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Ask a Food Scientist 2005

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The Food Commodities and Ingredients Group originally ran its 'Ask A Food Scientist' initiative in 2005 (questions and answers below)

Safety

I have a long question about GM food!
What's the real reason for uncertainty about GM (genetically modified) food? What do scientists really think the risks are? Is it to do with potential health risks to humans (and if so is there any evidence that this is a real threat); or is it more to do with not knowing what the long-term effects on the environment/ecosystems will be (e.g. pest-resistant crops might lead to a reduction in the populations of pests, which might mean less food for certain species of birds, which might mean... etc)? Or is it really just about people having an instinctive feeling that ‘meddling with nature is bad’?

Secondly, what is the UK's position on GM food in the UK? Is there any distinction between (a) GM crops (b) GM animals and (c) animals fed on GM crops? If not, should there be such a distinction?

Thirdly, what is the UK's position on GM food in developing countries? I'm curious to know whether it's not considered safe for consumers in the UK, while simultaneously being encouraged in developing countries (e.g. which tend to be subject to drought and subsequent famine).

Fourthly, are we already eating GM foods without being aware of it? I've heard in the past that pretty much all the corn (maize) and soya available now is GM... is this true, and if so are there other food products that are basically only available in their new-and-improved GM form now?

1) The issue of GM is one where the concept of zero risk has enabled the objectors to seize the moral high ground. Scientists will of course, not say there is zero risk, and the objectors have been able to play on a variety of potential negatives such as you mention - particularly with the longer term ones, knowing the scientists cannot say there is no risk. Whilst accurate, this does not help the consumer make an informed decision. It is like trying to prove a negative.

In addition, the companies developing the GM items have been slow off the mark to demonstrate the advantages to the general public, rather than advantages to the farmer or the pesticide companies. If you ask the public their feelings about GM, there is certainly a feeling ‘meddling with nature is bad’.

2) UK position on GM food - there are definite differences:

  • GM crops - not liked but people aware that they exist and are being used.
  • GM animals - definitely not liked - as too close to humans, is seen as playing God.
  • Animals eating GM - bit of a grey area. Some retailers are seeking to claim an advantage for it, but not widespread.

3) Developing Countries: This goes back to what is the advantage and who gets it? GM technology needs to show clearly defined benefit for the people.

4) GM - are we already eating it? I do not believe that to be true - yet - although within next 3-5 years then it will become likely for certain products or ingredients. Is the consumer ready for this? I am not sure.

I understand that scientists have introduced fish genes into strawberries because the antifreeze component in fish blood is beneficial in preventing early frost damage. Has any of this GM crop ever reached the wild?
This was a new one for us – but we have found some information on the Cornell University website for you. You will see the article starts on the slightly more palatable combination of fish and tomato genes, before moving on to strawberries.

Despite its finding ‘There are no published studies involving strawberries, no companies which have announced research or marketing plans for such a product, no government records of field testing such a plant, and no trace in the media to explain how this story may have originated,’ it does feature a charming picture of a ‘fishberry’.

Is it safe to swallow chewing gum?
While I wouldn’t recommend it as a regular habit, the general view is that it is not harmful. Chewing gum contains familiar ingredients like sweeteners, sugar syrups and flavours. All of these will dissolve in the mouth as the gum is chewed. The ingredient that gives chewing gum its chewy properties is called gum base. This doesn’t dissolve in the mouth and it will not be digested by the body if swallowed. It will pass through the body and be excreted, in a similar way to fibre.

The threat of bird flu seems to have dropped out of the headlines. Is there any danger in eating poultry or eggs in the UK? And if it's safe here, what about in south east Asia?

All I can do is refer you to the advice given by the UK Food Standards Agency and EFSA (European Food Safety Authority) and many other agencies around the world, which states that avian flu does not pose a food safety risk for UK consumers.

In Asia, the main risk is for those in contact with live poultry that have the disease.

How long should you keep food in the freezer for?
From a food safety point of view there is no time limit on the storage of food in a freezer that operates at -18 degrees Celsius. This is because harmful micro organisms are unable to grow at freezer operating temperatures.

Recommended storage times in freezers are for quality only as the eating quality of the food will deteriorate over time, even though it will remain safe.

What temperature should my fridge and freezer be kept at, to keep my food safe in the summer?
Your freezer should be at -18°C and the temperature of the food in the fridge should be at 8°C. Keep the air temperature in your fridge between 1° and 4°C and your food should be safe provided you eat it within date.

What kind of food is most likely to cause food poisoning?
Bacteria (germs) love moist food containing protein e.g. meat, fish, eggs and milk. Any of these foods eaten without further treatment e.g. sandwiches, are called high risk food and are a main cause of food poisoning. Undercooked burgers and chicken can also cause food poisoning as the bacteria (germs) will not have been killed.

