Determination of the Sodium Concentration in ...

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Determination of the Sodium Concentration in Brazilian Light and NonLight Powdered Instant Soups by Flame Photometry Barbara S. Martineza, Adriana P. de Oliveira*b, Francisca G. G. Pedrob, José Carlos de Oliveirab and Ricardo Dalla Villaa a

Department of Chemistry, Institute of Exact and Earth Sciences (ICET), Federal University of Mato Grosso (UFMT), Campus Cuiabá (UFMT), Cuiabá, Mato Grosso, Brazil; b Federal Institute of Education, Science and Technology of Mato Grosso (IFMT), Campus Cuiabá - Bela Vista, Cuiabá, Mato Grosso, Brazil Abstract: This work aimed to develop a method for sodium determination in Brazilian light and non-light powdered instant soups by flame photometry using the dry decomposition sample preparation. The analytical curve presented linear correlation coefficient (r) higher than 0.99. The limits of detection and quantification were 0.16 and 0.49 mg L-1 Na, respectively. The instrumental precision (n=10) was 3.0%. Recoveries of 97% were obtained in the addition and recovery tests, with relative standard deviations (RSD %) lower than 16%. The Na concentrations determined in the samples by the proposed method did not show significant differences (p 0.01) when compared with the results obtained by flame atomic absorption spectrometry. The simplicity, low cost, accuracy and precision suggest that the proposed method is an alternative for sodium determination in powdered instant soups. The results of this study also indicate that excess consumption of instant soup should be avoided, especially by individuals with hypertension because it can be a significant source of Na in the diet.

Keywords: FAES, food safety, sodium, soups. 1. INTRODUCTION Economic growth and urbanization have generated profound changes in food habits in the world’s population, causing an increase in access to processed and ready-to-eat foods. Snacks, instant food and fast food are growing in popularity over healthier diets rich in fruits and vegetables [1-3]. The high consumption of these foods by the world population has generated a high-sodium diet, because sodium (Na) is a food component that can be used as a preservative and flavoring in processed foods [4, 5]. Excess sodium intake can be related with high blood pressure, cardiac problems and others diseases [6-10]. In this context, health area workers in world have played important decisions in reduction of the sodium quantities in the diet and in processed foods [11, 13]. The average daily per capita intake of sodium in Brazil is 3.8 g, which is about 40% higher than the amount recommended by the World Health Organization (WHO) (2.3g) [14]. Recently, the Brazilian Ministry of Health and the Brazilian Association of Processed Food Producers signed a commitment to gradually reduce the level of sodium in foods by approximately 40% [15]. With an increasing need to control the Na concentration in foods, there is a growing requirement for suitable methods for the determination of this metal.

*Address correspondence to this author at the Federal Institute of Education, Science and Technology of Mato Grosso (IFMT), Campus Cuiabá - Bela Vista, Cuiabá, Mato Grosso, Brazil; Tel: ----------------; Fax: ----------------; E-mail: [email protected]

1573-4013/15 $58.00+.00

Cost-effective quality control of food products demands the development of analytical methods that are not only inexpensive, but also simple, precise, and accurate. At present, the determination of metals in foods is usually performed by inductively coupled plasma optical emission spectrometry (ICP-OES), flame atomic absorption spectrometry (FAAS) and graphite furnace atomic absorption spectrometry (GFAAS). These techniques generally provide low limits of detection and quantification, but have high operational and maintenance costs [16-18]. Conversely, flame atomic emission spectrometry (FAES) or flame photometry is the most simple and inexpensive spectroanalytical technique for the sodium determination in biological fluids, soils, fuels, and other matrices [19], and can also be a useful tool for the measurement of Na concentration in foods [20-23]. Based on this, this study aimed to develop a method for the determination of Na in different Brazilian powdered instant soups by FAES. 2. MATERIAL AND METHODS 2.1. Instrumentation A flame photometer, Analyser 910, was used for analyte determination. The measurements were carried out according to the producer’s recommendations. The aspiration rate was adjusted to 2.00 ± 0.2 mL min-1 of standard and samples. An analytical balance (±0.0001 g, Bel Marck 210A, Monza, Italy) was used for weighing the samples and in the fortification tests. In the addition and recovery tests, for the © 2015 Bentham Science Publishers

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Current Nutrition & Food Science, 2015, Vol. 11, No. 2

Martinez et al.

