Extraction, Isolation, and Characterization of Pectin from Citrus
Peels
Dan Paul Aaron B. Torres
Department of Chemistry
Central Luzon State University
Science City of Munoz, Nueva Ecija, Philippines
torres.dan@clsu2.edu.ph
I.
INTRODUCTION
Lemon (Citrus Limon from Rutaceae) is one of the citrus
fruits, the most commonly grown tree fruit in the world.
Citrus fruits are the top not only in total production but also
in economic value. Citrus fruits, consist of two parts namely
the peels (rind skin) and pulp. These two parts are easily
separated from each other with the pulp serving as the edible
parts of the fruit while the peels as a good source of pectin
[6].
II.
METHODOLOGY
A. Collection and Preparation of Materials
The glass wares and the reagents used in this experiment
were gathered from CRL including NaOH, HCl, pH paper,
beakers, ethanol, phenol red, centrifuge, test tubes, hot plate,
glass rod, acetone, Erlenmeyer flask, burette, thermometer,
wash bottle, pipette, watch glass, parafilm, and the
Brookfield DV-II+ Pro viscometer.
Pectin powder was purchased from an online retail shop.
Pectin is the methylated ester of Poly galacturonic acid
that contains 1, 4-linked ∝-D-galacturonic acid residues [4].
It is commonly found in the cell walls and middle lamellae of
higher plants. These polysaccharides consist of 300-100
chains of galacturonic acid units [10]. Pectin is widely used
in the food industry as a thickener, emulsifier, texturizer, and
stabilizer. Pectin is usually added in jams and jellies as a
gelling agent. It has also been a fat substitute in spreads, ice
cream, and salad dressings. In terms of nutrition, pectin has
been shown to lower blood cholesterol levels and low-density
lipoprotuncholesterol fractions, which is beneficial for
human health [5].
According to the FAQ (1969) [1], pectin is considered to
be a safe additive that can be taken daily. Pectin can be
obtained from many sources with a variation in the
percentage yield. Sugar beet and sunflower head residues
consist of 10 to /20% pectin. Other sources for pectin include
cocoa husk, with about 9%of the dry weight pectin [8], and
soya hull, with pectin contents at about 26-28% [3].
Brookfield DV-II+ Pro viscometer used in the
experiment.
Fig. 1.
The yield of pectin usually depends on the extraction
conditions, such as temperature, extraction time, pH, type of
extraction solvents [10], and drying [9]. Before extraction
begins, alcohol- insoluble, residue is prepared to remove lowmolecular weight compounds, including any traces of free
galacturonic acid [2]. Pectin can be divided into two types
based on the degree of esterification (DE) of the pectin: high
methoxyl pectin (DE >50%) and low methoxyl pectin
(DE<50%).
B. Isolation of Pectin
A 25 g citrus peel was homogenized with 150 mL distilled
water in a blender. The resulting mixture was transferred to a
250-mL beaker and the pH was measured using pH paper.
The pH was adjusted to 2-3 with citric acid dropwise. The
solution was heated at 80°C for 1 hour with constant stirring.
The water lost due to evaporation was replaced, except during
the last 20 minutes of the extraction period. The solution was
filtered rapidly in a moistened cheesecloth. The volume of the
filtrate was collected and measured. A 25 mL of the filtrated
was pipetted out into a 250-mL beaker immersed in an ice
bath. 25 mL of acidified 95% ethanol was added slowly. The
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Torres, D.P.A.B.
mixture was stirred continuously for 10 minutes. For 10
minutes, the mixture was then centrifuged at maximum
speed. The supernatant was decanted. The precipitate was
washed with 10 mL acidified 70% ethanol. The precipitate
was washed three times with 5 mL 95% ethanol. Finally, the
precipitate was washed with 3 mL acetone. The extract was
lyophilized overnight. The precipitate was weighed. The
percent yield in the original filtrate was determined.
III.
