INTRODUCTION:
Tamarindus indica is a long lived, evergreen raw material for the extraction of tartaric acid. This fruit belongs to the family Leguminosae and is cultivated throughout the world1. The tamarind fruit has many industrial and commercial applications2. It comprises organic acids such as tartaric acid, citric acid, malic acid with sugars3. Tartaric is a di-hydroxyl derivative of succinic acid belonging to alpha-hydroxy-carboxylic acid4. Tartaric acid along with citric acid has been used in the production of effervescent salts5. The acid has been observed to chelate metal ions such as calcium and magnesium. Tamarind fruit pulp appears as pea-like pods and its extract contains natural compounds that have antimicrobial effects6. In fact, studies have shown that this plant possess anti-fungal7, antiviral8 and antibacterial9 activity.
In traditional medicine it is used as a laxative10, anti-inflammatory11 and antioxidant12 property. Studies have indicated that the tamarind contains elevated titratable acidity, rich in pectin, minerals, carotenoids and vitamins13. Tamarind pulp is composed of carbohydrates (50.07 g/100 g) and moisture (35.29 g/100 g); it can be considered a good source of dietary fiber14,15. Potassium bi-tartarate can be mixed with an acidic liquid to make a paste-like cleaning agent for metals. It is commonly mixed with sodium bicarbonate and is sold as baking powder used as a leavening agent in food preparation16. Potassium bi-tartarate when mixed with hydrogen peroxide can be used to clean rust from hand tools. Liquid extraction has been used for a very long time for recovery of substances from waste streams17. It is an economical and eco-friendly method for the recovering the biologically active products from fermentation liquids18. For the extraction carboxylic acid using the conventional solvents was not efficient because of the low distribution coefficients19,20. So the reactive extraction process was adopted for the extraction of tartaric acid from the tamarind pulp. The distinction between the two extraction systems is because of the presence of a hydrophobic complex, which is obtained as the result of chemical reaction between solute and extract. The separation efficiency depends on solute characteristics, extraction properties and process conditions (pH-values, mixing time and temperature of aqueous solution). The aim of the study was to recover the organic acid such as tartaric acid and pectin from the tamarind pulp using less expensive and easily available solvents and also to investigate the kinetic aspect of the extraction process.
EXPERIMENTAL:
Chemicals and Reagents:
Tamarindus indica sample were obtained from local market in Chennai. The samples were cleaned to expel impurities21. For chemical analysis, seeds are seeds are disposed of from the sample pulp. For the extraction studies the tamarind samples washed, soaked in water for 24 h.
Extraction of Tartaric Acid from Tamarind Pulp:
Tamarind pulp was extracted using 1:3 volume ratio of water and ethanol as a solvent at the temperature of 25°C and 50°C for about 1 to 3 h. The extract was cooled to 10°C in order to precipitate potassium bi-tartarate. The obtained potassium bi-tartarate was dissolved in sufficient amount of water along with the known quantity of calcium carbonate. The calcium tartarate was formed with the release of CO2. The obtained precipitates was filtered and treated with 20mL of 96% sulphuric acid. After 30 min of reaction, calcium tartarate was decomposed to pure tartaric acid and calcium sulphate settles out as shown in the following reactions. The amount of tartaric acid present in unknown sample is calculated by equation 1
(1)
Where W is the Weight of tartaric acid present in unknown sample
C is the Concentration of C4H6O6
V is the Extract volume
Extraction of pectin from Tamarind Pulp:
The pectin was extracted from the mother liquor obtained from the previous step using hydrochloric acid as a solvent22,23. The time of mixing and temperature were varied in order to determine the optimized value. When the magnetic stirring was completed the pectin was removed and filtered using Whatman filter paper. The precipitated substance was washed with water to remove impurities and dried24.
Analysis of Acid Composition:
Samples were analyzed with the help of thin layer chromatographic method using a suitable solvent (Hexane) and the retardation factor (Rf) value was determined for each sample25 Substance whose structure resembles the stationary phase will have low Rf, while one that has a similar structure to the mobile phase will have high Rf.
Distance form the baselinetravelled by solute
Rf = ––––––––––––––––––––––––––––––––––– (2)
Distance form baseline travelled by solvent
RESULTS AND DISCUSSION:
Tartaric acid was extracted from tamarind pulp as discussed in section 2.1. The obtained tartaric acid was qualitatively and quantitatively identified using UV-Visible spectroscopy respectively 26. From the UV - Vis studies we have observed a shift in wavelength from 246 nm - 283 nm as shown in Fig. 1 and 2. The shift in absorbance of the solution confirms the obtained solution is indeed tartaric acid. The amount of tartaric acid extracted at 25 and 50°C were calculated from UV-Visible absorbance measurements and was represented in Table 1.
