FOOD AND NUTRITIONAL ANALYSIS / Packaging Materials 341
Kirk RS and Sawyer R (1991) Pearson s Composition and
Further Reading
Analysis of Foods, 9th edn. London: Longman Scientific
AOAC (1990) AOAC Official Methods of Analysis, 15th and Technical.
edn. Arlington, VA: AOAC. Kratochvil B and Taylor JK (1981) Sampling for chemical
Codex Alimentarius (1969) Codex Alimentarius Sampling analysis. Analytical Chemistry 53(8): 924A 938A.
Plan for Prepackaged Foods. Arlington, Virginia CAC/ Nagy S and Attaway JA (1980) Citrus Nutrition and
RM 42-1969. Quality. Washington DC: American Chemical Society.
Hulme AC (1970) The Biochemistry of Fruits and Their Pomeranz Y and Meloan CE (1987) Food Analysis, Theory
Products. London: Academic Press. and Practice, 2nd edn. New York: AVI.
Packaging Materials
A W Lord, Pira International, Leatherhead, UK
glass. The individual properties of the different ma-
terials are used to produce food packaging with the
& 2005, Elsevier Ltd. All Rights Reserved.
required characteristics. For example, in a packaging
This article is a revision of the previous-edition article by Philip
material with two layers of different plastics, one
Tice, pp. 3698 3706, & 1995, Elsevier Ltd.
layer might provide the basic strength whilst the
other layer enables the packaging to be easily heat-
sealed. Coatings are also often added to the basic
plastic packaging material to provide additional bar-
Introduction
riers to the permeation of oxygen and water vapor.
Analytical measurements on food packaging materi-
These coatings can be polymeric or vacuum depos-
als are generally carried out for three main purposes:
ited aluminum.
With some metal cans used for foods and
To identify the components of the packaging.
beverages there is an inner lacquer (plastics) coating
To identify and measure substances present that
for the purpose of either preventing corrosion of
could migrate into the packaged foods and cause a
the metal by the food/beverage, or preventing con-
health hazard to the consumer of the food. This work
tamination of the food/beverage by the can metal.
is often accompanied by measurements of the migra-
A combination of a polymer layer with a board is
tion of particular substances into either the actual
used to package liquids such as milk, where the
packaged foods, or into food simulants.
plastic layer provides the barrier to contain the milk
To identify and measure substances present that
within the package and the board the basic strength.
could migrate into the packaged foods and result in
Where it is necessary to store the beverage for long
adverse effects on the organoleptic properties, such
periods, such as fruit juices, additional barrier prop-
as taste or odor.
erties are required to prevent permeation of oxygen
into the food product. To achieve this additional
protection, an aluminum layer is incorporated within
Food Packaging Materials
a plastic/board composite.
The main categories of basic materials used for food
With many of the multilayer packaging materials
packaging are:
adhesives are used to bind the layers together. The
printing on the outside is a further important com-
*
plastics,
ponent of food packaging.
*
regenerated cellulose films,
*
paper and board,
*
metal, and
Identifying the Components of
*
glass.
Packaging Materials
Of these, plastics are the most widely used and with- It is often necessary to identify or confirm the basic
in this category there are also the largest numbers of composition of the packaging materials. This applies
variants. Many packaging materials are, however, particularly with plastics due to the range of polymer
multilayered with either different layers of plastics or types that are used. Six major polymer types are used
combinations of plastics with paper/board, metal, or for packaging and these are shown in Table 1, with
342 FOOD AND NUTRITIONAL ANALYSIS / Packaging Materials
Table 1 Types of plastics used for food packaging and typical polyethylene and the other surface as poly(ethylene
uses
terephthalate) by the very different spectra obtained.
With the standard KRS5 (thallium bromide/iodide)
Plastic type Typical uses
ATR crystal the depth of penetration of the infrared
Polyethylene Bags and bottles
radiation is a few micrometers. This is less than the
Polypropylene Wrapping films and pots
individual polymer layers and consequently the ad-
Poly(vinyl chloride), Trays, bottles, and containers
hesive is not shown in either of the ATR spectra.
unplasticized
Poly(vinyl chloride), plasticized Wrapping film and cling film
Where the polymer material is a copolymer it is
Polystyrene Trays, pots, and containers
often possible to obtain a measurement of the re-
Poly(ethylene terephthalate) Lidding films and oven
lative amounts of the various monomer components
containers
from an infrared spectrum. For example, with an
Polyamide (nylon) Laminated with polyethylene,
ethylene vinyl acetate copolymer the relative heights
boil-in-bag pouches
of absorption bands from both the ethylene and vinyl
acetate are measured and ratioed with the spectrum
recorded in the absorbance mode. The most conveni-
1
typical uses. In addition to these basic polymer types, ent absorbance bands are: 720 cm for polyethyl-
1
various copolymers are also used. For example, eth- ene and 1235 or 1740 cm for vinyl acetate.
ylene is copolymerized with vinyl acetate to produce Copolymers of known composition are required for
ethylene vinyl acetate, styrene is copolymerized with calibration. It is possible to obtain an assessment on
both acrylonitrile and butadiene to produce the ter- the butadiene and acrylonitrile contents in styrene/
polymer ABS. butadiene/acrylonitrile copolymers. The bands
1
On simple, one- or two-layer structures, identifi- usually used are: for styrene 1600 cm , for acrylo-
1 1
cation of the polymer type is conveniently achieved nitrile 2240 cm , and for butadiene 996 cm .
