27.1 Introduction
Modified atmosphere (MA) techniques for horticultural products are based on the
principle that manipulating or controlling the composition of the surrounding
atmosphere affects the metabolism of the packaged product. By creating
favourable conditions, quality decay of the product can be inhibited. The different
MA techniques come with different levels of control to realise and/or maintain the
composition of the atmosphere around the product. Passive MA packaging (MAP),
as an extreme, relies solely on the metabolic activity of the packaged product to
modify and subsequently maintain the gas composition surrounding the product.
Temperature has a major effect on the rates of all processes involved in
establishing the gas conditions in MAP (rates of gas exchange by the product and
rates of diffusion through the packaging materials) and also on the rates of all
metabolic processes that will inevitably lead to deterioration of the product and
finally death. Ideally, steady state gas conditions should be obtained that, from the
point of retaining quality, are optimal for the product packed. The time needed for
a package to reach a steady state is extremely important as only from that moment
in maximum benefit from MA being realised. Depending on conditions, the time
to reach a steady state could theoretically outlast the shelf life of the packaged
product. Given the ubiquitous role of temperature in MAP, success or failure of the
ultimate MA package for a certain product largely depends on the level of integral
temperature control from the moment of packing up to the moment of opening the
package by the consumer. In logistic chains without integral temperature control,
the application of MAP is often a waste of time, money and produce.
In spite of the important role of temperature in MAP, most MAP research
trials are performed at constant temperatures, at temperatures often close to what
27
MAP performance under dynamic
temperature conditions
M.L.A.T.M. Hertog, Katholieke Universiteit Leuven, Belgium
is known as the optimum storage temperature for the product under study. No
extensive literature data is available on monitoring MAP in terms of
temperature, gas conditions and product quality throughout a logistic chain.
Without such a complete set of data it is difficult, if not impossible, to know why
a certain MAP design failed. This could, for instance, be due to a direct
temperature effect on the product’s metabolism, or due to an indirect effect
through a failure to establish the intended steady state gas conditions (too high
or too low), or an unfortunate combination of other factors like leakage or issues
related to product quality (maturity, microbial load, etc.).
This chapter will focus on the effects of dynamic temperature conditions on
the performance of MAP. First of all it will discuss how to define MAP
performance; when MAP can be regarded as being successful and how this can
be measured. Subsequently it will discuss what risks are involved in MAP and
how these risks are affected by a lack of integral temperature control in a logistic
chain. This chapter will conclude with a discussion of several simple strategies
to maximise MAP performance, making the best of MAP given the limited
resources available. The different aspects discussed in this chapter are illustrated
using simulation results from a fully dynamic MA model
12
using realistic
settings for both film and product characteristics.
27.2 MAP performance
The first question to answer when discussing MAP performance is how MAP
performance should be defined. The aim of MAP is to inhibit retardation of
product quality, the means employed to reach this aim is the application of
certain optimal MA temperature and gas conditions. To grade the performance
of MAP one can test whether the aim was reached (in terms of product quality)
or whether the means were employed correctly (in terms of temperature or gas
conditions). If life were simple these two measures would be interchangeable, as
they would be strongly correlated to each other.
From a technical point of view, tracing and tracking gas conditions and
temperature in the logistic chain is much easier than tracing and tracking those
product properties responsible for the overall product quality. However,
assessing the benefits and losses in terms of product quality gives much more
insight than just the observation of MA conditions getting below or above their
target levels. The question that should always be asked is how possible
deviations in temperature or gas condition affect the quality and keeping quality.
Product quality gives static information on the status of the product at a certain
moment, for instance at the point of sale. Keeping quality provides dynamic
information on how long a product can be stored, kept for sale, transported to
distant markets or remain acceptable to the consumer.
