Module 12 Flashcards
Define toxicant.
A poison or a poisonous agent.
Poisons are chemicals that, in very small quantities, produce illness or death. Legally, a poison is defined as a chemical that has a lethal dose of 50 milligrams or less of chemical per kilogram of body weight.
When we refer to toxicants in food, we are generally referring to substances responsible for a whole spectrum of possible results, ranging from relatively minor discomfort or sickness to poisoning that can lead to death.
Define: toxicity.
The intrinsic or inherent capacity of a substance to damage a biological system (produce injury) when tested by itself.
Substances vary in their toxicity, as reflected in their dose-response curves.
A toxicant can have an effect on several different functions within an individual. The individuals can vary among themselves with regard to the sensitivity of their different functions.
Define: hazard.
A thing or action that can cause adverse health effects in animals (including fish), plants or humans. The capacity to produce injury under the circumstances of exposure.
Why is hazard a more complex concept than toxicity?
Because it includes a consideration of conditions of use; in other words, two components are involved in assessing a hazard:
1. the inherent capacity to cause harm (toxicity), and
2. the ease or probability of contact between the substance and the target object.
“An extremely toxic chemical, such as strychnine, when sealed in an unopenable vial, can be handled freely by people with no chance that a poisoning will occur. Its toxicity has not changed, but it presents no hazard because no contact can be established between the chemical and people. Conversely, a chemical that is not highly toxic, such as boric acid, can be very hazardous when used in a manner that makes it readily available for accidental ingestion.” Dr. Ottoboni
Define: risk
A function of the probability of an adverse health effect and the magnitude of that effect, consequential to a hazard; the likelihood of the occurrence and the magnitude of the consequences of an adverse event.
Describe a dose response curve.
- The dose at which a substance begins to have an undesirable effect, that is, the upper limit of its “no effect” dose, is its threshold. This value is unique for each substance.
- The slope of the increasing dose-increasing effect portion of the curve is also characteristic of the particular substance. A chemical with a very steep dose-response curve offers very little flexibility in trying to avoid harmful exposure. A one- or two-fold difference in the amount of chemical consumed might be the difference between no-effect and serious consequences.
List 6 naturally occurring toxicants (i.e., constituents).
- Cholinesterase inhibitors
- Cyanogenic glycosides
- Glucosinates
- Protease inhibitors
- Nitrites
- Allergens
List 3 naturally occurring toxicants (i.e., contaminants).
- Mycotoxins
- Bacterial toxins
- Seafood toxins
List 5 environmental toxicants.
- Food packaging residues
- Pesticide residues
- Heavy metals
- Animal drugs
- Radioisotopes
Solanine in potatoes
Cholinesterase inhibitors
Constituents
Amygdalin in apple seeds
Cyanogenic glycosides
Constituents
Sinigrin in cabbage
Glucosinates
Constituents
Protease inhibitors in soybeans
Protease inhibitors
Constituents
Beta-lactoglobulin
Allergen
Constituent in milk
Peanut or soy proteins
Allergens
Constituents
Cholinesterase inhibitors
Constituents
Solanine in potatoes
Cyanogenic glycosides
Constituents
Amygdalin in apple seeds
Glucosinates
Constituents
Sinigrin in cabbage
Protease inhibitors
Constituents
Protease inhibitors in soybeans
Allergen
Constituent in milk
Beta-lactoglobulin
Allergens
Constituents
Peanut or soy proteins
Aflatoxin
Mycotoxin
Contaminant in mouldy meat
Patulin
Mycotoxin
Contaminant
Ochratoxin A
Mycotoxin
Contaminant
Vomitoxin
Mycotoxin
Contaminant found in wheat
Zearalenone
Mycotoxin
Contaminant
Botulinum toxin
Bacterial toxin
Contaminant
Staphylococcal toxin
Bacterial Toxin
Contaminant
Histamine
Seafood toxin
Saxitoxin
Seafood toxin
Domoic acid
Seafood toxin
Tetradotoxin
Seafood toxin
Seafood toxins [4]
- Histamine
- Saxitoxin
- Domoic acid
- Tetrodotoxin
Bacterial toxins [2].
- Botulinum toxin
- Staphylococcal toxin
Mycotoxins [5].
- Aflatoxin
- Patulin
- Ochratoxin A
- Vomitoxin
- Zearalenone
Food packaging residues
Monomers of plastic resins
Environmental toxicant
Monomers of plastic resins
Environmental toxicant
Food packaging residues
Pesticide residues [3].
- Herbicides
- Insecticides
- Fungicides
E.g., malathion residues on fruit
Heavy metals [3].
- Lead
- Mercury
- Cadmium
E.g., lead in veg; mercury in large ocean fish like swordfish
Animal drugs [2].
- Antibiotics
- Hormones
E.g., penicillin in milk
Radioisotopes
- From soil or
- From radioactive fallout
What is the basis for distinction between Natural Constituents and Natural Contaminants?
- Constituents are chemical entities that are part of the normal composition of a food material - they are not the result of some external organism or activity.
