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DETERMINATION OF
TOXICANTS IN
FOODS
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Foods and drink can cause people to be ill becausethey are contaminated with harmful micro-organisms and/or their toxins (poisons) - this isoften called food poisoningfood poisoning.
To detect : food samples
Two major processes:
To detect the presence of a toxicant in foods To qualitate and quantitate the toxicants
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Food safety : An important step in the initial phase is
assessment to estimate the levels of the toxicant towhich the population is exposed.
Method: a) dietary survey
b) market basket analysis
chemical analysis in food toxicology involve separating
a toxicant from other chemicals and then determiningthe amount
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sampling
To obtain a portion for the estimation orobservation of attributes of the particular lot; thesample must be representative of the lot.
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Qualitative and quantitative
Require both an assay for detecting the poison and amethod for separating it from the rest of the chemicals inthe foods
Separation methods:
Gas chromatography (GC)
High performance liquid chromatography (HPLC)
Column & thin layer chromatography (CC,TLC)
Distillation
extraction
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chromatography GC
HPLC CC,TLC
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a way of separating out a mixture of chemicals, which are in
gas or liquid form, by letting them creep slowly past anothersubstance, which is typically a liquid or solid
involve the interaction of a mixture between a stationary anda mobile phase
The key thing to remember is that chromatography isa surface effect.
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Different types of chromatographic techniques.
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Gas chromatography
used in organic chemistry for separating and analyzing compounds thatcan be vaporized without decomposition.
include testing the purity of a particular substance, or separating thedifferent components of a mixture
moving phase (or mobile phase) is a carrier gas, usually an inert gas such
as helium or an un reactive gas such as nitrogen.
stationary phase is a microscopic layer of liquid or polymer on an inertsolid support, inside a piece of glass or metal tubing called a column.
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High performance liquid chromatography
utilizes a column that holds chromatographic packing material(stationary phase), a pump that moves the mobile phase(s)through the column and a detector that shows the retention timesof the molecules.
Retention time varies depending on the interactions between thestationary phase, the molecules being analyzed and the solvent(s)used.
one of the most powerful tools in analytical chemistry. It has the abilityto separate, identify, and quantitate the compounds that are present inany sample that can be dissolved in a liquid.
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Column chromatography
to purify individual chemical compounds from mixtures ofcompounds.
used for preparative applications on scales from micrograms uptokilograms, and for cleaning the analyte of the matrix
interferences, for use with more sophisticated techniques
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Biological Determination of
Toxicants
Genetic toxicity
Acute toxicity
Bioassay
Metabolism
Subchronic toxicity Teratogenesis
Chronic toxicity
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GENETIC TOXICITY
Definition:
refers to the ability of substances or physical agents todamage the DNA and/or chromosomes of cells. Such
damage can lead to mutations that increase thelikelihood of certain diseases, such as cancer and birth
defects.
determined using a wide range of test speciesincluding whole animals and plants (e.g., rodents,
insects, and corn), microorganisms, and mammaliancells.
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The most common gene mutation tests involve:
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Acute toxicity
Definition:
the toxicity produced by pharmaceutical when it is
administered in one or more doses during a periodnot exceeding 24 hours.
Acute toxicity tests are generally the first tests
conducted.They provide data on the relative toxicitylikely to arise from a single or brief exposure.
Standardized tests are available for oral, dermal,
and inhalation exposures.
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Purpose to identify the dose of the
pharmaceutical which causesmajor adverse effects, to helpset doses for further preclinical
studies and to predict theeffects of overdose in humans.
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Basic parameters of these tests
are:
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Bioassay
Definition:
the use of a living organism to test for the presenceof a compound or to determine the amount of thecompound that is present in a sample.
a procedure for the determination of theconcentration of a particular constituent of amixture.
a measurement of the effects of a substance on
living organisms.
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Types of Bioassays
[1]Quantal Assays [ Direct endpoint ] Elicits an All or None response in different animals
Eg.
Digitalis induced cardiac arrest in guinea pigs
hypoglycemic convulsions in mice.
Digitalis induced head drop in rabbits
Calculation of LD50 in mice or rats
[2]Graded Response Assays [mostly on tissues]
Graded responses to varying doses
Unknown dose response measured on same tissue
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Examples of Biological Assay:
LimulusTest
a sensitive method for detection of bacterial
endotoxins and endotoxin.
