edible coating

1. Indian Journal of Biotechnology
Vol 10, January 2011, pp 83-89
Enhancement of storage life and quality maintenance of papaya fruits using
Aloe vera based antimicrobial coating
Sai Lakshmi Marpudi, L S S Abirami, Pushkala R and N Srividya*
Food Technology Division, Department of Home Science, Sri Sathya Sai University, Anantapur 515 001, India
Papaya is one of the main tropical fruits of India. The desiccation of fruits and perishable nature of papaya is a major
drawback during transportation to distant markets and storage during glut in the market. Aloe vera gel, mainly composed of
polysaccharides, has been recently explored as an edible coating owing to its antifungal activity. To improve the
performance of edible coatings, various substances/chemical additives have been incorporated. Papaya leaf is a potential
antifungal agent that could be used as a bio-based additive, especially, by papaya growing farmers. The present study was
carried out to evaluate the ability of Aloe gel based antimicrobial coatings to reduce/control the loss of post harvest fruit
quality in papaya and to compare the effects with a natural polysaccharide-chitosan, an established coating material with
antifungal activity. Freshly harvested papaya fruits were coated with Aloe gel/AG (50%), papaya leaf extract/PLE
incorporated Aloe gel (1:1) and 2.5% chitosan. The coated and uncoated (control) fruits were stored at 30±3°C and 42-55%
RH for 15 d. Physical (PLW, fruit size), chemical (pH, titrable acidity and TSS), and sensory characteristics (colour, taste &
firmness); fruit disease index (FDI), and marketability were analyzed at regular intervals during the storage period. The
coated fruits survived the storage period of 15 d, whereas, all the uncoated controls decayed within 10 d. The
uncoated/control fruits exhibited significantly greater changes in all the parameters tested. Among the coated fruits, PLEAG
treated fruits exhibited least changes followed by AG and chitosan coated fruits. The coatings controlled the PLW, ripening
process (chemical changes, colour development and softening of fruit tissue) and decay to a great extent and thereby
extended the shelf life quality of the fruits. Marketability was also found to be better for PLEAG coated fruits among the 3
coatings, followed by AG and chitosan coated fruits. The effectiveness of AG coating was found to improve on incorporation
of PLE. Shelf life could be further extended in low temperature storage. This is probably the first study on utilizing a natural
alternative such as Aloe-gel and PLE to extend shelf life quality in papaya. On the basis of the over all physiological changes,
Aloe gel based antimicrobial coating has been identified as a suitable method to extend the shelf life of papaya fruits.
Keywords: Carica papaya, edible coating, Aloe gel, chitosan, papaya leaf, post-harvest shelf life
Introduction
One of the major growth segments in the food
retail industry is fresh and minimally processed fruits
and vegetables. This new market trend has, thus,
increased the demands for the food industry for
seeking new strategies to increase storability and shelf
life and to enhance microbial safety of fresh produce.
The most important quality attributes contributing to
the marketability of fresh and minimally processed
produce include appearance, colour, texture, flavour,
nutritional value, and microbiological safety. These
quality attributes are determined by plant variety,
stage of maturity or ripening, and the pre- and post-
harvest conditions, and all can change rapidly during
post-harvest storage1
. In general, desiccation and
decay are the two major causes of the termination of
commercial life span of fruits and vegetables. The
water loss resulting from transpiration causes not only
shrinkage and wilting, but also softening of produce.
The main tropical fruits produced in India include
banana, mango, guava, pineapple and papaya. India is
the second amongst papaya producing countries and
produces around 250 lakh quintals of papaya
annually2
. The perishable nature of papaya is a major
drawback for transport of the fruits to distant places
and storage during glut in the market. The estimated
post-harvest losses of papaya fruits in India has been
reported to be between 40-100%3
. The different
storage methods used to preserve papaya fruits
include low temperature storage, controlled
atmospheric storage, plastic film wraps and wax
coatings. But there are many reports that papaya in
refrigerated storage is susceptible to fungal decay4
. In
controlled atmosphere storage, papaya fruits were
benefitted only slightly from storage in low oxygen
——————
*Author for correspondence:
E-mail: saisrivn @yahoo.co.in
Note: This paper was presented in the International Conference on
‘Challenges in Biotechnology and Food Technology’ organized at
Annamalai University, Annamalai Nagar during 8-10 October, 2009.

