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Characterization of Natural Orange Juices Employing Physicochemical Properties and FTIR Spectroscopy: A Study with the Storage Time

Laura Cecilia Bichara1, Hernán Enrique Lanús2, María Jimena Márquez1 and Silvia Antonia Brandán1*

1Cátedra de Química General, Facultad de Bioquímica, Química y Farmacia, Universidad Nacional de Tucumán, Ayacucho 471, 4000, San Miguel de Tucumán. Tucumán, Argentina

2Cátedra de Fisicoquímica I, Instituto de Química Física, Facultad de Bioquímica, Química y Farmacia, Universidad Nacional de Tucumán, San Lorenzo 456, T4000CAN, S. M. de Tucumán, Argentina

*Corresponding Author:
Silvia Antonia Brandán
Cátedra de Química General. Facultad de Bioquímica
Química y Farmacia, Universidad Nacional de Tucumán
Ayacucho 471, 4000, San Miguel de Tucumán.
Tucumán, Argentina
E-mail: sbrandan@fbqf.unt.edu.ar

Received date: 28/08/2015 Accepted date: 08/09/2015 Published date: 15/09/2015

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Abstract

In this work, the physicochemical properties and the infrared spectra of three different natural orange juices derived from the sour orange (Citrus aurantium), the common orange (Citrus bigardia Riss) and the sweet orange (Citrus sinensis) varieties, named A, C, and D respectively were studied at room temperature with the storage days during the 92 days. The physicochemical properties studied were the pH, refractive index, density, conductivity and the quantity of total soluble solids expressed as degree Brix. The natural A and C juices show a great quantity of bands attributed principally to the ascorbic and citric acid while the natural D juice evidence a higher content of bands associated with sucrose. The assignments of the bands observed in the infrared spectra of the natural A, C and D varieties in the 4000-400 cm-1 region was proposed. From the three natural studied juices, the D juice is the most instable with the time, as evidenced by the Infrared (IR) spectra and the physicochemical properties.

Keywords

Natural orange juices, Density, Refractive index, Soluble solids, Infrared spectrum

Introduction

The orange juices are of great importance in nutrition because they are sources of nutrients, such as vitamins C, B6, B9, proteins and minerals calcium, potassium and Mg, among other [1-3]. For this reason, the quality of these beverages should be permanently controlled and directed toward the safety and human health protection since the adulteration represents a serious problem actual [4,5]. From recent times, the Fourier Transform Infrared (FT-IR) spectroscopy is a rapid technique used to control falsifications in the final products [6-11] and, also as an alternative for the classification of orange varieties, as reported by Suphamitmongkol [12]. In this work, we have considered only the references of some recent papers taking into account the great diversity of related studies [1-12]. Industrially, the acid content in a natural juice is one of the important quality attributes in the orange fruit, being the ascorbic and citric acids the main organic acid components [2,13,14]. On the other hand, from the four varieties of oranges known, the bitter (sour) orange (Citrus aurantium), the sweet orange (Citrus sinensis), and the common orange (Citrus bigardia Riss), the most important for juice production is the sweet orange in its four varieties, namely the common orange, the acidless orange, the pigmented orange, and the navel orange [2]. Industrially, there is a significant difference between the commercial and natural orange juices because the pasteurization process in the commercial juices is very important for food safety and quality requirement previous to packaging and distribution while a fresh juice is highly susceptible to contamination and, for this reason, it should be consumed quickly [3]. The recent spectroscopic studies [15-20] reported for the ascorbic and citric acids and sucrose have permitted their vibrational assignments and their quick identifications by using Fourier Transform Infrared (FT-IR) and Raman spectroscopies. Consequently, the constituents of major proportion in an orange juice can be easily identified by using IR spectroscopy. Thus, recent studies on model orange juices combining the Fourier Transform Infrared (FT-IR) spectra with physicochemical properties at room temperature with the storage time were reported by Bichara [21]. Hence, these authors have performed the assignments of the bands observed in the spectra of aqueous solutions of sucrose containing ascorbic (AA) and citric acids (CA) in different concentrations together with the study of their physicochemical properties [21]. These results are very important taking into account that the mixtures simulate diluted model orange juices. So far, for a fresh orange juice there are no experimental Infrared (IR) studies related to their main components in the 4000-400 cm-1 region combined with studies on their physicochemical properties during a storage time of 92 days. The changes performed in the Infrared (IR) spectra and in the physicochemical properties of the three natural juices with the storage days are of importance for known the stability of the different natural juices in relation to the diverse orange varieties and to the identification of its main components taking into account that they are the fruit juices of high consumption in many countries. Moreover, to know the profile of the infrared spectra of natural juices during the storage time is of importance to detect adulteration in these juices. For these reasons, the goal of this work is the characterization of three natural orange juices derived from the sour orange (Citrus aurantium), the common orange (Citrus bigardia Riss) and the sweet orange (Citrus sinensis) varieties by using Fourier Transform Infrared (FTIR) spectroscopy and some physicochemical properties simultaneously at room temperature in order to observe the modifications performed by the storage time during the 92 days. Then, the results for the three natural juices are compared with results obtained for model juices of different concentrations [21]. Here, the pH, refractive index, density, conductivity and the quantity of total soluble solids expressed as degree Brix are the physicochemical properties evaluated at room temperature.