Endpoint Determination
an establishment of the level of a quantifiable
effect indicative of a biologic process.Theevaluation is frequently to detect the degree of
toxic or therapeutic effect.
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Metabolism
First, Santorio in 1614 in his book Ars de statica medicina(vital force which later known as metabolism)
Metabolic studies can be conducted after mutagenicity
test. Objective:
To gain understanding of the:
Absorption,
Biotransformation,
Disposition (storage),
Elimination characteristics of an ingested substance after singleand repeated doses.
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Metabolism
Knowledge of the metabolism and
pharmacokinetics of a substance is essential
for establishing the relevance of results fromanimal testing to projecting likely hazards in
humans.
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Subchronic toxicity
Objective
Determine the possible cumulative effects on
tissue or metabolic system To evaluate the safety of food components.
Determine if test substance toxic or not.
Performed for several months duration.
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Subchronic toxicity
Procedure :
Inspection of physical appearance and behavior
Body weight Food consumption
Characteristics of excreta
Blood, urine, hepatic, body temperature renal and
more.
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Teratogenesis
Birth defects are known to occur in 3-5% of all newborns.
They are the leading cause of infant mortality in the United States,accounting for more than 20% of all infant deaths.
7% to 10% of all children will require extensive medical care to diagnose ortreat a birth defect.
And although significant progress has been made in identifying the etiology
of some birth defects, approximately 65% have no known or identifiablecause.
It was previously believed that the mammalian embryo developed in the
impervious uterus of the mother, protected from all extrinsic factors. However, after the thalidomide disaster of the 1960s, it became apparent
and more accepted that the developing embryo could be highly vulnerableto certain environmental agents that have negligible or non-toxic effects toadult individuals.
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What is teratogenesis ?
Teratology is the study of abnormalities of
physiological development. It is often
thought of as the study of birth defects, but itis much broader than that, taking in other
developmental stages, such as puberty; and
other life forms, such as plants
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Wilson's 6
principles
These principles of teratology were put forthby Jim Wilson in 1959 and in his monograph
Environment and Birth Defects.Theseprinciples guide the study and understanding
of teratogenic agents and their effects ondeveloping organisms:
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Teratogenic agents
A wide range of different chemicals and environmental factors aresuspected or are known to be teratogenic in humans and in animals.A selected few include:
Drugs andmedications: tobacco, caffeine, drinking alcohol
(ethanol), isotretinoin (13-cis
-retinoic acid, Roaccutane).
Environmental chemicals: polychlorinated biphenyls (PCBs),polychlorinated dibenzodioxins a.k.a dioxin, polychlorinateddibenzofurans (PCDFs), organic mercury, ethidium bromide.
Ionizing radiation: background radiation, diagnostic x-rays,
radiation therapy. Infections: cytomegalovirus, herpes virus, parvovirus B19, rubella
virus (German measles), syphilis, toxoplasmosis, Venezuelanequine encephalitis virus.
Metabolic imbalance: alcoholism, endemic cretinism, diabetes,
folic acid deficiency, iodine deficiency, hyperthermia.
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Chronic toxicity
chronic toxicity: the adverse effects occurring after the administration
of a test sample for a major part of the lifespan (usually 6-12 months).
Chronic toxicity represents cumulative damage to specific organsystems and takes many months or years to become a recognizableclinical disease.
With repeated exposures or long-term continual exposure, the damagefrom these subclinical exposures slowly builds-up (cumulative damage)until the damage exceeds the threshold for chronic toxicity. Ultimately,the damage becomes so severe that the organ can no longer function
normally and a variety of chronic toxic effects may result.
Examples of chronic toxic affects are:
cirrhosis in alcoholics who have ingested ethanol for several years
chronic kidney disease in workmen with several years exposure tolead
chronic bronchitis in long-term cigarette smokers
pulmonary fibrosis in coal miners (black lung disease)
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Objective:
To assess toxicity resulting from long-term, relatively low
-level
exposure, which would not be evident in subchronic testing.
Test designed so that each treated and control group will includesufficient numbers of animals of both sexes of the chosen species
and strain to have an adequate number of survivors. The chronic toxicity test provides the final piece of biological
information on whether to accept or reject a substance suggestedfor food use.
If no carcinogenic effects are found, this information will be used in
the overall risk assessment of a substance
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