Kerry J., Butler P. Smart Packaging Technologies for Fast Moving Consumer Goods
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136 Smart Packaging Technologies for Fast Moving Consumer Goods
−2
0
2
4
6
8
10
12
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Water A
ctivity
Relative Rates
Free Radical
Enzymatic
Figure 8.2 The effect of a
w
on oxidation of unsaturated oil, enzymatic and free radical au-
tooxidation.
Several other detrimental effects that are inhibited by an optimal a
w
of a food are pointed
out in Figures 8.2 and 8.3. These curves are generic, but illustrative of the reactions covered.
Detailed discussion is beyond the scope of this paper.
Figure 8.2, demonstrates that lipidoxidases begin to catalyze oxidation of unsaturated
fats at a significant rate above an a
w
of about 0.3. The rate of oxidation increases rapidly
as the a
w
increases. On the other hand, the rate of non-enzymatic, free radical oxidation
of unsaturated lipids decreases from a
w
= 0.0 to about a
w
= 0.35 upon which the rate
gradually increases with a
w
. This is explained by the observation that in most dry cereal
products, an a
w
of 0.35 corresponds to a moisture level of 8 to 10 %, which is the amount
of water necessary to form a protective monolayer over the surfaces of polysaccharides and
proteins that are associated with unsaturated lipids. This monolayer acts as a barrier to free
radical oxygen attack on the carbon-to-carbon double bond system.
Figure 8.3, shows the relationship between four other modes of deterioration of a food
and the a
w
of the product.
Hydrolytic rancidity is the enzymatic hydrolysis of fatty acids from glycerol. Normally
this is of little consequence except when the fatty acids are of largely short or intermediate
chain-length from butyric to lauric acid. Butyric and the ‘goat acids’, capric, caproic and
caprylic, are volatile enough to be recognized as off flavors at very low concentrations
except, of course, in cheeses, Myristic and lauric acids impart an undesirable ‘soapy’ taste
to a product in which they develop.
The maillard browning reaction is undesirable because of the color change in a product
and production of bitter components in a food product. This complex series of reactions,
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−2
0
2
4
6
8
10
12
14
16
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Water Activity
Relative Reaction Rate
Vitamin C Loss
Chlorophyll
Loss
Maillard
Browning
Hydrolytic
Rancidity
Figure 8.3 The effect of changes in a
w
on various rate of deterioration of food products by
various mechanisms during storage.
beginning with an amine (protein or amino acid) combining with a carbonyl moiety (re-
ducing sugar), progresses through a broad range of compounds leading to dark colored
polymers. The rate accelerates as the a
w
increases above 0.25–0.3.
Color losses occur as the a
w
increases. This process is illustrated by the curve for chloro-
phyll, which begins to deteriorate above a
w
= 0.35. Similar curves can be drawn for
carotenoids, anthocyanins, and others.
Vitamins such as ascorbic acid are susceptible to oxidative processes but are less reactive
at very low a
w
conditions. Others, such as Vitamin A, are subject to free radical autoxidation
processes as mentioned in Figure 8.1.
8.4 An Active Moisture-Management System
In many cases, the food product has the best, moist, tender texture at an a
w
near that at which
microorganisms grow. A system that controls the a
w
in a narrow range near this optimal
point will enable the manufacturer to formulate and assure the best product possible with
such a system with assurance of microbiological safety.
There are a number of factors apart from moisture that impact the shelf-life of a food
product. They can include oxygen, ultraviolet light, heat, freezing conditions, as well as
others that may be unique to certain products. There are commercially available means to
control these factors that accelerate a product’s deterioration with the exception of moisture.
Chemists, and evenalchemists, haveunderstood for years that addition of a solute to water
or other solvent will raise the boiling point and reduce the freezing point of the solvent.
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138 Smart Packaging Technologies for Fast Moving Consumer Goods
Later it was observed that a saturated salt solution will create a headspace environment
of a specific relative humidity as a function of the salts employed. These phenomena are
collectively known as colligative properties and are all a function of particles in solution in
a unit weight of solvent, i.e., molality (Raoult’s law).