Where should foods be stored in the refrigerator? Ie which shelves for dairy, cooked meat, raw meat, and vegetables?
Domestic refrigerators are not really designed to store food correctly. As a rule raw food go at the bottom and cooked foods at the top, with salad and vegetables in the containers provided at the bottom. The important thing is to prevent cross-contamination of food poisoning bacteria from raw foods to cooked. Therefore, wherever possible, food should be stored in sealed containers.

Should duck be cooked to an internal temperature less than 70°C as per the requirements for poultry? It is common practice to have duck pink and bloody in the middle - but is it associated with salmonella?

The practice of serving duck pink in the middle is traditional practice in restaurants, and yes there is a potential risk of salmonella. It is suggested that if the duck is not pierced by a knife or similar object then bacteria have not been introduced to the duck breast. This is similar to rare or blue steaks. However, to be safe, cook your ducks thoroughly.

What chemicals are used in the preparation of washed and 'ready to eat' lettuce? Do significant amounts of these chemicals remain on the lettuce, and are they harmful?
The biggest cause for concern is probably that of pesticide residues left over from the cultivation of the lettuce itself. Lettuce is quite a demanding crop and therefore to grow it all the year round, especially in the UK with our often damp and grey climate, the growers will use pesticides/fungicides to increase their rate of success.

The UK's Dept of Environment, Food and Rural Affairs (DEFRA) has a monitoring programme that samples and takes action against growers who exceed the MRL (max recommended limit) or who are found to use non-approved pesticides. Historically the residues found have been of inorganic bromide, particularly in winter lettuce, originating from the use of methyl bromide, this chemical is however in the process of being phased out (because of its ozone depleting properties) and should be less of a concern moving forward. I'm not a toxicologist, so for more information I would suggest looking at the DEFRA website.

Once the lettuce is harvested it is washed in chlorinated water, the levels of chlorination being typically higher than used for drinking water - but not swimming pool strength! The leaves are then gently spun dry and any chlorine left should wash off quite quickly. Some concerns have been expressed about chloramines, which form due to reaction of the cut sap from the lettuce and the chlorine. These are more stable compounds, and in fact mono-chloramine is routinely added to our tap water, as it has less of a taste than regular chlorine treatment. However in lettuce washing another chloramine - nitrogen trichloride has been found which in very much higher concentrations is known to have some irritancy effects.

I would like to know the facts on the 2005 Sudan I scare
These links will help you:

Is there any problem in re-freezing frozen products that have partially defrosted?
It all depends upon the product and what you mean by partially-defrosted. If the product is raw and going to be cooked, there is no problem, as cooking kills bacteria. If it is a high risk food e.g. cooked chicken, any bacteria which may be present, will start to multiply during the defrosting process and the food becomes unsafe to eat.

Is it true that organic foods contain higher levels of fungal aflatoxins than conventional foods?
There is no reason why this should be true. Aspergillus species which produce aflatoxins are fungi which grow on warm damp materials. Usually found on ground nuts. which are left to get wet after harvest. It may be that systemic fungicides would prevent development during cultivation, but I am not aware of tests on harvested nuts showing differential levels of aflatoxins.

Before expiry and 'best before' dates came in, we used food (jam, bread, cheese for instance) until it was visibly mouldy or smelled bad. Did this do us any harm?
I cannot comment on whether more people were ill when shelf-life dates did not exist. However a number of moulds can produce mycotoxins, which can make people very ill and penicillin mould sometimes found on jam can cause an allergic response in some individuals.

I heard a report recently that said we are wasting too much money throwing away food, because of the sell-by date. They said it was alright to eat fruit and veg if you cut away the bad bits, and as long as meat is cooked thoroughly, it can be used after the sell-by date. Also that tinned food can be used years after the sell-by date had passed, as long as the tin wasn't rusted, dented or pierced. I was always told this as a child, and then dates started appearing on tinned produce. Would you like to comment?
All foods are required by law to have a shelf-life date. This may be best-before date or use-by date. Shelf-life dates are based on safety and quality. A product may remain safe but not of the quality expected e.g. live yogurt kept correctly will deteriorate in quality due to enzyme action although it is still safe to eat. Many products are still safe and of a reasonable quality after their shelf-life date but the manufacturers cannot assume the public will store food safely, therefore they err on the side of caution.

How many times can I reheat a meat-based meal? Eg if I make a batch of chili on day 1, reheat on day 2 but do not eat it all, can I reheat it again on day 3, 4 etc?
Reheating foods is never a good idea, as apart from the safety issues you also lose food value. Regarding your chilli, heating and cooling must be controlled. The preparation and cooking of the chilli must ensure the product is safe, i.e. reach 75°C or above. Boiling achieves 100°C and is best. The chilli should be cooled as quickly as possible, and stored correctly at less than 8°C. The first re-heating of the product should reach the original cooking temperature, i.e. boiling point. In theory you can repeat this process, but with careful management to ensure that no spore-forming bacteria fill the food full of toxins between each re-heating process.