using Fourier transform infrared spectroscopy Modern packaging materials are very often mul-
(FTIR). Each of the major polymer classes or copol- tiple-layered structures. If the packaging material is a
ymers has unique infrared spectra and are easily laminate or coextrusion each layer will produce an
identified by comparison of the spectra to reference infrared spectrum. The resulting composite spectrum
spectra. becomes difficult to interpret. In most cases lami-
The infrared spectrum of a plastic packaging ma- nates are manufactured using adhesive to bond the
terial is most easily obtained when the sample is in layers together. It is sometimes possible to select a
the form of a film sufficiently thin to allow the in- solvent to dissolve the adhesive thereby enabling
frared spectrum to be obtained through the film. the individual polymer layers to be separated. The
However, with most plastic packaging, even those separated polymers can then be identified by their
that are used in the form of films, the thickness is infrared absorption spectra. Spectra from a polyeth-
usually too great to obtain a good transmission spec- ylene/poly(ethylene terephthalate) laminate and the
trum. With some film materials stretching can ade- separated layers are shown in Figures 1A 1D.
quately reduce the thickness. Alternatively, it may be Polyurethane-based adhesives are widely used to
possible to produce a solvent solution and cast a film bond poly(ethylene teraphthalate) to polyolefins.
of the required thickness. Thin films may also be Hot benzylalcohol is a good solvent for a range of
pressed from the sample by careful melting on a hot- polyurethanes. Other solvents include tetrahydro-
plate. Caution should be exercised with melt pres- furan and chloroform for acrylate-based adhesives.
sing, as apart from polymer degradation, there is the This approach also enables the adhesive to be
risk of altering the structure, for example, by skewing identified.
a polymer layer away from the region of analysis. An approach that can be applied to laminates and
Infrared spectra may be obtained from surfaces coextrusions is to selectively dissolve and remove
using a variety of techniques. These included atten- polymer layers by careful selection of solvents. Thus,
uated total internal reflectance (ATR) and specular the nylon layer in a polyethylene/nylon/polyethylene
and diffuse reflectance. These techniques involve the coextrusion can be isolated by boiling in xylene. Al-
infrared beam passing through only the outer few ternatively, the nylon could be removed by boiling
micrometers of the sample. The most widely appli- in formic acid. Solvents for the selective removal of
cable is ATR. A typical two-layer plastic material polymers are listed in Table 2. Acids or alkalis should
used for lidding on plastic food trays consists of po- be avoided on some polymers where there is a risk of
lyethylene and poly(ethylene terephthalate) bound reaction with the polymer. An example would be the
together with an adhesive. ATR infrared spectra of use of concentrated sodium hydroxide solution on a
the two surfaces will easily identify one surface as metallized film comprising certain acrylic/ethylene
FOOD AND NUTRITIONAL ANALYSIS / Packaging Materials 343
Figure 1 Infrared transmission spectra of: (A) polyethylene/poly(ethylene terephthalate) laminate; (B) separated poly(ethylene
terephthalate) layer; (C) separated polyethylene layer plus adhesive; and (D) separated polyethylene layer with adhesive removed.
Table 2 Solvents for plastics
rarely possible or wise to use the technique on its
own without recourse to other analytical techniques.
Plastic type Solvents
There has in recent years been a trend toward the use
Polystyrene and copolymers Chloroform, ethyl acetate,
of coextrusions, and away from adhesive bonded
ketones
laminates. Coextrusions of a wide range of polymers
Polyethylene Decalin, hot toluene
can be produced using thin tie layers (a few microm-
Polypropylene Decalin, hot xylene
Poly(vinyl chloride) Tetrahydrofuran,
eters) of polymer with compatibility for the different
cyclohexanone
polymer types. For example, polypropylene and eth-
Poly(ethylene terephthalate) o-Chlorophenol, trichloroacetic
ylene vinyl alcohol can be extruded into films and
acid
bottles. Layers within coextrusions cannot be readily
Polyamide Formic acid, phenols
separated using solvents. In addition, the time and
cost constraints upon the analysis of coextrusions
mean that physical isolation of layers is often
ionomer types, where marked alterations to the impractical.
infrared spectra can result from such treatment. The most efficient approach to establishing the
It is sometimes difficult to obtain thickness meas- structure of packaging is a combination of optical
urements on layers due to swelling of layers with the microscopy, differential scanning calorimetry (DSC),
solvent or partial break up of thin layers. If the den- and infrared spectroscopy. The first stage in estab-
sity of the polymer is known or measured the thick- lishing the construction of an unknown packaging
ness of a layer may be calculated from the weight of material is to subject it to the following optical mi-
the polymer. croscopy techniques. A section (typically 5 10 mm) is
Although infrared spectroscopy is a useful tech- cut from a 10 10 mm area using a microtome. It is
nique for identifying polymers in packaging materi- important that the sample is held rigid but strain free
als it is important to emphasize that as a result of the and cut with a very sharp knife. The best knife for
development of packaging technology, it is now packaging material is usually a freshly made glass
344 FOOD AND NUTRITIONAL ANALYSIS / Packaging Materials
knife. Thicker sections (42 mm) require use of a recycled process scrap. It is quite common for off-
steel knife. It is sometimes beneficial to cool samples cuts to be recycled in an inner layer of a coextrusion.
