ArticlePDF AvailableLiterature Review

Analysis of Food Taints and off-flavours - A review

Authors:
  • Unilever R&D, U.K

Abstract

Taints and off-flavours in foods are a major concern to the food industry. Identification of the compound(s) causing a taint or off-flavour in food and accurate quantification are critical in assessing the potential safety risks of a product or ingredient. Even when the tainting compound(s) are not at a level that would cause a safety concern, taints and off-flavours can have a significant impact on the quality and consumers' acceptability of products. The analysis of taints and off-flavour compounds presents an analytical challenge especially in an industrial laboratory environment because of the low levels, often complex matrices and potential for contamination from external laboratory sources. This review gives an outline of the origins of chemical taints and off-flavours and looks at the methods used for analysis and the merits and drawbacks of each technique. Extraction methods and instrumentation are covered along with possible future developments. Generic screening methods currently lack the sensitivity required to detect the low levels required for some tainting compounds and a more targeted approach is often required. This review highlights the need for a rapid but sensitive universal method of extraction for the unequivocal determination of tainting compounds in food.
For Peer Review Only
Analysis of Food Taints and off-flavours - A review
Journal:
Food Additives and Contaminants
Manuscript ID:
TFAC-2009-220.R1
Manuscript Type:
Review
Date Submitted by the
Author:
28-Aug-2009
Complete List of Authors:
Ridgway, Kathy; Unilever Colworth, Safety and Environmental
Assurance Centre
Lalljie, Samuel; Unilever Colworth, Safety and Environmental
Assurance Centre
Smith, Roger; Loughborough University, Chemistry
Methods/Techniques:
Chromatography, Chromatography - Headspace, Clean-up - SPME,
Sensory analysis
Additives/Contaminants:
Volatiles, Taint, Packing migration
Food Types:
Beverages, Canned foods, Drinking water, Wine
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1
ANALYSIS OF FOOD TAINTS AND OFF-FLAVOURS– A REVIEW
Kathy Ridgwaya*, Sam P.D. Lalljiea, Roger M. Smithb
a Safety and Environmental Assurance Centre, Unilever Colworth, Bedfordshire, MK44 1LQ
U.K.
bDepartment of Chemistry, Loughborough University, Loughborough, Leics,
LE11 3TU UK
Abstract
Taints and off-flavours in foods are a major concern to the food industry. Identification of the
compound(s) causing a taint or off-flavour in food and accurate quantification is critical in
assessing the potential safety risks of a product or ingredient. Even when the tainting
compound(s) are not at a level that would cause a safety concern, taints and off-flavours can
have a significant impact on the quality and consumers' acceptability of products. The
analysis of taints and off-flavour compounds presents an analytical challenge especially in an
industrial laboratory environment because of the low levels, often complex matrices and
potential for contamination from external laboratory sources. This review gives an outline of
the origins of chemical taints and off-flavours and then looks at the methods used for analysis
and the merits and drawbacks of each technique. Extraction methods and instrumentation are
covered along with possible future developments. Generic screening methods currently lack
the sensitivity required to detect the low levels required for some tainting compounds and a
more targeted approach is often required. This review highlights the need for a rapid but
sensitive universal method of extraction for the unequivocal determination of tainting
compounds in food.
* Corresponding author. Tel. : + 44(0)1234 264892; fax: +44 (0)1234 264744
E-mail address: Kathy.Ridgway@Unilever.com
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Keywords:- Food taints; off-flavour; sensory; headspace; GC-O; SPME; SBSE; SDE;
chlorophenols; electronic-nose
Introduction
A taint in food results from contamination by a foreign chemical derived from an external
source (e.g. from packaging or storage), whereas an off-flavour is an atypical odour or taste
resulting from a compound formed by internal deterioration in the food, such as
microbiological spoilage or lipid oxidation. However, this distinction is seldom made,
particularly in consumer complaints, as both can be picked up by odour or taste and give the
impression of poor food quality. Previous reviews on food taints have discussed the origins of
food taints in detail (Mottram 1998; Whitfield 1998), but this review also considers the
analytical approach to the determination of both known and unknown tainting compounds
and includes methods introduced in recent years for taint analysis.
Methods of analysis for the determination of compounds causing taints and off-flavours are
generally the same. The presence of a taint may cause a food to be unfit for consumption,
however, unlike most chemical contamination, where there are established validated
analytical procedures and maximum permitted levels, there are no set limits for tainting
compounds.
The compounds responsible for taints are frequently only present at trace levels (low ng g-1),
and hence rarely pose a health risk to the consumer. However, the first question that must
always be asked following the discovery of a chemical taint in food being discovered is
whether there is any risk to human health based on risk assessment. This requires rapid
accurate analysis to identify and quantify the chemical(s) responsible for the taint and would
then typically be followed by root cause analysis and risk reduction measures, such as a
product recall. In general although a food with the taint or off-flavour is often not a safety
risk to the consumer, the perception of low quality, brand damage and adverse publicity can
be extremely costly to the food industry. Therefore it is imperative that the most appropriate
approach is used to reliably identify and quantify the taint and its occurrence. In rare cases,
where a food taint is due to gross contamination from a chemical leak (such as a solvent or
refrigerant), outbreaks of illness can occur (Dworkin et al.,2004).
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Sensory aspects and threshold values
The first step in any taint investigation is sensory analysis. This will only be briefly described
in this review and more details can be found in books (Baigrie 2003; Heymann and Lawless,
1999; Howgate, 1999) and numerous papers on the subject (Dijksterhuis and Piggott, 2000;
Piggott, 2000; Piggott, 1995; Sidel and Stone, 1993). The flavour of food is defined by both
its odour and taste and most food taints are detected by odour. Odour refers to both the
volatile compounds released in the mouth and those perceived from the food when external to
the body (aroma). The ‘taste’ of food is technically experienced in the mouth by the taste-
buds and can be attributed to both volatile and non-volatile compounds. Some compounds
can be detected at extremely low concentrations (Table 1) and individuals may be more
sensitive to certain odours and compounds. The possibility of someone detecting a taint is
concentration dependent and if the sensitivity to detection is plotted against the log of
concentration then an s-shaped curve is obtained (Figure 1).
Threshold values are used for the sensory analysis of taints, and are generally defined as the
probability of detection being 0.5, that is 50% of the general population will detect a taint at
that level. However, care should be taken when using such values, as each individual will
have a different threshold and most compounds are measured in air or water and this may not
be representative of detection in a real food matrix.
The sensory descriptor of a taint can often be the key to performing targeted chemical
analysis. Sensory panels are trained to give objective assessments and descriptions of taints
and can provide an insight, when a public consumer has complained that the foodstuff tastes
‘funny’. A control/reference sample should always be assessed alongside the problem sample
to enable a comparison with the ‘normal’ flavour of the product. Descriptors associated with
specific tainting compounds can be used from reference guides (Bairgrie, 2003; Saxby et al.,
1992; Saxby, 1993), or specialised websites (www.odour.org.uk and www.flavornet.org).
Artificial taste sensors have been developed in an attempt to replace or support the use of
human panellists and were discussed in a recent review (Citterio and Suzuki, 2008). They
concluded that currently no absolute models can correlate the taste that a human perceives
with the chemical composition of a sample.
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It may be that more than one compound is responsible for a taint or off-flavour in food and
this further complicates the sensory descriptors, as in the case of fishy off-flavour in dried
spinach (Masanetz et al., 1998) caused by two compounds, neither of which possessed a fishy
character as an individual compound.
The origin of food taints
Taints and off-flavours can originate from many sources, including microbiological
degradation, migration from packaging, contaminated process-water, or an unsuitable storage
environment of ingredients or finished products. Some common taints associated with these
sources are discussed in this section and summarised (Table 2), although it should be noted
that the list is not exhaustive as changes in practices and developments in processes can lead
to previously unknown taints being formed. Mottram (1998) described the origins of some
chemicals responsible for taints and off-flavours in foods and gives details of several specific
incidents. Examples of the causes of taints investigated in our own laboratories concluded
that ‘musty’ tea was due to the presence of tribromoanisole; a soapy taint in soup was from
decanoic and octanoic acids; disinfectant taints in soft drinks and instant soup powder from
di- and tri-chlorophenols and in fish sticks were due to chlorocresol, all of which were a
direct result of cross contamination during processing or storage. The move towards a more
global supply chain and the possibilities for joint storage or transport has the potential to
increase taint incidents in the food industry.
