Traceability of Protected Geographical Indication (PGI ...

Journal of Food Composition and Analysis 69 (2018) 122–128

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Original research article

Traceability of Protected Geographical Indication (PGI) Interdonato lemon pulps by chemometric analysis of the mineral composition

T

⁎

Angela Giorgia Potortìa, Giuseppa Di Bellaa, , Antonio Francesco Mottesea, Giuseppe Daniel Buaa, Maria Rita Fedea, Giuseppe Sabatinob, Andrea Salvoa, Roberta Sommaa, Giacomo Dugoa, Vincenzo Lo Turcoa a b

BioMorf Department, University of Messina, Messina, Italy MIFT Department, University of Messina, Messina, Italy

A R T I C LE I N FO

A B S T R A C T

Keywords: Food analysis Food composition Traceability Lemons Mineral elements Lanthanides ICP-MS Multivariate statistics

In the last years, element content has been used as geographical tracer to determine the provenance of food. In the present work the content of 19 minerals (K, Ca, Mg, Na, Fe, Zn, B, Cu, Al, Mn, Ni, Cr, Pb, Co, As, Se, Cd, Sb and V) and 13 lanthanide elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Lu) in Protect Geographical Indication (PGI) Interdonato lemon Messina (Italy) and non-PGI Turkish lemon pulps was evaluated by ICP-MS. The collected data were used to discriminate geographical origin of lemon samples (PGI or non-PGI) through statistical analyses. The discrimination between Italian and Turkish lemons was achieved by Principal Component Analysis (PCA) and also by Canonical Discriminant Analysis (CDA). The results indicate that the 100% of total samples were correctly classified. The present study suggests that it is possible to relate lemons to their geographical origins, representing a necessary condition for traceability of these peculiar products. Unfortunately, Italian and Turkish lemon pulps cannot be considered “rich in” or “source of” analyzed minerals. However, these fruits can be considered safe for their low content in toxic elements.

1. Introduction

The traceability keynote is based on a chemical link between food and territory. It is very important in order to promote the products, that addition information are provide to consumers about both the origin and way of production. Actually, several studies propose to trace and to define the food “fingerprint” (Cicero et al., 2015; Luykx and Van Ruth, 2008; Salvo et al., 2016), through many analytical techniques, such as food genetic map creation (Primrose et al., 2010; Terzia et al., 2005) and macro-microelements and rare earth elements (REEs) investigation in food chain (Bua et al., 2016; Di Bella et al., 2013; Gaiad et al., 2016; Gonzalvez et al., 2009; Perez et al., 2006; Potortì et al., 2013; Potortì et al., 2017; Romano et al., 2014). Several chemometric tools are used also for the food authenticity (Barbosa et al., 2014a,b, 2015, 2016; Batista et al., 2012; Borges et al., 2015; Maione et al., 2016). In the present study, the analysis of 19 minerals and 13 lanthanides elements in Italian PGI and non-PGI Turkish lemons was carried out by using ICP-MS. This work had two objectives: (1) to evaluate the element content in Interdonato Lemon pulps; (2) to differentiate the geographical origin of lemons, since it represents an important topic for consumers.

EC regulations N° 2081/92 and 510/2006 contain all general provisions regarding the protection and enhancement of agricultural and food products. The same regulations recognize a close correlation between “food quality” and “territoriality of the same” through the establishment of legally protected trademarks such as PDO (Protected Designation of Origin) and PGI (Protected Geographical Indication). Interdonato Lemon Messina obtained PGI brand with EC Regulation N° 1081/2009. The production area for Interdonato Lemon Messina PGI is extending for about 50 km and includes all countries of the Ionian Coast of Messina Province. The production field of this crop covers 1500 ha (ha = 10.000 m2) (ISTAT, 2014) and it is possible to obtain a mean yield of fresh product of about 2800 kg/ha, with a gross salable production of about 15.000.000 kg. Lemon cultivation, in PGI protected area, is important for economy. The same variety of lemons is produced in Çukurova region (Turkey). Turkish lemon production rate consists in about 725.320.000 kg. Moreover, Çukurova area produce about 95–98% of the exported lemons (Yildirim et al., 2010; FAOSTAT, 2013). ⁎

Corresponding author at: BioMorf Department, University of Messina, V.le Annunziata 98168, Messina, Italy. E-mail address: [email protected] (G. Di Bella).

https://doi.org/10.1016/j.jfca.2018.03.001 Received 9 May 2017; Received in revised form 26 January 2018; Accepted 12 March 2018 Available online 15 March 2018 0889-1575/ © 2018 Elsevier Inc. All rights reserved.

