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Food Chemistry 418 (2023) 135807
Available online 7 March 2023
0308-8146/© 2023 Elsevier Ltd. All rights reserved.
Microwave-assisted extraction of pectin from jackfruit rags: Optimization, 
physicochemical properties and antibacterial activities 
Ngan Thi Kim Tran a, Viet Bao Nguyen a, Thuan Van Tran b,*, Thuy Thi Thanh Nguyen a,* 
a Nong Lam University Ho Chi Minh City, Ho Chi Minh City 700000, Viet Nam 
b Institute of Applied Technology and Sustainable Development, Nguyen Tat Thanh University, 298-300A Nguyen Tat Thanh, District 4, Ho Chi Minh City 755414, Viet 
Nam 
A R T I C L E I N F O 
Keywords: 
Pectin 
Jackfruit rags 
Microwave assisted extraction 
Response surface methodology 
Optimization 
A B S T R A C T 
While fruit biowastes pose an environmental hazard, they can be utilized as a source of beneficial biopolymers 
such as pectin. However, conventional extraction techniques require long processing time with low, impure 
yields, and microwave assisted extraction (MAE) can suffer from these drawbacks. Here, MAE was applied to 
extract pectin from jackfruit rags and compared with conventional heating reflux extraction (HRE). Response 
surface methodology was adopted to optimize pectin yield, based on pH (1.0–2.0), solid–liquid ratio (1:20–1:30), 
time (5–90 min), and temperature (60–95 ◦C). Pectin extraction by MAE required lower temperatures (65.99 ◦C) 
and shorter reaction times (10.56 min). Pectin HRE resulted in a product with amorphous structures and rough 
surfaces, while pectin-MAE was high crystalline with smooth surfaces. Although both pectin samples showed 
shear-thinning behavior, pectin-MAE exhibited higher antioxidant and antibacterial activities. Therefore, mi-
crowave assisted extraction was an efficient method to extract pectin from jackfruit rags. 
1. Introduction 
Pectin, a carbohydrate polymer, is commonly found in the primary 
cell walls and middle lamella of plants. Pectin is composed of gal-
acturonic acid (Gal-A) with three major structures involving rhamno-
galacturonan I, rhamnogaclacturonan II, and homogalacturonan 
(Voragen et al., 2009). Based on degree of esterification (DE), pectin 
compounds are subdivided into two types low-methoxyl pectin (DE <
50%) and high-methoxyl pectin (DE > 50%). Gelation of low-methoxyl 
pectins is formed, called egg-box model, in the presence of Ca2+ while 
high-methoxyl pectins form gel under acid condition and high sugar 
content (Wan et al., 2021). During low-methoxyl pectin gelation, elec-
trostatic interactions, hydrogen bonding and van der Waals are 
responsible for stabilizing methylated groups and free carboxyl groups 
while high-methoxyl pectin gelation is an esterification process of car-
boxylic groups, decreasing the number of hydrogen bonds and hydro-
philicity of pectin (Huang et al., 2021). Pectin offers a wide range of 
applications in food stabilizer, natural gelling agent, drug carriers, and 
wound healing (Picot-Allain et al., 2022). It should be noted that com-
mercial pectins are mainly extracted from citrus peels, apple pomaces, 
sugar beet pulp, and sunflower seed heads (Hu et al., 2022). Neverthe-
less, pectin can be recovered from other biowaste sources, such as 
byproducts from mango, banana, durian, grapefruit, and other agricul-
tural wastes (Picot-Allain et al., 2022). 
Jackfruit (Artocarpus heterophyllus L.), a tropical fruit, is widely 
planted in many countries including Thailand, Myanmar, Indonesia, and 
Vietnam. While this fruit is a major product for food and beverage 
purposes, large amounts of jackfruit wastes (e.g., rag, seed, peel, bulb, 
and central core) accounting for 60% of jackfruit weight are non-edible, 
and usually discarded as biowaste, causing serious environmental issues 
(Brahma & Ray, 2022). In fact, jackfruit wastes were found to be rich in 
pectin (approximately, 8.9–15.1% dry weight), and the extraction was a 
feasible process (Begum et al., 2014). Although extraction methods use 
ethanol or inorganic acid aqueous solutions for pectin extraction from 
jackfruit waste, greener solvents such as hot water and acid citric solu-
tion have partly replaced them (Sundarraj et al., 2018). Valorizing these 
fruit by-products by recovering their biopolymers using green solvents 
is, therefore, worth considering. 
Some advanced techniques, including ultrasound-assisted extraction, 
microwave-assisted extraction and physical field-based extraction, have 
been introduced to recover pectin from fruits and biowastes (Adetunji 
et al., 2017). In comparison to conventional methods, the extraction 
time and temperature of these nonconventional methods are signifi-
cantly reduced, while the extraction efficiency is somewhat competitive. 
* Corresponding authors. 
E-mail addresses: tranvt@ntt.edu.vn (T.V. Tran), nguyenthanhthuy@hcmuaf.edu.vn (T.T.T. Nguyen). 
Contents lists available at ScienceDirect 
Food Chemistry 
journal homepage: www.elsevier.com/locate/foodchem 
https://doi.org/10.1016/j.foodchem.2023.135807 
Received 15 November 2022; Received in revised form 18 February 2023; Accepted 25 February 2023 
mailto:tranvt@ntt.edu.vn
mailto:nguyenthanhthuy@hcmuaf.edu.vn
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https://doi.org/10.1016/j.foodchem.2023.135807
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Food Chemistry 418 (2023) 135807
2
For example, Lal et al. successfully combined pulsed electric fields and 
microwave-assisted extraction to isolate pectin from jackfruit rind and 
core with a high yield of up to 18.24% within 10 min (Lal et al., 2021). 
Xu et al. (2018) applied ultrasonic-microwave-assisted extraction to 
recover pectin from jackfruit peel, which obtained a yield of 21.5% at 
86 ◦C in 29 min. These techniques that enhance pressure and tempera-
ture in a short time significantly modify the tissues of the precursor, 
breaking down the cell structure to aid extracting solvents penetrating 
into these tissues and increasing the yield of pectin extraction. From the 
mentioned studies, it could be hypothesized that microwave-assisted 
extraction could enhance the pectin yield from jackfruit rag biowaste. 
