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Food Sci Nutr. 2024;12:3935–3948.
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3935wileyonlinelibrary.com/journal/fsn3
Received: 13 October 2023
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Revised: 20 January 2024
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Accepted: 14 Februar y 2024
DOI: 10.1002/f sn3 .40 52
ORIGINAL ARTICLE
Gum tragacanth, a novel edible coating, maintains biochemical
quality, antioxidant capacity, and storage life in bell pepper
fruits
Mohammad Reza Zare- Bavani1 | Mostafa Rahmati- Joneidabad1 | Hossein Jooyandeh2
This is an op en access arti cle under the ter ms of the Creative Commons Attribution L icense, which pe rmits use, dis tribu tion and reprod uction in any med ium,
provide d the original wor k is properly cited.
© 2024 The Aut hors. Food Science & Nutrition published by W iley Periodicals LLC.
1Depar tment of Horticultural Scie nce,
Faculty of Agriculture, Agricultural
Science s and Natu ral Resources University
of Khuzestan, Mollasani, Iran
2Depar tment of Food Science, Faculty
of Animal a nd Food Science, Agric ultural
Science s and Natu ral Resources University
of Khuzestan, Mollasani, Iran
Correspondence
Mohammad Reza Zare- Bavani,
Depar tment of Horticultural Scie nce,
Faculty of Agriculture, Agricultural
Science s and Natu ral Resources University
of Khuzestan, Mollasani, Iran.
Email: mzarebavani@asnrukh. ac.ir and
mzarebavany@gmail.com
Funding information
Agricultural Scien ces and Natural
Resources University of Khuzes tan,
Grant /Award Number: 928/411/1
Abstract
Bell pepper fruits (Capsicum annuum L.) are prone to both physiological and patho-
logical deterioration following har vest, primarily due to their high metabolic activity
and water content. The storage of bell peppers presents several challenges, includ-
ing weight loss, softening, alterations in fruit metabolites and color, increased decay,
and a decline in marketability. The application of edible coatings (ECs) is one of the
environmentally friendly technologies that improves many post- harvest quantitative
and qualitative characteristics of products. This research investigated the impact of
different levels of gum tragacanth (GT) coating (0, 0.25, 0.5, 1, and 2%) on the physio-
logical and biochemical traits of stored bell pepper fruits (BPFs) (8 ± 1°C, 90–95% RH)
for 28 days. The results showed the positive effect of coating treatments with higher
concentrations of GT, up to 1%. Increasing the concentration of GT to 2% decreased
the marketability and quality characteristics of fruits compared to 1% GT. After stor-
age, the physiological weight loss of the fruits treated with 1% GT (10.46%) was lower
than that of the uncoated fruits (18.92%). Furthermore, the coated fruits (1% GT)
had more firmness, total phenol content, ascorbic acid, and titratable acidity content
than uncoated fruits during storage. At the end of storage, the coated BPFs with 1%
GT showed higher SOD (97.02 U g−1 ), CAT (24.38 U g−1 ) and POD (0.11 U g−1) activi-
ties and antioxidant capacity (81.74%) as compared to other treatments. Total soluble
solids, total carbohydrates, total carotenoids, pH, malondialdehyde, and electrolyte
leakage content increased in coated fruit during storage but were significantly lower
than in uncoated fruits. Moreover, the samples coated with GT (1%) maintained good
marketability (about 75%), while the marketability of the control (about 40%) was un-
acceptable. The study shows that GT (1%) coating can be a promising novel treatment
option for increasing the storage quality of BPFs.
KEYWORDS
antioxidant enzymes, lipid peroxidation, marketability, total carotenoid, total phenol
3936
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Z AR E- B AVAN I et al .
1 | INTRODUCTION
Bell peppers (Capsicum annuum L.) are one of the most significant
commercial crops, cultivated and consumed on an enormous scale.
BPFs are one of the most widely consumed foods worldwide due to
their attractive colors, strong taste, high nutrients, bioactive com-
pounds such as vitamins C, A, B, and E, carotenoids, phenolic com-
pounds, as well as antioxidant and antimicrobial substances (Kumar
et al., 2021; Rodríguez et al., 2020). It has been reported that the
global cultivation of bell peppers spans an area of 1.99 million hect-
ares, with a total produc tion of 38 million metric tons. This crop is
grown in 126 countries across the world (Tiamiyu et al., 2023). More
than 70% of greenhouse products are dedicated to vegetables.
Among them, greenhouse bell peppers, with 270,000 tons of an-
nual production, are the third most important greenhouse product
in Iran (MA J, 2023) and many other countries, which has found a
good export market. Despite the high quality and compliance with
health conditions in greenhouse pepper production, pepper fruits
usually suf fer from many post- harvest problems, such as quality loss
and reduced shelf life, chilling injury at temperatures below 7°C,
susceptibility to diseases, and shriveling, along with rapid weight
loss (Edirisinghe et al., 2014; Kumar et al., 2021; Martinez- Romero
et al., 2006; Xing et al., 2011).
Packaging plays a crucial role in the food industry, ensuring
the protection and preservation of products. Edible coatings, as
a specific type of packaging, offer unique advantages in terms
of extending shelf life, enhancing quality, and reducing waste
(Han, 2014). One of the successful methods used in the storage
and handling of fruit and ve get able prod ucts to preserve th e post-
harvest qualit y and quantity of these products is the use of edible
coatings (ECs) (Andriani & Handayani, 2023; Dhall, 2013; Salehi,
2020). By creating a semi- permeable membrane layer, ECs reduce
gas exchange with the environment, moisture loss, respiration,
physiological disorders (such as browning, color change, taste
change, and loss of nutrients), and microbial activity, and thus
increase the shelf life and better preserve the quantitative and
qualitative traits of these products (Ali et al., 2015; Andriani &
Handayani, 2023; Nasiri et al., 2017; Salehi, 2020). Anot her ad van -
tage of ECs is their naturalness. They can be consumed with fruits
and vegetables (Andriani & Handayani, 2023). Various compounds
are used as ECs and are usually protein- , lipid- , or polysaccharide-
based compounds (Andriani & Handayani, 2023; Dhall, 2013;
Salehi, 2020). Some ECs used to maintain the freshness and qual-
ity of fruits and vegetables are derived from hydrocolloids, includ-
ing gums, chitosan, and alginate (Valero et al., 2013; Raghav et al.,
2016). Among ECs, polysaccharide- based ones have the most ap-
plication to increase the shelf life of fruit s and vegetables (Nasiri
et al., 2017).
