4
A number of examples are presented to give an idea of how a processing chain can look.
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Depending on the raw material and unit operations involved in the processing, potential contaminants vary.
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Raw materials in examples include cereals, root crops, grapes, pig liver, chicken meat and milk.
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Feed contaminants may be carried over to meat-based products.
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● there were seven glyphosate occurrences, all of which were in wholemeal or brown flour;
● there were nine pirimiphos-methyl occurrences, seven of which were in wholemeal or brown flour; and
● 13 samples contained more than one pesticide, 11 of which were wholemeal or brown flour.
With regard to mycotoxins, both OTA and the so-called trichothecenes often contaminate cereals under temperate growth conditions. However, since we are dealing here with a product often based on rye, it is only natural to mention that rye especially can be contaminated by the toxic sch-lerotia of the fungus Claviceps purpuria ‘ergot’.
These contain the toxic so-called ergot alkaloids.
A survey from 2008 including 24 unknown rye flour samples from Danish mills showed that these contained on average 46 mg of total alkaloids per kilogram, with a maximum content of 234 mg kg−1. The most common ergot alkaloids found were ergotamine and ergocryptine.
The carcinogenic and neurotoxic substance acryl-amide can be formed during heat processing of starch-rich food products in particular. In addition to starch the presence of the amino acid asparagine also seems to be crucial for the reaction, leading to the formation of acrylamide. At the present time intense research and development activities are ongoing in order to reduce the resulting concentra-tion in the final marketed products. Crisp bread is one of the products in which acrylamide concentra-tions have been found to be high relative to many other generally consumed food products. This has prompted industries to develop methods to reduce this content. As an example one can mention the commercialization of an asparaginase by the inter-national enzyme producer Novozymes. Company trials carried out in its bakeries and in industry showed that this product, Acrylaway®, can reduce acrylamide by up to 90% in crisp bread. Also, the company states that no changes in the taste and appearance of the crisp bread occur.
From cassava roots to ‘garri’ (‘gari’)
‘Garri’ is a fermented dry food product with a long shelf-life produced after harvest of the very perishable, starchy tuber cassava root, from the plant Manihot esculenta. Cassava roots form the staple food (source of energy) for approximately 800 million people worldwide. The plant originates
in the Amazonian region of South America, but today cassava is grown in all tropical regions nour-ishing hundreds of millions in Africa and elsewhere.
‘Garri’ is made from cassava tubers that have been peeled, washed and grated to produce mash.
Different methods exist for the further processing.
In one of these the mash is put into a non-water-proof bag and allowed to ferment for 1 or 2 days, while weights are placed on the bag to press the water out. During this part of the processing pH is decreasing as a result of lactic acid fermentation, which gradually becomes dominating. The fer-mented dewatered mash is then sieved (or sifted) and roasted by heating in a bowl. During the roast-ing palm oil may be added to produce so-called
‘yellow garri’ instead of the white quality. The resulting dry granular ‘garri’ can be stored for long periods and used in several ways, such as to make
‘eba’, a pastry made by soaking ‘garri’ in hot water, or ‘kokoro’, a common snack food in Nigeria made from a paste of maize flour mixed with ‘garri’ and sugar and deep-fried.
Cassava contains in all its parts the compounds linamarin and lotaustralin, which liberate the toxic chemical entity hydrogen cyanide (HCN) upon processing and chewing. The glucosides are stored in the plant cell, while a b-glucosidase (linamarase) able to hydrolyse these is bound to the cell wall.
When the plant tissues are damaged as a result of chewing/processing, the linamarase comes into con-tact with the glucosides and the process of degrada-tion takes place. Linamarin and lotaustralin thus are cyanogenic glucosides and their degradation to HCN involves cyanogenic intermediates in the form of cyanohydrins (a-hydroxynitriles). Together the glucosides, the cyanohydrins and HCN – all of which are toxic – may be termed cyanogens. The toxicity seen after consumption includes acute poi-soning, which can be fatal. Also some studies have shown a strong association between a monotonous diet on insufficiently processed cassava and the CNS disease konzo, which gives rise to walking disabili-ties. Konzo mostly affects women of childbearing age and children over 2 years of age and is persistent in, for example, Mozambique and Tanzania.
