Additives and contaminants 2 - Principle of food chemistry

Other Additives
In addition to the aforementioned major
groups of additives, there are many others in-
cluding clarifying agents,
humectants,
glazes,
polishes,
anticaking
agents, firming agents,
propellants, melting agents, and enzymes.
These intentional additives present consider-
able scientific and technological problems as
well as
legal,
health, and public relations
challenges. Future introduction of new addi-
tives will probably become increasingly dif-
ficult, and some existing additives may be
disallowed as further toxicological studies
are carried out and the safety requirements
become more stringent.
INCIDENTAL ADDITIVES OR
CONTAMINANTS
Radionuclides
Natural radionuclides contaminate air,
food, and water. The annual per capita intake
of natural radionuclides has been estimated
to range from 2 Becquerels (Bq) for
232
Th
to

about 130 Bq
for
40
K
(Sinclair 1988). The
Bq is the International System of Units (SI)
unit of radioactivity; 1 Bq = 1 radioactive
disintegration per second. The previously
used unit of radioactivity is the Curie (Ci); 1
Ci = 3.7 x
10
10
disintegrations per second,
and 1 Bq = 27 x
10~
12
Ci. The quantity of
radiation or energy absorbed is expressed in
Sievert (Sv), which is the SI unit of dose
equivalent. The absorbed dose (in Gy) is
multiplied by a quality factor for the particu-
lar type of radiation. Rem is the previously
used unit for dose equivalent; 100 rem = 1
Sv.
The effective dose of Th and K radionu-
clides is about 400
|nSv
per capita per year,
with half of it resulting from
40

K.
The total
exposure of the U.S. population to natural
radiation has been estimated at about 3
mSv.
In addition, 0.6 mSv is caused by man-made
radiation (Sinclair 1988).
Radioactive
Fallout
Major concern about rapidly increasing
levels of radioactive fallout in the environ-
ment and in foods developed as a result of
the extensive testing of nuclear weapons by
the United States and the Soviet Union in the
1950s. Nuclear fission generates more than
200 radioisotopes of some 60 different ele-
ments. Many of these radioisotopes are harm-
ful to humans because they may be incor-
porated into body tissues. Several of these
radioactive isotopes are absorbed efficiently
by the organism because they are related
chemically to important nutrients; for exam-
ple,
strontium-90 is related to calcium and
cesium-137
to potassium. These radioactive
elements are produced by the following
nuclear reactions, in which the half-life is
given in
parentheses:

p-
p-
90
Kr(BBsCC)
^
90
Rb(IJmIn)
^
90
Sr
(28
y)
P- p-
137
I
(22
sec)
**
137
Xe
(3.8
min)
*•
137
Cs
(29
y)
The long half-life of the two end products
makes them especially dangerous. In an
atmospheric nuclear explosion, the tertiary

fission products are formed in the strato-
sphere and gradually come down to earth.
Every spring about one-half to two-thirds of
the fission products in the stratosphere come
down and are eventually deposited by precip-
itation. Figure
11-6
gives a schematic out-
line of the pathways through which the
fallout may reach us.
Previous page
Among the radioisotopes that can be taken
up in the food chain, the most significant as
internal radiation hazards are
barium-140,
cesium-137,
iodine-131,
iodine-133,
stron-
tium-89,
and
strontium-90.
131
I
is chemically similar to ordinary
iodine and, therefore, accumulates in the thy-
roid gland. It has a half-life of eight days and
is a beta-gamma emitter. Because milk is
produced year round and is consumed within
one half-life, the presence of this isotope in

milk was a major concern during the atmo-
spheric testing period in the early
1960s.
137
Cs
has a half-life of 29 years and,
because of its chemical similarity to potas-
sium, accumulates in muscle tissue.
137
Cs
may cause several types of cell damage,
including genetic damage. It is not retained
in the body for a long time.
137
Cs
is a gamma
emitter.
90
Sr
has a half-life of 28 years and is a beta
emitter. This isotope collects in the bones
because of its chemical similarity to calcium.
It can result in bone cancer and leukemia.
Children are very sensitive to this isotope
because they require large amounts of cal-
cium for bone formation and as a result
deposit relatively more
90
Sr.
They also face a

longer life span, which is important because
radiation effects are cumulative.
In 1964, the rate of fallout of
90
Sr
was
about 40 pc/day/m
2
. Total intake of
90
Sr
dur-
ing that period was about 40 pc/day/person
in some Western countries. Because about
3,000 m
2
of arable land are required to pro-
duce food for one person, the total amount of
90
Sr
deposited on that surface was estimated
to be 120 nc per day. This means a reduction
of about 3000-fold, indicating a highly effec-
tive barrier mechanism. The amount of
radioactivity gradually diminished after the
United States and the Soviet Union ceased
their atmospheric test programs. Emergency
measures for decontaminating essential food
items such as milk have been developed.
Such procedures use ion-exchange methods

to remove radioisotopes (Glascock
1965).
The distribution of radioactive fallout in
the environment and therefore in foods is
nonuniform.
The distribution is influenced
by latitude; most of the fallout comes down
between 30° and 60° latitude (Miettinen
Figure
11-6
Pathways
of the
Transfer
of
Nuclear
Fallout
to
Humans
MAN
INGESTION
WASTES
ANIMALS
ANIMAL
PRODUCTS
FORAGE
CROPS
IRRIGATION
FISH
SHELLFISH
WATER

WATER
SOIL
PRECIPITATION
FALLOUT
NUCLEAR
TEST
AIR
EXHALATION
1967).
Because the fallout comes down with
precipitation, precipitation is a major factor.
In addition, uptake by plants is influenced by
soil type. Wiechen (1972) found that the
137
Cs
content of milk from a small herd of
cows averaged 26 pc per kg when the ani-
mals grazed on an area of sandy soil but
increased to 244
pc/kg
when they were trans-
ferred to moorland. The primary contamina-
tion level of the two soil types was 280 and
262 pc per kg, respectively. The higher trans-
fer rate of
137
Cs
in the moorland soil-grass-
milk chain was the result of the low potas-
sium content of this soil