Table 1. Nutritional information (per portion) of the powdered instant soups evaluated in this work. Sample/Nutritional Information

A1 (non light)

A2 (light)

A3(non light)

A4(non light)

A5 (light)

Soup mass contained in each package (g)

22

14

19

22

14

Caloric value (kcal)

70

57

79

66

58

Carbohydrates (g)

11

12

14

8.5

12

Proteins (g)

1.7

1.4

1.1

1.3

1.6

Total fat (g)

1.9

0

2.2

2.8

0

Saturated fat (g)

0.9

0

1.0

1.6

0

Trans fat (g)

0

0

0

0

0

Dietary fiber (g)

0.9

0

0

0.8

0

Sodium (mg)

670

660

650

690

620

minor fortification level, an analytical balance was used with ±0.00001 g accuracy (Shimadzu AUW 220, Japan). The dry decomposition was performed on a muffle furnace (Quimis , Brazil). Micropipettes (Boeco, Germany) with adjustable volumes were used during the standards preparation. A Varian® model Spectra AA220 flame atomic absorption spectrometer and Na Varian® hollow cathode lamp (= 589 nm, current 5.0 mA, slit width 0.5 nm) were used for the comparison of the precision and accuracy of the proposed method with other analytical techniques. Acetylene (99.5%, White Martins, Rio de Janeiro, Brazil) and compressed air were used as the fuel and oxidant gas, respectively. 2.2. Reagents and Samples High purity deionized water (resistivity 18.2 μS cm-1, Millipore, USA) was used to prepare the analytical standards and samples. The standards were prepared by successive dilution of 1000 mg L-1aqueous Na stock solutions (Carlo Erba®, Italy). The fortifications were performed using sodium chlorite (purity 99.5%, Merck, Germany) addition. All flasks and glassware were cleaned with tap water, immersed in 1.0% (v:v) aqueous Alcaline Extran MA01 (Merck, Germany) for at least 24 h, rinsed with tap water, immersed in 7.0% (v/v) HNO3 aqueous solution for at least 24 h and washed thoroughly with deionized water. Five powdered instant soup samples were collected in a supermarket in Cuiabá city, Mato Grosso state, Brazil. Two light flavors (meat and chicken) and three non-light flavors (chicken and corn, arracacha with parsley and cheese with tomato and basil) were selected. The samples were identified as A1 (non-light chicken with corn flavor), A2 (light meat flavor), A3 (non-light arracacha with parsley flavor), A 4 (non-light cheese with tomato and basil flavor) and A5 (light chicken flavor). The Table 1 shows the nutritional information per portion of the samples. The powdered instant soup samples were classified as light and non light based on fat content. 2.3. Sample Preparation Procedure In order to ensure the homogeneity and the representativity, the samples were homogenized and divided into four parts and reduced to laboratory samples.

0.2500 g of each sample was weighed in porcelain crucibles and placed in a heating muffle furnace. The temperature was progressively elevated to 300oC and maintained for 8 h for organic matter elimination. After cooling, the resulting inorganic residues (ashes) were transferred to 25.00 mL volumetric flasks and filled with deionized water. This procedure was performed in triplicate (n = 3) and with an analytical blank. 2.4. Instrumental Parameters For the determination of the instrumental parameters, an analytical curve was made using the external standard method in the concentration range of 0.0–30.0 mg L-1 Na. The linearity was evaluated using the linear correlation coefficient (r) value [24]. The limits of detection (LOD) and quantification (LOQ) were calculated according to Currie (1999) [25]. The instrumental precision was assessed by ten sequential repeated measurements of sample 1 (A1). All measurements were performed in triplicate (n = 3) and included an analytical blank. 2.5. Assessment of the Precision and Accuracy of the Proposed Method The addition and recovery tests were performed by fortification of the sample A1 in three addition levels: 10.0 mg g-1, 15.0 mg g-1 and 20.0 mg g-1 Na. For this, 0.2500 g of the sample A1 was weighed in volumetric flask and NaCl masses previously calculated were added to obtain the final concentration for each fortification level. The fortified samples were allowed to rest for 24 h in order to guarantee interaction between the analyte and matrix. After this time, the dry decomposition was made as described in 2.3 items. All determinations were made in triplicates (n = 3), and were accompanied by blanks. The precision and accuracy were also evaluated by the comparison of the results by means different analytical techniques (FAAS). The ANOVA with the post-hoc T test (p < 0.01) was used to identify any significant differences among the samples. These procedures were performed using Assistat software version 7.7.

Determination of the Sodium Concentration in Brazilian Light


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Emission intensity (I)

50 INa= 0,6633 + 1,4373 [Na, mg L-1]

40

r = 0,99802 30 20 10 0 0

5

10

15

20

25

30

[Na, mg L-1] Fig. (1). Analytical curve for Na obtained in the concentration range of 0.0 –30.0 mg L-1 . Table 2.

Percentage of Na recuperation from spiked A1 sample (mean ± RSD%).

