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Preliminary studies on the quality changes of eggplant as influenced by active packaging

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The effects of active packaging on the surface stiffness, mass, volume, density and weight changes of fresh as well as stored eggplant were studied at 11 and 25°C for 10 days with active packaging material Type 1 and 2 and control. Mass, volume, and surface stiffness of eggplant decreased linearly throughout the storage period regardless of storage conditions; while the mass density showed a reverse trend in the case of 11°C storage. Reduction rate of mass, mass density and weight was observed minimum at 25°C storage temperature with active packaging Type 1. The weight of eggplant decreased at a higher rate in the initial 4 days compared to that in the later period of storage regardless of storage temperature and type of packaging.
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Journal of Korea TAPPI
Vol.38.No.5, 2006
Printed in Korea
Preliminary Studies on the Quality Changes of Eggplant as
Influenced by Active Packaging
Li Zuo, Eun Ju Seog, Jun Ho Lee
and Jong-Whan Rhim*1
(Received September 15, 2006: Accepted November 11, 2006)
ABSTRACT
The effects of active packaging on the surface stiffness, mass, volume, density and weight
changes of fresh as well as stored eggplant were studied at 11 and 25oC for 10 days with
active pack aging material Type 1 and 2 a nd c ontrol. Mass, volume, and surface stiffness of
eggplant decreased linearly throughout the storage period regardless of storage conditions;
while the mass density showed a reverse trend in the case of 11oC storage. Reduction rate
of mass, mass density and weight was observ ed minimum at 25oC storage temperature with
active packaging Type 1. The weight of eggplant decreased at a higher rate in the initial 4
days compared to that in the later period of storage regardless of storage temperature and
type of packaging.
Keywords : corrugated fiberboard, active packaging, eggplant, stiffness, density
1. Introduction
Eggplant (Solanum melongena L.) is a common
vegetable available in retail outlets worldwide
but has a very limited shelf life for freshness (1-3).
It is also known as aubergine, guinea squash or
brinjal and a good source of vitamins and
minerals (particularly iron) making its total
nutritional value comparable with tomato (4).
Eggplant has been used in traditional medicine
(5), for example, tissue extracts have been used
for treatment of asthma, bronchitis, cholera and
dysuria; fruits and leaves are beneficial in
lowering blood cholesterol.
Eggplant belongs to a family of plants of
tropical origin. Its fruit is a non-climacteric large
berry and is chilling sensitive. Below 12oC
b
ut
above their freezing point, eggplants suffer rapid
physiological disorders manifested mainly
by
the appearance of surface injuries such as pitting,
and seed browning, especially in the calyx (6).
Therefore, chilling injury (CI) is a serious
problem in storage and processing of these fruits
(7). The texture of flesh and processed vegetable
is one important quality aspect.
When the eggplant become mature, the tender
Dept. of Food Sci. & Engr., Daegu University, Gyeongsan, Gyeongbuk 712-714, Korea
*1 Dept. of Food Eng., Mokpo National University, Muangun, Chonnam 534-729, Korea
Corresponding author: E-mail; leejun@daegu.ac.kr
Preliminary Studies on the Quality Changes of Eggplant as Influenced by Active Packaging 67
texture characteristic is lost and becomes spongy.
Successful marketing relies on increasing the
shelf life of the fresh eggplant. A number of
methods are available for increasing the shelf life
including low temperature (8, 9), modified
atmosphere (10) and gamma irradiation (11).
These methods involve control of storage
conditions, but still the quality of eggplant
decreases appreciably. Recent development in
packaging methods could be another answer to
prolonged shelf life of eggplant.
The aim of this research was to study the effects
of different types of active packaging materials
which generate numbers of anion (Type 1 and
Type 2) on the stiffness and density of eggplants
which are the most important quality
characteristics of eggplant, during storage at 11
and 25oC and correlate the density of the eggplant
with storage period and temperature and
packaging materials.
