476 MASS SPECTROMETRY / Food Applications
Food Applications
F A Mellon, Institute of Food Research, Norwich, UK
can sometimes be conducted on samples that have
undergone minimal preparation. Finally, sample
& 2005, Elsevier Ltd. All Rights Reserved.
preparation for inorganic MS, zinc or chromium in
food or biological fluids, for example, can be highly
demanding because it is essential to avoid contam-
Introduction
ination.
Mass spectrometry (MS) is a very versatile technique
with an established and rapidly growing record of
successful applications in the food and nutrition sci- Major Food Components
ences. Major advances in organic MS over the last
Amino Acids, Peptides, and Proteins
decade, include the refinement and widespread adop-
tion of electrospray ionization (ESI), atmospheric
The analysis of amino acids by GC MS of suitable
pressure chemical ionization (APCI), and matrix-as- volatile derivatives is a well-established technique.
sisted laser desorption ionization time-of-flight (MA- Despite the availability of amino acid analyzers, GC
LDI-TOF) MS. These techniques have substantially
MS is still occasionally used because it is useful for
extended the scope of mass spectrometric applica- qualitative and quantitative analysis of unusual (i.e.,
tions in the food and nutrition sciences. Furthermore,
nonprotein) amino acids. GC MS is also valuable for
alternative mass spectrometric techniques, including
conducting studies of the racemization of amino ac-
isotope ratio MS (CIRMS), inductively coupled
ids during cooking or food processing, when used in
plasma MS (ICP-MS), proton transfer reaction MS
conjunction with chiral GC columns and deuterium
(PTR-MS), and accelerator MS (AMS) are having an
labeling. GC MS methods are also often used for
increased impact in the study of food authenticity,
determining stable isotope labeled amino acids in
nutrient metabolism, and, in the case of PTR-MS,
nutritional, metabolic studies. ESI LC MS may also
flavor research. This article will briefly review appli- be used for determining amino acids.
cations of MS in the analysis of a wide range of food
Peptides and proteins are of interest in several ar-
components, including nutrients, structural constitu- eas of food and nutrition science, including allergenic
ents of foods, flavors, biologically active nonnutri- response, food material properties, flavorings, toxic-
ents, and toxicants.
ology, and nutritional value. An increasing number
of analytical papers in the food and nutrition field
now describe applications of modern MS techniques
Sample Preparation
such as ESI and MALDI-TOF for molecular weight
Sample preparation techniques vary from rudimen- determination or (in MS/MS mode) full or partial
tary to elaborate because of the very wide range of sequencing. The variety of applications appearing in
analytical problems presented in food analysis and the current literature is also impressive: represen-
research. Preparation methods are highly dependent tative examples include the effects of irradiation on
on both the nature of the analyte and on the type of egg proteins, pH-related conformational changes in
mass spectrometric procedure used. At one extreme, egg lysozyme, measurement of lactosylation of whey
the processing of food samples prior to pyrolysis MS proteins, determination of the heterogeneity of casein
(PyMS) may entail little more than the drying of a proteins, authentication of cheeses by determining
few micrograms of material, followed by introduc- protein profiles, characterization of flavor peptides in
tion of the sample into the mass spectrometer on a protein hydrolysates, quantification of wheat glia-
pyrolysis probe. Flavor components are frequently dins, characterization of soya and other legume pro-
isolated by solvent extraction, headspace sampling, teins, and the characterization of the food
or solid-phase microextraction (SPME), or in the preservative peptide antibiotic nisin, its genetically
case of PTR-MS analysis, simply by direct sampling modified variants and its inactivation by glutathione
of volatile components of the analyte. In contrast, by Fourier transform ion cyclotron resonance (FT-
linkage analysis of cell wall polysaccharides in food ICR) MS and MALDI-TOF, respectively. Figure 1
plants requires extensive chemical derivatization shows a comparison of the sustained off-resonance
before samples are analyzed by gas chromato- irradiation collisionally activated decomposition
graphy mass spectrometry (GC MS). Combined (SORI-CAD) spectra of  wild-type nisin A and three
liquid chromatography mass spectrometry (LC MS) genetically modified variants. The ions shifted in
and tandem mass spectrometry (MS/MS or MSn) mass (marked by an asterisk) relative to the wild-type
MASS SPECTROMETRY / Food Applications 477
NISIN A
b30
b32
z30 + S
0.1
(y + 2)26 + S
b31
0.0
(A) 1300 1350 1400 1450 1500 1550 1600 1650
m/z
S5A
b30*
0.10
0.05
b32*
(y + 2)26 + S
b31*
0.00
(B) 1300 1350 1400 1450 1500 1550 1600 1650
m/z
H27K
b32*
b30* z30 + S*
0.10
(y + 2)26 + S*
b31*
0.05
0.00
(C) 1300 1350 1400 1450 1500 1550 1600 1650
m/z
130W-H
b30*
z30 + S*
b32*
0.2
(y + 2)26 + S*
b31*
0.1
0.0
(D)
1300 1350 1400 1450 1500 1550 1600 1650
m/z
Figure 1 Comparison of parts of the SORI-CAD ESI FT-ICR mass spectra of the [M þ 3H]3 þ precursor ions of (A) nisin A (wild-type
nisin), (B) nisin S5A, (C) nisin H27 K, and (D) nisin I30W-H, showing the region containing doubly charged fragment ions. The ions in
the transgenic variants that are shifted in mass compared to nisin A are marked with asterisks. (Reprinted from Lavanant H, Heck A,
Derrick PJ, et al. (1998) Characterization of genetically modified nisin molecules by Fourier transform ion cyclotron resonance mass
spectrometry. European Mass Spectrometry 4: 405 416, with permission; & IM Publications.)
