Introduction to Toxicology
EV 460/660 & BI 460/660
Fall 2014
Food Toxicology
1.
Uniqueness of food toxicology
A.
anecdotal comments – evolutionary biology, human evolution, long history in toxicology,
management is a mixture of science, tradition, and pragmatism
B.
essential for life, contributes to quality of life, rich cultural traditions, personal and emotional
C.
in many areas of world, microbiological contamination is greatest food-borne risk
D.
in U.S. highly regulated by complex mixture of FDA standards and legal regulations (CFRs)
E.
food more chemically complex and variable in composition than other substances to which
humans are exposed, however, there is nothing to which humans have greater exposure (with
exception of air and water)
F.
some nutrients, like vitamin A or selenium, may be toxic at levels slightly above those required
to prevent deficiencies
2.
Chemical complexity of foods
A.
contain hundreds of thousands of naturally present compounds, many more form in situ when
food is cooked or prepared, most of which have not been fully identified or tested
B.
presumption of safety for these is based on a history of common use as a food
C.
compounds can be divided into nutrients and anutrients
D.
nutrients divided into macronutrients (carbohydrates, proteins, lipids) and micronutrients
(vitamins and minerals), macronutrients have caloric value
E.
majority of anutrients are naturally occurring substances in foods
F.
naturally occurring anutrients include organoleptics which confer flavor, texture, color, or aroma
to foods, e.g., make an apple look, taste, and smell like an apple
G.
other naturally occurring anutrients include substances vital for the growth and survival of the
plant (i.e., plant hormones) or plant secondary compounds
H.
not naturally occurring anutrients include direct food additives (intentionally added to foods) and
indirect additives (contaminants, and chemicals in food as result of processing or
packaging of foods)
-- these are regulated and held to a higher standard of safety than natural components of food
3.
Importance of gastrointestinal tract in food toxicology
A.
large surface area, highly vascularized, extensive absorption by diffusion, active transport, and
endocytosis
B.
extensive bacterial flora responsible for many metabolic chemical transformations
C.
intestinal epithelium has extensive capacity for phase I and phase II biotransformation reactions,
perhaps second only to liver
D.
majority of absorbed compounds pass to liver via hepatic portal vein, but lipid-like compounds
pass into lymph (miss the “first-pass” processing by the liver)
E.
may include compounds swallowed in mucus from respiratory system
4.
Direct food additives divided into two major categories on the basis of the level of consumption
and the similarity to food itself
A.
food-like additives – may be present at 1% or more in the food
-- virtually indistinguishable from food, such as fats, oils, fatty acids, modified fats,
starches, modified starches, cellulose, modified cellulose, sugars and sugar alcohols,
proteins, hydrolyzed proteins, and amino acids
-- specific limitations may be set by FDA regulations or may be on the FDA’s list of GRAS
compounds (Generally Regarded As Safe, established by a panel of food science
experts)
B.
non-food-like additives – typically present at levels far below 1%, often at ppm levels
-- specific limitations may be set by FDA regulations or may be on the FDA’s list of GRAS
compounds (Generally Regarded As Safe, established by a panel of food science experts)
-- additives classified by functionality, FDA recognizes 32 classes of functionality
1. anticaking agents and free-flow agents
2. antimicrobial agents
3. antioxidants
4. colors and coloring adjuncts
5. curing and pickling agents
6. dough strengtheners
7. drying agents
8. emulsifiers and emulsifier salts
9. enzymes
10. firming agents
11. flavor enhancers
12. flavor agents and adjuvants
13. flour-treating agents
14. formulation aids
15. fumigants
16. humectants
5.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
leavening agents
lubricants and release agents
nonnutritive sweeteners
nutrition supplements
nutritive sweeteners
oxidizing and reducing agents
pH control agents
processing aids
propellants, aerating agents, and gases
sequestrants
solvents and vehicles
stabilizers and thickeners
surface-active agents
surface-finishing agents
synergists
texturizers
Safety standards for direct and indirect food additives – FD&C Act provides for a balance between
science-based safety and practicable, workable approach
A.
Evaluation of safety – exposure and dose
-- based upon EDI = C x I , Estimated Daily Intake (EDI), daily Intake (I) of the food containing
the substance, and Concentration (C) of the substance in the food
-- Intake (I) is estimated from several large, well-established databases on food consumption
patterns, recognition of changing food habits
-- many additives are present in more than one food type
-- also taken into consideration is non-food exposure, e.g., in toothpaste, lipstick, etc.
B.