A wide range of equipment is available to monitor temperature throughout a
logistic chain. Given that most MA packages are relatively small consumer
packs and given the potentially large spatial and temporal variation in
564 Novel food packaging techniques
temperature within cold stores and truckloads, there is a need to measure
temperature at the level of the individual packs. Cheap versatile time
temperature indicators (TTI) have been developed to give an indication of the
temperature history to which individual packs have been exposed (See chapter
6). Even though these TTIs can give an indication of temperature abuse
somewhere in the chain, they are not intended to reconstruct a complete
temperature history and, therefore, cannot be expected perfectly to explain the
resulting product quality.
To give an example, a TTI will not discriminate between one week’s storage
at 4oC disrupted by either 12 hours of continuous 12oC or six two-hour periods at
12oC. However, for the packed product this might make a difference, especially
as the product needs time to heat up. With 12 hours of continuous 12oC the
product will actually be at 12oC for part of that time. Exposed to the six two-
hour periods of 12oC it depends on the time in between the warm periods how
warm the product eventually will get. As a consequence, the two identical TTI
readings from this example, can relate to two completely different qualities in
the final product. Also the order of imposed temperatures will not make a
difference to a TTI reading. However, for product quality, the order of the
subsequent temperatures the product was exposed to might make a difference.
For instance, pre-climacteric fruit generally responds less vigorously to
temperature than the same fruit in its climacteric stage. With the effect of
temperature on fruit physiology depending on the physiological stage of the
fruit, two comparable temperature profiles (in terms of the total temperature
sum) can have different effects in terms of product quality as this depends on the
timing of the temperature relative to the physiological development of the fruit.
The other important aspects of the established MA conditions are the gas
conditions, which are inextricably related to temperature. As for temperature,
several indicators have been developed to monitor oxygen (O
2
) and carbon
dioxide (CO
2
) in individual packages.
16
As with TTIs, these gas indicators give
only an indicative value. The potential strength of the different types of
indicators arises from their combined application where information on
temperature and gas conditions together can give a better indication of the
realised MA conditions in individual MA packs. However, defining MAP
performance by the realised MA conditions in terms of temperature and gas
conditions is only an indirect measure.
The ultimate unambiguous measure of the success of MAP is the final quality
of the product. Some aspects of product quality can be related to volatiles
produced by the product (ethylene as a measure of ripening stage, specific
volatiles produced during spoilage or anaerobic conditions, etc.). This opens the
door to adding product specific indicators to the range of indicators already
available, resulting in the type of integrated freshness indicators as described in
Chapter 7. Such freshness indicators might come close to giving a good
evaluation of MAP performance incorporating several aspects of product quality
into the equation. However, other aspects of product quality might never lend
themselves to measurement in this way.
MAP performance under dynamic temperature conditions 565
In spite of the importance of product quality as the ultimate determinant of
MAP performance, this chapter will mainly focus on the effect of dynamic
temperature conditions on the gas conditions developing inside MAP. Most of
this is ruled by relatively simple physics. The link to product quality will be
made when possible, but given the vast range of products and their different
ways of responding to the applied MA conditions,
2, 11
no simple rules can be laid
down on how dynamic temperature conditions will affect the quality of an MA
packed product. For this, product specific knowledge is required on how product
physiology responds to surrounding gas and temperature conditions in relation
to the product at its own developmental stage. For now, one should be made
aware that MAP performance is determined by more than just temperature and/
or the established gas conditions.
27.3 Temperature control and risks of MAP
Like most techniques, MAP comes with a number of potential risks that largely
depend on the level of integral temperature control in a logistic chain.
27.3.1 Low oxygen
Generally, MAP is designed to create low levels of O
2
that give maximum
benefit by suppressing the metabolism without getting into the range of O
2
levels that might induce fermentation. The critical O
2
level at which
fermentation starts to occur is defined as the fermentation threshold.
18
The O
2
level in the package is the resultant of the influx through the package and
consumption by the product. Both processes depend on temperature. O
2
consumption by the product generally increases much faster with increasing
temperature (3- to 10-fold from 0–15oC
11
) rather than the permeance of the
packaging material (2- to 3-fold from 0–15oC
9
). As a result, the steady state O
2
levels in the pack will decrease with increasing temperature. The O
2
level in a
MA package designed to operate just above the fermentation threshold will, as a
result of an increase in temperature, drop below this fermentation threshold; the
product will start to ferment resulting in the development of off-odours and off-
flavours. To make life more complicated, the fermentation threshold is not a
constant but can vary with temperature.
