Effect of silver nanoparticles and gum Arabic coatings on ...

<strong>Effect</strong> <strong>of</strong> <strong>silver</strong> <strong>nanoparticles</strong> <strong>and</strong> <strong>gum</strong> <strong>Arabic</strong> <strong>coatings</strong> on physicochemical <strong>and</strong>
microbial properties <strong>of</strong> green bell pepper (Capsicum annuum)
Sara Hedayati/ Ms.C student
Department <strong>of</strong> Food Science <strong>and</strong> Technology, School <strong>of</strong>
Agriculture, Shiraz University
Shiraz, Iran.
e-mail: sara_hedayatiii@yahoo.com
Mehrdad Niakousari/ Assistant pr<strong>of</strong>essor
Department <strong>of</strong> Food Science <strong>and</strong> Technology, School <strong>of</strong>
Agriculture, Shiraz University
Shiraz, Iran.
e-mail: niakosar@shirazu.ac.ir
Abstract— Gum <strong>Arabic</strong> in aqueous solution <strong>of</strong> 10%, <strong>silver</strong>
<strong>nanoparticles</strong>, <strong>and</strong> <strong>silver</strong> <strong>nanoparticles</strong> -<strong>gum</strong> <strong>Arabic</strong> solution
blend, <strong>coatings</strong> were formed directly on the surface <strong>of</strong> green
bell peppers (Capsicum annuum) <strong>and</strong> were incubated at 7˚C
with a relative humidity <strong>of</strong> about 90%. Pepper quality was
evaluated by weight loss, firmness retention, ascorbic acid
content <strong>and</strong> microbial decay. Although <strong>coatings</strong> <strong>of</strong> any
composition delayed these changes the comparisons <strong>and</strong>
evaluations suggest that the <strong>gum</strong> <strong>Arabic</strong>-<strong>silver</strong> <strong>nanoparticles</strong>
blend significantly hindered microorganisms' growth <strong>and</strong>
physicochemical losses <strong>and</strong> enhanced the shelf-life <strong>of</strong> green bell
peppers.
Keywords- edible coating, bell pepper, <strong>silver</strong>
<strong>nanoparticles</strong>, <strong>gum</strong> <strong>Arabic</strong>
I. INTRODUCTION
Green bell peppers (Capsicum annuum) are perishable
products <strong>and</strong> are susceptible to chilling injuries. Bell pepper
shelf life is prolonged by cold storage <strong>and</strong> humidity control,
modified atmosphere packaging <strong>and</strong> different films <strong>and</strong>
<strong>coatings</strong>. Edible films <strong>and</strong> <strong>coatings</strong> are thin layers <strong>of</strong> edible
materials applied on food products that play an important
role on their conservation, distribution <strong>and</strong> marketing. Some
<strong>of</strong> their functions are to protect the product from mechanical
damage, physical, chemical <strong>and</strong> microbiological
activities[6]. Coating can give the same effect as modified
atmosphere storage in modifying internal gas composition.
It reduces oxygen availability <strong>and</strong> increases internal carbon
dioxide concentration <strong>and</strong> lowers the respiration rates <strong>and</strong>
therefore delays senescence [5]. Edible <strong>coatings</strong> provide
more advantages than synthetic materials in terms <strong>of</strong>
edibility, biocompatibility, being non-toxic <strong>and</strong> low cost.
Currently, research has led to development <strong>of</strong> new
environmentally friendly approaches based on
biodegradable polymers [2]. Silver <strong>nanoparticles</strong> have
recently gained increasing interests due to their
antimicrobial activities in food processing applications[4].
Gum <strong>Arabic</strong>, an exudate from Acacia trees, has a unique
combination <strong>of</strong> excellent emulsifying properties <strong>and</strong> low
solution viscosity [11]. It is a branched-chain, complex
polysaccharide, either neutral or slightly acidic. In recent
studies by Ali et al, 2010 <strong>and</strong> Maqbool et al, 2011 <strong>gum</strong>
<strong>Arabic</strong> coating showed beneficial effects in <strong>coatings</strong>.
The purpose <strong>of</strong> present study was to examine the effect <strong>of</strong>
<strong>silver</strong> <strong>nanoparticles</strong> <strong>and</strong> <strong>gum</strong> <strong>Arabic</strong> coating on
physicochemical <strong>and</strong> microbial properties <strong>of</strong> green bell
pepper (Capsicum annuum) during storage at 7˚
C.
II.
MATERIALS AND METHODS
A. Plant materials
Bell pepper (Capsicum annuum) samples were harvested at
green stage from a local farm in Shiraz, Iran <strong>and</strong> transferred
to laboratory immediately. They were visually inspected for
freedom from defects <strong>and</strong> blemishes <strong>and</strong> nonuniform,
damaged, poor quality peppers were removed. Before
treatment was applied, peppers were washed with distilled
water <strong>and</strong> air-dried at ambient temperature. The 320
remaining peppers were sorted according to their weight <strong>and</strong>
color <strong>and</strong> divided into four groups
B. preparation <strong>of</strong> coating solutions
• Gum <strong>Arabic</strong>
The method to prepare <strong>gum</strong> <strong>Arabic</strong> coating solution was
developed by Ali et al.2010. To prepare the coating solution
10% (w/v), 10g <strong>of</strong> <strong>gum</strong> <strong>Arabic</strong> powder was dissolved in
100ml distilled water <strong>and</strong> stirred with low heat(40˚c) for 60
minutes on a magnetic stirrer/hot plate then filtered to
remove any undissolved impurities <strong>and</strong> glycerol
monostearate (1%) was added <strong>and</strong> was cooled to room
temperature.
Silver <strong>nanoparticles</strong>
4000 ppm nano<strong>silver</strong> solution was supplied by Nanocid Co.
Tehran, Iran <strong>and</strong> was diluted to 20 ppm concentration by
adding distilled water then glycerol monostearate (1%) was
added <strong>and</strong> stirred for 15 minutes with a magnetic stirrer at
room temperature.
Gum <strong>Arabic</strong>-<strong>silver</strong> <strong>nanoparticles</strong> blend
100ml <strong>of</strong> the <strong>gum</strong> <strong>Arabic</strong> solution was prepared as
mentioned <strong>and</strong> 0.5 ml <strong>of</strong> 4000 ppm nano<strong>silver</strong> solution was
added <strong>and</strong> stirred with a magnetic stirrer for 5 minutes
C. Coating procedure
Control samples were just washed with distilled water <strong>and</strong>
for other treatments fresh bell peppers were dipped
completely into the coating solutions for about 2 minutes at
room temperature <strong>and</strong> taken out then the <strong>coatings</strong> dried with
a fan. The treated peppers <strong>of</strong> each solution were placed in an

