MSG Part 2. Is MSG and allergen?

If MSG was in a court of law accused of causing harm, the lawyer would be screaming ‘SHOW ME THE EVIDENCE’.  Speculative reports of ill harm after consuming MSG laced foods are rife and where there is smoke there is often fire.  But an evidence trail is needed, and in the case of MSG as an allergen the evidence is missing without a trace. In 2010 I watched a TV program while on holiday in New Zealand where the presenter talked with some authority and conviction about the food additive MSG being a major problem in foods.  The presenter was a local chef and he was going to prepare some good tasting Asian food without the MSG. After the show I requested the evidence to support the MSG harm proposition from the show’s producers.  To their credit they eventually responded with data, but it was not relevant to MSG as a ‘cause of harm’ in the food supply. The producers should have checked with any of the following organisations who have extensively reviewed the topic: The Joint Expert Committee on Food Additives of the United Nations; Food and Agricultural Organization and; World Health Organisation, all who placed MSG in the safest category for food additives. Or perhaps International and National bodies for the safety of food additives including: International Food Information Council; U S Food and Drug Administration; the National Academy Sciences; the European Community’s Scientific Committee for Food; and the American Medical Association who all report MSG safe for human consumption as a flavor enhancer. In Australia, FSANZ quoted from overwhelming evidence from considerable scientific studies to explicitly deny any link between MSG and "serious adverse reactions" or "long-lasting effects", declaring MSG "safe for the general population". The problem as I see it was the producers and presenter were naïve regarding the topic of MSG, but would have heard anecdotal evidence from unreliable sources that MSG was bad. They then produce a harmless cooking program further propagating the myth that MSG is harmful to the general public.   

The question remains why is MSG such a public-touchstone for allergens? The history is intriguing.  In 1968, Robert Ho Man Kwok, MD described a collection of symptoms he experienced after eating Chinese food. He coined the phrase “Chinese Restaurant Syndrome” (CRS) to describe these symptoms such as hypersensitive reaction; headache; tightness in the chest; asthma; flushing; body tingling in addition to numbness at the back of the neck and a feeling of pressure in the face and upper chest muscles.  He named many potential causes from the foods eaten and among them MSG was mentioned. It was MSG amongst all other contenders that was followed up by some other speculative reports in scientific literature.  Once it made the general media the foundation was set, MSG caused CRS. (It is important to note that I am not stating people do not suffer hypersensitive response to certain foods or CRS, but believing MSG is the cause before studies were conducted was premature.)

In 1970, Morselli and Garattini examined 17 males and seven females in a well-controlled study. The researchers administered 3 g doses of MSG in 150 ml of beef broth and evaluated the subjects every 20 minutes for a three-hour period. The researchers concluded that there was no evidence that CRS was associated with the ingestion of MSG.  Four additional double blind design (neither researchers nor subjects knew if the food contained MSG) studies with subjects who believed they adversely reacted to MSG have been conducted. In all cases the data were inconsistent with subjects responding to all stimuli including those without MSG, or none, including the foods with MSG.  The results were also inconsistent, meaning they could not be reproduced. The well-controlled science is conclusive, MSG is not a problem. Taking this into account can MSG be the problem? For the vast majority of people who believe they have an allergy/hypersensitivity/CRS to MSG, the evidence trail makes that clear that MSG is not the problem. It doesn’t mean there weren’t compounds in foods that caused a reaction, but it was not MSG.  I have included a relevant bibliography at the end of this blog for those who are interested in reading the studies mentioned. 

After all the evidence presented, if you are still adamant MSG is an allergen for you and others, then avoid foods with glutamate. In most countries the food label will show whether MSG has been used as an additive. The label will bear the food additive class name (e.g., flavor enhancer), followed by either the name of the food additive (e.g. MSG), or its International Numbering System (INS) number 621.    

Some Relevant Literature

Simon RA. Additive-induced urticaria: Experience with monosodium glutamate (MSG). J. Nutr. 130:1063S-1066S, 2000.

Tarasoff, L. & Kelly, M.F. Monosodium L-glutamate: A double-blind study and review. Food and Chemical Toxicology 1993; 31:1019-1035.

