BRITISH BROADCASTING CORPORATION
RADIO SCIENCE UNIT
CASE NOTES
Programe no. 1 - Tasting Food and Drink
RADIO 4
TX DATE; TUESDAY 30TH DECEMBER 2008
PRESENTER: MARK PORTER
CONTRIBUTORS: LUCY DONADLSON
ZOE ADAMS
JESSICA NEWTON
JULIE MONELLA
CLAIRE LANGTON HEWER
PRODUCER: PAULA MCGRATH
NOT CHECKED AS BROADCAST
CLIP
DONALDSON
We're going to start off with parmesan cheese.
PORTER
Now that to me is heaven.
DONALDSON
And what does it taste like?
PORTER
It's just smooth and mellow and deep ...
DONALDSON
But it's difficult putting your finger on one specific taste like salt or anything?
PORTER
No, yeah I mean I 'm sure there's salt in it but I can't ...
DONALDSON
Yeah, it's partly because one of the predominant tastes is glutamate, which is difficult to identify. Okay? Next one.
PORTER
Not looking forward to this, this is a bit of anchovy and I absolutely hate anchovies. And I can report I still hate them. And that is - well it's fishy but salty ....
DONALDSON
Yeah, so they've got a large concentration of salt in them, predominantly salty.
PORTER
And another one, which I have to pick out of the Christmas pudding here - marzipan - which I don't like either.
DONALDSON
But you quite like sugar and quite like sweet things.
PORTER
I quite like sweet things yeah but I don't like the way it combines with that sort of almondy flavour, it's a bit strange.
DONALDSON
Okay, so sugar's fine as the predominant taste but when it's mixed with something that's maybe slightly bitterish, like an almond, it's not good.
PORTER
Giving the gastronomic excesses of the last few days it's only fitting to start another series of Case Notes with a look at how we taste food and drink.
How does our sense of taste develop as we grow, and how does that influence our likes and dislikes? It's a process that starts before we are born and a better understanding might help mothers reduce the likelihood of ending up with a fussy eater.
And I'll be discovering how my sense of taste means I am more likely to make a better doctor than chef.
But first some physiology. Taste is closely linked to another sense - smell. To really appreciate food or drink you need both. We have all noticed how food can seem bland when you get a blocked nose, but someone who has lost their sense of smell completely can't even tell the difference between liquidised apple and onion. Lucy Donaldson is senior lecturer in physiology and pharmacology at the University of Bristol and one of the UK's leading experts on taste.
DONALDSON
We often talk about taste as being the taste of what we eat when actually what we really mean is flavour. So flavour is a combination of the tastes that are constituent parts of the food and their odour. So what you get as you're putting food in your mouth and the smell that's coming into your nose. And then also the odour that you get once you start to swallow and the odour comes up behind the soft palate and into the nose and all that integrates together.
PORTER
I mean is most of the odour coming through the nostrils or is it actually creeping up at the back?
DONALDSON
You get both. So when you're putting food into your mouth the initial perception of what you're eating a lot of that is odour because odour is - odorants are detected at very low concentrations. So when you smell delicious food that's all in the smell then you put it in the mouth, the combination of the two is what makes it taste really good.
ADAMS
Until you've lost your sense of smell and you really think that you're never going to smell or taste anything ever again you really don't know what it's like, it is something - it's one of the senses that you really do take for granted.
PORTER
Zoe Adams lost her sense of smell after a heavy cold in 2005.
ADAMS
Coffee is an example - when I first lost my sense of smell it tasted like paint stripper and I couldn't bear to smell it. Then when you go out for dinner with friends and everyone's kind of saying how wonderful their meal is and you kind of sit there thinking well this tastes either very bad to me or I can't - it's just like eating a plate of cardboard.
PORTER
We will be hearing more from Zoe later in the programme, but first let's start with the mouth. So what structures are involved when we taste something? Lucy Donaldson.
DONALDSON
The ones that we think about as being most involved with how we taste when we're eating or little groups of cells that are called taste buds that are found on various different bumps on the surface of the tongue and those bumps we call papillae, in the trade, and they are very different shapes and in very different locations of the tongue, which means that you can taste different things in different parts of your tongue. And that all adds together to give you a sense of flavour.
