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© Inštitut za sanitarno inženirstvo, 2013.
International Journal of sanitary engineering research
Vol. 7
No. 1/2013 International Journal of Sanitary Engineering Research 21
Received: 27. 9. 2013
Accepted: 11. 11. 2013
1 University of Ljubljana
Faculty of Health Sciences
Department of Sanitary Engineering
Zdravstvena pot 5, SI-1000 Ljubljana
Slovenia
2 IPC, ESTeSC, Coimbra Health School,
Rua 5 de Outubro, Apartado 7006, Sa
~
o
Martinho do Bispo, 3046-854 Coimbra,
Portugal
*Corresponding author
Andrej Ovca
University of Ljubljana
Faculty of Health Sciences
Department of Sanitary Engineering
Zdravstvena pot 5
SI-1000 Ljubljana, Slovenia
Phone: +386 1 300 11 82
Fax: +386 1 300 11 19
E-mail: andrej.ovca@zf.uni-lj.si
Andrej 1
*
, Telma 2, Silvia
2,
Mojca 1
It has been demonstrated that temperature control is critical in the last three
steps in the cold chain including transport between retail and the consumer’s
home. The aim of this study is therefore to evaluate the efficiency of thermal
insulating bags meant to transport frozen foods from stores to consumers’
homes also in case of transporting chilled foods. The efficiency of three
insulating and one typical PVC bag as a control is evaluated. Evaluation is done
at different internal (related to the load of the bag) and external (related to the
outside temperature) conditions, also taking their price into consideration.
During evaluation, measurements of test objects’ internal temperature were
executed at five-minute intervals with a Testo 177-T4 data logger. The
measurements reveal variations of the test objects’ internal temperature in
accordance with air temperature outside the bag and the degree of load in the
bag. The evaluated insulating bags are not efficient enough to preserve
appropriate temperature environments for chilled food items under experimental
conditions. There was also no confirmation of any significant impact of
insulating bag purchase price.
Food safety, food transport, cold chain, insulating bags
Original scientific article
© Inštitut za sanitarno inženirstvo, 2013.
22
Considering the potential
microbiological risk presented
by perishable food items,
maintaining the cold chain
should continue up to and
within a consumer’s home.
In addition to a high
resistance to the transfer of
heat, a good insulating
material must have various
characteristics (depending
upon the application); low
cost, low moisture
susceptibility, ease
transportation, consumer
appeal, and mechanical
strength are the most
relevant ones.
Refrigeration is one of the most widely practiced methods of preserving
the quality and safety of foodstuffs. Maintaining a cold chain is an im-
portant preventive step for ensuring food safety, and temperature is one
of key parameters effecting growth of microorganisms and their survival
in food. Therefore, in order to provide safe food at high quality, atten-
tion must be paid to every aspect of the cold chain from production to
consumption. It is important that the process of maintaining the cold
chain does not end with the retailer. Considering the potential microbio-
logical risk presented by perishable food items, maintaining the cold
chain should continue up to and within a consumer’s home.
Transfer points are well known problem areas for temperature mishan-
dling and refer to points in the cold chain where products are trans-
ferred from one cold area to another. In a survey conducted in France
[1], in which refrigerated products were monitored throughout the cold
chain, it was revealed that maintaining appropriate temperature is espe-
cially critical in the last three steps in the cold chain (the display cabinet
in store, domestic transport and the household refrigerator). Further-
more, several studies reveal consumers’ insufficient knowledge about
the importance of maintaining the cold chain and carelessness in han-
dling perishable foodstuffs [2,3,4].
Lack of time is the reason consumers frequently and regularly buy
chilled and frozen food that either has a short preparation time or does
not even require any further heat treatment. Jackson et al. [5] report
that chilled and frozen foods including products that can be consumed
without further heat treatment represent more than 60 % of the typical
shopping basket of an average European consumer. To reduce the risk
of temperature mishandling in case of perishable food items, transport
in an insulating bag or box is generally recommended. In addition to a
high resistance to the transfer of heat, a good insulating material must
have various characteristics (depending upon the application); low cost,
low moisture susceptibility, ease transportation, consumer appeal, and
mechanical strength are the most relevant ones [6]. Furthermore, a
clean insulating bag interior is essential to avoid contamination or cross-
contamination of food and to prevent changes in sensory properties,
especially the adsorption of foreign smells.