Kwok, R.H.M. Chinese Restaurant Syndrome. N. Engl. J. Med; 1968:17:796.

Morselli, P.L. & Garattini, S. Monosodium glutamate and the Chinese Restaurant Syndrome. Nature 1970; 227:611-612.

Kenney, R.A. The Chinese Restaurant Syndrome: An anecdote revisited. Food and Chemical Toxicology 1986; 24(4):351-354.

Wilkin, J.K. Does monosodium glutamate cause flushing (or merely “glutamania”)? J. Amer. Acad. Dermatol 1986;15:225-230.

Geha RS, Beiser A, Ren C, Patterson R, Greenberger PA, Grammer RC, Ditto AM, Harris KE, Shaughnessy MA, Yarnold PR et al. Glutamate Safety in the Food Supply: review of alleged reaction to monosodium glutamate and outcome of a multicenter double-blind placebo-controlled study. J. Nutr 2000;130: 1058S–1062S.

European Food Information Council. The facts on Monosodium glutamate. 2002. Center for Science in the Public Interest. Food additives.

(23) Carvan M. MSG: the controversy. LEDA at Harvard Law School, 1997.

(24) Rhodes J, Alison C, Titherley JA et al. A survey of the monosodium glutamate content of foods and an estimation of the dietary intake of monosodium glutamate. Food Additives and Contaminants 1991: 8:265-274.

(25) National Academy of Sciences, National Research Council. The 1977 Survey of the

Industry on the Use of Food Additives: Estimates of Daily Intake. Vol. 3, Washington,

D.C.: National Academy Press, 1979

MSG (Monosodium glutamate) Part 1

            Monosodium glutamate, also known as sodium glutamate or MSG, is the sodium salt of glutamic-acid or glutamate, the most abundant naturally occurring non-essential amino-acids and can be found in many protein-rich food products such as meat, poultry, fish, eggs, dairy products and other plant sources. In general, protein-rich foods contain large amounts of glutamate usually bound in the muscle.  Most vegetables contain relatively meagre quantities of glutamate, certain vegetables such as peas, tomatoes, and potatoes have significant amounts of free glutamate.

Glutamic-acid was discovered and isolated from wheat gluten and identified in the year 1866, by the German chemist Karl Heinrich Leopold Ritthausen. Later in 1907 Japanese researcher Kikunae Ikeda identified the taste properties of glutamate as brown crystals left behind after the evaporation of a large amount of Kombu broth. He found that these crystals had a hard-to-describe but undeniable flavor, something he termed ‘umami’. Other descriptors used to describe the taste of glutamate are savory, broth-like or meaty.  The best way to describe the taste is similar to a chicken broth.

            When MSG is added to foods, it provides a foundation flavour for traditional salt/savoury based foods. As discussed in my previous blogs on salt taste the majority of the global populations’ consume NaCl to excess which associates with adverse health effects e.g. hypertension, disability, cardiovascular disease. As a consequence, the WHO and the health authorities of most of the countries, including the Australian Division of World Action on Salt and Health (AWASH) advocate reducing the NaCl consumption in order to combat this health burden. It is possible, even plausible that MSG may be used to replace NaCl in food. The main advantage for MSG as a replacement for NaCl in foods is that at approximately equal intensity it contains approximately one-third the amount of Na as NaCl, and appropriate use of MSG is possible to reduce sodium in foods by up to 40% without adversly influencing liking or preference of the food. So why is such an easy solution overlooked by the food industry, could it be that there is a problem with MSG?  Perhaps allergies? That is for MSG part 2.

           

Beer Part 1

One of the world’s oldest foods has stood the test of time.  From accidental beginnings (presumably), perhaps a mistake from leaving bread uncovered in a rain storm a few thousand years ago, to a widely consumed incredibly diverse beverage enjoyed today.

The ingredients are simple, a source of carbohydrate/sugar, water, hops, and yeast.  But each of the ingredients can be modified prior to production thereby having multiple influences on flavour. 