2. Experimental
2.1 Eggplant samples
Mature suitable eggplants were purchased
from a local supermarket in 5 kg lots and directly
used in experiment. The degree of maturation
was decided based on the size of the eggplant
usually preferred by consumer in supermarkets
and street shops.
2.2 Treatment and storage conditions
Eggplants were randomly selected for each
experiment. They were initially washed with
0.1% w/v NaClO for 1 min to prevent surface
contamination and then air-dried for 30 min. The
excess liquid was removed by hand with tissues,
then put into two different active packaging
boxes at two different temperatures (11 and 25oC)
for up to 10 days. The samples without package
were treated as control. Samples were evaluated
in terms of several quality attributes listed below
at different times of storage (0, 1, 3, 5, 7 and 10
days at 11oC and 0, 1, 4, 7, and 10 days at 25oC).
Samples placed in a corrugated fiberboard box
coated with 15% of polyvinyl alcohol (PVA) and
10% of Monazite were treated as Type 1. Forty L
of 15% PVA and 4 kg of Monazite were mixed at
1,000±100 rpm for 10 min in an agitator. Coating
was done using a roller coating machine
operating at 160and 20 m/min. The coating
thickness was approximately 30 µm. In case of
Type 2 packaging, samples were placed in an
uncoated fiberboard box. Numbers of anion
generated by each types of packaging were
300-500/mL and 20-60/mL for Type 1 and Type 2,
respectively. The fiberboard box was made of
SK180/K200/K200 A type of corrugated
fiberboard.
2.3 Mass, volume and density
The mass of the eggplant was measured on an
electronic precision balance to within 0.01 g,
while the volume was measured by a water
displacement method using a graduated
measuring cylinder having an inner diameter of
105 mm and a capacity of 3 L (3, 12). The minimum
graduation of the cylinder was 5 cm3. The whole
eggplant was immersed, by holding its stem, into
water and the differential volume minus the
volume of the holder was noted as the volume of
the eggplant. The density of the individual
eggplant was computed by dividing its mass by
volume and expressed in kg/m3.
2.4 Moisture content and weight of
eggplant
Moisture content of the eggplant samples was
measured as an indicator of water loss during
68 Li Zuo, Eun Ju Seog, Jun Ho Lee and Jong-Whan Rhim J. of Korea TAPPI 38(5) 2006
Fig. 1. Changes in mass of eggplant as influenced by active packaging conditions.
Time (days)
0246810
Mass (g)
90
105
120
135
150
165 11oC
Time (days)
0246810
Control
Type 1
Type 2
25oCٛ
storage using an oven drying method (13, 14). A
certain amounts of samples (c. 5 g) were weighed
onto aluminum weighing dishes. After 24 h in the
drying oven (105oC), the samples were reweighed
and percent moisture was calculated.
Weight measurement of the eggplant was
carried out at 0, 1, 3, 5, 7, and 10 days using an
electronic precision balance.
2.5 Surface stiffness ratio
Texture characteristics were evaluated with a
computer controlled Advanced Universal
Testing System (model LRXPlus, Lloyd
Instrument Limited, Fareham, Hampshire, UK)
at room temperature. A 100 Newton (N) load cell
and a 5 mm diameter stainless steel cylinder
probe were used and the cross head speed was 10
mm/min. Each treatment was repeated 3 times,
and their mean values were compared. Results
were expressed as the maximum force Newton
(N) from 30% compression of individual the
eggplant fruit (15). From the typical force
deformation curve, stiffness was derived using
the following relationship:
Stiffness (N/mm2) = [F/A0]/[D/L]
where F is the maximum force (N), A0 is the
area of cross section (mm2), D is the maximum
deformation (mm), and L is the original length
(mm). The surface stiffness ratio was calculated
by dividing the stiffness at a given time of storage
by the stiffness of the fresh eggplant.