Material And MethodS

Natural Orange Juices

Three natural orange juices were prepared from fresh oranges obtained from different cultivars of San Miguel de Tucumán (Argentine) and of the sour orange (Citrus aurantium), the common orange (Citrus bigardia Riss) and the sweet orange (C. sinensis) varieties, named A, C, and D respectively. The compositions of these varieties of juices expressed as total solids, total sugars, acidity, and pectin contents of oranges were taken [3] and they can be seen in Table S1 while in Table 1 are presented the composition for a sweet orange juice according to Sandhu [3]. Here, these juices were used after of their manual extraction and, then their Fourier Transform Infrared (FTIR) spectra and physicochemical properties at room temperature were studied with the storage time during the 92 days. In all this study the juices were maintained free of the light and the heat.

Valor nutricional por cada 100 g (citrus sinensis)
Energía 50 Kcal. 200 kJ
Carbohidratos 11.57 g Vitamina B6 0.060 mg (5%)
Azúcares 9.35 g Ácido fólico (Vit. B9) 30 µg (8%)
Fibra alimentaria 2.4 g Vitamina B12 0 µg (0%)
Grasas 0.12 g Vitamina C 53.2 mg (89%)
saturadas 0.015 g Vitamina D 0 µg (0%)
monoinsaturadas 0.023 g Vitamina E 0.18 mg (1%)
poliinsaturadas 0.025 g Vitamina K 0 µg (0%)
Proteínas 0.94 g Calcio 40 mg (4%)
Agua 86.75 g Hierro 0.10 mg (1%)
Vitamina A 11 µg (1%) Magnesio 10 mg (3%)
β-caroteno 71 µg (1%) Manganeso 0.025 mg (1%)
Tiamina (Vit. B1) 0.087 mg (7%) Fósforo 14 mg (2%)
Riboflavina (Vit. B2) 0.040 mg (3%) Potasio 181 mg (4%)
Niacina (Vit. B3) 0.282 mg (2%) Sodio 0 mg (0%)
Ácido pantoténico (B5) 0.250 mg (5%) Zinc 0.67 mg (7%)

Table 1. Composition of a sweet orange juice (Citrus sinensis) [3].

Natural orange juices
Variety Total Solids, % Total Sugars, % Acidityc Pectin, %d
C Orange (bitter)
Edible portion 13.59 5.49 3.30 0.86
Peel and pith 27.27 5.86 0.46 0.89
Juice 10.72 5.74 3.77  
D Orange (sweet)
Edible portion 12.98 7.88 0.79 0.59
Peel and pith 25.52 6.81 0.27  
Juice 11.09 8.47 1.17 0.13

Table S1. Total Solids, Total Sugars, Acidity, and Pectin Contents of Orangesa,b.

Physicochemical Properties

The equipments used in the determinations of pH, refractive index, density, conductivity and the quantity of total soluble solids expressed as degree Brix for the three natural orange juices at 25 ºC were reported in an above paper [21].

Infrared Spectra

The infrared (IR) spectra of the natural orange juices were recorded between Silver Chloride (AgCl) windows from 4000 to 400 cm-1. FTIR GX1 Perkin Elmer spectrometer, equipped with Raman accessory and a Deuterated Triglycerine Sulfate (DTGS) detector cooled at liquid nitrogen temperature was used for all measurements. All spectra were recorded with a resolution of 1 cm-1 and 60 scans.

Results And Discussion

Physicochemical Properties

Densities (d): Table 2 summarizes the studied physicochemical properties for the three natural orange juices at 25 ºC with the storage time while Figure 1 show the density variations with the time for the three juices. The comparisons with commercial orange juices and with model orange juices are shown in Figure S1 (Supporting information). Note that the graphics for the A, C and D juices show clearly different behaviors on the densities in function of the time. Thus, it is important to observe for D a similar variation with the time than the commercial juices, it is a decrease quick in the density values from the first up to the 7 days. Later, an increase immediate in the density up to a maximum value in the 15 days continued with a decrease up to the 92 days is observed. On the contrary, the densities of the A and C juices increase slightly up to the 7 days, being higher the variation of C than A while the values decrease fast for C up to the 15 days but in lower proportion than A. When these variations are compared with those graphics studied for the commercial and model juices by Bichara [21], as observed in Figure S1a, we observed that: (i) the density of the D juice have a similar behaviour with the time than the commercial C2 juice up to the 30 days changing drastically the values up to the 92 days in similar form than B1, (ii) the density values for the A juice present a behavior similar to the model juices being more quick the variation from the 30 days than the other ones and, (iii) the sweet oranges C and D evidence different behaviour of the density with the storage time. The commercial C2 juice is constituted by higher quantity of orange juices, has a higher proportion of ascorbic acid and, besides no present conserving agent while, the natural D juice has an acidity lower but a higher content of total sugars. Probably, the difference between the natural D and the commercial C2 juice from the 30 days is justified in part by the presence of other components, such as proteins and vitamins. On the other hand, in the components of the model juices, these are ascorbic acid, citric acid and sucrose, sucrose have (Figure S1b) a higher proportion (2.5% of ascorbic acid, 2.5% of citric acid, 10% of sucrose and 85% of water) where the solution 1 is the more concentrated. A very important observation is that the behaviour of the density in A (sour orange) is similar to the model juice which has the highest proportion of sucrose while the behaviour of D is similar to a commercial juice. Thus, perhaps the similitude for these juices justifies the variations observed in the densities with the storage time because the density is a property depends on the volume.