Carbohydrate is usually malted barley (can be wheat, sorghum, but other grains may not have appropriate enzymes to help carbohydrate and protein breakdown sugars and amino acids which yeast use during fermentation), which is roasted to various levels of colour, and adding one or more varieties of colours of malts is the basis behind a light golden beer such as American style lagers versus black beers like Guinness.  As you go from light to darker colours, flavours change, with straw-like grainy flavours, converting to caramel/malt, going to caramel/burnt flavours.  

Water is water, but throughout history the good brewing regions are associated with good sources of water. Burton-on-Trent brewing region was founded on medicinal spring water we now know as ‘hard water’ (alkaline and mineralised), that has been shown to produce higher quality darker style of ales traditionally produced there.  Water is added to the malted barley to make a sugary solution, pretty much the base for the beer, but at this stage it does not taste like beer.

The next ingredient is hops which are used for bitterness and aroma, and there are many varieties of hops.  The brewer decides what level of bitterness is required, what level of hop aroma and adds the appropriate hops at the appropriate time of wort boiling.  For bitterness, the hops must be added early in the boil to help conversion to the bitter form, while aroma hops must be added late to ensure the volatile aromas do not evaporate during the boiling. The flavour at this stage would still not resemble beer, but would have distinct bitterness, and depending on the type of aroma hops may be aromatic, fruity and floral.

The last ingredient, yeast is also vitally important.  The yeast is added to the liquid wort, a mix of sugars, amino acids, hop compounds and given the right temperature yeast will happily grow, and in doing so turn the sugars into alcohol and other compounds that add to the flavour of the beer.  The type of yeast is important, lager yeast work well at low temperatures and produce less fruity flavours, but more sulphur flavours. Ale yeasts ferment at higher temperatures and produce a more fruity/floral and alcoholic type aromas.  If you taste the product at the end of fermentation it will taste like beer, but the final product still requires maturation to settle the yeast and mellow some of the flavours.

I find it remarkable that four primary ingredients cover such a wide spectrum of flavours.  But if four ingredients isn’t enough there are others that are added to beers, for example wheat beers with added fruit (raspberry), or around Halloween Pumpkin Ales are available.  The limit to what ingredients can be added to beer is equivalent to the limits of imagination of the brewer. 

There is certainly science and a good deal of art in brewing, but the successful brewer must understand the consumer, whether that is the mass-market consumer who consistently purchases Budweiser, or the beer enthusiast who loves discovering a rare oak aged Porter.  If the final product meets expectations of the consumer, then the ingredients and brewer have accomplished their mission.  

The title to a country song sung by Tom T Hall is appropriate to finish this blog 'I like beer'. 

Salt Taste Part 4

The food industry loves salt, it is a magic ingredient with the ability to change an unpalatable food to one that is flavoursome and appealing. As Heston Blumenthal stated, it is the most important ingredient in the kitchen. Let’s take bread as a food that uses the multiple functions of salt.  Bread produced without salt has a vastly different taste to bread produced with salt – not only taste, but the texture is different, and 99.99% of consumers prefer their bread produced with salt.  It may seem hard to believe, but bread is the single largest source of salt in our diet; yet bread is not salty like potato chips are salty.  That is because the majority of salt is bound within the matrix and unavailable to activate our taste receptors.  It is within the bread matrix that salt has some functions, salt controls growth of yeast and promotes the development of gluten structure/texture in bread, as well as adding or enhancing flavour.  As a cook, baker or food manufacturer you would be crazy not to use salt.  The reason for salts continued (increased in the case of Australia, if you trust the recent data from Australian division World Action on Salt and Health (AWASH)) use in processed foods, given the multiple health reasons not too, is the multiple positive functions salt has in the food matrix. 

            Take meat and cheese products as examples, both are high in salt and if a manufacturer was making a reformulated meat product (chicken patties or similar), reducing the salt would adversely affect texture and require other additives to replace the water-holding, protein-binding, and fat-binding functions of the salt. In cheese, additional additives would be needed to help promote good bacteria and inhibit bad bacteria during fermentation and aging.   But what compounds can replace the function of salt, and what's the cost; consumers may not be able to afford or willing to pay for a significant increase in the cost of salt reduced foods.  In addition, we must not forget the role salt plays in preservation, as it reduces water activity in foods and acts to control growth of pathogens and spoilage organism.  If salt levels are decreased, it will be necessary to use other preservatives to ensure safe foods with a reasonable shelf life.