(180
mg/kg versus
720
mg/kg
in sandy soil) and, to a lesser
extent, different mobilities of Cs and K in the
various soils. Lindell and Magi
(1965)
found
a general similarity between precipitation
distribution and distribution of
137
Cs
levels in
milk. In Sweden, the lowest levels of the iso-
tope
90
Sr
were found for the island of Got-
land, which has low precipitation and a soil
rich in calcium.
Johnson and
Nayfield
(1970) reported a
case of true selective concentration of
137
Cs.
They found that high levels of
137
Cs

in game
animals from the southeastern United States
resulted from their feeding on mushrooms
in wooded areas. Common gill mushrooms
(Agaricaceae)
from these areas had
137
Cs
levels as high as 29,000
pc/kg
wet weight,
with a mean of 15,741
pc/kg.
These elevated
levels occurred without similar concentration
of potassium-40. White-tailed deer in these
regions had
137
Cs
levels ranging from 250 to
152,940 pc/kg body weight.
The 1986 nuclear reactor accident at Cher-
nobyl in the Soviet Union distributed radio-
active fallout over most of Western Europe
and the rest of the world. In addition to short-
term problems with radionuclides of short
half-life, there are ongoing concerns in coun-
tries far removed from the source of the con-
tamination. In the United Kingdom there are
concerns over the contamination of sheep,

whose levels still exceed the interim limit of
1,000
Bq/kg;
bentonite is being used experi-
mentally to reduce Cs uptake from grazing.
In addition to the Chernobyl accident,
there have been nuclear reactor accidents at
Windscale in the United Kingdom in 1957
and at Three Mile Island in the United
States in 1979. Low-level emissions from
nuclear reactor plants apparently are not
uncommon.
Pesticides
Contamination of food with residues of
pesticides may result from the application of
these chemicals in agricultural, industrial, or
household use. Nearly 300 organic pesticides
are in use, including insecticides, miticides,
nematocides, rodenticides, fungicides, and
herbicides. The most likely compounds to
appear as food contaminants are insecticides,
of which there are two main
classes—chlori-
nated hydrocarbon insecticides and organo-
phosphorous insecticides.
The chlorinated hydrocarbon insecticides
can be divided into three
classes—oxygen-
ated compounds, benzenoid nonoxygenated
compounds, and nonoxygenated nonben-

zenoid compounds (Exhibit
11-3)
(Mitchell
1966).
In addition to the pesticide com-
pounds, there may be residues of their metab-
olites,
which may be equally toxic. Two
important properties of the chlorinated hydro-
carbons are their stability, which leads to per-
sistence in the environment, and their
solubility in fat, which results in their depo-
sition and accumulation in fatty tissues. The
structure of some of the chlorinated hydro-
carbon insecticides is given in Figure
11—7.
Aldrin
is a technical compound containing
about 95 percent of the compound
Exhibit 11-3 Classes of Chlorinated Hydrocar-
bon Insecticides
Class
I—Oxygenated
Compounds
• Chlorobenzilate • Methoxychlor
• Dicofol • Neotran
• Dieldrin • Ovex
• Endosulfan • Sulfenone
• Endrin • Tetradifon
• Kepone

Class
II—Benzenoid,
Nonoxygenated
Compounds
• BHC •
Perthane
• Chlorobenside • TDE
• DDT •
Zectran
• Lindane
Class
III—Nonoxygenated,
Nonben-
zenoid Compounds
• Aldrin • Mirex
• Chlordan • Strobane
• Heptachlor • Toxaphene
Source: From L.E. Mitchell, Pesticides: Prop-
erties and Prognosis, in Organic Pesticides in
the
Environment,
R.F. Gould, ed., 1966, Ameri-
can Chemical Society.
l,2,3,4,10,10-hexachloro-l,4,4a,5,8,8a-hexa-
hydro-exo-1,4-£rafo-exo-5,8-dimethanonaph-
thalene. It has a molecular weight of 365,
formula
C
12
H

8
Cl
6
,
and contains 58 percent
chlorine. Residues of this compound in ani-
mal and plant tissues are converted into
dieldrin by epoxidation. The epoxide is the
stable form and, thus, it is usual to consider
these compounds together.
Dieldrin contains about 85 percent of the
compound 1, 2, 3, 4, 10, 10-hexachloro-6, 7-
epoxy-1,
4, 4a, 5, 6, 7, 8,
8a-octahydro-exo-l,
4-endo-exo-5,8-dimethano-naphthalene
(HEOD). It has a molecular weight of 381,
formula
C
12
H
8
Cl
6
O,
and contains 56 percent
chlorine. DDT is a technical compound that
contains about 70 percent of the active ingre-
dient pp'-DDT. In addition, there are other
isomers, including op'-DDT, as well as

related compounds such as TDE or rhothane.
The insecticide
pp'-DDT
is
1,1,1-trichloro-
2,2-di-(4-chlorophenyl) ethane, formula
C
14
H
9
Cl
5
.
It has a molecular weight of 334.5
and contains 50 percent chlorine. Residues
of DDT in animal tissue are slowly dehydro-
chlorinated
to
pp'-DDE,
which may occur at
levels of up to 70 percent of the original
DDT. It is usual to combine DDT, DDE, and
TDE in one figure as "total DDT equiva-
lent."
Heptachlor contains about 75 percent of
1,4,5,6,7,10,10-heptachloro-4,7,8,9-tetrahyro-
4,7-methyleneindene,
formula
C
10

H
5
Cl
7
.
It
has a molecular weight of 373.5 and contains
67 percent chlorine. In animal and plant tis-
sues,
it epoxidizes to heptachlor epoxide,
which is analogous in structure to HEOD
(dieldrin).
Although relatively stable, the organochlo-
rine pesticides undergo a variety of reactions
that may result in metabolites that are as
toxic or more toxic to mammals than the
original compound. An example is the effect
of ultraviolet light on DDT (Van Middelem
1966).
Under the influence of ultraviolet
light and air, 4,4'-dichlorobenzophenone is
formed. Without air,
2,3-dichloro-l,l,4,4-tet-
rakis-(p-chlorophenyl)-2-butene
is formed.
The latter may be oxidized to 4,4'-dichlo-
robenzophenone (Figure
11-8).
In mamma-
lian tissue, 2,2-bis

(p-chlorophenyl)
acetic
acid (DDA) is formed by initial dehydrochlo-
rination of DDT to DDE, followed by
hydrolysis to DDA (Figure
11-9).
The organophosphorous insecticides are
inhibitors of cholinesterase and, because of
their water solubility and volatility, create
less of a problem as food contaminants than
the chlorinated hydrocarbons. A large num-
ber of organophosphorous insecticides are in
use;
these can act by themselves or after oxi-
dative conversions in plants and animals
(Exhibit
11-4).
The water solubility of these
compounds varies widely, as is indicated by
Table
11-6.
The organophosphorous insecti-
cides may be subject to oxidation, hydroly-
Figure
11-7 Structure of Some Chlorinated Hydrocarbon Pesticides
HEPTACHLOR
EPOXIDE
HEPTACHLOR
pp
1