Nutrition

chipsIs tinned pineapple as nutritious as real pineapple?
Pineapple is good stuff tinned or fresh. Fresh pineapple is very low in saturated fat, cholesterol and sodium. It is a good source of fibre, vitamin C, thiamine and vitamin B6 as well as manganese and potassium. It also contains the proteolytic enzyme bromelain which acts as an aid to digestion. There is also mounting evidence that this and other related enzymes in pineapple may have anti-cancer effects and preventative effects against cardiac disease.

The trouble with the canning process is that it denatures heat-sensitive components including vitamin C, bromelain and other enzymes. The canning industry usually adds back vitamin C in the syrup, but not the other components so the associated benefits they are thought to have will be lost. The syrup is also likely to have added sugar, so if you are concerned about your calorific intake you should take this into account.

I'd like some clarification about the five portions of fruit and vegetables a day we are supposed to have. Does this include fruit juice, and if so, should it be freshly-squeezed or is a carton OK? And what about dried fruit or canned or frozen products?
The concept of the five-a-day message is to try and get across, in as simple as possible a way, the idea of increasing fruit and veg intake and at the same time to give some realistic guideline as to by how much. Since there are an enormous number of nutritional factors that interact together in fruit and veg such as fibre, vitamins, minerals, antioxidant components etc and a very large number of possibilities of fruit and veg that one may consume, the government has sought to give an 'average best practice' message.

Consequently there are going to be some significant variabilities between different types of fruit and veg and the ways in which it may have been processed and prepared, and, of course, the physiology of the individuals concerned who are consuming it. However for the population overall, more fruit and veg has got to be a good thing, even with all the possible variations.

To answer your question; fruit juice is included, one portion being considered as 150ml, so a carton of orange juice prepared from concentrate will certainly qualify. However for overall benefit, freshly squeezed with all the bits in will go one better since some nutritional components will not have been damaged by heat during processing and you'll get some fibre from the bits. A note of caution, fruit juice can only count towards one of your five a day no matter how much you drink.

Dried fruit is also good as are frozen and canned products, a portion of all these is 80g. My own view is that 'fresh is best' since processing will reduce some of the heat sensitive nutritional components. Having said that, there is evidence with frozen peas for example, which are famously frozen within four hours of picking, that the frozen product is better than a fresh one which will have been around at ambient temperature for a lot longer by the time you get it with a consequent loss of nutrients through enzymic reactions.

The final thing to remember is to have some variety. Five a day does not work if you restrict yourself to one type of fruit or veg. If you ate 400g of raw carrots a day you might end up looking like a carrot or growing floppy ears and a fluffy tail! Also don't forget that starchy foods like potatoes do not count. Five portions of chips a day is unlikely to improve your chances of avoiding a coronary.

Is it true that frozen vegetables (peas, cauliflowers, etc) don't contain as much nutrition as fresh raw vegetables? And what does freezing do to the nutritional value of meat?
Vegetables eaten immediately after harvesting will have the greatest nutritional value, provided they are cooked correctly. Frozen vegetables are processed as soon as possible after harvesting. However as soon as a plant is harvested it starts to lose nutritional value. Most vegetables are blanched before freezing so this causes more loss, and the freezing process tends to rupture the cell structure, so on thawing, more nutrients are lost, in particular the water-soluble vitamins.

However, frozen vegetables still contain a useful amount of nutrients and make an important contribution to the diet. Fresh vegetables bought at the supermarket may be quite old, so the nutritional value of these will have been reduced. To get the best nutritional value out of vegetables, grow your own. The next best thing is to buy the freshest vegetables you can.

When meat is frozen some damage occurs to its structure, causing loss of fluid during thawing. This fluid will contain some proteins and minerals, so some nutritional value is reduced. However, because meat does not contain Vitamin C, which is the main issue with vegetables, this does not significantly alter its nutritional contribution to the diet. Freezing meat, however, does tend to toughen it.

Why is it that chickens that eat green food, like grass and vegetables, produce an egg with a yolk that is more yellow than chickens that don't? And is the ‘yellower’ colour of the yolk an indication of a more nutritious egg? Grass contains the pigment carotene which is a strong orange/yellow colour. There are various forms of carotene of which beta carotene is a commonly used additive in food to give it an orange/yellow colour. You may have noticed that the fat on beef when the animal has been fed outside is more yellow than when the animal has been fed inside.

Carotenes are fat-soluble and as the egg yolk contains fat it picks up the carotene from the grass. Carotene is a precursor of Vitamin A, the body converts approximately 55% of carotene eaten into Vitamin A. The vitamin is needed to maintain healthy eyes and deficiency can lead to night blindness. The old adage that you should eat carrots to see in the dark therefore has an element of truth in it. It is very unlikely in developed countries that we should become short of Vitamin A as it can be stored in the body, in fact too much can lead to Vitamin A toxaemia.

