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Mineral and centesimal composition evaluation of conventional and organic cultivars sweet potato (Ipomoea batatas (L.) Lam) using chemometric tools
Accepted Manuscript Mineral and centesimal composition evaluation of conventional and organic cultivars sweet potato (Ipomoea batatas (L.) Lam) using chemometric tools Ana M.P. dos Santos, Jeane S. Lima, Ivanice F. dos Santos, Emmanuelle F.R. Silva, Fernanda A. de Santana, Dominique G.G.R. de Araujo, Liz O. dos Santos PII: DOI: Reference:
S0308-8146(17)32028-9 https://doi.org/10.1016/j.foodchem.2017.12.063 FOCH 22160
To appear in:
Food Chemistry
Received Date: Revised Date: Accepted Date:
16 August 2017 2 December 2017 16 December 2017
Please cite this article as: dos Santos, A.M.P., Lima, J.S., dos Santos, I.F., Silva, E.F.R., de Santana, F.A., de Araujo, D.G.G., dos Santos, L.O., Mineral and centesimal composition evaluation of conventional and organic cultivars sweet potato (Ipomoea batatas (L.) Lam) using chemometric tools, Food Chemistry (2017), doi: https://doi.org/ 10.1016/j.foodchem.2017.12.063
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Mineral and centesimal composition evaluation of conventional and organic cultivars sweet potato (Ipomoea batatas (L.) Lam) using chemometric tools
Ana M. P. dos Santos 1*, Jeane S. Lima1, Ivanice F. dos Santos1,2, Emmanuelle F. R. Silva1, Fernanda A. de Santana1,4, Dominique G. G. R. de Araujo1, Liz O. dos Santos 3.
1
Universidade Federal da Bahia, Instituto de Química, Grupo de Pesquisa em
Química e Quimiometria, Campus Ondina, 41170-115, Salvador, Bahia, Brazil. 2
Universidade Estadual de Feira de Santana, Departamento de Ciências
Exatas, 44036-900, Feira de Santana, Bahia, Brazil. 3
Universidade Federal do Recôncavo da Bahia, Centro de Ciência e
Tecnologia em Energia e Sustentabilidade, Feira de Santana, 44042-280, Feira de Santana, Bahia, Brazil.. 4
Instituto Federal de Educação, Ciência e Tecnologia Baiano, Campus
Guanambi, 46430-000, Guanambi, Bahia, Brazil.
*Correspondence author: E-mail: [email protected] FAX: + 557132374117
Abstract Sweet potato is a food consumed in the world. In this work, the minerals and centesimal composition in sweet potatoes of organic and conventional cultivars was investigated. The accuracy was confirmed with a certified reference material of apple leaves (NIST 1515). The quantification of the samples was performed by inductively coupled plasma optical emission spectrometry and the digestion efficiency was evaluated by residual carbon content. The mean concentrations (in mg / 100 g) of minerals were: 23.5 and 40.7 (Ca); 0.082 and 0.159 (Cu); 0.303 and 0.481 (Fe); 197 and 381 (K); 166 and 35.7 (Mg); 0.183 and 1.15 (Mn); 68.6 and 0.433 (Na); 54.1 and 62.2 (P) and 0.197 and 0.261 (Zn) for conventional and organic cultivars, respectively. Average centesimal concentrations in conventional and organic cultivars (in %), were: 72 and 72 (moisture); 0.87 and 0.90 (ashes); 1.5 and 1.4 (proteins); 0.63 and 0.54 (lipids) and 24.8 and 23.9 (carbohydrates).
Keywords:
Sweet
potato;
mineral
content;
centesimal
composition,
Conventional cultivar; Organic cultivar; PCA; HCA.
1. Introduction
2
Sweet potato (Ipomoea batatas (L.) Lam.) is a vegetable classified as root tuber originated in tropical America, with a promising potential in the view of world agriculture for the ease of adaptation to climate conditions and a low-cost cultivation (Soares et al., 2014). Sweet potato roots are preferred for human consumption and can be eaten boiled, baked, fried or mashed, for making homemade sweets and salty. In industrial process, it is included in the preparation of breads and starch (Nzamwita, Duodu & Minnaar, 2017) as raw material in the production of paper, cosmetics, adhesives tissues (da Silva et al., 1995) and bioethanol (Widodo, Wahyuningsih & Ueda, 2015). It also has medicinal benefits, primarily in the treatment of diseases such as type 2 diabetes, cancers, inflammations, anemia and hypertension, reported by Mohanraj and Sivasankar (2014) in a number of scientific papers that highlight nutritional values and the phytochemical compositions in various parts of sweet potato (Ludvik, Neuffer & Pacini, 2004 and Grace, Yousef, Gustafson, Truong, Yencho & Lila, 2014). Williams et al. (2013) showed that the sweet potato clones of orange pulp had nutritional values and detectable levels of β-carotene, contributing to food security and reduction of vitamin A deficiency in East Timor. Luis, Rubio, Gutiérrez, González-Weller, Revert & Hardisson (2014) reviewed the mineral composition (Na, K, Ca, Mg, Cu, Fe, Mn, Cr, Ni and Zn) and toxic elements (Cd and Pb) in three sweet potato varieties (white, red and orange pulps) obtained in Tenerife, Spain, in order to provide information on the nutritional values. Suárez et al. (2016) determined the proximate and mineral composition of sweet potato samples grown in the Canary Islands, also in Spain. In the evaluation of the results, the multidimensional scaling techniques (MDS) were used to classify the main differences between the samples, mainly geographic location and maturation cycle. The search for healthy foods by the population has increased the consumption of organic food crops compared to conventional crops. Organic farming uses techniques that favor the balance of the soil, leading to socio-economic and ecological sustainability. The organic cultivation system has several advantages such as: the use of organic fertilizers, divided in vegetable fertilizer, biofertilizers and compost; the crop rotation, and the natural insecticides for pest 3