A
T (days) d (g/cm3) pH k(mS/cm) n 25°C ºBrix
0 1.03640 3.97 2.410 1.3462 9.0
7 1.03670 4.15 2.410 1.3464 9.1
14 1.04690 4.11 2.650 1.3462 9.0
31 1.03020 4.06 3.230 1.3450 8.2
92 0.99870 4.12 3.150 1.3430 6.8
B1
0 1.04270 3.24 1.832 1.3480 10.0
7 1.04455 3.45 1.910 1.3480 10.2
14 1.05330 3.49 2.000 1.3484 10.3
31 1.02360 3.55 2.140 1.3432 7.0
92 1.00050 3.67 1.950 1.3386 3.8
B2
0 1.02050 3.21 1.976 1.3460 5.1
7 1.02249 3.14 1.990 1.3406 5.3
14 1.03450 3.45 2.200 1.3406 5.3
31 1.01670 3.49 2.240 1.3384 3.7
92 1.00980 3.86 2.060 1.3364 2.4
C1
0 1.05320 3.61 2.240 1.3520 12.6
7 1.05455 3.79 2.410 1.3522 12.8
14 1.06960 3.81 2.650 1.3518 12.5
31 1.04100 3.86 2.520 1.3494 11.0
92 1.00310 4.14 2.700 1.3412 5.6
C2
0 1.04580 3.32 2.60 1.3486 10.5
7 1.04205 3.59 2.74 1.3492 10.8
14 1.06690 3.61 2.31 1.3486 10.5
31 1.02820 3.67 3.02 1.3450 8.2
92 1.02672 3.84 2.81 1.3450 8.2

Table 2. Physicochemical properties of commercial orange juices with the storage time.

food-and-dairy-technology-density-against-time

Figure 1: Variation of density against time, for the natural A, C and D juices at 25 °C.

food-and-dairy-technology-Variation-density-against-time

Figure S1. Variation of density against time, for (a) the commercial A, B1, B2, C1 and C2 juices and, (b) model 1, 2, 3 and 4 juices at 25 °C [21,22].

Conductivities (k): Figure 2 shows the conductivity values for the three studied natural juices at 25ºC against at the storage time during the 92 days. There are differences notable in the values during the studied time, thus, in the first 15 days the conductivity values increase for D while for A and C decrease in the first 7 days and later increase up to the 15 days. For A and D, after the 15 days and up to the 92 days the conductivities of both juices decrease with the time while only for C an increase in the values is observed between 15 and 92 days, as showed in Figure 2. When these natural juices are compared with the conductivity values corresponding to the commercial and model juices, studied [21] and presented in Figures S2a and S2b, the behaviors show similitude and differences among them. Hence, in the first 15 days the variations for A and C are similar to the commercial B2 juice; it is the values decrease to the 7 days and then increase up to the 15 days. For D, the behaviour of the conductivity is similar to the remains commercial juices up to the 30 days and, then, the values decrease for A and D up to the 92 days. The increase in the conductivity values could be related in part to the presence of H+, OH-, ascorbate and citrate ions in the medium and to the A2- species derived from the ascorbic acid decomposition, in similar form to the more diluted model juice, because in aqueous medium the decomposition process is accelerated. Whereas, the decrease in the conductivity could be justified by the presence of the A and A2 species derived from the decomposition of the ascorbic acid and, also to the di-hydrate and penta-hydrate sucrose formation, as reported by Max and Chapados [22]. Here, the similitude between A, C and the commercial B2 juice are attributed to a higher quantity of ascorbic acid while the D juice has a higher quantity of soluble solid, as indicated in Tables 1 and 2. This way, the formation of H bonds and sugar in aqueous solution justifies the presence of higher neutral species that diminishing the conductivity.

food-and-dairy-technology-conductivity-against-time

Figure 2. Variation of conductivity against time, for the natural A, C and D juices at 25 °C.

food-and-dairy-technology-Variation-conductivity-against-time

Figure S2. Variation of conductivity against concentration, for (a) the commercial A, B1, B2, C1 and C2 juices and, (b) model 1, 2, 3 and 4 juices at 25 °C [21,22].