There is increasing publicity about 'trans fats'. Perhaps you can tell me what the problems are for human health. In particular, is there a safe threshold for trans fats in the diet? And are there any foodstuffs with high levels to avoid?
I’d like to know what I should spread on my bread .... butter, margarines based on various vegetable oils, or butter-mimicking margarines?

Trans fats are a hot topic at the moment, partly due to new legislation in the USA which stipulates that products on sale there must have details of trans fats ingredients declared on the label.

Trans fats are of concern as they tend to have a double downside effect on the human body. While it is accepted that the mono-unsaturated and polyunsaturated fats increase the levels of High Density Lipoproteins (HDL – the good cholesterol), and saturated fats increase the level of Low Density Lipoproteins (LDL – the bad ones), the trans fats tend to reduce the HDL as well as increasing the LDLs.

The main evidence for the concern about how much trans fat is consumed comes from looking at the effect of the long-term consumption of these fats in a large group of people (epidemiological studies). Until this type of study was undertaken it was felt that trans fats acted like saturated fats. In fact, the populations of most developed countries have been consuming trans fats since in margarines, cakes and biscuits since about 1910, during which time life expectancy has continued to increase.

Current data suggests that in the UK, the population gets about 2% of its energy from consuming trans fats, and the government advice is that this level should not increase. A more important statistic is that most people get about 39% of their energy from fats, and this should be reduced to about 30%, and of course, a large majority of this fat is saturated fat, which raises the LDL levels. In general, if you wish to avoid trans fats, you should try to avoid products which include ‘hydrogenated fats’, but this can be misleading as fully hydrogenated fats do not contain trans fats.

As you say, most of the top brands of margarine now contain hardly any trans fats at all (<0.9%). They used to contain trans fats, but the recent concern about trans fats has meant that they have changed the production technology so that they now contain no hydrogenated fats. It should also be noted that, although it has a superior flavour, butter naturally contains about 3.5% trans fats. So the choice of spread is down to butter, or a good quality margarine. Personally, I use butter, but thinly spread!! My maxim in life is – everything in moderation.

What method of cooking vegetables is the best for retaining their nutrients? Boiling, microwaving, steaming, or roasting?
Soluble vitamins such as vitamin C are easily lost in cooking. Therefore any drier process such as microwaving and steaming are better than boiling in water. Heat can also destroy vitamins, therefore cooking as quickly as possible is best, i.e. if you do boil in a pan of water, place the raw vegetables into boiling water not cold.

How much, if any, damage can I do to myself if I do not eat any fruit or vitamin supplements?
Eating no fruit and vegetables would lead to vitamin and mineral deficiency, in particular Vitamin C. Of course a number of essential vitamins are found in vegetables, so vitamin deficiency should not be a problem if you eat the full range. Vegetables such as spinach contain a useful source of iron, and vitamin C can be found in leafy vegetables and potatoes, where it lies under the skin (eat potatoes with their skins on). If you cut out both fruit and vegetables, you will develop scurvy, a condition associated with Vitamin C deficiency. It is not always a good idea to take too many vitamin and mineral supplements, as some of these can be harmful in large quantities.

Ingredients

salt and pepperI have a couple of questions about fats. Is there a difference between fats, eg the olive oil used in cooking, and the fat in a beef steak? Also do sweets or other sugars eaten on their own turn to fat?
Indeed there is a difference in the fats which are consumed as part of the various foods in the diet. As with humans, plants and animals store energy in the form of oils and fats, and the different species lay down the fat as different types of fats. The different types are saturated fats, mono-unsaturated fats, and polyunsaturated fats. The general view is that mono-unsaturated fats are the best type for nutrition, followed by polyunsaturated fats.

The worst type are saturated fats, which are associated with increased rates of heart disease and stroke, and are more abundant in meat and dairy products. Mono-unsaturated fats are often found in vegetable oils, particularly in olive oil and rapeseed oil. Most food labels give the breakdown of types of fat in the product, so keep an eye on them.

Further information and food advice about fats is given in the UK Government’s Eat well website.

Following your response on oils and fats, how do fish oils rank in the league table or good and bad fats? And are they really good for the brain?
Fish oils are very good for the human body as they contain many highly unsaturated long chain fatty acids (omega-3 type). According to the UK Foods Standard Agency: ‘Overall, the UK population should be encouraged to eat more fish, especially oily fish. An increase in population oily fish consumption to one portion a week, from the current levels of about a third of a portion a week, would confer significant public health benefits without appreciable risk from the contaminants in fish.’ See their website for more information.

You may recall that SCI's Oils and Fats Group held a well-attended event in February 2006 called ‘Omega-3 on the Brain’, which contained several very interesting lectures on this topic.