-DDE
pp
1
-DDT
ALDRIN
DIELDRIN
TDE
(RHOTHANE)
ENDOSULFAN
sis,
and demethylation (Figure
11-10).
Thio-
phosphates may be changed to sulfoxides
and sulfones in animals and
plants.
In animal products, chlorinated hydrocar-
bon residues are predominantly present in
the lipid portion, organophosphates in both
lipid and aqueous parts. In plant materials,
the residue of chlorinated hydrocarbons are
mostly surface bound or absorbed by waxy
materials,
but some can be translocated to
inner parts. Extensive research has demon-
strated that processing methods such as
washing,
blanching, heating, and canning
may remove large proportions of pesticide
residues (Liska and Stadelman 1969; Farrow

et
al.
1969). An illustration of the removal of
DDT and carbaryl from vegetables by wash-
ing,
blanching, and canning is given in Fig-
ure
11-11.
It has been reported (Farrow et al. 1969)
that 48 percent of DDT residues on spinach
and 91 percent on tomatoes are removed by
Figure 11-9
Dehydrochlorination
and Hydrolysis of DDT to DDE and DDA in Mammals. Source:
From C.H. Van
Middelem,
Fate and Persistence of Organic Pesticides in the Environment, in Organic
Pesticides in the
Environment,
R.F. Gould, ed.,
1966,
American Chemical Society.
Figure 11-8 Decomposition of DDT by Ultraviolet Light and Air. Source: From C.H. Van Middelem,
Fate and Persistence of Organic Pesticides in the Environment, in Organic Pesticides in the Environ-
ment,
R.F. Gould,
ed.,
1966, American Chemical Society.
UV
Light

Air
Absent
UV
Light
air
DOT
ooe
DOA
Exhibit
11-4
Classification of Organophospho-
rous Insecticides
Aliphatic
Derivatives
• Butonate • Mevinphos
• Demeton • Mipefox
• Dichlorvos •
Naled
• Dimefox • Phorate
• Dimethoate • Phosphamidon
• Dithiodemeton • Schradan
• Ethion • Sulfotepp
• Malathion • Tepp
• Methyl demeton • Trichlorofon
Aromatic (Cyclic) Derivatives
• Azinphosmethyl • EPN
• Carbophenothion • Fenthion
• Diazinon • Methyl parathion
• Dicapthon • Parathion
• Endothion • Ronnel

Source: From
L.E.
Mitchell, Pesticides: Prop-
erties
and
Prognosis,
in
Organic Pesticides
in
the
Environment,
R.F.
Gould,
ed., 1966,
Ameri-
can Chemical Society.
washing. Elkins (1989) reported that wash-
ing and blanching reduced carbaryl residues
on spinach and broccoli by 97 and 98 per-
cent, respectively. Washing, blanching, and
canning reduced carbaryl pesticides on toma-
toes and spinach by 99 percent. Although
this pattern of removal generally holds true,
Peterson and colleagues (1996) have pointed
out that there are exceptions. Pesticides may
accumulate in one part of an agricultural
product. Friar and Reynolds
(1991)
reported
that baking does not result in a decline in thi-

abendazole residues in potatoes, and Elkins
Table
11-6
Water Solubilities of Some
Organophosphorus
Insecticides
Insecticide
(ppm)
Carbophenothion
2
Parathion
24
Azinphosmethyl
33
Diazinon
40
Methyl
parathion 50
Phorate
85
Malathion
145
Dichlorvos
1000
Dimethoate
7000
Mevinphos
°o
Source:
From L.E.

Mitchell,
Pesticides: Properties
and
Prognosis, in
Organic
Pesticides
in the
Environ-
ment,
R.F.
Gould,
ed.,
1966, American Chemical
Soci-
ety.
et
al.
(1972) found that thermal processing
does not result in a reduction of methoxy-
chlor
residues on apricots. Sometimes pro-
cessing may cause a chemical to degrade,
producing a compound that is more toxic
than the original one.
The dietary intake of pesticide chemicals
from foods is well below the acceptable daily
intake (ADI) levels set by the FAOAVHO
(Table
11-7).
In recent years, severe restric-

tions on the use of many chlorinated hydro-
carbon pesticides have been instituted in
many areas. As a result, the intake of these
chemicals should further decrease in future
years.
Dioxin
The term
dioxin
is used to represent two
related groups of chlorinated organic com-
pounds,
polychlorinated dibenzo-/?-dioxins
(PCDD) and polychlorinated
dibenzofurans
Figure
11-10
Oxidation, Hydrolysis, and Demethylation Reactions of Organophosphorous Insecti-
cides.
Source: From L.E. Mitchell, Pesticides: Properties and Prognosis, in Organic Pesticides in the
Environment,
R.F. Gould, ed., 1966, American Chemical Society.
DDT
Tomatoes
Green
beans
Spinach
Potatoes
CARBARYL
Tomatoes
Green

Beans
Spinach
Percent removal
(dry
basis)
Figure 11-11 Removal of Pesticides DDT and
Carbaryl
by Washing, Blanching, and Canning. Source:
From R.P. Farrow et
al.,
Canning Operations That Reduce Insecticide Levels in Prepared Foods and in
Solid Food Wastes, Residue
Rev.,
Vol. 29, pp. 73-78, 1969.
DEMETHYLATlON
p-
MrTFOPHtNOL
DIETHYL
THIOPHOSPMATE
PARATHIOM
HYDROLYSIS
PARATHION
PARA-OXON
OXIDATION
(PCDF) (Figure
11-12).
A total of eight car-
bon atoms in each molecule can carry chlo-
rine substitution, which produces 75 possible
isomers

for PCDD and 135 for PCDF. These
compounds are lipophilic, have low volatil-
ity, and are extremely stable. They are also
very toxic, although the toxicity of each iso-
mer may vary widely. These compounds may
exhibit acute toxicity, carcinogenicity, and
teratogenicity (birth defects). They are ubiq-
uitous environmental contaminants and are
present in human tissues.
PCDD
PCDF
Figure
11-12
Chemical
Structure
of
Polychlorinated
Dibenzo-/?-dioxins
(PCDD)
and
Polychlorinated
Dibenzofurans (PCDF)
Current value accepted
1969
Meeting
Source:
From J.R.
Wessel,
Pesticide Residues in Foods, in
Environmental Contaminants

in
Foods,
Special
Report No.
9,1972,
Cornell University.
Table 11-7 Dietary Intake of Pesticide Chemicals
Milligrams/Kilogram
Body
Weight/Day
Pesticide Chemical
Aldrin-dieldrin
Carbaryl
DDT, DDE, TDE
Lindane
Heptachlor-heptachlor
epoxide
Malathion
Parathion
Diazinon
All chlorinated organics
All organophosphates
All herbicides
WHO-FAO Acceptable
Dally
Intake
0.0001
0.02
0.01
(0.005)

