Undesirables (NUT312 - Food Chemistry) PDF

10. Undesirables NUT312 - Food Chemistry 1  Introduction  Four groups of undesirables: 1. Endogenous toxins: natural components of food 2. Microbial toxins: they arise through the activity of contaminating molds or bacteria 3. Toxi...

10. Undesirables NUT312 - Food Chemistry 1  Introduction  Four groups of undesirables: 1. Endogenous toxins: natural components of food 2. Microbial toxins: they arise through the activity of contaminating molds or bacteria 3. Toxic residues: they are carried over into food from procedures applied to plants or animals that become our food 4. Toxic contaminants: they arise during food processing 2 Endogenous Toxins of Plant Foods  Solanine ◦ A bitter heat-stable glycoalkaloid in potatoes and aubergine ◦ Potatoes exposed to light and turned green → high level of solanine, mostly just under the skin  Growing popularity of prepared potato products with skin (e.g. potato wedges)! ◦ It inhibits the acetyl choline esterase, a key component of the nervous system ◦ It causes neurological impairment after ingestion at high doses 3 Endogenous Toxins of Plant Foods  Caffeine and Theobromine alkaloids ◦ These substances, found in tea, coffee, cocoa, and cola beverages, cannot be classified as toxins since they are stimulants  They could never be regarded as nutrients 4 Caffeine and Theobromine 5 Endogenous Toxins of Plant Foods  Roasted coffee beans have 1-2% caffeine, but the level in the beverage depends on the method of preparation ◦ 50-125 mg per cupful is normal  Black tea leaf contains 3-4% caffeine, giving around 50 mg per cupful  Cocoa powder contains 2% theobromine and 0.2% caffeine ◦ Plain chocolate contains 0.5% theobromine and 0.05% caffeine ◦ Milk chocolate contains 0.2% theobromine and 0.02% caffeine 6 Endogenous Toxins of Plant Foods  Caffeine content of cola drinks is restricted to 200 mg/L max., although the average value is around 65 mg/L ◦ ‘Energy drinks' include extracts of the South American plant, guarana, which provides additional caffeine to give a final concentration of 200-300 mg/L (= 5 cups of coffee)  Caffeine's stimulant action is due to its stimulation of the release of adrenaline and noradrenaline into the bloodstream ◦ Other effects observed on levels of glucose, triglycerides, and cholesterol in the blood of coffee drinkers can be traced back to this hormone release 7 Endogenous Toxins of Plant Foods  There have been few cases of death due to caffeine consumption; 150-200 mg/kg have proved fatal to humans ◦ ~30L of energy drinks!  Caffeine does not cause either birth defects or low birth weights, but its ordinary stimulant effects are not beneficial during pregnancy ◦ Consume decaffeinated instant coffee! 8 Endogenous Toxins of Plant Foods  Pyrrolizidine alkaloids or PAs are associated with herbal remedies ◦ They can appear in milk or honey when the concerned cows or bees were fed on unsuitable plants ◦ Comfrey plant, used to make herbal tea, contains 12 different PAs ◦ PAs are assumed to be behind cases of liver damage due to the use of herbal preparations 9 Comfrey 10 Endogenous Toxins of Plant Foods  Substances with adverse effects on humans turn out to be natural insecticides ◦ A good example are the psoralens of celery 11 Endogenous Toxins of Plant Foods  Psoralens exist widely in plants ◦ Reports of severe skin rashes in farm workers are linked to psoralens  Psoralens are present in the green leafy parts of celery  Psoralens from the plant are absorbed through the skin  This celery variety is no longer grown 12 Endogenous Toxins of Plant Foods  Chocolate causes migraine in susceptible individuals ◦ This is due to its content of phenylethylamine  A vasopressor amine  Product of the amino acid metabolism of the plant or of the fermenting microorganism in cheese and wine  Our body is well equipped to deal with it, but some individuals have difficulty in dealing with it  It causes constriction of the blood vessels in different parts of the body resulting in hypertension and intense headaches 13 Endogenous Toxins of Plant Foods  Cassava causes cyanogenesis ◦ Chronic CN- poisoning, caused by ingestion of low levels over prolonged periods, is widespread in parts of the world dependent on cassava ◦ 2 common diseases are attributed to interaction between CN- intake and deficiency of the vitamin B12  Degenerative neurological condition  A form of blindness 14 Endogenous Toxins of Plant Foods  2 types of toxins are linked to raw legume (peas, beans, peanuts, soybeans) 1. Protease inhibitors  Cooking! 2. Lectin proteins  They bind to the surface of RBCs, causing them to clump together; haemagglutinins  They represent a significant fraction of the total protein of legumes (3% in soybeans)  Experimental animals fed diets containing 1% unheated soybeans show impaired growth  Cooking! 