PORTER
So if I stick my tongue out in the mirror can I actually see my taste buds?
DONALDSON
Yes, yes you can, particularly if you can stick your tongue quite a long way. So the ones at the front of the tongue are very small and look like little mushrooms, they're called fungiform papillae and you can see those quite clearly if you've had one of those horrible purple ice lollies, they make your taste buds look like little white spots on your tongue. So if you stain your tongue with something then you can see those very clearly indeed.
PORTER
So the different tastes spread all over the tongue, they're not localised to a particular part?
DONALDSON
No, no our good old tongue map, that everybody gets taught about at school, is actually not - not even close to be the truth. We're taught that there are specific regions of the tongue that you can taste sweet on and only one bit of the tongue, so the tongue map would say the tip of your tongue you can taste sweet and that's where you taste sweet. Well that's not the case. You've got cells that will detect sugars all over your tongue and also the same sorts of cells on the roof of your mouth - on the soft palate. So you can actually detect sweet taste in many, many different areas and not just on the tip of the tongue.
PORTER
Going back further to the tongue, perhaps the bit that some people see is right at the back, there's quite an obvious taste bud, in fact I once rather embarrassingly referred a patient to dentist with what I thought was an abnormal lump on the side of the tongue. Got a lovely letter back saying it's a taste bud doctor.
DONALDSON
Yes, yeah, there are quite large taste papillae on the back of the tongue and there's actually two sorts. There are some on the sides of the tongue that look like folds in the tongue and they've got taste buds - the taste cells sort of embedded within them - and they're called foliate papillae because they make the sides of the tongue look a little bit like leaves, the edge of the leaf. And then the really big ones on the surface of the tongue at the back, which is possibly what you got confused with something else, are called circumvallate papillae and that's because they're sort of big lumps with a moat round them, if you like, there's a groove that goes all the way down into the surface of the tongue and the taste buds are down in that moat area.
PORTER
It seems a slightly strange place to have big structures like that for taste because you would have thought that the food that's right at the back of the tongue, it's the last bit to get hit when you're eating something or tasting something?
DONALDSON
That area of the tongue's particularly sensitive for bitter taste, so there are lots of taste buds in that area of the tongue. Circumvallate papillae have got hundreds of taste buds and they are particularly sensitive for bitter tastes. And often bitter is associated with things that might be poisonous. And so we think that that might have evolved to make a barrier, if you like, so that you taste things just before you're going to swallow them that might be toxic. And if you do taste something that's really horribly bitter at the back of your mouth it quite often initiates a gag and you don't swallow that. So we think that it's protective to have things right at the back of tongue to be able to detect them.
PORTER
You often hear taste buds being broken up into groups depending on - well you've already referred to like bitter and sweet - what can we actually taste, what modality?
DONALDSON
There are now five different tastes that are commonly accepted as being single tastes that you can't derive from combinations of other things. And so we're very familiar with sweet tastes - things like sugar and fruit sugars - fructose and glucose - bitter tasting things which are many and varied, hundreds of bitter tasting compounds; salt which is principally sodium and sour which is when you have something that's acid. And the fifth taste, which is only relative recently been accepted as a true taste, is the taste of glutamate, which is also referred to as umami, which is a Japanese word that means tasting delicious or tasting really good. And so those five tastes have all got specific cells within taste buds that are capable of detecting them and potentially generating a signal to the nervous system that then goes up to the brain.
PORTER
Because a lot of people when they hear the term glutamate will think of monosodium glutamate as a flavour, in inverted commas, enhancer, often in oriental food.
DONALDSON
Well it's a naturally occurring ingredient of many, many foods. And actually if you look at really good ripe cheese, particularly ripe parmesan, you know you often get crystals on the surface well that's pure monosodium glutamate that's derived from the cheese that has crystallised out on the surface during the maturation of a good parmesan.
PORTER
And what do we think that that affect has on the whole perception of taste by the brain, does it lift everything?