Cassava cultivars are classified as sweet (cool) or bitter depending on whether the tubers may be eaten without any prior processing or not. The bitter taste of the tubers has been shown to correspond with higher levels of linamarin (and lotaustralin).
Cassava is the only domesticated staple crop for which a significant part of the edible production is
toxic. In areas where cassava is a main staple crop, bitter and toxic cultivars often are preferred, whereas sweet (cool) cultivars abound in areas where cassava plays a secondary staple role.
All cassava-consuming societies have developed and adopted effective processing methods to reduce the potential toxicity of the root tubers upon con-sumption. Of these methods the production of
‘garri’ is among the most effective, giving rise to a safe and easy-to-store product with a long shelf-life. The reduction of the original content of cyano-genic glucosides in the roots during the production of ‘garri’ is due to: (i) the grating, which brings together the linamarase and the glucosides to start hydrolysis; (ii) the dewatering, where most of the remaining glucosides together with the HCN formed leave the mash; and (iii) the roasting, dur-ing which the remaindur-ing cyanohydrins and HCN leave the product by evaporation.
‘Garri’ is produced commercially in many coun-tries in West Africa and exported to most European countries among others.
From grapes to wine
Several moulds can develop on grapes. These include Botrytis cinerea, which is responsible for the disease ‘grey root’, and species of Alternaria, Cladosporium, Fusarium, Aspergillus and Penicillium. Analysis conducted in 1997 and 1998 showed that wines could contain significant levels of the mycotoxin OTA, a nephrotoxic substance leading to irreversible damage of the kidneys, as can cereals, coffee, beer and cocoa. OTA is synthesized by Aspergillus and Penicillium species. Experiments in France in 2001 proved that Aspergillus carbon-arius was the absolute most important source of OTA formation in grapes. The fungus establishes itself at a very early stage of the development of the grapes on the wine plant. It penetrates into the berry through already existing skin damage and starts its OTA production.
Today we know that for several groups of European consumers cereals are responsible for the main OTA burden (45–50% of average intake), while wine is responsible for the second largest contribution (10–20% of average intake). According to several analyses carried out in Europe since the middle of the 1990s, certain wines and grape juices at that time contained up to 10 mg OTA l−1. Within France it has been demonstrated that Mediterranean wines are more affected by OTA than wines from
other regions. Similarly, broader surveys have shown that wine produced in Europe varies in inci-dence and concentration of the toxin OTA, higher contents being found in wines from southern regions, increasing in the order white < rosé < red.
Later investigations of wines produced in Chile and Argentina have indicated that these may contain lower levels.
4.3 From Plant to Animal Products From feed to pig liver pˆaté
In modern agriculture most pigs are produced using very effective methods of reproduction and extremely intensive methods ensuring optimal growth rates. The composition of the feedstuff with regard to nutrients varies according to the animal’s age; however, the single components used to obtain the desired composition also vary depending on the prices of the different raw materials.
Barley is often used as a component in the feed-ing of pigs. The mycotoxin OTA produced by Aspergillus and Penicillium fungi is a common contaminant of barley and may occur in unaccept-able levels in cool wet conditions, as reported for example from the state of Alberta, Canada. OTA produces depressed appetite and reduced growth rate in pigs. At concentrations greater than 5 to 10 ppm, a number of conditions may arise such as impaired kidney function, necrosis of lymph nodes and fatty liver changes.
Barley by-products are alternative feeding sup-plies for animal production including swine feed. In a recent survey from Brazil, maize, brewers’ grains (barley by-product) and finished swine feed sam-ples were collected from different factories. Fungal counts were higher than 2.8×104 CFU g−1. Fusarium, Aspergillus and Penicillium genera were isolated at high levels. About 25% of the isolates produced from 9 to 116 mg OTA kg−1in vitro. Maize samples (44%) were contaminated with 42–224 mg OTA kg−1. Finished feed (31%) and brewers’ grains samples (13%) were contaminated with 36–120 mg OTA kg−1 and 28–139 mg OTA kg−1, respectively.