The benefits of eating oily fish (such as mackerel) is well known. But what are the benefits of eating white fish which is classed as non-oily (apart from being low in fat)?
White fish contains on average: Protein 17.5%, Fat 0.5% Carbohydrate none, Minerals 1.2% (sea fish contain iodine and fluorine), Vitamins B1 and B2, and 80% water.

Approximately 10% of white fish is waste. White fish therefore makes a useful contribution to the diet.

Do sweets, or other sugars eaten on their own, turn to fat?
Refined sugar has no nutritional value except to provide calories for energy. One of the primary functions of the food we eat is to supply energy for the body. Whether the energy comes from sugar or other foods, if more calories are eaten than are used, we store the excess as body fat.

Fat is the body’s store of energy for periods when food is not available and for reproduction. Periods of food shortage may have been a problem for early man who was never sure when he would get his next meal, but it is not a problem for us. There are a number of illnesses related to eating too much refined sugar including dental caries, obesity and associated diseases such as osteoarthritis, heart disease, malnutrition and Type 2 diabetes.

A government campaign suggests that we shouldn't eat more than 6 grams of salt. But what would happen if we were to eat considerably more?
Salt is essential to a healthy diet. We need about 1g of salt a day. However, many of us consume about 10g a day, ten times as much as we really need. A single dose of ten times that amount could be fatal! There is evidence that, for some people, too much salt can be a contributory factor to high blood pressure. Just how much is 'too much' varies from person to person.

In 1994, the Committee on Medical Aspects of Food and Nutrition Policy (COMA) recommended a reduction of the average salt intake of the adult population to 6g a day. This was detailed in its report Nutritional Aspects of Cardiovascular Disease. The recommendation for salt reduction was based on evidence of a link between high salt intake and high blood pressure.

In 2003 the Scientific Advisory Committee on Nutrition (SACN), in its report on Salt and Health, reviewed the evidence since 1994 to consider if COMA’s previous recommendation to reduce the salt intakes of the population was still valid.

SACN found that the evidence for a link between salt intake and blood pressure had increased since 1994. The current high levels of salt habitually consumed by the population raise the risk of high blood pressure, which increases the risk of stroke and premature death from cardiovascular diseases. SACN confirmed that the adult population as a whole would benefit from reducing their intake to 6g per day.

If you want more detailed information, including a copy of 'Salt and Health' produced by SACN in 2003 can be found at www.food.gov.uk. There's also a site on salt: www.salt.gov.uk

It’s not easy to reduce the salt content of many foods which are on sale to the public. The microbiological stability of many foods depends on the amount of salt present. Food companies need to carry out microbiological stability tests to determine if a reduction in salt level affects the microbiological growth in the food, before releasing the 'reduced salt level' food onto the market. The Institute of Food Science and Technology (IFST) issued an Information Statement on Salt in July 2003 which you might also find useful. You can find it on their website at www.ifst.org.

Is there are a recommended limit for sugar?
The UK Food Standards Agency (FSA) states that 'most adults and children in the UK eat too much sugar. We should all be trying to eat fewer sugary foods such as sweets, cakes and biscuits and drinking fewer soft drinks '

If a lot of sugar is consumed in the form of very sugary food (eg sweets) a balanced diet may not be achieved. A very high intake of sugar over a long period of time can also bring about the onset of Type-2 Diabetes in certain people. Sugar can cause dental decay if sweets or sugar-sweetened drinks are consumed too often.

As such, there are no defined maximum and minimum levels of sugar permitted in foods, but most authorities state that for most people cutting down on sugary foods is to be recommended. The FSA recommend that when you are checking food labels, the following may be used as a guide to what is 'A LOT' and what is 'A LITTLE' added sugar per 100g food.

'Look for the 'Carbohydrates (of which sugars)' figure in the nutrition information panel on the label.

  • 10g sugars or more per 100g is A LOT of sugar
  • 2g sugars or less per 100g is A LITTLE sugar

If the amount of sugars is between 2g and 10g per 100g, this is a moderate amount of sugar. So, to get a feel for whether the product is high in added sugars you might also need to look at the ingredients list.’

If you want more detail, go to the FSA website at www.food.gov.uk.

What is the difference between virgin and extra virgin olive oil?
Olive oil is the oil obtained solely from the fruit of the olive tree (Olea europaea L.), to the exclusion of oils obtained using solvents or re-esterification processes and of any mixture with oils of other kinds. It is marketed in accordance with the following designations and definitions:

Virgin olive oils are the oils obtained from the fruit of the olive tree solely by mechanical or other physical means under conditions, particularly thermal conditions, that do not lead to alterations in the oil, and which have not undergone any treatment other than washing, decantation, centrifugation and filtration. Virgin olive oils (which all have a free acidity, expressed as oleic acid) include:

  • Extra virgin olive oil:
    Not more than 0.8 grams per 100 grams
  • Virgin olive oil:
    Not more than 2 grams per 100 grams
  • Ordinary virgin olive oil:
    Not more than 3.3 grams per 100 grams

Are mushrooms nutritious?
Mushrooms have very little food value, being mainly water. Their calorie/KiloJoule level is low, provided you boil them and do not fry them.