Gum tragacanth (GT) is one of the three import ant and abundant
secretory gums secreted spontaneously or by scratching on differ-
ent species of Astraglus (Nasiri et al., 2 017). This natural polysaccha-
ride is safe and non- toxic for food consumption. It is also stable and
environmentally friendly in a wide pH range, and is mainly found in
the mountainous and semi- desert regions of Iran and Asian coun-
tries (Hemmati & Ghaemy, 2016). GT has been recognized as an ap-
proved additive by the European and American Scientific Committee
on Food for several decades (Ghayempour et al., 2015), and it is
widely utilized worldwide as a thickener, stabilizer, emulsifier, fat
substitute, and binding agent in food and pharmaceutical systems
(Kurt et al., 2016). GT contains natural antimicrobial and antioxidant
compounds, and it s use as an EC increases the shelf life and pre-
serves the quality of edible mushrooms (Nasiri et al., 2017, 2 019).
It has been reported that GT maintains the post- harvest quality of
apricots by reducing oxidative stress (Ali et al., 2015). Researchers
have shown that GT increases the shelf life of apricots (Ziaolhagh
& Kanani, 2021) and preser ves the storage quality of tomatoes
(Jahanshahi et al., 2023).
Currently, the advantages of chitosan as an edible coat-
ing for bell peppers have been scientifically substantiated, es-
tablishing it as one of the most effective options (Gholamipour
Fard et al., 2009; Kumar et al., 2021; Taheri et al., 2020; Xing
et al., 2011). Nonetheless, the issue of affordability remains a
challenge, particularly in developing and third- world nations. GT
posses ses desir able p hysical and chem ical prop er ti es f or u se a s a
coating. It is widely available and more cost- effective compared
to other coatings, such as chitosan. The objective of this study
was to examine the impact of GT, used without any additives, as
a tasteless and colorless food coating, on the shelf life, as well as
the physiological and biochemical characteristics, of greenhouse
BPFs.
2 | MATERIALS AND METHODS
2.1 | Sampling
The study utilized sweet red bell peppers (Capsicum annuum L.)
that were cultivated in a greenhouse (32°19′83″N, 48°72′19″E).
These BPFs were selected based on their uniform size and absence
of contamination, and they were harvested at the breaking point
stage. After the initial cooling st age (8°C, 12 h) (Xing et al., 2011),
the BPFs were transported to the laborator y (the Hor ticultural
Science Department of Agricultural Sciences and Natural Resources,
University of Khuzestan, Ahvaz, Iran).
2.2 | Preparation of raw materials and
experimental design
All the chemicals utilized in the research were obtained from Sigma
Chemical Corporation (St. Louis, MO). GT solutions (0.0 0, 0.25,
0.50, 1.00, and 2.0 0% W:V) were prepared following the methodol-
ogy outlined by Ziaolhagh and Kanani (2021). To elaborate, 2.5, 5.0,
10.0, and 20.0 g of GT powder were dissolved in 1000 mL of distilled
water at 40°C for 10 min. The control group was prepared using dis-
tilled water. Glycerol (1%, as a sof tener) and Tween 80 (0.05%, as an
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3937
ZA RE- BAVANI et al.
emulsifier) were added to the solutions, and the mixture was stirred
for 30 min with an electric stirrer to achieve a uniform solution. The
solutions were then refrigerated for 24 h before being utilized for
the treatments.
Prior to treatment, the fruits were disinfec ted with a 0.05%
sodium hypochlorite (NaClO) solution for 3 min and subsequently
air- dried at room temperature. The final coating solutions were
homogenized with a stirrer for 30 min prior to application, and
the BPFs were immersed in varying amounts of GT (0.00, 0.25,
0.50, 1.00, and 2.0 0%) for 5 min. Subsequently, the coated BPFs
were dried, packed in polystyrene boxes, and stored at 8 ± 1°C
with 90–95% relative humidity (Ullah et al., 2017 ) for a duration
of 28 days. At seven- day intervals, the BPFs were removed from
cold storage to assess physiological weight loss, fruit firmness,
total soluble solids, titratable acidity, total carbohydrates, total
phenol, ascorbic acid, total carotenoid, marketability, total antiox-
idant capacity, antioxidant enzyme activity, lipid peroxidation, and
membrane leakage.
2.3 | Physicochemical measurements
2.3.1 | Physiological weight loss
Physiological weight loss was measured according to the method
described by Samira et al. (2013). The stored BPFs were weighed at
the beginning and at seven- day intervals for 4 weeks. Total weight
loss was determined as the difference between the initial weight and
each sampling time, and was calculated as follows:
where Wi = the initial weight of the sample, and Wf = the final weight of
the sample at each measurement time.
2.4 | Fruit firmness
The texture firmness of BPFs was measured using a texture analyzer
(Stable Micro System Texture Analyzer, TA, XT2i, UK). The fruits
were analyzed with a 2 mm diameter probe at a speed of 10 mm min−1
to pierce the equatorial location of the fruit (five points), and the
results were expressed as the maximum penetration force (N) during
tissue breakage (Kumar et al., 2021).
2.5 | The percentage of marketable fruits
The visual assessment of the marketable fruit percent age was
conducted based on the out ward quality of the fruits. Initially, the
samples were placed in sealed plastic containers with random num-
bers assigned to them. These containers were then distributed to a
group of trained individuals known as the test panel, consisting of
20 panelists. The quality of the fruits was evaluated using a ranking
system ranging from 1 to 9, which determined their suitability for
the market. Parameters such as size, color, tissue firmness, and the
presence of fungal or bacterial decay were considered during the
visual assessment. Fruits with a score of five or above were consid-
ered marketable, while those with a score below five were deemed
unmarketable (Samira et al., 2013).
2.6 | Total soluble solids (TSS)
Three pieces of the BPFs (100 g) from each replication and three
replications per treatment were randomly taken and mixed into
homogeneous solutions using an electric mixer. This extract was
used for TSS, TA, and pH measurements. The total dissolved sol-
ids of pepper extracts were measured using a por table refractom-
eter (Milwaukee model 871, Romania). The device was calibrated
using distilled water. The results were expressed in °Brix (Kumar
et al., 2021).