Taints from packaging
Packaging, particularly for food and beverages is designed to ensure products remain
unchanged on storage, retaining the flavour and odour of the product whilst preventing
external contamination. It is therefore prudent to carefully select packaging and control
processes to minimise the likelihood that the packaging itself can become the source of a
food taint. The problems and causes of odours and taints originating from packaging have
been reviewed previously (Tice, 1993; Lord, 2003).
Taints from packaging can occur through direct contact or by vapour phase transfer of
substances from the packaging to the food. In general, foods with high fat content or dry
foods with a high surface area are most vulnerable. For direct contact, more migration will
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occur with fatty foods, where the oil and fat components can penetrate into the packaging and
their low polarity makes them a good matrix to absorb many organic contaminants. Neutral
products like bottled water can also be more susceptible to organoleptic influences. The food
packaging industry carries out regular taint and odour tests as part of their quality assurance
programs. These sensory tests assess the odour intensity of the packaging and usually involve
a taint comparison using a test food (e.g. a triangle test, including at least one control sample,
not exposed to the packaging).
A wide variety of materials are used in food packaging and odours can originate not only
from the principal components, but also from impurities, additives, reaction products formed
during manufacture, or environmental contamination. The origins of tainting substances
formed from packaging materials include; inappropriate or contaminated raw materials,
incorrect or poor control during processing, chemical reactions within the packaging material,
and storage and transport conditions. A good example of the investigations often required
was an instance in our own laboratory of taint in peanut butter, which was traced back to the
lacquer on storage drums, migrating through the plastic bags containing the product. This
also illustrates the importance of taking representative samples, as the taint was only
observed round the edges at the top of the drum.
Inks used on the outer surfaces or materials used for secondary packaging may migrate into
the packaged product, either by direct contact or transfer in the vapour phase. Paper and
carton board materials often form part of a multilayer packaging with adhesives, varnishes
and plastics. Each component could provide a source of compounds that may result in food
tainting.
The use of recycled or reuse of packaging can also lead to food taints, including consumer
misuse as illustrated in a study investigating contaminants in water from reusable PET bottles
(Widén et al. 2005).
Inks
Examples of taints originating from packaging include residual solvents from inks and
varnishes, which generally are a result of insufficient drying after printing. There are no
generally agreed maximum levels for residual solvents in food packaging as many factors
determine whether the residue will result in a taint in the food. UV-cured inks and varnishes
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are essentially solvent-less, but residual acrylate monomers, photoinitiators (Sagratini et al.,
2008), such as benzophenone, or reaction by-products from the polymerisation process, such
as benzaldehyde and alkyl benzoates, can lead to trace odours, that could migrate into the
food product. Mesityl oxide ( 4-methylpent-3-en-2-one), previously used as a solvent for
paints and lacquer coatings, can react with hydrogen sulphide (present naturally in many
foods) to form 4-mercapto-4-methylpentan-2-one, known to produce a catty odour (Mottram,
1998).
Residual monomers
In plastics packaging, residual monomers are one of the main sources of potential taints.
Styrene, for example, has a relatively low odour threshold and also can be formed from the
plastic packaging if excessive heat is used in processing. The detection of styrene taint in
food is very dependent on the type of food product (Gilbert and Startin, 1983; Linssen et al.,
1991). Contamination of cheese by styrene dibromide (used as a catalyst in polystyrene
manufacture up to the 1970s) has been reported following migration of leachate from
polystyrene cold storage insulation (Bendall, 2007). Monomers used in polyethylene
terephthalate (PET) packaging, although not particularly odorous, can form degradation
products, such as acetaldehyde, during the manufacturing process, which have been known
to cause taints in beverages (Lorusso, 1985). Similarly, although residual monomers present
in polyethylene, polypropylene and related copolymers are not generally responsible for
odours, oxidation compounds have been identified, such as 1-heptan-3-one and 1-nonenal
(Koszinowski and Piringer, 1986).
Paper and board
Odours can be present in paper and board packaging and can arise from bacteria, moulds,
auto-oxidation of residual resins, and the degradation of processing chemicals. Soderhjelm
and Eskelinen, (1985) gave a list of volatile compounds found in pulp samples, along with
odour descriptors. Decarboxylation and oxidation of lignin can produce vanillic acid and its
subsequent degradation causes the presence of guaiacol (Chatonnet et al., 2004). If a
synthetic resin binder is used, particularly one based on styrene/butadiene, odorous volatile
by-products can be produced. Hexanal is often found in paper and board at low levels and
can also give rise to a taint. Metallic ions present in the pulp can act as catalysts for the
oxidation of lipids and give odorous volatiles, such as aldehydes, alcohols and esters (Tice
and Offen, 1994), but these compounds are usually present at too low a level to impart a
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noticeable odour. However, some paper and board can become more odorous on storage due
to such oxidation reactions and complexing agents are commonly added to reduce the level of
free metal ions, which can act as catalysts. Surface coatings on paper and boards can add
another potential source of taints and careful selection of inks and varnishes and control of
the printing and drying process is advisable to minimise taint incidents. Migration studies of
model compounds have shown that migration depends on the nature of the paper samples and
that more migration occurs from packaging into products with higher fat content
(Triantafyllou et al., 2007). The use of recycled rather than virgin board for food contact
applications could also lead to potential contaminants from inks or previous use, if paper
sources and recycling processes are not strictly controlled and monitored.
Fungicides – halophenols
One of the most commonly reported taints in foods is due to contamination by chlorophenols
and chloroanisoles. Chlorophenols have been used industrially as fungicides, biocides and
herbicide intermediates, most commonly in the treatment of wooden storage pallets.
Chlorophenols can be microbially methylated by numerous organisms to the corresponding
chloroanisoles (Leonard et al., 1974). Pallets made from soft wood that has been treated with
certain fungicides can therefore be responsible for taints due to the migration of
chlorophenols or chloroanisoles into ingredients or products during storage.
Pentachlorophenol (PCP) is now rarely used in most countries due to concerns over toxicity
and as a consequence there are less taint incidents from trichloroanisole. However, the use of
bromophenols in place of chlorophenols can also lead to the formation of bromoanisoles
through microbial methylation. Brominated anisoles generally have lower sensory thresholds
than chlorinated anisoles. 2,4,6-Tribromoanisole in particular, has a very low sensory
threshold and has been linked to taints originating from treated wooden pallets. The use of
tribromophenol as a timber treatment can make an entire building unsuitable for food
production (Chatonnet et al. 2004). Halophenols can also be formed when phenols present in
wood/board from the decomposition of the lignin react with a source of bromine or chlorine
and similarly tribromophenol can be formed by the reaction of certain biocides with phenol.
There have been several reports of the contamination of food with chlorophenols and anisoles
originating from packaging materials (Lord, 2003). The packaging affected included jute
sacks, multi-wall paper sacks (where PCP was used as a biocide in an adhesive used to glue
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the seams), fibreboard cartons and even wooden pallets on which carton board has been
stacked.
Water as a source of taints
If food is produced using mains water that has been contaminated by tainting compounds,
then it is probable that the product will also be tainted. Water containing a source of phenol
(for example from peat soil), that is then chlorinated can easily produce chlorophenols.
Similarly if bromine is present then bromophenols can be produced. Tastes and odours in the
aquatic environment can originate from naturally occurring compounds derived from the
activity of micro-organisms in soil or water, or from oil or petroleum spills (Davis, Moffat
and Shepherd, 2002; Howgate, 1999). Most taints detected in fish originate from the aquatic
environment (Tucker 2000; Whitfield, 1999). Sulphur compounds formed from precursors,
such as plankton, can cause taints in fish. For example, a taint often described as petroleum
has been reported due to the presence of dimethyl sulfide (DMS) (Whitfield, 1999) and fish
and crustacean have been reported to have iodoform or iodine like taints, attributed to
bromophenols (Whitfield et al., 1988). A common taint reported in water as earthy-musty is
due to geosmin, 2-methylisoborneol (MIB) and haloanisoles (Zhang et al., 2005), and is
generally associated with micro-organisms, particularly bacteria (Watson et al., 2003). Other
compounds reported to cause taint in water, include 2-isopropyl-3-methoxypyrazine (IPMP)
and 2-isobutyl-3-methoxypyrazine (IBMP), which are metabolites of Actinomycetes and soil
bacteria. Various treatment processes have been developed to remove off-odours from
potable water (Suffet et al., 1993).