Evans [7] investigated the effect of the time period, and the manner of
transport on a food temperature purchased from a large retail store and
placed in a pre-cooled insulating box or left in the boot of a car unpro-
tected. In some products, temperatures in the boot rose up to 40°C
during a one-hour car journey during which most of the samples placed
in the insulating box did not change their temperature during the trans-
port. Those transported in a boot of a car then required approximately
five hours after being placed in a domestic refrigerator before the tem-
perature was again reduced below 7 °C.
A study among Slovenian population revealed that the average time a
consumer needs to travel from store to home is 25 min [4], which is less
than reported by Derens [1] for French consumers, where the duration of
A. Ovca, T. Novo, S. Seco et al. The efficiency of thermal insulating bags during domestic transport of chilled food items
International Journal of Sanitary Engineering Research Vol. 7
No. 1/2013 23
the domestic transport between retail and the consumer’s home is typi-
cally an hour. Others report up to or even more than 90 min for 7 % of
consumers investigated [8]. The study of Jevšnik et al. [4] also revealed
that 51.7 % of the respondents never even thought of using an insulating
bag, while additional 33 % believed that an insulating bag is not neces-
sary. Among all respondents (N = 985), only 15.5 % had ever taken an
insulating bag to the store when buying perishable foodstuffs, while this
percentage was significantly higher among respondents who also be-
lieved that the consumer is also responsible for food safety.
In spite of the issue addressed above, there is little evidence regarding
the efficiency of insulating boxes; such research is extremely rare and
mostly in the context of material testing [6,9]. The aim of the current
research is therefore to evaluate the efficiency of insulating bags meant
for maintaining the cold chain by consumers during the transport of per-
ishable food items from the store to the their home. The efficiency of
insulating bags will be evaluated at different internal and external condi-
tions, also considering their price, with different insulating bags at dif-
ferent prices are available to the consumer.
The efficiency of insulating bags available at different purchase prices and
one typical bag was tested. All three insulating bags are made of metal-
lized low-density polyethylene (LDPE) with snap-in type closures (poly-
ethylene terephthalate (PET)) and same outside dimensions (approx. 50
cm × 50 cm). A typical bag is made of Polyvinyl chloride (PVC). For fur-
ther presentation of the data, they were numbered as follows:
• Bag 1: typical PVC bag
• Bag 2: low price insulating bag (€0.79)
• Bag 3: middle price insulating bag (€1.49)
• Bag 4: high price insulating bag (€2.24)
The internal temperature was measured with an artificial “test object”
with weight of 246 g. The material used for its preparation is tylose gel
(77 % water, 23 % methylcellulose powder). Tylose gel is often used for
studying heat transfer during freezing and thawing operations, while its
thermal properties are similar to lean beef; it has been previously validat-
ed [10]; it is homogeneous and can be reused for several repetitions.
During the measurements of internal temperature, a probe was placed in
the interior of the test object. For the collection of data during tempera-
ture measurements, a Testo 177-T4 data logger with a -200 °C to +400
°C measurement range, 0.1 °C resolution and ± 0.3 °C accuracy was
used. The internal temperature was monitored in five-minute intervals.
Measurements were done at two different external air temperatures (15
°C and 30 °C) simulating different outside temperatures. Internal condi-
tions were related to the load of insulating bag during the experiment.
Three different situations were tested with i) one test object only, ii) three
The aim of the current
research is therefore to
evaluate the efficiency of
insulating bags meant for
maintaining the cold chain by
consumers during the
transport of perishable food
items from the store to the
their home.
The efficiency of thermal insulating bags during domestic transport of chilled food items A. Ovca, T. Novo, S. Seco et al.
© Inštitut za sanitarno inženirstvo, 2013.
24
Test product together with the
thermometer probe in the insulating
bag
Test product together with the data
logger and thermometer probe in the
insulating bag
Insulating bag with content in the
incubator
A. Ovca, T. Novo, S. Seco et al. The efficiency of thermal insulating bags during domestic transport of chilled food items
International Journal of Sanitary Engineering Research Vol. 7
No. 1/2013 25
test objects and iii) three test objects plus 1.5 L of water in PET bottle. In
all cases, a thermometer probe was inserted in only one test object to
monitor internal temperatures. For controlled experimental conditions, a
Kambič I-45 CK air temperature incubator (with a volume of 44 L, forced
air circulation, 0.1 °C resolution of temperature setting) and a Zanussi
ZRG309W refrigerator (with volume of 91 L) were used. The average air
temperature in the refrigerator during the measurements was 4.8 °C (SD
= 1.0). The average air temperature in the incubator during the measure-
ments was 15.4 (SD = 0.5) and 29.7 (SD = 0.6) respectively.