Moreover, microwave-assisted extraction can affect the physico-
chemical properties as well as the functionality of extracted pectin (Ling 
et al., 2023). Unfortunately, little is known about this topic and, there-
fore, should be studied. To date, there are no reports comparing con-
ventional heating and microwave-assisted extraction for the recovery of 
pectin from jackfruit rags. Our study, therefore, aims to examine the 
extraction yield, physicochemical properties and antibacterial activity 
of pectin extracted from jackfruit rags. Heat reflux extraction (HRE) and 
microwave-assisted extraction (MAE) were used for investigation and 
comparison of the effect of extraction factors on pectin yield. To maxi-
mize the extraction yield of pectin, the extraction procedure was opti-
mized based on the combination of central composite design (CCD) and 
response surface methodology. Four main extraction factors influencing 
the yield of pectin, including pH, solid–liquid ratio (%, w/v), time of 
extraction (min), and extraction temperature (◦C), were investigated. 
The structural properties of extracted pectin under the optimal 
conditions were characterized using classical technologies, including 
scanning electron microscopy (SEM), Fourier transform infrared spec-
troscopy (FTIR), X-ray diffraction (XRD), and rheology analyses. For 
more description, Fig. 1 shows a comparative diagram of the extraction 
of pectin from jackfruit rags using conventional heating reflux extraction 
and microwave-assisted extraction techniques. 
2. Materials and methods 
2.1. Materials 
Jackfruit rags (JFR) were collected from local markets in Ho Chi 
Minh City, Vietnam. Chemical substances suchas glycerol (≥99% pu-
rity), citric acid (ACS reagent, ≥ 99.5% purity), ethanol (≥99% purity), 
Folin-Ciocalteu reagent, gallic acid monohydrate (ACS reagent, ≥ 98% 
purity), sodium hydroxide (ACS reagent, ≥ 97.0%), phenolphthalein, 
sodium carbonate (≥99% purity), and carbazole (analytical standard) 
were purchased from Sigma-Aldrich, St. Louis, Missouri, USA. 
2.2. Sample preparation 
The JFR samples were washed several times with distilled water to 
remove the impurities and then dried in a forced-air oven at 50 ◦C for 24 
h. The dried JFR was ground in a domestic blender to obtain dried JFR 
powder with a particle size of 2 mm and stored at room temperature for 
pectin extraction. 
Fig. 1. A comparative diagram of extraction of pectin from jackfruit rags using conventional heating reflux extraction (HRE) and microwave assisted extraction 
(MAE) techniques, optimization procedure, characterization, physicochemical analysis, and major advantages of MAE in comparison to HRE. 
N.T.K. Tran et al. 
Food Chemistry 418 (2023) 135807
3
2.3. Extraction of pectin from jackfruit rags 
2.3.1. Screening study 
The extraction of pectin from JFR was carried out by two extraction 
techniques, HRE and MAE. Initially, screening studies (Fig. S1–S4) were 
performed to narrow the value range of the factors and find the central 
value of each factor. Afterward, the design of the experiment for opti-
mization by response surface methodology was determined based on 
these value ranges. 
2.3.2. Conventional heat reflux extraction (HRE) 
Pectin was extracted from dried JFR under reflux in a condensation 
system using acidified water as described previously with some modi-
fications (Zhang et al., 2018). Briefly, 1 g of dried JFR powder was 
extracted with acid citric solution (pH of 1.0, 1.5, 2.0, 2.5) into a 250 mL 
two-neck round-bottom flask. The solid–liquid ratios (SLR) were 1:15, 
1:20, 1:25, and 1:30, and the mixture was heated at various tempera-
tures (80, 85, 90, and 95 ◦C) for 30, 60, 90, and 120 min. Afterward, the 
extracted solutions were centrifuged using a compact clinical centrifuge 
at 5000 rpm for 30 min (EBA 200, Hettich, Germany). The supernatant 
was added to absolute ethanol at a ratio of 1:2 for pectin precipitation, 
and the resulting solution was then stored at 4 ◦C for 24 h. The 
precipitated pectin was filtered through a filter cheesecloth and washed 
three times with absolute ethanol to remove impurities. Thereafter, the 
pectin was dried in a laboratory oven (UNB400, Memmert, Germany) at 
50 ◦C until its weight was stabilized. The final product was then ground 
in a grinder and stored at room temperature for further experiments. The 
yield of pectin was calculated using the following equation (Eq. (1). 
Yield (%) =
Weight of dried pectin (g)
Weight of dried jackfruit straw (g)
× 100 (1) 
2.3.3. Microwave-assisted extraction (MAE) 
The extraction of pectin from dried JFR powder was performed using 
a laboratory microwave synthesis reactor (Discover SP, CEM, USA) at 
2455 MHz with a constant power of 50 W. Briefly, 1 g of the dried JFR 
was mixed with citric acid solution (pH of 1.0, 1.5, 2.0, 2.5) with SLRs of 
1:15, 1:20, 1:25, 1:30 into a 35 mL reactor glass vessel (Pyrex, USA). The 
reactor temperature was set to 60, 65, 70, and 75 ◦C, and the extraction 
time was varied in the range of 5, 10, 15, and 20 min. After finishing this 
process, pectin was recovered from the solution as outlined in Section 
2.3.2. 
2.3.4. Experimental design 
Based on screening studies (Fig. S1–S4), the range of values for the 
design of the experiment by RSM was determined with each factor. In 
this study, the extraction conditions for both HRE and MAE techniques 
were designed by CCD. It should be noted that the type of applied CCD is 
face centered (CCF), which requires three levels (-1, 0, 1) of each factor 
or α = ± 1. To be more specific, four independent factors were selected: 
pH (X1), SLR (X2), extraction time (X3) and extraction temperature (X4). 
These variables were investigated at three different levels coded as –1, 0, 
+1 (Table 1), and the pectin extraction yield was selected as a response. 
For this study, 28 experimental runs in a randomized order were carried 
out to evaluate the synergistic effect between variables and responses 
(Table 2). The obtained experimental data were fitted according to the 
following quadratic polynomial equation (Eq. (2), as presented below. 
Y (%) = β0 + β1X1 + β2X12 + β3X2 + β4X22 + β5X3 + β6X32 + β7X4 + β8X42 
+ β9X1X2 + β10X1X3 + β11X1X4 + β12X2X3 + β13X2X4 + β14X3X4 (2) 
where, Y is a response variable (i.e. pectin extraction yield); βo is 
Table 1 
Levels of the experimental scale and independent factors in the current study. 