Values pH: Figure 3 shows the pH variations for the natural juices at 25ºC versus the storage time during 92 days while the values obtained for the three juices can be observed in Table 2. Initially, the natural A and C juices present similar behaviors with the time up to the 30 days and, later, the values for A increase with the time but remain practically constant for C. As it is expected and as observed in Table 1, the C juice product of an orange bitter has lower pH values and, for this, it has the higher acidity than A and D in spite the value of the acidity expressed as 0.1N per 100 g is 3.77 different from D whose values is 1.17, as observed in Table S1. On the contrary, the variation of the pH with the storage time for D is different from A and C up to the 15 days and, then the values increase from the 15 to 92 days showing a medium acidity between A and C. When these natural juices are compared with the commercial juices we observed in the A and C juices behaviours similar to the commercial A, B1, C1 and C2 juices up to the 30 days and, later, the values increase strongly for A but remain practically constant for C (Figure S3a). While the behaviour of the pH values of D in the first 15 days is similar to the commercial B2 juice. On the other hand, when the natural juices are compared with the model juices the variation of the pH with the storage time for D are similar to the more concentrated solutions 1, 2 and 3 (Figure S3b). Possibly, this decrease in the pH values during the first 15 days are associated with a higher acid concentration, as in the model juices cases. The presence of other components in the natural juices could be justifying the low acidity of these juices than the model ones. Figure S3a show clearly the decrease in the pH values with the storage time for B2. Probably, the presence of the ascorbic acid, citric acid and sucrose support the variations in the pH values for B2 and the juices model. These results justify the increase in the conductivity in the aqueous medium and the decreasing in the pH values due to the acid species. These results agree with those obtained by means of conductivity values.

food-and-dairy-technology-pH-against-time

Figure 3. Variation of pH against time, for the natural A, C and D juices at 25 °C.

food-and-dairy-technology-pH-against-concentration

Figure S3. Variation of pH against concentration, for (a) the commercial A, B1, B2, C1 and C2 juices and, (b) model 1, 2, 3 and 4 juices at 25 °C [ 21,22].

Refractive index (n): The graphics of the refractive index for the natural A, C and D juices against to the storage time during 92 days at 25ºC are presented in Figure 4 while the comparisons with commercial and model juices can be observed in Figure S4. First, the behaviour of n versus the time are different in the three juices, presenting the more important modifications the C juice. Thus, for this juice n decreases significantly with the time from the first up to the 15 days and then the values increase until the 30 days and, from here diminish newly the values up to the 92 days. The A and D juices, both products of sweet oranges, present minima to the 7 days while both present maxima in different times, A has a maximum approximately at the 20 days while D to the 15 days. The results show clear differences in the compositions of both juices. This way, when the three juices are compared with the commercial and model juices, presented in Figure S4, A and D show behaviours similar to the commercial juices while for C, the variation of n with the time is similar to the commercial B2 and to the most diluted solution of the model juices. Probably the low quantity of soluble solids in the commercial B2 justifies such variations because the solution 4, which is the most diluted solution of the model juices, shows drastically lower proportion of ascorbic acid, citric acid and sucrose during the storage time than solution 1, 2 and 3. Thus, C is the natural juice with lower values of n while A show strong decreasing of n with the time.

food-and-dairy-technology-refractive-indexes-against

Figure 4. Variation of refractive indexes against time, for the natural A, C and D juices at 25 °C.

food-and-dairy-technology-Variation-refractive-indexes-against

Figure S4. Variation of refractive index against concentration, for (a) the commercial A, B1, B2, C1 and C2 juices and, (b) model 1, 2, 3 and 4 juices at 25 °C [21,22].

Quantity of soluble solid (ºBrix): In this work, the quantity of total soluble solids for the three natural juices was expressed as degree Brix and studied at 25ºC against at storage time during 92 days, as can be seen in Figure 5. On the other hand, the graphics for the natural juices were compared with those corresponding to different commercial and model oranges juices (Figure S5). Note that the behaviours of the soluble solids for the three juices are similar to the variations of n by the time, given in Figure 4, a result different from those obtained for the commercial juices (Figure S5a). A very important result for the D juice is observed in the ºBrix values due to that it has a higher quantity of soluble solid than A and C, as decrypted in Table S1. Probably, the low quantity of soluble solids in C can be justified in part by the ascorbic acid decomposition because it juice has low pH values and, for this, lower acidity than A and D. Moreover, these latter juices have behaviours similar than the commercial juices showing A and D decrease quick of the soluble solid with the time, being it more notable in A. Thus, the three juices after about 30 days show different slopes, as observed in Figure 5.

food-and-dairy-technology-Variation-soluble-solids

Figure 5. Variation of the soluble solids (°Brix) against time, for the natural A, C and D juices at 25 °C [21,22].

food-and-dairy-technology-Variation-soluble-solids-against

Figure S5. Variation of soluble solids (°Brix) against concentration, for (a) the commercial A, B1, B2, C1 and C2 juices and, (b) model 1, 2, 3 and 4 juices at 25 °C [21,22].