below their glass transition temperature (Tg) in order Infrared spectra are then obtained from the sur-
to provide a more rigid structure to section. It may faces of the packaging material after solvent removal
also be necessary to mount samples in potting resin of any print or lacquer. Spectra are best obtained by
for support prior to sectioning through the sample ATR. A further portion of the packaging material is
and resin. then subjected to DSC. This is a technique where a
The section is then examined under polarized light few milligrams of the sample is subjected to a
(using cross-polars). A tint plate is useful to provide programmed temperature ramp in a specified atmos-
color differentiation of layers. This enables the phere inside a sample chamber. The heat flow (pow-
number and thickness of each layer to be estab- er) to the sample is monitored against temperature as
lished. Thickness measurements are made by calcu- the sample is subjected to the heating ramp. For the
lation after measuring the total thickness of the purposes discussed here this provides a trace showing
sample using a micrometer. The ratio of total thick- the melting points of the polymers present. Typical
ness to layer thickness is calculated in arbitrary units melting ranges for common packaging polymers are
using the scale graduations on the microscope. The tabulated in Table 3.
thickness of each layer is then calculated from the The technique cannot be used to obtain melting
ratios knowing the true total thickness. An example points for amorphous polymers. The sample polymer
of a typical cross-section of a coextrusion is shown is heated and cooled and then reheated at a control-
in Figure 2. led rate to record the meting points. This procedure
Information on the composition of individual lay- removes hysterisis effects that may be present in the
ers in the structure can then be obtained by observat- polymer as a result of the manufacturing process and
ions of the layer under the microscope. Different which may alter the perceived melting point. DSC is
types of polymers have a recognizable morphology. capable of identifying polymers and polymer blends
Polypropylene has very large spherulites distinct
from many other polymers. Figure 3 shows a
photograph obtained from polypropylene cooled
slowly from a melt. Compounded poly(vinyl chlo-
ride) (PVC) can also be quite characteristic due to the
different phase regions arising from the presence of
impact modifiers as well as pigment specks from col-
or adjusters. Calcium carbonate filler and talc anti-
blocking agent have recognizable morphologies. It is
also possible to determine whether a layer contains
Foil
Polyurethane
Figure 3 Polypropylene spherulites viewed through a tint
adhesive
plate. (Reprinted with permission from Mr R Musgrove, Pira
International.)
PET
Surlyn
Nitrocellulose
(LD-MD) PE Table 3 Typical melting ranges for common polymers
lacquer/print
Polymer Melting range ( 1C)
Polyurethane
adhesive
Linear low-density polyethylene 115 130
Low-density polyethylene 100 115
Ethylene-co-acrylic
Ethylene vinyl acetate 100 110
acid (ionomer)
Polyamide 210 260
Poly(ethylene terephthalate) 240 260
Figure 2 Cross-section of a coextrusion viewed through a tint
Poly(vinylidene chloride) 220
plate on an optical microscope. PET ź Poly(ethylene terepha-
Polypropylene 160 170
late), (LD-MD) PE ź ? (Reprinted with permission from Mr R
Ethylene propylene random co polymer 149
Musgrove, Pira International.)
FOOD AND NUTRITIONAL ANALYSIS / Packaging Materials 345
not readily identifiable in packaging materials using Optical microscopy techniques can also be applied
infrared spectroscopy. Examples of these include, to packaging failure problems. Sections can be taken
low-density polyethylene, linear low-density poly- through a heat seal region to establish the integrity of
ethylene, high-density polyethylene, and blends of the seal. Molecular orientation, melt flow, blend
these polymers. The blend ratios of these polyolefins homogeneity, and crystallinity can be observed that
can be estimated after calibration using the pure can reveal the cause of stress cracking and other
polymers. types of packaging failures.
The construction of the packaging material is then
determined by comparing the data obtained from all
Analysis of Substances Related to
the analytical techniques. Any layers that are difficult
to identify are then identified by either detailed ana- Food Safety
lysis on the isolated layer using FTIR and other
It is sometimes necessary for technological reasons to
analytical techniques, or by applying additional
use chemicals that have toxic properties in the man-
analytical techniques to the whole structure. For
ufacture of a food packaging materials. Also, there is
example, pyrolysis gas chromatography mass spec-
the possibility that some of the chemicals and com-
trometry (GC MS) can confirm the presence of a
ponents used for food packaging materials can con-
styrene/acrylate copolymer adhesive or vinylidene
tain trace levels of toxic contaminants. Where toxic
chloride/acrylate copolymer coating. The pyrolysis
substances are unavoidably present in a food packa-
causes depolymerization, often to the starting mon-
ging material for any of these reasons, it is necessary
omers, which are then identified from their mass
to ensure that levels of these substances are restricted
spectra. The technique can be applied to the whole
so that any transfer to packaged food does not
construction. This is useful when FTIR analysis is not
exceed safety limits. The national regulations of
conclusive, or where the layer cannot be isolated for
individual countries control the safety of food
FTIR analysis. In the absence of a pyrolyser instru-
packaging with respect to the substances with known
ment, it is possible to perform the technique by
toxic properties. In some countries the specific re-
briefly heating the sample in an inert atmosphere in a
strictions are contained in official recommendations
sealed headspace vial over a gentle Bunsen burner
or codes of practice. The primary restrictions are on
flame. Static headspace GC MS analysis of the
the levels that migrate or transfer to the packaged
pyroloysate is then carried out. Hot stage micros-
food and are designated specific migration limits .
copy is a particular useful technique for identifying
However, in some cases the restriction is a permitted
layers. A key advantage of the technique is the ability
level in the packaging material, while for others the
to identify layers that cannot be isolated for analysis.
restriction is a limit on the quantity, which can be
In this technique, the packaging material cross-
extracted. As might be expected where the safety of
section is heated at a controlled rate under the mi-
food is concerned, the set limits are often low re-
croscope. The melting ranges of the individual layers
quiring sensitive analytical methods.
can be observed and compared with the melting
ranges observed by DSC. It should be noted that
Food Contact Plastics
there is a difference of a few degrees centigrade in
the melting ranges observed by DSC and hot stage Vinyl chloride monomer used for the manufacture
microscopy: of PVC plastics intended for contact with foods
The strategy for identification of a packaging
provides an example where there is a low specific
material construction is summarize: migration limit , plus a low limit on the level allowed
to be present in the packaging material. These limits
1. Examine a cross-section by optical microscopy; are contained in an EC Directive 78/142/EEC on
determine the number of layers and their thick- PVC plastics and are: 0.01 milligrams per kilogram
ness, tentatively identify the polymers in the lay- of food (10 ppb), and 1 milligram per kilogram of
ers. polyvinyl chloride.