DONALDSON
Yeah, well it is a taste in its own right, so if you get pure glutamate you can tell that it's different from anything else. When it's mixed with other things, if you know what it tastes like you can recognise it as being there but generally speaking most people perceive it as adding something in to all of the other tastes. And so when you eat parmesan or you eat very, very rich cooked tomatoes, which are also high in glutamates, you perceive this sort of yummy flavour to it but you can't quite put your finger on but you know it's really good.
ACTUALITY
Ooh do you want a yoghurt? Ooh which one? Sally strawberry? Sally strawberry.
PORTER
Jessica Newton's eldest son Lukas is nearly two and like many toddlers of his age is a fussy eater. But could his sweet tooth and dislike of anything savoury be a reflection of Jessica's tastes while she was carrying him?
NEWTON
Well when I was pregnant with him I craved really sweet things, in particular the full sugar coke which normally I can't stand, chocolaty things, biscuits, cakes, which I like anyway but I just wanted them all the time and every time I had a meal I had to ask something eat after it. And I had really, really bad morning sickness for about - up until about 20 weeks with him, so I did struggle to eat a lot of savoury foods. Lukas has also got a very sweet tooth - savoury foods are a real big issue with him. He'll pull his face and also make a disgusted noise. And sometimes even if I put something on his plate that he doesn't agree with he'll push the plate away or even on the floor. He won't eat anything with pepper in, he won't eat anything that's even slightly spicy either - I've tried him with ginger biscuits and if they've got that hint of spice in them he won't eat them. And in my second pregnancy I tried not to eat so many sweet things because I thought may be there was a kind of link. So I tried to eat more savoury foods and luckily my other son seems to like anything really.
PORTER
We know that flavours from our diet pass in to the amniotic fluid surrounding baby, and that he or she can start to smell and taste them from around the six month of pregnancy - a process that continues with breastfeeding. So does exposure during this critical formative period help familiarise babies with tastes and flavours that they will meet later in life?
Julie Monella is biopsychologist at the Monell Chemical Senses Centre in Philadelphia and has a special interest in the effect of maternal diet on a child's palate.
MONELLA
Our sense of taste and smell is pretty well developed even before birth. Both of these senses appear to be functioning mid pregnancy, the baby is born into this world preferring sweets, rejecting bitter and then at around four months they are able to mentally detect salt but from then onwards they like all that tastes salty as well.
PORTER
And does it make a difference what mum has during the pregnancy, so if she eats a lot of sweet foods does that influence the taste anymore?
MONELLA
When it comes to sweets I don't think the baby has to learn how to like sweets. What babies are learning is the flavour of the foods mum's eating. So what other fruits and vegetables she's eating - if mothers eat a lot of carrots, for example, during pregnancy or lactation the baby will be more accepting of carrot flavour; if mum's eaten more fruits during pregnancy and lactation the baby will not only eat more fruits but will make less negative faces while eating it. This preference for sweet and salt and this rejection of bitter remains heightened throughout childhood and teenage years. So not only is your child living in different sensory worlds but so are your teenagers and it doesn't start to look like the adult pattern until late adolescents.
PORTER
And I think most parents will relate to that, I mean we can see that in our children - they like sweet things, they like sausages, they like crisps - they like all of that stuff. So there is a physiological reason for that, it's not just them being difficult?
MONELLA
Yeah, the - what - it's a reflection of the child's basic biology. So you have - these senses evolve so that the child is attracted to energy rich food, is attracted to minerals - that's why they like salt - and avoids bitter because that's usually our signal that something is poisonous or harmful. Now we live in an environment where food is plentiful and these senses may actually be detrimental to a certain extent, they're eating too much sweets, too much salt, too much fat, not enough vegetables and not enough fruit. But salt plays an important role in foods, as it does in cuisines around the world, and one of the things that salt does is reduce bitterness. So not only is it an inherently positive taste for children but it helps reduce some of the bad tastes. So a little salt may go a long way in helping to reduce the bitter in vegetables for children and often you'll see the children will like maybe a little vegetables with cheese, basically the fat and the salt of the cheese is reducing the bitter component of the vegetable.