Infrared Spectra: Figure 6 shows the variations of the IR spectra of the natural A, C and D juices recorded on the first day compared with the corresponding to the mixture of ascorbic and citric acids and sucrose (model juice) in solid phase while from Figures 7-9 show the variations of each spectrum with the storage time. The observed wavenumbers and the assignments for the natural orange juices studied compared with the bands observed in the more concentrated juice model can be seen in Table 3. Figure S6 shows clearly the differences among the spectra for the A, C and D natural juices, in the form, positions and intensities of the bands observed while in the Figures S7-S9 it is possible to observe the comparisons with the Infrared (IR) spectra for ascorbic acid, citric acid and sucrose. Note that Figure S7 shows for the A juice a higher proportion of the ascorbic and citric acids than C and D while a high content of sucrose is expected in the D juice, as can be seen in Figure S9, and as expected because it juice is of sweet orange.

A (sour orange)
T (days) d (g/cm3) pH n 25°C ºBrix k (mS/cm)
0 1.0374 3.84 1.3462 9.60 4.42
7 1.0391 4.24 1.3448 8.00 4.25
14 1.0365 4.38 1.3448 8.00 5.35
31 1.0326 4.34 1.3444 7.80 5.13
92 1.0090 5.64 1.3380 3.50 4.91
C (common orange)
0 1.0383 2.92 1.3458 8.50 5.1
7 1.0405 3.20 1.3452 8.30 4.91
14 1.0179 3.32 1.3400 4.58 5.47
31 1.0153 3.40 1.3408 5.30 5.55
92 1.0085 3.46 1.3390 4.00 6.1
D (sweet orange)
0 1.0421 6.13 1.3492 11.00 4.75
7 1.0289 4.38 1.3484 10.50 5.06
14 1.0516 4.23 1.3482 10.30 5.64
31 1.0186 4.23 1.3462 8.90 5.55
92 1.0008 4.86 1.3418 6.00 5.14

Table 3. Physicochemical properties of natural orange juices with the storage time.

food-and-dairy-technology-Infrared-spectra

Figure 6. Comparisons of the Infrared spectra of the model juice in solid phase with those corresponding to the natural A, C and D juices at 25 °C.

food-and-dairy-technology-Infrared-spectra-natural-A

Figure S6. Infrared spectra of the natural A juice 1 at the first day (upper), for C (medium), and for D (bottom).

food-and-dairy-technology-Comparisons-Infrared-spectra

Figure 7. Comparisons of the Infrared spectra of the natural A with the storage time at 25 °C.

food-and-dairy-technology-Infrared-spectrum

Figure S7. Infrared spectrum for the natural A compared with the corresponding to ascorbic acid, citric acid and sucrose.

food-and-dairy-technology-Infrared-spectra-natural

Figure 8. Comparisons of the Infrared spectra of the natural C with the storage time at 25 °C.

food-and-dairy-technology-corresponding-ascorbic-acid

Figure S8. Infrared spectrum for the natural C compared with the corresponding to ascorbic acid, citric acid and sucrose.

food-and-dairy-technology-Comparisons-Infrared-spectra-natural

Figure 9. Comparisons of the Infrared spectra of the natural D with the storage time at 25 °C.

food-and-dairy-technology-citric-acid-sucrose

Figure S9. Infrared spectrum for the natural D compared with the corresponding to ascorbic acid, citric acid and sucrose.

Natural Orange A Juices: The Infrared (IR) spectra for this juice recorded each week from the first day can be seen in Figure 7. It is important to note the different variations that experiment this juice with the storage days especially during the 7 and 31 days, as observed in the physicochemical studies. The numbers of bands increase notably in this two week as a consequence of the decomposition products of ascorbic and citric acids and for this reason, increase the density and the pH in both times while decrease the conductivity. The broad Infrared (IR) bands at 3402 and 1654 cm-1 are strongly related with the presence of those two acids, as shown in Figure S7. The first band is assigned to the expected OH stretching modes of both acids while the band at 1654 cm-1 is assigned simultaneously to the C=O stretching mode of the ascorbic acid and to the OH deformation modes corresponding to the water molecules [17,18,20].

Natural Orange C Juice: Table 4 shows that the positions of the bands associated with the OH stretching and deformation modes for this juice are located at 3416 and 1650 cm-1, respectively. In Figure S8 can be seen the higher presence of acids in C and, for this juice, as for A, the more important variations are also observed at the 7 and 31 days, as shown in the different spectra of Figure 8. The probable formed species are those derived from of ascorbic acid which are the un-oxidized H2A, the HA- and A2- anions, the oxidized A and dimeric A2 forms, in accordance with reported data [17,18,20]. The increasing of the density and in the pH values and the decreasing in the conductivity, n and ºBrix values the 7 days justified the modifications in the bands observed in the IR spectrum fro this juice.