- Contaminants, on the other hand, are present because of the presence of moulds or bacteria, or because the plant or animal was grown in a condition which permitted the toxicant to become part of the food.
What is the distinction between natural and environmental toxicants?
- Less clear cut but may be generally determined by their origin.
- For example, we might be able to prevent the growth of moulds, but moulds are nevertheless naturally present in the environment.
- Pesticides, however, are introduced into the environment by us and while not intended to become part of the food, some do to a certain extent.
- Mercury and lead can enter the food supply because of heavy natural deposits in the soil, but in fact are found in food predominantly because we use these metals in a wide variety of ways.
Describe the perceptions of hazards in the food supply held by popular belief compared to regulatory agencies.
It is interesting to note that what is perceived by popular opinion to be the greatest hazard is indeed considered to be the least important by regulatory agencies, and vice-versa! Regulatory agencies base their ratings on a much broader information base (including statistical or epidemiological evidence) than does the general public.
What is a glycoalkaloid-cholinesterase inhibitor?
- Refers to a variety of chemicals which are able to inhibit the activity of the enzyme cholinesterase
- The enzyme is found in nerve tissues and plays an important role in the transmission of nerve impulses.
- When this enzyme’s function is inhibited, nerve function is affected.
Solanine is an example of such an inhibitor (found in high levels in greening potatoes)
Where is solanine found?
- Solanine can is found in potatoes, normally at levels of 2-13 mg/100 g fresh weight, the bulk of market potatoes probably contain only 3-6 mg/100 g.
- Levels as high as 80-100 mg/100 g, have been reported particularly if the potatoes have undergone greening (reaction of potato tubers on exposure to sunlight).
- Solanine is insoluble in water and is not lost or destroyed when potatoes are cooked.
- Because it is found primarily in the skin of potatoes, the peeling of potatoes reduces the concentration markedly.
Solanine is destroyed when potatoes are cooked.
True or False?
False.
Solanine is insoluble in water and is not lost or destroyed when potatoes are cooked.
Solanine is not destroyed when potatoes are cooked.
True or False?
True.
Solanine is insoluble in water and is not lost or destroyed when potatoes are cooked.
How can solanine concentration in potatoes be reduced markedly?
By peeling potatoes, since solanine is found primarily in the potato skin
What are clinical symptoms of solanine poisoning? [3]
- GI disturbances
- Neurological disorders
- Death
What are the symptoms of ingested (rather than injected) solanine exposure?
- Drowsiness
- Increased sensory activity
- Difficulty breathing after any oral dose of 100 mg (~ 2-8 mg/kg body weight)
- Higher doses may cause vomiting and diarrhea
Solanine is not readily absorbed and is fairly rapidly excreted by way of the feces and the urine.
Although the chemical solanine itself is quite a potent toxicant, the hazard of solanine poisoning by consumption of potatoes is quite low. Why is that?
- Potato growing and handling practices minimize the opportunity for greening, and hence minimize the production of abnormally high levels of solanine.
- Seed potatoes that are genetically low in solanine content are used, and during the growing season the potato plants are hilled, thereby decreasing the exposure of the potato to light.
- After harvesting, potatoes are put into storage facilities which minimize exposure to light.
- Consumers who ignore the hazards of consuming potatoes that have turned green during improper storage at home would face a high risk of poisoning by solanine!
What are cyanogenic glycosides?
- They yield hydrogen cyanide (HCN) upon treatment with acid or particular hydrolytic enzymes
- They are found widely in plants, and also occur in ferns, moths and insects (e.g., cassava, sweet potato, yam, maize, bamboo, sugar cane, peas, lima beans, almonds, lime, apple, pear, cherry, apricot, plum)
- Cyanide is very rapidly absorbed from the GI tract and produces recognizable symptoms at both fatal and non-fatal levels.
How does death result from fatal doses of HCN?
- General anoxic condition caused by the inhibition of cytochrome oxidase, with which the HCN complexes
- Cytochrome oxidase is an important component of the oxidative phosphorylation cycle which occurs in the mitochondria of cells.
- Inhibition of this enzyme causes the death of cells.
- Since the HCN binds reversibly to the cytochrome oxidase, non-fatal doses permit recovery by employing respiratory exchange and metabolic detoxification processes.
For humans, the minimum lethal dose of HCN taken orally has been estimated to be between 0.5-3.5 mg/kg of body weight.
What is an example of a cyanogenic glycoside?
- Amygdalin found in bitter almonds and some fruit pits
Which enzymes are responsible for the hydrolysis of cyanide glycosides?
- Beta-glycosides, which are highly specific for the beta-glycosidic linkage that is characteristic of cyanogenic glycosides.
- Hydrolysis of cyanogenic glycosides can occur during the cutting, crushing, bruising or maceration of tissue prior to consumption, or can be initiated upon the maceration of the tissue during eating.
- Cyanide poisoning can therefore occur when enough of a plant material that is rich in cyanogenic glycosides and enzymes is consumed, or when such material has been prepared with insufficient care to remove the HCN accumulated during preparation.