Initially, the test object (together with the thermometer probe) was
placed in the refrigerator for 24h to adapt (Picture 1). During each mea-
surement, the internal temperature of the test object was monitored af-
ter the first 15 minutes while still in the refrigerator. After 15 minutes,
the test object, together with thermometer probe and data logger, was
placed into the selected bag (Picture 2). The closed bag was transferred
into the incubator for 60 minutes (Picture 3). Afterwards, the test ob-
ject is again placed in the refrigerator, where the internal temperature
was still monitored for additional 300 minutes. The next measurement
was executed at least after 15 hours rest of the test object (together
with the thermometer probe) in a refrigerator.
The results presented in Table 1 clearly show that insulating bags are
not effective in preserving appropriate temperature environment for one
hour in the described experimental conditions to which test object was
exposed. An evaluation of results in Tab. 1 demonstrates the impact of
bag external conditions (temperature outside the bag) as well as bag
internal conditions (degree of load) on the test object’s internal temper-
ature. Although 30 °C was chosen as an experimental condition, it must
be mentioned that in real situations when food is transported in cars,
air temperature varies in accordance with solar radiation and cloud cov-
er. Kim et al. [11] report that the temperature difference between the
car trunk and outdoor can be up to 15.8 °C with no cloud cover and the
highest solar radiation (21.1 MJ/m2) or just 4.8 °C under the low solar
radiation (14.6 MJ/m2) and maximum cloud cover.
The difference between initial internal temperature of the test object
and the intermediate temperature after 60 minutes of exposure to de-
scribed bag internal and external conditions is expressed as ΔT. An av-
erage ΔT comparing only insulating bags (Bags 2–4) was 2.4 °C and
6.2 °C at outside temperatures 15 °C and 30 °C, respectively. An aver-
age ΔT of a typical PVC bag (Bag 1) was 2.6 °C and 8.2 °C at outside
temperatures of 15 °C and 30 °C respectively. Closer examination shows
that ΔT is decreasing in relation to the higher bag number and higher de-
gree of load. Differences between values of ΔT (when comparing different
bags) are becoming smaller when the degree of load is increased. Bag 1,
used as a control bag, proved to be at least efficient to preserve the initial
The efficiency of thermal insulating bags during domestic transport of chilled food items A. Ovca, T. Novo, S. Seco et al.
© Inštitut za sanitarno inženirstvo, 2013.
26
Internal temperatures of test object at different internal and external bag conditions
Δ
1
1 4.8 7.9 8.8 5.8 3.1 1
2 4.8 7.8 8.4 5.4 3.0 2
3 4.7 7.5 8.1 5.5 2.8 3
4 5.1 7.4 7.9 5.4 2.3 4
3
1 4.7 7.1 7.8 5.3 2.4 5
2 4.5 6.9 7.3 5.1 2.4 6
3 4.6 6.9 7.3 5.2 2.3 7
4 4.8 7.1 7.5 5.2 2.3 8
3+
1 4.9 7.2 7.8 5.5 2.3 9
2 4.9 7.1 7.4 4.8 2.2 10
3 4.4 6.4 6.4 5.4 2.0 11
4 4.8 6.8 7.3 5.5 2.0 12
1
1 4.8 13.5 15.1 6.7 8.7 13
2 4.9 12.2 13.6 6.4 7.3 14
3 5.0 12.3 13.5 5.8 7.3 15
4 4.7 11.9 13.3 6.4 7.2 16
3
1 4.6 12.5 13.4 6.1 7.9 17
2 4.8 11.5 13.0 6.1 6.7 18
3 4.4 10.8 12.2 5.8 6.4 19
4 4.7 10.8 12.2 5.9 6.1 20
3+
1 4.9 12.8 13.2 6.5 7.9 21
2 4.9 10.5 11.3 6.3 5.6 22
3 5.1 9.9 11.2 5.3 4.8 23
4 5.2 9.9 10.6 5.5 4.7 24
EC – Bag external conditions; IC – Bag internal conditions; Initial T – Initial internal temperature of test object in the refrigerator;
Intermediate T – Intermediate internal temperature of test object after 1h in selected bag exposed to experimental conditions;
Maximum T – Maximum internal temperature of test object measured; Final T – Final internal temperature of test object after taken out of
the selected bag and stored in refrigerator for 5 h; ΔT – Internal temperature difference of the test object during one hour exposure to
experimental conditions; 1 – one test object; 3 – three test objects; 3+ – three test objects with 1.5L of water in PET bottle.
temperature of the test object. In contrast, the most expensive insulating
bag (Bag 4) was the most efficient in comparison to the other bags. Con-
sequently, the smallest ΔT is observed for case number 12 and the highest
for case number 13 (Tab. 1). Comparing the typical plastic bag with insu-
lating bags also demonstrates that differences of ΔT are more obvious at
higher outside temperatures (30 °C) and higher degrees of load. Further
comparing ΔT only between insulating bags (Bags 2–4) reveals that the
differences are minimal with no significant impact of their purchase prices.