2. Obtain a DSC of the whole material. This will Vinyl chloride is a gas at ambient temperature and
identify all the crystalline polymers present in the the official EC analytical methods for both determi-
structure. nations use headspace GC with a flame ionization
3. Obtain infrared spectra from the surfaces. This detector (FID). Where a determination exceeds the
will confirm the composition of the outer layers. legislation limit, confirmation is required with head-
Isolate fractions of the construction and obtain space GC using either a different chromatography
their infrared spectra to confirm the identifications column, or a different detector, or with the gas chro-
made by DSC and optical microscopy. matograph coupled to a mass spectrometer.
346 FOOD AND NUTRITIONAL ANALYSIS / Packaging Materials
For the determination of free vinyl chloride mon-
omer in plastics, the test sample is dissolved or dis-
persed in N,N-dimethylacetamide in a sealed vial and
then equilibrated at 601C before sampling the head-
space. When determining vinyl chloride monomer in
foods or food simulants, N,N-dimethylacetamide is
again used with the sample in a sealed vial, with
equilibration at 601C.
Other volatile plastics monomers with similar
migration limits, such as acrylonitrile and butadiene,
are also determined by the headspace GC technique.
For the measurement of nonvolatile monomers in
plastic food packaging and in foods or food simul-
ants due to migration, high-performance liquid chro-
matography (HPLC) and ion-exchange chroma-
tography techniques can be employed. Food and
food simulants may give rise to interference problems
with the analysis. Sample clean-up procedures are
widely used such as solid-phase extraction of inter-
ference from extracts or size exclusion chromato-
graphy to remove fats and oils. Selective detectors
such as mass spectrometers are now widely used for
both liquid and gas chromatography.
Figure 4 is an ion-exchange chromatogram of
phthalic acids. Terephthalic acid and isophthalic acid
are monomers of polyester plastics. Orthophthalic
acid is the internal standard. There are migration
limits for both terephthalic acid and isophthalic acid
in EC regulations of 7.5 and 5.0 mg per kg of food.
The other main classes of substances in the safety
category, which can be present in food packaging
plastics and for which analytical measurements are
required, are the plastics additives. These substances
perform the functions of plasticizers, antioxidants,
antistatics, slip agents, and stabilizers. Of these add-
itives, the plasticizers have been most extensively
studied and analytical methods developed for their
Figure 4 Separation of terephthalic acid (TPA), isophthalic acid
determination in the plastics and in packaged foods.
(IPA), and orthophthalic acid (OPA) by ion-exchange chro-
The techniques are usually based on GC either with
matography. (From Ashby et al., 1992.)
an FID or with a mass spectrometer as the detector.
Key advantages offered by a mass spectrometer are
selectivity of response and the ability to add a de-
uterated internal standard to the sample to compen- 4.5 or less) the simulant is an acetic acid aqueous
sate for the incomplete and variable recovery of the solution, and for alcoholic beverages and other foods
analyte in the analysis. containing alcohol, the simulant is an ethanol aque-
Migration testing of plastics packaging prior to use ous solution with strengths more or less equal to the
for compliance with any legislation limits is usually alcoholic concentration in the beverage or food.
carried out with food simulants rather than actual Selecting a simulant for foods containing fats and
foods. First, the analytical task is more often simple oils has not been easy. In the USA, n-Heptane is
and, second, testing with a food simulant or simul- specified as the fatty food simulant in the Food and
ants for a class of foods covers use with all foods in Drug Administration (FDA) regulations, although it
that class. The food simulants are simple liquids that is now recognized to give migration levels of specific
represent different classes of foods. For foods where substances well in excess of those that occur with the
the liquid phase is largely water, distilled water is foods even after applying a suitable reduction factor.