Food chemists have employed this technique to help develop stable intermediate moisture
food products such as fruit leather, confections, sweet baked goods. Known constant humid-
ity environments have been generated in small chambers such as desiccators with saturated
salt solutions. Experimental products are equilibrated against these known environments,
establishing optimized formulae for such products.
These saturated salt solutions are not practical in a food package subjected to the typical
distribution system because of the potential for spillage. Electronic control systems are
not economically feasible for individual packages. Desiccants such as silica gel, molecular
sieves or hydration devices employing a wick from a reservoir of water are acceptable only
if the objective is to keep the product very dry or very moist respectively. These systems
cannot maintain a narrow range of water activity in the package.
Colligative properties, constant humidity of aqueous solutions, have been harnessed to
maintain constant relative humidities in chambers including guitar cases, woodwind reeds,
tobacco products, and pharmaceuticals, among other applications.
An inexpensive, safe, effective moisture management system described in this chapter
has not been available previously. This two-way moisture management technology that has
been patented by Humidipak, Inc.
†
It basically consists of a saturated salt solution with
excess crystalline solute thickened with a gum system. The thickening, to a viscosity of
about 5000 or more centipoises (cps), serves three important functions:
r
excess solute is suspended to assure uniform capability to absorb moisture from unit to
unit;
r
loss of the contents of the pack is minimized if the pack is punctured, suffers stress cracks
or a compromised seal;
r
permits use of more permeable films.
As discussed above, moisture management means that the product optimal water activity
is maintained over time as the product and package are exposed to varying environmental
conditions. It will provide moisture to the product when required or remove it by absorbing
it when conditions demand it so that the a
w
remains constant in the package. Both scenarios
are available at any time during the life of the moisture management system and are designed
to keep the product at the optimum a
w
.
This filling is packaged in a material that is highly permeable to water vapor (high
MVTR). This technology delivers the desired relative humidity in a range of less than a
w
=
0.02 within a closed environment over an extended period of time under normal commercial
distribution temperatures. Four patents have been issued and at the time of writing, two
more are pending.
This two-way moisture management system is currently available as packets, tubes and
tubs (shallow plastic cups or trays). Food compatible water activities available include:
0.95, 0.84, 0.80, 0.78, 0.75, 0.73, 0.70, 0.65, 0.62, 0.32, all made with food grade materials.
†
Humidipak, Inc., Wayzata, Minnesota, USA.
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Other a
w
values are available such as 0.69, 0.58, 0.52, 0.45, 0.13, but these are not of food
grade materials.
8.4.1 Application to Beef Jerky
Some products, such as jerky, are best in a very narrow range of a
w
that is very close to a
legally defined standard of identity. In these cases, the moisture management packet can
be employed to ‘finish’ the drying step in the retail package.
Meat jerky has been a fast growing product in the food industry. Jerky is marinated beef,
or turkey, or game or mixtures that has been dried to a USDA standard of identity level of
moisture. The maximum moisture allowed is on the order of 30 % with a water activity on
the order of 0.8. According to an expert taste panel, at a
w
of 0.78 to 0.8, ‘natural style’ jerky
is subjectively relatively easy to bite and has a moist mouth feel. This loss of moistness
becomes more apparent as the a
w
is reduced from 0.75. The texture of jerky becomes less
succulent and tough as the water activity decreases from 0.75 and becomes decidedly less
palatable as the value drops below 0.73 to a hard, tough product giving a noticeably dry
mouth feel.
Jerky is best at an a
w
at which molds grow. Therefore, jerky is usually packaged with an
oxygen free atmosphere and oxygen scavenger packets. The oxygen absorbing iron powder
has been successfully employed in maintaining a very low oxygen level in jerky packages.
Analysis of numerous samples of jerky from numerous manufacturers obtained by diverse
sellers such as groceries, convenience stores, sports stores, and warehouse markets, showed
a wide variety in the a
w
of product available to the consumer. Some of these are summarized
in Figure 8.4.
Table 8.2 shows that a Humidipak moisture regulator maintains the a
w
of jerky at room
temperature and reasonably well at a storage temperature of 100
◦
F (37.8
◦
C) for 90
days, a condition that predicts the storage deterioration equivalent to about 1 year at room
temperature (21
◦
C).