What is it about Yakult that is supposed to make you healthy, and does it work?
The alimentary canal is a tube, mouth to anus, with various changes in diameter, but essential a tube connected to the outside at both ends. The body's defences are designed to prevent bacteria from entering the body, but the alimentary canal can support bacteria which essentially are outside the body albeit in a special, protected, environment.

In this environment the bacteria acts as a commensal organism, using food materials to grow, but thereby digesting these materials to give a form that we can use as nutrients as well. An example in a very different circumstance is the termite and its bacteria. Termites eat wood but cannot use cellulose (nor can we) but some bacteria can reduce cellulose-yielding energy but producing sugars. The subunits of cellulose can be used by the termite as an energy source.

Termites have intestines full of wood digesting bacteria. We do not. In humans the alimentary canal can act as a host for a wide range of bacteria, including some which, if not contained, would be harmful. It was found that patients undergoing bowel surgery should have their bowel sterilised before surgery to prevent peritonitis due to bacterial infections arising as a result of these bacteria entering this peritoneal cavity from the bowel. However after such surgery the bowel bacteria reappear.

One fortunate observation was that patients re-colonised with bacteria recovered more quickly especially if the bacteria were selected as not harmful or even positively helpful. A preferred method is the eating of yoghurt which allowed 'good' bacteria to colonise a sterile intestine in preference to other bacteria.

The Yakult phenomenon is basically an attempt to restructure the bacterial flora of the gut by adding specific bacteria, which will possibly outnumber the existing bacteria in the gut and change the population. This is believed to have a positive effect.

What really goes into chicken nuggets? I am allergic to fish and have heard that some of them contain fish as well as chicken.
It would be illegal to put fish in chicken nuggets without declaring it on the label, and I have never heard of this happening. May I suggest you read the ingredients listing on all foods to avoid suffering from your allergy.

I believe that the health benefits of organic food are relatively small, but the environmental benefits are huge. Could you comment on this?
I totally agree. A reduction in the use of nitrate fertiliser will certainly benefit water supplies. A reduction in the use of pesticides will also help the environment. Unfortunately, going totally organic is not achievable or sustainable, and the health benefits of organic food are too small to take this route. Please note this is my personal opinion, and may not be the view of other members of SCI.

Does organic food pose more of a health risk than GM-sourced foods (mycotoxins etc)?
This is a complex question. The presence of mycotoxins is usually dependent upon the growth of fungi on the crop, but the removal of the fungi by killing it does not necessarily remove the toxin. This applies equally to bacterial and other toxic products. Essentially the toxin is produced as the organism grows and is either excreted or remains in the organism. If the organism is killed, the internal toxin is released. So in both cases the killing or removal of the organism may not remove the toxin, it simply stops further production.

Both farming systems aim to have crops free of pests and other detrimental organisms. Therefore in both cases the aim would be to minimise contamination. Which succeeds the best, would need to be a matter for research and comparison. Organic farmers may remove infected crop material before it is sold (not guaranteed 100% successful) and others may treat crops as soon as infection appears (also not guaranteed 100% successful). Thus neither should at present claim to be better or free of toxins.

Additives

sweetsIs the pink dye/additive supermarkets put into salmon fillets to make them look more visually appealing harmful to you? Is it better to buy organic?
Canthaxanthin E161g is added to fish feed intended for farmed salmon and trout to increase the intensity of colour in fish. Canthaxanthin occurs naturally and belongs to a group of substances called carotenoids. These substances are related to beta carotene, the red/orange pigment present in carrots. In 1999, the UK's food Advisory Committee and Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment, looked at the use of canthaxanthin in feed and agreed that this use of the substance did not give rise to any food safety concerns.

At its December 2001 meeting, the European Commission's Standing Committee on Food considered whether ingredients used in animal feed to colour the final product should be indicated on food labels. Most Member States, including the UK, supported the view that this should be required and the Commission has agreed to set up an expert group to discuss the issues in more detail.

New rules introduced across Europe on 1 January 2002 require certain fish and fish products, including salmon to be labelled with information about the production method (eg whether the fish has been caught at sea or inland waters or farmed) and the catch area.

The Food Standards Agency website: www.food.gov.uk has information on canthaxanthin.

Is it true that Australia has banned the addition of monosodium glutamate in foods? Is it a general ban or is it only for baby foods? Which other countries have done this?
This is more of a legal question than a scientific one so I cannot give an in-depth answer. Nevertheless monosodium glutamate and other glutamates are not banned in Australia, although its level of usage has limits applied.

