (29 China, 19 Korea, and 47 Japan (21 Sanriku and 26 Naruto)) were taken in our study for comparison of linear discriminant analysis (Table 1) and CART (Table 2). The overview of the sample preparation is below as follows:(1)cleaning samples with the ion-exchanged pure water thoroughly for getting rid of attached salt and the others, (2)drying them in the shade for one day under 20 degrees centigrade,(3)drying them in a vacuum with the pressure, about 5 mm Hg, under 107 degrees centigrade for one hour,(4)milling the dried samples into a fine small powder of less than 125 micrometers using a food processor (Millser IFM-700 G, Iwatani Corp.).


No.  Area No.AlBaCaFeKMgMnSrLiCoNiCuZnRbYMoCdLaNdSmGdW

115.41.94137513.66998730.881140.05420.014150.166830.981393.117050.171070.006490.023460.229120.002680.002470.000440.000790.00096
216.32.43161312.88919440.781530.054610.013310.177850.792134.70420.216720.015310.022050.20290.013350.005640.001350.00190
317.21.65145211.712308520.971130.063780.010490.750330.437956.85530.297840.006310.010180.170760.003040.0029400.000760
415.61.3412239.513267500.591010.05090.007750.063550.650153.137910.275960.007120.00840.342230.0030.002700.000690
515.71.35134014.596310031900.093920.012730.092591.575833.295070.217450.00610.037270.222320.002320.002460.0006900
615.41.56141412.314618290.891230.06170.01460.124311.583355.423480.33090.013420.09220.24580.003940.00460.0014900.00125
7171.54135313.310359901.181110.052920.00810.069420.684254.063850.244030.006110.016070.388520.002890.002460.00070.000660
8191.85131812.715737520.621150.068660.015850.172170.436626.687490.404280.01070.011520.094520.004380.004220.001010.000640
918.22.03131118.79928030.751140.087270.025290.172532.17494.321020.255870.010550.035690.09830.005730.00550.001290.001780.00071
1017.52.03147115.911529291.021320.065450.018740.141161.853786.645030.293210.007970.032390.331940.002910.002750.0007400.00067
1114.71.2312779.27269010.37820.087670.013430.079971.64297.326380.173850.009820.03660.039820.003110.003610.0012600
1215.61.78123510.67377810.281000.081990.013790.132741.3863223.759060.183610.007840.061150.057170.003640.003390.0010800
13151.37143512.710399520.981000.057380.011870.19290.714495.0060.218730.007080.084830.207730.002290.002120.000470.000780
14101.812108123075301630.062340.011510.183770.81012.677740.265630.009980.007260.197070.00290.003190.000730.001350.00217
15151.58169110061301010.057020.008360.128490.791452.435180.220740.006320.018180.282320.001980.001980.000550.000820
16101.9985981762901220.057640.010620.134310.761672.954640.169940.009230.025880.260330.002780.003540.000870.000980
17101.689648146941.041200.055510.011180.120280.817482.915430.150530.008040.004160.204250.002570.002440.000950.000940
181027818130059701270.068450.013010.130421.434382.968520.258510.010690.006330.191110.003080.003450.000970.001390
19102.183979085610.491250.059970.022120.122250.870652.864270.186320.008460.018750.249610.003720.003620.001350.00120
20102.1882611306060.081490.053530.011320.112770.802642.461420.223630.009220.017010.190420.002510.003080.000660.00120
21102.1818811805360.321130.058240.014710.156871.078143.74520.242630.013570.010210.059770.004880.005310.001660.001970
22191.881898025460950.06050.013080.114550.936494.277490.172620.005840.022820.038930.003040.00220.000430.000660
23212.22.98111113.912586351.731130.044330.011460.177010.834314.261960.321350.02510.011690.127840.009740.00990.002260.002560
24218.67.86152520.112917161.881260.056440.009670.194390.22215.596590.320560.026470.025490.28670.018190.010820.00240.003330
2528.72.59139811.413967840.831310.088490.0180.225890.888146.893410.384490.029640.012780.059260.009470.008230.003320.004470.00681
26215.22.17127917.814496610.931060.065720.039010.162640.980798.288820.40120.018660.021580.076150.009360.007290.002060.002730.00336
2726.81.3713727.96369220.531030.078930.00780.088741.618683.649240.185260.017150.025190.040930.002010.000020.000050.000950
2828.52.4217307.88129380.411420.105570.015990.217561.911995.118890.296880.029380.045980.04590.005240.002280.001210.001860.0034
