The food fighters
BBSRC-funded researchers reveal how food architecture affects wellbeing
14 May 2010
Interest in food has intensified over the past decades. Diets in western countries have broadened to include gastronomic delights from around the world that not so long ago were considered exotic.
More options are not without problems. Image: iStockphoto
And with increasingly food-savvy consumers comes wider appreciation of what food does to our bodies. Food is medicine - a carrier for essential vitamins and minerals - but allergic reactions are on the rise and increasing consumption of processed food is driving an obesity epidemic.
In biology, structure often determines function. Therefore, studying the molecular structure of foods can probe their nutritional and safety profile. Ultimately, the answers will direct how we shape our policies towards food, at a national and personal level, to keep us fitter, happier and healthier for longer.
Research on food structures has revealed that the recommended '5-a-day' regime of fruit and vegetables may be much better for us than previously thought; it's because scientists may have been underestimating the quantities of beneficial compounds called polyphenols that are found in fruit.
Dr Sara Arranz at work at IFR. Image: IFR
Polyphenols are found in many plants and include tannins (as found in wine) and flavinoids that can act as anti-oxidants and reduce damage to cells and DNA caused by rogue oxygen molecules called free radicals.
Professor Fulgencio Saura-Calixto from the Department of Metabolism and Nutrition, University of Madrid, estimates that the actual polyphenol content may be more than double the values have been reported Ref 1). "Usual analytical techniques are not able to detect these compounds because they are linked to dietary fibre and cell wall constituents and therefore are not extractable using aqueous organic solvents."
However, these non-extractable polyphenols are bioactive in the large intestine because bacteria in the colon release the compounds from the food matrix, which is the complete physical architecture of the ingested food. "These compounds have important physiological and nutritional role." says Saura-Calixto. Polyphenols have shown important effects on gut health, including a likely preventive effect for colorectal cancer (Ref 2, Ref 3).
Saura-Calixto's group in Madrid had been working on the concept of non-extractable polyphenols for some time. A scholarship from the Spanish Ministry of Science and a BBSRC Strategic Programme Grant then enabled his colleague Dr Sara Arranz from the Institute of Food Science and Technology and Nutrition (ICTAN) in Madrid to work at the Institute of Food Research (IFR, an institute of BBSRC) for 3 months with Dr Paul Kroon.
At IFR Arranz learned to apply high performance liquid chromatography analysis techniques presently used for extractable polyphenols to apple, peach and nectarine and found concentrations of non-extractable polyphenols up to 5 times higher than expected.
Food contains nutrients and many substances essential to our wellbeing, but sometimes foods can be mistaken by the body's immune system for a foreign invader and invokes a response that leads to allergic symptoms. Most reactions fade after time but hypersensitive reactions such as anaphylactic shock can in rare cases cause death if a person's respiratory system constricts enough to suffocate the victim.
Red wristband shows food allergy.
The symptoms can be different in the same person on each occasion, often determined by the route of exposure, and different amongst allergic individuals exposed to the same allergen. Symptoms include itching, swelling (of the whole body as well as of the joints, lips, mouth, tongue, throat, eyes or skin), runny nose and eyes, asthma, nausea, vomiting and rashes.
Dr Clare Mills is a Programme Leader in Food Structure and Health at IFR who also leads the EuroPrevall project (see 'continental') has been trying to unravel why food allergies occur, and what foods cause them, for years.
All food allergens are proteins, and previously Mills was involved in a bioinformatic analysis of the protein sequences of known plant food allergens (in collaboration with Rothamsted Research, also an institute of BBSRC) which revealed that 62% of plant food allergens belong to just 3 plant families. "That's given us evidence that something about the 3D structure of proteins may predisposes them to allergens," says Mills. A few years later, a similar analysis with animal food allergens showed a similar pattern, which means that food findings may relate to allergy in general.
Birch pollen is major allergen in the northern hemisphere. Image: iStockphoto
The 'cross-reactivity' phenomenon, when an allergic response to one stimulus brings out the same response for another, offers a clue as to what food structures are prompting the body's immune response. For instance, people who are allergic to birch pollen often react to some fruits because of a similar protein found in each. In Sweden for example, 70% of people with birch pollen allergy have allergies to a fresh fruit, particularly apple.
The major allergen in birch pollen is a protein called Bet V1. It causes allergic reactions in 10-15% of the populations of Northern Europe, the US and Russia. There are similar structures (homologues) of Bet V1 in many edible plant tissues which activate the allergic response via the antibody immunoglobulin E (IgE). "The proteins in birch pollen and apple have such similar structures that IgE also recognises that protein in apple," says Mills. "You tend to find that in areas where birch is endemic."
Digestion changes food structure. Image: iStockphoto
Cross-reactivity allergic responses do not comprise or explain the majority of reactions. Most food allergies result from digestion and how food reacts with the gastrointestinal tract and immune system.
One hypothesis to explain food allergy variability is that certain proteins are resistant to digestion. "We've been studying the susceptibility of allergens to simulated gastrointestinal digestion and looking at processed proteins because cooking affects food structure," says Mills. "What we are finding is that 3D structure is very much an indicator of behaviour of resistance to digestion."