control, resulting in the organic improvement of soil quality (de Alencar, Mendonça, de Oliveira, Jucksch & Cecon, 2013). Thus, organic food brings benefits to the health of the population because it does not contain pesticides and synthetic fertilizers, which have substances like the organochlorines and nitrates in their composition, and they have the ability to cause diseases as carcinogenic , mutagenic and teratogenic agents (da Silva, Ferreira, de Araújo Neto, Tavella & Solino, 2011). The study of nutritional and chemical composition is important to generate food information, enabling professionals to develop a therapeutic diet for treating and preventing diseases (Torres, Garbelotti & Moita Neto, 2006 and Khouzam, Lobinski & Pohl, 2011). Due to the complexity of evaluating nutritional parameters in plant foods, multivariate techniques have been applied, such as the principal component analysis (PCA), allowing the correlation of different variables to evaluate and characterize the analytical data, leading a trend and grouping in a sample set (Ferreira, 2015). The HCA (Hierarchical Component Analysis) seeks to organize the samples into classes, in order to group by similarity and differences among the participating members. This increases the internal homogeneity within the groups and reduces the heterogeneity between groups, allowing the detection of samples of anomalous behavior in the graph of dendrogram (Correia & Ferreira, 2007). The PCA and HCA were employed for the determination and evaluation of the composition of Chinese cabbage elements, showing that P, Cu, Fe and Mn are minerals that contribute to a greater variability, therefore considering the nutritional supplement (dos Santos, Oliveira, Souza, de Jesus & Ferreira, 2011). In another work, it was determined that the mineral composition of raw breadfruit and the cooked by boiling and heating in microwave through domestic methods one, applying the PCA and HCA, concluded that Fe, K, Na and P contributed by increasing the variability between raw and cooked samples. A reduction of the mineral composition occurred during cooking, as well as a significant decrease in the potassium content, being favorable for patients who have kidney problems (de Souza, Soares, Queiroz, dos Santos & Ferreira, 2016). According to Wu, Jiang, Nitin, Bao, Chen & Tao (2016), who applied 4
PCA in the evaluation of physical-chemical, bioactive and mineral parameters in yam samples cultivated in China, which allowed the classification of the chemical profile in different cultivars. In this paper, the centesimal (moisture, ash, protein, lipid and carbohydrate) and mineral composition was determined(Ca, Cu, Fe, K, Mg, Mn, Na, P and Zn) in white pulp sweet potato roots samples in natura, in both organic and conventional cultivation systems in the state of Bahia, Brazil. The multivariate analysis (PCA and HCA) were applied for the evaluation of the concentration of metals in the samples of different forms of cultures.
2. Experimental 2.1. Instrumentation An analytical balance model ALC/210.4 from Sartorius (Goettingen, Germany) was used. A digest block model TE-040/25 (Tecnal, São Paulo, Brazil) was used for the acid digestion of the blank and apple leaves samples (1515 NIST). Multi-element determination of C, Ca, Cu, Fe, K, Mg, Mn, Na, P and Zn was performed by using inductively coupled plasma optical emission spectrometer (ICP OES), model Vista PRO from Varian (Mulgrave, Australia), with axial viewing and a charge-coupled device detector. The instrumental parameters used for the multi-element determination were as follows: RF generator of 40 MHz, power of 1.3 kW, plasma gas flow rate of 15 Lmin−1, auxiliary gas flow rate of 1.5 L min−1 and nebulizer gas flow rate of 0.7 Lmin−1. The elements and the analytical spectral lines (nm) used were: C (193.027), Ca (317.933), Cu (324.752), Fe (234.350), K (404.721), Mg (279.553), Mn (260.568), Na (588.995), P (214.914) and Zn (213.857). For the centesimal composition, the following were used: greenhouse model Q317M from QUIMIS (São Paulo, Brazil) for determination of moisture; muffle model Q318S from QUIMIS (São Paulo, Brazil) for ash content; extraction 5
battery type sebelin model Q308-26B from QUIMIS (São Paulo, Brazil) for determination of lipids; and nitrogen distiller model MA-036 from Marconi (São Paulo, Brazil) for protein determination.
2.2. Reagents and Solutions Ultrapure water produced from a Milli-Q purification system (Millipore, MA, USA), with resistivity of 18 MΩ cm-1, was used throughout the experiments. The nitric acid (Merck, Darmstadt, Germany) and hydrogen peroxide (Merck, Darmstadt, Germany) reagents were of analytical grade. Fresh working standard solution was prepared daily by serial dilution from stock solutions containing 1000 to 4000 mg L-1 (Titrisol, Merck) of the elements Ca, Cu, Fe, K, Mg, Mn, Na, P and Zn. The stock solution of 20.000 mg L-1 carbon was prepared from citric acid to determine the residual carbon content. For the centesimal composition, the reagents used were: petroleum ether, sodium hydroxide, sulfuric acid, hydrochloric acid, boric acid, copper sulfate, potassium sulfate, methyl red, bromo-cresol green, methyl orange and calcium carbonate, obtained from Merck (Darmstadt, Germany).
2.3. Sample collection, acid digestion and determination of elements The samples of cultivation (organic and traditional) were obtained in several commercial points (fairs, farms and supermarkets) of Salvador, Bahia, Brazil. Triplicates of each sample were run for the determination of the total content of elements. About 2.0 g of the sample and 3.0 mL of 65% (w w-1) nitric acid were placed in a digest tube, then heated at 150 °C for 1 hour and 30 minutes on a digester block with a “cold finger” reflux system (Ferreira, Silva, de Santana, Silva Junior, Matos & dos Santos, 2013). Then, three times, in an interval of 30 minutes from each other, 1.0 mL of 30% (v v-1) hydrogen peroxide was added. The digest was then quantitatively transferred to centrifuge tubes and diluted with ultrapure water up to a final volume of 12.0 mL. A blank digest was carried 6
out in the same way as the samples. The multi-element determination of C, Ca, Cu, Fe, K, Mg, Mn, Na, P and Zn was carried out by the technique of inductively coupled plasma optical emission spectrometry (ICP OES).
2.4. Validation of the analytical method used for quantification of elements The accuracy of the method used for quantification of Ca, Cu, Fe, K, Mg, Mn, Na, P and Zn by ICP OES was confirmed by the analysis of certified reference material of apple leaves (NIST 1515) furnished by the National Institute of Standards and Technology (Gaithersburg, MD, USA). The procedure for analysis of the CRM was the same used for the samples of white pulp sweet potato roots.
2.5. Centesimal composition The centesimal composition of white pulp sweet potato root samples
was
determined by moisture, ash, protein, lipid and carbohydrate, according to the method described by the Adolfo Lutz Institute (2008). The moisture content was determined using the drying method in an oven at 105 °C to constant weight, and the determination of ash was carried out in a muffle heated up to 550 °C. For the quantification of protein, Kjeldahl used the factor of 6.25 for nitrogen conversion. For the lipid content, the Soxhlet method was used with ether solvent for extraction. The total carbohydrate content was calculated as the difference between 100 and the sum of the percentage of moisture, ash, lipid and protein.