1, 3, 18
When MA packed blueberries are
exposed to a temperature increase, the drop in O
2
level is combined with an
increase in fermentation threshold resulting in very little scope before anaerobic
conditions are reached.
Polymeric packaging materials that have the same responsiveness to
temperature as the packed product can prevent induction of anaerobic conditions
following increased temperature. In such cases an increase in O
2
consumption
rate is counteracted by exactly the same increase in O
2
influx through the
packaging material with the steady state gas conditions becoming independent
of temperature. One such example was described for capsicums packed using
566 Novel food packaging techniques
LDPE film.
7
One can argue whether a temperature-independent atmosphere
inside the package is important in its own right. The aim of MAP is to retain
quality. With constant gas conditions at increasing temperatures, respiration rate
and the rate of quality decay will still increase due to the increased temperature.
The O
2
levels in MA packages that make use of perforated films are even
more sensitive to changes in temperature, as diffusion through the holes (i.e.
diffusion through a barrier of standing air) is almost independent of temperature.
An increase in temperature will induce increased O
2
consumption by the product
without inducing a substantial increased influx through the packaging material,
resulting in a fast drop of the steady state O
2
levels.
27.3.2 High carbon dioxide
Besides reducing O
2
levels in MAP, CO
2
levels are increased to further inhibit the
product’s metabolism.
2
High CO
2
levels also inhibit decay by suppressing the
growth of microbes, although sometimes the CO
2
levels needed to suppress
microbial growth exceed the tolerance levels of the vegetable produce packaged.
4, 6
This identifies another dilemma in controlling the gas conditions in MAP.
For most polymeric packaging films the permeance for CO
2
is 2- to 10-fold
higher than for O
2
,
9
under aerobic conditions O
2
depletes much faster than CO
2
will accumulate. Assuming a respiratory quotient of 1 and a steady state O
2
level
of 2kPa, the maximum achievable steady state CO
2
level varies between 2 and
9kPa depending on the film material. To achieve higher steady state CO
2
levels
without inducing fermentation, microperforated films should be used that have
comparable permeances for O
2
and CO
2
. When using microperforated films, O
2
will deplete about as fast as CO
2
accumulates, such that the sum of O
2
and CO
2
partial pressure remains around 20kPa. A microperforated MA package
designed for 2kPa O
2
can therefore generate CO
2
levels of around 18kPa. For
soft fruit like strawberries, these high CO
2
levels are needed to prolong shelf-
life.
8, 13
However, after prolonged storage at high CO
2
(>15 kPa) CO
2
injury
becomes visible from tissue defects and fermentation off-flavours.
10, 14
When exposing MA packages to dynamic temperature conditions there is a
direct risk of inducing fermentation and an added secondary risk of inducing
CO
2
damage due to the accumulating fermentative CO
2
. Especially for
microperforated packs where the permeance does not increase with temperature,
the risk of inducing fermentation and consequently the accumulation of high
CO
2
levels is much larger. Scavengers to constrain the accumulation of CO
2
(Chapter 3) might limit the secondary risk of CO
2
damage but cannot prevent the
direct risk of inducing fermentation.
27.3.3 High humidity
With horticultural products generally consisting of up to 90% water and with
their economic value often determined by the saleable weight of the crop,
moisture loss needs to be limited under all conditions. Depending on how and
MAP performance under dynamic temperature conditions 567
for how long horticultural products are stored, they can easily lose up to 5% or
more of their harvested weight before they reach the consumer. Generally, MAP
films, either perforated or not, are relatively impermeable to water vapour and
therefore quickly generate high humidity levels in the package atmosphere close
to saturation.