Independent factors Unit HRE MAE 
Actual levels 
− 1 0 +1 − 1 0 +1 
pH (A) – 1.0 1.5 2.0 1.0 1.5 2.0 
SLR (B) w/v 1:20 1:25 1:30 1:20 1:25 1:30 
Extraction time (C) min 30 60 90 5 10 15 
Extraction temperature 
(D) 
◦C 85 90 95 60 65 70 
Table 2 
CCD matrix, predicted and experimental responses of pectin extracted from JFR by HRE and MAE methods. 
HRE run Independent variables Pectin yield (%) MAE runs Independent variables Pectin yield (%) 
X1 X2 X3 X4 Exp. Pred. X1 X2 X3 X4 Exp. Pred. 
1 1 20 30 85 15.27 15.49 1 1 20 5 60 16.08 16.68 
2 2 20 30 85 12.09 12.08 2 2 20 5 60 13.01 12.92 
3 1 30 30 85 15.40 15.69 3 1 30 5 60 17.99 18.73 
4 2 30 30 85 10.90 10.58 4 2 30 5 60 13.83 13.18 
5 1 20 90 85 17.04 17.05 5 1 20 15 60 19.44 19.35 
6 2 20 90 85 15.57 15.59 6 2 20 15 60 15.90 15.99 
7 1 30 90 85 16.29 16.03 7 1 30 15 60 19.80 18.90 
8 2 30 90 85 12.52 13.00 8 2 30 15 60 12.62 13.75 
9 1 20 30 95 16.54 16.12 9 1 20 5 70 17.06 16.49 
10 2 20 30 95 13.18 13.42 10 2 20 5 70 14.86 15.35 
11 1 30 30 95 16.92 16.93 11 1 30 5 70 19.01 18.49 
12 2 30 30 95 12.37 12.53 12 2 30 5 70 14.90 15.55 
13 1 20 90 95 17.26 17.63 13 1 20 15 70 19.66 19.88 
14 2 20 90 95 17.24 17.02 14 2 20 15 70 19.32 19.14 
15 1 30 90 95 17.30 17.36 15 1 30 15 70 18.73 19.38 
16 2 30 90 95 15.21 15.03 16 2 30 15 70 17.86 16.84 
17 1 25 60 90 27.30 27.20 17 1 25 10 65 27.95 27.85 
18 2 25 60 90 24.50 24.33 18 2 25 10 65 25.05 24.70 
19 1.5 20 60 90 26.57 26.57 19 1.5 20 10 65 27.65 27.21 
20 1.5 30 60 90 25.77 25.59 20 1.5 30 10 65 27.10 27.09 
21 1.5 25 30 90 22.99 22.81 21 1.5 25 5 65 24.67 24.07 
22 1.5 25 90 90 24.86 24.77 22 1.5 25 15 65 25.89 26.05 
23 1.5 25 60 85 25.92 25.66 23 1.5 25 10 60 27.39 26.60 
24 1.5 25 60 95 27.00 27.01 24 1.5 25 10 70 27.71 28.05 
25 1.5 25 60 90 28.98 28.94 25 1.5 25 10 65 29.41 29.63 
26 1.5 25 60 90 28.44 28.94 26 1.5 25 10 65 29.03 29.63 
27 1.5 25 60 90 28.63 28.94 27 1.5 25 10 65 28.93 29.63 
28 1.5 25 60 90 28.89 28.94 28 1.5 25 10 65 29.78 29.63 
N.T.K. Tran et al. 
Food Chemistry 418 (2023) 135807
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intercept, βi, βii and βij are coefficients of the linear, quadratic and 
interaction term, respectively; Xi and Xj are independent variables. 
2.4. Characterization of JFR pectin 
2.4.1. Moisture, ash, and protein content 
The moisture content of JFR-pectin can be determined based on the 
change in weight before and after heating in a laboratory oven (UNB400 
Memmert, Schwabach, Germany) at 105 ◦C for 24 h (Jiang et al., 2012). 
Ash content can be evaluated based on burning the extracted pectin in a 
furnace (SH Scientific, Sejong-si, Korean) at 550 ◦C for 6 h (Hosseini 
et al., 2019). The protein (N × 6.25) of pectin samples canbe deter-
mined according to Kjeldahl’s method. 
2.4.2. Molecular weight of pectin 
The average molecular weight of the extracted pectin can be 
measured by gel-permeation chromatography (GPC) using an Agilent PL 
- GPC 220 (Agilent, California, USA) with an RID-A refractive index 
detector. For analysis, 2 mg of pectin samples were dissolved in 1.0 mL 
of double-distilled water and filtered using a 0.45 μm cellulose acetate- 
based membrane. The sample (20 μL) was added and eluted with 0.1 M 
NaNO3 at room temperature with a flow velocity of 0.5 mL/min. The 
calibration curve was created using pullulan standards at molecular 
weights of 103–105 Da. 
2.4.3. Degree of esterification (DE) and methoxyl content (MeO) 
The degree of esterification (DE) of pectin can be measured using the 
titrimetric method as reported previously with some modifications 
(Villamil-Galindo & Piagentini, 2022). Briefly, 50 mg of dried pectin was 
moistened with 2 mL of 96% ethanol and subsequently immersed in 20 
mL of double-distilled water at 40 ◦C. Thereafter, the mixture was 
titrated by using 0.1 N NaOH (V1, mL) with phenolphthalein indicator. 
Then, 10 mL of 0.1 N NaOH was added to neutralize the acid residue, 
and the solution was stirred for 2 h and kept stable for 15 min. After that, 
10 mL of 0.1 N HCl was added to titrate with 0.1 N NaOH (V2, mL) using 
phenolphthalein indicator. The degree of esterification (%) and 
methoxyl content were calculated using the following equations (Eq. 
(3), 4). 