2.7 | Titratable acidity (TA)
The prepared extract (10 mL) was passed through a funnel contain-
ing Whatman No. 1 filter paper for filtration. An equal volume of
distilled water was combined with the filtered extract. The resulting
solution was immediately titrated using NaOH (0.1 N) until reaching
a pH of 8.2. The amount of NaOH used in the following formula was
used to calculate TA and was reported as a percentage in terms of
citric acid (Kumar et al., 2021):
where VNaoH is the volume of sodium hydroxide used, and 0.64 is the
conversion factor for citric acid.
2.8 | Maturity index (TSS/TA)
The maturity index was calculated by dividing the TSS value of each
sample by the percentage of TA.
2.9 | pH
To begin, 20 mL of the prepared extract was carefully transferred
into a beaker. Subsequently, 100 mL of distilled water with a pH
of 7 was added to the beaker. Throughout t he measurement pro-
cess, an electric stirrer was utilized to stir the mixture. The pH
of the extracts was then determined using a digital pH meter
(InoLab 7110, Germany). Each measurement consisted of two
samples per replicate, ensuring a more comprehensive assess-
ment of the pH values.
Physiological Weight Loss
(%)=
(W
i
−W
f
W
i)
×
100
Titratable acidity
(%)=
(V
NaoH
×0.064
10
)
×
100
3938
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Z AR E- B AVAN I et al .
2.10 | Total soluble carbohydrates (TSC)
Total carbohydrate content was determined following the method
outlined by Dubois et al. (1956). 100 mg of coated and uncoated
BPFs were mixed with 5 mL of ethanol (80%) at 80°C. The mix-
ture was then subjected to centrifugation at 7155 g for 10 min. By
repeating these steps, the final volume was increased to 10 mL
using 80% ethanol. Two milliliter of the resulting extract were
transferred to a test tube, to which 1 mL of a 5% phenol solu-
tion was added. Immediately after, 5 mL of concentrated sulfuric
acid was introduced, and the mixture was vigorously vor texed for
1 min. Subsequently, the test tube was left at room temperature
for 10–15 min, resulting in the development of a brick- brown color.
Standard glucose was employed for calibration purposes. The ab-
sorbance of the samples was measured at 490 nm, and the total car-
bohydrate content was calculated in grams per gram of dr y weight
of the sample (Dubois et al., 1956).
2.11 | Total carotenoid content (TCC)
The determination of total carotenoid content (TCC) followed the
method described by Burgos et al. (2009). Two grams of treated
and untreated fruit tissue were homogenized with acetone. The
homogenization process was repeated until the samples became
colorless. Petroleum ether was added to the extracts, and then
they were washed with water to remove the remaining acetone.
Butylated hydroxytoluene was added to prevent the degradation
of carotenoids. Saponification was done with methanolic pot assium
hydroxide (10%) in a volume equal to the extract in a dark environ-
ment at room temperature. The absorption values of the samples
were measured at 450 nm, and TCC was determined by applying the
appropriate extinction coefficient for the carotenoid mixture, which
was set at 250 0.
2.12 | Total phenol content (TPC)
The total phenol content (TPC) was determined following the
methodology described by Ghasemnezhad et al. (2011). A gram
of powdered plant sample was extracted with 10 mL of cold
methanol solvent using liquid nitrogen. Subsequently, 125 μL of
the methanolic extract was mixed with 375 μL of distilled water
and 2.5 mL of a 10% Folin–Ciocalteu reagent in a test tube. The
mixture was then kept in the dark at room temperature for 6 min.
Next, 2 mL of a 7.5% sodium carbonate solution was added to neu-
tralize the reaction. The samples were left in the dark for 90 min
at room temperature, and the resulting solution's absorbance was
measured at 765 nm using a spectrophotometer. A standard curve
was constructed using gallic acid (ranging from 50 to 1000 mg/L).
The TPC was expressed as milligrams of gallic acid per 100 g of
fresh tissue.
2.13 | Ascorbic acid content (AsA)
The ascorbic acid content (AsA) of fruit samples was measured using
the method of Klein and Perr y (1982), with minor modifications. Five
grams of the pepper samples were extracted with 50 mL metaphos-
phoric acid (1% W:V). Then, the resulting extract was centrifuged
by a refrigerated centrifuge at 500 0 g for 5 min. Next, 1 mL of the
supernatant was mixed with 9 mL of dichlorophenol indophenol
(DCIPP) solution (0.05 mM), and immediately, the absorption of the
samples was read using a spectrophotometer at 515 nm. L- ascorbic
acid was used to prepare the standard. AsA was calculated in mil-
ligrams per 100 grams of fresh weight (Klein & Perry, 1982).
2.14 | Activity of antioxidant enzymes (superoxide
dismutase (SOD), peroxidase (POD), and catalase (CAT))
The extraction and activity assessment of SOD, CAT, and POD en-
zymes were conducted following the methodology outlined by Xing
et al. (20 11).
2.15 | Extraction
Fruit pulp samples (2 g) were homogenized with 10 mL of sodium
phosphate buffer solution (25 mM, pH = 7.8) containing PVPP
(0.8 g L−1) and EDTA (1 mM). The mixture was then subjected to cen-
trifugation at 12,00 0 g for 20 minu at 4°C. The successive superna-
tant was used as an extract to measure antioxidant enzymes.
To determine SOD enz yme activit y, 0.1 mL of the enzyme ex-
tract was mixed with 2.9 mL of sodium phosphate buffer (50 mM,
pH = 7.8) containing methionine (13 mM), nitroblue tetrazolium
(75 μM NBT), riboflavin (2 μM), and EDTA (10 μM). The resulting mix-
ture was treated for 10 min with a light intensity of 60 mol m−2 s−1,
and the absorbance was recorded at 560 nm. The blank solution was
the reaction mixture that was kept in the dark. One enzyme unit was
considered equivalent to a volume of an enzyme that causes 50%
inhibition of NBT reduction at 560 nm. Finally, the SOD activit y was
reported as U g−1 F W.
One milliliter of the enzyme extract was mixed with 1 mL of so-
dium phosphate buffer (50 mM, pH = 7.0) and 1 mL of H2O2 (40 μM)
to determine the CAT activity. The decrease in absorbance was mea-
sured at 240 nm. The amount of CAT activity was calculated accord-
ing to the following formula and finally reported as U g−1 F W.