2. INDIAN J BIOTECHNOL, JANUARY 201184
(1-1.5%) conditions, at 13°C 5
. Gamma irradiation has
also been used to increase the shelf life. However,
higher doses caused excessive softening of the flesh,
and low dose gamma irradiation though increased the
shelf life but reduced the levels of ascorbic acid.
Polymeric films and wax coatings were found to be
effective in reducing water loss from papaya but were
not effective in preventing fruit decay4
.
There are few studies on the efficacy of edible
coatings to reduce the perishability of papayas.
Application of various semi permeable edible coatings
has been found to be a satisfactory way of achieving
modified atmospheres. These coatings include a mixture
of fatty acids and carboxymethylcellulose, and
commercial coatings. Fruits coated with these edible
coatings were reported to extend the shelf life and delay
the onset of fungal infection4
. Chitosan, a modified
natural biopolymer, with broad antimicrobial activity
and film forming property 6
has also been reported to be
effective in extending the shelf life of papaya 7
.
There is, hence, scope to study economically viable
alternatives to improve the shelf life of papaya fruits
using other edible coatings that are biodegradable and
eco-friendly. Recently, there has been increased
interest in using Aloe vera gel as an edible coating
material for fruits and vegetables driven by its
antifungal activity8-10
. A. vera gel based edible
coatings have been shown to prevent loss of moisture
and firmness, control respiratory rate and maturation
development, delay oxidative browning, and reduce
microorganism proliferation in fruits such as sweet
cherry, table grapes and nectarines11-13
. In addition to
the traditional role of edible coatings as a barrier to
water loss and delaying fruit senescence, the new
generation coatings are being designed for
incorporating and/or for controlled release of
antioxidants, nutraceuticals, chemical additives and
natural antimicrobial agents14
. Extracts of papaya
leaves have been reported to possess antimicrobial
activity against fungal pathogens15
. There are no
reports presently on the post-harvest application of
Aloe gel coating on papaya fruits or the use of papaya
leaf extracts as an antimicrobial agent in coatings. A
study was, hence, conducted to evaluate the effect of
Aloe gel and papaya leaf extract incorporated Aloe gel
coatings on the storage life of papaya fruits in
comparison to chitosan coating.
Materials and Methods
Materials
Freshly harvested papaya (Carica papaya L.) fruits
were procured from from the local market of
Anantapur. They were selected on the basis of size,
colour and absence of external injuries. Chitosan was
purchased from Panvo Organics Pvt. Ltd., Chennai.
Fresh leaves of Aloe vera and papaya were obtained
from the University campus garden.
Methods
Preparation of Coating Solutions
Aloe vera gel matrix was separated from the outer
cortex of leaves and this colourless hydroparenchyma
was ground in a blender. The resulting mixture was
filtered to remove the fibres. The liquid obtained
constituted fresh Aloe vera gel. The gel matrix was
pasteurized at 70°C for 45 min. For stabilizing, the gel
was cooled immediately to an ambient temperature
and ascorbic acid (1.9-2.0 g L-1
) was added; citric acid
(4.5-4.6 g L-1
) was then added to maintain the pH
at 416
. The viscosity of the stabilized Aloe gel and its
coating efficiency was improved by using 1%
commercial gelling agent and was used as Aloe gel
(AG) coating. To prepare papaya leaf extract
incorporated Aloe gel coating (PLEAG), 100 g of
leaves were surface sterilized for 5 min in 0.1%
HgCl2, washed thoroughly with sterile distilled water,
crushed along with Aloe gel and its extract was
filtered and made up to 100 mL with Aloe gel.
To prepare chitosan coating, chitosan was first
purified by the method given by El Ghaouth17
.
Purified chitosan was prepared by dissolving chitosan
in 0.25N HCl and the undissolved particles were
removed by centrifugation. The viscous solution was
then neutralized with 2.5N NaOH (pH 9.8).
Precipitated chitosan was collected, washed
extensively with deionised water to remove the salts
and subsequently dried. Purified chitosan was re-
dissolved in 0.25N HCl and the pH was adjusted to
5.6 with 2N NaOH. The solution was autoclaved at
121°C for 15 min at 15 lb/inch2
and used.