The feeding of pigs with OTA-contaminated material for finishing before slaughter may lead to the development of so-called porcine mould nephro-sis. The kidneys are swollen and pale. This condition must be recognized during meat inspection at the slaughterhouse, since the liver especially will also contain unacceptably high levels of this nephrotoxic
substance. Since OTA is also relatively stable towards heat treatments, such carry-over from feedstuffs to the pig liver will also mean a risk for contamination of highly processed food products made from liver, for example, pig liver pˆaté produced industrially in high amounts in certain countries.
From feed to chicken meat
Chickens may be kept on the basis that they find their food themselves by pecking around the farm or they may be produced using much more inten-sive setups. Especially in certain regions of the world a substantial part of their feed could be cot-tonseed or cotcot-tonseed press cakes (meal) from the expression of cotton oil. Cotton plants (Gossypium spp.) are grown in dry climates at temperatures between 11 and 25°C in Asia and Africa as well as in North and South America, and are used for pro-duction of the raw material for cotton cloth and cottonseed oil. The total annual production of cot-ton in 2007/2008 was about 46×106 t from about 35 million ha, principally in the People’s Republic of China and India (31 and 23% of the global pro-duction, respectively).
When the fibres have been removed, the seeds undergo further processing to remove the oil by crushing and/or solvent extraction. The remaining meal is used as a feed material because of the high protein content. However, non-processed whole cottonseeds, as well as processed cottonseed meal, may contain large amounts of free gossypol, which may cause adverse and toxic effects if used as a
feedstuff. Gossypol is an intensely yellow com-pound that is insoluble in water and soluble in organic solvents and fats. Because of the presence of the polyhydroxylated aromatic aldehyde moieties in the molecule, gossypol exhibits complex tautomerism (Fig. 4.1), which influences its chemical reactions.
The two forms (+)-gossypol and (−)-gossypol gener-ally coexist in the cotton plant, usugener-ally with a slight predominance of the (+)-form.
Gossypol shows a variety of biological actions.
Signs of gossypol toxicity are similar in all animals and include laboured breathing and anorexia.
Acute toxicity has been shown in the heart, lung, liver and blood cells, resulting in increased erythro-cyte fragility. Post-mortem findings include gener-alized oedema and congestion of lungs and liver, fluid-filled thoracic and peritoneal cavities, and degeneration of heart fibres. Reproductive toxicity is seen particularly in males, where gossypol affects sperm motility, inhibits spermatogenesis and depresses sperm counts. Ruminants are less sensitive to gossypol than non-ruminants.
The presence of gossypol has been demonstrated in muscle tissue from broilers fed cottonseed- derived materials. In 2008 EFSA published a risk assessment on possible problems with the occur-rence of gossypol in feedstuffs. The assessment showed that gossypol concentrations in tissues from broiler chickens fed a diet containing the maximum permitted level of free gossypol in cottonseed meal and the maximum recommended inclusion rate (2.5%) in feed for poultry (30 mg kg−1) will mean that average human consumers can occasionally be
Fig. 4.1. Tautomeric forms of gossypol.
OH
OH
OH OH
CHO CHO
HO
HO
OH
HO
HO
O
2 HO
HO O
CHOH OH
2 2 CHO
HO
HO
exposed to 0.0036–0.036 mg gossypol kg−1 BW day−1, whereas for high consumers occasional expo-sure would range from 0.01 to 0.06 mg kg−1 BW day−1. This is not regarded as being a problem.
However, the risk assessment also states that ‘in some developing countries, live stock is to a large extent fed with cottonseed products with high levels of gossypol and its transfer to edible tissues might represent a hazard for human health’.
From feed to dairy products (yoghurt) Man has been making yoghurt for at least 4500 years. The name is derived from the Turkish word yog˘ urt, and is related to yog˘ urmak = to knead and yog˘ un = dense or thick. Today it is a common food product throughout the world, a nutritious dairy product rich in protein, calcium, riboflavin, vitamin B6 and vitamin B12. Yoghurt is produced by bacte-rial fermentation of milk. Fermentation of the milk lactose produces lactic acid, which acts on milk protein to give yoghurt its texture and its charac-teristic tang. Yoghurt is produced using a culture of two bacteria, Lactobacillus delbrueckii subsp.
bulgaricus and Streptococcus salivarius subsp.
thermophilus.