A volume of 0.5 mL of the enzyme extract was combined with
2 mL of sodium phosphate buffer (100 mM, pH = 6.4) containing
guaiacol (8 mM) to assess the activity of the POD enzyme. The mix-
ture was then incubated at a temperature of 30°C for a duration
of 5 min. Following this, 1 mL of H2O2 (24 mM) was added, and the
increase in absorbance at a waveleng th of 460 nm was measured at
U=0.1 ×ΔA240nm per min
|
3939
ZA RE- BAVANI et al.
30- second intervals for a total of 2 min. The POD enzyme activity
was ca lculate d us in g the pro vided for mul a an d rep or ted as U g−1 FW.
2.16 | Total antioxidant capacity (TAC)
The TAC of fruits was measured by inhibiting soluble free radicals 2,
2 diphenyl- 1- picrylhydrazyl (DPPH) (Ghasemnezhad et al., 2 011). For
this purpose, using a sampler, 50 μL of pe p pe r ext r act wer e pou re d into
small Falcon tubes, and 950 microliters of DPPH solution (6.25 × 10−5 M)
were added to it and vortexed. The resulting solution was stored at
room temperature in the dark. After 15 min, the absorbance of the
samples was read with a spectrophotometer (model PG Instrument
+80, Leicester, UK) at 515 nm. The TAC was expressed based on the
reduction of absorbance compared to the control in terms of the per-
centage of DPPH inhibitory power using the following formula:
where %DPPHsc = inhibition percentage, Acont = DPPH absorption
rate, and Asamp = absorption rate (sample + DPPH).
2.17 | Lipid peroxidation
The extraction and determination of membrane lipid peroxidation
were done as described by Xing et al. (2011). The lipid peroxidation
was measured and expressed based on the amount of malondialde-
hyde (MDA) produced. The fleshy tissue of pepper fruits (4 g) was
homogenized with 20 mL of trichloroacetic acid (10%). The resulting
mixture was then subjected to centrifugation at 50 00 g for 10 min.
One milliliter of the supernatant was combined with 3 mL of 0.5%
thiobarbituric acid dissolved in 10% trichloroacetic acid. Next, the
reaction mixture was incubated at 95°C for 20 min, rapidly cooled,
and then centrifuged at 10,000 g for 10 min to obtain the sedi-
ment. The absorbance of the samples at 532 nm and 600 nm was
recorded. The amount of MDA was computed using the extinction
coefficient
155 mM
−
1cm
−
1
and the provided formula:
In this context, Vt represents the total volume of the extrac t
solution, Vr signif ie s the tot al volume of th e re act ion mix tur e, Vm cor-
responds to the volume of the extract solution within the reaction
mixture, and m denotes the mass of the sample.
2.18 | Relative membrane permeability (RMP)
The measurement of membrane permeability, also known as the
relative leakage rate, was carried out following the procedure
outlined by Xing et al. (2011). Fifty- mm thick discs were pre-
pared from the middle part of the pepper fruits. These discs
were thoroughly washed three times with deionized water to
remove any electrolyte residue on the surface. Afterward, the
discs were gently dried using filter paper. For each measure-
ment, ten of these discs were placed in glass vials with lids, each
containing 30 mL of deionized water. The vials were then placed
on a rotary shaker at a temperature of 25°C for a duration of
30 min. The electrical conductivit y of the solution inside the
vials (
Lt
) was determined using an EC meter (model DDSJ- 308A,
Shanghai Precision & Scientific Instrument Co., Ltd., Shanghai,
China). Subsequently, the vials containing the samples and solu-
tion were boiled for 10 min, rapidly cooled, and the final elec-
trical conductivity (
L0
) was measured. The relative leakage rate
was calculated as the percentage of total electrolytes using the
following formula:
2.19 | Data analysis
The experiment was conducted using a completely randomized de-
sign in the form of a split plot design over time with 3 replications.
Each replication consisted of 10 fruits. The first experimental factor
considered was the 5 levels of edible coating (0.00, 0.25, 0.50, 1.00,
and 2.0 0), while the second experimental factor was the sampling
time (0, 7, 14, 21, and 28 days). Fruit weight loss was measured at
different time points using 10 fruits separately, with three replicates.
Statistical analysis of the data, including test s for normality of data
distribution, analysis of variance, and mean comparisons, was per-
formed using SAS soft ware (Version 9.1). Graphs were created using
Excel software (2013). The comparison of means was conducted
using the LSD test at the 5% significance level, and mean values
were reported as mean ± standard deviation (SD) based on three
samples (n = 3).
3 | RESULTS
3.1 | Physiological weight loss (PWL)
In this study, we examine the impact of GT coatings as natural
prot ec tors on the cu mul at ive PWL in BPFs. Weig ht ch an ges duri ng
storage show the effectiveness of coating methods compared to
uncoated peppers (Figure 1a). After 28 days, the peppers with GT
coating (1%) and without coating showed the lowest (10.46%) and
highest (18.92%) PWL, respectively. Increasing the concentration
of GT from 0.25 to 1% slowed down the PWL process (Figure 1a).
However, increasing the GT concentration to 2% during the first
and second weeks of storage did not show significant differences
compared to the 1%- coated fruits. Nonetheless, in the third and
fo urth we e ks of st orag e, it le d to an incr eas e in PWL. Fu r t her m ore ,
U=0.01 ×ΔA470nm per min
DPPHsc
(%)=
(A
cont
−A
samp
A
cont )
×
100
MDA (
𝜇mol g
−1
FW
)
=
(
OD
532
−OD
600)
×V
t
×V
r
×1000 ∕
(
V
m
×m×155
)
RMP
(%)=
(
L
t
∕L
0)
×
100
3940
|
Z AR E- B AVAN I et al .
among th e sampl es of peppe rs with gum coatings, th e sam pl e with
0.5% GT showed more PWL (Figure 1a).
3.2 | Fruit firmness
The results showed a substantial interaction (p ≥ .01) between coat-
ing treatment and storage duration on fruit firmness. Figure 1b
shows that throughout the storage period, the fruit firmness de-
creased in all treatments. Decreasing firmness was more evident
for uncoated and GT- coated (0.25%) fruit s. Increasing the coating
concentration up to 1% improved the fruit firmness in storage dura-
tion so that the treatments of 1% GT had the highest (2.89 N) and
uncoated fruits had the lowest (2.33 N) firmness. Increasing the level
of gum coating by 2% GT decreased the fruit firmness as compared
to samples having 0.5 and 1% GT.