molecule are clearly visible and were used to aid many monosaccharide residues, detailed mass spec-
structural confirmation of the variant molecules. trometric analysis is more difficult than for other
biopolymers. Furthermore, the anomeric configura-
tion and the nature of the linkages between sugar
Carbohydrates and Sugars
residues cannot generally be determined directly by
Carbohydrate analysis is of great importance in the MS. Many different schemes are available to convert
food sciences because of the significant role of sugars to derivatives sufficiently volatile for GC MS
polysaccharides as macronutrients, as major constit- analysis. These often involve trimethylsilylation or a
uents of dietary fiber, and as food structure compo- combination of this derivatization technique with
nents contributing to textural properties, and food oxime formation. A classic method for compositio-
additives. Because of structural similarities between nal and linkage analysis of large polysaccharides
Intensity
Intensity
Intensity
Intensity
478 MASS SPECTROMETRY / Food Applications
involves GC MS of partially methylated alditol d13C% is a measure of natural carbon-13 levels
acetates (PMAAs). Polysaccharides are methylated, against a reference standard and is defined by the
hydrolyzed, and reduced with NaBD4 to deuterated equation:
O-methyl alditols, which are then acetylated and "#
13
C=12Csample
analyzed qualitatively and quantitatively by GC MS. 13
d C% ź 1 1000
13
C=12Cstandard
PMAAs yield characteristic mass spectra that allow
determination of the number, nature, and linkage
position of the monosaccharides that comprise the
Lipids
polysaccharide.
The molecular weights of large polysaccharides
Dietary lipids may be analyzed mass spectrometri-
can be measured with the aid of ESI, in LC MS, cally as long-chain fatty acids, esters, triglycerides,
capillary electrophoresis/mass spectrometry (CE and phospholipids. Although the degree of unsatu-
MS), or direct injection modes, and by MALDI ration of fatty acids may be determined readily from
MS. For example, MALDI-TOF analysis of fruc- electron ionization (EI) mass spectra, double bond
tooligosaccharides has enabled the development of a location presents a more challenging problem. Long-
rapid method for analyzing these molecules in food chain unsaturated fatty acids rearrange extensively
plants. Examples of other important applications of under EI, so fragment ions do not yield reliable in-
organic MS in food carbohydrate analysis include formation regarding double bond position. A num-
determination of the structures of plant oligosaccha- ber of strategies have been devised to overcome these
rides that may be involved in eliciting allergic problems: one of the most popular is derivatization
response and direct analysis of plant cell wall followed by GC MS. Several different procedures
xyloglucans. are available, for example, oxidation followed by si-
Concerns over the adulteration of high value lylation, epoxidation, and the analysis of methoxy or
foods, for example, dilution of maple syrup, fruit dimethyldisulfide derivatives. Alternatively, chemical
juices, or of protected denomination of origin honeys derivatives that localize charge may be generated,
with corn syrup, have been addressed for some time thus preventing charge-induced double bond migra-
by combusting food samples and then measuring
tion. A good example is the formation of volatile
13
CO2/12CO2 ratios by high-precision IRMS. 2-substituted 4,4-dimethyloxazoline derivatives by
Subtle differences in isotope ratio are found in sugars condensation of the fatty acid with 2-amino-2-me-
derived from different sources and this property can thylpropanol. The  charge-localizing derivative is
be used to confirm their origin. Figure 2 exemplifies sufficiently volatile for GC MS analysis and yields
this by demonstrating the linear relationship between
ion clusters separated by 14 Da, reducing to 12 Da
d13C% and the ratio of an adulterant sugar, high when a double bond interrupts the chain. Alternative
fructose corn syrup, to honey sugar. techniques for locating double bond position include
high collision energy  charge-remote MS/MS frag-
mentation of molecules ionized by negative-ion
-10
chemical ionization (CI). Possible alternative tech-
niques employ ESI of lithiated adducts of unsatura-
ted fatty acids and low-energy MS/MS and acetonit-
rile CI ion trap MS/MS of polyunsaturated fatty acid
methyl esters.