3. Results and discussion
7
3.1. Evaluation of digestion procedures and validation of the analytical method by ICP OES A method of acid digestion and quantification by employing inductively coupled plasma optical emission spectrometry (ICP OES) was proposed to evaluate the content of C, Ca, Cu, Fe, K, Mg, Mn, Na, P and Zn in sweet potato samples. The residual carbon content (RCC) was in the range of 0.61 to 2.19% (m m-1) for the conventional cultivar and 0.46 to 2.23% (m m-1) for the organic cultivar, so the RCC values are considered low proving the efficiency decomposition in this study (Araújo, Gonzalez, Ferreira, Nogueira, & Nóbrega, 2002). The established analytical parameters are in the Table 1. The accuracy of the proposed method was confirmed by analysis of CRM NIST 1515 apple leaves, after performing the same digestion procedure proposed for sweet potato samples.
3.2. Evaluation of the results employing multivariate analysis techniques (PCA and HCA) The chemometric analysis of the auto-scaling results of 48 conventional and organic culture samples was performed by principal component analysis and hierarchical clustering analysis using the SPSS 24 and statistic 10 software. Before PCA, the adequacy of the data was evaluated by factorization. The Kaiser-Lawyer-Olkim measure of sampling adequacy was 0.71 above the critical level of 0.6. The Bartlet's sphericity test showed a Chi-square value equal to 182.4, with statistical significance p <0.001. Both tests indicated an appropriate matrix for PCA. The PCA analysis with 8 variables was reduced to three principal components with eigenvalues (3.73; 1.19 e 1.03) exceeding one were extracted, explaining 74.5 % of the total variance. The first principal component (PC1) represented 46.7 % and the next PC 14.9 % and 12.3 %, respectively. The communalities (variance proportion of each variable involved in the PC space) of every variable were found higher than 0.7, except for phosphorus (0.49). The 95 % 8
confidence interval ellipse was applied in PCA score plot, and despite the samples varying in growth type, samples were within the 95% confidence limit. In the figure of orthogonal vectors (PC1 x PC2), most of the coefficients have significant positive values in PC1, according to the linear combination of the loadings of the original variables PC1= 0.745Cu + 0.514Fe + 0.561 Mn + 0.736 Ca + 0.694K - 0.782 Mg - 0.811Na + 0.493P, which highlights copper, iron, manganese and calcium with high positive correlations . This shows that the organic potato samples projected on the right side of figure 1A and B have a predominance of these elements. However, Mg and Na have a positive expressive association, but are parameters with high levels in potato samples of conventional growth. The trend of separation of the samples is observed throughout PC1, evidencing that the samples of conventional culture have high contents (mg/100g) of Mg (18,2 - 254) and Na (50.7 - 98.3), while the organic ones showed Cu (0.0230 - 0.262), Ca (22.9 - 75.6), Fe (0.176-0.941), K (199 562), Mn (0.022 - 5.69) and P (40.8 - 86.5). The difference in nutrient content observed in the different cultivars can be attributed to the possible use of pesticides and insecticides in the conventional cultivar that can influence the absorption of soil nutrients by plants. Iron was the dominant variable in the second main component PC2 = 0.402Cu + 0.651Fe -0.443Mn -0.152Ca - 0.256K + 0.152Mg - 0.2771Na - 0.480P, indicating a high positive correlation with expressive value in this vector. This is confirmed in the chart of scores (Fig 1B), where the organic potato samples have high content of this nutrient. Manganese and potassium have a strong negative interrelationship in the third component PC3 = -0.137Cu + 0.133Fe + 0.581Mn + 0.447Ca - 0.558K + 0.336Mg - 0.116Na - 0.148P, displaying an inverse trend for the concentrations of these elements in the potato samples (figure 2 A and B). The results obtained are similar for the multivariate techniques used, HCA and PCA. The HCA was carried out using the Euclidian distance and complete linkage as measure of similarity, and the results were reported in a dendrogram figure 3 A and B. Considering a similarity at 7 % level (3a), all organic and 9
conventional potato samples were arranged into homogeneous groups, indicating that different types of growth can be differentiated based on the concentrations of the minerals. Both groups are subdivided into subgroups, characterizing different locations (Fig 3A). The position of the outlying samples (4OP1; 4OP2; 4OP3 and 7CP1; 7CP2; 7CP3) are worthy in Fig 3A. Fig 3B shows the hierarchic dendrogram that illustrates the similarity between the chemical parameters. These figures expose the presence of 2 groups corresponding to the mineral composition of the potato samples. The first group consists of the elements P, K, Ca, Mn, Fe and Cu, and the second group Na and Mg. Therefore, this may indicate a potential relationship between the origin of the samples and the groups of specific elements, which reflects the chemical composition of the different types of potato growth.
3.3. Evaluation of the mineral and centesimal composition of the sweet potato The average concentrations obtained demonstrate that sweet potato is an excellent source of minerals for feeding, as shown in Table 2. Organic cultivation samples presented the highest levels of the macro minerals Ca, K and P and the micro minerals Cu, Fe, Zn and Mn, with average values of 40.7, 381 and 62.2 mg/100g for Ca, K and P and 0.159, 0.481, 0.261, 1.15 mg/100g for Cu, Fe, Zn and Mn, respectively. The conventional cultivation presented the highest averages of the macro minerals as Mg and Na, with average values of 166 and 35.7 mg/100g of Mg and 68.6 and 0.433 mg/100g of Na for in the conventional and organic cultivars, respectively. Considering the data obtained for the centesimal composition samples of both cultivars did not show significant difference, with average values for conventional cultivars of 72%, 0.87%, 1.5%, 0.63%, and 24.8%, and for organic cultivars of 72%, 0.90%, 1.4%, 0.54%, 23.9% for moisture, ash, proteins, lipids and carbohydrates, respectively.
3.4. Comparing the concentrations of minerals 10
The comparison between the concentrations of minerals determined in this work with other vegetables showed that sweet potato has greater nutritional value in the macro minerals Mg, Na and P than carrot, okra and cabbage, and in K, Mg and Na than eggplant. Considering the micro minerals, sweet potato presented higher average contents of Cu and Mn than carrot, and similar contents of Fe than cabbage, as shown in Table 3.