29211.92.73140214.913537482.091380.069160.020390.237341.794356.434110.397690.028460.027410.040460.011470.007750.001650.002520
3027.92.4310699.618666230.851140.06230.008530.147041.641546.436110.508540.027590.021280.055560.006040.004420.001160.002170
3128.31.5510297.28716230.53870.053860.0080.202932.055864.4170.240110.020150.025970.048830.003870.002950.000530.001340
3224.95.61106710.712665341.671240.056550.00730.143790.814344.057030.292880.02120.016660.029690.003290.002290.000340.001730
33211.92.84135014.513387901.11340.067210.011040.170860.806288.036010.343090.023090.014880.031940.007990.005760.00140.00240
3426.12.46128010.311617790.891160.059090.0080.141450.692566.034110.283340.01690.035050.038750.004120.0030.000440.001530
35211.32.2612731210387951.11140.066110.011340.191130.743434.939270.257810.02410.018320.051490.007730.006240.001650.002490
36231.988498806580.231260.068740.005720.176481.213153.836840.16620.018770.018210.033630.003370.003690.000880.001220.0025
37232821910906230.391190.053920.003490.122091.034932.961450.196660.011850.025810.027060.002960.002880.000360.000960.00215
38226.75901110103681.771140.044940.006140.167511.493573.795870.166050.010890.006930.021640.00270.002930.000580.00110.00278
39205.7643129033992.241100.043650.003440.171231.549812.818970.155790.010530.017150.022920.002610.002420.000470.000570.00301
40231.782298885720.28980.047990.005230.129151.032873.388120.162270.01260.006160.024840.003680.00320.000690.001330
41201.7728108926250.46970.056380.011560.142211.014843.645880.176580.016080.017650.033930.006160.005970.001370.001730.00174
42221.7648812105441.121050.051170.006790.117560.773044.292340.226120.012940.014730.034250.003330.002920.000880.001310.00108
43202760910505640.361200.054830.011560.161620.958564.1290.217560.012940.030570.032520.003690.003320.000960.00190.00151
44231.9779812505870.531260.051760.007510.137180.956343.116550.251310.013590.026960.034820.00420.00390.001060.001640
45202.3822914006270.691280.066770.013110.182940.943964.197770.298560.015130.015330.032180.004710.004020.001160.002130.00272
46201.9781711905540.481040.06190.007710.147620.850243.228370.238420.019130.012170.032680.004780.005380.001310.001750
47222.49121214405180.491160.056040.028530.226840.869444.983160.316860.017010.016940.033750.00860.00720.001780.002340
48332.77.15133430.118629652.911200.085150.018020.168430.985437.209250.466050.031650.020040.203420.021110.021360.003930.005980.00143
49334.86.7100529.317877761.61050.086690.04070.287471.373027.392410.458820.042730.015460.292560.03780.030960.006340.007870
503117.57.25116341.614648611.611010.116910.024870.160761.205485.826870.553490.054350.024480.592950.059720.05370.011240.012170.00379
51325.56.85121325.916369451.721160.088740.018330.148320.974144.174260.444640.023110.014860.244710.02710.021520.003610.005540
523578.72156455.112519952.511370.088810.025080.199361.081246.731340.358130.045240.04490.176470.054550.041170.007740.008830.00115
5331508.23121488.121829183.391130.172480.039160.221371.123086.995150.739170.064610.023380.247620.103890.083670.01610.016290.00597
54332.15.95121125.316867781.891140.067990.020940.211721.170718.002610.452720.043270.011670.453910.01860.017530.003920.006450
55354.86.24161737.1154210953.321270.080710.01530.080680.252957.380760.408220.038190.017680.435950.02740.026120.005940.005480
56335.510.15162540.317839192.931590.068860.028780.294810.458876.217040.465240.044910.024490.231760.030270.027560.005780.006580
57366.46.97171044.8124212102.761150.09110.018980.135211.250597.76650.387810.045590.017940.370260.046110.041240.008110.0080
58320.76.07145922.6154110052.981130.061920.013240.158060.816745.927090.402550.026230.011840.317270.018970.018590.004320.003760
59340.56.3710802919068230.871180.076430.029110.317620.747076.596260.568040.037250.011360.330820.029290.03010.005520.006020
603181.97.15157780.9160314672.941170.083010.014830.121220.733075.66550.434860.030590.016470.32180.029530.025760.00540.005070
613147.37.29141393.517858553.41160.163420.039930.274271.002774.717140.680760.070620.014490.380320.092720.080810.015820.014090
623142.87.78174783.217928713.231310.158180.045470.263470.890044.053330.689240.072970.017230.331050.094840.081970.016820.014980