With dropping temperatures the saturating vapour pressure drops as well and
the colder air cannot continue to hold as much water vapour. Due to the
extremely low water vapour permeance of most films, water vapour cannot
leave the package fast enough, resulting in condensation in the package. This
will happen with temperature fluctuations as small as 0.5oC. In the heat of
harvest activities, there is often not enough capacity properly to cool the product
before packing. Packing warm product in plastic film, either for MA purposes or
as liners in carton boxes, followed by cool storage, also results in extreme
condensation inside the package thus wetting the product. The high humidity
levels generated inside MAP prevent excessive water loss from the product
retaining product quality, but the presence of free water following temperature
fluctuations creates favourable conditions for microbes to flourish and break
down this same product quality.
27.4 The impact of dynamic temperature conditions on MAP
performance
As outlined in Chapter 16, different sources of variation interact with the
performance of MA packages. In this chapter we discuss the effect of
temperature variation over time, and how that can affect MA conditions and
final product quality. To allow for some temperature flexibility, MAP should be
designed to prevent those risks outlined in the previous sections (too low O
2
, too
high CO
2
, too high humidity). The closer package atmospheres are targeted to
what is feasible, the more likely temperature variation can induce these risks.
How closely the theoretical ideal gas conditions can be approximated depends
not only on the amount of temperature variation one wants to allow for but also
on the amount of variation in other relevant aspects and on how temperature
interacts with these. For instance, when aimed for O
2
levels are close to the
fermentation threshold, depending on the variation in gas exchange rate, there is
a risk that some of the packages result in O
2
levels dropping below the
fermentation threshold.
5
Depending on the variation in the fermentation
threshold itself and the variation in film permeability, tightness of seal, number
of layers wrapped around the product, etc., the targeted safe gas conditions
might need to be far removed from the theoretical ideal gas conditions.
With the number of variables encountered in MA packaging it is difficult to
give full coverage of all aspects of the impact of dynamic temperature profiles
on MAP, as this strongly depends on the specifications of the package of
interest. Some of the important aspects are now discussed using simulations of
MA packaging of shredded lettuce.
568 Novel food packaging techniques
The quality of shredded lettuce is often limited by browning of the cut edges.
This can be controlled by packaging in <1% O
2
and 10% CO
2
atmos-
pheres.
15, 17
Shredded lettuce is a product with a relative high respiration rate
and a high responsiveness to temperature as expressed by the energy of
activation of respiration (see Chapter 16). As a reference we simulated MAP of
pre-cooled lettuce stored at a constant 4oC and packed in a polymeric bag with
an energy of activation of about one-third of the lettuce itself (Fig. 27.1b and c).
Steady state gas conditions (10kPa CO
2
and 1kPa O
2
) are reached after about
two and a half days of storage with O
2
levels reaching 2 kPa after one-day
storage. The realised steady state gas conditions correspond to the targeted
optimum values for shredded lettuce. When one realises that minimally
processed products generally have a limited shelf-life, the two and a half days
needed to establish steady state conditions is relatively long.
For subsequent simulations an artificial dynamic temperature profile was
created (Fig. 27.1a) consisting of one day at a constant 4oC followed by a two-
day period of slow fluctuating temperature around 4oC and a subsequent one-day
period of fast fluctuating temperature. After this, temperature was rapidly
increased to a constant 12oC. Instead of assuming the lettuce to be pre-cooled,
lettuce was assumed to be at room temperature when packed. As a result of
packing warm lettuce, depletion of O
2
and accumulation of CO
2
was accelerated
in comparison to the reference situation (Fig. 27.1b and c), the O
2
level of 2 kPa
was reached only half a day after packing. Both O
2
and CO
2
show fluctuating
levels in response to the fluctuating temperature of the environment.
The fluctuations in O
2
and CO
2
follow the fluctuations in temperature after a
short delay, as the product needs time to warm up and cool down. The larger the
thermal mass and heat capacity of the product, the slower the product will
respond to fluctuations in temperature. This explains why gas levels follow slow
temperature fluctuations more clearly than they follow the fast temperature
changes. Another reason why gas levels do not follow fast temperature changes
is because of the void volume in the package, which buffers the change in gas
conditions.