In the experiments summarized above, according to a panel, the jerky without a Humidi-
pak regulator was definitely inferior to the jerky with humidity regulators at an a
w
of 0.78.
8.4.2 Humidity Restoration in Beef Jerky
Since the regulator is two-way, it can restore a product that has been dehydrated. How-
ever, the process is slow in jerky, hence it is far more important to maintain the proper
moisture/water activity of jerky during storage and distribution.
Figure 8.5 shows how a package of jerky manufactured at a
w
of about 0.78 lost enough
moisture after 11 months in distribution to fall to a very poor quality a
w
= 0.67. When a
Humidipak regulator at a
w
= 0.75 was placed into the jerky package, the a
w
of the jerky
increased to 0.73 in 3 months. This rehydrated jerky had an acceptable texture. Had a higher
humidity Humidipak been added, the jerky would probably have attained a value of over
0.75. However, mold could probably have developed since nitrogen flush equipment was
unavailable for this experiment.
It is difficult for a manufacturing process to hold the a
w
of a product to +/− 0.02. By
introducing a two-way regulator into the package, the initial product will be adjusted to the
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140 Smart Packaging Technologies for Fast Moving Consumer Goods
0.58
0.6
0.62
0.64
0.66
0.68
0.7
0.72
0.74
0.76
0.78
ADCBEFGHIJKL
Manufacturer's Sample
Water Activity
Marginal Texture
Dry Texture
Good Texture
Figure 8.4 Water activities of samples of 4-oz bags of jerky by five manufacturers purchased
from various retail outlets ages 6 to 11 months. The shaded area between 0.73 and 0.75 is an
area of marginal moistness and tenderness.
target specification by either absorbing or giving off water to the product. This is especially
important for food items that are near the a
w
where microbial growth can occur. A superior,
yet safe, product can be provided for the consumer.
While restoration of moisture to a dehydrated product is possible by many methods, it
does not return most products to the same organoleptic condition as the original. Therefore
it is very important to maintain a constant humidity in the package so that the water activity
of the contents remains the same.
Table 8.2 Accelerated storage test of beef jerky with or without
Humidipak pouches that had an oxygen scavenger. The storage condition
was 100
◦
F (37.8
◦
C) at 25 % relative humidity, which corresponds to 12
months of storage at ambient room conditions of 70
◦
F (21
◦
C)
a
w
with Humidipak a
w
without Humidipak
Time RT 100
◦
F RT 100
◦
F
0 0.79–0.80 0.79–0.80 0.79–0.80 0.79–0.80
90 days 0.78–0.79 0.75–0.77 0.76–0.74 0.73–0.74
% Oxygen % Oxygen
Time RT 100
◦
F RT 100
◦
F
90 daya 0.0–0.0 0.0–0.09 0.0–0.02 0.0–0.12
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0.64
0.66
0.68
0.7
0.72
0.74
0.76
0.78
0.8
0246810121416
Time, Months
Water Activity
Introduce
Regulator 0.75
Marginal Texture
Good Texture
Poor Texture
Figure 8.5 Loss of moisture in jerky during 11 months of distribution storage (sample from a
convenience store) and rehydration with a Humidipak, a
w
= 0.75.
8.5 Mold Inhibition
An oxygen scavenger system can be added to many of these two-way humidity regulators.
While these scavengers do not have as rapid a reaction rate as do the dry, commercially
available, oxygen scavenger packets, the combined regulator/scavenger system has suffi-
cient reaction rate to be practical in nitrogen flushed applications such as meat jerky. Jerky
stored for at least 18 months at room temperature has retained a headspace oxygen level
of less than 0.1 % oxygen. In the test, the commercially available scavenger packets had a
slightly higher average but fully satisfactory oxygen level of about 0.15 %.
It has also been found that mold growth can be further reduced by adding a mold inhibitor
to the regulator packet, or applying some inhibitor onto the surface of the pouch.
Standard practice in the jerky industry employs commercially availableoxygen scavenger
packets to maintain a low level of oxygen in the headspace. Such an oxygen scavenging
system has been incorporated into the humidity regulator. Table 8.2 shows that the Humidi-
pak with scavenger packet is just as effective as commercially available oxygen scavenger
packets. These values are a composite of field tests conducted with two manufacturers and
represent some 30 samples of each test scheme.