1
0.012
0.0005
0.02
0.005
0.002
Average
1965-1969
0.00008
0.0005
0.0008
0.00005
0.00003
0.0001
0.00001
0.00001
0.001
0.0002
0.0001
Range
(0.00006-0.00013)
(None-0.0021)
(0.0005-0.0010)
(0.00002-0.00007)
(0.00002-0.00005)
(0.0001-0.0004)
(0.000001-0.00001)
(0.000001-0.00002)
(0.0008-0.0016)
(0.00007-0.00025)

(0.00005-0.0001)
The dioxins are produced as contaminants
in the synthesis of certain herbicides and
other chlorinated compounds, as a result of
combustion and incineration, in the chlorine
bleaching of wood pulp for paper making,
and in some metallurgical processes
(Startin
1991).
Dioxins first attracted attention as a
contaminant of the herbicide
2,4,5-trichloro-
phenoxyacetic acid (2,4,5-T). The particular
compound identified was 2,3,7,8-TCDD,
which was for some time associated with the
name
dioxin.
This compound was present in
substantial concentration in the defoliant
"Agent Orange" used by U.S. forces during
the war in Vietnam.
The various isomers, also known as conge-
ners,
vary in toxicity with the 2,3,7,8-substi-
tuted
ones being the most toxic. Humans
appear to be less sensitive than other species.
Dioxins can be generated from chlorine
bleaching of wood pulp in the paper- and
cardboard-making process. This can not only

lead to environmental contamination but also
to incorporation of the dioxins in the paper
used for making coffee filters, tea bags, milk
cartons, and so forth. Dioxins can migrate
into milk from cartons, even if the cartons
have a polyethylene plastic coating. Un-
bleached coffee filters and cardboard con-
tainers have been produced to overcome this
problem, and there have also been improve-
ments in the production of wood pulp using
alternative bleaching agents. The FDA guide-
line for dioxin in fish is 25 parts per trillion
(Cordle 1981). Dioxin is considered a very
potent toxin, but information on harmful
effects on humans is controversial.
Polychlorinated Biphenyls (PCBs)
The PCBs are environmental contaminants
that are widely distributed and have been
found as residues in foods. PCBs are pre-
pared by chlorination of biphenyl, which
results in a mixture of isomers that have dif-
ferent chlorine contents. In North America,
the industrial compounds are known as Aro-
clor;
these are used industrially as dielectric
fluids in transformers, as plasticizers, as heat
transfer and hydraulic fluids, and so forth.
The widespread industrial use of these com-
pounds results in contamination of the envi-
ronment through leakages and spills and

seepage from garbage dumps. The PCBs
may show up on chromatograms at the same
time as chlorinated hydrocarbon pesticides.
The numbering system used in PCBs and the
prevalent substitution pattern are presented
in Figure
11-13.
Table
11-8
presents infor-
mation on commercial Aroclor compounds.
In the years prior to 1977 production of
PCBs in North America amounted to about
50 million pounds per year. PCBs were first
discovered in fish and wildlife in Sweden in
1966,
and they can now be found in higher
concentrations in fish than organochlorine
pesticides (Zitko 1971).
PCBs decompose very slowly. It is esti-
mated that between 1929 and 1977, about
550 million kg of PCBs were produced in the
United States. Production was stopped vol-
untarily after a serious poisoning occurred in
Japan in 1968. Large amounts are still pre-
sent in, for example, transformers and could
enter the environment for many years. Fed-
eral regulations specify the following limits
in foods: 1.5 ppm in milk fat, 1.5 ppm in fat
portion of manufactured dairy products, 3

ppm in poultry, and 0.3 ppm in eggs. The tol-
erance level for PCB in fish was reduced
from 5 to 2 ppm in 1984. Although there has
been a good deal of concern about the possi-
ble toxicity of PCBs, there is now evidence
that PCBs are much less toxic than initially
assumed (American Council on Science and
Health 1985).
Zabik and Zabik
(1996)
have reviewed the
effect of processing on the removal of PCBs
from several foods. In the processing of veg-
etable oil the PCB present in the crude oil
was completely removed; some was removed
by the hydrogenation catalyst, but most was
lost by deodorization. The PCB was recov-
ered in the deodorizer distillate.
Asbestos
Asbestos is widely distributed in the envi-
ronment as a result of industrial pollution.
Many water supplies contain asbestos fibers,
which may become components of foods
(especially beverages). An additional source
of asbestos fibers may be asbestos filtration
Figure 11-13 The Numbering System Used in PCBs and the Prevalent Substitution Pattern of Chlorine
Table
11-8
Information
on Aroclor Preparations

Aroclor
Aroclor
1221
Aroclor
1232
Aroclor
1242
Aroclor
1248
Aroclor
1254
Aroclor
1260
Aroclor
1262
Aroclor
1268
%CI
21
32
42
48
54
60
62
68
Average
Number
of Cl per
Molecule

1.15
2.04
3.10
3.90
4.96
6.30
6.80
8.70
Average Molecular
Weight
192
221
261
288
327
372
389
453
pads;
such contamination has been suggested
to occur in the filtration of beer (Pontefract
1974).
The most common form of this con-
taminant is
chrysotile
asbestos, which occurs
as minute fibers of about 24 nm in size. The
amount of asbestos in water supplies is
extremely low, in the
nanogram

range, but
this may represent a large number of fibers.
Many Canadian water supplies have been
found to contain upward of 1 million asbes-
tos fibers per liter. Chrysotile asbestos is a
hydrated magnesium silicate of the composi-
tion
Mg
3
Si
2
O
5
(OH)
4
.
Inhalation of asbestos
has been related to cancer among asbestos
workers. It appears that asbestos fibers in-
gested with water or food may pass through
the intestinal wall and enter into the blood-
stream. Cunningham and Pontefract (1971)
have reported the occurrence of asbestos
fibers in a variety of beverages and in tap
water. Some of their results are presented in
Table 11-9.
Antibiotics
Growth-retarding or antimicrobial sub-
stances may be present in foods naturally,
Table