incubator at 7˚c with a relative humidity <strong>of</strong> 90% <strong>and</strong>
physicochemical <strong>and</strong> microbial quality was evaluated
routinely
D. Weight loss
the coated <strong>and</strong> uncoated green peppers were weighed on a
digital balance (Sartrious LB150S) with accuracy 1 mg at
day 0 <strong>and</strong> at the end <strong>of</strong> each storage interval <strong>and</strong> the net
weight <strong>of</strong> each sample was registered to follow the moisture
loss. The weight loss (%) was reported based on the original
weight.
E. Firmness
Loss <strong>of</strong> firmness is one <strong>of</strong> the main factors limiting quality
<strong>and</strong> the postharvest shelf-life <strong>of</strong> fruit <strong>and</strong> vegetables(fan et
al. 2009). Texture analysis <strong>of</strong> the peppers were carried out
using a puncture test performed on texture analyser (model
STEVEN-LFRA). 20mm×20mm pieces were cut from the
sidewalls. The sample was placed on the instron base
outside surface facing up. The pepper was punctured with a
7mm diameter cylindrical probe <strong>and</strong> the maximum amount
<strong>of</strong> force (load gram) was recorded.
F. Vitamin C determination
the effect <strong>of</strong> coating on vitamin C resistance was followed
by measuring the vitamin C content <strong>of</strong> both coated <strong>and</strong>
uncoated peppers during storage according to AOAC
<strong>of</strong>ficial method.
G. Microbiological quality
In order to study if the <strong>coatings</strong> have any inhibitory effect
on microbial growth the microbial population on the green
pepper was determined at day 0 <strong>and</strong> at the end <strong>of</strong> each
storage interval. The microorganism counts were expressed
in log CFU/g <strong>of</strong> green pepper sample. To enumerate the
microorganisms, 5 g <strong>of</strong> each green pepper sample was
combined with 45 ml <strong>of</strong> sterile 0.9% sodium chloride
solution in a sterile polyethylene bag, pummeled with a
stomacher for 2 min at medium speed. The extract was used
for various serial dilutions. The total aerobic counts were
determined by pouring 0.1 ml <strong>of</strong> diluted sample onto plate
count agar medium (Merck, Germany). The plates were
incubated at 35˚C for 48 h, <strong>and</strong> the colonies were counted.
The detection limit <strong>of</strong> this method was 1log CFU/g <strong>of</strong>
sample.
H. Statistical analysis
Experimental data were analysed using SPSS 16.0 s<strong>of</strong>tware
(SPSS Inc., USA). The mean values were calculated <strong>and</strong>
reported as the mean ± SD (n = 3). The one-way analysis <strong>of</strong>
variance (ANOVA) procedure followed by Duncan’s
multiple range test (p

Table3. The effect <strong>of</strong> <strong>coatings</strong> on firmness
[3]. Ali B.H ,Ziada A, Blunden G., 2009, Biological effects
<strong>of</strong> <strong>gum</strong> arabic: A review <strong>of</strong> some recent research Food <strong>and</strong>
Chemical Toxicology. 47, 1–8.
[4]. An J., Zhang M., Wang S., Tang J. (2008). Physical,
chemical <strong>and</strong> microbial changes in stored green asparagus
spears as affected by coating <strong>of</strong> <strong>silver</strong> <strong>nanoparticles</strong>-PVP.
Food Science <strong>and</strong> Technology. 41, 1100-1107.
3.4. Microbiological quality
Results <strong>of</strong> microbial tests are shown in table 4. Changes in
the total aerobic count Coatings containing <strong>silver</strong> particles
significantly hindered the increase in total aerobic count
compared with the control samples. At the end <strong>of</strong> 21-day
storage, visually apparent differences were observed
between coated bell peppers <strong>and</strong> the control samples.
Table4. The effect <strong>of</strong> <strong>coatings</strong> on microbial count
IV. CONCLUSION
Gum <strong>Arabic</strong>-<strong>silver</strong> <strong>nanoparticles</strong> coating has become a
promising alternative treatment for enhancing keeping
quality <strong>of</strong> bell peppers. After storage at 7ºC for 18 days,
samples treated with blend <strong>coatings</strong> showed lower
percentage <strong>of</strong> infected peppers <strong>and</strong> good appearance. The
maintenance <strong>of</strong> quality <strong>and</strong> the extension <strong>of</strong> shelf life <strong>of</strong>
sweet peppers by these <strong>coatings</strong> revealed that such <strong>coatings</strong>
can be considered for commercial application during storage
<strong>and</strong> marketing.
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