Capillary GC MS is useful for identifying the
-20 carbon and unsaturation number of acylglycerols.
However, APCI LC MS can be used to analyze less
volatile acylglycerols that may be unsuitable for GC
MS. APCI LC MS has become the method of choice
for qualitative and quantitative analysis of acylgly-
cerols and, when combined with MS/MS, is capable
of distinguishing fatty acid chains in the sn-2 position
-30
from those in the sn-1/3 positions.
0 20 40 60 80 100
The sensitivity, selectivity, and convenience of po-
% Honey (by volume)
sitive and negative-ion ESI LC MS makes this the
13
Figure 2 Plot of changes in CO2:12CO2 ratio (d13C%, de-
current benchmark technique for analyzing phos-
fined in text) of honey against concentration of high fructose corn
pholipid mixtures. Additional structural information
syrup adulterant. (Reproduced with permission from PDZ
Europa, Norwich, UK.) can be obtained by MS/MS. Where these advanced
13

C
MASS SPECTROMETRY / Food Applications 479
techniques are unavailable, a more laborious ap- to flavor research because of its ability to sample
proach of chromatographic class separation, chem- air directly. PTR-MS has already been applied to
ical degradation, and GC MS analysis of fatty acid analysis of flavor compounds. Other food-related
can be used to generate useful structural information. applications include the control of food produc-
tion by determining volatile organic compounds
Complete Foods and Food-Related Materials produced during fruit ripening and aging, the
study of coffee volatiles and monitoring of meat
PyMS is capable of generating useful data on intact
degradation.
foodstuffs or associated microorganisms (food poi-
Mass spectrometric methods are also useful for
soning bacteria, for example). PyMS is based on the
authenticating flavor components, using methods for
controlled thermal degradation of samples under in-
13
accurately measuring CO2/12CO2 ratios, similar to
ert conditions to produce mixtures of volatile com-
those already described for authenticating sugars
pounds that are swept into the mass spectrometer ion
(above). If more detailed analysis is required GC/
source and ionized by EI or CI. The resulting  finger-
combustion/isotope ratio MS will yield accurate iso-
print spectrum of the analyte contains characteristic
tope ratios on individual components of a flavor
features that can be classified by chemometric meth-
sample.
ods. Pyrolysis is sometimes combined with GC MS
in order to extract more information from the ana-
lyte. Applications of PyMS in the food sciences in-
Nutrition Studies
clude quality assurance and authentication of food
and drinks, analysis of cell wall material in food Stable Isotope Methods
plants, and identification of food microorganisms.
Interest in the use of stable isotope MS for studying
Direct analysis of microorganisms, including food
both the nutritional value of foods and diets and
poisoning microorganisms, has also been conducted
fundamental aspects of nutrient metabolism in hu-
by MALDI-TOF MS. This promising technique can
mans has increased considerably. The only major
be used to characterize bacteria rapidly by genus,
drawbacks of stable isotope studies are associated
species, and strain.
with the presence of endogenous isotopes of the
elements under investigation. Sufficient label must
Flavors and Taints
be administered to generate a measurable increase
Because most flavor components are highly volatile, in isotope ratio. However, care is needed to ensure
EI and CI GC MS have been primary techniques in physiological dosing as administration of excessive
flavor analysis and research since the early 1960s. doses yield physiologically contentious data.