RESULTS AND DISCUSSION
A. Determination of Equivalent Weight
The change in color during the titration of the pectin
solution was shown in Figure 1 and Figure 2. In which, as
seen in Figure 1, a yellowish solution was observed, while
in Figure 2, the neutralized solution observed was strong
pink.
C. Determination of Equivalent Weight
A 0.5g of the precipitate obtained from the isolation of
pectin was taken into a 250-mL conical flask and 5 mL of
ethanol was added. A 1.0g of sodium chloride and 100 ml of
water were added. Six (6) drops of 0.4% phenol red indicator
were added to the solution. Using 0.1 N NaOH, the sample
was titrated. The appearance of pink color was an indication
of the titration endpoint. This is labeled as a ‘neutralized
solution’ and this was stored for the determination of
methoxy content. The formula below was used for the
calculation of equivalent weight.
𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑡ℎ𝑒 𝑠𝑎𝑚𝑝𝑙𝑒 (𝑔) × 100
𝐸𝑞𝑢𝑖𝑣 𝑙 𝑛𝑡 𝑤 𝑖𝑔ℎ𝑡 =
𝑚𝐿 𝑜𝑓 𝑎𝑙𝑘𝑎𝑙𝑖 × 𝑁 𝑜𝑓 𝑎𝑙𝑘𝑎𝑙𝑖
D. Determination of Methoxy Content
The ‘neutralized solution’ was collected from the
determination of equivalent weight, and 10 mL of
standardized 0.1 N of sodium hydroxide was added. The
resulting mixture was stirred thoroughly and incubated at
room temperature for 30 minutes. After 30 minutes, 10 mL
of 0.1 N HCl was added. Using 0.1 N NaOH, the resulting
solution was titrated. The methoxy content was calculated
using the formula below.
𝑚 𝑡ℎ𝑜 𝑦 (%) =
Fig. 2.
Mixture of Pectin Solution from the Determination of
Equivalent Weight
𝑚𝐿 𝑜𝑓 𝑎𝑙𝑘𝑎𝑙𝑖 × 𝑁 𝑜𝑓 𝑎𝑙𝑘𝑎𝑙𝑖 × 100
𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒 (𝑔)
E. Viscosity of Pure Solvent
A 4-L of 0.10 N NaCl solution was prepared. Around
250-mL of this solution was used for the determination of its
viscosity, using the Brookfield DV-II+ Pro viscometer. The
remaining solution was used for the succeeding parts of the
experiment.
F. Viscosity of PVA Standards
A 250 mL of 1.5% (w/v) of PVA standard was prepared.
From this solution, 0.75%, 0.375%, and 0.1875% serial
dilutions (250 mL) were prepared and performed. The
remaining 0.10 N NaCl was used in the serial dilution. The
viscosity was measured using the Brookfield DV-II+ Pro
viscometer.
G. Viscosity of Pectin Solutions
A 250-mL of 1.5% (w/v) pectin solution was prepared by
dissolving dried pectin in 0.1 N NaCl. 0.75%, 0.375%, and
0.1875% serial dilutions (250 mL) were prepared and
performed. The viscosity was measured using the Brookfield
DV-II+ Pro viscometer.
Fig. 3.
Neutralized Pectin Solution from the Determination Equivalent
Weight.
𝐸𝑞𝑢𝑖𝑣𝑎𝑙 𝑛𝑡 𝑤 𝑖𝑔ℎ𝑡 =
𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑡ℎ𝑒 𝑠𝑎𝑚𝑝𝑙𝑒 (𝑔) × 100
𝑚𝐿 𝑜𝑓 𝑎𝑙𝑘𝑎𝑙𝑖 × 𝑁 𝑜𝑓 𝑎𝑙𝑘𝑎𝑙𝑖
0.5 𝑔 × 100
𝐸𝑞𝑢𝑖𝑣𝑎𝑙𝑒𝑛𝑡 𝑤𝑒𝑖𝑔ℎ𝑡 =
5.2 𝑚𝐿 × 0.1 𝑁
𝑬𝒒𝒖𝒊𝒗𝒂𝒍𝒆𝒏𝒕 𝒘𝒆𝒊𝒈𝒉𝒕 = 𝟗𝟔. 𝟏𝟓
The equivalent weight of pectin extracted from lemon
peel using sodium chloride was found to be 96.15. The high
equivalent weight would have a higher gel-forming effect.