Structure-activity relationships – three categories are used
-- Category A = low potential for toxicity
-- Category B = indeterminate or intermediate toxicity potential
-- Category C = high order of toxicity potential
C.
Assignment of Concern Level (CL)
-- three Concern Levels based upon a matrix of EDI vs. Structure Category
Concern
Level
Structure
Category A
Structure
Category B
Structure
Category C
I
<0.05 ppm in total diet
(<0.0012 mg//kg/day)
<0.025 ppm
(<0.0063)
<0.0125 ppm
(<0.00031)
II
>0.05 ppm in total diet
(>0.0012 mg//kg/day)
>0.025 ppm
(>0.0063)
>0.0125 ppm
(>0.00031)
III
> 1 ppm in total diet
(>0.25 mg/kg/day)
>0.5 ppm
(>0.0125)
>0.25 ppm
(>0.0063)
D.
Toxicity evaluation based upon Concern Level
-- once the CL is established, a specific test battery is prescribed
-- CL III tests are the most demanding and provide the greatest breadth for determination of
adverse biological effects
-- CL II tests are of intermediate breadth
-- CL I tests are least broad
-- if any potential problems are identified in lower level tests, the CL is raised and the next level
battery of toxicity tests are conducted
-- standard setting for safety levels are typically 1/100th of the NOEL (No Observable Effect
Level) determined in animal testing
CL I test battery includes: -- short-term (at least 28 days) feeding study in rodents
-- short-term tests for carcinogenic potential
CL II test battery includes: -- subchronic (at least 90 days) feeding study in rodents
-- subchronic feeding study in a non-rodent species
-- multigenerational reproduction study (minimum of two generations) with
a teratology phase in one rodent species
-- short-term tests for carcinogenic potential
CL III test battery includes: -- chronic (at least 1 year) feeding study in a rodent species
-- long-term (at least 1 year) feeding study in a non-rodent species
-- multigenerational reproduction study (minimum of two generations) with
a teratology phase in one rodent species
-- short-term tests for carcinogenic potential
-- carcinogenicity studies in two rodent species
6.
Pragmatic use of tolerance and action levels for contaminants
A.
based upon concept of CGMP (Current Good Manufacturing Practices)
B.
tolerance levels are set by formal CFR regulation, action levels are more informally established
by FDA
C.
contaminants that are unavoidable by CGMP have tolerance limits or action levels established
for different foods
-- ex. of action level standards – aflatoxins levels in peanuts, grain, and milk
D.
foods that contain CGMP unavoidable contaminants in excess of established tolerance limits or
action levels are declared adulterated and unfit for human [or animal] consumption
[note: FDA regulations also cover animal feeds]
E.
contaminants in foods that are avoidable by CGMP are declared unsafe under FDA regulations
and are deemed unsafe and unfit for human consumption
F.
foods declared unsafe are subject to FDA recall, level of recall depends upon health risk posed
by the contaminated food
-- Class I recall – reasonable probability that the use of or exposure to food will cause serious
adverse health consequences or death, provides the maximum public warning, greatest
depth of recall, and most extensive follow-up
-- Class II and III recalls represent progressively less health risk and require less public warning,
less depth of recall, and less follow-up
7.
Indirect food additives from processing and packaging
A.
enter food by migrating from surfaces that contact food
B.
surfaces may be those use in processing, holding, or transporting food or from packaging
materials (cans, paper, plastic) or the coatings applied to packaging materials
C.
safety tests assume four classes of foods for purpose of extraction studies with food-simulating
solvents, food/solvent classes are: aqueous, acidic, alcoholic, and fatty
D.
safety tests also take into consideration the temperature conditions under which the food will
contact the potentially contaminating surface
E.
calculations of EDI exposure take into account the fraction of food types subject to chemical
migration from various packaging categories
Color additives
A
subject to particular concern because of potential for toxicity, color additives are not eligible for
GRAS status
-- manufacturer may not add more than is reasonably required to produce a desired color effect,
ex., if desired color for strawberry ice cream is achieved with 1 ppm of red dye, then it is
a violation of CGMP to add an amount greater than 1 ppm
8.
B.
C.
D.
E.