For example, for many people allergic to tissues found in apple, cooking and processing seems to remove the allergenic effect. Not so with allergic reactions to peach, which is found in many Mediterranean countries, or the celery added to many foods in Switzerland.
The food matrix structure is thought to make a difference. "Maybe something in apple food matrix makes the protein less stable in apple than in celery, which appears more resistant to thermal processing."
Food structure research has important impact in the realm of food labelling. Mere traces of a food allergen can prompt a severe life-threatening reaction and consumers need to be protected, particularly from 'hidden' ingredients. For instance, dried celeriac is often hidden in celery spice and can provoke reactions in central Europe where it is consumed widely; likewise with lecithin and egg in the UK.
Currently, European Union legislation requires certain foods to be labelled irrespective of the level: wheat, products made from cows' milk, celery, mustard, soya, sesame seeds, tree nut, peanuts, shellfish, mollusc, lupin and cereals containing gluten (wheat, rye, barley and oats).
Mills says her research sheds new light on what foodstuffs are labelled because the list was based on the best estimates available at the time. "The regulations are not founded in fact," says Mills. "Our work will provide information to re-evaluate this labelling."
For instance, allergies are not common in Greece, but they show some of the severest anaphylactic reactions to sunflower, which is not on the list. "They don't have a lot of reactions but when they do it is a real problem," says Mills, adding that they don't see many reactions from sesame or mustard even though they are on the list.
Part of the process
Physicist Professor Athene Donald of Cambridge University has been putting food under the microscope for years. What surprised her was how little we knew about common foodstuffs when she began to look closely at the structure of starch, a key source of carbohydrates, when working in industry in the 1980s.
"When I started the company [Dalgety] was interested in the mechanical properties of processed snack foods rich in starch. It was then that I realised how little was known about starch itself," says Donald.
ESEM of potato granule concentric growth rings. Image: Jane Crawshaw
Processed foods are a multi-billion pound industry and because millions of tonnes are produced each year a small finding could make a big difference. Donald's work, later with food firm Unilever and a string of BBSRC-funded PhD students, thus delved into the starch granule to understand the hierarchy of the way that the molecules were packed inside it, and what the consequence would be for processing.
Using advanced imaging techniques, such as small angle x-ray electron scattering and environmental scanning electron microscopy (ESEM), Donald found that there were regions of the spherical starch granule that were amorphous with no crystal pattern. "But between the concentric growth rings of starch there are regions with a high degree of crystallinity, and water is less to likely enter the denser crystals," she says.
This helped to explain why the same wheat crops grown in different seasons needed different amounts of water to process properly - the pattern of growth of the starch rings changed seasonally - something the food industry had noticed during processing but couldn't explain.
Donald says the finding also gave a basis to understand processes during gelatinisation and freeze storage. "It wasn't a killer discovery in one sense, but it made more sense of a lot of the disparate information out there," she says. "From bread to biscuits to thickenings for sauces - all sorts of different applications."
Scientists are still looking at starch and how the arrangement of starchy carbohydrates affects processing. Food structure and processing affects our bodies' metabolism, which is of particular interest for researchers trying to understand the development of obesity and type II diabetes.
Mills is the head of the €14.7M EuroPrevall project that seeks to define the patterns and prevalence of allergens in Europe. It includes 67 partners including 17 European member states and collaborators from India to Iceland.
First, a birth-cohort study because the incidence of food allergy are much higher in young children. Co-ordinated from Berlin, this experiment follows more than 12,000 European children from birth to 2.5 years and collates data on maternal diet during pregnancy, weaning, and into toddlerhood.
Second, a London-based community-cohort survey of 20,000 school-age children and 20,000 adults. It is hoped that the large sample number will reveal patterns that may be hard to obtain because the overall incidence of food allergy is 1-2% of the adult population and 5-6% of under 16s (even though up to one in five people think they may have a food allergy).
The third project is a Madrid-based outpatient clinic study that gathers data from around 2000 people who all have food allergies.
Mills and her EuroPrevall colleagues are finding that there are big differences in the incidences of food allergy. The incidence in Athens is very low for example, as it is in eastern European countries like Lithuania and Bulgaria. By contrast, Mills says that in Amsterdam "The food clinician is struggling to cope."
Why such a difference? "There are lots of hypotheses about why this might be," says Mills. "It could be nutrition, infections early in childhood, and if a person lives in too clean an environment you see more allergic diseases in general - including food allergens."
The simple answer now, and until the data is fully analysed, is that we don't know. But Mills is hopeful the answers will come. "EuroPrevall will be the first time we've shown this heterogeneity in a co-ordinated study using the same sampling the same analysis everywhere."
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- High contents of nonextractable polyphenols in fruits suggest that polyphenol contents of plant foods have been underestimated (2009) (external link)
- Multi-targeted therapy of cancer by green tea polyphenols (external link)
- Inhibition of growth and induction of apoptosis in human cancer cell lines by tea polyphenols (external link)
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