For example, B1000 discrete compounds have been Conversely, administration of small quantities of la-
identified in coffee volatiles using capillary GC MS bel requires careful and accurate measurement of
methods. isotope ratios because the enriched material is diluted
The ease with which SPME GC MS studies may by the endogenous nutrients. In the case of mineral
be conducted has made this an important and useful metabolism studies, additional precautions are nec-
technique for sampling flavors and taints. GC MS essary because of the possibility of contamination
has been supplemented by LC MS techniques for during sample processing.
studying involatile flavor precursors or semivolatile Stable isotope studies usually involve administra-
or involatile food components that have important tion of the enriched stable isotope in or with a meal.
flavor characteristics. The method of labeling depends on the type of study
The availability of a large knowledge base of flavor undertaken. For elements such as selenium, where
profiles (largely defined by GC MS analysis) and re- absorption and metabolism are highly dependent on
cent instrumental advances have resulted in a shift in chemical form, it is usually necessary to use an in-
emphasis of mass spectrometric applications in flavor trinsic label (i.e., one that is biosynthetically incor-
research. Instead of characterizing complex mixtures porated into the food). Conversely, minerals believed
of volatiles, several researchers are now focusing on to form a  common pool in the digestive system may
flavor release and, more specifically, on sampling be mixed directly with the food (extrinsic labeling).
volatiles released into the mouth and nose. By using a In some cases a second isotope is injected or infused
special APCI probe coupled to a mouth or nose intravenously to correct for endogenous losses. Sam-
piece, it is possible to conduct dynamic, breath-by- ples of breath, blood, urine, saliva, or feces are
breath analyses of air expired during eating. The re- then collected for an appropriate period and subject-
cent development of PTR-MS for online trace gas ed to isotopic analysis. Isotope ratio measurement
monitoring has considerable potential for application often requires specialized instrumentation such as
480 MASS SPECTROMETRY / Food Applications
high-precision IRMS or dedicated inorganic instru- dilution-based analyses, for evaluating and calibra-
ments such as ICP-MS. ting alternative, non-MS techniques. However, the
most prominent role for MS in vitamin research is in
Mineral Nutrients studies of the metabolism of vitamins in humans,
especially by LC MS or LC MS/MS. The newer LC
Although several different mass spectrometric meth-
MS techniques of APCI and ESI are particularly
ods have been deployed to determine enriched stable
useful in this respect because many vitamins are too
isotopes in human studies of nutrient mineral me-
labile for EI and CI MS.
tabolism, thermal ionization mass spectrometry
Vitamins D2 and D3 and their major metabolites
(TIMS) and particularly ICP-MS are now used al-
have been studied extensively by GC MS of volatile
most exclusively. ICP-MS is rapid, very sensitive, and
derivatives; these studies include quantitative deter-
sample preparation and introduction is often simpli-
mination by isotope dilution. More recently, ESI LC
fied. Furthermore, ICP-MS can be coupled directly to
MS and LC MS/MS have been used in the qualitative
separation techniques such as size-exclusion chro-
and quantitative measurement of vitamin D and
matography (SEC), high-performance liquid chro-
vitamin D analogs.
matography (HPLC), or CE so that speciation, the
The association of folates with reduced chronic
determination of the chemical form of particular ele-
disease risk and prevention of neural tube defects has
ments, may also be studied. The two major draw-
generated increased interest in studies of the metab-
backs of ICP-MS, low precision relative to TIMS and
olism of these B group vitamins. Recent activity has
interference from polyatomic ions in the argon plas-
focused on developing improved mass spectrometric
ma, have largely been overcome by new generations
methods for determining the absorption, metabolism,
of instruments equipped with multiple collectors and
and bioavailability of these molecules. The folates are
collision/reaction cells, respectively.
polar, involatile molecules that are unstable in solu-
A wide range of human studies has been conducted
tion and must be derivatized if they are to be analyzed
using enriched stable isotopes of nutrient minerals.
by EI or CI MS. Pioneering studies of the human
Applications include the determination of the ab-
metabolism of folates were first conducted by selected
sorption and metabolism of iron, zinc, calcium, cop-
ion monitoring (SIM) GC MS of derivatized extracts
per, selenium, and molybdenum. An example of the
from biological fluids. Although the GC MS method
type of information that can be obtained is provided
has provided useful data on the kinetics of folate
by a study of iron absorption from different weaning
metabolism and on urinary excretion of folate and
foods, and the effects of vitamin C on iron absorp-
metabolites, the method has several drawbacks. Im-
tion. These measurements, conducted using enriched
provements both in mass spectrometric techniques
57 58
stable isotopes of Fe and Fe, demonstrated a do-
and in speed of analysis were clearly desirable and a
ubling of iron absorption when a drink containing
number of groups have focused on developing LC
50 mg of vitamin C was administered with the food.