F.
two classes of color additives
-- those requiring certification by FDA chemists
-- those exempt from certification
certification , which is based on chemical analysis, is required for each batch of most organic
synthesized colors because they may contain impurities that vary from batch to batch
currently certified colors include: FD&C Blue No. 1, FD&C Blue No. 2, FD&C Green No. 3,
FD&C Red No. 3, FD&C Red No. 40, FD&C Yellow No. 5, FD&C Yellow No. 6,
Orange B, and Citrus Red No. 2
certified colors are aromatic amines or aromatic azo structures
-- aromatic amines are generally considered relatively toxic compounds
-- however, the FD&C colors are notably nontoxic, extensively tested as CL III compounds
-- principal reason for low toxicity is sulfonation of the aromatic amine or azo compound
-- sulfonic acid groups are highly polar, which, added with their high molecular weight largely
prevents FD&C colors from entering cells or being absorbed by the GI tract
food colors exempt from certification are derived primarily from natural sources
-- currently 25 exempt food colors are approved
-- examples: beet powder, grape skin extract, paprika, caramel, carrot oil
-- lack precise chemical definition and variable in chemical composition
-- with exception of caramel, tend not to be widely used
-- lack uniformity, intensity, and stability characteristic of the synthetic colors
9.
Carcinogens in food and the Delaney Clause
A.
Delaney Clause of the FD&C Act prohibits the approval of regulated food additives “found to
induce cancer when ingested by man or animals”
B.
applies only to approval of food additives, color additives, and animal drugs; does not apply to
unavoidable contaminants or GRAS substances or ingredients sanction by the FDA or
USDA before 1958
C.
because of harsh consequences of finding a food additive to be a carcinogen, the FDA has
interpreted this clause as requiring clear and unequivocal demonstration of
carcinogenicity upon ingestion
D.
only a few substances have been banned from foods due to the Delaney Clause
E.
FDA excludes cancers that arise from secondary means, e.g., secondary to nutritional,
hormonal, or physiological imbalances
F.
FDA also does not exclude additives that may include carcinogenic contaminants, reasoning is
that all substances may contain trace levels of carcinogenic contaminants
G.
statistical vs. biological significance – for purposes of compliance with the Delaney Clause, the
FDA assumes that a lifetime risk of one case of cancer in a million people is equivalent
to zero.
10.
Transgenic or genetically modified plants
A.
if genetic modification does not result in a new, novel chemical in the plant, and the plant
contains only GRAS substances then the plant may be approved without additional
documentation
B.
if genetic modification does result in compounds that are not similar to substances commonly
found in food, then a food additive petition must be filed, FDA will subject novel
chemical(s) to same battery of tests required of other direct food additives
11.
Tolerance settings
A.
pesticide residues
-- pesticides regulated by EPA under FIFRA (Federal Insecticide, Fungicide, and Rodenticide
Act), only EPA registered pesticides may be marketed in the U.S., registration must
include designation of intended uses, e.g., on food crops or other uses
-- pesticides intended for use of food crops must be granted tolerances or be exempted from
tolerances under the FD&C Act
B.
C.
D.
E.
-- EPA cannot register use of a pesticide on food crops unless tolerances have first been
granted to cover residues that are expected to remain in or on food
-- there are two types of tolerances, one permitting the presence of pesticide residues in or on
raw agricultural commodities and the other permitting such residues in processed foods
drugs used in food-producing animals
-- food animal drugs widely used to promote animal health, growth, and food production
-- extremely complex and difficult area, complicated by biotransformation reactions in both the
food animal and humans, the tremendous sensitivity of modern analytical techniques to
detect minute trace quantities, and the mandate of the Delaney Clause
-- single parent compound may result in metabolites that may number in the hundreds in the
food animal and correspondingly many more in humans, clearly it is not practical to
subject all of these to complete toxicity screening
-- pragmatic approach taken by FDA is combination of structure-activity assessments and in
vitro screening of potentially problematic compounds
-- compounds identified as potential carcinogens by in vitro screening are subjected to animal
assays, if animal assays also suggest carcinogenic potential, then the “no residue” level
mandated by the Delaney Clause is applied
-- for many drugs used in food-producing animals safety limits require withdrawal of the drug a
specified number of days prior to slaughter, these time periods are based upon
pharmacokinetic studies in the food animal
heavy metals
-- of primary concern in foods are lead, arsenic, and cadmium
-- considered unavoidable contaminants by CGMP due to prevalence of these elements in
nature and their dispersion into the environment by human activities
N-nitroso compounds (NOCs)
-- two general classes are nitrosamines and nitrosamides, both classes are known carcinogens
-- many sources in foods, including: use of nitrate and/or nitrites as food additives, drying
processes involving open flames, spices, cooking over open flames
-- tolerance provisions protect sources from exclusion by Delaney Clause due to pre-1958
allowance and by virtue of practicality involved in banning all such foods
Food-borne molds and mycotoxins
-- include both “field fungi” and “storage fungi”
-- major classes are aflatoxins and tricothecenes
-- considered unavoidable contaminants by CGMP