The lower equivalent weight could be higher partial
degradation of pectin.
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Torres, D.P.A.B.
B. Determination of Methoxy Content
Solution
Blank (0.1N
NaCl)
Viscosity (cP)
1.8
Temperature (°C)
28.80
Table 1 shows that the viscosity of the 0.1N NaCl at 28.80oC
was 1.8 cP. According to the safety data sheet of Lab Chem
the viscosity of the 0.1N Nacl was 1.01 cP.
D. Viscosity of PVA Standards
TABLE II.
Solution
PVA
Standards
Fig. 4.
The resulting mixture after the addition of 10 mL of 0.1 N HCl.
Data for the determination of the viscosity
of PVA standards.
Concentration
(%w/v)
0.75%
0.375%
0.1875%
Viscosity
(cP)
3.60
3.00
2.40
Temperature
(28°C)
28.70
28.60
28.50
Table 2 shows the viscosity of PVA standards at different
concentrations. The highest viscosity of PVA at 28oC was
3.60 in 0.75% concentration, and the lowest viscosity of PVA
at 28oC was 2.40 in 0.1875% concentration.
E. Viscosity of Pectin Solutions
TABLE III.
Solution
Fig. 5.
Titration End Point for the Determination of Methoxy Content.
𝑜𝑓𝑜𝑥𝑦 (%)
𝑚𝐿 𝑜𝑓 𝑎𝑙𝑘𝑎𝑙𝑖 × 𝑁 𝑜𝑓 𝑎𝑙𝑘𝑎𝑙𝑖 × 3.1
=
𝑡ℎ𝑜𝑥𝑦 %
𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒 (𝑔)
12 𝑚𝐿 × 0.1 × 3.1
=
0.5 𝑔
𝒎𝒆𝒕𝒉𝒐𝒙𝒚 (%) = 𝟕. 𝟒𝟒%
The methoxyl content of pectin extracted from citrus was
found to be 7.44%. Methoxyl content is an important factor
in determining the gel formation capacity. Methoxyl content
is an important factor in controlling the setting time of pectin
and the ability of the pectin to form gels.
C. Viscosity of the pure solvent
TABLE I.
Data for the determination of the viscosity
of the blank solution.
Pectin
Solutions
(heated)
Pectin
Solutions
(not
heated)
Data for the determination of the viscosity
of pectin solutions.
Concentration
(%w/v)
0.75%
0.375%
0.1875%
0.75%
0.375%
0.1875%
Viscosity
(cP)
7.80
4.20
3.00
6.00
3.60
2.40
Temperature
(28°C)
29.2
29.5
29.5
29.0
28.7
28.6
Table 3 shows the viscosity of the pectin solution at different
temperatures and concentrations. The highest viscosity of
pectin solution when heated was 7.8 cP at 0.75%
concentration at 29.2oC, while the lowest viscosity of pectin
solution when heated was 3.0 cP at 0.1875% concentration at
29.5oC. The highest viscosity of pectin solution when not
heated was 6.0 cP at 0.75% concentration at 29oC, while the
lowest viscosity of pectin solution when heated was 2.4 cP at
0.1875% concentration at 28.6oC.
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Torres, D.P.A.B.
IV.
CONCLUSION
This experiment was focused on pectin extraction, isolation,
and characterization. The result indicated that the best
condition of the pectin was 96.15 of equivalent weight and
shows that partial degradation of pectin. The viscosity of
pectin was heated with 7.8 cP at 0.75% concentration at
29.2oC.
V.
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