3. Results and Discussion
3.1 Mass, volume and density
Mass of the eggplant at all storage conditions,
without exception, decreased linearly with
storage period, which are obvious due to loss of
moisture during storage (Fig. 1). The slope of
curves indicate the rate of decreases. In all
conditions, the slope of curves are the almost
same regardless of active packaging type at 11oC
storage. But the rate of decrease differs with
storage conditions at 25oC. The slopes of curves of
packaging Type 1 and 2 are lower than that of the
curve of control. But the rate of decrease at 11oC
was still lower than that of at 25oC. The similar
results were reported elsewhere (3).
The volume of eggplants decreased at a higher
rate and slowed down for all conditions (Fig. 2).
The decrease in volume is also due to moisture
Preliminary Studies on the Quality Changes of Eggplant as Influenced by Active Packaging 69
Fig. 2. Changes in volume of eggplant as influenced by active packaging conditions.
Time (days)
0246810
Volume (mL)
150
180
210
240
270
300 11oC
Time (days)
0246810
25oC
Control
Type 1
Type 2
Fig. 3. Changes in mass density of eggplant as influenced by active packaging conditions.
Time (days)
0246810
Mass density (kg/m3)
540
560
580
600
620
640 11oC
Time (days)
0246810
Control
Type 1
Type 2
25oC
loss with storage time. The rate of decrease is
higher for the first day at 11oC and decreased
steadily until 10th days regardless of packaging
type, whereas the volume did not change for the
first day at 25oC and decreased until 10th days
regardless of packaging type.
Density of eggplant increased significantly
during the storage period studied in general at
11oC for all active packaging materials in contrast
with mass and volume (Fig. 3). Density increased
over 5 days in the case of packaging Type 1 and 7
days in the case of control, after reaching the peak,
these fell gently. The increase in density may be
due to a higher rate of decrease in volume in
comparison to that of mass. The mass decreased
at a lower rate than that of volume for the
corresponding periods of storage of eggplant
(Fig. 1 and 2). The considerable difference in
density was found in the case of storage at 25oC,
density of eggplant decreased significantly over 1
day of storage for all conditions showing the mass
decreased at a higher rate than that of volume
(Fig. 1 and 2).
70 Li Zuo, Eun Ju Seog, Jun Ho Lee and Jong-Whan Rhim J. of Korea TAPPI 38(5) 2006
Fig. 4. Changes in moisture content of eggplant as influenced by active packaging conditions.
Time (days)
0246810
Moisture content (%)
93.0
93.5
94.0
94.5
95.0
95.5
96.0 11oC
Time (days)
0246810
Control
Type 1
Type 2
25oC
Fig . 5 . Change s in w eig ht of e ggplant as influe nced by activ e packag ing condi tions .
W
, wei ght at any
time; t, storage time in day.
Time (days)
0246810
Weight (g)
90
105
120
135
150
165 11oC
Time (days)
0246810
25oC
Control: W = -0.94t + 125.79, R2 = 0.97
Type 1: W = -1.23t + 161.34, R2 = 0.99
Type 2: W = -1.10t + 141.09, R2 = 0.99
Control: W = -2.43t + 116.40, R2 = 0.99
Type 1: W = -1.79t + 110.75, R2 = 0.98
Type 2: W = -2.12t + 122.22, R2 = 0.99
Control
Type 1
Type 2
3.2 Moisture content and weight of
eggplant
Figure 4 shows the moisture content of
eggplant. In the case of storage at 11oC, the
moisture content of control sharply decreased
during the first day of storage, whereas that of
packaging Type 1 and 2 decreased slowly. For
25oC, the moisture content of control and
packaging Type 2 sharply decreased for the first
day, whereas that of packaging Type 1 slowly
decreased.
The weight of eggplant decreased at a higher
rate in the initial 4 days compared to that in the
later period of storage (Fig. 5). The loss of weight
with storage period is obvious due to loss of water
by continual transpiration of eggplant during
storage. The weight of eggplant during storage
could best be predicted by the equation presented
in Fig. 5. These data were nicely fit to the linear
equations. The rates of weight loss (express as the
slope) were similar at 11oC storage regardless of
active packaging materials and even for control.