Application of Edible Coating Solutions
Before coating, papaya fruits were washed
thoroughly and dried. The coating solutions used for
papaya fruits were 50% Aloe gel, PLEAG (1:1), and
2.5% chitosan (the highest concentration reported in
literature for coating application and antimicrobial
activity). The fresh fruits were dipped completely into
the coating solutions at room temperature for 15 min.
They were allowed to drain and then dried at room
temperature with forced air drying to allow a thin film
layer to be formed on the fruits. Fifteen fruits were
used for each coating solution. The fruits were then

3. MARPUDI et al: ENHANCED STORAGE LIFE OF PAPAYA FRUITS USING ALOE VERA BASED ANTIMICROBIAL COATING 85
weighed and stored in bamboo baskets lined with
newspapers at room temperature (30±30
C) and at
42-55% RH. The experiments were replicated. Fruits
without coating were used as controls and were stored
under same conditions as those for coated fruits.
Various parameters were determined initially and at
5 d interval. The parameters analyzed included
physiological loss in weight (PLW), fruit size, pH,
titrable acidity, total soluble solids (TSS), sensory
analysis for fruit quality (peel colour, firmness,
appearance and taste), marketability and degree and
rate of fruit spoilage.
Physiological Loss in Weight (PLW)
Water loss was calculated in terms of PLW by the
following equation: (A-B)/A x 100,where, A is the
initial weight of fruits (0 d) and B is the fruit weight
after the storage period.
Size of Fruits
The mean size of the fruits was measured by using
digital Vernier calipers. Fruits were measured
vertically and across the fruit to the nearest 0.01 mm
and the average value calculated.
Titrable Acidity, pH and Total Soluble Solids
Fruits were homogenized and the resultant pulp
was filtered. The pH of the fruit juice was determined
using a digital pH meter. Ten mL of squeezed fruit
juice was diluted to 50 mL with distilled water and
titrated against 0.1N NaOH by using phenolpthalein
as indicator. The results were expressed as % total
acids (titrable acidity). Total soluble solids were
determined for both control and coated fruits by using
Abbe’s hand refractometer.
Sensory Analysis for Evaluating Fruit Quality
Sensory analysis was carried out by 10 selected
panelists. The fruits were randomly selected from
each batch and served on white plates. The sensory
quality of each batch of fruits was evaluated visually
in terms of peel colour (5-bright green, 4- <25%
yellow, 3 - > 30% to <50% yellow, 2-50% to <75%
yellow, 1 - >75% yellow); fruit firmness (5- very
firm, 4- firm, 3- moderately firm, 2- soft, 1-very soft);
and fruit taste (5 point hedonic scale from 5-sweet to
1-bland) as an indicator of respiration rate and
ripening. Marketability (5-Excellent, 4-Good with
slight defects, 3-Fair and moderate defects, 2-
Marketability limited, 1-Not marketable) of the fruits
was also determined.
Degree and Rate of Fruit Spoilage
The differently coated fruits were visually observed
for fungal spoilage and fruit rots. The number of fruits
infected or spoiled was recorded periodically to assess
the effect of the different coating on retarding fruit
spoilage. It was reported as percentage disease index
and calculated as follows:
% Disease index=
xedcba
xexdxcxboxa 100)4()3()2()1()(
×
++++
++++
Where - 0,1,2,3,4,5 are infection categories (0 – no
lesions, 1 – 5 to ≤15%, 2 - ≥15% to ≤25%, 3 - ≥25%
to ≤50%, 4 - ≥50% to ≤75%, 5 - ≥75% ); a,b,c,d,e are
number of fruits that fall into the infection categories
and X = maximum number of infection categories.
Statistical Analysis
The data obtained from the experiments were
expressed as mean ±SE. Duncan’s multiple range
tests with p<0.05 were employed to analyze the
results and to compare control and coated fruit
samples.
Results
The control fruits started deteriorating before 5 d
and only few fruits survived up to 10 d, whereas, shelf
life was extended to 15 d (study period) for majority
of the coated fruits. Therefore, data for uncoated
control was given only till 10 d storage period.