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2. Materials and methods

scissors to avoid the detachment of the calyx portion, and the yielding ranges from 80 to130 kg for plant. Lemon pulps (0.5 g) were weighed into acid prewashed PTFE vessels with 1 mL of internal Re standard. Samples were digested with 8 mL of HNO3 at 65%. Mineralization setting and parameters were: increase up to 200 °C for 10 min and then at 200 °C for 10 min. The certified matrices were prepared at the same conditions. Each evaluation was carried out in triplicate and after mineralization the samples were filtered and brought to a final volume of 25 mL with deionized water.

2.1. Chemicals and standard solutions Nitric acid 65% (v/v, TraceMetal Grade), hydrochloric acid 37% (v/ v, TraceMetal Grade) and deionized water with resistivity of 10 MΩ cm were bought from Merck (Darmstadt, Germany), whereas helium (99.9995% purity) and argon (99.9990% purity) gasses were provided by Rivoira (Milan, Italy). Tea leaves certified reference material (cod. GBW 07605) from National Research Centre for Certified Reference Materials (NRCCRM) and aquatic plants certified reference material (cod. BCR 670) from Institute for Reference Materials and Measurements (IRMM) were purchased from Nova Chimica (Milan, Italy) and were used in validation method to evaluate the accuracy, intraday repeatability and intermediate precision. In order to tune the instrument, an ICP-MS tuning solution containing 1 μg L−1 of Li, Co, Y and Tl in 2% HNO3 was obtained from Agilent (Santa Clara, CA, USA). Standard solutions of Sc, Rh, Bi and In at the concentration of 1 mg L−1 bought from Fluka (Milan, Italy) were used as on-line internal standards. Stock standard solutions of all the analyzed elements were purchased from Fluka (Milan, Italy) at a concentration of 1000 mg L−1 in 2% HNO3. The working standard solutions were prepared by appropriate dilutions with deionized water. In particular, for Cr, Ni, Co, Se, Sb, V, As, Pb, Cd working standard solutions were prepared with concentrations ranging from 0.020 to 2 mg L−1; for Cu, Mn, B between 0.010 and 5 mg L−1; for Ca, Fe, K, Mg, Mn, Na, Zn between 0.5 and 50 mg L−1; for La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Tb, Ho, Er, Tm, Lu between 0.5 and 15 μg L−1. Finally, a Re standard solution of 1000 mg L−1 in 2 % HNO3, bought from Fluka (Milan, Italy), was used to verify mineralization and to correct volumetric changes at the concentration of 0.8 mg L−1. All glassware used in sample preparation and analysis was washed keeping it overnight in a solution of HNO3 10% (v/v) and then rinsed with deionized water.

2.4. ICP-MS analysis

Mineralization of lemon samples was carried out in triplicate through a closed-vessel microwave digestion system Ethos 1 (Milestone, Bergamo, Italy) equipped with sensors for temperature and pressure control and provided with polytetrafluoroethylene (PTFE) vessels able to withstand pressures of up to 110 bar. Minerals levels were evaluated through an ICP-MS Agilent 7500cx (Agilent Technologies, Santa Clara, USA). The system was supplied with a quadrupole mass analyzer, an electron multiplier detector and off-axis ion lens. In addition, nickel sampler and skimmer cones of 1.0 mm and 0.4 mm were used.