3.3 | Marketability
Figure 1c shows the mar keta bi li ty of bell pe pp er fruits with dif fe re nt
coatings and without coating during 28 days of storage. Coated BPFs
presented higher acceptability than uncoated peppers. The percent-
ages of marketability of peppers treated with 1% GT and uncoated
fruits at the end of storage were 75 and 40.17%, respectively. Similar
to the decrease in fruit weight and firmness, increasing the concen-
tration of gum coating by 2% decreased marketability compared to 1
and 0.5% treatments. As depicted in Figure 2, the decline in market-
ability was primarily manifested as wrinkles and roughness.
3.4 | Total soluble solids (TSS)
Figure 3a shows changes in TSS in BPFs during the storage period.
The TSS of the control showed the highest increase with storage
time, while the fruits coated with GT (1%) showed a relatively smaller
increase. Increasing the concentration of gum coating up to 1% had
more reducing effects on increasing TSS, but its rise to 2% showed
the opposite impac ts (Figure 2a).
3.5 | Titratable acidity (TA)
As seen in Figure 3b, TA on the seventh day of storage in uncoated
BPFs increased compared to the first day of measurement and
showed a significant decrease until the 28th day of storage. No sub-
stantial differences were identified in the amount of TA in coated
BPFs on the first and seventh days of storage, but after that, a de-
creasing trend occurred in all treatments, and the decreasing trend
in the 1% GT was significantly lower than the other treatments.
Storage of the uncoated fruits led to a faster reduc tion of pepper
TA than coated storage. Increasing the coating concentration to 1%
decreased the TA reduction process, but the 2% concentration again
caused a further increase in TA (Figure 3b).
3.6 | Maturity index (MI)
The values of TSS/TA, which express the maturity index (MI), or the
degree of ripening, were not different on the seventh day compared
FIGURE 1 Cumulative weight loss (%)
(a), fruit firmness (b), and marketability
(%) (c) in pepper fruits coated with GT
(0.00, 0.25, 0.50, 1.00, and 2%). The fruits
were stored at 7°C, 95% RH, for 28 days.
LSD0.05 indicates the least significant
difference (p < .05). Vertical bars represent
the standard deviation (SD) (N = 3).
(a) (b)
(c)
|
3941
ZA RE- BAVANI et al.
to the first day, but these values boosted with increasing the storage
time in all treatments. The amount of increase in MI in BPFs treated
with GT was lower than that of uncoated fruits, and increasing the
level of coatings up to 1% had a more inhibitory effect on this index,
so fruits coated with 1% GT had the lowest MI values recorded at the
measurement times (Figure 3c). Increasing the coating concentration
FIGURE 2 The effect of different
concentrations of gum tragacanth as an
edible coating on red bell pepper fruit
(Capsicum annuum L.) at various storage
times.
FIGURE 3 Total soluble solids (Brix°)
(a), titratable acidity (%) (b), maturity index
(c), and pH (d) in pepper fruits coated with
GT (0.00, 0.25, 0.50, 1.00, and 2.00%).
The fruits were stored at 7°C, 95% RH,
for 28 days. LSD0.05 indicates the least
significant difference ( p < .05). Vertical
bars represent the standard deviation (SD)
(N = 3).
(a) (b)
(c) (d)
3942
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Z AR E- B AVAN I et al .
to 2% increased the MI values more than the coating concentration
of 0.5% (Figure 3c).
3.7 | pH
The pH o f un c o a t e d sa m p l e s decreased during st or age un til the seve nth
day and then increased until the end of storage (p < .05) (Figure 3d). No
substantial changes were recognized in the pH of fruits coated with
0.25% GT compared to the control during storage. Th e lowest increase
in pH at the end of storage was related to 1% TG- coated fruits. Fruit s
coated with concentrations of 0.50, 1.00, and 2.0 0% of GT indicated
no differences (p < .05) in terms of pH until the 14th day of storage
compared to the 7th and 1st days (Figure 3d).
3.8 | Total soluble carbohydrates (TSC)
The content of TSC in uncoated and coated fruit s increased dur-
ing storage (Figure 4a). However, this increase was less in coated
fruits. The lowes t increase was 2.13 times in 1% GT- coated fruits ,
and the highest was 3.3 times in uncoated fruit s. Increasing the
coating concentration to 1% decreased the rise, but the coat-
ing concentration of 2% again increased the TSC of the fruit
(Figure 4a).
3.9 | Total content of carotenoids (TCC)
Figure 4b shows changes in the TCC of pepper fruits during stor-
age time. Uncoated fruits had the highest TCC value during stor-
age (Figure 4b). This increase was slower in the fruits coated with
GT, and with increasing the coating concentration to 1%, this
trend showed a further decrease. The lowest increase in TCC
in 1% GT- coated fruits was about 1.4 times, and the highest in
uncoated fruits was about 2.9 times, almost twice that of fruits
coated with 1% GT.
3.10 | Total phenolic contents (TPC)
Figure 5a illustrates the changes in TPC of uncoated and coated
BPFs during storage. The graph shows that TPC decreased with
increasing storage time from day 14 in all treatments. This reduc-
tion was considerably higher in uncoated fruits, but the process
was slower in coated fruits. Over time, this difference bet ween
the treatments increased. In 1% GT- coated fruit s, the reduction in
TPC showed the lowest level among the treatments in all stages
of storage, so there was no substantial difference from the begin-
ning of storage until the 14th day. At the end of storage, TPC de-
creased in the control (24.85 mg GAE g−1 FW), the fr uit s coat ed wi t h
0.25 (28.30 mg GAE g−1 FW), 2.00 (30.79 mg GAE g −1 FW), 0.50
FIGURE 4 Total carotenoids (a) and
total soluble carbohydrates (b) in pepper
fruits coated with GT (0.0 0, 0.25, 0.50,
1.00, and 2.00%). The fruits were stored
at 7°C, 95% RH, for 28 days. L SD0.05
indicates the least significant difference
(p < .05). Vertic al bars represent the
standard deviation (SD) (N = 3).
(a) (b)
FIGURE 5 Total phenol (mg GAE g−1
FW) (a) and ascorbic acid (mg 100 g−1 FW)
(b) in pepper fruits coated with GT (0.0 0,
0.25, 0.50, 1.0 0, and 2.00%). The fruits
were stored at 7°C, 95% RH, for 28 days.