Ascorbic acid (H2A)a Citric acidb Sucrosec Mixtured Natural orange juicese
IR,Raman Assignment IR,Raman Assignment IR,Raman Assignmentc IR Solid IR Solut A C D
3523s nO-H (H2A), HA-, A2-, A) 3535 n O-H 3564 m n(O-H)w 3565 3538 vs,br 3642
3498 n O-H 3469 sh n O-H 3525
3409 vs nO-H (H2A), HA-, A) 3394 s n O-H 3412 3402 3416 3392
3316 s nO-H (H2A), HA-) 3350 n O-H 3337 s n O-H 3389 3302 vs.br
3247 n O-H 3257 sh n O-H 3322
3217 m nO-H (H2A)) 3132 m naCH2 3226 3087 vs,br 3249 3266
3030 s nO-H (H2A)) 3035 naCH2 op 3052 sh nC-H 3034 3044
3002 m naCH2 (H2A)), nC-H (A) 2994 naCH2 op 2993 w naCH2 2997
2978 m na CH2 (H2A)) 2975 naCH2 ip 2970 w naCH2 2971
2960 w na CH2 (A2-, A) 2961 w nsCH2 op 2958 sh nC-H 2958
2944 m nC-H (H2A)), na CH2 (HA-) 2933 w nO-H 2943 m nsCH2 2944 2945 sh 2940
2916 m nC-H (H2A), HA-), ns CH2 (H2A)) 2916 m nC-H 2915
2903 vs nC-H (H2A), HA-), ns CH2 (H2A), A2-, A) 2902 m nsCH2 2984 sh 2894
2854 w nO-H(H2A)),nsCH2(HA-)nC-H(H2A),HA-,A2-,A) 2849 sh 2859
2737 w nC-H (A2-) 2763 sh
2641 sh nO-H (A2-) 2650 sh
1753 m n C=O (H2A), HA-, A2-, A) 1756 vs nsC=O1 1733 w dH2O 1757
1708 vs naC=O3 1714 w dH2O 1709
1672 s n C=C (H2A)), dCOH (A2-), 1662 vw dH2O 1674 1677 vs
1667 vs n C=C (HA-),n C=O (A), d  CH2 dim(H2A)) 1698 sh nsC=O3 1648 s dH2O 1654 1645 1650
1538 vw n(C-C) 1546 1573
1525 vw dCH2
1517 vw dCH2
1495b m nC-Cdim (H2A)),wagCH2 (HA-), d CH2(H2A), A) 1493 vs dsCOH 1496 vw wagCH2 1502 1503
1459 m wagCH2 (H2A)), dCH2 (H2A), HA-, A2-) 1469 w naC-C2 1463 w rC-H 1465 1455 sh 1459 1460 1459
1438 sh dCOH(HA-),wagCH2(A),dHOC(H2A)),nC-C(H2A)) 1430 m nC-C, dCH2 ip 1432 w wagCH2 1432 1431
1426 w t(O---H),twH2O(2) 1428 s 1422 1421
1413 sh t(O---H),twH2O(2) 1419
1399 sh rC-H 1392
1387 w wag CH2 (H2A)) 1389 m daCOH, wagCH2op 1388 w d(O-H),r’(C-H) 1380
1363 sh dCOH (HA-), wagCH2 (A2-), dOCH (A) 1365 w wag CH2 ip 1365 m t(O---H),twH2O(2) 1366 1365 1363 1368
1353 m dCOH (H2A), HA-, A2-, A), d CCO (H2A)) 1358 w rCH2 ip 1354 sh rC-H 1347 w
1344 vw dCCH(H2A),HA-,A2-),dOCH (A) dCOH(H2A),HA-) 1340 sh ds COH 1348 m rC-H 1343
1321 m dCOH (H2A)), dCCH (HA-) 1325 vw ds COH 1325 m rCH2 d(O- H) 1323 1323 sh
1302 sh rCH2 (H2A), HA-), d OCH (A2-)n C-O (H2A)), 1308 w wagCH2 ip,daCOH 1302 w r’(C-H) 1306 1318 1320 1315
 tw CC2 (H2A))
1292 w rCH2 ip, wagCH2 ip 1293 w rC-H 1292
1274 s dOCH (HA-,A2-,A),rCH2 (A), wagCH2 (HA-), 1271 w dO-H 1276 1265 sh 1275 1280
dCOH(H2A)),dCCH(H2A))
1246 m dCOH (H2A)), rCH2 dim (H2A)), dOCH (HA-), 1242 m nsC-O 1241 m dO-H 1246 1253 1257
 rCH2 (A2-, HA-)
1233 m 1240 1242 1245
1221 w twCC2 (H2A)), d OCH (A2-),dCOH(A) 1214 m rCH2 ip 1212 w dO-H 1227
1197 w dCOH (H2A), HA-), n C-C (HA-, A2-), 1191 vw dO-H 1200 1192 1192
tw CC2 (H2A), A)
1174 s n C-O 1172 m dO-H 1177
1163 m nC-O 1152 m 1162
1139 m twCC2 (HA-, A2-), n C-O (H2A), A), n C-C (H2A)) 1140 s nC-O 1141 m nC-O 1140 1140 1138 1139
1130 s nC-O
1120 nC-O (H2A)), d COH (H2A)) 1126 m nC-O 1120
1112 s nC-C (HA-, A),n C-C (A2-) 1115 m nC-O 1112 1110 1110
1105 s nC-O 1107 w
1074b m nC-O (H2A), HA-, A2-, A) 1081 w daCOH 1074 m nC-O 1071 1079 sh 1080 1084 1078
1065b m nC-O (H2A)), n C-C (H2A)), tw CH2 (A2-) 1069 vs nC-O 1070
1053 m nC-C 1055 s nC-O 1054 1061 1065 1060