MS methods. Negative-ion ESI techniques developed
A recent development, especially useful for con-
to determine the four main food and supplementary
ducting long-term studies of the effect of diet on
folates, folic acid, 5-methyltetrahydrofolic acid, tet-
metabolism, is to administer extremely low levels of
rahydrofolic acid, and folinic acid, in selected food-
41
long-lived radioisotopes, e.g., Ca, that are then
stuffs and a vitamin supplement demonstrated the
measured by AMS. Because the activity of the radi-
feasibility of using ESI LC MS in folate analysis.
6
oisotope is extremely low (typically o10 of an-
Other laboratories have subsequently reported suc-
nual background radiation dose), it is considered to
cessful measurement of stable isotope labeled folates
be safe for human use. AMS opens up the exciting
in human plasma and/or urine by positive-ion ESI
possibility of conducting long-term metabolic and
LC MS, negative-ion LC MS/MS (in multiple reac-
dietary intervention studies where required; for ex-
tion monitoring mode), and SIM negative ion
ample, in studies of bone metabolism.
LC MS. Limits of quantification were sufficient to
13 15
conduct human metabolic studies using C, N,
Vitamins
2
and H folates, labeled both extrinsically and intrin-
Although vitamins can be determined, both quali- sically, on spinach and fortified cereal grain. The
tatively and quantitatively, by MS, routine analysis is low-collision-energy negative-ion tandem ESI mass
usually best conducted by other means (e.g., HPLC spectrum of 5-formyl tetrahydrofolate is shown in
with ultraviolet (UV) or fluorescence detection, Figure 3.
immunoassay methods, or microbiological methods). AMS has also been used to determine the meta-
Analytically, MS does have an important role as a bolic fate of folates labeled with low levels of the
14
reference technique, especially when used in isotope radioactive isotope C.
MASS SPECTROMETRY / Food Applications 481
315
100
%
272
228
357
472
400
444
164
343
0
150 175 200 225 250 275 300 325 350 375 400 425 450 475 500
m/z
Figure 3 The MS/MS product ion spectrum of m/z 472, the [M H] ion of 5-formyl tetrahydrofolate, at a collision energy of 35 V.
(& Institute of Food Research, reproduced with permission.)
The ability to conduct bioavailability studies on electron capture GC MS of trimethylsilyl derivatives
foods labeled intrinsically with stable isotopes is par- fulfills these increased demands and yields. The
ticularly important as this type of labeling is the  gold method worked on 200 ml blood samples, the amount
standard for metabolic studies, i.e., intrinsic label of blood typically collected in a heel-prick sample
should mimic the behavior of endogenous nutrients from an infant, and yielded measurements on en-
most closely. However, the mass spectrometric meas- richments as low as 0.01% of circulating retinol-D8.
urement of the metabolism of intrinsically stable iso- More recently, both APCI LC MS and LC MSn
tope labeled materials is far more challenging than methods have been developed to measure retinol
measuring extrinsically labeled nutrients. Low levels conjugates such as retinyl palmitate (which appears
of isotope incorporation must be determined in small in the blood soon after vitamin A containing meal is
samples and it is only quite recently that modern LC consumed). These techniques have advantages over
MS and LC MS/MS methods, as demonstrated by GC MS methods because there is no need to hydro-
the folate studies described above, have begun to rise lyze samples to release free retinol, or for derivat-
to this challenge. ization for GC MS. Carotenoid (pro-vitamin A)
Vitamin A is a generic descriptor for a family of metabolism is also being studied by LC MS tech-
fat-soluble vitamins that has the biological activity of niques because of epidemiological evidence of their
retinol, one of the most active and bioavailable putative role in cancer prevention. Although ESI LC
members of the group. Retinol, retinoids, and their MS has shown promise in preliminary mass spectro-
derivatives yield characteristic EI spectra, a property metric studies, APCI LC MS is now the method of
that has been exploited for over 25 years by GC MS choice because of its robustness and tolerance of a
methods that determine liver stores of retinol non- wider range of organic solvents.
invasively, following oral administration of deute- Many other vitamins have been determined by
rated retinol. A simple mathematical formula derives mass spectrometric methods; representative exam-
liver stores of retinol from isotope composition in ples include APCI LC MS/MS measurement of toco-
plasma. Various EI and positive ion CI GC MS pro- pherols and LC MS measurement of K vitamins.