Sample Preparation

Dry decomposition

Addition Level (mg g-1)

Recovery (%) ± RSD %

10

97 ± 14

15

97 ± 14

20

97 ± 15

3. RESULTS AND DISCUSSIONS 3.1. Instrumental Parameters The analysis showed an r value higher than 0.99 for Na, indicating a linear correlation between the emission intensity and the Na concentration (Fig. 1) [26]. The LOD and LOQ were 0.16 and 0.49 mg L-1Na, respectively. The LOQ value was low enough for the quantification of Na in samples at concentrations up to 1.96 mg Na g-1. The instrumental precision was 3.0%. 3.2. Assessment of the Precision and Accuracy of the Proposed Method For all fortification levels, the recoveries were 97% with a RSD % less than 16% (Table 2). It should be noted that a wider spread of recovery and RSD values may be acceptable, depending on the purpose of the analysis, the complexity of the matrix, and the analytical method employed. Depending on the complexity of the matrix, the recovery interval can be extended to between 50 and 120%, with precision of ±16% [27]. The comparison of the Na determination in the five samples and also at the addition level of 15 mg g-1 (Table 3) using flame photometry and FAAS indicated that there was no

significant difference (p 0.01) in results obtained using different analytical techniques [28]. Sodium concentrations found in the samples ranging from 26.8 to 43.7 mg g-1 with RSD less than 15%. The results obtained by proposed method were also compared with the value labeled (Table 3), which was established as a true value, and no verified significant difference (p 0.01) [28]. Ferreira, et al., (2004) determined the sodium content by Flow injection and sequential FAES in instant soup and the value found was of 61 ± 0.54 mg g-1 [29]. Krejcová et al. (2005) determined the sodium concentration in instant soups, soup base cubes and seasoning mixtures by ICP–OES, and concentrations ranging from 65.4 to 264 mg kg-1 with RSD less than 19% [16]. The flame photometry is considered an instrumental analytical technique simple and inexpensive to determine Li, Na, K and Ca in different types of samples, due to no use of sophisticated instrumental features such as specific nebulizers, radiation sources and reagents and gases high purity, In addition, for the determination of Na, K, Li and Ca, the technique has a suitable analytical performance when compared to other techniques [19]. The comparison analysis costs per sample performed by different analytical techniques are difficult, given the diversity of models / equipment brands and prices consumables available in the market. However, it is estimated that the use of flame photometry can reduce from 50 to 80% for the sample analysis costs when compared with FAAS and ICP-OES. According to the WHO, the recommended daily ingestion of sodium is 2.0 g. The consumption of two envelopes instant soup powder per day corresponds to approximately one half the maximum allowed amount of sodium daily for a healthy individual. In this context, it is worth highlighting that the majority of processed and unprocessed foods consumed by the population contain sodium. In this manner,

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Table 3.

Martinez et al.

Comparison of the Na determination in the samples and addition level of 15 mg g-1 (n=3) using flame photometry, FAAS and label. Na Concentration (mg g-1) ± RSD% Sample/Addition Level FAES

FAAS

26.8 ± 1.0a

21.7 ± 3.0a

43.7 ± 3.5a

36.7 ± 6.1a

A3(non light)

37.4 ± 6.8a

28.7 ± 8.7a

35.6

A4(non light)

28.9 ± 14.7a

23.5 ± 15.0a

29.4

A5(light)

43.3 ± 11.1a

37.4 ± 20.0a

45

16.0 ± 14.3a

13.1 ± 16.2a

A1(non light) A2(light)

Label

29

15 mg g-1

45

-

Values followed by the same letter (a, b, c, or d) in the same line indicate no significant difference between the samples at the 1% confidence level.

persons who include in their daily diet prepared ready-to-eat foods, such as powdered soups, can consume a sodium concentration above the values allowed by the WHO [14], which can result in serious health issues [6-10, 14].

[4] [5] [6]

CONCLUSION The results of this work indicate that the flame photometry is an effortless, fast and low-cost technique for Na determination in light and non-light powered instant soups. The addition and recovery tests, as well as the instrumental parameters evaluated, indicate that the proposed method is adequate to meet necessities for the food control. The results of this study indicate that excess consumption of instant soup should be avoided, especially by individuals with hypertension because it can be a significant source of Na. It was also observed that light soup had a greater sodium concentration than non-light soup. Thus, the term “light” should be better specified to avoid confusion in people who require special diets. CONFLICT OF INTEREST

[7] [8]

[9]

[10] [11] [12]

[13]

The authors confirm that they have no conflict of interests with respect to this manuscript.

[14]

ACKNOWLEDGEMENTS

[15]

The authors thanks the Laboratório de Análises de Contaminantes Inorgânicos (LACI) of the Universidade Federal de Mato Grosso.

[16]

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Received: January 30, 2015

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Revised: March 27, 2015

Accepted: April 15, 2015