DE (%) =
V2
V1 + V2
× 100 (3) 
MeO (%) =
V2 × normality × 3.1
Weight of sample (g)
× 100 (4) 
2.4.4. Galacturonic acid (GA) content 
The galacturonic acid content of JFR pectin can be determined by 
carbazole and sulfuric acid according to a report by Yamei et al. with 
some alterations (Jin & Yang, 2020). In brief, dried pectin was immersed 
and stirred in deionized water at 50 ◦C to obtain a 0.2 mg/mL pectin 
solution. Then, 1 mL pectin solution was mixed with 5 mL of 98% H2SO4 
in a heated water bath at 75 ◦C for 20 min and subsequently cooled to 
room temperature to terminate the reaction. Next, alcohol-based 
carbazole solution (500 μL, 0.15% w/v) was poured into the mixture, 
gently shook and kept stable in the dark for 90 min. Afterward, the 
absorbance was recorded at 530 nm using a UVD-2950 spectropho-
tometer (Labomed, Los Angeles, CA, USA). Galacturonic acid solution 
(0–200 μg/mL) was used to set the standard curve. 
2.4.5. Total phenolic content (TPC) 
The TPC of JFR pectin can be determined using the Folin-Ciocalteu 
method (Piagentini & Pirovani, 2017). One milligram of JFR pectin 
was dispersed in 10 mL of deionized water. Then, 500 μL of pectin so-
lution was added to 500 μL of the reagent Folin-Ciocalteu, 2 mL of 
saturated Na2CO3 solution and 2 mL of deionized water. The mixture 
was shaken and placed in darkness for 60 min at room temperature. 
Next, absorbance was measured at 765 nm in a spectrophotometer 
(Spectro UVD-2950, Labomed, Los Angeles, CA, USA). Gallic acid so-
lutions of 0–100 μg mL− 1 were used for standard calibration. The TPC of 
the extracted pectin was expressed as mg gallic acid equivalents/g of 
dried pectin (mg GAE/g JFR pectin). 
2.4.6. Pectin solubility (PS) 
The solubility of dried JFR pectin was determined according to a 
previous method (Ren et al., 2019). Fifty milligrams of dried JFR pectin 
was dissolved in 40 mL of deionized water, and the mixture was stirred 
for 20 min at room temperature. Then, the solution was centrifuged at 
5000 rpm for 20 min (Hettich model EBA 200, Westphalia, Germany), 
and the undissolved JFR pectin was collected prior to drying using a 
laboratory oven (UNB400 memmert, Schwabach, Germany) at 55 ◦C 
until its weight was stabilized. The percentage of pectin solubility was 
calculated as follows (Eq. (5). 
PS (%) =
Initial dry weight (g) − final dry weight (g)
Initial dry weight (g)
× 100 (5) 
2.4.7. Pectin characterization 
The FTIR spectra of the JFR pectin were obtained using an FTIR 
spectrophotometer (Nicolet, Impact 410, Madison, WI, USA) with po-
tassium bromide (KBr) pellets. The wavenumbers were measured be-
tween 400 and 4000 cm− 1 with a resolution of 4 cm− 1. Scanning 
electron microscopy (SEM) (SU 8010 Hitachi, Chiyoda City, Tokyo, 
Japan) was used to analyze the morphological and structural charac-
teristics of JFR pectin. X-ray diffraction patterns (XRD) of JFR pectin 
were recorded by an X–ray diffractometer with a Cu–kα radiation source 
(Shimadzu XRD–6000, Kyoto, Japan). 
2.4.8. Antioxidant activity 
The antioxidant capacity of the JFR pectin was determined using the 
1,1-diphenyl-2-picrylhydrazyl (DPPH) method. The scavenging activity 
of DPPH was determined based on a method reported previously with 
some modifications (Yang et al., 2008). Briefly, 3 mL of pectin solution 
with different concentrations was mixed with 1 mL of DPPH solution 
(0.3 mM, prepared in ethanol). The mixture was gently stirred and 
allowed to stand in the dark at room temperature for 30 min. The 
absorbance was measured against ethanol at 517 nm using a spectro-
photometer (Spectro UVD-2950, Labomed, Los Angeles, CA, USA). The 
scavenging capacity of the JFR pectin solution was calculated using the 
following equation (Eq. (6). 
DPPH• radical scavenging activity (%) =
A1 − A2
A1
× 100 (6) 
where A1 is the absorbance of the control against ethanol and A2 is the 
absorbance of the mixture of DPPH and the JFR pectin solution. 
2.4.9. Antibacterial activity test 
The antibacterial activities of pectin were evaluated using gram- 
positive bacteria (Staphylococcus aureus and Bacillus cereus) and gram- 
negative bacteria (Pseudomonas aeruginosa and Klebsiella pneumoniae) 
according to the agar diffusion method (Qin et al., 2019). The bacteria 
were incubated in 5 mL lysogeny broth (LB) medium at 37 ◦C for 24 h. 
Then, 100 µL of bacterial liquid was applied to petri plates containing 
brain–heart agar medium. Thereafter, the agar media were punctured to 
form 4 wells, and the pectin solution (concentration of 5 mg/mL, ster-
ilized with ultraviolet light for 15 min) was added into 3 wells. Ultra- 
pure water used as the negative control was placed into the remaining 
well and incubated at 37 ◦C for 24 h. Finally, the antibacterial activity of 
pectin was expressed by the diameter of the inhibition zone formed 
around the well. 
2.4.10. Viscosity and pH 
First, JFR pectin was dispersed into deionized water at different 
N.T.K. Tran et al. 
Food Chemistry 418 (2023) 135807
5
concentrations (0.5, 1.0, 1.5 and 2.0%) at 40 ◦C. The pH of the solutions 
was determined at room temperature using a pH meter Hanna HI2002- 
02 (Hanna Instruments, Woonsocket, United States). The viscosity of 
JFR pectin solutions was determined at room temperature using a 
viscometer (DV2T, Brookfield, Toronto, Canada) equipped with a cone/ 
plate geometry (CPA-40, Brookfield, USA). The samples were investi-
gated in a shear rate range of 1–180 s− 1, and the data were collected by 
rheological software (Rheocalc, Brookfield, USA). 
2.4.11. Statistical analysis 
RSM-based CCD and regression coefficient analysis were conducted 
using Design Expert software version 11.0 (Stat-Ease Inc., Minneapolis, 
USA) and Excel software version 2021 (Microsoft, Washington, USA). 
All experiments were carried out in three replicates, and the results are 
expressed as the mean value ± standard deviation. The differences were 
considered significant at P < 0.05. 
3. Results and discussion 
3.1. Extraction optimization 
The effects of pH, SLR, extraction time, and temperature on the 
extraction yield of pectin from jackfruit rags are summarized in Table 2. 