The ICP-MS spectrometer was equipped with a MicroMist glass concentric pneumatic nebulizer coupling with a cooled Scott double pass type spray chamber made of quartz and powered by a 27.12 MHz radiofrequency solid-state generator at 1500 W and an integrated sample introduction system. A classic Fassel-type torch with a diameter of 2.5 mm was the ICP torch equipped with a shield torch system. The instrument also consisted of an autosampler ASX520 (Cetac Technologies Inc., Omaha, NE, USA). In order to reduce polyatomic interferences coming from plasma and matrix an octopole collision/ reaction system with helium gas was utilized. Operative conditions for ICP-MS were: generators power 1500 W, sample depth 9 mm, nebulization chamber temperature 2 °C, plasma gas flow rate 15 L min−1, auxiliary gas flow rate 0.9 L min−1, carrier gas flow rate 1.1 L min−1, sample introduction flow rate 0.88 mL min−1, extract lens 1.5 V, nebulizer pump 0.1 rps, collision gas flow rate 4 mL min−1. ICP-MS operated in no gas mode for the isotopes 55 Mn, 208Pb, 66Zn, 44Ca, 23Na, 39K, 11B; and in helium mode for 52Cr, 59 Co, 51V, 24Mg, 60Ni, 75As, 78Se, 111Cd, 57Fe, 63Cu, 121Sb and 27Al, in order to remove the spectral interferences. Moreover, for all lanthanides, ICP-MS operated in no gas mode and the quantified isotopes were 139 La, 140Ce, 141Pr, 142Nd, 147Sm, 157Gd, 153Eu, 159Tb, 164Dy, 165Ho, 166 Er, 169Tm and 175Lu. Integration times were 0.5 s/point for Cu, Cr, Ni, Se and As, 0.1 s/point for the other elements. Integration times for lanthanides were 1.0 s/point. All analyses were carried out in triplicate. To integrate the peaks, 3 point for each mass and 3 replicates acquisitions were taken into consideration. All samples were analyzed in batches, together with internal standards and with a reagent blank in order to estimate the potential contamination during the experimental process. The limits of detection (LODs) and of quantification (LOQs) were experimentally calculated as 3.3σ/S and 10σ/S, respectively, where σ is the standard deviation of the response of ten blanks and S is the slope of the calibration curve.

2.3. Sampling and sample preparation

2.5. Statistical analysis

The analyses were carried out on 22 lemons come from Italy and 18 lemons from Turkey, both collected in November 2015, at the same degree of maturation. The position of each sampling point was georeferenced using a DGPS (differential global position system). The coordinates of Sicilian lemon fields are included from 37° 59′ 49.09″ N to 38° 0′ 4.75″ N of latitude and 15° 24′ 19.09″ E 15° 24′ 43.95″ E of longitude. Fig. 1 shows the production sites of Sicilian PGI Interdonato lemon. The Turkish studied region is located between 36° 58′ 00.8″ N and 36° 37′ 57.6″ N for the latitude and between 36° 50′ 42.8″ E and 36° 59′ 50.9″ E of longitude. For altitude, fields are located from 160 m to 250 m above sea level. Each lemon sample corresponds to the homogenization of 3 lemons chosen randomly from an initial pool of 2 kg. The mean weight of this lemon variety is ranging between 80 and 350 g, whereas the shape is typically elliptical with a pronounced nipple. The color is variable from dull green (at the first step of maturity) to yellow (at the final maturity) and seeds are rare or absent. Harvested, from the September 1st to April 15th, is performed by using

All statistical calculations were made by SPSS 13.0 software for Windows (SPSS Inc., Chicago, IL, USA). Statistical methods have been conducted on starting multivariate matrix constituted by 40 cases representing the lemon pulp samples analyzed and 15 variables which represent the concentrations expressed in μg·g−1 of certain elements determined in at least 80% of the analyzed samples, namely Cr, Ni, Pb, Mn, Al, Ca, K, Mg, Na, Fe, B, Cu, Zn, La and Ce. According to Škrbić et al. (2010) when concentrations were below the LOQ (only in few samples), these were replaced with the LOD/2 value and element concentrations were loge-transformed to reduce the effect of outliers on the data distribution. The datasets were subdivided into two groups according to the geographical area of origin: the first (N1 = 22) consisted of PGI Interdonato Lemon Messina samples, the second (N2 = 18) involved the samples from Turkey. Initially, the significance of the differences between samples of different geographical origin was evaluated by applying the non-parametric Mann-Whitney U test. Successively, data sets were normalized in order to achieve independence on the scale factors of the different variables (Marengo and Aceto,

2.2. Instrumentation

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Fig. 1. Sicilian production areas of PGI Interdonato lemon.