The direction of the fluctuation in CO
2
level is the same as for temperature
while the direction of the fluctuation in O
2
level is the opposite. As temperature
increases, film permeance increases. However, the rate of O
2
consumption
increases faster than the increase in film permeance resulting in dropping O
2
levels. With dropping O
2
levels fermentative CO
2
production increases resulting
in increasing levels of CO
2
. During the period of fluctuating temperature the
same average gas levels are reached as seen before. When temperature is
increased to 12oC, the O
2
level drops to 0.5kPa while CO
2
accumulates up to
18kPa due to the fermentation induced. It will be clear that such an increase in
temperature to 12oC when a package is designed to operate around 4oC is fatal
for the packed product. Depending on the product such temperature increase
might irreversibly affect product quality.
Packing warm product has the advantage of rapidly establishing the targeted
gas conditions. The downside is the induction of condensation as the warm
MAP performance under dynamic temperature conditions 569
Fig. 27.1 Simulation results of MA packed shredded lettuce stored at a constant 4oC or at
dynamic temperature conditions. (a) Temperature profile used for the dynamic temperature
conditions; air temperature (——) and product temperature ( ). (b) O
2
levels observed
in the package during different simulation runs. (c) CO
2
levels observed in the package
during different simulation runs. (d) Condensation formed during dynamic temperature
conditions. The following simulations are depicted in (b) and (c): reference simulation of
pre-cooled lettuce packed in polymeric film and stored at a constant 4oC (——), lettuce
packed warm using polymeric film and stored at dynamic temperature conditions ( ),
lettuce packed warm and stored at dynamic temperature conditions but with a reduced void
volume (
. . . . .
), lettuce packed warm using microperforated polymeric film and stored at
dynamic temperature conditions (
.
–
.
–
.
–
). The boxes in (b) and (c) contain an enlargement
of what is happening during the period with fluctuating temperatures.
570 Novel food packaging techniques
product evaporates more water than the cold air can contain, quickly
oversaturating the air with an excess water condensating on the inside of the
cold packaging material (Fig. 27.1d). During the subsequent period, con-
densation slowly disappears again by evaporation and diffusion through the film.
With fluctuating temperatures the amount of condensate fluctuates as well. Once
temperature is increased to 12oC there is a fast drop in the amount of condensate.
These relative fast changes are due to changes in the air saturation levels for
water vapour as a function of temperature. This example shows that
condensation can be rapidly induced but once present is hard to remove without
increasing temperature again.
When the void volume in the package is eliminated (Fig. 27.1b and c) steady
state gas conditions are rapidly realised within half a day. Because of the warm
lettuce, the CO
2
level peaks to initially extremely high levels, rapidly
disappearing when the product cools down. By reducing the void volume we
have removed the buffering capacity of the system as a consequence of which
the gas levels respond much more vigorously to the fluctuating temperature and
also become more sensitive to fast fluctuations. When temperature is increased
to 12oC, the increase in CO
2
is much faster than before.
When the film is replaced by a microperforated material, permeance of the
packaging film has become almost independent of temperature. The resulting
gas conditions are now different (Fig. 27.1b and c) with O
2
going towards 3kPa
and CO
2
continuing to increase with time. The reason for not reaching steady
state conditions is the relatively much lower permeance for CO
2
as compared to
the permeance for O
2
. Therefore the steady state conditions for CO
2
are at much
higher CO
2
levels than before, which takes more time and the MA package
never reaches this situation. Because of the temperature independency of film
permeance the fluctuations in O
2
levels respond vigorously to changes in
temperature. The final temperature increase to 12oC results in a drop of O
2
to
1kPa and an increase of CO
2
towards 40–50kPa. This increase is clearly the
result of fermentative CO
2
production that, due to the low permeance for CO
2
is
trapped inside the package. As the accumulating CO
2
has an inhibitive effect on
the respiration of lettuce, O
2
consumption is inhibited, resulting in a subsequent
slight increase of the O
2
level.