PORTER
Because as adults - as parents - you know we're encouraged to not use salt in our cooking anymore, not to add it at the table, not to put it in with the vegetables, so do you think we might be causing problems for ourselves there?
MONELLA
Well I think a little salt is going to help make the vegetable a little bit more palatable for the child and I think a little salt or fat could go a long way.
ACTUALITY
Oh mummy's making potatoes for your tea, are you going to have some carrots as well?
NEWTON
If I want him to eat something like vegetables, like broccoli or cabbage, I have to put gravy on it otherwise he won't eat it. Mix it up with potatoes and carrots, which he thinks are okay, and some chicken or beef - I do always use the lo salt gravy because obviously I'm worried that he's getting too much salt. And I'm assuming it's the taste of the gravy that's masking the bitterness of like the broccoli and the cabbage because I've tried it without and there's not a chance that he'll eat it.
MONELLA
In the States there's been a resurgence of cookbooks for hide the broccoli in the brownie, well that's fine - it's going to increase the fibre content of the brownie but if you want your child to eat broccoli or spinach the sensory system that detects these tastes has to learn and the only way it learns is through tasting it. Children - there's been research having children look at the food isn't going to work, they've got to taste it to learn to like it.
PORTER
And what about the sense of smell, are children born with a fully developed sense of smell?
MONELLA
Yes they're very sensitive to smells, if not more so. Before I started doing this research in humans I was struck by the large research area in dairy cows and there there was a lot of research that showed - and anybody who lives near a farm knows this second hand - is that not only do dairy cows prefer to thrive on onion and garlic but these flavours, these odours, in the diet get transferred into milk. And I also learned from that literature that it's not just what the cow eats, it's what she breathes - that's why they control the ventilation in barns because these odours get into the lung, then get into the bloodstream that get into the milk. And so we've shown the same thing in humans is that the flavours of the foods mum eats when she's lactating flavour mother's milk and again it's not just what she eats - if a mother smokes tobacco these odours get into the milk as well and the milk will taste musty or like my grandmother's house who smokes. So it's those flavours and odours get into the milk as well. I mean breastfeeding is just such a beautiful elegant and simple system and for the baby to learn to like a food the mother has to eat it in order to have the effect. I would also say that there's a lot of variabilities, not only do children live in different sensory worlds from adults but so do you and I.
DONALDSON
We know in the population that some people can taste some bitter things and some people can't. And some bitter tastes and whether or not you can taste them we know and have known for a long time that they're genetically determined.
PORTER
Back in Bristol physiologist Lucy Donaldson.
DONALDSON
There's been quite a revolution over the last few years and identification of a whole family of receptors, all of which can be switched on by things that taste bitter. If we go next door into the lab we can do some testing on your taste because as I said bitter taste is genetically determined. So I've got some bitter compounds that I can give you.
PORTER
I thought they might be bitter, how did I know that?
DONALDSON
To find out whether or not you can taste things particularly well. There are people who are very good at tasting bitter things at very low concentrations and then there are some people who are not good at it at all.
PORTER
Well let's find out which I am.
DONALDSON
You'll need to be beside the sink for this. Not because it's going to be so horrible that you're going to need a sink for anything but mostly because when we test your taste what we ask you to do is to take a little bit into your mouth and swill it round your mouth and then spit it out rather than swallow it.
PORTER
Okay, like wine tasting.
DONALDSON
Like wine tasting. So you've got four cups there that have just got colourless liquid in them, I'd like you to start with number one. Okay? And then when you've sipped and spat that one if you just go on to the next one and work your way up and we'll see how you get on with them.
PORTER
Well that tastes like water to me. Okay so that's number one. I couldn't taste anything really. Number two. I'm starting to worry now because that one tastes like water too.
DONALDSON
Okay that's fine.
PORTER
Not sure.
DONALDSON
Anything at all?
PORTER
Something.
DONALDSON
Don't know what it is.
PORTER
Yeah, not particularly remarkable for me. Oh dear.
DONALDSON
Anything?