There are categories of foodstuffs where it is not permitted, the legal approach being similar in many countries, certainly in Europe, the USA and the Antipodes. These tend to be certain commodity type foods such as butter, oils and fats, milk, certain types of bread etc, and in particular foods for infants and young children. My advice for anyone wishing to sell products in any country is to check the legislation carefully according to the specific product and country.

PS - The Australia New Zealand Food Standards Code includes a Standard on food additives - standard 1.3.1. Schedule 2 of this lists monosodium glutamate as a miscellaneous additive permitted in accordance with GMP in processed foods specified in Schedule 1.

Schedule 1 makes it clear that while MSG can be widely used, it cannot be used in foods for infants (see page 18 of 26). I can find no evidence that changes to the provisions in relation to MSG are in the pipeline.

Do we really need all the food additives that are currently being used?
This is huge topic, so here are some points for and against. The argument in favour of additives is as follows:

  • Preservatives in food means less is wasted, so reducing costs. This also suits our lifestyles so we don't need to shop daily, gives us a wider variety and out of season products, and stops or slows down product deterioration, as in some cases preservatives can control micro organisms.
  • Colours make foods more attractive, and manufacturers suggest we will not eat undyed canned peas because they are not green, likewise canned strawberries which go brown.
  • Flavours allow for the restoration of lost flavour and a whole range of new products which can be consistently reproduced.
  • Texture aids and processing aids allow maximisation of ingredients and the use of waste e.g. potato powder for crisp type products. Nutritional additives are now very big business and for many products the addition of vitamins and minerals is useful. However this can be abused by making nutritionally poor products appear healthy .

These are just a few of the arguments put forward against:.

  • We have too many additives and no one is really aware of the long-term affects.
  • We also consume a chemical cocktail of additives, as they are found in such a wide range of products.
  • There are some additives already known to have health issues, e.g. sodium nitrate.
  • Suggestions have also been made that some additives can cause hyperactivity in children and that some people are allergic to some of them.

There are as many points for the use of additives, as there are against, and it is the consumer who must make the decision. Food labelling has improved, although it could be even better, and people need to start reading labels. The EC has begun to look at additives and there has been recent legislation controlling the use of additives such as artificial colours, but we are a long way from European harmony.

Two questions, both related:

Firstly, I have always thought of colourings as the least trustworthy group of artificial additives, due to the number of aromatic rings that appear in their structures. Natural colourings tend to use conjugated alkenes rather than aromatics (or in the case of chlorophyll, such big rings that they're unlikely to cause trouble), which seems a better idea. Does this chemical prejudice of mine have a sound basis?

Secondly, I have read that use of artificial additives, particularly colourings, is decreasing, and that they are being replaced with natural colourings like curcurmin, lycopene and chlorophyll in more and more products. Are artificial colours likely to disappear completely?

Among artificial colours it is the Azo dyes that are of concern, their structure being very similar to aspirin. If people are allergic to aspirin they may show a similar response to these dyes. Carotenes, in particular beta carotene, appears to be a popular alternative for yellow/orange artificial dyes such as Tartrazine and Sunset Yellow. Based on hydrocarbon chains, they appear to cause less allergic reaction.

Unfortunately I cannot agree with your comment that fewer artificial colours are being used. Have a look at products designed for children. Blue raspberry is very common, children's 'penny tray sweets' often contain artificial colourings, along with jams, jellies, a variety of canned goods, confectionery and soft drinks. Until natural colours can be produced at the same cost as artificial, with the same variety, stability in processing, and consistency, I rather think they will remain.

I am concerned about artificial sweeteners - each product claims to contain them within legal levels, but is the combined impact of consumption across all foods and drinks being considered?
There has been some concern expressed in the media regarding this issue. The legal limit is set after much research and is always set considerably lower than the maximum no effect limit. I agree that there is a problem here, but as far as I am aware, there does not appear to be any conclusive research on the long term affects of taking sweeteners from a wide range of sources. A similar problem also occurs with other additives, such as artificial colours and preservatives.

Vegetarianism

chicoryMy teenage daughter has announced she's becoming a vegetarian. How do I make sure she remains healthy?
She should eat dairy products and soya, plus a wide range of vegetables including pulses, nuts, cereals and grain. She can be perfectly healthy, the most common problem is usually iron deficiency which can cause anaemia so she needs to eat plenty of dark green vegetables.

The food industry appears to be increasing its awareness of vegetarian diets, and providing alternative products/new designs to cater for such. Is this observation valid, and is it solely based on the increased market audience for such products?
The food industry has always been aware of vegetarian food and diets. So it is not a question of awareness, it is more a question of meeting consumer demand. Vegetarian foods are not the sole province of vegetarians, and I think the increasing consumer awareness has also led to the realisation that there is more to vegetarian food than lentils and tofu. In the past, the label 'vegetarian' may have deterred non-vegetarians from trying a food or meal.