Cleaning products
A large number of reported taints each year originate from cleaning products or disinfectants
(Olieman, 2003). These taints can occur accidentally due to the transfer of volatiles or poor
rinsing, or from direct contact if ‘no-rinse’ products are used. Disinfectants based on active
chlorine, iodine or oxygen can react with food components (such as phenols) to form
additional compounds for example halophenols and potentially haloanisoles. Methyl
ketones present in the majority of foods at low concentrations can react to form chloroform or
iodoform. These reactions can depend on the presence of other compounds, for example
sequestering agents for metals can be added to decrease metal-catalysed formation reactions,
whereas the presence of quaternary ammonium compounds can increase reactions (Olieman,
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2003). New polymer flooring, contaminated with traces of phenol, can react with chlorine-
based disinfectants to produce chlorophenols (Mottram, 1998). If chlorine-based disinfectants
are used on the same site as phenolic disinfectants then a reaction can occur – not only in the
drain but also potentially in the atmosphere. The presence of microorganisms can lead to the
formation of tribromoanisole, which has an extremely low sensory threshold and can lead to
considerable taint problems in a factory environment.
Micro-organisms
The micro-organisms generally associated with off-favours in food, bacteria and fungi have
been reviewed by Whitfield (1998). The food affected, includes meat, dairy products, fruit,
vegetables and cereals, and a wide range of compounds with varied sensory descriptors can
be produced (Whitfield, 2003; Springett, 1993). Examples include the production of guaiacol
from vanillin (Perez-Silva et al., 2006; Varez-Rodriguez et al., 2003), a compound
responsible for the vanilla flavour in products, such as ice cream, and an off-flavour produced
by Penicillium species in margarine (Hocking et al., 1998). Sorbic acid, used as a
preservative in food, can be converted by mould to give pentadienes and 1,3-pentadiene
causes taints in various foodstuffs (Loureiro and Querol, 1999). Pinches and Apps (Pinches
and Apps, 2007) described the production in food of 1,3–pentadiene and styrene by
Trichoderma species. The production of styrene in foods has been linked to the action of a
specific yeast on cinnamaldehyde, although the presence of cinnamon or cinnamon flavours
is not a prerequisite for styrene production (Spinnler et al., 1992). Two bacterial species and
their metabolites have been linked to the production of compounds, such as guiacol,
dibromophenol, geosmin and 2-methylisoborneol, in apple juice (Zierler et al., 2004), leading
to an off-flavour described as musty/earthy or medicinal–like.
Food reaction off-flavours
Thermal processing and the Maillard reaction are responsible for many food flavours and can
also be responsible for some off-flavours in foods. Examples include the browning and
flavour deterioration of fruit juices on storage, attributed to Maillard reaction products such
as substituted furfurals, furans and pyrroles (Handwerk, and Coleman, 1988) and similarly
the deterioration of UHT milk flavour during storage (Valero et al., 2001). However, lipid
oxidation is generally considered the main source of off-flavours in foods. There are several
mechanisms for lipid oxidation, which have been reviewed by Saxby (Saxby, 1993) and
Hamilton (Hamilton, 2003). Common compounds associated with the resultant ‘rancid‘ off-
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flavours, include aldehydes, ketones, lactones and furans, carboxylic acids, alcohols and
hydrocarbons.
Cork taint
One of the most well known food taints is the musty taint in “corked” wines, and many
papers have been dedicated to the subject (Evans et al., 1997; Ezquerro and Tena, 2005;
Gomez-Ariza et al., 2004a; Insa et al., 2005; Juanola et al., 2004; Juanola et al., 2002;
Martinez-Urunuela et al., 2004a; Martinez-Urunuela et al., 2004b; Martinez-Urunuela et al.,
2004c; Martinez-Urunuela et al., 2005; Riu et al., 2002; Taylor et al., 2000; Zalacain et al.,
2004). Several compounds are thought to contribute to the ‘cork’ taint in wine and can
originate from practices during wine production. (Soleas et al 2002). Chloroanisoles, in
particular 2,4,6-trichloroanisole, due to its low sensory threshold, have been identified as a
potential cause. The presence of chloroanisoles in cork can be due to the microbial
degradation of chlorophenols (used in insecticides and herbicides) or chlorinated solutions
used to bleach the cork. Other off-flavours in wine can originate from a number of sources,
including fungal flora on the grape, formation by yeasts or bio-methylation of phenols
(Boutou and Chatonnet, 2007). 2,4,6-Trichloroanisole has also been identified as causing a
musty/muddy off-flavour in sake and was thought to originate from the wooden tools used in
preparing rice koji for sake brewing (Miki et al., 2005).
Methods of chemical analysis
As the majority of taints are detected through odour (inside or outside the mouth) , most of
the compounds that cause taints in food are volatile. As discussed earlier, sensory thresholds
mean that extremely low levels can give rise to a taint which presents a challenge to the
analyst trying to identify the chemical compound(s) responsible. Following sensory analysis,
the identification of the compound causing the taint is necessary to determine the cause and
prevent re-occurrence. If the compound is known, then targeted analysis can be performed.
However, often this is not the case and a more investigative approach is required. The
description of the taint provides key information to the analyst, as any potential compound
identified in the sample must have the same taste and odour characteristics as those described
from sensory analysis. It is often necessary to predict what the compound might be from
sensory descriptors and background information before starting the chemical analysis.
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Requirements
The determination of taints and off-flavours in foods often involves two approaches as
illustrated in the schematic in Figure 2. The initial procedure to identify differences in the
volatile profile of the tainted sample compared to a ‘good’ control sample, followed by
chromatographic analysis to enable the identification and quantitation of any compounds
against standards. The sampling procedures employed are very important as a chemical
causing a taint may not be evenly distributed throughout a product or ingredient. This is
particularly the case for gross chemical contamination, such as solvents or with compounds
migrating from packaging, where ‘hot spots’ can occur.
If the initial tests suggest a potential suspect then a targeted extraction can be employed. For
a true screening method, where the cause of the taint is unknown, a wider more universal
method is required than for targeted extraction and analysis. The tainting compound,
however, may be present at very low levels and will need to be isolated from high
concentrations of matrix components. Sometimes large sample sizes are needed to obtain a
high enough concentration to enable detection, therefore the removal of matrix interferences
without the loss of the compound(s) of interest presents a challenge to the analyst. As the
majority of compounds responsible for taints are volatile, care must be taken to avoid losses
during sampling and analysis, in particular during any solvent removal step, particularly if
concentrating to small volumes (Ferreira et al., 1998, Jakobsen et al. 2003)
Determination of chemicals causing food taints is a not an easy procedure and care must be
taken to avoid all possibilities of contamination from external laboratory sources (including
perfumes and personal care products used by the analysts). A dedicated area is preferred and
all control and suspect samples, and reference standards should be handled and stored
separately. Whereas initial identification of a compound can be predicted using library
spectral searches (such as NIST mass spectral library), the use of analytical standards are
essential in the unequivocal identification of a chemical compound. Extreme care should be
taken with identification of ‘extra’ peaks observed in the chromatographic profile of the
suspect sample and results should always be compared with sensory analysis and other
available information to ensure an accurate diagnosis is made.
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Extraction methods
There are several methods for the extraction of flavour volatiles (Marsili, 1996; Wilkes et al.,
2000), including liquid-liquid extraction (Weurman, 1969), simultaneous steam distillation
solvent extraction (SDE) (Nickerson and Likens, 1966), static headspace (Chialva et al.,
1983), dynamic headspace (Chatonnet et al., 2004), direct thermal desorption (Hoffmann and
Sponholz, 1994) solid-phase microextraction (SPME) (Yang and Peppard, 1994) and more
recently headspace sorptive extraction (HSSE) (Lorenzo et al., 2006) and stir bar sorptive
extraction (SBSE) (Nakamura et al., 2001). Miniaturised techniques have more recently been
employed, such as headspace liquid phase microextraction (HS-LPME) for chlorophenols
(Hui et al., 2007) and geosmin (Bagheri, and Salemi, 2006) in water. Closed loop stripping
techniques (CLSA) have also been used for odorants in water (Hassett and Rohwer, 1999;
Zander and Pingert, 1997). The choice of extraction method will depend upon the matrix and
the predicted cause of the taint. The sensory data should give an indication of the compounds
responsible for the taint and therefore the sensitivity of technique required. Sample
preparation methods for chlorophenols in environmental, enological and biological samples
were recently reviewed by Quintana and Ramos (Quintana and Ramos, 2008) who
highlighted the need for different approaches for different matrix types. A ‘fit for purpose’
approach should be taken, considering both identification and quantification requirements.