used as the simulant. For acidic foods (typically pH In Europe, olive oil has been selected as the fatty
FOOD AND NUTRITIONAL ANALYSIS / Packaging Materials 347
food simulant with alternatives of sunflower oil or a In addition to the requirement to measure the
synthetic triglyceride, known as HB307, developed levels of individual specific substances that have
specifically for migration testing. Alternatives to migrated from plastic food packaging into foods or
olive oil were considered necessary as it was known food simulants and have toxic properties, there is
that various analytical problems arise with olive oil. sometimes also the necessity to measure the total
The food simulants required for regulatory migration quantity of substances that are likely to transfer from
testing in the EC Member States on plastics packa- the plastics to the food. This is called overall migra-
ging intended for use with foods, are listed in EC tion or global migration. The tests are carried out
Directives 97/48/EEC and 85/572/EEC. These are with food simulants as they are impracticable with
shown in Table 4 together with the classes of foods foods. No attempt is made to identify the nature of
and beverages that they represent. The 85/572/EEC the substances that have migrated from the plastic
Directive also contains a table that specifies the material. In the current EC food contact plastics
simulant or simulants to be used for individual regulations there is an overall migration limit of
categories foods and beverages, and the 97/48/EEC 60 mg of substances from the plastics material per
1
Directive gives the test conditions of time and tem- kilogram of food simulant (60 mg kg ), or ex-
perature corresponding to the intended conditions of pressed alternatively as 10 mg of plastic substances
use. Fatty foods contain various amounts of oils and from 1 dm2 surface area of plastics test specimen
2
fats. For those that have high oil or fat content the (10 mg dm ). With the three aqueous based food
extent of migration of substances from the plastics is simulants distilled water, acetic acid, and ethanol
often higher than for those with low oil or fat con- solutions the overall migration is measured by de-
tents. Consequently, reduction factors are applied to termining gravimetrically the nonvolatile residue in
migration values obtained with olive oil to allow for the simulant following exposure to the plastic test
the various levels of oil and fat in particular foods. specimen. The values normally obtained with these
It has been generally accepted that migration from aqueous-based food simulants are usually well below
packaging materials into dry foods will be low com- the regulation limit and in the region of 6
1 2
pared to moist, liquid, or fatty foods. Accordingly, 18 mg kg (1 3 mg dm ). As the tests are most
more work has been completed in developing simul- often carried out on test specimens with a surface
2
ants for these foods than dry foods. At the present area of 1 3 mg dm the total quantities of migra-
time the only regulatory or generally recognized si- ting substances are typically a few milligrams. Con-
mulant for dry foods is Tenax (poly(2,6-diphenyl-p- sequently, care has to be taken with the gravimetric
phenylene oxide)). Tenax has been adopted as a dry measurement to ensure reliable results are obtained.
food simulant because it is a dry porous polymer After evaporating the simulant to dryness the
with a large surface area that exhibits high-adsorp- nonvolatile residue is dried in an oven at 1101C un-
tion characteristics for a wide range of volatile til constant weight is obtained. It has been found,
organic compounds. Tenax is therefore considered to however, that particular care has to be taken when
be a worst-case dry food simulant for a wide range of using glass evaporating dishes to ensure that there is
dry foods. Other food simulants have been investi- adequate time allowed for both the heating period in
gated for use with paperboard. A semisolid food the oven and the cooling period in the desiccator for
simulant consisting of a mixture of diatomaceous the mass to stabilize before each weighing. With
earth, water, and olive oil has been used, as well as metal evaporating dishes the mass of the dish and
filter paper impregnated with olive oil. residue stabilize more quickly, but with the acetic
acid simulant it is necessary to use dishes made of
platinum, or a metal with similar chemical resist-
ance, to prevent additional errors from corrosion
Table 4 EC food simulants for migration tests and the corre-
products.
sponding classes of foods
To measure overall migration with olive oil or alter-
Food simulant Class of food or beverage
native simulants, the method used with the aqueous-
Distilled water Aqueous foods and beverages
based food simulants is obviously not applicable.
3% (w/v) aqueous solution of Foods and beverages with
With oil-type simulants the test is carried out by
acetic acid pH 4.5 or less
measuring the loss in mass of the test specimen after
10% (v/v) aqueous solution of Foods and beverages with
exposure to the food simulant. However, most plas-
ethanola 15% or less alcohol
Olive oil or sunflower oil or Foods containing fats and oils tics absorb some of the oil that then has to be ex-
HB307
tracted and quantitatively measured before the true
a
loss in mass can be calculated. The extraction solvent
For a food or beverage with an alcohol content greater than 10%
(v/v), a simulant with a similar ethanol concentration is used. that has been most commonly used in the past is
348 FOOD AND NUTRITIONAL ANALYSIS / Packaging Materials
1,1,2-trichlorotrifluoroethane, as it is a good solvent possible contaminants include: the toxic heavy ele-
for olive oil but does not dissolve most plastics. As ments arsenic, mercury, lead, cadmium, and chro-
this solvent is a chlorofluorocarbon its main use and mium, plus chlorophenols and polychlorinated
supply is being phased out and pentane and diethyl biphenyls (PCBs). With extraction liquids such as
ether are now used instead for the extractions. water or dilute aqueous acid solutions, the toxic
Once the extraction has been completed the olive heavy elements can be analytically determined using
oil is quantitatively analyzed by hydrolyzing to the atomic absorption spectroscopy. Arsenic can be
fatty acids, methylating to form the methyl esters, measured with the hydride generation technique,
and measurement by GC. The value obtained is sub- mercury with the cold vapor technique, and the other
tracted from the mass of the test specimen after ex- metals by the standard flame technique. Inductively
posure to the olive oil, to allow the overall migration coupled plasma atomic emission spectroscopy is now
value to be calculated. The test method has a rep- also widely used. Pentachlorophenol and other
utation of poor precision and reliability not only due chlorophenols can be determined by either GC or
to the complex procedure, described above, but also HPLC. When using GC the chlorophenols are best
due various other factors that are known to influence derivatized to form the methyl or acetyl derivatives
results, such as moisture absorption by the plastic in order to improve the chromatographic perform-
test specimens, incomplete extraction of the olive oil, ance and the analytical precision. These analytical
and change in composition of the extracted olive oil. techniques have also been used in the detection and
The overall and specific migration analytical test analysis of chlorophenols suspected of being respon-
methods have been established as Standards by the sible for odors and food tainting, as described later.
European Committee for Standardisation (CEN). The PCBs are determined in extracts from paper and
Reference plastics are also available with certified board materials by GC with an electron capture de-
migration values in olive oil (Institute for Reference tector or mass spectrometer.