From a food industry perspective, in addition to processing and safety challenges involved in producing low sodium foods, there is also an economic consideration. If it becomes apparent to a food manufacturer that consumers prefer a higher concentration of salt over the current concentration, salt may be added to that food at very little cost.  For example, the approximate price of salt is 34 cents/ kg, if food manufacturers wish to increase the salt concentration of bread by 5% the approximate cost would only be 0.000756 cents/100 g. Salt is very cheap and any substitute used will increase the cost of the product. Production of foods with reduced salt will require reformulation and additional associated costs of consumer testing and pilot plant tests.  Are we as consumers willing to pay the extra costs associated with reduced salt products, or are we willing to accept inferior products? Possibly not.  Are we willing to accept myriad new additives that will be needed to replace the functions of salt? Again, possibly not. While the flavour aspects of salt are undoubtedly the main reason why salt is in foods at the level it is, there are also technical reasons to maintain salt levels in foods

It is widely accepted we have a food supply that delivers to much salt for population health.  How to fix the problem is the issue.  The most effective strategy is to reduce the level of salt in manufactured foods, as they deliver 75% of dietary salt.  The food industry correctly states salt reduction is not easy to do, and there are costs involved. And we as consumers are likely unwilling to accept increased costs that will be involved with salt reduction.

One thing for certain, the last thing we need is food manufacturers increasing the current levels of salt in foods, as AWASH reported recently.  There is no need for more salt in bread, or increased levels in cereals. If voluntary food industry targets cannot be determined or met for specific foods, the next step should be to legislate maximum levels of salt in foods.  Perhaps this is needed, if so, start with bread at a maximum level of 800mg NaCl/100g bread – this is a good compromise value, the functionality the bread matrix is maintained, taste is fine and will be a significant step forward in reducing population salt intake.

As (hopefully) explained over the past 4 blogs, salt is a problem with no easy answer.

Salt Taste, Part 3

NaCl is an easy additive for the cook to use, as it is a cheap and convenient way to increase liking; therefore from a cooks perspective it is like magic powder, add NaCl to a food and the food becomes more palatable.  To health advocates NaCl is a slow working poison, added to foods in excess, slowly killing the population via myriad disease conditions.

If salt is a poison then why are we allowed to use it as a food ingredient?  The answer lies in the rate we consume NaCl, and if you over-consume there are consequences (to help with quantities mentioned in this article, 5g NaCl is equivalent to 1 teaspoon).  It is calculated that human species evolved with intakes of 1.8g NaCl/day, in comparison we now consume >9g NaCl/day, with approximately 75% of intake coming from processed foods.  As a result there has been a 400% increase in NaCl consumption during recent human history.  The excess consumption of NaCl is the source of the problem identified by health advocates who have suggested an adequate intake of between 1.2-2.3 g NaCl, and an upper limit of approximately 6 g NaCl for chronic disease prevention.  It is important to note that it is the Na or sodium portion of NaCl that is implicated in the adverse health effects, but for simplicity, I will continue to use NaCl.

Evidence that excessive NaCl intake has an adverse effect on blood pressure regulation is well established, as is the relationship between raised blood pressure and cardiovascular disease.  In a confusing twist, the link between NaCl intake and cardiovascular disease is more tenuous, but we presume that chronic excessive NaCl intake increases blood pressure, which in turn increases incidence of vascular diseases. It is reported that approximately 30% of Australians are diagnosed with high blood pressure (hypertension) and for every known case of high blood pressure it is believed that there is one case that goes undiagnosed.  