than their LOQ values. Although the data showing mineral content of lemon fruits were quite scarce in the literature, it is possible to compare them with the results obtained in this study. In fact, a research analyzing the levels of the most important macro and micro elements in lemon fruits in the Bangladesh market, reports Ca and Cu concentrations higher than those detected in Italian and Turkish pulps. Whereas, the contents of K, Zn and Fe were higher in Italian samples than in Bangladesh samples. Finally, the concentration of Mg and Na were rather comparable (Dipak Kumar and Ranajit Kumar, 2004). A comparison with a Brazilian study on Citrus fruits showed that the concentrations of K, Mg, Fe and Zn were lower than the Italian and Turkish ones, instead Mn content was higher. Calcium, Na, and Cu levels were similar to Italian pulp, whereas Ca and Na amount were lower than those reported in Turkish samples. Furthermore, copper content was similar for Brazilian and Turkish pulps (Barros et al., 2012). Few researches have been conducted on lanthanides levels in lemon pulp. Generally, the content of lanthanides in the main organs of the Citrus fruits decreased in the following order: root > leaf > peel > pulp (Cheng et al., 2015). In fact, in the analyzed pulp samples we have found La and Ce only. In Europe, according to UE Regulation 1169/2011, fruits can be classified as a “source of” or “rich in” minerals when these provide 15% or 30% of the element’s Dietary Reference Intake (DRI) specific for age and gender, per 100 g per fruit. The DRI is the daily amount of a nutrient that is considered to be sufficient to meet the requirements of 97–98% of healthy individuals and prevent the development of diseases (Barros et al., 2012). Unfortunately, Italian and Turkish lemon pulps cannot be considered “rich in” or “source of” as regards the analyzed minerals.

2003). After verification of the adequacy of the initial data through Kaiser-Meyer-Olkin test (KMO test) and Bartlett’s test, the data were subjected to the Principal Component Analysis (PCA) to try to differentiate between samples from different geographic areas. Finally, we did the Canonical Discriminant Analysis (CDA) to classify the different Interdonato lemon pulp samples. 3. Results and discussion 3.1. Quality assurance In Table 1 are given the validation parameters according to EURACHEM (2000). The evaluation of the linearity was based on injections of the 4 standard solutions. Each solution was injected five times. Good linearity was observed in each investigated concentration range with R2 up to 0.9891. LOD values ranged from 0.001 to 0.018 μg g−1, while LOQ values ranged from 0.003 to 0.059 μg g−1. Accuracy was assessed evaluating five determinations over the certified reference materials and was reported as the percent recovery between the value found with the calibration curve and the true value reported, together with the relative standard deviation percentage (RSD %). The accuracy ranged between 63.2% (Tm) and 106.1% (Zn), with the RSD% always under 5.8%. Intraday repeatability was obtained from the analysis of ten replicates of the same material in the same batch. Intermediate precision was obtained from the analysis of twelve replicates of the same material in different days. These parameters ranged from 1.9% to 5.9% and from 2.7% to 9.9%, respectively. 3.2. Mineral content in interdonato PGI and non-PGI pulps

3.3. Statistical analysis Mean concentrations ± SD (μg g−1 w/w) of elements in all lemon pulp samples are reported in Table 2. Potassium was the most abundant element in all samples, followed by Ca, Mg, Na, Fe and Zn; the other elements were below of 2 μg g−1; among lanthanides, only La and Ce were revealed in amount higher than their LOQ. Italian lemon pulps showed the presence of Pb and Cd in 100% and 27% of all the samples analyzed, respectively, however they not exceed the MRLs (0.1 μg kg−1 for Pb and 0.05 μg kg−1 for Cd) imposed by EC Regulation n. 1881/2006. In Turkish pulps these elements were lower

Elements comparison between Interdonato lemon pulps of different geographical areas, carried out by Mann-Whitney U test with significant p level below 0.05, showed that the PGI Interdonato lemon pulps have significantly higher values for Mn, Cr and Pb contents, whereas non-PGI Interdonato lemon pulps have significantly higher content of K, Ca, Mg, Na, Zn, B and Ni. The differences between the two groups were detected for Fe, Cu, Al, La and Ce (Table 2). PCA was applied to normalize data by using as variables the 124

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Table 1 Linearity, sensibility, accuracy, short and intermediate repeatability of the method. Element

R2

LODs (μg g−1)

LOQs (μg g−1)

Certified values ± SD (μg g−1)

Accuracy ± RSD (%)

Intra day repeatability (%)

Intermediate precision (%)