4. Conclusion The developed method was promising to evaluate the sweet potato mineral content by ICP OES. The application of chemometric tools, such as PCA and HCA, showed the formation of two groups, separating the sweet potato from the organic cultivation and the conventional one. Samples of organic cultivars showed higher concentrations of minerals, such as Ca, Cu, Fe, K, Mg, Mn and P, suggesting that this is a good alternative for nutritional supplementation. However, the sodium content of the conventional culture presented higher levels, indicating alertness for hypertensive patients, although the Brazilian government establishes through the ANVISA nº 24/2010 resolution that a food rich in sodium is the one that contains an amount equal to 400 mg / 100g or greater. The centesimal composition in both cultivars presented no significant difference.
Acknowledgements The authors are grateful to Brazilian agencies PRONEX/Fundacão de Amparo à Pesquisa
do
Estado
da
Bahia
(FAPESB),
Conselho
Nacional
de
Desenvolvimento Científico e Tecnológico (CNPq) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for grants and fellowships.
11
Table 1. Analytical parameters of the method employed for determination of the chemical elements. LOD
Analyte
LOQ -1
mg100g
mg100g
-1
Certified valuesa
Obtained valuea
Ca
0.141
0.470
1.52 ± 0.015%
1.52 ± 0.153
Cu
0.012
0.0410
5.64 ± 0.24 µg/g
5.55 ± 0.5
Fe
0.026
0.0900
83 ± 5 µg/g
87 ± 4
K
0.040
0.130
1.61 ± 0.02 %
1.61 ± 0.19
Mg
0.870
2.91
0.271± 0.008 %
0.270 ± 0.017
Mn
0.002
0.005
54 ± 3 µg/g
51 ± 4
Na
0.252
0.840
24.4 ± 1.2 %
24.6 ± 0.740
P
0.067
0.222
0.159 ± 0.011 %
0.159 ± 0.001
a
Results of CRM of apple leaves NIST 1515 analyzed for method evaluation expressed as interval confidence at 95% level.
Table 2. Averages and ranges of concentrations of minerals in sweet potato of conventional and organic cultivars (in mg/100g). Minerals
Cultivars Conventional
Macro
Micro
Organic
average
range
average
range
Ca
23.5
16.8-34.2
40.7
22.9-75.6
K
197
85.6-500
381
199-562
Mg
166
18.2-254
35.7
19.9-55.8
Na
68. 6
50.7-98.3
0.433
0.050-1.29
P
54.1
19.4-68.7
62.2
40.8-86.5
Cu
0.082
0.027-0.156
0.159
0.023-0.262
Fe
0.303
0.122-0.522
0.481
0.176-0.941
Zn
0.197
0.045-0.297
0.261
0.154-0.405
Mn
0.183
0.018-0.486
1.15
0.022-5.69
Table 3. Macro and micro mineral nutrient content in different vegetables (expressed in mg/100g). Minerals
Sweet potato*
Carrot
Min-max
Ca
23.4
(16.8-34.2)
b
Okra
Min-max
40.6
(22.0-87.0)
c
Cabbage
d
Eggplant e Brinjal
Min-max
366
(273–528)
44.6
30.0
12
K
198
(85.6-500)
271
(146-678)
267
(211–353)
253
28.0
Mg
166
(18.2-254)
10.4
(4.91-21.3)
45.3
(34.6–64.2)
16
17.0
Na
68.5
(50.7-98.3)
35.5
(5.73-115.0)
18.3
(8.1–43.1)
11
17.0
P
54.1
(19.4-68.7)
30.4
(15.6-70.1)
44.5
(59.1–33.9)
46
n/a
Cu
0.082
(0.027-0.156)
0.044
(n/a-0.535)
n/a
n/a
n/a
0.190
Fe
0.303
(0.122-0.522)
0.395
(0.125-1.58)
n/a
n/a
0.3
2.00
Zn
0.197
(0.045-0.297)
0.569
(n/a- 1.89)
0.233
(0.08–0.429)
0.3
0.730
Mn
0.183
(0.018-0.486)
0.077
(n/a-0.939)
n/a
n/a
0.2
0.240
* This work (conventional) n/a: not available b (Krejcova, Navesnik, Jicinska & Cernohorsky, 2016) c (dos Santos, dos Santos, Barbosa, Lima, dos Santos & Matos, 2013) d (Anunciação, Leão, Jesus & Ferreira, 2011) e (Bangash, Arif, Khan, Rahman & Hussain, 2011)
13
Figure captions
Figure 1. A) Representation of the variables and samples potato of organic and conventional and B) Functions of the PC1 vs PC2. Figure 2. A) Representation of the variables and samples potato of organic and conventional and B) Functions of the PC1 vs PC3. Figure 3. A) Dendrogram of the organic and conventional potato samples and B) Dendrogram of the variables.