Physical Characteristics
Abnormal loss of firmness due to over ripening and
pitting of the skin causes changes in the weight and
size of fruits. The effect of selected edible coatings on
PLW and fruit size was observed. PLW during
storage was found to be significantly (P<0.05)
different among the papaya fruits treated with the
three different coatings and from control fruits at the
end of 10 d storage (Fig. 1). PLW was observed to be
Fig. 1—Effect of edible coatings on physiological loss in weight
(PLW) of papaya fruits stored at 30±30
C (AG: Aloe gel coated fruits,
PLEAG: Papaya leaf extract incorporated Aloe gel coated fruits).

4. INDIAN J BIOTECHNOL, JANUARY 201186
32%, 26%, 26%, and 27% for control, AG, PLEAG
and chitosan coated fruits, respectively. Among the
coated fruits, PLW of AG and PLEAG coated fruits
were similar (33%), but significantly (at p<0.05)
different from chitosan coated fruits (38%) after 15 d
of storage.
The mean values of the fruit size are shown in Fig. 2.
The size of coated fruits was significantly (P<0.05)
different from control fruits at the end of 10 d storage.
The mean fruit size of coated and uncoated fruits after
10 d was found to be 68.76±0.7, 106.64±2.6,
107.17±2.1 and 105.67±1.75 mm for control, AG,
PLEAG and chitosan coated fruits, respectively. The
maximum reduction (53.03 mm) in size was seen in
control and least reduction in PLEAG coated fruits
(8.96 mm). Coated fruits survived up to 15 d, and the
fruit size was found to be similar in AG and chitosan
coated fruits with a reduction of 22.81 and 22.18 mm,
respectively. In PLEAG coated fruits, a lower
reduction of 20.98 mm was observed.
Chemical Characteristics
The values of the chemical parameters such as pH,
titrable acidity (TA) and total soluble solids (TSS)
determined are shown in Table 1. The mean pH
values of the fruits on the initial day was 5.7 and were
found to increase to 7.2±0.03 after 10 d of storage in
control. In AG, PLEAG, and chitosan coated fruits
there was minimal change in the pH values. Titrable
acidity in the fruit samples decreased with storage
time in both control and treated fruits. However, the
difference was to a lesser extent in coated fruit
compared to control. Titrable acidity values were
found to be 0.12, 0.16, 0.18 and 0.15 for control, AG,
PLEAG and chitosan coated fruits, respectively,
compared to the initial value of 0.20. Total soluble
solids (in 0
Brix) of fruits stored up to 10 d were found
to be 11.1, 8.7, 8 and 8.8 for control, AG, PLEAG and
chitosan coated fruits. After 15 d storage the pH
values of coated fruits increased further with the
lowest value of 5.82 in PLEAG coated fruits. The
same treatment recorded least change in TA (0.12%)
compared to 0.5% in chitosan coated fruits. The TSS
was also lowest (8.2) in PLEAG fruits indicating
slight ripening.
Sensory Characteristics
Colour, firmness and taste, the major sensory
attributes, were scored by panel members (Table 2).
Colour was evaluated based on the peel colour with
‘5’ as a score for green to a score of ‘1’ for complete
yellowness. Bright green colour of papaya peel
changed to yellow during storage in both control and
coated fruits except in PLEAG coated fruits. The
control fruits had shown a greater degree of
yellowness by 5th
d. Colour values were given as 1,
2.5, 5 and 2.5 for control, AG, PLEAG and chitosan
coated fruits, respectively, after 10 d of storage.
Firmness values were observed to be 1.0, 2.5, 4, and
2.2 for control, AG, PLEAG and chitosan coated
fruits, respectively, stored up to 10 d. Taste values
were found to be 5±0, 4.5±0, 2±0.35, and 4±0 for
control, AG, PLEAG and chitosan coated fruits,
respectively. The mean values of coated fruits for
these parameters were significantly (P<0.05) different
from control.
Fig. 2—Effect of edible coatings on fruit size of papaya fruits
(AG: Aloe gel coated fruits, PLEAG: Papaya leaf extract
incorporated Aloe gel coated fruits).