63321.96.14117921.316887862.261090.055330.01570.158390.920136.771090.436310.027560.018730.414780.016480.015110.003660.003490
64354.37.04138936.616519252.751140.04780.015030.139070.845625.236220.440870.036990.02640.370850.044150.03760.00720.007040
65342.86.39162934.316818111.981360.068810.015770.143140.724714.411370.445540.027530.026630.225860.038930.035150.005850.005650
66383.27.8157838.51733105231210.089260.013890.083520.668914.236320.522410.042160.008190.297820.048220.04440.008690.007410
673327.59213416905671.851160.068040.050740.191720.752334.272290.374510.028830.045090.163580.024280.023960.005530.005160.01321
6835957252313004891.53810.074870.015770.1690.643463.498190.342440.034970.020440.343330.048510.044180.008550.007350.00081
693356.29382115706181.51060.066540.023350.206230.589885.00140.354090.028610.014130.158920.032470.024750.004640.00530
703335.88792313006191.31850.067270.01330.153090.733614.520060.302750.023170.014280.304240.022880.020180.004950.0040
713224.76391615505521.29770.082780.020690.23280.831114.768530.370430.032260.012320.405660.027220.023730.005260.004740
72317.35.9984016.211307801.48830.089940.011910.170590.956052.800270.262870.019510.020060.333150.014460.012840.002710.002870
73367.46.9778740.711407582.51840.104180.035710.321611.051283.722280.333740.04060.019560.161760.042120.040080.008780.008120
74357.76.57111031.714007831.971080.094850.016860.164810.7723.167610.414930.037860.01160.324010.065110.060570.010580.00940.00151
75324.85.99122024.418007391.431230.086950.01610.417910.878354.675140.44840.030130.018850.319460.05190.043660.008660.007190
76341.55.6892831.515806651.04990.097370.027020.263210.888375.335640.424190.033040.010860.360170.032440.031050.006670.00630
77462.17509.98794500.93760.039650.009690.098922.328015.91160.202720.012180.016760.124670.004780.004550.000920.001250
78467.56.2131538.116659611.751080.118770.025770.240071.725615.987510.556250.045590.014870.384360.052180.041040.008580.007490.00193
79415.12.5117919.920017131.461240.074290.015530.361341.432874.450660.571570.017680.025080.118130.014070.011830.003160.003270.00099
80414.62.38116637.617247191.751260.07220.016910.026972.364.959320.500720.016470.021170.1390.008630.00720.001490.002030
81415.12.87128218.918457351.171380.078570.02640.12181.827785.226420.557820.022060.025450.165040.012660.010660.002190.003070
82423.42.21109820.617697231.241190.08090.015540.037171.847974.408110.550190.019260.022010.15790.016580.01360.002850.003310
8347.52.92147721.5118410141.61520.062530.014840.074422.294625.772010.319750.013840.035890.129250.00930.006880.001740.001730
8447.52.69142021.311149831.431410.052480.01120.07730.788835.127850.306490.012270.028120.135890.008820.008890.00190.001790
85418.42.1117121.6177175911090.066160.01320.112240.786164.778610.483120.014430.017970.204850.012570.010670.002260.001890
8649.32.54147221.516018981.511400.05940.013260.226470.940035.245770.438460.016410.023870.081450.009370.007990.002010.002360
8748.92.76145718.615838861.51450.056280.0119100.812965.440630.426090.013390.017620.083270.006850.00560.006020.001410
88411.42.57145219.216668631.481390.058820.016280.036430.844295.782410.440120.017130.020790.07290.008110.007310.001840.001810
89423.42.6313632620097581.491470.077480.019410.246890.881045.121010.572460.0230.020620.103810.019110.01650.004020.004310
90410.32.51130617.518117661.841380.057330.012990.149190.679414.806550.475690.015860.031410.170620.010730.009890.002270.002260
91427.83.15121731.217267361.731260.078360.020270.114420.625794.996790.477990.021370.021460.275680.025660.020150.004320.003790
924484.1711903713197421.321240.099680.021340.196241.182333.005840.360420.022670.025080.147950.022870.021870.004420.002210.00094
934113.614392214518491.811450.056590.010070.124010.767673.52020.335060.014340.021820.122540.007660.00720.00150.001760
94452921913206210.781440.059180.017430.160711.54543.139960.33010.018220.017190.119880.01010.010160.002740.002810
954154.36111513304280.69730.056680.017310.166611.199034.806150.313850.02240.013360.357790.012530.012570.002940.003210