Solvent extraction
Some methods have been reported for taints and off-flavours in foods that use direct solvent
extraction. Indole and skatole have been associated with a taint in meat from male pigs and
methods using direct solvent extraction, followed by HPLC, have been reported (Regueiro
and Rius, 1998). In this example, fluorescence detection provided selectivity, but generally
further clean-up stages are required. By performing several liquid-liquid partitions, and using
pH adjustment it is possible to obtain a fraction containing the problem odour, but for
complex matrices, such as foods, several matrix components may still be present, making
accurate identification and quantitation difficult. Solvent extraction has been used for the
analysis of chlorophenols and chloroanisoles in cork (Juanola et al., 2002) and
tribromoanisole in wine (Chatonnet et al., 2004).
Solvent extraction methods generally require a subsequent concentration of the solvent by
rotary evaporation or the use of solid phase extraction (SPE), but this can lead to a loss of
analytes (Ezquerro and Tena, 2005; Riu et al., 2002). Juanola et al. (Juanola et al., 2002)
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used a ‘shake-flask extraction’ followed by silica column clean-up for the analysis of 2,4,6-
trichloroanisole in corks and compared the results to the use of Soxhlet and ultrasound
extraction methods. In all the methods a concentration step using a rotary evaporator and then
drying under a nitrogen flow was necessary. Procedures using SPE as a clean-up step can be
developed if sensory analysis can provide clues to the target compounds. SPE methods have
been reported for chloroanisoles (Insa et al., 2005; Soleas et al., 2002) and for both
chloroanisoles, and chlorophenols with derivatisation (Martinez-Urunuela et al., 2005).
Other solvent extraction methods include supercritical fluid extraction for 2,4,6-
trichloroanisole (TCA) in cork (Taylor et al., 2000) and androsterone and skatole in pigs
(Zabolotsky et al., 1995), Soxhlet extraction for analysis of trichloroanisole from corks
(Juanola et al., 2002) as well as microwave extraction and pressurized fluid extraction
(Ezquerro et al., 2006; Gomez-Ariza et al., 2005).
However, for true unknowns, isolation from matrix components and concentration can be a
challenge. Therefore direct solvent extraction is generally only used for targeted taint analysis
when the compound responsible for the taint is known and is present at a relatively high
concentration.
Steam Distillation and SDE
As the majority of compounds that cause a taint or off-flavour are volatile, steam distillation
can be used for extraction from the non-volatile food components. The distillate can then be
further extracted or concentrated. Distillation has been used for the analysis of
trichloroanisole in wine (Juanola et al., 2002). For thermally labile compounds, the
distillation can be performed under vacuum using lower temperatures. Microwave assisted
steam distillation has also been employed for tainting compounds, such as the extraction of
geosmin and methylisoborneol from catfish (Conte et al., 1996; Lloyd and Grimm, 1999) and
chlorophenols from solid samples, such as soil and wood (Ganeshjeevan et al., 2007).
Combined steam distillation and solvent extraction (SDE) is one of the most widely used
techniques for the extraction of volatile tainting compounds and has been reported for the
analysis of trichloroanisole in wines (Hill et al., 1995). SDE can avoid the extraction of major
matrix components as described (Landy et al., 2004) in a study on odour-active compounds
in packaging. The use of SDE was required to enable the identification of compounds
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following spectral interferences from the high concentration of hydrocarbons using other
techniques. The original apparatus was first described by Likens and Nickerson (Likens and
Nickerson, 1964). A recent review of the technique (Chaintreau, 2001) describes some
changes and variations. The sample is placed in one flask (with water) and the extracting
solvent in the other. Both are boiled and the vapours mix and condense in a central chamber,
with the condensates returning to their original flasks. Volatile compounds distil out of the
sample with the steam, are extracted into the solvent in the central chamber and are
transferred to the solvent flask. Large sample sizes can be used as only the volatile
components are extracted and as volatilisation, condensation and extraction form a cyclic
process, a minimal amount of extracting solvent can be used. For some compounds, where
ultra-trace levels can be responsible for a taint, a further concentration step may still be
required. The method is matrix and analyte dependent and samples with high fat/lipid content
can reduce recoveries. However, for most matrices, good recoveries can be obtained, and
adjustment of pH can be made to encourage the extraction of certain compounds, such as 2,6-
dibromophenol (Whitfield et al., 1988).
One disadvantage of SDE is the potential break down of labile compounds and the possibility
of the formation of extra compounds either thermally or by oxidation (Chaintreau 2001,
Siegmund 1997).Vacuum SDE has been shown to reduce artefact formation by enabling
extraction at lower temperatures (Chaintreau, 2001) although a relatively non-volatile
extracting solvent should be used to avoid losses during the extraction.
The advantage of SDE is that it can be used for a wide variety of food matrices and produces
a clean extract of volatile components. Large sample sizes can be taken and with the
inclusion of a concentration step excellent sensitivity is achievable (sub µg/kg (ppb) levels).
The major disadvantage of this technique is the need for specialist glassware and the
possibility of cross contamination and losses on concentration. It is important to analyse both
a ‘control’ sample and suspect sample using each set of glassware, to enable identification of
genuine differences.
Thermal desorption
For solid samples, direct thermal desorption can be used including, for example, the
determination of trichloroanisole in corks (Caldentey et al., 1998). Thermal decomposition
GC/MS of food packaging has been successful in identifying off-odour components in
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packaging material as well as in the original polymer (Hartman, 2007; Woodfin and George,
2003). This technique is only suitable for solid samples and requires the contaminant to be at
a level that can be detected above matrix components. Quantitation methods also need to be
optimized to replicate sample analysis. For complex matrices and unknown taints, direct
static headspace is more commonly used.
Direct static headspace
Static headspace is very useful for the general profiling of volatiles and can be used as a first
step to detect differences between ‘good’ and ‘bad’ samples. Examples include the quality
control of aromatic herbs (Chialva, 1983), musty taints from packaging (Mcgorrin et al.,
1987) and the determination of off-flavours in infant formula (Romeu-Nadal et al., 2004). If
the tainting compound is present at a relatively high level then the additional
chromatographic peaks in a "bad" sample can be identified using a mass spectral library.
Standards should always be run under the same conditions for confirmation of retention time
and mass spectra. For accurate quantitation, the method of standard additions is
recommended, or if possible, the use of an internal standard (ideally an isotopically labelled
analogue). Although static headspace allows for a representative sample to be taken for
flavour analysis, often it only detects the most intense compounds. It is useful as an initial
screening method for detecting differences between control (untainted) samples and those
contaminated with a tainting compound. Recent developments in software that can allow for
chromatographic subtraction and difference analysis can be employed to aid the analyst in
differentiating complex volatile profiles. It is often the first step in a taint investigation and
can be used for most food types (or packaging), however, the sensitivity of the technique may
still be inadequate for some taints and techniques that include a concentration step (such as
headspace-SPME) are increasingly being used.
Dynamic headspace
Some tainting compounds will illicit an adverse olfactory response at extremely low levels
and can be difficult to detect using direct static headspace, particularly where the cause of the
taint is unknown. So-called dynamic headspace techniques, such as purge and trap, enable
concentration from the sample headspace and can improve sensitivity. In the determination of
bromophenols in water with in situ acetylation (Blythe et al., 2006) the analytes were trapped
on a very small quantity of activated carbon (1.5 mg Grob tube) and eluted using 20-30 µl of
solvent prior to GC-MS analysis. Purge and trap systems using Tenax traps have also been
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reported for odorous compounds in water (Salemi et al., 2006) and volatile compounds from
cork (Caldentey et al., 1998).
A recently reported technique comparable to a dynamic headspace method is pervaporation
(Gomez-Ariza et al., 2004a) based on evaporation and diffusion through a membrane which
helps to minimise matrix effects and prevent water vapour interferences. It can be used online
with GC (Gomez-Ariza et al., 2004b) and to achieve better sensitivity the technique can be
used with a solid phase trap (Gomez-Ariza et al., 2006) or packed inlet liner (Gomez-Ariza et
al., 2004c). Dynamic headspace techniques are rarely used for food taint analysis and the
traditional purge and trap devices can have problems with carry over. Although dynamic
headspace provides a concentration step, for complex matrices such as food, matrix volatiles
are also concentrated and thus the technique provides little advantage over direct static
headspace for most applications.