PORTER
Something but not...
DONALDSON
Nothing disgusting?
PORTER
No I was expecting something disgusting but it tastes very similar.
DONALDSON
Okay, what that is is increasing concentration of a bitter compound okay and it may very well be that you are what we call a non taster. And there are many people in the population who cannot taste bitter substances particularly well and then there are other people in the population who can taste bitter substances really well. And that's genetically determined, it depends on which receptors they've got expressed in their taste buds and it depends on how many taste buds they've got. So those people would have we think more taste buds than somebody who doesn't taste it as strongly.
PORTER
Explains why I like lime pickles then when I go out because I can handle them because I can't taste them properly.
DONALDSON
It may be.
PORTER
Of course the other conclusion Lucy is that there's nothing in them before and you made them up incorrectly, so I think I vote my producer here - Erika - as an experiment. If you want to try that - that's the most bitter one that I couldn't really taste. Have a sip.
ERIKA
Alright, I'll give it a go.
PORTER
Ooh she's pulling a face.
ERIKA
Oh yeah, that's disgusting.
PORTER
Yeah bitter taste. I couldn't taste that at all. That's worrying me because if ever I have Erika round for dinner and I was to cook something and I'm tasting it, I mean, that's a big difference isn't it.
DONALDSON
There are huge differences in the population, yeah absolutely. And it does influence the things that you eat. So you know people who are very good at tasting bitter things tend not to eat things like green vegetables in as greater quantities because they're very bitter.
MONELLA
The only way they're going to learn is through experiences and what the research is showing the earlier the better. By the age of eight some people think that may even be too late. We know it's hard to change adult eating habits, so we've got to start early and I think we can't lose sight that food is much more than calories - it's pleasure, it's comfort, it's family.
PORTER
Is there an age at which the child's likes and dislikes are at their most plastic, the most malleable? Is there a window of opportunity for parents?
MONELLA
That's a good question and we most likely if we're to learn from other sensory systems like vision and hearing there's probably many sensitive periods that are starting early that maybe the systems are a little bit more plastic. We know the first year of life is important but I don't think the door is closed, we're pretty successful animals, if you will, there's a lot of plasticity. We have these inborn responses to like sweet, to like fat, to like salt, to reject bitter but we learn and there's tremendous plasticity and it's through experience - the forces of culture, the forces of family - that teach us what food should be eaten when, how it should be prepared. And so these systems aren't fixed but we've got to start earlier than we are.
PORTER
So your child's likes and dislikes will be largely determined by a combination of their genes, the tastes and flavours they are exposed to in the womb and the breast milk, and their natural tendency to favour sweet and salty foods. All we can do as parents is give them as many different foods as possible during this formative period, a process worth carrying on right up until they reach adulthood and leave home.
Unless of course they get a nasty cold! Which is what happened to Zoe Adams who developed a rare complication and lost her sense of smell completely after a cold three years ago. Most of us have noticed that our ability to savour food and drink can be limited temporarily when we have a blocked nose, but in Zoe's case it went way beyond that.
ADAMS
I'd say a week after I realised that I had the cold, it started where I bit into a doughnut and then realised that there was no taste and it was just literally consistency and texture which without taste isn't very pleasant. And I remember spitting it out actually and sort of going that's vile what is it. Chocolate, I actually remember tasting some chocolate and I literally had to spit it out because it was so vile. And then about nine days I'd say after losing my sense of smell then the distortions came in, the distorted smell. So what I was smelling around me, like fresh air, would smell like pond water, like algae, like really dirty pond water. It's just everything vile. I remember in the early stages really sort of scrubbing myself thinking, you know, because you really are concerned that as this stench is kind of hovering around you that you really feel like it is you. Nobody smokes in my house and I could walk into my home and I'd say someone's been smoking in the house and what's going on, I don't understand this smell and I would just check with everyone in my house and say can you smell that and they'd say no. So I'd say okay well at least I know it isn't the house.
PORTER
A story that's all too familiar to Claire Langton Hewer who's a consultant ear, nose and throat surgeon at St Michael's Hospital in Bristol.