1046 sh nC-O (H2A), HA-, A2-, A) 1042 sh twH2O(2),t(O---H)
1036 sh wagCH2 op,twCH2 op 1039 s 1033 1034 1040
1026 vs nC-C (HA-), n C-O (H2A), A) 1022 w nC-C 1028
1015 m twH2O(2),t(O---H) 1015 1013 1015
1004 m nC-O
990 m nC-O (HA-, A2-),n C-C (H2A), HA-, A)bC=O (A) 994 s nC-O 991 998 sh 995 996 999
966 vw ns C-C2 966 sh nC-O 945 963 966
945 w ns C-C1 946 w tR1(A6) 922 925 w 920 920 928
924 vw twCH2 (H2A), A) t (OH) (A2-),n C-C (HA-) 914 sh twCH2 op 912 908
904 w twCH2 op, nC-O 899 sh tR1(A5) 872 892
870 nC-O (A) 881 w twCH2 ip 885 sh n(C-O) 852 867
820b m nC-C (H2A)), twCH2 (HA-, A2-, A), n C-O (HA-) 842 vw na C-C1 836 s d(OCC),twCH2,nC1-C5) 825 821 829
795 sh gCOO2  799 vs 806
783 vw gC-C (H2A), HA-) 785 vw wagH2O(1) 774 776
756b s t(OH)ip dim (H2A)), bC-O (A2-) 755 sh bR1(A6) 759
722 m gC=O dim  (H2A)), gC-C (A) 729 sh dCOO5 722 w bR2(A6) 736
711b vw gC=O (H2A)), bC-O (HA-) 714 sh bR3 (A6) 713 sh 714
697 s tw CH2 dim(H2A)),  bC=O (H2A)), bR1 (A2-), 700 w dCOO4 701 vw rH2O
 n C-C (A), gC=O (HÁ-)
686 w  bC=O (H2A)), n C-C (H2A)) 686 w gCOO5 686 w dC-C-C 686 684 676
675b m n C-O (H2A), HA-), t (OH) (HA-) 666 vw gCOO3  666 sh dO-C-O
649  t(OH)op dim(H2A)),  gC=O (A2-) 640 w t(O-H) 644 w rH2O 643 653
628 m bR1 dim(H2A)),  bC=O (A), bR1 (HA-) 627 vw t(O-H),dCOO3 636 m rH2O 632
591 w gC-O (HA-), n C-C (A2-)bR1 (H2A), A),  599 s t(O-H),dCOO5, 594 m bR1(A5) 600 605 603
bR2(HA-)  dCCC,rCOO5
581 vs 573
565b m dOCH(H2A)), gC-O (H2A), A2-),bR2 (H2A), A2-, A), 571 w gCOO4 570 w dO-C-O 573 565
 wagCC2 (A)
541 w dCOO1 548 s rH2O(1) 553
520 sh gCOO6 537 w tO-Hw 520
496 w dCCO(H2A)), wagCC2 (A2-) 504 w gCOO1  504 m twH2O 498 498
482 w tO-H
473 w gC=O (A) 477 sh gCOO6 474 m dO-C-C 474 477 w 473
467 w wagH2O
449 w rCC2 (H2A)), Wag CC2(H2A), HA-)t(OH) (A) 438 vvw rCOO4 451 w twH2O 434 432
412 s tO-H 424 404 sh 420 418 420
396 w t(OH) (H2A)), bC-O (HA-, A2-) 397 w dCCC 393 s tO-H 406 403
378 s tO-H
363 m  t(OH) (H2A)), gC-O (A2-)r CC2 (A2-), bC=O (A) 367 w rCOO3, rCOO1 368 vs dC-C-O
357 sh dC-C-O
340b w   gC-O (H2A), HA-), gC=O (A) t (OH) (H2A)), 348 w rCOO6 342 sh tO-H
 bC-O (A2-), d CCO (A)
323 vw dCCC 329 w tO-H
320 sh dO-C-C
292b w βC-O(H2A)), dCCO (A2-), bC=O (A),   gC-O (HA-) 306 w dCCC 309 vw tw (O-C)
254 sh dCCC 252 sh d(OCC),r’(C-C)
238b m t(OH) dim(H2A)),d CCC (A2-), 247 vw dCCC 241 sh dO-C-C
t (OH) (H2A), HA-, A), β C-O(HA-)
223 m t(OH) (H2A), HA-), β C-O(H2A)), 237 vw dCCC 235 m dO-C-C
 tCC (A2-), d CCC (A)
212 w dCCC op 212 vs dO-C-C
208 m dCCC (H2A)), t (O-H) (A2-) 204 sh nOH---Ow
180 w  gC-C dim(H2A)) 180 vvw tw2O(2),t(O---H)
172 vw nOH---Ow
166 vvw tR1(A5)
163 m tCCCO dim(H2A)) 160 vw tO-Hw
148 m gC-O(H2A),) d OCH (H2A)), 140b ns (O-H--O)# 153 vvw tO-Hw
138 m tR1 (H2A), HA-,A)  138 vvw tR3(A6)
122 w tR1 (H2A)),  tCCCC (HA-) 129 vvw nOH---Ow
113 w t CCCO (H2A)), tR2 (A2-), d CCC (A) 105b na(O-H--O)#,dCCC ip 114 vvw OH---Ow
91 m t CCCO (H2A)),  tCCCC (HA-) 88b dCCC ip 90 twO-C
81 s tR2 (H2A)) ,tCCCO (A2-), tCCCC (A) 82 twO-C
73 s tR2 (H2A), tR1 (A2-), tCCCO (A), tw Ring(HA-) 68b twCC ip 70 tR2 (A5)
43 vw tw Ring (H2A)), tCCCC (A2-), tR2 (A), tR1 (HA- 44b twCC op 41 t(O---H)          