In general, the extraction yields of pectin using the HRE and MAE 
methods were in the rangeof 10.90–28.89% and 12.92–29.63%, 
respectively. Based on RSM data, the quadratic regression models for the 
extraction of pectin can be shown by two equations (Eq. (7), 8) as 
follows. 
YHRE (%) = 28.94–1.43 X1 − 0.4451 X2 + 0.9831 X3 + 0.6638X4 −
0.4256X1X2 + 0.5189 X1X3 + 0.1776 X1X4 − 0.2715X2X3 + 0.1552 X2X4 +
0.0198 X3X4 − 3.18X12-2.91X22 – 5.15 X32 – 2.62 X42 (7) 
YMAE (%) = 29.63–11.57 X1 – 0.0626 X2 + 0.9899 X3 + 0.7256X4 − 0.4489 
X1X2 + 0.1004 X1X3 + 0.6531 X1X4 – 0.6256X2X3 − 0.0133X2X4 + 0.1805 
X3X4 − 3.36X12-2.48 X22 – 4.57 X32 – 2.31 X42 (8) 
where YHRE and YMAE are the coded pectin extraction yield (%) under 
HRE and MAE methods; X1, X2, X3, and X4 are defined as independent 
variables, including pH, SLR (w/v), time (min), temperature (◦C), 
respectively. 
According to Fig. S5, there is no remarkable difference between the 
practical and predicted yield results of pectin for both methods, indi-
cating that the proposed models had a high compatibility with the 
experimental data. Moreover, the normality assumption seemed to be 
satisfactory since the residual plot nearly followed a straight line, sug-
gesting that the residuals scattered randomly against the variance of 
biowaste origin. As a result, these quadratic models are compatible for 
experimental setups and highly efficient in extracting pectin from 
jackfruit rags. 
The CCD-RSM-based ANOVA results are presented in Table 3. The 
data showed that the linear parameters X1, X2, X3, X4 (HRE) and X1, X3, 
X4 (MAE), all quadratic parameters (X12, X22, X32, X42 for both HRE and 
MAE methods) and interaction models X1X2, X1X3, X2X3 (HRE) and 
X1X2, X1X4, X2X3 (MAE) had significant effects on the responses (P <
0.05). Otherwise, the linear term of solid to liquid ratio X3 (MAE), the 
interaction coefficients of the model X1X4, X2X4, X3X4 (HRE) and X1X3, 
X2X4, X3X4 (MAE) were not significant (P > 0.05). 
Remarkably, pH was considered the most influential parameter on 
the pectin extraction efficiency, followed by the solid-to-liquid ratio, 
time and temperature. The high F value (597.81 for HRE and 96.14 for 
MAE) and P value (<0.0001) of the two models for both methods were 
all<0.05, revealing that the models were totally significant. The corre-
lation coefficients R2 of YHRE and YMAE were 0.9984 and 0.9904, 
respectively, meaning that approximately 0.16% and 0.96% of the total 
variation were not explained by these models. Furthermore, the P values 
of the “lack-of-fit” value (LOF) of the regression model for both re-
sponses were 0.2660 (HRE) and 0.0951 (MAE) (P > 0.05), indicating 
that the lack of fitness for each case was insignificant, corresponding to 
pure error. 
To visualize the interaction between pH, SLR, extraction time, and 
extraction temperature on pectin extraction, three-dimensional (3D) 
response surfaces are shown in Fig. 2. For pectin extraction, a low pH is 
often favored to disrupt ester linkages and hydrogen bonds between 
pectin and the cell wall of the fruit. In the case of HRE (Fig. 2a1-a3), the 
maximum pectin yield was reached at pH 1.47, and above this pH, the 
yield of pectin probably decreased. Similar behavior was also observed 
at pH 1.35 in the case of the MAE technique (Fig. 2b1-b3). These find-
ings were consistent with the results obtained by Hosseini and co-
workers (Hosseini et al., 2016b), who extracted pectin from an orange 
peel by a microwave-assisted method. The effect of SLR on the extrac-
tion yield is depicted in Fig. 2a3-6 and Fig. 2b3-6. Increasing the solid to 
liquid ratio up to 1:24 g/mL improved the contact area between jackfruit 
rag powder and extraction solvent, leading to an increase of pectin in the 
solution. It can be explained that a further increase in the SLR leads to a 
decrease in pectin yield as a result of the dynamic balance between the 
solid and the liquid, which could reduce the rate of the mass transfer 
process (Prakash Maran et al., 2014). 
According to Fig. 2a2, 3, 6 and Fig. 2b2, 3, 6, the extraction yield of 
Table 3 
CCD-based on ANOVA to investigate the significance of model parameters on pectin yield (%) under HRE and MAE methods. 
Source HRE MAE 
Coefficient F-value P-value Coefficient F-value P-value 
Model 28.94 597.81 <0.0001 29.63 96.14 <0.0001 
X1 − 1.43 294.89 <0.0001 − 1.57 67.29 <0.0001 
X2 − 0.4451 29.11 0.0001 − 0.0626 0.1064 0.7495 
X3 0.9831 142.05 <0.0001 0.9899 26.60 0.0002 
X4 0.6638 64.76 <0.0001 0.7256 14.29 0.0023 
X1X2 − 0.4256 23.66 0.0003 − 0.4489 4.86 0.0461 
X1X3 0.5189 35.17 <0.0001 0.1004 0.2431 0.6302 
X1X4 0.1776 4.12 0.0645 0.6531 10.29 0.0069 
X2X3 − 0.2715 9.63 0.0086 − 0.6256 9.44 0.0089 
X2X4 0.1552 3.14 0.1010 − 0.0133 0.0043 0.9489 
X3X4 0.0198 0.0510 0.8256 0.1805 0.7858 0.3915 
X12 − 3.18 227.58 <0.0001 − 3.36 43.83 <0.0001 
X22 − 2.91 172.54 <0.0001 − 2.48 23.93 <0.0003 
X32 − 2.98 549.65 <0.0001 − 4.57 81.40 <0.0001 
X42 − 1.62 139.54 <0.0001 − 2.31 20.71 0.0005 
Lack-of-Fit 2.31 0.2660 5.44 0.0951 
R2 0.9984 0.9904 
Adj R2 0.9968 0.9801 
Pred R2 0.9899 0.9329 
N.T.K. Tran et al. 