HEWER
The nerves involved in smell are primarily the first cranial nerve, which is called the olfactory nerve, and that's the one that's found in the roof of the nose. What happens is sometimes if you get a really nasty flu virus you can actually permanently damage the olfactory nerves.
PORTER
And do they notice that it's their smell that they're losing or do they - is it their lack of taste that brings them forward to start with or a combination of the two?
HEWER
Usually it's taste initially. When I first started out as an ENT surgeon I had a patient referred to me because of weight loss and his GP had noticed that he was complaining that he couldn't taste or smell very well. And in fact he used to drink quite a lot of beer, he said to me that since he'd had the flu his beer tasted of nothing, in addition to not really enjoying his beer anymore he'd just completely lost interest in food. So he'd lost four stone. And we did some imaging on him, we did some scans to make sure that he had no problem with his sinuses and we checked out the brain as well and in fact it was all normal, he'd just had damage to his olfactory nerves from his flu virus.
PORTER
And the olfactory nerve is unusual isn't it, it's unique actually?
HEWER
It is unique, that's right. The olfactory nerves are attached to an area of the brain called the olfactory bulb and the olfactory bulb projects down into the nose, you've literally got tiny little nerves which are poking through a thin bony plate and are directly in contact with the lining in the nose, so that when we smell something the molecules are coming directly into contact with the nerve ending.
PORTER
Almost a part of the brain.
HEWER
Yes.
ADAMS
This virus had damaged all the nerves in the back of my nose and that's why I was experiencing the smells and the bad taste and everything. I had the distortions and the smell hallucinations - they lasted for about a year. It progressively got better from there really. And as time's gone on I can actually taste coffee now. It doesn't taste exactly how it used to but it's a lot better and it resembles what it should taste now to what it used to be. So as things go on it can only get better. But I think that I've still got quite a way to go.
PORTER
Zoe Adams. And you don't have a viral infection like Zoe to be temporarily affected - anything that blocks airflow in the nose can also affect flavour appreciation, particularly allergies like hay fever.
Back in Bristol, physiologist Lucy Donaldson hadn't quite finished testing my sense of taste, and had one last trick up her sleeve.
DONALDSON
One of the things that's interesting about sweet taste is that we can manipulate it, we can sort of play with the way that you perceive sweet things. And what I've got here for you to try is actually a naturally occurring manipulator of sweet taste and it comes from a berry that grows in Ghana called the Miracle Berry and it's a protein that when you taste it will change your perception of what you're tasting. So what I've got for you to taste is some cranberry sauce ...
PORTER
Cranberry sauce - very topical.
DONALDSON
Absolutely.
PORTER
I've had more than my fair share of this recently.
DONALDSON
And normally that tastes a little bit sweet but quite tart, so a little bit acid. And when you taste it normally mostly what you get is acid. After you have the Miracle Berries all of that acid should go and it should become sweet instead.
PORTER
So I just pop it on my tongue.
DONALDSON
You pop it on to your tongue and let it dissolve in your mouth and what it will do is affect the way that your taste cells are detecting things.
PORTER
It's already working.
DONALDSON
So if you want to try some more of the cranberry - the same cranberry - and tell us how you think it tastes.
PORTER
Ah completely different - ooh it's like super sweet redcurrant jelly or something.
DONALDSON
So it's lost ...
PORTER
It's just all sugar really. Not tart at all.
DONALDSON
So you're not getting any of the acid coming through at all?
PORTER
No I'm just getting sickly, sickly sweet.
DONALDSON
Last week I gave some of my students the Miracle Berry and gave them lemons to eat and you can eat a lemon like it's an orange and it sort of tastes like lemon sweets - you can still taste the lemon but all the acid goes.
PORTER
If only it worked for toddlers and broccoli! Lucy Donaldson putting my palate to the test
I'll be back next week with a look at how new guidelines for GPs on prescribing antibiotics are going to affect you - put simply if you have got a typical cough, ear infection, tonsillitis or sinusitis then you won't be given a prescription. Join us next week to find out more.
Back to main page
|
听Print this page