Area No.1 sanriku (Japan), 2 naruto (Japan), 3 China, 4 Korea.
(a) By nation ( )

Production correctJapanChinaKorea
Center

Japan934412
China1000290
Korea743214

(b) By area ( )

Production correctSanrikuNarutoChinaKorea
CenterRatio (%)

Sanriku8719201
Naruto9202311
China10000290
Korea7421214

(a) By nation ( )

Production correctJapanChinaKorea
Center

Japan1004700
China1000290
Korea741117

(b) By area ( )

Production correctSanrikuNarutoChinaKorea
CenterRatio (%)

Sanriku10022000
Naruto9202311
China10000290
Korea7420116

Sample preparation and analysis conditions for ICP-MS of the study are described in [5].

A total of 10 samples were independently taken in the present study: 3 samples each from China and Korea and 4 samples from Japan (2 each from Sanriku and Naruto). Samples for X-ray fluorescence analysis were prepared according to the method described in [10]. A Shimadzu XRF-1800 was used for detecting trace elements by fundamental parameter methods. Sample briquettes were formed under 20 ton/cm2 pressure for 30 seconds with the MP-35-02 press.

Because we supposed that there could be the possibility of finding more convenient methods with using an equipment such as an X-ray fluorescence analysis, we gathered independent 10 samples from Riken Food Company.

3. Results and Discussion

3.1. CART Results and Comparison to Linear Discriminant Analysis

At first, we introduce the overview of how CART works.

In case of CART, if the target variable is categorical, then a classification tree is generated. To predict the category of the target variable using a classification tree, use the values of the predictor variables to move through the tree until you reach a terminal (leaf) node, then predict the category shown for that node. An example of a classification tree is known well in case of the Fisher’s Iris data (from the UCI Machine Learning Repository: Iris Data Set [11]). The target variable is “Species”, the  species of Iris. We can see from the tree that if the value of the predictor variable “petal length” is less than or equal to 2.45 the species is Setosa. If the petal length is greater than 2.45, then additional splits are required to classify the species. Because CART is a nonparametric classification method, it is necessary to validate the obtained model. However, CART is usually more potent than LDA.

On the other hand, Linear discriminant analysis is a linear and parametric method with discriminating character. LDA focuses on finding optimal boundaries between classes.

Classification results between China, Korea, and Japan by CART are shown in Figure 1. Parent and terminal nodes had 2 and 1 minimum cases, respectively. In node 1, the discriminant condition is given by the following equation.In node 2, the discriminant condition is given by Ba  .In node 3, the discriminant condition is given by Cu  .In node 4, the discriminant condition is given by Sr  .