The control consisted of the product as manufactured with nitrogen flushing of the filled
jerky pouch with a commercial 50-ml oxygen scavenger packet. The other two test samples
had Humidipak humidity regulators at 78 % relative humidity. The data from the regulator
with scavenger system is reported in the middle column, the data with plain regulator and
the same oxygen scavenger packet as the control is given in the right-hand column.
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These samples were stored for 90 days at 100
◦
F and 25 % relative humidity, conditions
that generally predict storage deterioration of 1 year at 70
◦
F. Samples held for 90 days at
70
◦
F had values approximately 25 % of the results of the 100
◦
C samples. This was also
true of the weight loss of the whole package with jerky as well as the jerky itself, thus
corroborating the validity of this accelerated storage test.
8.6 Printing Potassium Sorbate
Standard mold inhibitors such as sodium propionate, calcium propionate and potassium
sorbate are only partially effective, if incorporated into the filling of the humidity regulator.
The rate of diffusion of the anion is inhibited by the nature of the semipermeable film used
in these trials. A more effective method is to ‘print’ a pattern of concentrated solution at the
same time that graphics are printed on the film. In any case, because of the low volatility
of sorbic acid, the regulator must be slightly acidic and be in very close proximity to the
product. It will add 14 to 21 days to the life of a properly hydrated jerky after opening a
nitrogen flushed, resealable package.
Flavors can be added to the filling. When about 0.4 % of a smoke flavor was incorporated
into the packets, the product had a fresher, somewhat more ‘smoky’ flavor than jerky in a
package without the moisture management system.
8.7 Packaging Executions
The salt solution required for a specific application can vary from 1 gram to 60 grams or
more as a function of what the requirements are. It is often packaged in a pouch or other
container and sealed shut to prevent leakage. This pouch or container is then placed, along
with the food product being protected, in an outer package that has a moisture barrier to
the outside environmental conditions.
Examples that have been commercialized or thoroughly lab tested are as follows (partial
list):
r
Printing/35# Kraft Paper/1.5 mil extruded Hytrel
∗
film;
r
Thermoformed polypropylene cup/heat seal coating/Tyvek
∗
membrane;
r
Printing/35# Kraft Paper/1.1 K-Resin from Phillips;
r
Nylon film 1 mil thick formed into a chub package.
It is very critical that the package and weight of salt solution be determined and designed
properly for each food application. There are many variables and we have found that if the
detailed laboratory analysis and studies are completed at the start of an investigation, the
actual results of the recommendations will be found to be acceptable and comparable to
the laboratory testing.
The rate at which of water vapor enters and exits the container holding the salt solution
is a variable that can be matched with the desired function. If the moisture management
system is to preserve the food product over an extended period of time, the permeability
of this system can be slower. If it is to manage moisture levels while a package is being
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opened and reclosed numerous times, the moisture permeability rate needs to be faster so
that the desired levels can be reached within a few hours.
Once the product has been selected for a study and the a
w
has been determined, the salt
solution will be formulated such that it will keep the product being protected in its optimum
state. In order to determine and define the specifications for the package size and material,
we need answers to a number of pertinent questions:
(i) What is the water activity (a
w
) of the product being managed? Has a moisture sorption
isotherm been made?
(ii) What is the product weight?
(iii) How much water, in weight, is present in this quantity of product?
(iv) What tolerance does the product have to moisture gain and loss?
(v) How long is the desired shelf-life before opening?
(vi) Are there conditions of reclosure that must be managed?
(vii) Inwhat geographic area and environmentalconditions is this product being distributed
or held?
(viii) What is the package profile and general construction?
(ix) What is the surface area of the exterior package holding the product?
(x) What is the water vapor transmission rate of this outer package?
(xi) Any other product characteristics that might be unique?
With these answers, we can then select the pouch or container material to be used in this
application, calculate the weight of salt solution required and conduct laboratory trials to
observe the moisture management system’s impact on shelf-life and product quality over
time.
There is significant flexibility in designing the pouch or container to hold the salt so-
lution. It must be designed to be cost effective for the application while delivering on the
performance required.