Solid-phase microextraction (SPME)
Solid-phase microextraction can be used to increase the selectivity and sensitivity for some
volatile compounds. Initially SPME was used to quickly obtain volatile profiles of a wide
range of foodstuffs, including fruits, vegetable oils, coffee and milk (Yang and Peppard,
1994; Marsili, 1999). Yang and Peppard, (1994) compared direct immersion and headspace
sampling for 25 common flavour compounds. More recently, headspace-SPME extraction has
been increasingly used for flavour volatiles and Steffen and Pawliszyn, (1996) described the
quantitative analysis of some flavour volatiles in orange juice. A number of papers have
reported the use of HS-SPME for chloroanisoles and chlorophenols (Ezquerro and Tena,
2005; Bianchi et al., 2003; Insa et al., 2005; Juanola et al., 2005; Martinez-Urunuela et al.,
2004b; Riu et al., 2002; Riu et al., 2006) and other compounds responsible for musty-earthy
off-odours (Prat, 2008) in cork (Figure 3).
SPME has been employed for the determination of iodinated trihalomethanes in water
(Cancho et al., 1999), 2-methylisoborneol and geosmin in environmental waters (Saito et al.,
2008) and off-flavours in milk (Marsili, 1999). The selectivity of SPME sampling means that
although some compounds will not be adsorbed by the fibre (Yang, and Peppard, 1994),
generally the background will be less than using direct static headspace (Marsili, 1999).
However, it should be noted that for very volatile compounds, direct headspace often gives a
better response than SPME (Zhang et al., 1994) and matrix effects in SPME can be a
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problem. Consideration should also be made for the sample type, as for oil based samples the
matrix can decrease the sensitivity of headspace SPME sampling and higher temperatures
may be required (Yang and Peppard, 1994). As SPME is an equilibrium technique, the results
depend strongly on the experimental conditions and sample matrix.
External calibration methods are generally not suitable for quantitation and the use of a
labelled internal standard or the method of standard additions may be required for accurate
quantitation. Boutou and Chatonnet, (2007) used HS-SPME for wine off-flavours with
labelled internal standards for quantitation. Similarly McCallum et al. (2008) used deuterated
geosmin and 2-methylisoborneol for the determination of the native compounds in water
Vlachos et al., (2007), used HS-SPME GC-ECD for the analysis of 2,4,6-trichloroanisole in
wine and cork soaks, employing 2,3,6-trichlorotoluene as an internal standard for
identification. However, due to matrix affects when more than 3 corks were extracted,
external calibration and the method of standard additions was necessary for accurate
quantification.
The sample matrix can be modified to increase the recovery of the target compounds, such as
acidification for extraction of phenols or the addition of salt (Riu et al., 02). However, Evans
et al., (1997) reported that the addition of salt did not increase the response for the analysis of
2,4,6-trichloroanisole in wines. For some analytes, such as the detection of limonene in
aqueous systems (Yang and Peppard, 1994), it can have a negative effect. Derivatisation can
also be used in SPME, either in the matrix solution prior to extraction (Martinez-Urunuela et
al., 2004b) or on-fibre after analyte absorption (Pizarro et al., 2007b).
Fibres can be chosen to suit the analyte properties. Yang and Peppard concluded that
polyacrylate fibres suited higher polarity compounds compared to PDMS (Yang and Peppard,
1995) and Adams et al. (Adams et al., 1999) used polyacrylate fibres for the determination of
bromophenols in water and model systems. A PDMS/DVB fibre has been reported to give the
best sensitivity for chloroanisoles (Carasek et al., 2007), and was also chosen for
determination of geosmin and 2-methylisoborneol (McCallum et al., 1998).
Multiple headspace SPME has been used to study the volatiles in cork (Ezquerro, and Tena,
2005), haloanisoles and chlorophenols in wine (Martinez-Urunuela et al., 2005; Pizarro et al.,
2007a). Using repeated consecutive extractions from the same sample, this technique enables
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an estimate of the complete extraction of the analyte, overcoming problems with matrix
affects. Juanola et al., (2004) compared sensory and instrumental analysis using HS-SPME
and results showed the ability of sensory measurement to predict trichloroanisole content in
wine.
Zhang et al., (2005) used SPME with cool inlet PTV injection, to improve sensitivity for
several odorous compounds in water. A recent development in SPME – that of cold fibre
SPME, (CF-SPME), which allows for the simultaneous cooling of the fibre coating whilst
heating the sample, has also been employed for the determination of chloroanisoles in cork
(Carasek et al., 2007). This technique was compared to normal HS-SPME and was shown to
give improved quantification limits, with recoveries >90% providing almost exhaustive
extraction.
SPME is used widely for flavour profiling, and is increasingly being employed for targeted
taint analysis. However, the need to optimise the technique for each matrix limits its use as a
screening method for unknown taints . The technique can be used where the compound
responsible for the taint is known and can provide relatively low detection limits for specific
applications. For accurate quantitation, the method of standard additions is often required, or
the use of a suitable internal standard. It has been used successfully for a range of tainting
compounds (Boutou and Chatonnet, 2007) and provides superior sensitivity compared to
direct headspace analysis, but to date no screening method has been reported for
determination of unknown taints.
Stir bar sorptive extraction (SBSE)
Chloroanisoles and chlorophenols in cork have been studied by Hayasaka et al., (2003) and
Callejon et al., (2007), using an initial liquid-solid extraction of the corks followed by SBSE.
By adjustment of the pH, migration of the phenols into the non-polar PDMS extracting phase
was enhanced (Chatonnet et al., 2004; Zalacain et al., 2004). Alternatively in-situ
derivatisation can be used as described by Kawaguchi et al., (2005) for the determination of
chlorophenols in river water and urine. Derivatisation is commonly used for determination of
chlorophenols due to the poor GC response and tailing peaks obtained for these compounds
(Figure 4). SBSE has also been used for the determination of 2,4,6-trichloroanisole in sake
(Miki et al., 2005) and benzophenone and derivatives in river water (Kawaguchi et al., 2006).
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Similarly to SPME, SBSE can also be used to selectively extract volatiles from the headspace
above a sample after heating, known as headspace sorptive extraction (HSSE). Marsili and
Laskonis, (2006) compared SBSE and HSSE for the determination of off-flavour chemicals
in beer and concluded that SBSE detected more odour active compounds and provided the
most accurate quantitation. HSSE has been used for the determination of chloroanisoles in
cork (Lorenzo et al., 2006), enabling a non-destructive method to be developed (Figure 5).
The larger volume of coating compared to SPME, means that analytes are extracted into the
bulk phase and this allowed higher temperatures to be used to enable extraction of the
contaminants from the cork matrix.
SBSE and HSSE are not exhaustive extraction techniques and as with all equilibrium based
techniques internal standards or the method of standard additions are generally employed for
quantitation. Both techniques provide the high concentration factors which are necessary for
detecting trace level tainting compounds, but to date have only been employed for targeted
analysis.
Instrumentation
GC-MS
As the majority of flavour compounds (and therefore off-flavours and taints) are volatile, the
analytical instrumentation of choice is invariably GC-MS. In order to allow for mass spectral
matches with libraries to identify unknown compounds the most common instrumentation is a
single quadrupole instrument using electron impact ionisation (EI (+)) at 70 eV. Ion trap
instruments (Insa et al., 2005) and more recently time of flight (TOF) instruments (Carasek et
al., 2007; Marsili and Laskonis, 2006), offer full spectra information and can also provide
adequate sensitivity for quantitation. The automation of the sample preparation step now
enables on-line extraction, including headspace systems and SPME with direct injection or
automated thermal desorption in SBSE.
GC-Olfactometer (GC-O)
A GC-O or ‘sniffer port’ can be used alongside a traditional GC detector to allow an analyst
to identify the odour of a peak as it elutes from the GC column. The GC effluent is mixed
with humid air and a trained panellist records the time, intensity and descriptor of the odour,
producing an ‘odourgram’ of retention time vs sensory response. The GC-O detector can be
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coupled (via a splitter) with FID for quantitation or more commonly now with MS to provide
identification of the odour causing compounds. The sensory response can be overlaid with the
GC-MS chromatogram. GC-O can be useful in correlating odours to compounds, and can be
used as an initial screening of volatile compounds or to confirm the presence of a specific
taint compound. Quantification can be performed subsequently using instrumental techniques
such as GC-MS.
