Utilization of Punica granatum Peels for the Extraction of Pectin

 

Sathish S.*, Gowthaman K.A., Haaresh Augustus

Department of Chemical Engineering, Sathyabama University, Chennai – 600 119

 

ABSTRACT:

Pectin can be used as food and pharmaceutical additives. Pectin was extracted using acid extraction method. The extraction condition has a major impact on the yield of extraction. Temperature, extraction time and pH showed a significant effect on the pectin yield. The optimum temperature, time and pH for the extraction of pectin from peels were determined to be 60°C, 60 min and 6 respectively. The yields of pectin under these optimum conditions were found to be 27% for fresh dried Punica granatum peels. The characteristics of pectin from Punica granatum peel were found to be molecular weight of 277.78 g/mol, methoxyl content of 4.96. The anhydrouronic acid content was found to be 91.5% and the degree of esterification was 30.77%. The moisture content of pectin obtained under the optimum conditions was found to be 69.6%. This study investigated the effect of temperature, time and pH on the yield and physicochemical characteristics of pectin extracted from Punica granatum peels.

 

 

INTRODUCTION:

Pectin’s have been utilised for their functionality in foods for many years. Pectin's are complex polysaccharides that contain 1, 4-linked α-D- galacturonic residues¹. It is possible to separate essentially pure galacturonan fractions from other high molecular weight pectin fractions by degrading purified pectins either chemically or enzymatically² . Pectin is found in most plants, but is most concentrated in citrus fruits and they are industrially extracted by hot acidified water³. A mixture of pectin with other polysaccharides such as alginate has found that good gels are formed from high methoxy pectin. Mixtures of proteins and polysaccharides are prone to incompatibility or undesirable complex formation. Texture behaviour of the product can be regulated by the pectin/gelatin ratio. Pectin favourably influences the cholesterol levels in blood. It has been shown to be effective in removing lead and mercury from the gastrointestinal tract and respiratory organs⁴.

 

When injected intravenously, pectin shortens the coagulation time of drawn blood, thus being useful in controlling haemorrhage or local bleeding. Pectin gives a feeling of satiety these attribute that pectin can be used in the treatment of disorders related to overeating⁵. The esterification of galacturonic acid residues with methanol or acetic acid is a very important structural characteristic of pectin substances. The degree of methylation is the percentage of carbonyl groups esterified with methanol. If more than 50% of the carboxyl groups are methylated the pectins are called high methoxy pectins (HM), and less than that degree are called low methoxy (LM) pectin⁶. HM pectins have the ability to form gels with sugar and acid. LM pectin can gel in the presence of divalent cations, usually calcium. The gel forming ability of LM pectin increases with decreasing degree of methylation. Commercial pectin’s can be amidated, this improves the gelling ability of LM pectin in that they require less calcium to gel and are less prone to precipitate at high calcium levels. This study focused on separation oil from pomegranate peels by simple distillation method and to optimize the process parameter for the extraction of pectin from the dried pomegranate peels also from the peels obtained after simple distillation.

MATERIALS AND METHODS:

SAMPLE PREPARATION:

The fresh fruit peels were segregated, cut into pieces for easy drying and washed with water. Sample drying was carried out in oven at 60°C for 48 hours to obtain easily crushable material. The dried peel was milled in sieve size of 80 meshes and packed in airtight, moisture-proof bag at room temperature and ready to the extraction process.

 

EXTRACTION OF PECTIN:

10gms of fresh dry pomegranate peel was taken for extraction. HCl of different pH were prepared as a solvent. The time of mixing and temperature were varied in order to determine the optimised value. After the magnetic stirring is completed the pomegranate peel in the solution is removed and it is filtered using Whatman filter paper. The pectin substances were precipitated using alcohol juice treatment of 2:1 volume basis. The precipitated substance was washed and dried to remove impurities. The effect of yield of pectin on various temperature, pH and time were studied by varying one parameter at a time.  The yield of the pectin can be calculated⁷.

                         Amount of Dry pectin obtained

% Yield =------------------------------------------- X 100

                              Amount of Feed

 

RESULTS AND DISCUSSIONS:

EFFECT OF TEMPERATURE:

Extraction was carried at temperature ranges from 30°C, to 70°C at constant time of 60 minutes and pH of 6 respectively.  Extraction efficiency is the percentage of solute moving into the extracting phase. Maximum yield was obtained at 60 °C. Increasing the temperature of extraction process would favour the yield by enhancing the distribution coefficient of pectin. But at the high temperature thermal destruction of compounds can also be taken place and caused a reduction in the quantity of crude extract. As the extraction temperature increased above 60°C, the heat sensitive pectin would be destroyed and caused a reduction in yield of pectin ⁸.

 

Table 4.1 Effect of Temperature on extraction

 

 

Fig. 1 Effect of Temperature on extraction of pectin from Punica granatum

 

EFFECT OF TIME:

At the temperature of 60°C and the pH 6 the effect of time on extraction of pectin from Punica granatum was observed. As the time increases at fixed temperature and pH the yield of pectin increases beyond which the yield become saturated. Increasing the extraction time would lead to decomposition of pectin since pectin is composed of galacturonic acid and methyl ester⁹.