Materials and Measurements BCR, Geel, Belgium, Two compounds are currently of particular inter-
sales@irmm.jrc.be). est in paper and board. Diisopropyl naphthalene
(DIPN) is a mixture of isomers that until recently
were widely used in carbonless copy papers as ink
Paper and Board
solvents. Although it is currently being replaced it
Most paper and board food packaging materials are occurs as a persistent contaminant in recycled paper
not used in direct contact with liquid foods and con- and board. Various studies have shown that it is able
sequently migration tests with liquid food simulants to migrate from paperboard into food. There is a
are not considered appropriate. Paper and board draft CEN analytical method available. This method
packaging does, however, come into direct contact involves acetone extraction and quantification by
with various moist and fatty foods where migration GC MS using diethyl naphthalene as an internal
of substances into the food can sometimes occur. No standard. There is currently no limit for DIPN but
simulants have yet been selected to specifically rep- levels are being monitored to reduce concentrations
resent these classes of foods in migration tests on in recycled paperboard.
paper and board. To ensure that the paper and board Two related compounds are 3-monochloropro-
material is suitable and safe to package foods, ex- pane-1,2-diol (3-MCPD) and dichloropropanol.
traction tests are often carried out. The extraction These arise in paper board due to the hydrolysis of
test is performed with cold or hot water, or some- epichlorohydrin-based wet strength agents. 3-MCPD
times with dilute acids and solvents and is considered can occur in food from hydrolyzed vegetable protein.
to be a more severe test than a migration test. An- The limit in food is 120 ppb. In packaging the spe-
alytical measurements are then carried out for cific migration limit is 12 ppb in the food. The di-
specific substances on the extraction liquid. For ex- chloropropanol does not at present have a limit.
ample, tests are carried out for free formaldehyde, However, the German BGVV recommendations
which can arise from wet-strength additives of the (widely accepted as useful guidelines) list a limit of
melamine formaldehyde or urea formaldehyde types. 2 ppb in a hot water extract. A convenient method of
analysis is to extract the two compounds with water.
A typical analytical method for the determination of
free formaldehyde in the extracts is based on colori- The water extract is then totally absorbed onto a
metric procedures using chromotropic acid or ace- diatomaceous earth cartridge. The cartridge is then
tylacetone (pentane-2,4-dione). With paper and washed with a large volume of diethyl ether. The
board products there is concern that there could be water is retained on the cartridge and the 3-MCPD
toxic contaminants present that in turn could trans- and dichloropropanol extracted and eluted by
fer to the food when used as packaging. These the diethyl ether. The ether is then concentrated by
FOOD AND NUTRITIONAL ANALYSIS / Packaging Materials 349
evaporation and the two compounds derivatized and A as well as BADGE arising from the use of BADGE
injected for analysis by GC MS. in organosol and epoxy phenolic coatings. Possible
residues remaining in the coatings are listed below,
Metal Packaging
all of which have been found to contaminate the
food:
Cans are widely used to pack food. In some cases
tinplated steel cans are used, for example, for
*
BFDGE
packing fruit. Predominantly, the cans are internally
*
BADGE
coated with a polymeric coating to prevent corrosion
*
Bisphenol A
or food spoilage. A considerable amount of work has
*
Bisphenol F
been done in recent years investigating the extent to
which compounds present in the lacquers migrate
BADGE and BFDGE undergo hydrolysis and addi-
into food.
tion of hydrogen chloride released from the PVC
Attention has focused on the chemical compounds
organosol in aqueous foods and a series of reaction
bisphenol A, BADGE, and BFDGE. Bisphenol A is
products result. Concern has been raised over these
manufactured from the reaction of phenol with
reaction products. These are listed below:
acetone. The bisphenol A is further reacted with epic-
hlorohydrin to produce bisphenol A diglycidyl ether
*
BADGE HCl
(BADGE). BADGE is then polymerized and cross-
*
BADGE 2HCl
linked in a stoving process to produce an epoxy phe-
*
BADGE H2O HCl
nolic coating that has high chemical and mechanical
*
BADGE H2O
resistance. These coating are called bisphenol
A-epoxies.
These decomposition products result from the ring
Alternatively, phenol may be reacted with formal-
opening on the epoxy group of which there are two.
dehyde to generate bisphenol F. Unlike bisphenol A,
The legislation (Directive 2002/16/EC, February 20,
bisphenol F is a mixture of isomers rather than a
2002, on epoxy food contact materials) specifies a
discreet compound. Bisphenol F can be subjected to a
migration limit of 1 ppm in the food. This limit is the
condensation process in which a polymeric resin
total of all the reaction products and BADGE added
called Novalac is produced. The Novolac can be re-
to the BFDGE and its reaction products. In addition,
acted with epichlorohydrin to produce a polyglcidyl-
there is a requirement of no detectable migration of
1
ether and these are called novolac glycidyl ethers
NOGE at a detection limit of 0.2 mg kg in the
(NOGE). NOGE is not used to produce epoxyphe-
food or 0.2 mg/6 dm2 in the can. The decomposition
nolic coatings, as is the case with BADGE.
product BADGE 2H2O in food is ignored as this is
Organosol coatings are dispersions of PVC in sof-
not of toxicological significance. However, it must be
tener, solvent, and other resins. Solid contents are
included if the migration test is done on food simul-
typically 40 80%. The coating is stoved to evaporate
ants as there is the risk of forcing decomposition
off the solvents and cure the resin. BADGE is often
through to the BADGE 2H2O and underestimating
added as an additive to scavenge for hydrochloric
the other compounds. The legislation is due for
acid generated from the PVC during curing. Alter-
review in 2004 as the toxicity of the chlorohydrins is
natively, NOGE is used as an additive instead of
not at present established.