In the case of storage at 25oC, the slopes were
Preliminary Studies on the Quality Changes of Eggplant as Influenced by Active Packaging 71
Fig. 6. Changes in stiffness ratio of eggplant as influenced by active packaging conditions.
Time (days)
0246810
Stiffness ratio
0.4
0.6
0.8
1.0
1.2 11oC
Time (days)
0246810
25oC
Control
Type 1
Type 2
much steeper than those of storage at 11oC,
showing the highest slope in control sample.
3.3 Surface stiffness ratio
Figure 6 shows the changes in surface stiffness
ratio of fresh eggplant as influenced by storage
conditions. All three texture parameters
including hardness, stiffness and firmness,
decreased with an increase in the time and
storage temperature (data not shown). It can also
be observed that the three texture parameters
(hardness, stiffness, and firmness) behaved
similarly in describing the textural qualities, so
that any of them may be effectively considered as
a representative parameter for texture evaluation
of eggplant. Nourian et al. (16) also showed very
similar behaviors of texture parameters with
cooked potatoes. The rate of decrease in stiffness
ratio was initially high till 4 days storage in
packaging Type 2 and 1 day storage in control at
25oC. In the case of storage temperature at 11oC,
the rate of decrease in stiffness ratio with storage
time was slow for all conditions. These are due to
the shrinkage of the eggplant during storage. The
upper layer (epidermis) of the eggplant became
loose during storage and thus had minimal
resistance to compression. In both temperatures,
packaging Type 1 showed the minimum changes
in texture and thus could be successfully used in
high temperature storage while maintaining the
stiffness which was the advantage of cold storage.
Jha and Matsuoka (3) showed the increased
stiffness after some time during storage. And
these phenomenon was explained by the loss of
epidermis' firmness during storage followed by
contact with the inner surface which resist the
compression result in increased stiffness
temporarily. And indicated that the eggplant
could be safely stored up to that period. Figure 6
did not show clear trend but still showing high
stiffness ratio over 0.6 except the control at 25oC.
And the stiffness ratio was found to be lower at
higher storage temperature than at lower
temperature, which indicated that the stiffness of
eggplant decreases more rapidly at higher
temperature than at the lower one.
No scientific evidence yet exists to support the
notion that anions offer positive benefits to
human health. Kim et al. (17) reported that low
dose ionizing radiation increased germination
rate, growth and yield of soybean cultivar. Kim et
al. (18) showed stimulating effects of low dose
gamma-radiation on the seed germination, early
growth and physiological activity in the gourd.
72 Li Zuo, Eun Ju Seog, Jun Ho Lee and Jong-Whan Rhim J. of Korea TAPPI 38(5) 2006
And Baek et al. (19) investigated the promoting
effects of low dose gamma-radiation on
germination and early growth of vegetable crops.
Our experiment of active packaging with anion
generating materials on quality characteristics of
fresh as well as stored eggplant at 11 and 25oC for
10 days showed reduction rate of mass, mass
density and weight was observed minimum at
25oC storage temperature with active packaging
Type 1.
4. Conclusions
The following conclusions may be drawn from
the results:
(1) Mass, volume, density, moisture content,
and surface stiffness of eggplants changes
appreciably with storage time ranging between 0
and 10 days at 11 and 25oC.
(2) Mass, volume, and surface stiffness
decreased linearly throughout the storage period
regardless of storage conditions.
(3) The effectiveness of active packaging
material was very clear, specially with package
Type 1 showing minimum changes in texture,
mass density, moisture content and weight
during storage at 25oC.
Acknowledgements
This work was supported by the research grant
(a grant No.: R01-2003-000-10389-0) from the
Basic Research Program of the Korea Science and
Engineering Foundation (KOSEF).
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