Table 4.2 Effect of Time on extraction

 

 

Fig. 2 Effect of Time on extraction of pectin from Punica granatum

EFFECT OF pH

Extraction was carried out at various pH ranges from 2 to 8 at a constant temperature and time of 60°C and 60 minutes. The percentage yield of pectin was increases with increase in pH and reaches the maximum yield at the pH of 6, beyond that pH the yield was decreases. The acidic extraction hydrolyses the insoluble pectin constituents into soluble pectin as it comes in contact with it, thus the pectin recovery is maximum at acidic pH. The increasing the pH retarded the pectin release may be due to the aggregation of pectin¹⁰. The optimized pH value for the extraction of pectin was found to be 6.

 

Table 4.3 Effect of  pH on extraction

Run	Sample (g)	pH	Time (min)	Temperature (°C)	Dry Pectin obtained (g)	Percentage Yield (%)
1	10	2	60	60	1.81	18.1
2	10	4	60	60	1.90	19.0
3	10	6	60	60	2.67	26.7
4	10	7	60	60	1.93	19.3
5	10	8	60	60	1.5	15.0

 

Fig.  3 Effect of pH on Extraction of pectin  from dried pomegranate peels

 

QUALITATIVE AND QUANTITATIVE ANALYSIS SOLUBILITY:

Pectin is partially soluble in cold water and insoluble in alcohol and organic solvents. Dry powdered pectin, when added to water, has a tendency to hydrate very rapidly, forming jellied lumps.

 

MOLECULAR WEIGHT:

Pectin sample (0.5 g) was weighed into a 250 mL conical flask and moistened with 5 mL ethanol. A 1.0 g NaCl was added to the mixture followed by 100 mL distilled water and few drops of phenol red indicator. Care was taken to ensure that all the pectin had dissolved and that no clumping occurred. The solution was then slowly titrated with 1/10 N NaOH to an end point appearance of pale permanent pink colour ¹¹. The molecular weight was determined as 277.78g/mol.

 

METHOXYL CONTENT:

Methoxyl refers to the functional group consist of a methyl group bound to oxygen. This value decides whether the pectin obtained has a high or low gelation property¹². The neutral solution was collected from the previous step, and 25 ml of NaOH was added. The mixed solution was stirred thoroughly and kept at room temperature. After 30 min 25 ml of 0.25 N HCl acid was added and titrated against 0.1 N NaOH to the  end point of appearance of pale permanent pink colour¹³, The methoxyl content of extracted pectin was found to be 4.96%. Methoxyl content is the important factor that determine the setting time of pectin.

 

MOISTURE CONTENT:

5g of pectin sample was taken in a crucible and placed in a hot air oven set at 100°C for 1 h. Thereafter the petri dish was removed, cooled in a desiccator and weighed. The moisture content of the pectin was found to be 69.6%.

 

                  

ANHYDROURONIC ACID CONTENT:

Uronic acids are a class of sugar acids with both carbonyl and carboxylic acid functional groups. The estimation of anhydrouronic acid content is required to determine the purity of pectin and degree of esterification¹⁴. The AUA content of the pectin obtained from Punica granatum was found to be 91.5%.

 

DEGREE OF ESTERIFICATION (DE):

The DE of extracted pectin was calculated by, applying the data from methoxyl and AUA content determinations¹⁵. The degree of esterification was found to 30.77%. The pectin obtained from Punica granatum was categorised as LM pectin since the percentage DE was less than 50%.

 

 

SPECTRAL ANALYSIS:

Fourier transform infrared spectroscopy (FTIR) is a spectrum of the signal at a series of discrete wavelengths ranging from 4000 to 400 cm^-1. Such approach was effective to confirm the pectin functional identity from the peaks concerned^{16, 17}.  The major functional groups in pectin are usually in the region between 1000 and 2000 cm^-1. The absorption bands between 1100  and 1380 cm^-1 were from ether and cyclic C-C bonds in the ring structure of pectin molecules with the esterified carboxyl groups (1749 cm^-1) and related to free carboxyl groups (1636.98 cm^-1). The broad band, from 3200 to 3600 cm^-1, was due to moisture adsorbed in the pectin samples.

 

Fig.  4  FT–IR Spectrum of pectin obtained from dried pomegranate peels

 

CONCLUSION:

In the present work, different extraction conditions were performed to extract the pectin from the peels of Punica granatum. The optimized values of temperature, pH and time were found to be 60°C, 6 and 1hr respectively .The maximum yield of dry pectin obtained using these optimized process condition was found to be 27%. The pectin obtained from the peels of Punica granatum is low methoxy pectin since the degree of esterification was 30.77%. The present work reported the basic properties of the extracted pectin. The results suggest that peels of Punica granatum can be a potential source of gelling pectin.

 

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Accepted on 24.10.2017        © RJPT All right reserved

Research J. Pharm. and Tech 2018; 11(2): 613-616.