Unwanted chemical substances in the final prod-uct here could include the mycotoxin AFM1. In the EU legislation that sets the maximum accepted levels for unwanted substances in feedstuffs, the lowest level found is that for the mycotoxin AFB1 in feedstuffs for dairy cows. This is due to the fact that this extremely toxic and strongly carcinogenic com-pound is metabolized by the cow to form the almost as toxic compound AFM1, of which a fraction is
excreted into the milk. Hence, we immediately see that a well-functioning control for the occurrence of aflatoxins in feedstuffs as well as in raw milk is crucial.
4.4 From Water Quality to Shellfish Dish Water quality is important for the final quality of the shellfish (molluscs and crustaceans) that live and grow in the water. Thus, shellfish accumulate arsenic present in the water and furthermore they may contain toxic levels of a number of different algal toxins (marine biotoxins) concentrated as a result of their filter feeding. The latter is the reason why state/regional authorities can close fishing/
production areas if an algal bloom is occurring or if the level of such algal toxins has been found to be too high in shellfish from the area.
4.5 Conclusion
A thorough understanding of the existing interrela-tionships in the overall production chain from plant to plate or meat to meal is crucial for the suc-cess of our work to ensure a good chemical food safety situation.
Further Reading
Parker, R. (2003) Introduction to Food Science. Delmar-Thomson Learning, Albany, New York.
Singh, B.P. (ed.) (2010) Industrial Crops and Uses.
CABI Publishing, Wallingford, UK.
Varnam, A.H. and Sutherland, J.P. (1995) Meat and Meat Products: Technology, Chemistry and Microbiology.
Chapman & Hall, London.
Our daily activities at home, in our neighbourhood and at work constantly brings us into contact with a large number of chemical substances. Some of these are well known to our body, such as the mix-ture of gases we breathe and call ‘air’, the water we swim in and the amino acids that the proteins in our food are degraded into before being absorbed into the bloodstream. Others are foreign to our body such as the plant alkaloid caffeine present in the coffee and tea we drink during the day and the polycyclic aromatic hydrocarbon (PAH) benzo[a]
pyrene formed through pyrolysis (decomposition of a substance by heat) in the engine of our car, present in the smoke from our cigarette and maybe on the surface of the steak we have grilled a little too much.
While our body has distinct routes for the uptake, distribution, interconversion (metabolism) and excretion of the chemical compounds that make up our cells and tissues, things are different when it comes to foreign compounds. Such compounds we often term xenobiotic compounds, or in short just xenobiotics. This definition includes both natural and man-made compounds; others prefer to restrict the term to man-made compounds only.
No organism on Earth can risk being able to deal only with its own constituents. This is due to the fact that, although the barriers which protect an organism from the outside world are astonishingly effective, they are not perfect. Animals (including man) are protected by the skin, the mucous mem-branes in the eyes, nose and mouth, bronchioles and lungs, and by the surfaces that our mechanically
degraded food meets in the stomach and the intes-tines. As we immediately understand from this, no chemical compound has entered our body before it has penetrated one of these barriers; thus, the gut surface with its villi and microvilli is also an outer surface of our body.
All of the barriers mentioned have several func-tions besides being barriers. The understanding of this is crucial when analysing the possibilities for a given compound to pass a given barrier. Thus, the skin has sweat glands and hair follicles, structures that can be entrance ports; the pulmonary alveoli – of which each human lung contains about 300 million, each wrapped in a fine mesh of capil-laries covering about 70% of its area – are specially designed to allow effective gas exchange; and the surface of the small intestine is designed to allow uptake of nutrients essential to our survival.
A toxic substance can act locally at the site of exposure. Thus, an acidic or alkaline solution can irritate or corrode the skin or a mucous membrane, while several salts of different metals such as cop-per and lead can cause cell necrosis in the intestines upon ingestion. The latter effect is due to the action of the metal ions binding to thiol (–SH) groups in enzymes essential to the function of the borderline cells. When discussing chemical food safety we are lucky only to have to focus on the oral intake of xenobiotic substances and the effects that may follow such an intake. Hence, the following discus-sion looks at the possible local effects on the gas-trointestinal tract and the effects caused by the substance after its absorption into the bloodstream