Fig. 1. UV Spectroscopy graph for the extract at 25°C
Fig. 2. UV Spectroscopy graph for the extract at 50°C
Table I. Amount of tartaric acid from Rfa data
|
Temperature (°C) |
Spot Value (cm) |
Rf Value |
Absorbance at 505 nm |
Concentration (gL-1) |
Weight of Tartaric acid present in sample (g) |
|
25 |
0.18 |
0.12 |
1.93 |
10.422 |
7.82 |
|
50 |
0.19 |
0.13 |
2.17 |
11.718 |
8.78 |
aLength of the plate = 2.5 cm and Distance travelled by solvent from baseline = 1.5 cm
Effect of stirring speed on rate constant:
The effect of the stirring speed on extraction rate constant was shown in Fig. 3. In case of diffusion controlled extraction, the extraction rate increases linearly with increasing stirring speed and the extraction will have no effect with the stirring speeds if the process was controlled by chemical reaction. When the stirring speed was increased from 100 rpm to 150 rpm, the extraction rate constant increases linearly with stirring speed indicating the extraction process is diffusion controlled. When the stirring speed was further increased to 200 rpm, the extraction rate remains constant and do not changes much with stirring speed. As stirring speed is increased, it not only accelerates the extraction rate of the diffusion type, but also may cause the change of extraction types27, 28. The effect of diffusion on mass transfer was found to follow first-order kinetics 29, fixing the relative interfacial area, the extraction rate constant (k) is calculated as follows:
KL is the positive apparent extraction rate constant, t is the extraction time, is the initial concentration of acid, is the equilibrium concentration of acid, CL is the concentration of acid at time t. If the initial concentration of acid in organic phase is zero, the phase ratio is 1:1, the oxygen transfer coefficient was calculated by plotting a graph of against time the slope of the graph is , and the intercept of. As shown in Fig 2 and 3, a differential equation plot of ln (CL0-C*) against time were observed that the extraction process is linear30, 31.
Fig. 3. Extraction kinetics with varying mixing speeds at 25°C
Fig. 4. Extraction kinetics with varying speeds at 50°C
The kL value obtained for the extraction of acid was 0.017 min-1 for 50°C and 0.012 min-1 for 25°C at the agitation speed of 100 rpm. Similarly the rate constant value was 0.019 min-1 for 50°C and 0.014 min-1 for 25°C at the agitation speed of 150 rpm and 0.02 min-1 for 50°C and 0.017 min-1 for 25°C at the agitation speed of 200 rpm respectively (Fig. 4).
Effect of temperature on the extraction rate constant:
Extraction which controlled by chemical reaction is very sensitive to the change of temperature 32, 33. The effect of temperature on extraction rate constant which controlled by diffusion is not significant as shown in Table 2. The extraction process follows First-order kinetics (Fig. 5). From the rate constant values, KL, the thermodynamic properties are calculated using Arrhenius equation. The activation energy was calculated from the equation,
Where, KL is the reaction rate constant, A is the Arrhenius constant or frequency factor in min-1, Ea is the activation energy, R is the universal gas constant and T is the absolute temperature. The equation is in its logarithmic form can be written as,
Fig. 5. First order kinetics studies
A plot of ln KL versus 1/T gives a straight line whose slope represents the activation energy (-Ea/R) and intercept represent the Arrhenius constant (Fig. 4). The activation energy and Arrhenius constant for extraction of tartaric acid was found to be 14.71 kJmol-1 and 0.7297min-1. The thermodynamic properties namely enthalpy of activation (∆H°), entropy of activation (∆S°) and free energy of activation (∆G°) are calculated based on transition state theory. The enthalpy of activation (∆H°) is determined from Ea by the equation,
The entropy of activation (∆S°) is calculated from Arrhenius constant,
Where, N and h are the Avogadro constant and Planck constant respectively.