Individual compounds can be quantified using GC-O, either by using extract-dilution analysis
(AEDA) (Grosch, 1993) or combined hedonic and response measurements (CHARM)
methods (Acree et al., 1984). Dilution analysis, as the name suggests, involves the trained
assessors analysing successive dilutions of the sample until no odour is perceived, providing
a semi-quantitative measurement useful for profiling. CHARM methods compare only the
magnitude of each odour, by recording the concentration when the sensory threshold is
exceeded and then when it is no longer detected. Generally these approaches are used for
profiling the entire volatile profile of a food and the relative importance of each compound,
rather then as quantification methods for taint analysis.
As with all analytical techniques, the use of reference standards with GC-O is important both
for matching retention times and odour characteristics (Molyneux and Schieberle, 2007).
A review on GC-olfactometry in aroma analysis was published in 1999 (Feng and Acree,
1999) and more recently, Plutowska and Wardencki reviewed the use of GC-O in the analysis
and quality assessment of alcoholic beverages (Plutowska and Wardencki, 2008).
The electronic nose
Digital aroma technology like the ‘electronic nose’ is designed to mimic the function of
sensory panels and can therefore offer an objective method for the detection and
measurement of some odours. In most electronic nose systems an array of sensors, with
different surface properties, is used, and the volatile compounds are absorbed and desorbed at
the surface of the sensors, causing a change in electrical resistance (Arnold and Senter, 1998).
The odours are classified based on previous readings. It should be noted that it is the total
odour of the sample headspace that is being analysed and individual volatile compounds are
not separated as in GC instruments. As the headspace vapour crosses the array of sensors, an
odour profile similar to a fingerprinting technique is produced.
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The electronic nose has been used to detect tainting compounds in raw and treated portable
water (Stuetz, 2007), in ham (Otero et al., 2003) and pork (O'Sullivan et al., 2003) and to
monitor lipid oxidation in nuts (Pastorelli et al., 2007). Stuetz, (2007) described a semi-
quantitative analysis for a range of tainting compounds in water, although it was noted that
the background matrix influenced the response pattern and for any environmental analysis,
seasonal variations in matrix background would need to be considered. Cimato et al., (2006)
used both SPME-GC-MS and the electronic nose for the analysis of olive oil defects (off-
flavours) and Esposto et al., (2006) concluded that discrimination of virgin olive oils was
possible using both techniques.
However, Berna et al., (2008) compared a sensor electronic nose (metal oxide) and MS
electronic nose with the GC-MS method and concluded that performance of the electronic
noses did not approach the sensitivity accuracy or specificity of GC-MS when analysing wine
for 4-ethylphenol and 4-ethylguaiacol. The sensors were unable to predict spoilage accurately
when a range of wines were analysed due to the variation in other volatile components, even
when an additional drying step was used in an attempt to minimise interferences from
ethanol. An electronic nose metal oxide sensor device gave good correlation compared to
SPME, as a screening tool for monitoring lipid oxidation in nuts (Pastorelli et al., 2007).
Applications using the electronic nose for quantitative measurement are limited and follow-
up confirmatory analysis is nearly always required. The technique is often seen more as a
screening technique to replace olfactory analysis by human sensory panels – which can
produce varying results and can be expensive and time-consuming.
Future developments
Developments in software for pattern recognition and background subtraction are allowing
better profiling of food samples and enable a more rapid comparison of ‘good’ and ‘bad’
samples using techniques, such as principal component analysis (Kallithraka et al., 2001;
Pigani et al., 2009; Rodríguez-Delgado et al., 2002; Rudnitskaya, 2009). This will allow for
more rapid identification of the tainting compound, particularly in samples with very
complex volatile profiles containing trace level contamination. Developments in sorptive
extraction techniques, such as SBSE and cold fibre SPME, are leading to more rapid methods
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that can achieve the necessary sensitivity to determine compounds even with extremely low
sensory thresholds in the presence of large matrix components.
Other extraction techniques, still under development include droplet or dispersive extraction,
which to date have only been applied to aqueous solutions (Rezaee et al., 2006; Yangcheng et
al., 2006; Zhou, et al., 2008). The use of GC x GC (d'Acampora Zellner et al., 2007) and
TOF-MS for profiling is likely to lead to the use of such techniques in taint analysis.
However, currently quantitation down to low levels is a problem and suitable software is not
available for many applications. As with most screening or multi-residue methods, where
selective sample preparation cannot be used for targeted analysis, instrumentation and
adequate data processing must be relied upon to provide the unequivocal identification and
sensitivity that is required for accurate quantitation.
Conclusions
The prevention of taints and off-flavours in foods by controlling processes, packaging and
storage conditions is paramount to ensure food quality and potentially food safety. Risk
management and reduction measures should be considered for areas where potential taints
can occur.
As this paper illustrates, for the investigation and analysis of taints and off-flavours a flexible
approach needs to be taken. Each case must be viewed individually, gathering as much
background information as possible. The analytical methods employed will depend on many
factors, including instrument availability and analyst experience. If targeted analysis can be
performed then several techniques may be suitable, but for unknown taints, the choice is
more limited. An example approach is given in Figure 2, which illustrates some of the steps
involved in deciding which method is fit for purpose. An experienced taint analyst may
follow a more targeted approach to provide a more rapid response, as it is frequently critical
to the food industry to obtain early identification of a tainting compound.
When a taint or off-flavour is detected, accurate methods of analysis are required to rapidly
identify and quantify the compounds responsible to enable consumer safety risk assessments
and help identify the origins of the taint. Current extraction methods for taint analysis fall into
two categories. Those that are more generic and are therefore useful for screening but may
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not have the required sensitivity for some analytes, and those developed for more targeted
analysis that will only be useful for certain known compounds. The rate limiting step is
sample extraction and many of the more generic techniques based on liquid extraction are
time consuming and still require a solvent concentration step.
Direct static headspace can often lack the sensitivity required or if dynamic systems are used
then matrix affects can be a problem with some foodstuffs. Headspace techniques that
incorporate a selective concentration step, such as SPME are increasingly being used, but
may not be applicable to all analytes. SBSE and HSSE offer some selectivity and high
concentration factors, and have been applied to specific tainting compounds.
Once a taint has been detected then the course of action will depend on several factors, such
as whether the product is already on the market, the number of batches affected and whether
the contamination poses a potential risk to human health. If there is a consumer safety risk
then a public recall must be considered, but even where the tainting compound represents no
risk to consumers, a silent recall may be undertaken to minimise brand damage or perception
of poor quality.
This review highlights the need for a rapid universal method of extraction for determination
of taints in food to enable detection of compounds at trace and ultra-trace levels in foods (sub
ng g-1).
Acknowledgements
This research was financially supported by Unilever Safety and Environmental Assurance
Centre, Colworth.
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Figure 1: Variations in taste thresholds
(reproduced with kind permission of Springer Science and Business Media, from
Food taints and off-flavours Ed M J Saxby (1993)
Figure 2: An example analytical approach for investigation of food taints.
Figure 3: Chromatogram obtained by HS–SPME–GC–MS for the VOC determination
in a cork stopper in full scan and Selected Ion Storage (SIS) mode.
(Reproduced from Ezquerro and Tena, (2005) J. Chromatogr. A 1068: 201-208, with
permission from Elsevier).
Figure 4: Comparison of chromatogram of chlorophenols subjected to SBSE with in
situ derivatization with that subjected to SBSE without derivatization. (10 ml of
chlorophenol standard solution (10 ng ml−1) stirring for 60 min at 25 °C).
(Reproduced from Kwaguchi, (2005) Anal. Chim. Acta 533: 57-65 with permission
from Elsevier).
Figure 5: (a) Spiked natural cork stopper chromatogram analysed by headspace stir
bar sorptive extraction (HS-SBSE) with gas chromatography–mass spectrometry.
(b) Overlaid selected ion chromatograms of the six target compounds at 25 ng g-1 in
spiked cork stoppers; internal standard (I.S.); (1) 2,4,6-trichloroanisole (TCA); (2)
2,3,4,6-tetrachloroanisole (TeCA); (3) 2,4,6-tribromoanisole (TBA); (4) 2,4,6-
trichlorophenol (TCP); (5) pentachloroanisole (PCA);(6) 2,3,4,6-tetrachlorophenol
(TeCP).