14
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Ludvik, B., Neuffer B., & Pacini, G. (2004). Efficacy of Ipomoea batatas (Caiapo) on diabetes control in type 2 diabetic subjects treated with diet. Diabetes Care, 27, 436–440. Luis, G., Rubio, C., Gutiérrez, Á. J., González-Weller, D., Revert, C., & Hardisson, A. (2014). Evaluation of metals in several varieties of sweet potatoes (Ipomoea batatas L.): comparative study. Environmental Monitoring and Assessment, 186, 433–440. Mohanraj, R., & Sivasankar, S. (2014). Sweet Potato (Ipomoea batatas [L.] Lam) - A Valuable Medicinal Food: A Review. Journal of Medicinal Food, 17, 733–741. Nzamwita, M., Duodu, K. G., & Minnaar, A. (2017). Stability of β-carotene during baking of orange-fleshed sweet potato-wheat composite bread and estimated contribution to vitamin A requirements. Food Chemistry, 228, 85–90. Soares, I. M., Bastos, E. G. P., Sobrinho, T. J. S. P., Alvim, T. C., da Silveira, M. A., Aguiar, R. W. S., & Ascêncio, S. D. (2014). Conteúdo fenólico e atividade antioxidante de diferentes cultivares de ipomoea batatas (l.) lam. obtidas por melhoramento genético para produção industrial de etanol. Revista de Ciências Farmacêuticas Básica e Aplicada, 35, 479– 488. Suárez, M. H., Hernández, A. I. M., Galdón, B. R., Rodríguez, L. H., Cabrera, C. E. M., Mesa, D. R., Rodríguez-Rodríguez, E. M., & Romero, C. D. (2016). Application of multidimensional scaling technique to differentiate sweet potato (Ipomoea batatas (L.) Lam) cultivars according to their chemical composition. Journal of Food Composition and Analysis, 46, 43–49. Torres, E. A. F. S., Garbelotti, M. L., & Moita Neto, J. M. (2006). The application of hierarchical clusters analysis to the study of the composition of foods. Food Chemistry, 99, 622–629. 17
Widodo, Y., Wahyuningsih, S., & Ueda, A. (2015). Sweet Potato Production for Bio-ethanol and Food Related Industry in Indonesia: Challenges for Sustainability. Procedia Chemistry, 14, 493–500. Williams, R., Soares, F., Pereira, L., Belo, B., Soares, A., Setiawan, A., Browne, M., Nesbitt, H., & Erskine, W. (2013). Sweet potato can contribute to both nutritional and food security in Timor-Leste. Field Crops Research, 146, 38–43. Wu, Z. G., Jiang, W., Nitin, M., Bao, X. Q., Chen, S. L., & Tao, Z. M. (2016). Characterizing diversity based on nutritional and bioactive compositions of yam germplasm (Dioscorea spp.) commonly cultivated in China. Journal of Food and Drug Analysis, 24, 367–375.
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Highlights
1 - A mineral and centesimal evaluation of sweet potatoes was performed. 2 - The results showed that organic samples showed high mineral content. 3 - Conventional culture samples showed high sodium content. 4 - Multivariate analysis proved to be a good tool to evaluate different forms of cultivation.
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S0308-8146(17)32028-9 https://doi.org/10.1016/j.foodchem.2017.12.063 FOCH 22160
To appear in:
Food Chemistry
Received Date: Revised Date: Accepted Date:
16 August 2017 2 December 2017 16 December 2017
Please cite this article as: dos Santos, A.M.P., Lima, J.S., dos Santos, I.F., Silva, E.F.R., de Santana, F.A., de Araujo, D.G.G., dos Santos, L.O., Mineral and centesimal composition evaluation of conventional and organic cultivars sweet potato (Ipomoea batatas (L.) Lam) using chemometric tools, Food Chemistry (2017), doi: https://doi.org/ 10.1016/j.foodchem.2017.12.063
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Mineral and centesimal composition evaluation of conventional and organic cultivars sweet potato (Ipomoea batatas (L.) Lam) using chemometric tools
Ana M. P. dos Santos 1*, Jeane S. Lima1, Ivanice F. dos Santos1,2, Emmanuelle F. R. Silva1, Fernanda A. de Santana1,4, Dominique G. G. R. de Araujo1, Liz O. dos Santos 3.
1
Universidade Federal da Bahia, Instituto de Química, Grupo de Pesquisa em
Química e Quimiometria, Campus Ondina, 41170-115, Salvador, Bahia, Brazil. 2
Universidade Estadual de Feira de Santana, Departamento de Ciências
Exatas, 44036-900, Feira de Santana, Bahia, Brazil. 3
Universidade Federal do Recôncavo da Bahia, Centro de Ciência e
Tecnologia em Energia e Sustentabilidade, Feira de Santana, 44042-280, Feira de Santana, Bahia, Brazil.. 4
Instituto Federal de Educação, Ciência e Tecnologia Baiano, Campus
Guanambi, 46430-000, Guanambi, Bahia, Brazil.
*Correspondence author: E-mail: [email protected] FAX: + 557132374117
Abstract Sweet potato is a food consumed in the world. In this work, the minerals and centesimal composition in sweet potatoes of organic and conventional cultivars was investigated. The accuracy was confirmed with a certified reference material of apple leaves (NIST 1515). The quantification of the samples was performed by inductively coupled plasma optical emission spectrometry and the digestion efficiency was evaluated by residual carbon content. The mean concentrations (in mg / 100 g) of minerals were: 23.5 and 40.7 (Ca); 0.082 and 0.159 (Cu); 0.303 and 0.481 (Fe); 197 and 381 (K); 166 and 35.7 (Mg); 0.183 and 1.15 (Mn); 68.6 and 0.433 (Na); 54.1 and 62.2 (P) and 0.197 and 0.261 (Zn) for conventional and organic cultivars, respectively. Average centesimal concentrations in conventional and organic cultivars (in %), were: 72 and 72 (moisture); 0.87 and 0.90 (ashes); 1.5 and 1.4 (proteins); 0.63 and 0.54 (lipids) and 24.8 and 23.9 (carbohydrates).
Keywords:
Sweet
potato;
mineral
content;
centesimal
composition,
Conventional cultivar; Organic cultivar; PCA; HCA.