In parts of the world where some of these cyanide-producing plants are used extensively for food, means of preparation have been developed to remove or hydrolyze the glycosides and to destroy the ß-glucosidase that is present. While these steps minimize the hazard, they do not completely eliminate it.
It is important, however, that while the cyanide-producing capacity of a plant is important in determining its toxicity, there are other factors which must also be considered. What are they? [5]
- The size and kind of subject
- The speed of ingestion
- The type of food ingested simultaneously with the cyanogen
- The presence of active degradative enzymes both in plant and in the subject’s digestive tract
- The subject’s ability to detoxify the HCN
The hazard associated with the presence of cyanogenic glycosides in food for those individuals who consume large quantities of the affected plant foodstuff is much more significant than for those who accidentally eat the occasional apple seed or apricot kernel.
Describe the natural toxicant: protease inhibitors.
- Proteinaceous compounds are found in many of the legume species.
- They have the ability to make a complex and thereby interfere with certain proteolytic enzymes.
- Proteins need to be hydrolyzed into their constituent amino acids by digestive enzymes such as trypsin and chymotrypsin.
- If these enzymes are rendered inactive by complexing inhibitors, the body cannot fully hydrolyze the proteins, thereby creating the possibility of amino acid deficiencies.
Describe the natural toxicant: nitrates.
- Widely found in constituents of plant materials, especially green leafy plants
- Nitrates themselves are not very toxic; however, bacteria can reduce them to nitrites.
- A primary concern about nitrites is their ability to interact chemically with hemoglobin, interfering with the blood’s ability to transport the required oxygen to the body’s cells.
- By a rather complex series of reactions, not only bacteria but also metabolic pathways within the digestive system of humans can utilize nitrate/nitrite as a precursor for the formation of nitrosamines, potent carcinogens.
What is the primary concern about nitrates?
- Bacteria reduce them to nitrites, which are a precursor for nitrosamines, potent carcinogens
Describe the natural toxicants: allergens.
- Have the ability to induce allergic reactions in sensitive individuals.
- Foods that are most frequently reported to cause allergic responses are cereals such as wheat, rye and rice; legumes such as peas, peanuts and soybeans; tree nuts; milk; eggs; and seafood such as shrimp, crab and lobster.
- The case of allergens provides a good example of the need to consider individual (genetic) differences in assessing risks and hazards.
- For most of us, consumption of the foods listed above does not pose any significant risk.
- However, for someone who is severely allergic to a particular food or food component, accidental ingestion may lead to a life-or-death situation!
What are mycotoxins?
- Substances produced by mould which may be toxic
- Mycotoxins may occur by direct contamination (due to mould growth on the food) or by indirect contamination (by using a food ingredient that was contaminated).
- Mycotoxins can be highly toxic to the body, some have been known to cause cancer in animal tests, others are mutagenic and able to cause mutation, and others are teratogenic and capable of causing deformities in embryos.
- Mycotoxins are invisible to the eye, are often unchanged by heat and can potentially spread throughout a product.
- As a result, any sign of visible mould could indicate that the product contains mycotoxins and should be thrown away.
Examples: aflatoxins, sterigmatocystin, ochratoxin A, citrinin and patulin
What is this?
- Saxitoxin is a contaminant which the shellfish consume as part of their occasional food supply.
- The shellfish feed on a variety of microscopic plankton among which are certain toxic dinoflagellates.
- At certain times of the year, under certain conditions, these dinoflagellates increase greatly in number and concentration in the oceans.
- This is often referred to as a bloom or “red tide.”
- During red tide, the shellfish are exposed to and concentrate large amounts of saxitoxin.
- Saxitoxin is extremely stable and takes a long time to be flushed from the tissues of the shellfish.
- It is for this reason that during red tide season and for a considerable time afterwards, harvesting shellfish is prohibited.
Saxitoxin is considered one of the potent toxins, the minimum lethal dose being about 1.0-4.0 mg/kg of body weight. However, because of the variability in the concentration of the toxin in the shellfish, it is very difficult to indicate a maximum amount of shellfish tissue that can be consumed. This is obviously a situation which is not at all hazardous to anyone who rarely harvests and consumes shellfish. However, the hazard increases significantly, for those who are uninformed and are fond of shellfish, particularly those harvested in areas known to be subject to red tide situations.
These are the number of cases reported in BC - what do they represent?
- the “tip of the iceberg”
- only 1-4% of all foodborne disease outbreaks are reported and documented
List 6 pathogenic microorganisms.
How important is hand washing?
- The following figure dramatically illustrates the importance of washing hands thoroughly after handling raw meats.
- In this experiment, a previously sanitized hand was rubbed with a cube of raw pork for about 15 seconds.
- The hand was then pressed gently onto a 9” agar plate and labeled as “soiled hand” (A).
- Hands were again washed with Hibitane hand sanitizer (4% w/v chlorhexidine gluconate) for 30 seconds and the right hand was gently pressed onto a second agar plate labeled as “washed hand” (B).
- Both plates were incubated at room temperature for 2 days.