cedures have been used; the most successful tech-
niques involve measurement of silylated derivatives
of retinol. Although these methods have provided Trace Components in Foods
useful nutritional data, further improvements in sen-
Food Additives
sitivity were still desirable for conducting serial in-
fant studies or when sampling under nonideal field
Food additives comprise a wide variety of com-
conditions. A technique based on negative ion pounds that are generally monitored by techniques
482 MASS SPECTROMETRY / Food Applications
other than MS; however, occasional quantitative conjugates of isothiocyanate breakdown products of
applications do occur, exemplified by GC MS deter- glucosinolates.
mination of antioxidants in stored products. Phenolics are a distinctive feature of all plant tis-
sues and are of interest because they can affect pal-
atability, taste, nutritional value, and particularly the
Biologically Active Nonnutrients (Dietary
health properties of foods. For example, the flavono-
Phytochemicals)
ids occur very widely in plants and there is great
Biologically active (bioactive) nonnutrients in foods
interest in their role as protective factors in the diet.
comprise a wide range of phytochemical substances.
More recently, the modern methods of LC MS ana-
Lack of space permits discussion of mass spectro-
lysis, APCI and electrospray, have been applied to
metric analysis of only a small range of these com-
the detection and quantification of flavonoids and
pounds here.
isoflavonoids. Although early mass spectrometric
Glucosinolates (Figure 4) and their biologically
techniques for analyzing these molecules focused on
active breakdown products are found in many plant
GC MS methods (after appropriate derivatization),
foods. More than 100 different types of glucosinolate
the newer LC MS methods are now widely used. For
have been isolated from plants. Although some
example, isoflavones and their conjugates have been
glucosinolates may have toxic (e.g., goitrogenic)
determined in soy foods by positive and negative ion
properties, they are known to be potent inducers of
APCI LC MS. ESI and APCI LC MS methods are
Phase II enzymes that protect against carcinogens
also now used for conducting studies of flavonoid
and other toxic electrophiles.
metabolism, by following the disappearance and
The structural variability is in the aglycone, R that
deconjugation of flavonoid glycosides and the ap-
may comprise linear or branched alkyl and alkenyl
pearance of glucuronides, sulfates, and methylated
side chains, alcohols, methylthioalkyl, methylsulfinyl,
metabolites.
aralkyl, or heterocyclic groups. GC MS is a useful
mass spectrometric technique for analyzing volatile
Natural Toxicants
glucosinolate breakdown products. Negative-ion ESI
LC MS is now the method of choice for determining Mycotoxic secondary metabolites produced by As-
intact glucosinolates and positive ion APCI LC MS pergillus (aflatoxins) and Fusarium (tricothecenes,
for analyzing the more thermally labile breakdown etc.) food-spoilage molds comprise two of the most
products (e.g., sulforaphane) and their human prominent groups of natural toxicants. Many differ-
metabolites. ESI LC MS and MS/MS are also ent mass spectrometric techniques, including EI,
useful for conducting metabolic studies, for positive and negative ion CI, GC MS, LC MS, super-
example, by detecting and determining glutathione critical fluid chromatography/mass spectrometry, and
S- -D-Glucose
R-NCS
Isothiocyanate
R Myrosinase
R-CN
-
Nitrile
NOSO3 K+
Sulfate +
Glucose R-SCN
Thiocyanate
R group Semisystematic name Common dietary source
CH3-
Methylglucosinolate Capers (Capparis spinosa)
CH3-SO-(CH2)4-
4-Methylsulfinylbutylglucosinolate
Broccoli (Brassica oleracea)
2-Phenylethylglucosinolate Watercress (Nasturtium officinalis)
CH2-CH2-
CH2-
3-Indolylmethylglucosinolate Most Brassica Crops
NH
Figure 4 General structure of the glucosinolates and their common myrosinase hydrolysis products. (Reproduced with permission
from Institute of Food Research; & Institute of Food Research.)