In the event of the inclusion of 1 case of terminal node 3 and terminal node 4 in China and Japan, respectively, the maximum rate of error was 0/952/95. The ranking of variable importance was arranged in descending order, Nd, La, Fe, Sm, Al, Y, Gd, Cd, Ba, Cu, Li, and Sr. Rare earth elements, Fe, and Al were ranked as important. The classification results between Sanriku (Japan), Naruto (Japan), China, and Korea are shown in Figure 2. In node 1, the discriminant condition is given by the following equation:In node 2, the discriminant condition is given by Ba   .In node 3, the discriminant condition is given by Y  .In node 4, the discriminant condition is given by Cu  .In node 5, the discriminant condition is given by Cu  .In node 6, the discriminant condition is given by 0.974 Y 0.226 Cd  .In node 7, the discriminant condition is given by Ba 0.0164 Sr  .

In the event of inclusion of 1 case each of terminal nodes 2, 3, 5, and 7 for samples from Korea, China, China, and Sanriku, respectively, the maximum rate of error was 0/955/95. The ranking of variable importance was arranged in descending order: La, Nd, Fe, Y, Sm, Al, Cd, Gd, and Ba. Rare earth elements, Fe, and Al were ranked as important.

Based on the above CART method, more on the production centers could be extracted by the ICP-MS analysis results of Kadowaki and Tatsuguchi [4] and the proceeding for the discrimination of production centers of U. pinnatifida, FAMIC [5], than from the previous linear discriminant analysis.

3.2. Analysis Results by the CART on the Elemental Analysis with an X-Ray Fluorescence Method

The classification results from U. pinnatifida collected in China, Korea, and Japan based on CART with analysis of 9 major detectable elements detected by X-ray fluorescence method [10](Figure 3)—Fe, I, Br, As, Zn, Mn, Cu, Ni, and Cr—are given as follows.In node 1, the discriminant condition is given by the following equation: Br .In node 2, the discriminant condition is given by the following equation: Fe  .

Terminal nodes 1, 2, and 3 mapped Japan, Korea, and China, respectively. These results suggest that bromine is an important parameter for the discrimination of production centers (characteristic of Korea samples, see Figure 4). Significant differences between Br content for China and Korea samples and between Japan and Korea samples were observed for multiple comparison of means values of Br content (ppm.) between China, Korea, and Japanese Undaria pinnatifidas by the Ryan-Joiner testing method [12]. On the other hand, no differences were observed in I content between China and Korea and between Japan and Korea samples by the Ryan method ().

Bromine could not be completely dissolved and, further, Br has a tendency to vaporize in the acid decomposition sample preparation process for the ICP-MS. However in the case of X-ray fluorescence method, which is characterized by the rapid and easy handling, the above problem can be avoided and, hence, this could be a better and more promising method than ICP-MS. We earlier reported the rapidity and convenience of a discrimination method by near-infrared spectroscopy [3]. By combining the two different methods of NIR and X-ray fluorescence methods, which essentially give different organic and inorganic information, respectively, before the final method, ICP-MS method, a more convenient and rapid discrimination method can be developed. One of the main reasons for this is that NIR and X-ray fluorescence methods do not require that powder samples be prepared as solutions. We conclude that the above combination of methods could be used as a convenient discrimination method to meet the regulatory requirements as those of 2006 for the display of the production centers on U. pinnatifida in Japan.

4. Conclusion

(1)When using CART for the discrimination analysis on the production area from the elemental analysis results from the point of error rates, we take better discrimination results comparing to the LDA.(2)As one of convenient discrimination methods, we found the feasibility of using the elemental analysis, especially, the quantity of Br with the X-ray fluorescence analysis.

Acknowledgments

The author is grateful to Riken Food Company and the Director of the Department of Quality Control, Junichi Satoh, for providing a variety of Undaria pinnatifida samples and information about them. She is also grateful to Shimadzu Company for helping her with the X-ray fluorescence analysis and the grant from Sanriku Research Fund by Iwate Prefectural Government from 2005 to 2006.

References

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Copyright © 2010 Mikio Kaihara. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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