BADGE.
The most widely used lacquer types for food cans,
Analysis of Substances Causing Taint
where the food is retorted in the can to ensure pre-
Taint from food packaging is very rare when one
servation are:
considers the tonnage of packaged food consumed
*
each year. Tainting chemical compounds present or
epoxyphenolic and
*
derived from the food packaging are often volatile
organosol
compounds. With plastics these odorous volatiles can
Epoxyphenolic lacquers are universally used for both be: monomer residues, reaction by-products from
can bodies and ends for two- and three-piece con- the polymerization process, breakdown products of
structions, although more usually for shallow draw certain additives and contaminants. For example,
cans. Beverage can bodies are commonly epoxyami- with polystyrene plastics high levels of styrene mono-
no coated, and the easy-open end and deeper draw mer produce a very characteristic odor and a number
two-piece cans are organosol coated. Coatings may of incidents of tainting from styrene monomer
contain residual BFDGE and bisphenol F arising have been reported. With polyethylene terephthalate
from the NOGE in organosol coatings and bisphenol (PET) plastics, acetaldehyde can be formed during
350 FOOD AND NUTRITIONAL ANALYSIS / Packaging Materials
the polymerization process and when PET is used for For odor investigation the chromatograph is fitted
beverage bottles the acetaldehyde can cause tainting with an odor port so that the flow from the analytical
of the beverage. With paper and board materials the capillary column is split via a T piece to an odor port.
volatiles arise mainly from natural lipids and resins By this means it is possible to smell compounds elu-
originating from the wood raw material, but some ting from the capillary column simultaneously with
can come from synthetic resins used in surface coa- their detection by the mass spectrometer. This ena-
tings that are applied for improved printability and bles an odorous compound to be identified and
appearance. The predominant volatiles originating quantified in food and packaging.
from the wood lipids and resins are usually alde- Isolation and concentration of tainting compounds
hydes, carboxylic acids, and alcohols. The odors of from the rejected food and packaging prior to ana-
some of these aldehydes are not unpleasant being lysis is usually the most challenging step in the
described as grassy , but others have rancid odors. investigation. Dynamic headspace sampling is widely
Many of the carboxylic acids and alcohols have used. In this technique, a sample of the packaging
strong sharp odors. The synthetic resin binder used in material is placed in a vessel that is closed, heated to
the surface coatings is typically a styrene/butadiene a temperature of B701C, and then purged with an
copolymer that can contain odorous reaction by- inert gas such as nitrogen or helium. Volatiles re-
products such as 4-phenyl cyclohexene. If solvent- leased from the packaging are removed by the purge
based adhesives are used in sealing the packaging or gas, trapped, and concentrated on a porous polymer
to bind layers together, and if the finished packaging such as Tenax. Transfer of the volatiles from the po-
is printed with solvent-based inks, solvent residues rous polymer to the gas chromatograph is performed
can add to the list of volatile substances. If the more by thermal desorption or by solvent elution and in-
odorous of these print solvents and volatile sub- jection as a solvent solution. The chromatogram in
stances are present in sufficient quantities they can Figure 5 shows volatile substances that have been
cause the packaging to be odorous and in turn result collected by the dynamic headspace technique from a
in tainted foods. printed carton-board that had caused tainting in a
Two classes of highly odorous substances that have packaged cake. The tainting was attributed to the
been known to contaminate food packaging and benzophenone that appears as the large peak at just
result in food tainting are the halophenols and below 16 min. Benzophenone is used as an initiator
the related haloanisoles (methylated chlorophenols in ultraviolet radiation cured printing inks. The peak
and bromophenols). In the past contamination was at 3.1 min is the aldehyde, hexanal, which originated
invariably with the chlorophenols and corresponding from the pulp used to make the board. The cluster of
anisoles from wooden pallets and surfaces treated peaks from B5.5 to B7 min is volatiles from the
with wood preservers or phenol-based disinfectants. synthetic resin binder in the board coating. None of
The ansioles are generated by microorganisms such these substances produced detectable odors.
as molds from the phenols. Recently, there has been a The Likens Nickerson extraction technique can
noticeable trend toward increased contamination also be used as a concentration technique, particu-
with the bromophenol and corresponding anisoles. larly for those volatile substances that are steam
This reflects the substitution of bromophenols volatile such as the chlorophenols and chloroani-
for chlorophenols in wood treatments. The odor soles, and also when carrying out an analysis for the
1
threshold for tribromoanisole in water is 8 pg l packaging volatiles in foods. The sample is boiled in
12 1
(8 10 gl or 8 parts per trillion, ppt). Low- a flask with water. Consideration must be given to
detection limits are therefore required for such taint the pH of the sample in the water. Basic compounds
investigations. Concentrations above 1 ppb in the will be present as water-soluble involatile salts in
packaging are often sufficient for tainting to occur. boiling water at low pH, and acids as the corre-
Polyethylene is the most widely used polymer in sponding salts in boiling water at high pH. The pro-
contact with food, usually in the form of a thin inner cedure is therefore best carried out under basic
layer of a food pack. It therefore only requires con- conditions and then repeated after acidification with
tamination of a few sacks of polyethylene granules a few drops of nitric acid. The steam is condensed
with the ansiole to result in tainting of a large and continuously extracted with a suitable nonwater-
amount of food. miscible solvent, any solvent-soluble volatile sub-
Analytical measurements and investigations are stances being transferred to the solvent. After con-
therefore carried out to detect and measure volatile centration of the solvent solution by evaporation of
odorous substances in food packaging either for the solvent with a Kuderna Danish apparatus, the
quality control purposes or when odor and taint analysis is again performed using a gas chro-
problems arise. The technique of choice is GC MS. matograph coupled to a mass spectrometer.