LSD0.05 indicates the least significant
difference (p < .05). Vertical bars represent
the standard deviation (SD) (N = 3).
(a) (b)
|
3943
ZA RE- BAVANI et al.
(32.53 mg GAE g−1 FW), and 1.00% GT (34.59 mg GAE g−1 FW), re-
spectively (Figure 5a).
3.11 | Amount of ascorbic acid (AsA)
As presented in Figure 5b, the highest amount of AsA in different
BPF treatments was obser ved on the 7th day (117 mg 100−1 g FW).
However, there was no significant difference from the first day re-
sult. The amount of AsA was significantly affected by coating and
storage time. Although the amount of AsA in all treatments de-
creased during storage from days 14 to 28, GT significantly reduced
the loss of AsA in pepper samples. After 28 days of storage, the AsA
of BPFs coated with 1% GT was 82.28% (95.36 mg 100 g−1 FW) com-
pared to the control samples, which preserved 59.90% (68.99 mg
100 g−1 FW ) of the initial amount of AsA .
3.12 | Antioxidant enzyme activities
3.12 .1 | SOD
As seen in Figure 6a, the SOD activity initially increased until day 7,
decreased until day 21, and increased again until the end of storage.
This trend was similar in all treatments, but in general, coated fruit s
showed higher SOD activit y throughout the period, which was in
line with the increase of coating gel up to 1%. At the end of storage,
the uppermost level of the SOD engagement in BPFs coated with 1%
GT was 122.53 U g−1, and the lowermost was observed in uncoated
fruits, which was 82.86 U g−1 .
3.12.2 | CAT
The CAT activity in uncoated and coated fruits decreased during
28 days of storage (Figure 6b). Until the 21st day, the highest level
of CAT activity was related to the control, and after that, a sharp
decrease was obser ved so that on the 28th day, the lowest amount
of CAT was found in the uncoated (control) sample. The CAT activity
in peppers coated with GT (1%) on the 28th day was 56.5% higher
than uncoated fruits.
3.12.3 | POD
As presented in Figure 6c, the POD activity in uncoated and coated
fruits decreased until the 21st day of storage and then amplified
until the 28th day (Figure 6c). In the entire storage period, the POD
activity in coated fruits was superior to that of uncoated BPFs, and
this trend was in line with the increase in coating quality.
3.13 | Total antioxidant content (TAC)
The TAC based on the DPPH radical inhibitor ac tivit y was the high-
est on the 7th day of storage in the control and then decreased with
FIGURE 6 Enzyme activities of SOD
(a), CAT (b), POD (c) and total antioxidant
activity (d) in pepper fruits coated with
GT (0.00, 0.25, 0.50, 1.00, and 2.00%).
The fruits were stored at 7°C, 95% RH,
for 28 days. LSD0.05 indicates the least
significant difference ( p < .05). Vertical
bars represent the standard deviation (SD)
(N = 3).
(a) (b)
(c) (d)
3944
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Z AR E- B AVAN I et al .
increasing storage life (Figure 6d). TAC had no significant difference
in GT- coated fruits (1%) from the beginning of the experiment to day
14 and began to decline after day 14, but had the lowest rate of de-
cline compared to other treatments. In general, the coated fruits had
a higher TAC than the uncoated BPFs at the end of storage.
3.14 | Lipid peroxidation (MDA content)
Figure 7a shows an increase in the MDA content in all treatments
during 28 days of storage. However, using GT- coated BPFs signifi-
cantly showed a delayed process for increasing MDA. At the end of
storage, the MDA of the samples coated with 1% GT was 47.67%
lower than that of the control.
3.15 | Relative membrane permeability (RMP)
As shown in Figure 7b, the change in leakage of electroly tes from
the membrane increased with increasing storage time in all treat-
ments. The RMP in uncoated fruit s was significantly higher than in
coated fruits. The lowest level of RMP in 1% GT- coated fruit s was
18.15%, which was 55.24% less than the control.
4 | DISCUSSION
In this study, GT- coated samples showed less PWL than the un-
coated samples. Furthermore, increasing the coating concentra-
tion up to 1% affected more maintaining the fruit weights, and
the higher concentration (2%) again increased the weight loss.
Similar inhibitory effects of GT on fruit weight loss in tomatoes
(Jahanshahi et al., 2023), apricots (Ali et al., 2015; Ziaolhagh &
Kanani, 2021), and mushrooms (Mohebbi et al., 2012) when used
with different concentrations or in combinations with other coat-
ings have been reported. The PWL of fruits and vegetables is due to
the water reduction caused by active metabolic procedures, such
as respiration and transpiration (Dhall, 2013; Ullah et al., 2017).
Lower PWL in coated fruits is due to the effects of the coating
as a semi- permeable physical barrier against moisture escape and
oxygen and carbon dioxide exchanges, leading to reduced respira-
tion and water loss (Ali et al., 2015; Dhall, 2013). Reducing the
carbon dioxide output from the produc t and the entry of oxygen
into the product reduces ethylene production. As a result, it de-
lays senescence, increases shelf life, and preserves product qual-
it y. Th e t ype an d amo unt of coa tin g affe c t the am oun t of ch ang e in
the internal atmosphere of the produc t (O2, CO2) and the amount
of weight loss (Dhall, 2013).
Pepper fruits coa te d wi th 1% GT showed mor e fi rmnes s th an un-
coated ones during storage. It has been reported that the softening
enzymes, including pectin esterase and polygalacturonase, change
the cell wall and soften the fruit tissue (Manganaris et al., 2005). It
has been stated that the softening of bell peppers is related to the
destruction of the middle lamella of cortical parenchyma cells and
the increase in pectin dissolution, minor changes in pectin molecu-
lar weight, and hemicellulose content reduc tion (Nasiri et al., 2019).
As illustrated by Abad Ullah et al. (2017 ), ECs likely inhibit cell wall
softening enzymes by decelerating metabolic actions, resulting in
firmer tissue. In addition, the ECs may increase the resistance of
BPFs against compositional alterations in the cell wall, therefore re-
taining moisture and delaying fruit softening. Our findings are con-
sistent with Ziaolhagh and Kanani (2021) on apricots and Mohebbi
et al. (2012) on mushrooms, who reported that GT as a palatable
coating significantly preserves the firmness of the fruit texture.
