HEART OF THE MATTER"
a special program of the National Emergency Medicine Association (NEMA)
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Guest: Dr. Stephen Roper, Prof. Biophysics, Univ. of Miami School of Medicine
Topic: MSG's role in taste & hunger
Host/Producer: Steve Girard
NEMA: Umami....no...it's not a Hawaiian verb or a South American wildflower. it's an oriental term for a certain taste...something we westerners have not traditionally included in our vocabulary of taste - you know, sweet, sour, bitter, salty. Well, there's new research that points out umami is a separate taste related to MSG, monosodium glutamate... for which we have special taste buds and innate craving. Dr. Stephen Roper is a Professor of physiology and biophysics at the University of Miami. Dr. Roper.... we're going to be talking today about kind of an esoteric area for most people...their sense of taste. Can we give them a bit of background into how it works...how our organ of taste is laid out?
ROPER: Neuroscientists like myself are just starting to explore this sensory organ in detail, and nobody knows very much about it...at least at the molecular and cellular levels. Or let's put it in another way...that more and more and more information is coming out, but it's certainly not as well known and appreciated as say, the sense of vision or hearing. Probably what's important for all of us to know is that taste originates from tiny sensory organs called taste buds. Taste buds are collections of sensory receptor cells...each taste bud has, let's say for ease, a hundred sensory receptor cells. And a taste bud is a football shaped or onion shaped sensory organ. Now, there are 2 to 5 thousand of these individual taste buds scattered throughout our oral cavity. The predominant density of taste buds are on the tongue, but they're also found on the soft palate and on the epiglottis. Basically, in our oral cavity. Now, taste buds then contribute to our awareness of our chemical environment, therefore we call it one of the chemical senses. But taste is our immediate chemical sense, and it's involved predominantly in appetite and feeding, and therefore in nutrition.
NEMA: Why is there such a discrepancy in the number of taste buds people have...you mentioned 2 to 5 thousand...but some people have as many as 10 thousand...?
ROPER: Exactly, colleagues at Yale University specifically Linda Bartishuk and her associates are studying people called "super tasters", that have maybe 10 thousand or more taste buds. And it's a...myself, I'm not an expert in this...it may be a genetic trait, but why these individuals have that many taste buds, I don't know.
NEMA: Tell me about the research efforts...in many different camps...that led you to the discovery of an area of the tongue that reacts to something other than the regular sweet, sour, salty and bitter tastes...
ROPER: Well, you're referring to this taste...this curious taste that the Oriental literature has called Umami, which is basically the taste of monosodium glutamate and related molecules. Now, the sense of Umami has been known by Oriental cooks for over a millennia. But the actual research into it, and what generates this taste probably started about the turn of this century, when Japanese scientists isolated the flavorful compound from...I think it was from seaweed, and found that, yes...it was glutamate...or monosodium glutamate, they're very similar compounds - one is just the salt of the amino acid. And ever since then, people have been attempting to identify, what is the basis for this...is it really a separate and independent taste quality, like sweet, sour, salty and bitter? And that research intensified over the last two or three decades...and has perhaps been accepted by many, but not all scientists certainly, in the recent few years, as a separate taste quality.
NEMA: How does it taste on its own?
ROPER: When you go home...look for that little bottle of ...I believe one commercial product is called Accent, and just put a little bit in...put a teaspoon in a glass of water and taste it. And it doesn't...on it's own, it's not extremely palatable. it's not something that I'd select to drink. It has sort of a savory, or meat-like, or chicken broth-like flavor to me. Everyone reports, most westerners report it as a slightly different wording...most Orientals would say, "Oh...that's Umami".
NEMA: MSG...is it really a salt...? Why was it suspected of being dangerous a while back? I mean especially since it's a form of an amino acid...and since we're now finding the body has special sensory equipment and craving for it?
ROPER: You're absolutely correct in saying that the body has a craving for it, and we have receptors for glutamate. And specifically to answer your question, the short answer is, I don't know. I'm not in the field of nutrition or psychophysics, or certainly the clinical aspects. I read about it, like any informed citizen can, and evaluate the evidence. But it's really a mystery how certain fads come about...they come and they go...and certain things are considered dangerous, and then they're not considered dangerous. And I can't speculate on why that is.
NEMA: It seems so many different foods have this substance, MSG, why is that...?
ROPER: it's a basic amino acid, and not an essential amino acid, but a fundamental amino acid, and a natural component of proteins, so all foods that have proteins will have glutamate in them. And will also have some free glutamate...the amino acid that's not bound into a protein, is the active taste form. So, why they...why foods contain glutamate? it's just because it's a fundamental building block of proteins.
NEMA: I know the diet industry, the medical community, and food companies will all be interested in learning why the MSG receptors make us hungry for the foods that contain the stuff...and for different reasons. I know you're not an expert on the effects on nutrition or application of these ideas, but project a bit about what help work in umami might be to doctors?
ROPER: I'm going to tell you what I've read from other researchers, such as Sue Shiffman and Gary Beacham at the Monell Institute. And uses that I've heard where it could be helpful would be in elderly nutrition, where malnutrition is a very serious concern. As one ages, one loses our sense of taste and smell...food becomes less palatable. We tend to eat less and less...and our nutritional state goes down. So, if there were some easy way to increase the palatability of food...that would be one use.(I've heard). Another use could be after certain therapies such as radiation therapy for cancers of the oral cavity...salivary gland tumors, for example, that respond to radiation therapy...patients typically lose their sense of taste, because taste buds are also sensitive to radiation. And they tend to disappear immediately after radiation. And these patients tend to lose pounds very quickly because they lose their sense of taste, and they stop eating. Which incidentally argues perhaps for the importance of our sense of taste, and why we have a sense of taste. If you lose it, it's a very robust sensory organ...taste buds are...and they tend not to malfunction. But when they do, when one loses a sense of taste, it's very serious for the organism, for the human.
NEMA: What's next for Umami? Where does the research go from here?
ROPER: About a half dozen laboratories across the nation and abroad are studying this fundamental act of how the glutamate molecule stimulates these taste buds. What is going on there? And no one has any insights, specific insights or proof, as yet...as to what's going on with glutamate...or sugar for that matter, or any taste substance. And the name of the game is to identify the receptor at the molecular, biological level.
NEMA: We tend to think about taste as this esoteric, subjective sense that's totally individual, but trying to find the overall, underlying mechanical process is quite a challenge...I mean, we mentioned earlier that some people have 2 thousand taste buds, some of us have 10 thousand - all of us have two ears to hear, two eyes to see...why such a difference when it comes to the sense of taste?
ROPER: Exactly, and I like how you put it. it's very important to realize that the perception of taste is very individual. What you and I respond to and perceive in a complex meal can be totally different, based not only on the biology of our brains, but cultural perspectives...a whole raft of information for how we perceive. And what Dr. Chaudari and I and Dr. Brand, Teeter and others are looking at are very fundamental first steps into how this occurs, how this takes place. it's a critical step, but in no way will explain differences in individuals as to perceptions....that's a brain and cultural phenomenon.
NEMA: MSG....monosodium glutamate...an amino acid that's contained in all proteins...and for which we have special taste buds, and a special chemical attraction for. In the Orient...all that can be summed up, or should I say yummed up, in one word: Umami. Thanks to Dr. Stephen Roper of the University of Miami for joining us today.
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