This change in the perception of vegetarian food may also have led to manufacturers seeing an opportunity of taking an extra step to make a product vegetarian, if that means removal or change of only one ingredient.

Cooking best practice

cup of teaWhy is some meat tough if you undercook it, and some meat tough if you overcook it?
There are several reasons why meat is tough after cooking. Firstly it depends upon the cut. Generally the parts of the animal used the most, are tougher than parts rarely used like the rump, and these would be better cooked using a moist method such as stewing. The age of the animal also affects tenderness, as does the slaughtering process. Animals not rested or stressed before slaughter may become tough due to a condition called DFD (dark dry and firm cutting). This is normally associated with beef.

Cooling the carcase after slaughter also affects tenderness. If it is done too soon, a condition known as cold shortening occurs. Freezing too soon can also toughen meat due to 'thaw rigor', which happens as the meat defrosts. Domestic freezing can also toughen meat, as the average domestic freezer tends to freeze rather slowly, which causes damage to the cell structure. This results in loss of moisture and flavour on thawing.

Hanging meat after slaughter allows enzymes to tenderise it, therefore hanging time also influences tenderness. Some caterers buy a large piece of beef and keep it under refrigeration until the surface appears almost black. This gives time for the meat to tenderise. With cooking methods such as grilling, heat causes the muscle proteins to 'denature'. They then shrink causing loss of moisture. A tough piece of meat becomes tougher when cooked right through, and will appear more tender if it is rare or blue. A tender piece of meat will toughen to some extent, but if you overcook it will become very tough indeed.

The skill lies in knowing when to stop applying heat. Moist meat is always more palatable than dry meat, which will always appear tough when eating it.

Why does chicken meat turn white when cooked, but other meats turn a brown/grey colour?
The pigment in meat is due to a muscle protein called myoglobin. The amount present depends upon species and the part of the animal. Parts used the most tend to have more muscle myoglobin. Myoglobin is red. Chicken has very little myoglobin, whereas beef has a lot. When cooked the myoglobin changes to brown haematin, if there is no or very little myoglobin present the change is not obvious.

What is the chemical difference between brewed and stewed tea? What effect does water temperature have on the chemistry of brewing v stewing?
Tea contains a number of volatile flavours which are lost if the tea is allowed to stew. Stewing also brings out the flavour of the tannins, which make the cup of tea rather bitter. Therefore ideally, boiling water and a warm teapot, will bring out the flavour in most Indian teas, and allowing it to brew or infuse gives a good flavour. Chinese teas tend to be more delicately flavoured and their chemical composition makes hot, rather than boiling water, better.

Ugly rumours

kittenIs there any scientific proof that some foods can affect your libido?
Foods believed to be aphrodisiacs include oysters, figs, asparagus, bananas and eels, as well as hot foods such as onions, ginger and pepper, and a variety of herbs. Do they work? The answer sadly is no, there is no scientific evidence to support this idea. Such foods cannot effect the sexual organs, sexual desire or performance.

Some foods however, can affect mood, eg a little alcohol is relaxing, and caffeine and sugar give a quick boost making people feel more energetic. A healthy diet will increase the feeling of well-being and consequently sexual desires and abilities. But malnutrition has the opposite effect.

Is grass edible?
I once ate a pasty type product made from cooked grass. It was a strange green/khaki colour and unfortunately tasted of nothing. I am still here today some 20 years later.

Many of the plants we recognise and eat as bread belong to the grass family. Like all plants, grass contains cellulose, a complex carbohydrate which gives the plant rigidity. Humans cannot digest cellulose as we do not have the enzyme cellulase, therefore uncooked plant material provides roughage which helps the movement of waste food through the intestines.

Cooking breaks down the cellulose and allows our digestive system to utilise the proteins, carbohydrates, vitamins and minerals present. Grass therefore could be eaten if cooked and prepared as a vegetable, but from personal experience it would need a lot of additives to make it acceptable.

Do humans really taste of chicken?
As far as I am aware, no members of the SCI have reported eating human flesh.

Is it true that food tastes different in aeroplanes? If so, why?
It is true that food tastes different. Our taste buds are dulled, mainly because of the altitude, and oxygen levels. Chefs working for airline catering companies try to take this into account when developing menus. However food is not cooked on aeroplanes but reheated, and this can have different effects on different foods. Most menus take this into account - eg you rarely see fried food, because it is very difficult to retain crispness on reheating in a steam oven.

I hear a lot of rumours about take-away premises using cat instead of chicken. Can you tell by looking, or do you have to have it analysed?
You cannot tell whether it is cat or chicken by eye if it is curried, unless there are complete bones present. It can be analysed in a laboratory by meat speciation techniques. However, now that chicken is so cheap, it is doubtful it is viable to use cat or dog and risk prosecution.

Supported by the Royal Institute of Public Health.

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