Pepper fruits coated with 1% GT had the highest marketability
score until the end of the storage period, while the uncoated sam-
ples showed a 60% decrease in marketability. As reported by other
researchers (El- Gioushy et al., 2022; Liguori et al., 2021; Shehata
et al., 2023), ECs positively affec t the overall appearance of the
fruit during storage. Maintaining the appearance and quality of
the fruit can be related to the effect of EC on preventing moisture
loss and preserving the color and composition of the fruit (Kumar
et al., 2021). The ECs are a semi- permeable barrier to prevent mois-
ture loss and gas exchange (CO2 and O2) on the fruit surface, which
reduces water loss, respiration rate, metabolism, and deterioration
due to increased enzymatic activity and microbial rot (Velickova
et al., 2013). In addition, coatings can reduce the physiologic al dete-
rioration and spoilage of fruits by increasing the activity of antioxi-
dant enzymes and their ability to inhibit free radicals during storage
(Wang & Gao, 2013).
FIGURE 7 Lipid peroxidation (MDA)
(a) and relative membrane permeabilit y
(b) in pepper fruits coated with GT (0.0 0,
0.25, 0.50, 1.0 0, and 2.00%). The fruits
were stored at 7°C, 95% RH, for 28 days.
LSD0.05 indicates the least significant
difference (p < .05). Vertical bars represent
the standard deviation (SD) (N = 3).
(a) (b)
|
3945
ZA RE- BAVANI et al.
An increase in the TSS content of all BPFs was observed
througho ut storage, but this inc re as e was sig ni fi cantly lo we r in 1%
GT- coated fruits than in the control. The increase in TSS is men-
ti on e d as an in di c at or of th e rip eni ng an d sene scenc e of fr u it s. Th e
TSS of pepper fruits increases with the enhancement of fruit rip-
ening due to the degradation or biosynthesis of more polysaccha-
rides and the accumulation of sugars (Antoniali et al., 2007). In this
research, it was observed that the TSS of coated fruits was lower.
The lower upsurge in TSS of coated BPFs may be due to reduced
water loss and volatile compounds (Ochoa- Reyes et al., 2013) and
delayed ripening (Ullah et al., 2017). These findings were con-
sistent with those of other researchers on the effects of GT on
TSS levels (Abebe et al., 2017; Mohebbi et al., 2012; Ziaolhagh &
Kanani, 2021).
The results revealed that as the storage time increased, the TA in
both coated an d un co at ed BPFs decre as ed sig nific an tly. Bes id es, the
application of ECs after harvesting maintained a higher TA than the
control. The fast decrease in TA in uncoated fruits is probably owed
to higher respiration and oxidation of organic acids, while higher TA
in coated fruits could be the result of lower respiration, which finally
prevents oxidation of organic acids (Ullah et al., 2017; Ziaolhagh &
Kanani, 2021). Previous findings showed that the GT coating leads
to higher TA in apricots (Ziaolhagh & Kanani, 2021) and tomatoes
(Abebe et al., 2017; Jahanshahi et al., 2023), which is in line with the
findings of this research.
The fruit taste is affected by TSS and TA and their ratios. The MI
determines the taste and nutritional properties of the fruit. In the
present study, TSS exhibited an upward tendency and TA showed
a downward tendency with the progress of the storage period, and
these trends were less than in the bell pepper fruits coated with
GT1%. A s a result, the MI also changed less in these treated fruits.
These lower changes in TSS and TA could be due to delayed ripen-
ing and senescence for lower respiration or reduced moisture loss,
and for the protective effects of these coatings (Ullah et al., 2017 ).
The results were consistent with those of other studies on tomatoes
(Abebe et al., 2017) and strawberries (Aitboulahsen et al., 2018).
The results showed that bell pepper fruits coated with GT 1%
had fewer pH changes during the storage time. The variations in pH
are mostly based on changes in organic acids. The concentration of
these acids decreases during ripening, and this decrease can be as-
sociated with an increase in the rate of respiration, which is likely to
use titratable acids as a respirator y substrate (Antoniali et al., 2007;
Samira et al., 2013). It has been suggested that higher fruit acidity
is an advantage that causes less spoilage (Mohammed et al., 1999).
The current result is consistent with previous reports that showed
that immediately after harvest, the total acidity of pepper fruits in-
creased and then decreased during storage (Morales- Castro, 2002;
Nasiri et al., 2019; Samira et al., 2013). Fur thermore, the significant
effect of GT on pH in this study was consistent with the results of
other researchers on tomatoes (Jahanshahi et al., 2023) and apricots
(Ziaolhagh & Kanani, 2021).
The TSC of fruits was meaningfully af fected by GT coating and
the storage period. There was an increase in TSC during a prolonged
storage period for all treatments. The findings of this study are in
contrast to those of Shehata et al. (2023), which stated a decrease
in soluble sugars during storage in peppers. The lower TSC in fruits
during storage by GT as a palatable coating may be related to the
reduction in respiration rate and enzymatic actions of these sub-
stances, which leads to a decrease in the breakdown of polysaccha-
rides into simple and soluble carbohydrates during storage (Antoniali
et al., 20 07).
TCC in BPFs increased with increasing storage period, especially
in the cont rol . The colo r cha nge in pe p per s cou ld be due to the tr ans-
formation of chloroplast to chromoplast and changes in the pigment
content of BPFs with the progress of ripening. Furthermore, the
reduction in red color during storage is due to the progress in rip-
ening and the formation of carotenoids (Ullah et al., 2017; Shehata
et al., 2023; Saleh, 2020). The lower increase of TCC in pepper fruits
coated with 1% GT at the end of storage describes the ability of ECs
to retard the breakdown and synthesis of these pigment s (Ullah
et al., 20 17). These findings obviously express the efficiency of ECs
in enhancing the visual quality of BPFs. Our results are consistent
with those of other researchers (Ali et al., 2015; Gholamipour Fard
et al., 2009; Shehata et al., 2023; Ullah et al., 2017), who reported
that discoloration was delayed in fruits coated with ECs due to re-
duced respiration.
The TPC in bell pepper fruit s showed a significant decrease at
the end of storage. At the end of storage, the coated BPFs with 1%
GT showed the lowest level of changes in the content of total phe-
nolic compounds. The reduction in TPC in the control compared to
coated fruits during storage is most likely owing to the higher en-
zymatic activity of PPO in pepper fruits (Ajmal et al., 2022; Kumar
et al., 2021). The findings of other researchers about BPFs (Kumar
et al., 2021; Taheri et al., 2020) suppor ted the present results. They
reported that ECs retained TPC in BPFs during storage, possibly by
delaying ethylene production, lessening lipid oxidation, and con-
trolling enzyme reactions (Ajmal et al., 2022; Kumar et al., 2021).