Food Chemistry 418 (2023) 135807
6
pectin significantly increases when prolonging the extraction time, 
attaining a maximum value at 60.41 min for HRE and 10.56 min for 
MAE. A longer extraction duration could lead to diminished extraction 
yield of pectin as a result of overexposure of the matter under heating 
and thereby disintegration of the as-obtained pectin (Simsek et al., 
2012). Temperature is also an influential parameter affecting the pectin 
extraction efficiency. As shown in Fig. 2a3,5,6 and Fig. 2b3,5,6, the yield 
of pectin increased when the temperature increased to 90.47 ◦C (HRE) 
and 65.99 ◦C (MAE), which was probably because of the enhanced 
solubility and diffusivity of pectin from the solid particles into the 
extraction solvent (Hosseini et al., 2016a). Furthermore, swelling and 
loosening effects are the two major factors that improve the penetration 
Fig. 2. 3D response surface of experimental design on the pectin extraction yield from jackfruit rags obtained by HRE (a1-a9) and MAE (b1-b9) methods. 
N.T.K. Tran et al. 
Food Chemistry 418 (2023) 135807
7
of solvent as well as the infusion of pectin into the liquid medium (Lu 
et al., 2019). However, a higher temperature could lead to the partial 
degradation of the pectin structure, decreasing the pectin yield. 
With high correlation coefficients R2 (0.9984 for HRE and 0.9904 for 
MAE), Eqs. (6) and (7) could be applied to predict the extraction yield of 
pectin. According to RSM models, the optimum extraction conditions for 
HRE were a pH of 1.47, SLR of 1:24.87 (g/mL), a duration time of 60.41 
min and a temperature of 90.48 ◦C. In the case of MAE, the extraction 
should be conducted under the following conditions: pH of 1.35, SLR of 
1:24.87 (g/mL), duration of 10.56 min, and temperature of 65.99 ◦C. At 
these optimum conditions, the predicted extraction yields for HRE and 
MAE were 28.71 and 29.87%, respectively. Similar results were recor-
ded for experimental data with 29.06% (for HRE) and 29.59% (for MAE) 
extraction yields. In the comparison between the two methods, the 
advantage of MAE is very clear. These results were in line with some 
studies described in a recent publication (Baltacıoğlu et al., 2021). The 
extraction efficiencies of HRE and MAE were similar, but the latter 
required a lower extractiontemperature, reducing the extraction time 
Fig. 3. XRD patterns (a), FTIR spectra (b) of pectin extracted from jackfruit rags under HRE and MAE methods, SEM images (c-f) of pectin extracted from jackfruit 
rags by HRE (c, d) and MAE (e, f) methods at 300 and 1.0 k × magnification. 
N.T.K. Tran et al. 
Food Chemistry 418 (2023) 135807
8
by approximately six times. Compared to other studies relating to pectin 
extracted from jackfruit wastes, the extraction efficiency of JFR pectin 
was higher than that produced from ultrasonic-microwave assisted 
(17.2%) and conventional heating methods (25.1%) (Xu et al., 2018) but 
lower than the slimy sheath pectin obtained from the conventional 
heating method of jackfruits (35.52%) (Kumar et al., 2021). 
3.2. Characterization of pectin extracted from jackfruit rags 
3.2.1. X-ray diffraction 
XRD patterns of pectin obtained from jackfruit rags by heating reflux 
and microwave heating methods were recorded to provide more infor-
mation about their structural characteristics. As shown in Fig. 3a, the 
crystalline material exhibits several sharp peaks, while the amorphous 
material shows a broad peak. A series of sharp peaks at 2θ degrees of 
12.8◦, 14.2◦, 16.6◦, 18.0◦, 19.4◦, 21.6◦, 24.0◦, 26.0◦, 28.8◦, 31.1◦, 33.4◦, 
36.1◦, 37.1◦, 41.0◦, 43.1◦, and 51.4◦ could be observed in the XRD dif-
fractogram of pectin from microwave heating, indicating that the pectin- 
MAE showed a crystalline structure (Kazemi et al., 2021). In pectin-HRE, 
several sharp and intense peaks were observed at 14.7◦, 18.2◦, 21.1◦, 
31.0◦, 36.4◦, and 43.1◦, revealing that this sample had an amorphous 
nature, but there were also some crystalline regions in the pectin-HRE 
structure. A slight difference between the two XRD patterns could be 
explained by the different pectin extraction techniques from jackfruit 
rags. Based on the combination of XRD and SEM, it can be assumed that 
MAE had a stronger influence on disrupting plant cell walls than HRE. 
This phenomenon may be because the molecular weight of MAE-pectin 
was smaller than that of HRE-pectin. Because long-chain biopolymers 
are not favored for the formation of crystalline structures, amorphous 
particles dominated in HRE-pectin, while some crystals were detected in 
MAE-pectin. 
3.2.2. Surface chemistry 
Infrared spectroscopy (FTIR) can be used to investigate the presence 
of chemical bonds in pectin polysaccharides extracted from jackfruit 
rags with different methods. As depicted in Fig. 3b, the FTIR spectra of 
JFR pectin produced from the HRE and MAE methods are highly similar. 
The peaks at 3457 cm− 1 (HRE) and 3625 cm− 1 (MAE) were associated 
with the vibration of O–H stretching. The bands associated with the 
C–H stretching of the –CH, –CH2 and CH3 groups of pectin were 
ascribed to 2942–2892 cm− 1. The two absorption peaks at 1735–1731 
cm− 1 and 1633–1624 cm− 1 were attributed to C––O stretching of 
esterified carboxyl groups (COO–R) and carboxylate groups (COO–), 
respectively (Wang et al., 2015). In addition, the peaks observed at 
1441–1440 cm− 1 and 1370–1332 cm− 1 correspond to the stretching 
vibration of carboxyl and hydrocarbon groups, indicating the existence 
of protein in the HRE and MAE pectin samples. The peaks at 1233 cm− 1 
and 1105 cm− 1 were attributable to the C–C cyclic linkages and 
C–O–C glycoside linkages in the pyranose rind, while the bands in the 
range of 1079–1016 cm− 1 were possibly related to the presence of 
sugars, e.g., galactose, arabinose and xylose (Baum et al., 2017). Based 
on the FTIR spectra of pectin samples, our findings are in good agree-
ment with those of pectin extracted from hawthorn (Qin et al., 2022). 