Table 1—Effect of edible coatings on pH, titrable acidity and TSS of papaya fruits stored at 30±3°C
pH Titrable acidity (%) Total soluble solids ( 0
Brix )Storage
Period (d) Control AG PLEAG Chitosan Control AG PLEAG Chitosan Control AG PLEAG Chitosan
O 5.7±0 5.7±0 5.7±0 5.7±0 0.2±0 0.2±0 0.2±0 0.2±0 8.1±0.07 8.1±0.07 8.1±0.07 8.1±0.07
5 5.86± 0 5.77± 0 5.69± 0 5.77± 0 0.18±0 0.19± 0 0.2± 0 0.19±0.0 9.4±0.03 8.12±0.01 7.9±0.03 8.3±0.03
10 # 7.2±0.03a 5.85± 0d 5.72± 0c 5.91± 0b 0.12±0a 0.16± 0a 0.18± 0a 0.15±0b 11.1±0.04a 8.7±0.15b 8±0.02c 8.8±0.02b
15 * 5.96± 0 5..82± 0 6.13± 0 * 0.07± 0 0.12± 0.0 0.05±0.02 * 9.1±0.04 8.2±0.02 9.2±0
*Indicates complete decay of fruits.
# Significant test carried out at the end of storage period of control fruits. Mean ± S.E. values in a row followed by different letters are
significantly (p<0.05) different (DMRT).
(AG: Aloe gel coated fruits, PLEAG: Papaya leaf extract incorporated Aloe gel coated fruits)

5. MARPUDI et al: ENHANCED STORAGE LIFE OF PAPAYA FRUITS USING ALOE VERA BASED ANTIMICROBIAL COATING 87
Marketability
The commercial quality of control fruits decreased
greatly by 5th
d itself, whereas, coated fruits had
maintained the quality (Figs 3 & 4). Marketability
values were found to be 1.5, 3.5, 4 and 3.2 for control,
AG, PLEAG and chitosan fruits, respectively, stored
for 10 d. From the analysis it was observed that
control fruits were having least marketability and
PLEAG coated fruits the maximum. At the end of 15th
d,
marketability was found to be better for PLEAG
coated fruits among the 3 coatings, followed by AG
and chitosan coated fruits.
Fruit Disease Index (FDI)
FDI was used as a measure to indicate the effect of
selected coatings on the microbial quality of fruits.
Over ripening and decay were greater in non-coated
than in coated fruits (Fig. 5). FDI was found to be
100, 40, 30 and 50 for control, AG, PLEAG and
chitosan coated fruits, respectively, after 10 d storage
period at 33±30
C. FDI was found to be similar (40) in
AG and PLEAG coated fruits with a higher FDI of 60
in chitosan coated fruits after 15 d of storage.
Discussion
The results have proved the ability of the various
bio-based coatings used in the present study to extent
the shelf life of papaya fruits. From the analysis, it
can be observed that PLEAG coating had shown the
maximum effect in retarding the change in pH,
titrable acidity and total soluble solids, and had
controlled colour development and softening of fruit
tissue even at the end of 15th
d to a greater extent than
AG and chitosan coatings. Maintenance of fruit
firmness could be related to lower PLW, as reported
earlier in sweet cherry treated with edible coating18
and Aloe gel coated nectarine fruits13
. The retardation
Table 2—Effect of edible coatings on sensory qualities of papaya
fruits stored at 30 ± 3°C
Type of coating Colour Firmness Taste
0 d 5 ± 0 5 ± 0 2.0 ± 0.35
5 d storage
Control 1.5 ± 0.3 2.66 ± 0.27 5 ± 0
AG 3.5 ± 0.35 3.66 ± 0.27 4 ± 0
PLEAG 5 ± 0 5 ± 0 2 ± 0.35
Chitosan 3 ± 0.70 2.33 ± 0.54 4 ± 0
10 d storage #
Control 1 ± 0 a 1.0 ± 0 a 5 ± 0 a
AG 2.5 ± 0.35 db 2.5 ± 0.35 bc 4.5 ± 0 b
PLEAG 5 ± 0 c 4 ± 0 bc 2 ± 0.35 c
Chitosan 2.5 ± 0.70 b 2.2 cb 4 ± 0 b
15 d storage
Control * * *
AG 2 ± 0 2.3 ± 0.35 4.5 ± 0
PLEAG 4 ± 0 4 ± 0 2.5± 0.35
Chitosan 1 ± 0 2.0 ± 0.35 5 ± 0
*Indicates complete decay of fruits.