11-9
Asbestos Fibers in Beverages and
Water
Sample
No.
ofFibers/Lx 1CP
Beer
4.3
Sherry
4.1
Soft
drink 12.2
Tap
water, Ottawa 2.0
Tap
water, Toronto 4.4
Source:
From
H.M.
Cunningham and
R.D.
Ponte-
fract,
Asbestos Fibers in Beverages and Drinking
Water,
Nature,
Vol. 232, pp. 332-333,
1971.
may be produced in a food during process-
ing, or may occur incidentally through the

treatment of diseased animals. The latter
problem has created the greatest concern.
The use of antibiotics in therapy, prophy-
laxis,
and growth promotion of animals may
result in residues in foods. These residue lev-
els rarely exceed the range of 1 to 0.1
ppm
(where toxicological interest ceases). How-
ever, levels well below those of toxicological
interest may be important in food processing,
for example, in cheese making, by prevent-
ing starter development. The low levels may
also be important in causing allergies and
development of resistant organisms. Highly
sensitized persons may experience allergic
reactions from milk that contains extremely
low amounts of penicillin. The various anti-
biotics used in agriculture, including some
used in food processing, are listed in Exhibit
11-5.
The tetracyclines, CTC and OTC, are
broad-spectrum antibiotics and act against
both gram-positive and gram-negative bacte-
Exhibit 11-5 Antibiotics Used in Agriculture
and Food Processing
• Benzylpenicillin, cloxacillin, ampi-
cillin,
phenethicillin
potassium

•
Chlortetracycline
and oxytetracy-
cline
• Streptomycin and
dihydrostrepto-
mycin
•
Neomycin,
oleandomycin,
spiramy-
cin
• Chloramphenicol
• Framycetin, bacitracin, and
poly-
myxins
• Tylosin
1
and
nisin
1
• Nystatin
1
NoI
used in human therapeutics
ria.
The action is bacteriostatic and not bac-
tericidal. The tetracyclines have been used to
delay spoilage in poultry and fish. Their
effectiveness seems to decrease quite rapidly,

because the contaminating flora quickly
become resistant. Nisin, which is one of the
few antibiotics not used in human therapeu-
tics,
has been found to be effective as an aid
in heat sterilization of foods. It is a polypep-
tide with a molecular weight of about 7,000
and contains 18 amino acid residues. It is
active against certain gram-positive organ-
isms only, and all spores are sensitive to it.
Trace Metals
A variety of trace metals (such as mercury
and lead) may become components of foods
through industrial contamination of the envi-
ronment. Some trace metals (such as tin and
lead) may be introduced into foods through
pickup from equipment and containers (espe-
cially tin cans).
Mercury
Large amounts of mercury are released
into the environment by several industries.
Major mercury users are the chloralkali
industry, where mercury is used in electro-
lytic cells; the pulp and paper industry,
where mercury compounds are used as
slimi-
cides;
and agriculture, where uses include
seed dressings and sprays. Mercury is now
known to be converted in sediments on river

and lake bottoms into highly toxic methyl
mercury compounds. This conversion scheme
is shown in Figure
11—14.
Formation of the
more volatile dimethyl mercury is favored at
alkaline pH. The less volatile monomethyl
form is favored at acid pH. Because much of
the mercury pollution ends up in rivers and
lakes where it is converted into methyl mer-
cury, contamination of fish with mercury has
been a great concern. In many animal tissues,
methyl mercury may comprise as much as 99
percent of the total mercury present. The
present interest in mercury and its effect on
humans and wildlife originated with the dis-
covery of mercury as the causative agent in
the Minamata disease in Japan. Near the
town of Minamata, a chemical industry used
mercury compounds as catalysts for the con-
version of acetylene into acetaldehyde and
vinyl chloride. Organic mercury compounds
Figure 11-14 Conversion of Inorganic Mercury and Some Mercury-Containing Compounds to Methyl
Mercury. Source: From N. Nelson, Hazards of Mercury, Environmental
Res.,
Vol. 4, pp. 41-50, 1971,
Academic Press.
were released into the waters of Minamata
Bay and contaminated fish and shellfish.
Many cases of mercury poisoning occurred,

resulting in the death of close to 50 patients.
This event triggered research into mercury
contamination in many areas of the world.
Table
11-10
summarizes the mercury levels
found in foods in various countries. The high
mercury level in Japanese rice should be
noted. High levels of mercury have been
observed in fish in many lakes and streams as
well as in the oceans. Table
11-11
presents
the results of mercury analyses in Atlantic
coast fish. The high level of mercury
in
tuna
and
swordfish
is probably the result of the
predatory lifestyle and long life of these fish.
Generally, 0.5 ppm of mercury in fish is con-
Table 11-10 Mercury Levels Found in Foods in
Various Countries
Hg, Range
Food Country
(ng/g)
Haddock United States 17-23
Herring Baltic States 26-41
Apples United Kingdom 20-120

Apples New Zealand
11 -135
Pears Australia 40-260
Tomatoes United Kingdom
12-110
Potatoes United Kingdom 5-32
Wheat Sweden 8-12
Rice Japan 227-1000
Rice United Kingdom 5-15
(imports)
Carrots United States 20
White bread United States 4-8
Whole milk United States 3-10
Beer United States 4
Source:
From N. Nelson, Hazards of Mercury,
Envi-
ronmental
Res.,
Vol. 4, pp. 41-50,
1971,
Academic
Press.
Table
11-11
Mercury Levels in Atlantic Coast
Fish
Species Hg
Level Range
(ppm)