Closer examination of the maximum internal temperature reached also
reveals that when the outside temperature is 30 °C the test object’s in-
ternal temperature reaches 13.6 °C if stored in insulating bag. Although
some previous studies [7] report that during a one-hour car journey
most of the samples placed in the pre-cooled insulating box did not
change their temperature during the transport, this was not confirmed
with our measurements. This could be due to the fact that insulating
bags were not pre-cooled, and the relatively small test object (246 g)
A. Ovca, T. Novo, S. Seco et al. The efficiency of thermal insulating bags during domestic transport of chilled food items
International Journal of Sanitary Engineering Research Vol. 7
No. 1/2013 27
used. In our study, bigger test objects were not evaluated. As reported
by Kim et al. [11], among the food items examined the temperature dra-
matically increased immediately after storage in the trunk by food items
with the lowest weight.
The maximum internal temperatures (Tab. 1) measured already present
a rather favourable temperature environment for the progress of psycho-
tropic microorganisms which grow well at 7 °C and have their optimum
at 10–15 °C, depending on nutrient content, pH and the availability of
liquid water [12]. However, the higher surface temperature of the test
object (not measured) and time of exposure to these temperatures
should not be neglected.
Closer examination of the test object’s internal temperature rise if placed
in different bags at different external temperatures (Fig. 1) reveals that
internal temperatures also rise after the test object is placed back into the
refrigerator. The maximum internal temperatures of the test object were
reached 15 to 20 minutes after placement in the refrigerator, and re-
tained at a maximum level for an additional 10 minutes, exceptionally 15
minutes in cases 6 and 11 (Tab. 1), before they began to drop. Closer
examination (Fig. 1) of the test objects’ internal temperature inclines be-
tween initial and maximum value, calculating the slope, additionally re-
veals that at both (15 °C and 30 °C) outside temperatures, the internal
temperature of the test objects placed in Bag 1 increases faster (higher
slope) compared to the insulating bags after exposure to experimental
Comparison of internal temperatures
movement of test object placed in
different bags at a) 15 °C and b) 30
°C external temperature. The grey area
indicates the time period
(60 minutes) when the insulated bag
and its content were exposed to
controlled outside temperature.
0
2
4
6
8
10
12
14
16
0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375
Temperature (°C)
Time (minutes)
Bag 1 Bag 2 Bag 3 Bag 4
0
2
4
6
8
10
12
14
16
0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375
Temperature (°C)
Time (minutes)
a)
b)
The efficiency of thermal insulating bags during domestic transport of chilled food items A. Ovca, T. Novo, S. Seco et al.
© Inštitut za sanitarno inženirstvo, 2013.
28
0
2
4
6
8
10
12
14
16
0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375
Temperature (°C)
Time (min)
0
2
4
6
8
10
12
14
16
0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375
Temperature (°C)
1 test object
3 test objects
3 test objects and water (1.5L)
a) 0
2
4
6
8
10
12
14
16
0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375
Temperature (°C)
b)
0
2
4
6
8
10
12
14
16
0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375
Temperature (°C)
Time (min)
c) d)
Comparison of internal temperature
movement of test object at 30°C
external temperature and different
internal conditions in a) bag 1,
b) bag 2, c) bag 3 and d) bag 4. The
grey area indicates the time period
(60 minutes) when the insulated bag
and its content were exposed to
controlled outside temperature.
conditions. Furthermore, a slope comparison between insulating bags re-
veals that the value decreases in correlation with the bag’s price (Fig. 2).
However, this is true only if one test object is present in the bag.
A comparison of the test objects’ internal temperature at 30 °C external
temperature and different internal conditions demonstrates that increas-
es of internal temperatures of the test object is diminished when the
degree of load is increased in all bags examined (Fig. 2a–d). The high-
est internal temperatures of test objects’ are achieved with one test ob-
ject only. A closer examination of temperature rises in correlation to
time also reveals that approximately five hours are necessary after test
object is placed in a refrigerator, for the internal temperature to be again
reduced below 6 °C.