8.8 Marketplace Executions and Testing
The current commercial uses of moisture management systems are in the tobacco market,
which is very similar to food products in deterioration modes and the potential impact of
moisture on shelf-life of these products.
The primary initial use of a moisture management system has been in the cigar area. Here
it is used to keep high quality cigars that were purchased from a retailer with a walk in humi-
dor in a pristine state until consumed by the user. These cigars may sell for anywhere from
$ 5 to $ 35 each. It is also being used commercially for such items as the 25 count boxes of
cigars that are packaged in very humid Central American countries and protects the products
as they travel via various carriers and through unknown environments to the end point.
A further application is in the retail package of expensive cigars being merchandized
in gasoline stations or convenience stores. Cigars of high quality that would normally
only be sold from a walk-in humidor at a tobacco shop, can now be packaged and fully
protected over their shelf-life under ambient conditions in any geographic location. For
cigars, this means keeping them exposed to the optimum level of 70 % relative humidity
that the moisture management system is fully capable of doing.
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Reletive Humidity (RH)
Fruits and Vegetables
Raisins
Cigars
Wooden
Instruments
Artwork
Coffee Beans
Elelctronic
Circuits Boards
Ideal Relative Humidity Chart courtesy of Humidipak.
Dry Cereal
Figure 8.6 Ideal relative humidity chart.
Laboratory testing is underway for a wide variety of applications, only a few of which are
itemized below. For security and confidential disclosure agreements that are in place, other
products under test cannot be revealed at this time. See Figure 8.6 for generic product targets.
8.8.1 Beef Jerky
Beef jerky is a product that can become very tough and chewy when moisture levels drop
and are not at their optimum levels. If the moisture is too high, the product can become
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Active Moisture-management Packaging 145
moldy or fail to meet the legal definition of jerky. The moisture management system can
target about 0.02 below this optimum point and provide a high quality performance of the
product over its 12 to 18 month shelf-life.
8.8.2 Dry Spices
The unique flavor nodes and free flowing characteristics of many spices are significantly
harmed when moisture levels are too high or too low. The consumer expects these products
to last indefinitely but it is apparent to the gourmet using them that the standard packaging
used is often inadequate for protecting a spice for more than a very few months. This is
especially true if the reclosable container is opened repeatedly under dry conditions.
8.8.3 Dried Fruit
These products can be a delicacy when availablein the proper state. But again this is a critical
and relatively narrow moisture range where the product is in its pristine and delectable state.
A moisture management has proven to yield long term stability and can even be used to
salvage dried out products, restoring them to nearly their original condition.
8.8.4 Musical Instruments Made of Wood
When a stringed instrument such as a violin or guitar is exposed to a low or high humidity,
the wood will lose or gain moisture. This will result in the wood shrinking or expanding,
thus bringing about warping that changes the sound characteristics of the instrument. Worse,
cracks may appear and even cause the adhesive joints to break apart. The appearance of
cracks will reduce the value of the instrument by as much as one half of its value which
can be several hundred thousand dollars, or priceless in the case of a Stradivarius violin.
Ownersof these instruments will readily relate to the issues in keepingguitars, violins, etc.
under widely varying conditions that change with the seasons. It is almost farcical to explain
methods being used today to provide moisture protection. Ideally, these instruments should
be stored between 40 and 60 % RH +/− 3 % according to moisture sorption isotherms
prepared from the woods used in manufacture. Wet sponges are the most common element
in many of the systems used today and naturally they try to reach 100 % RH, but because
of leakage in the packaging, may average out at something in the middle of the range. They
also require daily monitoring and most likely the addition of distilled water to protect the
instrument properly. A suitably designed moisture management system has been introduced
to deliver several months of optimum conditions for an instrument without any required
daily effort. See one such application in Figure 8.7.
8.8.5 Works of Art
Museums around the world expend considerable time and effort to maintain the optimum
temperature and humidity conditions for a wide variety of historical and extremely valuable
works. This may include timeframes for the artworks while on display, in warehouses, or
while being transported short and long distances. Today, one of the systems in use requires
the conditioning and monitoring of silica gel, which if not properly handled, can cause