MASS SPECTROMETRY / Food Applications 483
MS/MS have been devised to monitor the levels of The importance of ICP-MS in multielement anal-
mycotoxins in foods, body fluids, and tissues. The ysis of foodstuffs is already well established, as is the
most recent developments include ESI LC MS deter- use of this technique in human metabolic studies.
mination of aflatoxins down to low picogram levels. Both types of application are being augmented by
Additional selectivity was provided by MS/MS se- increased applications of combined chromatography/
lected reaction monitoring. Examples of other natu- ICP-MS for conducting speciation studies. The
rally occurring food toxicants determined with the advent of a new generation of high-precision isotope
aid of MS include mutagenic compounds related to ratio ICP-MS instruments also opens up the exciting
quinoxaline that may be formed in cooked meats. possibility of conducting metabolic studies without
The most notorious recent example of a food natural using enriched labels, by observing isotopic fraction-
toxicant is the discovery, made with the aid of GC ation between different body compartments. High-
MS, ESI LC MS, and LC MS/MS, that the genotoxic precision ICP-MS also has considerable potential in
carcinogen acrylamide is formed during some coo- food authentication (by linking isotopic composition
king processes. to geographical origin, for example).
Fundamental studies of the metabolism of pro-
Anthropogenic Toxicants
teins, fats, and starches by GIR-MS are increasing
and it is anticipated that practical applications to the
Many examples of mass spectrometric methods for
metabolism of extrinsically labeled foods will make
determining toxic or potentially deleterious ant-
an impact in the future.
hropogenic compounds in foods can be found in
Mass spectrometry has a central role in the
the scientific literature. The range of compounds
postgenomic science of proteomics, the qualitative
analyzed is wide and includes dioxins, polyaromatic
and quantitative comparison of the entire protein
hydrocarbons, pesticide and veterinary drug residues,
complement of a genome under different conditions.
plasticizers from packaging materials, and environ-
The new science of metabolomics, the global, quan-
mental contaminants. LC MS, MS/MS, GC MS,
titative analysis of all the low and intermediate mo-
and GC MS/MS techniques are used widely for de-
lecular weight metabolites expressed by a genome
termining these compounds down to parts per billion
under specific conditions, has obvious applications in
or even parts per trillion levels. For example, polar
food science, for example, in assessing the safety of
organophophorus pesticides can be quantified by
1
transgenic plants or in studying environmental ef-
LC MS/MS down to levels of 0.01 mg kg in fruits
fects on food poisoning microorganisms and mass
and vegetables and dioxins are regularly determined
spectrometry is one of the pivotal analytical tech-
in food matrices at femtogram levels.
niques in metabolomics. This type of application is
Isotope dilution mass spectrometry is an accurate
expected to increase in the future.
and sensitive technique for determining toxic trace
elements in food matrices. Lead, cadmium, and
See also: Carbohydrates: Overview. Elemental Specia-
thallium have been analyzed rapidly down to very
tion: Overview. Food and Nutritional Analysis: Over-
low levels by ICP-MS. The latter technique is par-
view. Gas Chromatography: Mass Spectrometry.
ticularly useful for simultaneous measurement of a
Lipids: Overview. Liquid Chromatography: Liquid
wide range of elements. Because the toxicity of an
Chromatography Mass Spectrometry; Food Applications.
element can be highly dependent on its chemical
Mass Spectrometry: Overview; Principles; Ionization
form, ICP-MS is also useful in the speciation of toxic
Methods Overview; Atmospheric Pressure Ioniza-
minerals in foodstuffs by combination with HPLC or
tion Techniques; Electrospray; Matrix-Assisted Laser
SEC.
Desorption/Ionization; Pyrolysis. Proteins: Traditional
Methods of Sequence Determination. Vitamins: Over-
view.
Future Trends
Enormous advances in the scope and sensitivity of
mass spectrometric techniques have occurred in the
Further Reading
last decade. The use of modern techniques of organic
Alomirah HF, Alli I, and Konishi Y (2000) Applications of
MS, particularly APCI and ESI LC MS, CE/MS, and
mass spectrometry to food proteins and peptides. Journal
MS/MS, has grown apace in the food and nutritional
of Chromatography A 893: 1 21.
sciences. Applications of MALDI-TOF in the food
Byrdwell WC (2001) Atmospheric pressure chemical ion-
sciences are also increasing, although at a lower rate
ization mass spectrometry for analysis of lipids. Lipids
(the frequent need for chromatographic separation in
36: 327 346.
food-related applications has led to an understand- Careri M, Bianchi F, and Corradini C (2002) Recent
able bias toward LC MS methods). advances in the application of mass spectrometry in
484 MASS SPECTROMETRY / Forensic Applications
food-related analysis. Journal of Chromatography A by means of proton-transfer-reaction mass spectrometry
970: 3 64. (PTR-MS) medical applications, food control and
Dennis MJ (1998) Recent developments in food authenti- environmental research. International Journal of Mass
cation. Analyst 123: 151R 156R. Spectrometry and Ion Processes 173: 191 241.