15 Endogenous Toxins of Plant Foods  Phytoestrogens ◦ They were the cause of fertility problems in sheep that had consumed a diet rich in clover, now recognized as major source of phytoestrogens ◦ Foods based on soya (soya milk and tofu) are the main sources in human diets ◦ With the exception of infants being fed soya milk as an alternative to human/cow's milk, human intakes are very low ◦ There is some evidence that the incidence of breast cancer may be lower in diets rich in soya 16 Endogenous Toxins of Plant Foods  Myristicin ◦ Significant levels in nutmeg and smaller amounts in black pepper, carrots and celery ◦ There is sufficient myristicin in 10g of nutmeg powder to cause euphoria, hallucinations, and narcosis ◦ Higher doses induce nausea, delirium, depression, and stupor ◦ Myristicin levels in the quantities of nutmeg used as a flavoring are way below these effects, but the consumption of nutmeg- flavored foods during pregnancy is not advised 17 Endogenous Toxins of Animal Foods  Puffer fish is a delicacy in Japan ◦ Tetrodotoxin occurs in various organs of the puffer fish including the liver and ovaries ◦ The minimum lethal oral dose is 1.5-4.0 mg ◦ Stringent licensing of expert cooks is required, but fatalities remain a regular occurrence 18 Endogenous Toxins of Animal Foods  At certain times of year, the coastal waters of hot parts of the world develop a reddish color (red tide) due to the massive proliferation of red-pigmented dinoflagellates ◦ These contain toxins that find their way up the food chain to shellfish  Saxitoxin is one of the best known of the toxins causing paralysis and other effects on the nervous system PSP - paralytic shellfish poisoning 19 Endogenous Toxins of Animal Foods  Scombrotoxin (histamine) poisoning is associated with tuna and sardines consumption ◦ When freshly caught, the fish are not toxic, but if held at temperatures above 10oC for several hours, high levels of histamine are formed from histidine by bacteria ◦ Consumption of histamine from contaminated fish lead to severe headaches, palpitations, gastrointestinal upsets and skin flushes 20 Mycotoxins  While the value of the fermentative microorganisms involved in dairy products is recognized, most people will reject food that is ‘moldy’ ◦ The growth of many species of fungi on foods is accompanied by the production of toxins that are often extremely dangerous 21 Ergotism 22 Mycotoxins  Ergotism: its onset is usually slow, but generally catastrophic in outcome ◦ The victim initially suffers discomfort and then intense burning pains in the hands and feet ◦ These give way to a total loss of sensation in the limbs often accompanied by mental derangement and gastrointestinal failure and then death  The comparative rarity of the disease today can be ascribed to a number of factors 1. Modern fungicides reduce the incidence of infected plants to a minimum 2. Nowadays, millers inspect all grain shipments 23 Mycotoxins  Aspergillus flavus produces a group of toxins known as aflatoxins ◦ Aflatoxin B1 is one of the most potent liver carcinogens known  Aflatoxins are recognized as hepatotoxins ◦ Long term exposure is a probable cause of liver necrosis, liver cancer and hepatitis B ◦ Although few plants are immune from aflatoxin contamination, peanuts and peanut butter can present particular hazards 24 Mycotoxins  Preventive measures for aflatoxin production focuses on controlling the temperature and humidity  Wherever contaminated animal feedstuffs are used, aflatoxins can be expected in milk ◦ Aflatoxins B1 and G1 are converted into M1 by liver enzymes, which then appear in liquid milk, presenting a serious problem for the dairy industry 25 Mycotoxins  Ochratoxins is another mycotoxin that occurs in warm climates and contaminates cereals ◦ A serious form of kidney disease affecting humans in the Balkans has been associated with ochratoxins  Patulin is not a dangerous mycotoxin ◦ It is used in apple juice as a marker for the use of moldy fruit ◦ It is found in home-made jam that has mold growing on its surface 26 Bacterial Toxins  The growth of bacteria, unlike molds, is not visible ◦ The most feared of the bacterial food intoxications is botulism, caused by the toxin secreted by the anaerobic Clostridium botulinum ◦ Its vegetative cells are not particularly resistant to heat, unlike the spores ◦ Canning is designed to eliminate C. botulinum spores 27 Bacterial Toxins  Acidic foods (fruit or pickles) present no hazard since their pH is too low for clostridial growth  Once absorbed, botulinum toxin blocks the transmission of nerve impulses to the muscles (neurotoxin) ◦ Dizziness and general weakness, followed by paralysis and death by