(Reproduced from Lorenzo et al., (2006) J. Chromatogr. A 1114: 250-254 with
permission from Elsevier)
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Table 1: Sensory threshold values for some common tainting compounds
[Main source – “Index of chemical taints” Leatherhead Foods RA 1992, and “Food Taints and off
flavours” Saxby (Ed)]
Compound Taint descriptor Odour Threshold µg/l
(ppb)
Taste Threshold µg/l (ppb)
4-cresol Phenolic, horse manure 200 2
2-bromophenol Disinfectant, phenolic 0.1 (18 µg/kg reported in oil) 0.03 ( 2 µg/kg reported in
prawns)
2-chlorophenol Disinfectant, medicinal 3ug/l 0.1 µg/l( 2µg/kg in milk)
Chlorophenol 1.2ppm 0.006ppm
6-chloro-o-cresol Disinfectant, medicinal, TCP 0.05µg/kg in blancmange,
0.03µg/l in tea,
2µg/kg in margarine
2,6-dibromophenol Iodoform 0.0005 (0.06 µg/kg reported
in prawns)
2,4-dichlorophenol Phenolic, chemical 200 ng g-1 0.3
2,6-dichlorophenol Phenolic, chemical 3 0.2, ( 0.5ug/l in beer)
2,4,6-trichlorophenol Disinfectant 300µg/l 2 µg/l
Dimethyl sulphide Cabbage, sweet, repulsive 0.33 6 µg/l in milk,
60 µg/l in beer
Decanoic acid soapy 0.02%
Decanal green 0.1 7
Ethyl acrylate Acrid 67µ g/l
Geosmin Earthy, musty, muddy 0.02 (0.007) 0.05µg/l ( 6µg/kg in fish)
2,4,6-tribromophenol Iodoform 0.6
Guaiacol Smoky, phenolic, medicinal 21 (70µg/l in paraffin oil,
20µg/l in wine)
13µg/l (50, 21)
Hexanal Rancid 0.19-30 ng g-1(ppb) 0.2-10
Indole Faecal 0.3mg/kg (ppm) 0.5mg/kg (ppm)
Methyl methacrylate Plastic 0.2mg/kg (ppm) in air
2,4,6-trichlorophenol Disinfectant 300 2
1-octen-3-ol Mouldy, musty, metallic 10µg/l 1µg/l
Oct-1-en-3-one Oily, green, metallic, mushroom,
apple, cardboard
0.09µg/l
80µg/l in oil
1µg/kg in butterfat,
10 µg/kg in skimmed milk
Cis-Oct-2-enal Sour, rancid 3µg/l 83µg/l in oil/water emulsion
2,4-dichloroanisole Musty, sweet, fruity, scented 0.4
-
2,6-dichloroanisole Musty, medicinal, phenolic 0.04
2,4,6-tribromoanisole Musty 0.000 008 ( 8pg/l (ppq)
2,4,6-trichloroanisole Musty, earthy 0.000 03µg/l (0.03ng/l (ppt)
in water
0.02µg/l in water
0.01µg/l in wine
2.4 µg/kg in egg yolk
pentachloroanisole Musty, earthy 4µg/l 2.8mg/kg (ppm) in egg yolk
Styrene Hydrocarbon, Plastic, Acrid 0.7mg/kg in water,
50µg/l in air
37 µg/l (or 22 ppb, 0.022
ppm) in water
0.2 tea 0.5 yoghurt, 1.2 whole
milk, 5µg/kg (ppb) in sour
cream
Skatole Faecal, animal, nauseating 10µg/l in water
0.0012mg/l in air
50 µg/l in water
Trans-1,3-pentadiene Plastic, paint, paraffin, kerosene 2.5ml/l in 10% brine 4mg/kg in cheese
Terpineol Musty, Piney 2mg/l (ppm) in orange juice
2-pentylfuran Beany, rancid-greasy 6µg/l 1mg/l (ppm)
Note: Thresholds in water unless stated otherwise (Values as reported in the literature, therefore, more
than one for some compounds).
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Taint compound
tentatively identified?
Risk management/ reduction
(Follow up root cause, possible further analysis)
Sensory descriptors
(consumer vs panel?)
Background information provided
(suspected compounds /causes of taint)
No
Yes
Targeted
extraction and analysis.
Method depends on sensitivity required i.e. level of
sensory threshold / Predicted levels in samples?
Low (ppb/ ppt): SDE / SPME / SBSE
High (ppb/ ppm): Headspace /SPME /solvent
ex
traction
Screening
"Generic" method required as first step.
GC-O, Headspace GC-MS (scan acquisition)
comparing control and suspect/complaint sample.
Addit
i
onal peaks identified in suspect sample
?
No
Yes
Tentative
identification of peaks
using spectral library
(+ sensory)
Run reference
standard and confirm
retention time and
spectra (SIM).
Perform quantitation
(consider standard
additions depending
on matrix)
Risk assessment
Run with
alternative GC
column.
Additional peaks?
Yes
No
Taint or off-flavour in food reported
Yes
Use more sensitive
method or follow
screening procedure Run reference standard
and confirm retention
time and spectra (SIM).
Perform quantitation
(consider standard
additions depending on
matrix)
No
More sensitive
method required,
SDE with GC-MS
and/or GC-HRMS
(scan)
Additional peaks?
No
Re-interrogate
background information
(sensory data/suspected
compounds).
Follow targeted analysis
approach for possible
‘known’ tainting
compounds.
Yes
Check compounds identified and levels
match sensory descriptors
Is there sufficient information to predict the identity of the compound(s) responsible for the taint?
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... Sources for volatile compounds as initiators of off-flavor are manifold. Ridgway et al. (2010) give a thorough review of published off-flavor compounds and possible sources of these. Due to their low odor thresholds, the identification and quantification of off-odor compounds represent an enormous challenge due to the limited sensitivity of the available instrumentation. ...
... Compounds from different chemical classes are made responsible for this category of off-flavor. On the one hand, halogenated phenols and anisoles such as 2,4,6tribromoanisole or 2,4,6-trichloroanisole are known as musty-smelling compounds with extraordinarily low odor thresholds (e.g., 8 pgL À1 for 2,4,6-tribromoanisole; Ridgway et al., 2010). Halogenated phenols are frequently used for preservation purposes, fungicides, or also fire retardants in polymers. ...
Chapter
With this chapter, we aim to contribute to a deeper understanding of the addressed off-flavor problem and the sensory evaluation of packaging materials. For a decent interpretation of the obtained results and for the identification of the off-flavorcausing compounds, it is necessary to discuss possible ways of contamination, potential sources, and formation pathways of potentially odor-active compounds. The sensory knowledge and the training standard of the panelists are of particular importance in this context and are thus discussed in detail.
... Over the past few decades, many researchers have studied the various aspects of phenolic compounds such as antioxidant activity and disease-preventing properties [3], abiotic and biotic stress tolerance in plants [4], and the role in food industries including taste and color production of food and beverages [5]. On the other hand, phenolics in foods also have negative side effects such as off-flavor, sour taste and discoloration due to enzymatic and non-enzymatic reactions [6], serve as antinutritional factors [3], and have progoitrogenic and carcinogenic role [7]. In addition, phenolic compounds also play an important role in the storage stability of major grain crops such as cereals and millets by inhibiting the lipid peroxidation pathway [8] and are simultaneously oxidized to impart a role in off-flavor and browning of flour/products during storage [9]. ...
Article
Full-text available
Whole grain consumption has been linked to enhanced health benefits, in which phenolic compounds play a vital role. Apart from this, phenolic compounds in cereal grains also make a significant contribution in browning and off-flavor generation of cereal products during storage. This review discusses the nutritional role of phenolic compounds present in major grains, along with their storage stability and how these compounds affect the lipid oxidation of cereal flour during its period of storage. This study also highlights how different processing treatments, i.e., thermal, mechanical, bioprocessing, etc. in the grain/flour affect the phenolic composition and antioxidant properties of the stored products, together with the influence of various treatments on the prevention of browning of flour products. This study will aid the industries and researchers working in the field of nutritional improvement, to select and optimize the treatments with enhanced health benefits, along with an emphasis on consumer's sensory satisfaction.
... TCA may be present at low concentrations (even ppt) and will need to be isolated from high concentrations of matrix components. Moreover, TCA is volatile, care must be taken to avoid losses during sampling and analysis, in particular during any solvent removal step, particularly if concentrating to small volumes (Jakobsen et al. 2003, Ridgway et al. 2010. Combining sensorial methods, such as odour detection ports (ODP) with GC-MSD systems can overcome some drawbacks as assessors directly sniff the GC effluent identifying where sensorial relevant compounds occur in the chromatogram. ...