The outlined simulations were focused on a single average MA pack. When
the dynamic temperature condition is applied to a batch of MA packages, each
prepared package will differ slightly from another. Given that biological
variance is the most variable parameter, we simulated a batch of 500 packages
assuming 25% variation on product respiration rates, and 10% variation on
packed product weight and film thickness (Fig. 27.2). The simulation result
clearly shows the effect of variation in MA design parameters on the resulting
MA gas conditions. At the same time it shows that variation in MA gas
conditions depends on time and temperature. As, depending on the respiration
rates, some packages establish MA conditions faster than others, initially a large
variation in MA gas conditions is observed. Some packages reached a level of
2kPa O
2
within three hours after packing while others took two days to reach
MAP performance under dynamic temperature conditions 571
this stage. By reducing the void volume, packing warm product, or flushing the
package with nitrogen, the process of establishing MA conditions can be
facilitated reducing the initial large variation in MA gas conditions.
The variation in O
2
levels is generally much smaller than the variation in CO
2
levels, especially when the temperature increase to 12oC induces fermentation.
Under these conditions the high CO
2
levels in some of the packs will induce
CO
2
injury. Controlling temperature in such a way that none of the packs
develop fermentation would keep the variation in CO
2
levels within limits.
27.5 Maximising MAP performance
From the simulations in the previous section it became clear that it is of the
utmost importance to prevent all sources of variation, whether that is
temperature variation (time but also spatial variation), variation in the product
(maturity differences causing variation in respiration rate or variation in the
amount of product packed), or variation in the homogeneity of the package
itself (variation in thickness, perforations, layers of wrapping, tightness of seal,
etc.).
Biological variation tends to average itself out when large enough batches of
product are packed. The variation between consumer MA packs containing a
limited amount of product will be much larger than variation between MA
Fig. 27.2 Simulation results of 500 MA packages of shredded lettuce packed using
polymeric film stored at dynamic temperature conditions (Fig. 27.1a). The average CO
2
(——) and O
2
levels ( ) are plotted together with their 95% confidence intervals
(
. . . . .
).
572 Novel food packaging techniques
packed pallets containing a large amount of product per pallet. So increasing the
size of MA packages can cope with within-batch variation. Potentially, there is
also a large variation related to the maturity of the packed product during the
course of the season. As a consequence, early harvested product might have
different packaging needs from product harvested later in the season. Ideally, the
design of a MA pack is adapted during the season to cope with these changes in
maturity. Fine-tuning the design of MA packages to these changing needs during
the season can theoretically be done by relatively simple measures as long as
one knows what the changing needs of the product are. Close co-operation
between product and packaging experts is needed to develop guidelines for the
horticultural packaging companies. Variation in the homogeneity of the physical
package (variation in thickness, perforations, layers of wrapping, tightness of
seal, etc.) is a technical issue that is relatively easy to control during the
production process by appropriate quality control.
To enable rapid establishment of the intended MA conditions several simple
techniques can be applied such as gas flushing the package before sealing.
Although this is the most expensive technique, it can establish steady state gas
reliably and instantaneously. Packing of warm fruit is the simplest way but
comes with the risk of inducing lots of free water in the pack. Depending on how
vulnerable the product is to microbial breakdown this might not be an option.
Reducing the void volume is the third way of speeding up the process of
establishing steady state gas conditions. However, this is not only speeding up
the initial process of establishing steady state gas conditions but is increasing the
overall responsiveness of the package allowing it rapidly to follow any
temperature fluctuations in the logistic chain.
Temperature variation can be minimised only by an integral temperature
control throughout the whole logistic chain from field to table. It is of the utmost
importance to involve all partners in the chain in this integral temperature
control as any temperature abuse might nullify the efforts of all other partners. In
the end, the success of a chain is determined by the weakest link in the chain.
When designing MAP for a certain product one should consider whether the
potential benefits are worth the possible risks of a lack of temperature control. If
this is questionable, one might consider designing a safe MA system by
designing it for the highest temperature likely to be encountered. Although this
approach does not utilise the maximum benefits it rules out all associated risks.
In the end, MAP can only be successful when good temperature control can be
guaranteed.