Excessive NaCl consumption is a big problem, to illustrate the effect excessive NaCl consumption has on public health, consider this; a 3g/day reduction in dietary NaCl would have the same effect on rates of heart disease as a 50% reduction in tobacco use, and a 5% reduction in body-mass index among obese adults.  Also, a 5 g/day increase in dietary NaCl is calculated to increase the risk of stroke by 13-32% and heart disease by 50-61%, with the higher risk associated with overweight/obese individuals.  Excessive NaCl intake has also been linked to gastric cancer via enhancing H.Pylori colonisation, and decreased bone density by increasing calcium loss from bones.  There have also been suggestions of a link between NaCl intake and obesity with an increase in dietary NaCl inducing thirst resulting in an increase of the amount of high kilojoule drinks consumed, consequently leading to excess energy intake.  The potential health benefits from reducing sodium are staggering and hard to believe more is not done to reduce NaCl levels in the food supply. But…. there is, of course, conflicting data and an investigation of NaCl intake over the past 50 years suggests NaCl intake has been stable.  Yet rates of cardiovascular disease have declined over the same period. Such inconsistency do not mean excess NaCl intake is harmless, it just means there are other factors involved in vascular diseases that have influenced disease rates.

NaCl intake seems a little like Russian Roulette, there is a chance that the bullet (NaCl) may not be in the chamber, but is it worth the risk when the only benefit appears to be better tasting food?  Perhaps the only effective way to have population based reduction in salt intake is government regulation, targeted to the foods that contribute most to salt intake – bread, processed meats.  That way all food manufacturers must adhere and no one manufacturer will have a competitive advantage by adding more salt.  This will strike stern opposition from food manufactures because……. That is for Part 4.

Salt Taste Part 2

Why is NaCl, according to some cooks, the most important ingredient when cooking?  The reason is simple, added NaCl has a positive influence on liking and preference for foods.  And it is not just due to saltiness, although saltiness is one component. Apart from savoury foods where it appears naturally complementary, it is also added to caramel, chocolate and foods we associate with another taste, sweet.  Perhaps it is the subtleness of small amounts of salt in sweet foods we like, maybe the sharp contrast when you taste a some NaCl in a sweet food, or maybe it is something else.

When two compounds with different taste qualities are mixed a number of interactions may occur including suppression of bitterness by NaCl. NaCl also enhances sweetness at low concentrations, and through NaCl effect on bitterness, sweetness maybe further enhanced.  NaCl also has the ability to enhance aromas associated with sweetness (we like them) and suppress aromas associated with bitterness (we don’t like them).  In this situation, adding NaCl to a food has created saltiness, increased sweetness and sweetness associated aromas, all aspects of food that we like.  NaCl has also decreased bitterness and bitterness associated aromas, thereby reducing the negative aspects of food and also increasing our liking of food.  You start to appreciate the wisdom of Heston Blumenthal’s statement – but there is even more. NaCl also acts as a preservative and water binding agent in processed meats and influences on the texture of foods such as breads.

When you have one compound with so many positive influences on the flavour of food, and is cheap, convenient to use, and not acutely toxic, all this adds weight to being the cooks most useful ingredient.  In a way I agree with Heston Blumenthal, NaCl is the most useful ingredient for the cook, just as the hammer is the most useful tool for the builder.  Using an analogy, a builder (or handy person) faces a problem, the hammer is close by, the hammer becomes the solution; it is low tech, easy to use and it may work. The same happens with NaCl in the kitchen, perhaps it becomes the ingredient that is the solution to everything, it is at hand and easy to add some NaCl to every dish, at every stage of production. The accumulation of NaCl in a food adds up and there begins another problem. Much of the added sodium is trapped within the food matrix and unavailable to fulfill its role in taste, it becomes taste invisible (this will come up in Part 4 of salt).  Yet when the food is swallowed and the food matrix broken down, the NaCl is adsorbed and available for physiological function.

After consideration and remembering the old nutrition mantra, ‘everything in moderation’, I would qualify the Blumenthal statement that ‘salt is the most important ingredient for the cook’, by saying NaCl is the easiest ingredient a cook can use to increase liking of a dish. It is a process similar to delayed gratification, using excessive NaCl in the dish you are preparing may (not will) increase the liking of the dish, but the excess sodium may also cause detrimental health effects in a few years.  The evidence that we consume excessive sodium which is associated with many detrimental health effects.  That is for Part 3.