3.2.3. Morphology 
In this study, SEM was applied to visualize the microstructure of the 
pectin sample. Fig. 3(c–f) presents the SEM images of pectin extracted 
from jackfruit rags by the HRE and MAE methods with different mag-
nifications. The surface morphology of pectin extracted by HRE was 
rougher and tighter than that of pectin extracted by MAE. However, 
pectin produced from MAE exhibited a smooth, loose and continuous 
morphology with some irregularly shaped particles on the surface. From 
these results, it could be suggested that the structure of pectin samples 
extracted by both HRE and MAE was slightly different, which might be 
due to the difference in extraction methods (Liew et al., 2016). Specif-
ically, pectin extracted by HRE endured a long process at high 
temperature. This might lead to a change in textual structure and 
inherent physicochemical properties, causing more defects and rough-
ness on the surface. The looser structure of extracted pectin from orange 
skin under the microwave heating method could be due to the stronger 
destructive influence on the degree of disintegration of the plant mate-
rial, which not only helped to ease the release of the pectin but also had 
effects on its structural surface. 
3.3. Properties of pectin extracted from jackfruit rags 
3.3.1. Physicochemical properties 
It is well known that the characteristics and properties of pectin have 
a strong influence on the method of extraction as well as the different 
sources. The physicochemical properties consisted of moisture, ash, pH, 
1,4-linked α-d-galacturonic acid (GaIA) content, degree of esterification 
(DE), number average molecular weight (Mn) and average molecular 
weight (Mw) for the pectin extracted from jackfruit rags by both HRE 
and MAE methods, which are summarized in Table 4. It can be seen that 
HRE pectin and MAE pectin were quite similar in moisture content, ash 
content and pH, while the protein content of the latter was smaller. The 
GaIA content and DE are often considered important parameters to 
evaluate the gelling capacity and the applications of pectin. In com-
parison between HRE and MAE pectins, the GA content of HRE pectin 
(66.31 ± 0.80%) was significantly higher than that of MAE pectin 
(61.53 ± 0.70%). A similar result was obtained by researchers who re-
ported a higher GA content (95.54 ± 5.84%) for lime peel pectin 
extracted under the conventional heating method in comparison with 
the microwave heating extraction (81.95 ± 2.14%) (Rodsamran & 
Sothornvit, 2019). The DE values of HRE and MAE pectins were 65.54 ±
0.07% and 64.61 ± 0.20%, respectively, meaning that these samples 
could be classified as high methoxyl pectin (HMP, DE > 50%). The re-
sults were in line with the findings of Sucheta et al., who also recorded a 
similar trend of DE values of pectin extracted from black carrot pomace 
using three different methods (microwave, ultrasound, and conven-
tional heating) (Sucheta et al., 2020). In contrast, Bagherian et al. found 
that pectin extracted from grapefruit under the MAE process gave a 
higher DE than the pectin obtained by conventional heating (Bagherian 
et al., 2011). 
The molecular weight of pectin is closely associated with its func-
tional properties, i.e., emulsifying and rheological behavior. According 
to Table 4, the pectin from jackfruit rags under the microwave heating 
process had a Mw of 232.75 kDa, which was lower than that of pectin 
produced from heating reflux (Mw = 431.85 kDa). This finding was also 
in accordance with the research conducted by a recent study, which 
obtained a higher Mw (280 kDa) of potato pectin produced from con-
ventional citric acid extraction in comparison with the Mw (154 kDa) of 
potato pectin produced from MAE (Yang et al., 2018). In another study 
extracting pectin from grape jackfruit peel with citric acid, Xu et al. also 
reported that the Mw of pectin produced from conventional heating 
Table 4 
Characteristics of pectin extracted from jackfruit rags under HRE and MAE 
methods. Note that each experiment was carried out three independent timesto 
calculate mean of data points and error bars. 
Component HRE MAE 
Moisture content (%) 9.25 ± 0.06 11.38 ± 1.15 
Ash content (%) 1.31 ± 0.12 1.15 ± 0.02 
GaIA content (%) 66.31 ± 0.80 61.53 ± 0.70 
DE (%) 65.54 ± 0.07 64.61 ± 0.20 
Protein content (%) 4.11 ± 0.02 2.10 ± 0.01 
Solubility (%) 99.9 ± 0.115 97.87 ± 0.23 
MeO (%) 6.53 ± 0.03 5.81 ± 0.04 
pH 2.16 ± 0.05 2.18 ± 0.02 
TPC (mg GAE/g pectin) 3.72 ± 0.02 4.64 ± 0.04 
Mn (kDa) 249.05 130.73 
Mw (kDa) 431.85 232.75 
Mw/Mn 1.73 1.78 
N.T.K. Tran et al. 
Food Chemistry 418 (2023) 135807
9
(Mw = 52.3 kDa) was higher than that of pectin produced from 
ultrasonic-microwave-assisted extraction (Mw = 51.5 kDa) (Xu et al., 
2018). 
3.3.2. Properties of viscosity 
Pectin is one of the most popular additives in the food and phar-
maceutical industries. It is mainly used as a gelling/thickening agent, 
and therefore, it is necessary to know the rheological behavior of pectin 
solutions. Viscosity profiles of jackfruit pectin solutions at different 
concentrations are depicted in Fig. 4a,b. As expected, the apparent 
viscosity of both the HRE and MAE-pectin solutions substantially 
decreased with increasing shear rate. This shear-thinning behavior was 
also reported by Hosseini et al., who studied the viscosity of pectin 
extracted from sour orange peel (Hosseini et al., 2016a). When 
increasing pectin concentrations in a range of 0.5% to 2.0% (w/v), the 
viscosity of solutions strongly increased due to the interactions between 
polysaccharide chains of biopolymer with water molecules. In compar-
ison between HRE and MAE-pectin solutions, the latter showed a lower 
viscosity at the same concentrations (1–2%). This result was in line with 
the findings from SEM and XRD. Because MAE-pectin had a smaller Mw 
and a higher degree of crystallinity than HRE-pectin, the effect of flow 
orientation on MAE-pectin molecules was stronger, resulting in a lower 
viscosity. 
3.3.3. DPPH radical scavenging activity 
DPPH• scavenging, a well-known stable free radical with unpaired 
electrons, can be used as a simple approach for the assessment of the free 
radical scavenging activity of antioxidants. The DPPH• scavenging ca-
pacities of pectin obtained from jackfruit rags by heating reflux 
extraction and microwave heating are shown in Fig. 4c. With an increase 
in the pectin concentration from 5 to 50 mg/mL, the scavenging effect of 
free radicals also improved for the pectin obtained from both methods. 