1. Introduction
2
Sweet potato (Ipomoea batatas (L.) Lam.) is a vegetable classified as root tuber originated in tropical America, with a promising potential in the view of world agriculture for the ease of adaptation to climate conditions and a low-cost cultivation (Soares et al., 2014). Sweet potato roots are preferred for human consumption and can be eaten boiled, baked, fried or mashed, for making homemade sweets and salty. In industrial process, it is included in the preparation of breads and starch (Nzamwita, Duodu & Minnaar, 2017) as raw material in the production of paper, cosmetics, adhesives tissues (da Silva et al., 1995) and bioethanol (Widodo, Wahyuningsih & Ueda, 2015). It also has medicinal benefits, primarily in the treatment of diseases such as type 2 diabetes, cancers, inflammations, anemia and hypertension, reported by Mohanraj and Sivasankar (2014) in a number of scientific papers that highlight nutritional values and the phytochemical compositions in various parts of sweet potato (Ludvik, Neuffer & Pacini, 2004 and Grace, Yousef, Gustafson, Truong, Yencho & Lila, 2014). Williams et al. (2013) showed that the sweet potato clones of orange pulp had nutritional values and detectable levels of β-carotene, contributing to food security and reduction of vitamin A deficiency in East Timor. Luis, Rubio, Gutiérrez, González-Weller, Revert & Hardisson (2014) reviewed the mineral composition (Na, K, Ca, Mg, Cu, Fe, Mn, Cr, Ni and Zn) and toxic elements (Cd and Pb) in three sweet potato varieties (white, red and orange pulps) obtained in Tenerife, Spain, in order to provide information on the nutritional values. Suárez et al. (2016) determined the proximate and mineral composition of sweet potato samples grown in the Canary Islands, also in Spain. In the evaluation of the results, the multidimensional scaling techniques (MDS) were used to classify the main differences between the samples, mainly geographic location and maturation cycle. The search for healthy foods by the population has increased the consumption of organic food crops compared to conventional crops. Organic farming uses techniques that favor the balance of the soil, leading to socio-economic and ecological sustainability. The organic cultivation system has several advantages such as: the use of organic fertilizers, divided in vegetable fertilizer, biofertilizers and compost; the crop rotation, and the natural insecticides for pest 3
control, resulting in the organic improvement of soil quality (de Alencar, Mendonça, de Oliveira, Jucksch & Cecon, 2013). Thus, organic food brings benefits to the health of the population because it does not contain pesticides and synthetic fertilizers, which have substances like the organochlorines and nitrates in their composition, and they have the ability to cause diseases as carcinogenic , mutagenic and teratogenic agents (da Silva, Ferreira, de Araújo Neto, Tavella & Solino, 2011). The study of nutritional and chemical composition is important to generate food information, enabling professionals to develop a therapeutic diet for treating and preventing diseases (Torres, Garbelotti & Moita Neto, 2006 and Khouzam, Lobinski & Pohl, 2011). Due to the complexity of evaluating nutritional parameters in plant foods, multivariate techniques have been applied, such as the principal component analysis (PCA), allowing the correlation of different variables to evaluate and characterize the analytical data, leading a trend and grouping in a sample set (Ferreira, 2015). The HCA (Hierarchical Component Analysis) seeks to organize the samples into classes, in order to group by similarity and differences among the participating members. This increases the internal homogeneity within the groups and reduces the heterogeneity between groups, allowing the detection of samples of anomalous behavior in the graph of dendrogram (Correia & Ferreira, 2007). The PCA and HCA were employed for the determination and evaluation of the composition of Chinese cabbage elements, showing that P, Cu, Fe and Mn are minerals that contribute to a greater variability, therefore considering the nutritional supplement (dos Santos, Oliveira, Souza, de Jesus & Ferreira, 2011). In another work, it was determined that the mineral composition of raw breadfruit and the cooked by boiling and heating in microwave through domestic methods one, applying the PCA and HCA, concluded that Fe, K, Na and P contributed by increasing the variability between raw and cooked samples. A reduction of the mineral composition occurred during cooking, as well as a significant decrease in the potassium content, being favorable for patients who have kidney problems (de Souza, Soares, Queiroz, dos Santos & Ferreira, 2016). According to Wu, Jiang, Nitin, Bao, Chen & Tao (2016), who applied 4
PCA in the evaluation of physical-chemical, bioactive and mineral parameters in yam samples cultivated in China, which allowed the classification of the chemical profile in different cultivars. In this paper, the centesimal (moisture, ash, protein, lipid and carbohydrate) and mineral composition was determined(Ca, Cu, Fe, K, Mg, Mn, Na, P and Zn) in white pulp sweet potato roots samples in natura, in both organic and conventional cultivation systems in the state of Bahia, Brazil. The multivariate analysis (PCA and HCA) were applied for the evaluation of the concentration of metals in the samples of different forms of cultures.
2. Experimental 2.1. Instrumentation An analytical balance model ALC/210.4 from Sartorius (Goettingen, Germany) was used. A digest block model TE-040/25 (Tecnal, São Paulo, Brazil) was used for the acid digestion of the blank and apple leaves samples (1515 NIST). Multi-element determination of C, Ca, Cu, Fe, K, Mg, Mn, Na, P and Zn was performed by using inductively coupled plasma optical emission spectrometer (ICP OES), model Vista PRO from Varian (Mulgrave, Australia), with axial viewing and a charge-coupled device detector. The instrumental parameters used for the multi-element determination were as follows: RF generator of 40 MHz, power of 1.3 kW, plasma gas flow rate of 15 Lmin−1, auxiliary gas flow rate of 1.5 L min−1 and nebulizer gas flow rate of 0.7 Lmin−1. The elements and the analytical spectral lines (nm) used were: C (193.027), Ca (317.933), Cu (324.752), Fe (234.350), K (404.721), Mg (279.553), Mn (260.568), Na (588.995), P (214.914) and Zn (213.857). For the centesimal composition, the following were used: greenhouse model Q317M from QUIMIS (São Paulo, Brazil) for determination of moisture; muffle model Q318S from QUIMIS (São Paulo, Brazil) for ash content; extraction 5
battery type sebelin model Q308-26B from QUIMIS (São Paulo, Brazil) for determination of lipids; and nitrogen distiller model MA-036 from Marconi (São Paulo, Brazil) for protein determination.
2.2. Reagents and Solutions Ultrapure water produced from a Milli-Q purification system (Millipore, MA, USA), with resistivity of 18 MΩ cm-1, was used throughout the experiments. The nitric acid (Merck, Darmstadt, Germany) and hydrogen peroxide (Merck, Darmstadt, Germany) reagents were of analytical grade. Fresh working standard solution was prepared daily by serial dilution from stock solutions containing 1000 to 4000 mg L-1 (Titrisol, Merck) of the elements Ca, Cu, Fe, K, Mg, Mn, Na, P and Zn. The stock solution of 20.000 mg L-1 carbon was prepared from citric acid to determine the residual carbon content. For the centesimal composition, the reagents used were: petroleum ether, sodium hydroxide, sulfuric acid, hydrochloric acid, boric acid, copper sulfate, potassium sulfate, methyl red, bromo-cresol green, methyl orange and calcium carbonate, obtained from Merck (Darmstadt, Germany).
2.3. Sample collection, acid digestion and determination of elements The samples of cultivation (organic and traditional) were obtained in several commercial points (fairs, farms and supermarkets) of Salvador, Bahia, Brazil. Triplicates of each sample were run for the determination of the total content of elements. About 2.0 g of the sample and 3.0 mL of 65% (w w-1) nitric acid were placed in a digest tube, then heated at 150 °C for 1 hour and 30 minutes on a digester block with a “cold finger” reflux system (Ferreira, Silva, de Santana, Silva Junior, Matos & dos Santos, 2013). Then, three times, in an interval of 30 minutes from each other, 1.0 mL of 30% (v v-1) hydrogen peroxide was added. The digest was then quantitatively transferred to centrifuge tubes and diluted with ultrapure water up to a final volume of 12.0 mL. A blank digest was carried 6
out in the same way as the samples. The multi-element determination of C, Ca, Cu, Fe, K, Mg, Mn, Na, P and Zn was carried out by the technique of inductively coupled plasma optical emission spectrometry (ICP OES).