K Ca Mg Na Fe Zn B Cu Al Mn Ni Cr Pb Co As Se Cd Sb V La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Lu

0.9991 0.9993 0.9993 0.9997 0.9999 0.9999 0.9999 0.9999 0.9998 0.9999 0.9999 0.9998 0.9999 0.9891 0.9996 0.9995 0.9999 0.9999 0.9988 0.9999 0.9999 0.9999 0.9998 0.9999 0.9991 0.9998 0.9998 0.9999 0.9997 0.9993 0.9999 0.9999

0.016 0.017 0.015 0.016 0.017 0.016 0.010 0.018 0.018 0.014 0.010 0.011 0.005 0.010 0.010 0.010 0.010 0.010 0.015 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001

0.053 0.056 0.049 0.053 0.056 0.053 0.033 0.059 0.059 0.046 0.033 0.036 0.016 0.033 0.033 0.033 0.033 0.033 0.049 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003

16600 ± 250 4300 ± 817 1700 ± 404 44 ± 12 264 ± 32 26.3 ± 4.2 15 ± 2.5 17.3 ± 1 300 ± 41 1240 ± 149 4.6 ± 0.35 0.80 ± 0.05 4.4 ± 0.24 0.18 ± 0.01 0.28 ± 0.05 0.072 ± 0.01 1.23 ± 0.15 0.053 ± 0.01 0.86 ± 0.12 0.60 ± 0.02 1 ± 0.04 0.12 ± 0.006 0.44 ± 0.015 0.085 ± 0.007 0.018 ± 0.001 0.093 ± 0.008 0.011 ± 0.001 0.074 ± 0.007 0.019 ± 0.002 0.044 ± 0.003 0.09 ± 0.001 0.07 ± 0.001

96.3 ± 3.8 97.4 ± 3.2 98.9 ± 3.0 96.4 ± 2.2 94.1 ± 2.4 106.1 ± 3.4 97.1 ± 3.5 94.6 ± 2.6 90 ± 2.7 96.6 ± 3.1 95.6 ± 3.3 93.7 ± 2.2 105.4 ± 2.0 88.9 ± 3.1 92.8 ± 2.9 93.1 ± 2.7 101.7 ± 2.5 92.8 ± 3.1 96.5 ± 3.4 95.7 ± 3.3 81.0 ± 2.6 101.6 ± 2.7 87.3 ± 3.8 95.3 ± 5.1 98.3 ± 2.9 101.9 ± 4.1 85.7 ± 2.5 92.4 ± 3.2 79.7 ± 2.1 70.2 ± 5.8 63.2 ± 3.8 65.1 ± 3.4

2.8 2.7 3.4 1.9 3.0 5.0 3.1 3.0 3.5 3.9 3.4 2.7 3.9 4.8 2.6 4.0 3.7 3.9 3.6 2.2 3.0 2.7 3.1 4.9 4.7 4.7 3.3 3.5 2.4 5.9 4.1 3.8

3.4 3.6 4.0 2.7 5.1 8.1 3.9 5.5 4.5 4.4 6.1 6.6 6.8 7.9 4.0 4.9 4.7 4.0 5.8 4.1 6.3 4.2 3.9 5.3 5.7 7.6 5.7 5.5 3.7 9.9 7.6 6.1

LODs, Limits of Detection; LOQ, Limits of quantification.

approximate Chi-squared value equal to 403.942 (at p level below 0.0001). Thus, the correlation matrix was factored and appropriate for PCA analysis. The analysis of the correlation matrix showed that the value of the determinant was low (9.199·10−6) and that the 78% of matrix

concentration of elements found significantly differents for geographical analysis (K, Ca, Mg, Na, Zn, B, Mn, Ni, Cr and Pb). The suitability of the data for factor analysis was checked. The Kaiser–Meyer–Olkin measure of sampling adequacy revealed a value of 0.815 (higher than 0.500) and the Bartlett’s test of sphericity showed

Table 2 Mean content of element composition in lemon pulp samples for both sampling area (Italy and Turkey). Mann-Whitney U test results indicating the significant differences between the values of the two areas. PGI Interdonato lemon (Italy, n = 22) Mean (μg g K Ca Mg Na Fe Zn B Cu Al Mn Ni Cr Pb Co As Se Cd Sb V La Ce Other lanthanides

1721 193 124 13.1 4.07 2.68 0.651 0.540 0.495 0.218 0.0766 0.0596 0.0383 < 0.033 < 0.033 < 0.033 0.0282 < 0.033 < 0.033 0.00179 0.00302 < 0.033

−1

)

S. D. (μg g 516 149 57.7 13.9 0.564 1.18 0.422 0.309 0.384 0.114 0.0383 0.0364 0.0253

0.0101

0.00118 0.00197

−1

)

Non-PGI Interdonato lemon (Turkey, n = 18) Mean (μg g

−1

)

Mann_Whitney U

Wilcoxon W

Z

Asymp. Sign.