In this context, consumer behaviour should be taken into account. God-
win & Coppings [13] report that consumers using insulating bags con-
sequently extend the time of transport to their home, which also other-
wise differs between different countries [1, 3, 4, 7, 14]. If insulating
bags are not as efficient as consumers would expect or believe, irre-
spective of the outside temperature and degree of load in the bag, the
risk for infection or spoilage is increased. Additionally it must be consid-
ered that consumers often do not pay any particular attention to the
temperatures in domestic refrigerator. As reported by James and others
[15], it is clear that many refrigerators throughout the world are already
running at higher temperatures than recommended.
A. Ovca, T. Novo, S. Seco et al. The efficiency of thermal insulating bags during domestic transport of chilled food items
International Journal of Sanitary Engineering Research Vol. 7
No. 1/2013 29
From the total cold chain point of view based on the measurement done
by Darens et al [1], a refrigerated product spends two thirds of its life in
an environment managed by professionals and the rest managed by the
consumer. However, professionals in food stores do not always maintain
appropriate temperatures. As reported by others [16,17], the tempera-
tures measured differed from the required ones by for up to 10 °C.
Guidelines of good hygienic practices and the principles of the HACCP
system in stores [18] recommend to consumers that food items requiring
maintaining of the cold chain should be stored in insulating bags during
the transport. A commercial insulating bag is a type of shipping container
in the form of a bag made of materials with thermal insulation properties
used to maintain the temperature of its contents. Most insulating materi-
als utilize low thermal conductivity as a means of restricting the transfer
of heat, although radiation and convection are also significant means.
Resistance to heat transfer depends on various characteristics that deter-
mine the insulating ability of a container [6,19]. The wall thickness af-
fects heat transfer via conduction, the number of surfaces via convection
and the number of reflective surfaces (such as aluminium foil) via radia-
tion. According to the manufacturer, the insulating bags used in this study
should be effective up to one hour, and are intended for repeated use.
However, it has to be stressed that, according to the manufacturers’
statement written on the exterior of the insulating bag, they are effective
up to one hour for deeply frozen food items.
The results revealed in this study indicate that insulating bags whose
primary purpose is to preserve appropriate temperature environment for
deeply frozen food items are not sufficiently effective to preserve appro-
priate temperature environment for chilled food items. Although insulat-
ing bags proved to be more efficient in comparison to the typical PVC
bag, the difference was not as significant as expected. Furthermore, the
differences between insulating bags are not correlated with their pur-
chase price. The measurements revealed that the internal temperature
of the test object varies in accordance with air temperature outside the
bag and the degree of load in the bag.
The measurements suggest that insulating bags are not sufficiently ef-
fective to preserve chilled foods, especially when not filled with many
food products. This suggests a need to modify the insulating bags re-
garding their effectiveness for chilled foods and highlights the impor-
tance of short transport times from the store to home.
Transport between retail and the consumer’s home is quite short in
comparison to other links in the cold chain, sometimes leading to the
idea that the impact of this link on food safety should be less impor-
tant. Nevertheless, its impact on the quality and safety of the product
should not be considered negligible. To obtain exact prove of food safe-
ty, microbiological predictive models or microbiological analysis should
be performed in the future, establishing an integrated approach of the
evaluation of chilled product’s safety.
Guidelines of good hygienic
practices and the principles of
the HACCP system in stores
recommend to consumers
that food items requiring
maintaining of the cold chain
should be stored in insulating
bags during the transport.
To obtain exact prove of food
safety, microbiological
predictive models or
microbiological analysis
should be performed in the
future, establishing an
integrated approach of the
evaluation of chilled product’s
safety.
The efficiency of thermal insulating bags during domestic transport of chilled food items A. Ovca, T. Novo, S. Seco et al.
© Inštitut za sanitarno inženirstvo, 2013.
30
The experimental work as well as preparation of the paper was done in the
framework of the ERASMUS programme during training period of students
(Telma Novo and Silvia Seco) from Coimbra Health School, Portugal at
University of Ljubljana, Faculty of Health Sciences, Department of Sanitary
Engineering, during the 2012/13 study year. Special thanks also to An-
dreja Mirt and Anja Petelinšek, who have executed the preliminary meas-
urements and provided photo material of the experimental procedure.
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A. Ovca, T. Novo, S. Seco et al. The efficiency of thermal insulating bags during domestic transport of chilled food items