2.4. Validation of the analytical method used for quantification of elements The accuracy of the method used for quantification of Ca, Cu, Fe, K, Mg, Mn, Na, P and Zn by ICP OES was confirmed by the analysis of certified reference material of apple leaves (NIST 1515) furnished by the National Institute of Standards and Technology (Gaithersburg, MD, USA). The procedure for analysis of the CRM was the same used for the samples of white pulp sweet potato roots.
2.5. Centesimal composition The centesimal composition of white pulp sweet potato root samples
was
determined by moisture, ash, protein, lipid and carbohydrate, according to the method described by the Adolfo Lutz Institute (2008). The moisture content was determined using the drying method in an oven at 105 °C to constant weight, and the determination of ash was carried out in a muffle heated up to 550 °C. For the quantification of protein, Kjeldahl used the factor of 6.25 for nitrogen conversion. For the lipid content, the Soxhlet method was used with ether solvent for extraction. The total carbohydrate content was calculated as the difference between 100 and the sum of the percentage of moisture, ash, lipid and protein.
3. Results and discussion
7
3.1. Evaluation of digestion procedures and validation of the analytical method by ICP OES A method of acid digestion and quantification by employing inductively coupled plasma optical emission spectrometry (ICP OES) was proposed to evaluate the content of C, Ca, Cu, Fe, K, Mg, Mn, Na, P and Zn in sweet potato samples. The residual carbon content (RCC) was in the range of 0.61 to 2.19% (m m-1) for the conventional cultivar and 0.46 to 2.23% (m m-1) for the organic cultivar, so the RCC values are considered low proving the efficiency decomposition in this study (Araújo, Gonzalez, Ferreira, Nogueira, & Nóbrega, 2002). The established analytical parameters are in the Table 1. The accuracy of the proposed method was confirmed by analysis of CRM NIST 1515 apple leaves, after performing the same digestion procedure proposed for sweet potato samples.
3.2. Evaluation of the results employing multivariate analysis techniques (PCA and HCA) The chemometric analysis of the auto-scaling results of 48 conventional and organic culture samples was performed by principal component analysis and hierarchical clustering analysis using the SPSS 24 and statistic 10 software. Before PCA, the adequacy of the data was evaluated by factorization. The Kaiser-Lawyer-Olkim measure of sampling adequacy was 0.71 above the critical level of 0.6. The Bartlet's sphericity test showed a Chi-square value equal to 182.4, with statistical significance p <0.001. Both tests indicated an appropriate matrix for PCA. The PCA analysis with 8 variables was reduced to three principal components with eigenvalues (3.73; 1.19 e 1.03) exceeding one were extracted, explaining 74.5 % of the total variance. The first principal component (PC1) represented 46.7 % and the next PC 14.9 % and 12.3 %, respectively. The communalities (variance proportion of each variable involved in the PC space) of every variable were found higher than 0.7, except for phosphorus (0.49). The 95 % 8
confidence interval ellipse was applied in PCA score plot, and despite the samples varying in growth type, samples were within the 95% confidence limit. In the figure of orthogonal vectors (PC1 x PC2), most of the coefficients have significant positive values in PC1, according to the linear combination of the loadings of the original variables PC1= 0.745Cu + 0.514Fe + 0.561 Mn + 0.736 Ca + 0.694K - 0.782 Mg - 0.811Na + 0.493P, which highlights copper, iron, manganese and calcium with high positive correlations . This shows that the organic potato samples projected on the right side of figure 1A and B have a predominance of these elements. However, Mg and Na have a positive expressive association, but are parameters with high levels in potato samples of conventional growth. The trend of separation of the samples is observed throughout PC1, evidencing that the samples of conventional culture have high contents (mg/100g) of Mg (18,2 - 254) and Na (50.7 - 98.3), while the organic ones showed Cu (0.0230 - 0.262), Ca (22.9 - 75.6), Fe (0.176-0.941), K (199 562), Mn (0.022 - 5.69) and P (40.8 - 86.5). The difference in nutrient content observed in the different cultivars can be attributed to the possible use of pesticides and insecticides in the conventional cultivar that can influence the absorption of soil nutrients by plants. Iron was the dominant variable in the second main component PC2 = 0.402Cu + 0.651Fe -0.443Mn -0.152Ca - 0.256K + 0.152Mg - 0.2771Na - 0.480P, indicating a high positive correlation with expressive value in this vector. This is confirmed in the chart of scores (Fig 1B), where the organic potato samples have high content of this nutrient. Manganese and potassium have a strong negative interrelationship in the third component PC3 = -0.137Cu + 0.133Fe + 0.581Mn + 0.447Ca - 0.558K + 0.336Mg - 0.116Na - 0.148P, displaying an inverse trend for the concentrations of these elements in the potato samples (figure 2 A and B). The results obtained are similar for the multivariate techniques used, HCA and PCA. The HCA was carried out using the Euclidian distance and complete linkage as measure of similarity, and the results were reported in a dendrogram figure 3 A and B. Considering a similarity at 7 % level (3a), all organic and 9
conventional potato samples were arranged into homogeneous groups, indicating that different types of growth can be differentiated based on the concentrations of the minerals. Both groups are subdivided into subgroups, characterizing different locations (Fig 3A). The position of the outlying samples (4OP1; 4OP2; 4OP3 and 7CP1; 7CP2; 7CP3) are worthy in Fig 3A. Fig 3B shows the hierarchic dendrogram that illustrates the similarity between the chemical parameters. These figures expose the presence of 2 groups corresponding to the mineral composition of the potato samples. The first group consists of the elements P, K, Ca, Mn, Fe and Cu, and the second group Na and Mg. Therefore, this may indicate a potential relationship between the origin of the samples and the groups of specific elements, which reflects the chemical composition of the different types of potato growth.