268 81.10 15.9 16.6 0.354 0.237 0.218 0.103 0.0841 0.0277 0.0408 0.0258

357.500 366.000 330.500 388.000 176.500 312.000 381.500 270.000 145.000 115.000 324.000 80.500 0.000

528.500 537.000 501.500 559.000 347.500 483.000 552.500 441.000 316.000 286.000 495.000 251.500 171.000

4.337 4.568 3.600 5.165 −0.585 3.099 4.989 1.957 −1.441 −2.257 3.427 −3.207 −5.646

0.000 0.000 0.000 0.000 0.559 0.002 0.000 0.052 0.150 0.024 0.001 0.001 0.000

0.00190 0.00193

252.000 175.000

423.000 346.000

1.471 −0.625

0.141 0.532

S. D. (μg g

2413 423 189 66.1 3.93 3.67 1.83 0.603 0.307 0.149 0.125 0.0270 < 0.016 < 0.033 < 0.033 < 0.033 < 0.033 < 0.033 < 0.033 0.00258 0.00272 < 0.033

The significance asymptotic values in bold indicate significantly different concentrations for p < 0.05.

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−1

)

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Fig. 2 shows the 2D Scatterplot on the plane defined by the first two principal components, which explain the 73.653% of the total variance, for the 40 Interdonato lemon pulps samples. Two groups were sufficiently distinguished: the PGI samples were separated from non-PGI on the first component, which explained 58.340% of the total variance; Sicilian samples were placed in an average negative values of PC1 and were characterized by higher values of Pb and Cr, instead those Turkish were placed in average positive values of PC1 and had the highest concentrations of Na, Ca, Mg, Zn and K. It can also be stressed that the only four samples with positive PC1 scores in PGI samples showed the highest Na, Ca, Mg, Zn and K concentrations, although data were lower than the minimum value determined within the not PGI samples. In order to aid the separation of these two groups, oblimin rotation and Kaiser normalization were performed. After this rotation, as can be seen in the 2D Scatterplot reported in Fig. 3, two clusters were clearly distinguished according to the geographic collection area. The Turkish lemon samples were clearly separate from the Sicilian ones and were located in the fourth quadrant. Therefore, the correlation between the lemon pulps and the geographical area on the basis of elements content was achieved. Finally, in order to understand if the samples were from Italy or Turkey, the CDA was applied. The canonical discriminant function obtained showed a high discriminatory power, ginving a high correlation value (0.962) and a low value of Wilks’ lambda (0.074). The unstandardized and standardized coefficients are presented in Table 4. The unstandardized coefficients were used as coefficients of the canonical variables to compute the canonical variable scores for each case, while the standardized coefficients showed that the variables which better discriminate between the two groups of samples were Zn (1.094), Mg (−0.841), Pb (0.819), Ni (−0.763) and Mn (0.621). The obtained canonical discriminant function was applied to the data set. Each case was assigned to group in which it has achieved the highest value of probabilities of group

Table 3 Components matrix and variables communalities (h2) for the Principal Component Analysis applied to differentiation between Interdonato lemon pulps as PGI (Italian origin) or non-PGI (Turkish origin). Element

PC1

PC2

PC3

h2

Na Ca Mg B Zn Pb K Mn Cr Ni

0.935 0.925 0.890 0.843 0.843 −0.833 0.824 −0.102 −0.561 0.439

0.036 0.167 0.213 −0.179 0.198 0.380 0.248 0.883 0.564 0.288

0.053 −0.038 −0.303 0.157 −0.370 −0.260 −0.022 −0.097 0.227 0.808

0.878 0.884 0.929 0.767 0.887 0.907 0.741 0.799 0.684 0.928

PC, Principal component. Bold values indicate the dominant variables in each factor.