The free energy of activation (∆G°) is calculated from ∆H° and ∆S° by the expression,
The activation thermodynamic parameters for the extraction of tartaric acid are presented in Table 3. The ∆S° is found to be negative indicating the activated complex is more ordered than the reactants. Large negative ∆S° value (-247 to -248 Jmol-1K-1) indicates that the extraction process proceeds slowly and the reaction is thermodynamically stable. The ∆G° for the extraction process increases with the increase in temperature from 25°C to 50 °C and possess a high value of 88 kJmol-1. From the extraction rate, the Gibb’s free energy of reaction (ΔG) was calculated. The extraction rate constant at 50°C was found to be 0.017 to 0.02 min-1 for the various mixing speeds ranging from 100 to 200 rpm. The impact of temperature on the extraction rate constant is relatively small. The ΔG of the reaction was found to be −190 to −206 kJmol-1. The decrease in ΔG° values shows the feasibility of process as the temperature increased from 25°C to 50 °C34.
Table II. Rate constants values at different temperatures and mixing speeds
|
Mixing speed (rpm) |
KL at 25 °C (min-1) |
KL at 50 °C (min-1) |
|
100 |
0.012 |
0.017 |
|
150 |
0.014 |
0.019 |
|
200 |
0.017 |
0.02 |
Table III. Thermodynamic activation parameters for the extraction of tartaric acid
|
Temperature (K) |
∆H° |
∆S° |
∆G° |
|
kJmol-1 |
JK-1mol-1 |
kJmol-1 |
|
|
298 |
12.23 |
-247.52 |
85.99 |
|
303 |
12.19 |
-247.65 |
87.22 |
|
313 |
12.10 |
-247.92 |
89.70 |
|
323 |
12.02 |
-248.18 |
92.18 |
Extraction of Pectin:
The effect of temperature and extraction time on the yield of pectin from tamarind pulp was studied and is presented in Table 3. For the extraction process, the mother liquor was subjected to extraction by adding 1M HCl as a solvent (pH of 2 – 3) at various time and temperature35, 36. The extraction process was performed in ultra-sonic bath sonicator37. During acidic extraction, the insoluble pectin constituent was converted into soluble pectin and the maximum pectin recovery was at acidic pH38, 39. As the pH is increased, the yield of pectin is decreased may be due to the aggregation of pectin40. The effect of time on pectin yield was examined by taking three different extraction periods of 2h to 5h as shown in table 3. The maximum yield of pectin was observed in case of an intermediate time of 4h. The protein content of tamarind pulp was found to be 6.0 ± 0.4 g per 100kg of tamarind pulp. The highest yield of 84.5% pectin was obtained when the pulp was treated at 50°C, 200 mL of acidified solvent maintained at the pH 3 for 4h.
Table IV. Amount of pectin extracted
|
Run |
Time (h) |
Temperature (°C) |
Yield (g) |
Percentage extraction (%) |
|
1 |
2 |
40 |
3.058 |
50.96 |
|
2 |
2 |
50 |
4.725 |
78.75 |
|
3 |
2 |
60 |
3.528 |
59.67 |
|
4 |
3 |
40 |
3.258 |
54.3 |
|
5 |
3 |
50 |
5.01 |
83.3 |
|
6 |
3 |
60 |
3.95 |
75.08 |
|
7 |
4 |
40 |
3.45 |
57.5 |
|
8 |
4 |
50 |
5.09 |
84.5 |
|
9 |
4 |
60 |
4.05 |
71.0 |
|
10 |
5 |
40 |
3.51 |
62.17 |
|
11 |
5 |
50 |
5.02 |
83.67 |
|
12 |
5 |
60 |
3.98 |
68.33 |
CONCLUSION:
When comparing with previous processes, the modified reactive extraction processes from the tamarind pulp resulted in two commercially important constituents namely tartaric acid and pectin. The following parameters for the extraction process such as temperature, extraction time, and stirring speed have been optimized for the maximum recovery. It was concluded at pH 3 and 50°C the maximum extraction of tartaric acid was obtained. The values of the extraction rate constants was found to be 0.017 min-1 to 0.02min-1 at varying agitation speed with R2 value of 0.95 to 0.98. The maximum extraction of pectin was at acidic pH. The highest yield of pectin 84.5% was obtained when the pulp was treated at 50°C, 200mL of acidified solvent maintained at the pH of 3 for 4h. As a whole, the process is economically benign and competitive with other process and to utilize the product in both industrial and agricultural applications.
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Received on 06.06.2019 Modified on 01.08.2019
Accepted on 29.08.2019 © RJPT All right reserved
Research J. Pharm. and Tech. 2020; 13(1): 91-95.
DOI: 10.5958/0974-360X.2020.00017.7