Conference Paper
Full-text available
Odours from biosolids emission are a complicated matrix. Still a little is known about chemical composition of odours from biosolids. Apart from well-known odorants such as sulphur compounds and ammonia participation of other volatile organic compounds (VOCs) in overall odour may be non neglectable. Especially if this chemicals have low odour threshold, exists in low concentrations and their analytical identification is not trival. In this work occurrence of 2,4,6-Trichloroanisole (TCA) into biosolids emission was measure using GC-MS/O system. Thirty six anaerobically stabilised dewatered biosolids samples from wastewater treatment plant were stored over a 35 days under ambient conditions. Emissions from samples were collected onto Tenax TA sorbent tubes using a U.S. EPA flux hood method on days 1, 3, 7, 10, 14, 21 and 35. Odour intensities classified on a scale of 1 to 4 and character were specified by three ODP operators. TCA was identified in all biosolids cake emission. Intensities levels of TCA do not shown any increasing or decreasing trend as the biosolids were aged. However the intensities of TCA as samples were stored varied.
... Food is a complex mixture of chemical compounds, often numbering well over a thousand different compounds in any individual food item (1)(2)(3). That complexity expands when considering processing (4), the food matrix (5,6), or byproducts, such as those derived from both human and microbial metabolism (7), as well as taints and off-flavors derived from degradation and packaging (8). Nonetheless, any catalog of the metabolites of food compounds coupled to research on their health effects ought to begin with knowledge of a chemical inventory of what is in the food, and in the forms in which it will be consumed. ...
Article
Full-text available
Sweet dessert watermelon (Citrullus lanatus) is one of the most important vegetable crops consumed throughout the world. The chemical composition of watermelon provides both high nutritional value and various health benefits. The present manuscript introduces a catalog of 1,679 small molecules occurring in the watermelon and their cheminformatics analysis for diverse features. In this catalog, the phytochemicals are associated with the literature describing their presence in the watermelon plant, and when possible, concentration values in various plant parts (flesh, seeds, leaves, roots, rind). Also cataloged are the chemical classes, molecular weight and formula, chemical structure, and certain physical and chemical properties for each phytochemical. In our view, knowing precisely what is in what we eat, as this catalog does for watermelon, supports both the rationale for certain controlled feeding studies in the field of precision nutrition, and plant breeding efforts for the development of new varieties with enhanced concentrations of specific phytochemicals. Additionally, improved and comprehensive collections of natural products accessible to the public will be especially useful to researchers in nutrition, cheminformatics, bioinformatics, and drug development, among other disciplines.
Article
The change in consumer behaviour towards healthier lifestyles since the Covid-19 pandemic has seen a steep rise in popularity of low-calorie, low-sugar food and beverage alternatives, like flavoured hard seltzers. In this study, a fully automated, high-capacity sorptive extraction (HiSorb) technique, coupled with gas chromatography–mass spectrometry (GC–MS), was developed to investigate volatile and semi-volatile organic compounds (VOCs and SVOCs) used for flavouring of hard seltzers. As part of methos optimisation we trialled various sample preparation protocols and compared extraction via direct immersion vs. extraction from the headspace. The best headspace and immersive techniques were then further analysed in a ‘stacked’ extraction, whereby extracts from both were collected onto a focusing trap and fired to the GC to produce a single chromatogram. HiSorb probes with 4 alternate phases were compared: Polydimethylsiloxane (PDMS), divinylbenzene/PDMS (DVB/PDMS), carbon wide range/ PDMS (CWR/PDMS) and a triple phase (DVB/CWR/PDMS), with the DVB/PDMS phase proving to extract the highest number of compounds. The DVB/PDMS probe was further applied to a study of four berry/cherry flavour hard seltzer drinks, produced by 4 different leading commercial brands, with 64 compounds extracted and identified. Chemometrics were able to distinguish each brand's flavour profile by detection of unique compounds, these having potential for use as quality and authenticity markers.
Article
Volatile sulfur compounds play a crucial role in the aroma profile of food and fermented beverages. We explore chemical-ionization mass spectrometry (CI-MS) ion-molecule reaction kinetics of commonly used reagent ions to a list of volatile organic sulfur compounds (VOSCs). We compute the rate coefficients of ion-molecule reactions, useful for the accurate identification and quantification of trace gases, using capture collision models based on the electric dipole moment and polarizability of the neutral VOSCs. To this aim, we evaluate molecular properties, such as the electric dipole moment, polarizability, proton affinity (PA), and ionization energy (IE) for each VOSC, by means of hybrid density functional theory (DFT) simulations. The PA and IE values are useful in the selection of appropriate reagent ions to be used in CI-MS. We thoroughly investigate collision rate coefficients at effective temperatures and internal energies, as relevant for highly energetic proton transfer reaction mass spectrometry (PTR-MS) drift tube conditions. The data provided will be valuable for the rapid quantification of VOSCs in food and fermented beverages.
Article
Sensory evaluation is a key component of food production strategy. The classical food sensory evaluation method is time-consuming, laborious, costly, and highly subjective. Since flavor (taste and smell), texture, and mouthfeel are all related to the chemical properties of food, there has been a growing interest in how they affect the senses of food. In the past decades, emerging metabolomics has received much attention in the field of sensory evaluation, because it not only offers a broad picture of chemical composition for sensory properties but also revealed their changes and functions in food proceeding. This article reviewed food chemicals regarding the flavor, smell, and texture of foods, and discussed the advantages and limitations of applying metabolomics approaches to sensory evaluation, including GC-MS, LC-MS, and NMR. Taken together, this review gives a comprehensive, critical overview of the current state, future challenges, and trends in metabolomics on food sensory properties.
Chapter
Modern packaging materials have been developed to protect foods and enhance their shelf life. Nevertheless, some interactions between the packaging material, food, and its surrounding environment may alter the sanitary, nutritional, and sensory characteristics of foods, and eventually, could make them unsuitable for human consumption. In order to control and reduce to a minimum these potential problems, a great effort has been made in the last 5 decades to develop legislation on sanitary aspects of food contact materials at national (e.g., China, European countries, Japan, United States) and international level (e.g., European Union, Common Market of the South (MERCOSUR) in South America). The main objectives of these legislations are to protect consumers' health and food sanitary quality. However, different regulatory requirements worldwide may pose technical barriers to trade. Harmonization and mutual recognition of legislations between different countries and blocks are therefore considered as a necessary future goal. Several useful websites and references are provided.
Chapter
Auxiliary compounds enhance the properties of the initial material. The design and processing of food packaging materials is becoming more and more challenging. This chapter presents the types and properties of barrier coatings, inks and adhesives used for food packaging. The coating process can be described as the application of a very thin layer of a specified functional material to a substrate. Coatings applied on metal are principally aimed at separating metal from a corrosive environment. In the packaging industry, adhesion and wettability play key roles in successful coating applications. Adhesives are an unavoidable part of packaging structure. Many types of adhesives are available for any specific application. They are used to: manufacture rigid packs from cardboard, seal flexible packaging, attach labels, and laminate layers of food contact materials. Various printing inks and varnishes are used for food packaging. The choice of ink may vary depending on the printing method used.
Book
Off-flavours and taints are defined as unpleasant odours or tastes, the first resulting from the natural deterioration of a food, the second from its contamination by some other chemical. Both are major problems for the food industry. With its distinguished editor and international team of contributors, this important collection describes some of the most important causes of taints and off-flavours, how they can be identified and dealt with. The book begins with chapters on sensory and instrumental methods for detecting and analysing taints and off-flavours in food. There are chapters on two of the most common causes of taints: packaging and residues from cleaning and disinfection. A number of chapters discuss the various causes of off-flavours, from those caused by microbial action and oxidation to those caused by the Maillard reaction and interactions between food components. With its authoritative coverage, Taints and off-flavours in food is a standard work for the food industry.
Article
A taint or an off-flavour is caused by the presence of a chemical that imparts a flavour that is unacceptable in the food. This chapter surveys these taints, and includes a number of specific examples. It is possible to differentiate between a taint and an off-flavour by defining the former as the presence of a substance that is totally alien to all foods, and the latter as the chemical reaction of a naturally occurring component in the food, giving a compound with an undesirable taste. For instance, dimethyl trisulphide is a desirable flavour component of cooked cabbage but this same compound is most objectionable when found in red prawns (Whitfield et al., 1981). However, a disinfectant taste due to a chlorophenol is unacceptable in any foodstuff.