The amount of AsA gradually decreases during storage. This de-
crease could be due to increased respiration and oxidation of acids
to sugar (Ullah et al., 2017). The present study showed that the BPFs
coated with 1% GT were more effective in reducing the loss of AsA
as compared to other treatments. Our results are consistent with
those of other researchers who showed that ECs were ef fective in
reducing the loss of AsA in BPFs (Adetunji et al., 2019; Hedayati &
Niakousari, 2015; Ullah et al., 20 17). The use of ECs may reduce the
release of oxygen, thus reducing the speed of fruit ripening; thus,
it preserves AsA content and delays fruit senescence (Adetunji
et al., 2019; Xing et al., 2011). Some researchers showed that ECs
can increase the level of CO2 and decrease the level of O2 around
the fruit, thereby helping to prevent the oxidation of AsA (Amal
et al., 2010).
As can be seen, BPFs treated with 1% GT had higher SOD, POD,
and CAT activities during storage (Figure 5). When senescence ap-
pears, it seems to be related to the defense system, comprising an-
tioxidant enzymes such as CAT, SOD, and POD and non- enzymatic
antioxidants (Xing et al., 2011; Xu et al., 2009). These findings were
3946
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Z AR E- B AVAN I et al .
consistent with those of previous research regarding the effect of
chitosan coating on the activity of antioxidant enz ymes in BPFs
(Ajmal et al., 2022; Xing et al., 2011). SOD, CAT, and POD are signif-
icant enzymes for detoxicating free oxygen radicals in plant tissues
(Xu et al., 2009). The decline in enzyme activity may be related to
the reduction in the ability to preclude destruction, and ECs induce
the activity of antioxidant enzymes and possibly can improve the
protection system of fruit s and vegetables (Meng et al., 2008).
Antioxidant substances in food neutralize many oxidation pro-
cesses caused by free radicals, control tissue damage, and reduce
the possibility of devastation of functional and nutritional properties
(Kumar et al., 2021). During the storage time, a decreasing trend in
TAC was observed. The lowest reduction in TAC was recorded in
BPFs coated with 1% GT. The results showed that TG can help pre-
vent the worsening of BPFs during storage by maint aining TAC. The
results of this study were in agreement with previous research about
the effect of edible coating on the TAC of BPFs (Kumar et al., 2021).
The MDA content and the relative amount of electrolyte efflux
are applied as direct and indirect indexes of membrane damage. MDA
is frequently utilized as an indicator of cellular oxidative destruc-
tion because it is a product of lipid peroxidation (Xu et al., 2009).
Ele ctrol yte ef flux is usually regarded as an indirec t me as ur e of mem -
brane damage in cells caused by adversarial conditions and tissue
senescence (Jiang et al., 2001). A continuous increase in MDA and
electrolyte leakage was observed for all treatments during pepper
fruit storage. However, a 1% GT coating for bell peppers significantly
reduced the increase in MDA and electrolyte efflux. As observed in
coated fruits, TG reduces the activities of SOD, CAT, POD, and other
antioxidant compounds such as ascorbic acid, total phenol, and an-
tioxidant capacity compared to uncoated fruits during storage. As
a result, the oxidative stress reduced the amount of MDA and the
leakage of electroly tes. These findings are in agreement with the
results of other researchers about the effect of ECs on reducing
the amount of MDA and electrolyte leakage in bell peppers (Ullah
et al., 2017; Xing et al., 2011).
5 | CONCLUSION
The GT coating is a promising alternative treatment to increase the
shelf life of bell peppers. After storage at 8°C for 28 days, the coated
samples treated with the GT had a higher percentage of marketable
peppers with lower physiological weight loss and more firmness.
TSC, TCC (color changes), TPC, and AsA were better preserved in
fruits coated with 1% GT. Enzymatic antioxidant activities and TAC
were induced in GT- coated fruits. The values of RPM and MDA in
the sample treated with GT were much lower than those without
coating during the storage period. Regarding the higher shelf life of
coated BPFs, it may be said that GT can be considered as an innova-
tive coating for commercial applic ations during the stor age and mar-
keting of BPFs. This is due to the affordability of GT as compared to
chitosan and other ECs, and its effectiveness in low concentrations.
AUTHOR CONTRIBUTIONS
Mohammad Reza Zare- Bavani: Conceptualization (equal); data
curation (equal); formal analysis (equal); funding acquisition (lead);
investigation (equal); methodology (equal); project administration
(lead); resources (equal); software (equal); supervision (equal); vali-
dation (equal); visualization (equal); writing – original draft (lead);
writing – review and editing (lead). Mostafa Rahmati- Joneidabad:
Conceptualization (equal); data curation (equal); formal analysis
(equal); investigation (equal); methodology (equal); resources (equal);
software (equal); supervision (equal); validation (equal); visualization
(equal); writing – review and editing (equal). Hossein Jooyandeh:
Conceptualization (equal); data curation (equal); formal analysis
(equal); investigation (equal); methodology (equal); resources (equal);
software (equal); supervision (equal); validation (equal); visualization
(equal); writing – review and editing (equal).
ACKNOWLEDGEMENTS
The authors of the article would like to thank and acknowledge the
financial and administrative support from the Agricultural Sciences
and Natural Resources University of Khuzest an, as well as the genu-
ine cooperation of the Khuzestan Agriculture and Natural Resources
Research and Education Center.
FUNDING INFORMATION
The work was supported by the Research Affairs of the Agricultural
Sciences and Natural Resources University of Khuzestan (Grant No.
928/411/1).
CONFLICT OF INTEREST STATEMENT
None declared.
DATA AVAIL AB I LI T Y STATE MEN T
The dat a that support the findings of this study are available on re-
quest from the corresponding author.
ORCID
Mohammad Reza Zare- Bavani https://orcid.
org/0000-0002-0784-2599
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How to cite this article: Zare- Bavani, M. R., Rahmati-
Joneidabad, M., & Jooyandeh, H. (2024). Gum tragac anth, a
novel edible coating, maintains biochemical quality, antioxidant
capacity, and storage life in bell pepper fruits. Food Science &
Nutrition, 12, 3935–3948. https://doi.org/10.1002/fsn3.4052