3.3. Evaluation of the mineral and centesimal composition of the sweet potato The average concentrations obtained demonstrate that sweet potato is an excellent source of minerals for feeding, as shown in Table 2. Organic cultivation samples presented the highest levels of the macro minerals Ca, K and P and the micro minerals Cu, Fe, Zn and Mn, with average values of 40.7, 381 and 62.2 mg/100g for Ca, K and P and 0.159, 0.481, 0.261, 1.15 mg/100g for Cu, Fe, Zn and Mn, respectively. The conventional cultivation presented the highest averages of the macro minerals as Mg and Na, with average values of 166 and 35.7 mg/100g of Mg and 68.6 and 0.433 mg/100g of Na for in the conventional and organic cultivars, respectively. Considering the data obtained for the centesimal composition samples of both cultivars did not show significant difference, with average values for conventional cultivars of 72%, 0.87%, 1.5%, 0.63%, and 24.8%, and for organic cultivars of 72%, 0.90%, 1.4%, 0.54%, 23.9% for moisture, ash, proteins, lipids and carbohydrates, respectively.
3.4. Comparing the concentrations of minerals 10
The comparison between the concentrations of minerals determined in this work with other vegetables showed that sweet potato has greater nutritional value in the macro minerals Mg, Na and P than carrot, okra and cabbage, and in K, Mg and Na than eggplant. Considering the micro minerals, sweet potato presented higher average contents of Cu and Mn than carrot, and similar contents of Fe than cabbage, as shown in Table 3.
4. Conclusion The developed method was promising to evaluate the sweet potato mineral content by ICP OES. The application of chemometric tools, such as PCA and HCA, showed the formation of two groups, separating the sweet potato from the organic cultivation and the conventional one. Samples of organic cultivars showed higher concentrations of minerals, such as Ca, Cu, Fe, K, Mg, Mn and P, suggesting that this is a good alternative for nutritional supplementation. However, the sodium content of the conventional culture presented higher levels, indicating alertness for hypertensive patients, although the Brazilian government establishes through the ANVISA nº 24/2010 resolution that a food rich in sodium is the one that contains an amount equal to 400 mg / 100g or greater. The centesimal composition in both cultivars presented no significant difference.
Acknowledgements The authors are grateful to Brazilian agencies PRONEX/Fundacão de Amparo à Pesquisa
do
Estado
da
Bahia
(FAPESB),
Conselho
Nacional
de
Desenvolvimento Científico e Tecnológico (CNPq) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for grants and fellowships.
11
Table 1. Analytical parameters of the method employed for determination of the chemical elements. LOD
Analyte
LOQ -1
mg100g
mg100g
-1
Certified valuesa
Obtained valuea
Ca
0.141
0.470
1.52 ± 0.015%
1.52 ± 0.153
Cu
0.012
0.0410
5.64 ± 0.24 µg/g
5.55 ± 0.5
Fe
0.026
0.0900
83 ± 5 µg/g
87 ± 4
K
0.040
0.130
1.61 ± 0.02 %
1.61 ± 0.19
Mg
0.870
2.91
0.271± 0.008 %
0.270 ± 0.017
Mn
0.002
0.005
54 ± 3 µg/g
51 ± 4
Na
0.252
0.840
24.4 ± 1.2 %
24.6 ± 0.740
P
0.067
0.222
0.159 ± 0.011 %
0.159 ± 0.001
a
Results of CRM of apple leaves NIST 1515 analyzed for method evaluation expressed as interval confidence at 95% level.
Table 2. Averages and ranges of concentrations of minerals in sweet potato of conventional and organic cultivars (in mg/100g). Minerals
Cultivars Conventional
Macro
Micro
Organic
average
range
average
range
Ca
23.5
16.8-34.2
40.7
22.9-75.6
K
197
85.6-500
381
199-562
Mg
166
18.2-254
35.7
19.9-55.8
Na
68. 6
50.7-98.3
0.433
0.050-1.29
P
54.1
19.4-68.7
62.2
40.8-86.5
Cu
0.082
0.027-0.156
0.159
0.023-0.262
Fe
0.303
0.122-0.522
0.481
0.176-0.941
Zn
0.197
0.045-0.297
0.261
0.154-0.405
Mn
0.183
0.018-0.486
1.15
0.022-5.69
Table 3. Macro and micro mineral nutrient content in different vegetables (expressed in mg/100g). Minerals
Sweet potato*
Carrot
Min-max
Ca
23.4
(16.8-34.2)
b
Okra
Min-max
40.6
(22.0-87.0)
c
Cabbage
d
Eggplant e Brinjal
Min-max
366
(273–528)
44.6
30.0
12
K
198
(85.6-500)
271
(146-678)
267
(211–353)
253
28.0
Mg
166
(18.2-254)
10.4
(4.91-21.3)
45.3
(34.6–64.2)
16
17.0
Na
68.5
(50.7-98.3)
35.5
(5.73-115.0)
18.3
(8.1–43.1)
11
17.0
P
54.1
(19.4-68.7)
30.4
(15.6-70.1)
44.5
(59.1–33.9)
46
n/a
Cu
0.082
(0.027-0.156)
0.044
(n/a-0.535)
n/a
n/a
n/a
0.190
Fe
0.303
(0.122-0.522)
0.395
(0.125-1.58)
n/a
n/a
0.3
2.00
Zn
0.197
(0.045-0.297)
0.569
(n/a- 1.89)
0.233
(0.08–0.429)
0.3
0.730
Mn
0.183
(0.018-0.486)
0.077
(n/a-0.939)
n/a
n/a
0.2
0.240
* This work (conventional) n/a: not available b (Krejcova, Navesnik, Jicinska & Cernohorsky, 2016) c (dos Santos, dos Santos, Barbosa, Lima, dos Santos & Matos, 2013) d (Anunciação, Leão, Jesus & Ferreira, 2011) e (Bangash, Arif, Khan, Rahman & Hussain, 2011)
13
Figure captions
Figure 1. A) Representation of the variables and samples potato of organic and conventional and B) Functions of the PC1 vs PC2. Figure 2. A) Representation of the variables and samples potato of organic and conventional and B) Functions of the PC1 vs PC3. Figure 3. A) Dendrogram of the organic and conventional potato samples and B) Dendrogram of the variables.
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Highlights
1 - A mineral and centesimal evaluation of sweet potatoes was performed. 2 - The results showed that organic samples showed high mineral content. 3 - Conventional culture samples showed high sodium content. 4 - Multivariate analysis proved to be a good tool to evaluate different forms of cultivation.
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