FOOD AND NUTRITIONAL ANALYSIS / Packaging Materials 351
Figure 5 Chromatogram of volatile substances from a carton-board food packaging printed with a UV-cured ink. Benzophenone, the
printing ink component responsible for tainting of packaged food, is represented by the peak at 15.7 min.
Solid-phase micro extraction is a useful technique at a set temperature for a prescribed period of time.
in which volatiles are partitioned from the sample The headspace is then sampled by means of a gas
onto fibers coated with polar or nonpolar bonded syringe or automatic sampling unit and injected into
phases. The fiber is then placed directly into the a suitable gas chromatograph with an FID. As the
heated injection port of the GC where compounds measurements are often carried out for quality con-
are volatilized and carried onto the capillary column. trol purposes, short heating times are sometimes used
The technique is less sensitive than the techniques with external calibration and the measurements do
described above as it is an equilibrium process. not always accurately determine the solvent residues
However, modern ion trap mass spectrometers have in the packaging, but do give reproducible results.
increased in sensitivity and the technique is becoming This is the case with UK, BSI Standard BS6455
widely used. Monitoring the levels of residual solvents in flexible
packaging materials and also the corresponding
American ASTM Standard F 151-86. There are two
Residual Solvents
draft EN standard methods in existence, prEN
Solvent residues from printing and adhesives have 13628-1 (absolute method) and prEN 13628-2 (in-
the potential to cause food tainting. Typical solvents dustrial quality control monitoring method).
used in printing with characteristic, easily detectable
See also: Adhesives and Sealants. Food and Nutri-
odors are aliphatic esters, such as ethyl acetate, iso-
tional Analysis: Oils and Fats. Infrared Spectroscopy:
propyl acetate, and n-propyl acetate, the alcohols
Overview; Sample Presentation; Industrial Applications.
isopropyl alcohol and n-propyl alcohol and hydro-
Liquid Chromatography: Food Applications. Plastics.
carbon mixtures, particularly aromatics. Regular
Sensory Evaluation.
tests are carried out by printers of food packaging
to ensure that the concentrations of solvent residues
are maintained below the odor and tainting thresh-
Further Reading
old levels. The most widely used analytical technique
to measure the levels of solvent residues is GC head-
Ashby R, Cooper I, Harvey S, and Tice P (1997) Food
space analysis. Portions of the packaging are placed
Packaging Migration and Legislation. Leatherhead, UK:
in sealed vials or other suitable containers and heated Pira International.
352 FORENSIC SCIENCES / Overview
Bradbury S and Bracegirdle B (1998) Introduction to Light Kolb B (1984) Analysis of food contamination by head-
Microscopy. Oxford: BIOS Scientific Publishers. space gas chromatography. In: Gilbert J (ed.) Analysis of
Bradbury S and Evennett PJ (1996) Contrast Techniques Food Contaminants, pp. 117 156. Barking, UK: Elsevier.
in Light Microscopy. Oxford: BIOS Scientific Krause, Lange, and Ezrin (1983) Schultheis KR (trans.)
Publishers. Plastics Analysis Guide Chemical and Instrumental
Briston JA and Katan LL (1974) Plastics in Contact with Methods. Munich: Carl Hanser Verlag.
Food. London, UK: Food Trade Press Ltd. Lord AWT (2003) Packaging materials as a source of
Crosby NT (1981) Food Packaging Materials Aspects of taints. In: Baigrie B (ed.) Taints and Off-Flavours in
Analysis and Migration of Contaminants. London: Ap- Food, pp. 64 111. London: Woodhead Publishing.
plied Science Publishers Ltd. MAFF (January 1999) Diisopropylnaphthalenes in Food
Food Contact Materials, Practical Guide (March 2002) A Packaging Made from Recycled Paper and Board. Food
Practical Guide for Users of European Directives. Euro- Surveillance Information Sheet Number 169, MAFF
pean Commission, Health and Consumer Protection Joint Food Safety Standards Group.
Directorate-General, http://cpf.jrc.it/webpack/. Synoptic Document (updated 15 January 2002) European
FSA (April 2001) Survey of Bisphenols in Canned Foods. Commission, Health and Consumer Protection Directo-
Food Surveillance Information Sheet Number 13/01, rate-General, http://cpf.jrc.it/webpack/.
Food Standards Agency. Tice PA (1993) Packaging as a source of taints. In: Saxby
Haslam J, Willis HA, and Squirell DCM (1972) Identifi- MJ (ed.) Food Taints and Off-Flavours, pp. 202 233.
cation and Analysis of Plastics. London: Iliffe Books. Glasgow: Blackie Academic Professional.
FORENSIC SCIENCES
Contents
Overview
Alcohol in Body Fluids
Arson Residues
Blood Analysis
Carbon Monoxide and Cyanide from Fire and Accident
DNA Profiling
Drug Screening in Sport
Explosives
Fibers
Fingerprint Techniques
Glass
Gunshot Residues
Hair
Illicit Drugs
Paints, Varnishes, and Lacquers
Questioned Documents
Systematic Drug Identification
Thin-Layer Chromatography
Volatile Substances
Introduction
Overview
Forensic sciences group the scientific principles and
technical methods applied to the investigation of
P Margot, Université de Lausanne, Lausanne, Switzerland
crimes, litigations in civil matters, or regulatory and
& 2005, Elsevier Ltd. All Rights Reserved. state administrative matters. Results are presented as
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