Table 4. Observed wavenumbers (cm-1) and assignments for all the natural orange juices [17,18,20,22].

Natural Orange D Juice: Figure S8 shows the comparisons of the Infrared (IR) spectra for this juice with those corresponding to the ascorbic and citric acids and sucrose while Figure 8 shows the variations observed in the spectra for this juice with the storage time. In particular for this juice notable variations are observed in the positions of the bands, as shown in both Figures. First, in the higher wavenumbers region the position of the band at 3392 cm-1 attributed to the OH stretching modes of the components are in agreement with the strong band observed in the spectrum of sucrose at 3394 cm-1 and the band at 1650 cm-1 associated with the hydrate-sucrose at 1648 cm-1 support the higher presence of sucrose in this natural juice, as expected because this juice is prepared from the sweet orange. Also, in the 1500-400 cm-1 region for this juice are observing a higher presence of bands associated with those corresponding to sucrose. During the studied time it is possible to observe changes significant in all the spectra presented in Figure 9. The permanent changes in the density values, the increase in the conductivity values and the decreasing in the pH, n and ºBrix values justify all the modifications observed in the Infrared (IR) spectra for this juice during the storage time.

Conclusions

In the present work, three natural orange juices derived from the sour orange (Citrus aurantium), the common orange (Citrus bigardia Riss) and the sweet orange (Citrus sinensis) varieties, named A, C and D, respectively, were characterized by using physicochemical properties and Fourier Transform Infrared (FTIR) spectra with the storage time during 92 days. The natural A and C juices show bands attributed to the ascorbic and citric acid and exhibits notable variations in the physicochemical properties especially at the 7 and 30 days supported by the new Infrared (IR) bands during these times while the infrared spectrum of the natural D juice evidence a higher content of sucrose and during all the studied time the infrared spectra show change in the form, positions and intensities of the observed bands. Thus, the changes in the density values, the increase in the conductivity values and the decreasing in the pH, n and ºBrix values reveal the high instability of this juice with the storage time. The significant decreasing in the n and ºBrix values for all the natural juices confirm that the fresh juices are highly susceptible to decomposition and, for this reason, it should be consumed quickly. In this study, we demonstrated that the Fourier Transform Infrared (FTIR) spectroscopy can be easily used for differentiation of natural juices if its technique is used in combination with the determination of their physicochemical properties. The assignments of the bands observed in the infrared spectra of the sour orange (Citrus aurantium), the common orange (Citrus bigardia Riss) and the sweet orange (Citrus sinensis) varieties in the 4000-400 cm-1 region was proposed. In conclusion, from the three natural studied juices, the D juice is the most instable with the time, as evidenced by the Infrared (IR) spectra and the physicochemical properties.

Acknowledgements

This work was subsidized with grants from CIUNT (Consejo de Investigaciones, Universidad Nacional de Tucumán).

References