Salt Taste, Part 1

The story of salt will be in multiple parts, due to the importance of the topic, and the complexity.  Salt, a.k.a sodium chloride, a.k.a. NaCl, a.k.a. sodium, is an essential element in the chefs or cooks toolbox to make things taste good. I read somewhere that Heston Blumenthal (one of the high priests of cooking, TV personality) stated salt is the most important ingredient in his kitchen. Why would that be the case? Below I begin the discussion on the many functions that salt has in foods, hopefully giving a clue to why such statements are made. Part 1 does not address the health issues and controversies around salt, just why we, as consumers and cooks, love salt. Also an explanation on terminology, I will use the term salty when referring to the taste we perceive, and NaCl when discussing salt (opps NaCl).

Taste perception is very complex, with highly sophisticated biological systems at work, but it can also be quite simple, put something in your mouth and you experience the taste/flavor of the food.  Salt taste is experienced when the concentration of NaCl in the oral cavity reaches a level that not only activates a taste receptor, but the signal sent from the receptor is strong enough to elicit a salty perception, meaning low concentrations of NaCl may be present in the oral cavity yet not elicit a salty taste.  There are multiple perceptual phases associated with salt taste perception and as the concentration of NaCl increases the detection threshold will be reached, the level at which NaCl in solution may be discriminated from water.  As the concentration of NaCl increases further the recognition threshold is reached, the point at which the quality (e.g., salty) can be identified.  As the concentration of NaCl increases still further, the intensity of saltiness mutually increases to a strongest salty intensity we can experience.  It then starts to activate another sensory system (not taste) and becomes painful.  

Two factors dictate the level of perceived saltiness for a given concentration of NaCl: 1/ an individual’s sensitivity to NaCl (which is highly variable for all tastes), and 2/ the food matrix being consumed. To further explain: 1/ just because you find something too salty does not mean I will, as we have variation in the biology or physiology relating to taste processing.  And 2/, the food matrix will be important, potato chips are a salty food, they have NaCl at the surface of the chip, bread is not a salty food, yet it contains about the same amount of NaCl.  The reason for the difference is that the NaCl in bread is trapped in the bread matrix and unavailable for taste activation.  Therefore a salty food such as potato chips are not necessarily a food high in NaCl.

NaCl adds saltiness to foods, depending on the amount you add, the food matrix and individual taste will depend on the level of saltiness you experience.  This doesn’t adequately explain why NaCl is the most important ingredient in Blumenthal’s toolbox.   That can wait till Part 2.

What is Oleocanthal? (an irritating compound in virgin olive oil)

Virgin olive oils have been characterised by a stinging or burning sensation localised to the back of the throat that can have sufficient intensity to force involuntary coughing, but the compound/s responsible were unknown. 

The virgin olive oil contains different phenolic compounds such as phenyl acids, flavonoids and secoiridoids that are reported to have health benefits and contribute to oxidative stability and flavour. However, very little is known about the influence individual compounds contribute to the organoleptic properties.  Of particular interest was the stinging almost exclusively in the throat region, which was similar to the irritation elicited by the nonsteroidal anti-inflammatory drugs (NSAIDs) ibuprofen (Nurofen/Advil).  So, colleagues at Monell Chemical Senses Center in Philadelphia and I started to investigate the interesting irritant sensation associated with virgin olive oils in the hope that we could find the irritant compound.  It was a long process, but here is the short version.  

The irritating compound was isolated and identified using a combination of HPLC-G and NMR.  The irritating compound was synthesised, tasted and named oleocanthal (oleo-Latin for olive, canth-Latin for sting, al-for aldehyde).  Finally, the pharmacologic activity of oleocanthal was assessed and compared to ibuprofen. Oleocanthal, was a classic NSAIDs with potency superior to that of ibuprofen.