coefficient had values with significance higher than 95%. The highest positive correlations were observed for Zn-Mg (0.982), Na-Ca (0.852), Na-Mg (0.840), Mg-Ca (0.834) and Zn-Na (0.801), instead the highest negative correlations were observed for B-Pb (−0.809), Na-Pb (−0.747) and Ca-Pb (−0.689). According to Kaiser-Guttman Criterion, three principal components with eigenvalues exceeding one (5.834, 1.531 and 1.040) were extracted, which together explain the 84.054% of the total variance (58.340%, 15.313% and 10.401%, respectively). Component matrix and communalities (h2) are reported in Table 3. The extracted components were able to reproduce satisfactory results for all variables because there were no variables with low saturation in each factor, and communality was always higher than 0.684. The first component showed the highest positive correlation with Na, Ca, Mg, B, Zn and K, while negative correlations were observed for Pb and Cr; Mn and to a lesser extent Cr (0.54964) had a positive correlation with the second component. The most dominant variable in the third component was Ni.

Fig. 2. PCA for Interdonato lemon pulps categorized as PGI Interdonato lemon (from Sicily) and non-PGI Interdonato lemon (from Turkey). Inserts: loadings plot for PC1 and PC2. Outcome obtained without any rotation.

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Fig. 3. PCA for Interdonato lemon pulps categorized as PGI Interdonato lemon (from Sicily) and non-PGI Interdonato lemon (from Turkey). Inserts: loadings plot for PC1 and PC2. Outcome obtained with oblimin rotation and Kaiser normalization.

membership, calculated by equations reported in Di Bella et al. (2012). The classification matrix reported in Table 5 indicates that the 100% of total samples were correctly classified, also the cross-validation procedure was applied and the results showed again that classification was correct at 100%. Thus, a suitable model to discriminate the Interdonato lemon pulp samples according to geographical origin could be generated by CDA. Chemometric analyses may provide with a high degree of confidence information about geographical origin of numerous agricultural products (Di Bella et al., 2015; Di Bella et al., 2016; La Torre et al., 2008; Louppis et al., 2017; Saitta et al., 2014). In fact chemometric analysis carried out in this study allowed to correctly differentiate IGP Interdonato samples, demonstrating to be a reliable tool to verify the geographical origin of these lemons.

Table 4 Canonical Discriminant Analysis coefficients used for classify Interdonato lemon pulp samples as PGI (Italian origin) or non-PGI (Turkish origin). Element

Unstandardized coefficients

Standardized coefficients

Cr Ni Pb Mn Ca K Mg Na B Zn Constant

0.405 −0.909 2.415 0.659 −0.432 −0.402 −1.027 −0.473 −0.105 1.266 0.405

0.298 −0.763 0.819 0.621 −0.301 −0.311 −0.841 −0.290 −0.064 1.094

Bold values indicate the most discriminative variables.

4. Conclusions The present research furnished a detailed characterization of the mineral composition of lemon samples from different geographical

Table 5 Classification matrix of Canonical Discriminant Analysis obtained from classify of Interdonato lemon pulp samples as PGI (Italian origin) or non-PGI (Turkish origin). Predicted Group Membership

Original dataset

Count %

Cross-validated dataset

Count %

PGI Interdonato lemon pulps Non-PGI Interdonato lemon pulps PGI Interdonato lemon pulps non-PGI Interdonato lemon pulps PGI Interdonato lemon pulps non-PGI Interdonato lemon pulps PGI Interdonato lemon pulps non-PGI Interdonato lemon pulps

127

Total

PGI Interdonato lemon pulps

non-PGI Interdonato lemon pulps

22 0 100 0 22 0 100 0

0 18 0 100 0 18 0 100

22 18 100 100 22 18 100 100

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origin produced in Italy and Turkey. The results obtained highlighted that the discrimination between Italian and Turkish lemons achieved by both PCA and CDA indicate that the 100% of total samples were correctly classified. Furthermore, these classifications suggest that it is possible to correlate lemons with their geographical origins, an essential condition for traceability of this peculiar product. Italian and Turkish lemon pulps analyzed in this study cannot be considered “rich in” or “source of” as regards any of the mineral element considered in the meanwhile, these fruits can be considered safe for their low contents in toxic elements.

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