respiratory and cardiac failure 28 Bacterial Toxins  In contrast to the severity and rarity of botulism, the consequences of consuming food contaminated by the toxin from Staphylococcus aureus are not fatal, but experienced by almost everyone at one time or another ◦ S. aureus can be found on the skin, hair and nose (40-50% of people can positive) ◦ S. aureus secretes enterotoxin proteins resistant to heat and digestive enzymes 29  Bacterial Toxins ◦ Cooking will not inactivate S. aureus toxin  Practicing good personal hygiene  Consuming food straight after cooking, unless adequately refrigerated 30 Allergens  1-2% of individuals suffer from food components, food allergens  Allergy (hypersensitivity) is an overreaction of the immune system to a foreign material (the allergen), leading to symptoms including: ◦ Skin reactions ◦ Vomiting and diarrhea ◦ Difficulty in breathing ◦ Anaphylaxis  In recent years, particular attention has been devoted to nut allergies, especially to peanuts 31  Allergens  Cow’s milk allergy (CMA) affects up to 7% of infants ◦ Soy milk does not cause CMA  Coeliac disease is the allergy to wheat, barley and rye proteins, more specifically the gliadin fraction of gluten ◦ It occurs throughout the world, wherever wheat is the staple cereal ◦ It starts after weaning ◦ It damages the cells lining the jejunum, causing impaired digestion and absorption of nutrients resulting in failure to thrive, anemia and gastrointestinal disorders 32 Allergens  Complete removal of gluten from the diet is the only satisfactory treatment ◦ As with the allergens of cow’s milk, the allergenicity of the gliadins is unaffected by cooking ◦ Both maize and rice are safe for coeliac sufferers ◦ The use of wheat flour in too many processed food products poses special problems and emphasizes the importance of accurate food labeling  A number of other foodstuffs are well known for their allergenicity, even though the number of sufferers is small ◦ Egg proteins (notably ovomucoid) can produce similar symptoms to those produced by milk  The allergenicity of ovomucoid survives cooking 33 Toxic Agricultural Residues  Pesticides are so universally distributed through our environment that for they are unavoidable components of our diet ◦ DDT insecticide had reached humans from meat and dairy products ◦ Its use is either banned or greatly constrained in Europe, North America 34 Toxic Metal Residues  Sources: 1. Soil in which plants are grown 2. Sewage sludge, fertilizers, and other chemicals applied to agriculture 3. Water used in food processing 4. Contaminating dirt on unwashed vegetables 5. Equipment and utensils used for food processing 35 Lead  Lead is the metal that springs to mind when the question of metal contamination of food is raised ◦ Considerable amounts find their unwanted way into our lives ◦ Sources:  Lead from gasoline combustion  Lead water pipes and tanks ◦ Lead content of the body builds up as we get older 36 Mercury  Sources ◦ Consumption of cereal grains dressed with antifungal mercurial compounds ◦ Industrial pollution of coastal waters and consequently of seafood  It is converted in sediments on river and lake bottoms into highly toxic methyl mercury compounds ◦ Contamination of fish with mercury has been a great concern ◦ 0.5 ppm of mercury in fish is considered the maximum permitted level  Symptoms of mercury poisoning include damage to the central nervous system 37 Toxins Generated during Heat Treatment of Food  The polynuclear hydrocarbons (or polyaromatic PAHs), components of smoke, are carcinogens ◦ When carbohydrates or fatty acids are heated above 500oC, they give rise to PAH ◦ Barbecued meats have high levels of PAH caused by fat dripping out of meat onto the burning charcoal of the barbecue ◦ Designs grills that prevent dripping fat from reaching the fire (vertical design like shawarma) 38  Packaging Residues  Plastics used to package our food can be the source of traces of low molecular weight compounds that migrate into the food ◦ Plasticizers  Substances incorporated into plastics to prevent them from becoming too brittle  Phtalates plasticizers may mimic female sex hormones and affect male fertility ◦ Bisphenol A (BPA) is used to make certain plastics  Banned for use in making baby bottles 39  Environmental Pollutants  Dioxins ◦ Major source is the combustion of materials that contain chlorinated compounds (waste incinerators and vehicle exhausts) ◦ Their ubiquitous character and persistence in the environment leads them to accumulate in fatty tissues of animals and humans  PCBs (polychlorinated biphenyls) ◦ In the light of their toxicological problems and persistence in the environment, their use is now banned (they also accumulate in fatty tissues of animals and humans) 40