27.6 Future trends
The eventual success of MA depends on temperature control between the
moment of packing and the moment of opening of the package by the consumer.
Instead of relying solely on one’s gut feeling when optimising MAP, a MAP
model to simulate a package going through a logistic chain will give insight into
MAP performance under dynamic temperature conditions 573
the strong and weak parts of that chain in terms of temperature control.
12
It will
make clear which parts of the chain are responsible for the largest quality losses
of the packaged product and need improvement. It enables the optimisation of a
whole chain considering the related costs and benefits. To operate such a model,
information is needed on temperature, O
2
and CO
2
dependencies of gas
exchange and on temperature dependency of film permeance.
With regard to the temperature effect on the oxidative respiration of different
fruits and vegetables there is some data available.
11
Information on fermentation
and on the effects of O
2
and CO
2
on gas exchange is much more fragmentary.
This makes it almost impossible to identify at what temperature anaerobic
conditions are going to be induced. Also a good database on permeance of
packaging films that includes their temperature dependency is lacking. Before a
new film can be used for MAP its temperature characteristics need to be
identified at temperatures relevant to MAP (0 25oC). To be able to bring MAP
to the next level and to predict what the effect of certain dynamic temperature
conditions is on a particular MAP design it is vital to establish such databases on
product and film characteristics. Without this elementary knowledge, MAP will
remain at the level of trial and error. Ultimately, any temperature variation in the
logistic chain should be ruled out. Meanwhile, technical solutions like
temperature sensitive films are emerging to cope with some of the existing
dynamic temperature conditions.
27.7 References
1. BEAUDRY R M, CAMERON A C, SHIRAZI A and DOSTAL-LANGE D L, ‘Modified-
atmosphere packaging of blueberry fruit: effect of temperature on package
O
2
and CO
2
’, J. Amer. Soc. Hort. Sci., 1992 117 436–41.
2. BEAUDRY R M, ‘Effect of O
2
and CO
2
partial pressure on selected
phenomena affecting fruit and vegetable quality’. Postharvest Biology &
Technology, 1999 15 293–303.
3. BEAUDRY R M and GRAN C D, ‘Using a modified-atmosphere packaging
approach to answer some postharvest questions: Factors affecting the
lower oxygen limit.’ Acta Hort. 1993 362 203–12.
4. BENNIK M H J, Biopreservation in modified atmosphere packaged
vegetables, Thesis Wageningen Agricultural University. ISBN 90-5485-
808-7, 1997.
5. CAMERON A C, PATTERSON B D, TALASILA P C and JOLES D W, ‘Modeling the
risk in modified-atmosphere packaging: a case for sense-and-respond
packaging’, in: Blanpied. G D, Bartsch, J A and Hicks, J R (eds), Proc. 6th
Intl. Controlled Atmosphere Research Conference, Ithaca NY, 1993.
6. CHAMBROY Y, GUINEBRETIERE M H, JACQUEMIN G, REICH M, BREUILS L and
SOUTY M, ‘Effects of carbon dioxide on shelf-life and post harvest decay of
strawberries fruit’, Sciences des Aliments, 1993 13 409–23.
7. CHEN X Y, HERTOG M L A T M and BANKS N H, ‘The effect of temperature on
574 Novel food packaging techniques
gas relations in MA packages for capsicums (Capsicum annuum L., cv.
Tasty): an integrated approach’. Postharvest Biology & Technology, 2000
20 71–80.
8. COLELLI G and MARTELLI S, ‘Beneficial effects on the application of CO
2
-
enriched atmospheres on fresh strawberries (Fragaria ananassa Duch.).’
Adv. Hortic. Sci., 1995 9 55–60.
9. EXAMA A, ARUL J, LENCKI RW, LEE L Z and TOUPIN C, ‘Suitability of plastic
films for modified atmosphere packaging of fruit and vegetables.’ J. Food
Sci., 1993 58 1365–70.
10. GIL M I, HOLCROFT D M and KADER A A, ‘Changes in strawberry
anthocyanins and other polyphenols in response to carbon dioxide
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