Clam
0.02-0.11
Cod
0.02-0.23
Crab 0.06-0.15
Flounder 0.07-0.17
Haddock 0.07-0.10
Herring 0.02-0.09
Lobster 0.08-0.20
Oyster 0.02-0.14
Swordfish 0.82-1.00
Tuna 0.33-0.86
Source:
From E.G.
Bligh,
Mercury in Canadian
Fish,
Can.
lnst.
Food
Sd.
Technol.
J.,
Vol. 5, pp.
A6-A14,
1972.
sidered the maximum permitted level. Fish in
Canada exceeding this level cannot be sold.
Lead and Tin
The presence of lead in foods may be the

result of environmental contamination,
pickup of the metal from equipment, or the
solder of tin cans. It has been estimated that
nearly 90 percent of the ingested lead is
derived from food (Somers and Smith 1971).
However, only 5 percent of this is absorbed.
In the early 1970s, the average North Ameri-
can car was reported to emit 2.5 kg of lead
per year (Somers and Smith 1971), and
Zuber and colleagues (1970) reported that
crops grown near busy highways had a high
lead content (in some cases, exceeding 100
ppm of lead in the dry
matter).
The removal
of lead from gasoline has eliminated this
source of contamination. Lead can also be
picked up by acid foods such as fruit juices
that are kept in glazed pottery made with
lead-containing glazes. Both lead and tin
may be taken up by foods from the tin of
cans and from the solder used in their manu-
facture. The amounts of lead and tin taken up
depend on the type of tin plate and solder
used and on the composition and properties
of the canned foods. In a study on the
detinning of cans by spinach, Lambeth et
al.
(1969)
found that detinning was significantly

related to the oxalic acid content and pH of
the product. Detinning in excess of 60 per-
cent was observed during nine months' stor-
age of
high-oxalate
spinach.
The present levels of lead that humans
ingest cause concern because ADI calcula-
tions range from 0.1 to 0.8 mg lead per day.
The average daily intake is in the vicinity of
0.4 mg lead per day. This means that lead is
one of the
few
toxic food components for
which the acceptable daily intake is
approached or exceeded by the general popu-
lation (Clarkson 1971).
Cadmium
As are lead and mercury, cadmium is a
nonessential trace metal with high toxicity.
Crustaceans have the ability to accumulate
cadmium as well as other trace metals, such
as zinc. Cadmium levels in oysters may
reach 3 to 4 ppm, whereas in other foods,
levels are only one-tenth or one-hundredth of
these (Underwood 1973).
Polycyclic
Aromatic Hydrocarbons
(PAHs)
These compounds form a large group of

materials that are now known to occur in the
environment. The structural formulas of the
major members of this group are presented in
Figure
11-15.
Several of these, especially
benzo(a)pyrene (3,4-benzopyrene), have been
found to be carcinogenic. Usually, the poly-
cyclic hydrocarbons occur together in foods,
especially in smoked foods, because the aro-
matic hydrocarbons are constituents of wood
smoke. Trace quantities of PAHs have been
found in a variety of foods, and this may be
the result of environmental
contamination.
The PAHs may be carcinogenic and mu-
tagenic. The level of carcinogenicity may
vary widely between different members of
this group. Minor constituents of PAH mix-
tures may make large contributions to the
carcinogenic activity of the mixture. Certain
methylchrysenes, particularly the 5-isomer,
which is one of the most carcinogenic com-
pounds known, may dominate the carcino-
genic activity of a mixture
(Bartle
1991).
Rhee and Bratzler (1968) analyzed hydro-
carbons in smoke, and the amounts found in
smoke and in the vapor phase (smoke filtered

to remove particles) are listed in Table
11-12.
Small amounts of these smoke constituents
may be transferred to foods during smoking.
Howard and Fazio
(1969)
reported the levels
of aromatic polycyclic hydrocarbons in
foods,
and results for smoked foods are listed
in Table
11-13.
These compounds have also
been found in unsmoked foods, as is shown
in Table 11-14. Higher levels than those
found in smoked food may occur as a result
of barbecuing or charcoal broiling. Roasting
of coffee and nuts results in formation of
PAHs. The levels present in roasted coffee
increase with more intense roasting; this is
shown in Table 11-15, which is based on
results obtained by Fritz (1968). PAHs occur
in vegetables (Grimmer and Hildebrand
1965),
and the levels are thought to be
related to the leaf area and the relative level
of atmospheric pollution.
Surprisingly, the largest proportion of the
total human intake of PAHs does not come
from smoked or roasted foods, but from

other common products.
Bartle
(1991) has
stated that cereals are likely to be a greater
hazard, especially in the form of flour, than
smoked or barbecued foods. Although cereal
has a much lower PAH content than smoked
or roasted foods do, cereal is consumed in
much greater
amounts.
Bacterial and Fungal Toxins
Microbial toxins are some of the most
potent toxins known to humans. They may
be the result of microbial growth in foods or,
as in the case of fungal toxins, growth of
molds during the production of many agri-
cultural crops.
Bacterial toxins are produced mainly from
species of the genera
Staphylococcus
and
Clostridium. The Staphylococcus poison usu-
ally results from improperly handled food in
food service establishments and in the home,
but rarely from food processing plants.
Although the toxin seldom causes human
death, it is highly toxic. In contrast, botuli-
num toxin has a high fatality rate. The neuro-
Figure 11-15
Chemical Structure of Some Polycyclic Aromatic Hydrocarbons

1.2-BENZOPYRENE
3.4-
BENZOPYRENE
FLUORANTHENE
1.2-
BENZANTHRACENE
CHRYSENE
PYRENE
ANTHRACENE
PHENANTHRENE
NAPHTHALENE
ACENAPHTHENE
FLUORENE
Table
11-12
Aromatic
Polycyclic
Hydrocarbons
in Wood Smoke and in Wood Smoke Vapor
Phase
Amount,
\ig/45
kg
Sawdust
Hydrocarbon
Phenanthrene
Anthracene
Pyrene
Fluoranthene
1

,2-Benzan-
thracene
Chrysene
3,4-Benzopyrene
1 ,2-Benzopyrene
Whole Smoke
51.5
3.8
5.5
5.7
7.0
2.6
1.2
0.9
Vapor Phase
28.4
1.9
4.1
4.2
4.3
0.3
0.4
Trace
Source:
From K.S.
Rhee
and LJ. Bratzler, Polycy-
clic Hydrocarbon Composition of Wood Smoke, J.
Food
ScL,