#Significant test carried out at the end of storage period of control
fruits
Mean ±S.E. in a column followed by different letters are
significantly (p<0.05) different (DMRT).
(AG: Aloe gel coated fruits, PLEAG: Papaya leaf extract
incorporated Aloe gel coated fruits)
Fig. 3—Effect of edible coatings on marketability of papaya fruits
(AG: Aloe gel coated fruits, PLEAG: Papaya leaf extract
incorporated Aloe gel coated fruits).
Fig .4—Control and coated fruit samples after 5 d of storage at
30±3°C (AG: Aloe gel coated fruits, PLEAG: Papaya leaf extract
incorporated Aloe gel coated fruits).
Fig. 5—Effect of edible coatings on fruit disease index of papaya
fruits stored at 30±3°C (AG: Aloe gel coated fruits, PLEAG:
Papaya leaf extract incorporated Aloe gel coated fruits.

6. INDIAN J BIOTECHNOL, JANUARY 201188
of physiological changes in the fruits indicate the
ability of the selected coatings to modify the
respiration rate and delay the ripening process,
thereby extending the shelf life and maintaining the
quality of the fruits. A delayed and smaller increase in
TSS as seen in the present study has also been
reported in Aloe vera gel coated sweet cherry11
and
table grapes12
. This could be again attributed to the
delayed ripening process. In climacteric fruits such as
papaya, an increase in ethylene production during
ripening is a normal physiological process. Earlier
studies have shown a reduction in ethylene production
in A. vera gel coated fruits13
. The retardation of the
ripening process observed in the present study may be
attributed to reduced ethylene production caused by
the modified atmosphere. Surface coating has been
reported to increase resistance of fruit skin to gas
permeability, creating a modified internal
atmosphere19
and reducing the respiration rate.
Reduced respiration rate has been reported in A. vera
gel coated sweet cherry11
and table grapes12
; in peach
fruits coated with wax emulsions20
, and in avocado
fruits coated with methyl cellulose21
. AG coated fruits
had shown optimal colour development and softening
of pulp followed by chitosan. Since, PLEAG had
greatly delayed the physiological changes, it can be
used for fruits that needs to be transported over longer
distances and when longer shelf life period is
necessary. The effect on the fruit physiology could be
altered by changing the proportion of papaya leaf
extract to Aloe gel. In the present study equal
proportion of PLE and AG was used.
In the present study, Aloe based coatings showed
the least disease index. A. vera gel based coatings
have been reported earlier to reduce microorganism
proliferation in sweet cherries and table grapes11
.
Earlier in vivo studies in our laboratory had shown
even unstabilised aqueous extracts of A. vera gel to
have antifungal activity against Colletotricum
gloeosporioides, a major post-harvest pathogen of
papaya fruit15
. Antimicrobial activity of A. vera inner
gel against Gram-positive and Gram-negative bacteria
has been also demonstrated by Habeeb et al22
.
Coating of fruits with PLEAG resulted in better
control of fruit decay compared to AG and chitosan
coating during storage. In the present study,
incorporation of PLE into AG had only marginally
improved the antimicrobial activity of AG coating.
The effectiveness could be improved by incorporating
solvent extracts of papaya leaf than the aqueous
extracts, as the former are reported to have better
antimicrobial activity than aqueous extracts15,23
.
Preservation of the coated papaya fruits at their
ambient storage temperature (10-13°C) is likely to
further extend the shelf life of this tropical fruit. In the
present study, shelf life extension could be observed
even at a higher storage temperature of 30°C. Studies
are in progress to evaluate the efficacy of Aloe and
chitosan composite coatings on different papaya
varieties for a longer period (>15d).
The present investigation is probably the first to
report the efficacy of using A. vera gel based
antimicrobial coating in tropical fruits such as papaya
with promising results. The utilization of papaya leaf
extracts as an antifungal natural additive in coatings
has been also presented here for the first time. These
are bio-based substances and are thereby eco-friendly.
Being available easily in the tropical regions, they
could be used as a cost-effective simple method for
extending the post harvest shelf life and quality of
fruits and vegetables.
Acknowledgement
The authors thank the Chancellor and Management
of Sri Sathya Sai University for providing the
facilities.
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