However, there was a slight difference between the DPPH• radical 
scavenging ability of pectin produced from HRE and MAE. The IC50 
(15.79%) value of the DPPH• radical scavenging rate was lower in the 
case of pectin-MAE than in the case of pectin-HRE (IC50 = 21.43%), 
indicating that the scavenging activity of pectin produced from micro-
wave heating was significantly stronger than that of pectin produced 
from heating reflux. The difference in the antioxidant activities of the 
pectin obtained from both methods was probably due to the difference 
Fig. 4. Viscosity curves of pectin extracted from jackfruit rags by HRE (a) and MAE (b) methods, DPPH radical scaveging activities (c) of the jackfruit rags pectin 
produced by HRE and MAE methods at various concentrations; vitamin C was used as a positive control. Note that each experiment was carried out three independent 
times to calculate mean of data points. 
N.T.K. Tran et al. 
Food Chemistry 418 (2023) 135807
10
Table 5 
Antibacterial pictures of pectin against P. aeruginosa, S. aureus, K. pneumoniae, B. cereus. 
N.T.K. Tran et al. 
Food Chemistry 418 (2023) 135807
11
in the total phenolic contents and the molecular and structural proper-
ties of the polymers (Bayar et al., 2018). 
3.3.4. Antibacterial analysis of pectin 
The antimicrobial activities of pectin extracted from jackfruit rags 
were investigated against the test organism shown in Table 5. The di-
ameters of the inhibition region of MAE-pectin against S. aureus, B. ce-
reus, P. aeruginosa, and K. pneumoniae were 18,33 ± 1.15 mm, 5.43 ±
0.47 mm, 4.67 ± 0.37 nm, and 6.67 ± 0.57 nm, respectively. The in-
hibition zone diameter of HRE-pectin for S. aureus was 10.67 ± 1.15 
mm, for B. cereus was 4.77 ± 0.56 nm, for P. aeruginosa was 5.33 ± 0.63 
mm, and for K. pneumoniae was 7.67 ± 0.58 mm. These results are 
competitive with those of a recent study, which reported that the inhi-
bition zones of films incorporated with pectin extracted from Morinda 
citrifolia fruit extract against E. coli and S. aureus were 8.68 and 11.42 
mm, respectively (Lin et al., 2023). 
4. Conclusion 
In this study, conventional heating reflux and microwave heating 
methods to extract pectin from jackfruit rags under optimized conditions 
were compared using the RSM-CCD approach. The optimized conditions 
for pectin extraction efficiency were found at pH 1.47, SLR of 1: 24.87 
(g/mL), duration of 60.41 min, temperature at 90.48 ◦C for HRE and pH 
1.35, SLR of 1: 24.87 (g/mL), duration of 10.56 min, temperature at 
65.99 ◦C for MAE. The highest extraction efficiency was predicted at 
29.06% for HRE-pectin, compared with 29.87% for MAE-pectin. This 
outcome was in agreement with results from other validation experi-
ments (29.59 ± 0.79% for pectin-MAE and 28.71 ± 0.98% for pectin- 
HRE). The structural properties of pectin-HRE, such as DE, GA, and 
Mw, were higher than those of pectin-MAE. However, the DPPH scav-
enging activity and viscosity value of the pectin-MAE were significantly 
higher than those of pectin-HRE. Our findings also displayed a higher 
antibacterial activity of pectin-HRE than that of pectin-MAE. This study 
might provide a new source of pectin extraction from jackfruit rags, and 
the obtained pectin could be a promising ingredient in food packaging. 
Funding 
This work was funded by Nong Lam University Ho Chi Minh City, 
Vietnam under project ID: CS-CB22-KH-02. 
CRediT authorship contribution statement 
Ngan Thi Kim Tran: Conceptualization, Methodology, Investiga-
tion, Data curation. Viet Bao Nguyen: Data curation. Thuan Van Tran: 
Writing – review & editing, Conceptualization, Supervision. Thuy Thi 
Thanh Nguyen: Writing – review & editing, Supervision. 
Declaration of Competing Interest 
The authors declare that they have no known competing financial 
interests or personal relationships that could have appeared to influence 
the work reported in this paper. 
Data availability 
Data will be made available on request. 
Acknowledgements 
The authors gratefully acknowledge Nong Lam University Ho Chi 
Minh City for financial support for facilities provides through project ID: 
CS-CB22-KH-02. 
Appendix A. Supplementary data 
Supplementary data to this article can be found online at https://doi. 
org/10.1016/j.foodchem.2023.135807. 
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	Microwave-assisted extraction of pectin from jackfruit rags: Optimization, physicochemical properties and antibacterial act ...
	1 Introduction
	2 Materials and methods
	2.1 Materials
	2.2 Sample preparation
	2.3 Extraction of pectin from jackfruit rags
	2.3.1 Screening study
	2.3.2 Conventional heat reflux extraction (HRE)
	2.3.3 Microwave-assisted extraction (MAE)
	2.3.4 Experimental design
	2.4 Characterization of JFR pectin
	2.4.1 Moisture, ash, and protein content
	2.4.2 Molecular weight of pectin
	2.4.3 Degree of esterification (DE) and methoxyl content (MeO)
	2.4.4 Galacturonic acid (GA) content
	2.4.5 Total phenolic content (TPC)
	2.4.6 Pectin solubility (PS)
	2.4.7 Pectin characterization
	2.4.8 Antioxidant activity
	2.4.9 Antibacterial activity test
	2.4.10 Viscosity and pH
	2.4.11 Statistical analysis
	3 Results and discussion
	3.1 Extraction optimization
	3.2 Characterization of pectin extracted from jackfruit rags
	3.2.1 X-ray diffraction
	3.2.2 Surface chemistry
	3.2.3 Morphology
	3.3 Properties of pectin extracted from jackfruit rags
	3.3.1 Physicochemical properties
	3.3.2 Properties of viscosity
	3.3.3 DPPH radical scavenging activity
	3.3.4 Antibacterial analysis of pectin
	4 Conclusion
	Funding
	CRediT authorship contribution statement
	Declaration of Competing Interest
	Data availability
	Acknowledgements
	Appendix A Supplementary data
	References