Vol. 33, pp. 626-632,
1968.
toxin is produced by six types of
Clostridium
botulinum,
which differ in immunological
properties. These organisms are gram-posi-
tive,
spore-forming anaerobic bacteria. The
prevention of the outgrowth of the spores is a
major responsibility for the heat-sterilized
processed-food industry.
Fungal toxins, also called mycotoxins, are
produced by fungi or molds. Most of the
interest in fungal toxins is concerned with
the so-called storage fungi, molds that grow
on relatively dry cereals and oilseeds. These
belong to two common genera, Aspergillus
and Penicillium. The most common of the
fungal toxins are the
aflatoxins
formed by
members of the Aspergillus flavus group.
The aflatoxins were discovered as a result of
widespread poisoning of turkeys in the early
1960s in England through feeding of toxic
peanut meal. The aflatoxins belong to the
most powerful toxins known and are highly
Table
11-13

Polycyclic Aromatic Hydrocarbons Found in Smoked Food Products (ppb)
Source:
From J.W. Howard and T. Fazio, A Review of Polycyclic Aromatic Hydrocarbons in
Foods,
Agr.
Food
Chem.,
Vol. 17, pp.
527-531,1969,
American Chemical Society.
Food
Product
Beef,
chipped
Cheese, Gouda
Fish
Herring
Herring (dried)
Salmon
Sturgeon
White
Ham
Frankfurters
Pork roll
Benzo
(a)-
anthracene
0.4
1.7
0.5

2.8
Benzo
(a)-
pyrene
1.0
0.8
3.2
Benzo
(e)-
pyrene
1.2
0.4
1.2
Benzo
(9M)-
perylene
1.0
1.4
Fluoran-
thene
0.6
2.8
3.0
1.8
3.2
2.4
4.6
14.0
6.4
3.1

Pyrene
0.5
2.6
2.2
1.8
2.0
4.4
4.0
11.2
3.8
2.5
4-Methyl-
pyrene
2.0
Table
11-14 Polycyclic
Aromatic Hydrocarbons
In
Unsmoked Food Products
Fluoran- Pyrene
Food
Product
thene (ppb) (ppb)
Cheese, cheddar 0.8 0.7
Fish,
haddock 1.6 0.8
Fish,
herring (salted) 0.8 1.0
Fish,
salmon 1.8 1.4

(canned)
Source:
From
J.W.
Howard and T.
Fazio,
A Review
of Polycyclic Aromatic Hydrocarbons in Foods, Agr.
Food
Chem.,
Vol. 17, pp.
527-531,
1969, American
Chemical Society.
carcinogenic. A dose of 1 mg given to rats
for short or long periods can result in liver
cancer, and a diet containing
0.1
ppm of
afla-
toxin produces liver tumors in 50 percent of
male rats (Spensley
1970).
There are at least
eight
aflatoxins,
of which the more important
are designated
B
1

, B
2
,
G
1
,
and
G
2
.
The
names result from the blue and green fluores-
cence of these compounds when viewed
under ultraviolet light.
Aflatoxin
B
1
is a very
powerful liver carcinogen; a level of 15 ppb
in the diet of rats resulted in tumors in 100
percent of cases after 68 weeks (Scott 1969).
Ducklings are used as test animals because
they are especially sensitive to aflatoxins.
The aflatoxins, for which the formulas are
shown in Figure
11-16,
can occur in many
foods but are particularly common in pea-
nuts.
Roasting of peanuts reduces the level of

aflatoxin;
for example, roasting for a half
hour at 150° may reduce aflatoxin
B
1
content
by as much as 80 percent (Scott 1969). How-
ever, aflatoxin may still be carried over into
peanut butter. In addition, aflatoxins have
been found in cottonseed meal, rice, sweet
potatoes, beans, nuts, and wheat. Through
Table
11-15
Polycyclic Aromatic Hydrocarbons
in Coffee
(^ig/kg)
Heavy Normal
Compound Roasting Roasting
Anthracene 6.2
1.5
Phenanthrene 74.0 28.0
Pyrene 28.0 3.5
Fluoranthene 34.0 3.9
1,2-Benzanthracene
14.2
1.5
Chrysene 14.8 —
3,4-Benzopyrene 5.8 0.3
1,2-Benzopyrene
7.0 0.7

Perylene 0.6 —
11,12-Benzfluoranthene
1.8 —
Anthanthrene 0.9 —
1,12-Benzperylene
2.2 —
3,4-Benzfluoranthene
1.2
—
Coronene 0.9 —
lndenopyrene 0.7 —
Source:
From W. Fritz, Formation of Carcinogenic
Hydrocarbons During Thermal Treatment of Foods,
Nahrung,
Vol.
12,
pp. 799-804,
1968.
ingestion of moldy feed by animals, aflatox-
ins may end up as contaminants in milk and
meat. Aflatoxins found in milk may be Ml
or M2, where M stands for metabolic; these
are also toxic. The development of aflatoxins
depends very much on temperature and
moisture conditions. With peanuts, contami-
nation occurs mostly during the drying
period. Improper drying and storage are
responsible for most of the contamination.
This has been found to apply for rice. Opti-

mum conditions for growth of Aspergillus
flavus
are 25° to
4O
0
C
with a relative humid-
ity greater than 85 percent.
Control measures for prevention of afla-
toxin production focus on reduction of water
activity to a point where the fungus is unable
to grow and maintenance of low water activ-
ity during storage. A moisture content of
18.0 to 19.5 percent in cereal grains is re-
quired for growth and toxin production by A.
flavus.
Aflatoxin-contaminated
commodities
can be detoxified by treatment with ammonia,
calcium hydroxide, or a combination of form-
aldehyde and calcium hydroxide
(Palmgren
and Hayes 1987).
Sterigmatocystin, which is a carcinogenic
metabolite of
Aspergillus
ochraceus,
has
been found to be a natural contaminant of
foods,

especially corn. Molds of the species
Fusarium produce several mycotoxins in
countries with moderate climates (Andrews
et
al.
1981).
Two of these are zearalenone
and deoxynivalenol (Figure
11-17).
Zearale-
none, of F-2 toxin, is produced by Fusarium
molds that grow on corn (Marasas et al.
1979) that is immature or high in moisture at
harvest. Deoxynivalenol, also known as
vomitoxin, has been found in wheat and bar-
ley (Trenholm et al. 1981; Scott et al. 1983).
During the wet summer of 1980, wheat
grown in Ontario showed sprouting of ker-
nels and pink discoloration. Experiments on
milling showed that the vomitoxin was dis-
tributed throughout the milled products and
was not destroyed by the bread-making pro-
cess.
Patulin is another Aspergillus metabo-
lite and has been indicated as a food con-
taminant, especially in fruits, as a result of
storage rot. It has been found as a constituent
of apple juice (Harwig et al. 1973).
Natural Toxicants
In spite of the prevalent perception that

"natural" is harmless or nontoxic, natural
food products contain an abundance of toxic
chemicals (Committee on Food Protection
1973;
National Academy of Sciences 1973).
The foods that are consumed by humans
(with the exception of mother's milk con-
sumed by infants) were not designed by
nature for human use; rather, they were
adapted by humans over the centuries, by
Figure 11-16 Chemical Structure of
Aflatoxins
B
1
, B
2
,
G
1
,
and
G
2
.
Source: From P.M. Scott, The
Analysis of Foods for Aflatoxins and Other Fungal Toxins: A Review, Can.
Inst.
Food
Technol /.,
Vol.