Fenselau C and Demirev PA (2001) Characterization of Linforth RST, Ingham KE, and Taylor AJ (1996) Flavour
intact microorganisms by MALDI mass spectrometry. Science: Recent Developments. Cambridge: Royal Soci-
Mass Spectrometry Reviews 20: 157 171. ety of Chemistry.
Garrido-Frenich A, Arrebola FJ, Gonzalez-Rodriguez MJ, Mellon FA, Self R, and Startin JR (2000) Mass Spectrome-
Vidal JLM, and Diez NM (2003) Rapid pesticide analysis try of Natural Substances in Food. Cambridge: Royal
in post-harvest plants used as animal feed by low-pres- Society of Chemistry.
sure gas chromatography-tandem mass spectrometry. Pico Y, Blasco C, and Font G (2004) Environmental and
Analytical and Bioanalytical Chemistry 377: 1038 1046. food applications of LC-tandem mass spectrometry in
Guillou C, Lipp M, Radovic B, et al. (1999) Use of pesticide-residue analysis: An Overview. Mass Spect-
pyrolysis mass spectrometry in food analysis: Applica- rometry Reviews 23: 45 85.
tions in the food analysis laboratory of the European Van der Werf MJ, Schuren FHJ, Bijlsma S, Tas AC, and van
Commissions Joint Research Centre. Journal of Analyt- Ommen B (2001) Nutrigenomics: Application of geno-
ical and Applied Pyrolysis 49: 329 335. mics technologies in nutritional sciences and food tech-
Kuiper HA, Kleter GA, Noteborn HPJM, and Kok EJ nology. Journal of Food Science 66: 772 780.
(2001) Assessment of food safety issues related to gene- Wolfender JL, Terreaux C, and Hostettmann K (2000) The
tically modified foods. Plant Journal 27: 503 528. importance of LC MS and LC NMR in the discovery of
Lindinger W, Hansel A, and Jordan A (1998) On-line new lead compounds from plants. Pharmaceutical
monitoring of volatile organic compounds at pptv levels Biology (Supplement) 38: 41 54.
Forensic Applications
R J Lewis, Civil Aerospace Medical Institute, Oklahoma
sporting events. MS-based methodologies are also
City, OK, USA
routinely used for the analysis of materials related to
RHLiu, Fooyin University, Kaohsiung Hsien, Taiwan
arson, explosives, and synthetic polymers. Applica-
tions in the characterization of inorganic elements
Published by Elsevier Ltd.
for forensic science purposes have also been reported.
This article is a revision of the previous-edition article by R H Liu,
Most MS applications utilize electron ionization
pp. 2989 2996, & 1995, Elsevier Ltd.
(EI) or chemical ionization (CI), a quadrupole analy-
zer, and a gas chromatograph (GC) as the sample in-
Introduction troduction device. However, other MS methodologies
such as tandem MS (MS/MS) and isotope-ratio are
Forensic science is the application of science to prob-
becoming more common. Recent advances in sample
lems encountered in the courts of law. Forensic lab-
evaporation/ionization, high-mass ion resolution, and
oratories specialize in the analysis, identification, and
liquid chromatography (LC) MS interfacing tech-
interpretation of physical evidence. Typically, analy-
nologies have significantly expanded the potential fo-
ses performed in such laboratories are concerned
rensic applications of MS-based approaches to the
with determining (1) component identification of a
analysis of biomolecules, i.e., proteomics.
sample, (2) quantitation or purity of sample compo-
nents, or (3) similarities or differences between two
or more samples. With automated instrumentation
Applications Resulting from
widely available, highly specific mass spectrometry
Advances in Ionization and Ion
(MS)-based technologies are now the most valuable
Resolution Technologies
tools used to achieve these desired analytical goals.
MS-based techniques, in the forensic setting, are With recent advances in matrix assisted laser des-
primarily used for the identification of specific com- orption/ionization (MALDI) and electrospray LC
ponents in drug-related samples. These samples may MS interface technologies (awarded the 2002 Nobel
contain drugs in dosage forms or in biological ma- prize in chemistry), MS can now be successfully
trices. The drugs analyzed may be abused by the applied to the analysis of compounds with high
general population, a specific age group, or those molecular weights or polar functional groups. Time-
used as performance enhancers in human or animal of-flight (TOF) MS is typically used to resolve and