2,
pp. 173-177, 1969.
B,
G,
B
2
G
2
trial and error. This process is effective in
eliminating foods that cause acute symptoms
of toxicity but is less effective in dealing
with the long-term effects. Coon
(1973)
has
stated that past experience has provided
more knowledge on the safety margins of
natural foods than animal experimentation.
Many natural food components, such as caf-
feine, goitrogens, and cyanogenic
glyco-
sides,
would not be approved for human
consumption if examined with the tech-
niques now required for intentional addi-
tives.
Because our foods contain so many
potentially toxic substances, the best defense
is to consume a varied diet.
Some natural toxins such as seafood toxins
or fungal toxins may occur at abnormally high

levels only in unusual circumstances, causing
disease in the normal individual who eats a
normal amount of food. Other natural toxins
are normal constituents of food and cause dis-
ease only in humans consuming abnormal
amounts of that food. In addition, normal food
components may cause harm in abnormal
Figure 11-17 Chemical Structures of Sterigmatocystin,
Ochratoxin
A, Zearalenone, Deoxynivalenol
(Vomitoxin), and Patulin. Source: From P.M. Scott, The Analysis of Foods for
Aflatoxins
and Other
Fungal Toxins: A Review, Can.
Inst.
Food
Technol
/.,
Vol. 2, pp. 173-177, 1969; P.M. Scott et
al.,
Effects of Experimental Flour Milling and
Breadbaking
on Retention of Deoxynivalenol (Vomitoxin) in
Hard Red Spring Wheat, Cereal
Chem.,
Vol. 60, pp.
421-424,
1983.
VOMITOXIN
ZEARALENONE

PATULIN
STERIGMATOCYSTIN
OCHRATOXIN
A
individuals (Coon 1973). The latter case is
probably the most difficult to deal with in reg-
ulatory aspects. Banning of foods that are
considered safe for most people is unthink-
able,
and protection of diseased or allergic
individuals becomes a problem. Some exam-
ples of natural toxins in foods are given below.
Sulfur Compounds
Many cruciferous plants contain goitro-
gens,
which are known as glucosinolates.
They are harmful if ingested in excessive
amounts. Plants of the genus
Allium,
includ-
ing onions, chives, and garlic, contain pre-
cursors of sulfur-containing compounds that
can be liberated by enzymic action.
Salunkhe and Wu (1977) have described
the enzymic breakdown of the glucosinolate
to isothiocyanate and goitrin (Figure
11-18).
In addition to being goitrogens, the isothio-
cyanates produced from glucosinolates in
rapeseed (canola) oil have been found to

have a poisoning effect on the nickel cata-
lysts employed in the hydrogenation of the
oil (Abraham and deMan
1987).
Sulfur compounds of the
Allium
species
result from enzymic action on precursors and
are responsible for the odor and flavor as
well as the lachrymatory properties of these
vegetables. These precursors are S-substi-
tuted cysteine sulfoxides, or combinations
with
peptides.
The enzyme alliinase liberates
labile
thiosulfinates,
which slowly decom-
pose into thiosulfonates and
disulfides.
The
latter are volatile and are responsible for the
characteristic flavor. Thiosulfinates have anti-
biotic activity.
Seafood Toxicants
Many of the seafood toxins are found in
shellfish and usually result from the growth
of certain marine algae. The toxins end up in
the shellfish through the food chain. The spo-
radic occurrence of these events makes the

problem more difficult to control. In 1987,
mussels cultivated in Eastern Canada were
found to be poisonous, and the cause was
established as the toxin domoic acid. Para-
lytic shellfish poisoning has been observed in
many of the world's fishing areas. Although
some of these toxins have been identified,
many remain
uncharacterized (Shantz
1973).
The poison saxitoxin, from California mus-
sels and Alaska butter clams, is a dibasic salt
and is highly soluble in water.
Caffeine
Caffeine is a naturally occurring chemi-
cal,
1,3,7-trimethylxanthine
(Figure
11-19),
which is found in the leaves, seeds, and fruits
of more than 63 species of plants growing all
over the world. It occurs as a constituent of
coffee, tea, cocoa, and chocolate, and is an
additive in soft drinks and other foods. Be-
cause humans have used it for thousands of
years,
caffeine has GRAS status in the
United States. Roberts and Barone (1983)
have estimated that daily caffeine consump-
tion in the United States is 206

mg
per per-
son. Caffeine shows a number of phys-
iological effects (Von Borstel 1983) and, as a
result, its regulatory status has been under
review (Miles 1983). Complicating the mat-
ter is the fact that caffeine is both a naturally
occurring chemical as well as a food addi-
tive.
Caffeine stimulates the central nervous
system, can help people stay awake, and can
relieve headaches. Adverse effects may
include sleep disturbance, depression, and
stomach upsets. Large overdoses of caffeine
may be fatal (Leviton 1983). Caffeine is a
good example of a widely occurring natural
toxicant that has been part of our food supply
for centuries.
Figure 11-19 The Structure of Caffeine
1,3,7-
Trimethylxanthine
Figure
11-18
Formation of Goitrin and Isothiocyanates from Glucosinolates in Cruciferous Products.
Source:
From
O.K.
Salunkhe and M.T. Wu, Toxicants in Plants and Plant Products, Food ScL
Nutr.,
Vol.

9, pp. 265-324, 1977.
GOITRIN
(S-
5-
VINYLOXAZOLIDINE-2-THIONE)
THIOCYANATE
ISOTHIOCYANATE
CYCLIZATION
NITRILE
S
SULFUR
UNSTABLEAGLUCON
GLUCOSE
BISULFATE
PROGO(TRIN
THIOGLUCOSIOE
GLUCOHYDROLASE
E.C.
3.2.3.1
REFERENCES
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