Taken together, these data are consistent with our hypothesis that the throat irritating compound in virgin olive oil is an ibuprofen-like antiinflamatory agent.  It is important to remember that the traditional Mediterranean diet is associated with reduction in many inflammatory related diseases.  We suggest long-term consumption of virgin olive oil containing oleocanthal (and many other phenolic compounds), with anti-inflammatory ibuprofen-like activity may enhance health and well being.  Assuming that an olive oil consumer in the high normal range ingests about 3 tablespoons of olive oil/day and that this oil contains up to 200 ug/g of oleocanthal, then the person would consume approximately 10% of the dosage of ibuprofen recommended for adult pain relief.  It is important to note virgin olive oil in this situation is no a pain reliving drug, rather it provides some protection for inflammatory response that occurs during food consumption. [1]

NOTE

It is vital the olive oil is labelled ‘virgin’olive oil, otherwise the phenolics are not present.  To take full advantage of oleocanthal, the virgin olive oil should be peppery – some consumers do not like the peppery character.  And finally, olive oil is a yearly harvest, usually Autumn to Autumn – purchase local and fresh to maximize the potential health benefiting compounds.

REFERENCE

[1] Beauchamp, G. K., Keast, R. S., Morel, D., Lin, J., Pika, J., Han, Q., et al. Phytochemistry: ibuprofen-like activity in extra-virgin olive oil. Nature. 2005,437:45-6.

Perceived Flavour (or Flavor if your spell it without an u)

As chefs, cooks, food producers, product developers, and scientists it helps to understand flavour perception, particularly if we want to develop foods that are widely liked and nutritionally sound. What follows is a basic overview of how we perceive the flavour of foods – the information should provide an interesting basis for your own discoveries about flavour.

FLAVOUR PERCEPTION

The positive expectations of consuming a food begin when we visualize it and handle it, but the majority of sensory information comes when we take the first bite.  The flavour of a food is a combination of three independent sensory systems are activated, 1/taste, 2/smell, and 3/oro-nasal somatosensations (irritation, thermal, texture) making flavour a multi-sense experience. 

 

THE SENSE OF TASTE

The term ‘taste’ is often used when ‘flavour’ is the more appropriate word. This is because flavour is a combination of others senses beside taste.  It is widely accepted that there are five basic taste qualities (sweet, sour, salty, bitter, and umami), yet there are many more flavours experienced when we eat a food or drink a beverage.  The sense of taste is housed in the mouth and the majority of taste receptor cells (TRCs) are organised into rosette-like structures called taste buds, which are embedded in folds or lingual bumps called papillae located on our tongue, others are located in other areas of the mouth and throat.  The taste system is stimulated when a food or beverage is placed in the mouth, the food is manipulated by the teeth and tongue, saliva is mixed with the food, new surfaces are created as the food is broken down, and during this process non-volatile compounds in the foods are in contact and stimulate TRCs. The chemically sensitive apical end of a TRC is a small membrane region near the tongue surface.

The importance of taste to overall flavour is illustrated in the development of high intensity (HI) sweeteners to replace sucrose.  For a HI sweetener to perceptually mimic sucrose, it must match the dimensions of flavour: quality, intensity, time course, and location.  HI sweeteners (e.g., aspartame, neotame, sucralose, saccharin…) match sucrose for quality (sweet), and the intensity of sweetness can be matched.  We have unconscious knowledge of the time course and location dimensions of sucrose that enables them to discriminate between a sucrose solution and a HI sweetener solution matched for intensity. The time course of sensation differs between sucrose and HI sweeteners as the sweetness of HI sweeteners tends to linger in the mouth longer than the sweetness of sucrose.  In addition, some HI sweeteners activate bitter taste.  The overall problem is that HI sweeteners match some of the flavour dimensions of sucrose, but not others.  Flavour dimensions are important because consumers have developed a flavour preference for sucrose, and while they do not cognitively assess time course and location differences elicited by HI sweeteners, they recognize it is not sucrose.  For a product to be successful, the consumer has to relearn and like the ‘new sweetness’.    

A common misrepresentation of taste is the often-recited theory of a tongue map (this was due to a mistranslation of a German PhD thesis into a text book back in the early 1900’s).  The tongue map states that the tip of the tongue is sensitive to sweet, the back of the tongue is sensitive to bitter, the sides to salt and sour (no mention of umami in the tongue map).  However, all taste qualities can be experienced at all sites in the oral cavity that contain TRCs.  To convince yourself that areas of the tongue respond to all qualities, dip the tip of your tongue into solutions of tonic water or strong coffee to assess bitterness, honey to assess sweetness, salt water to assess saltiness, lemon juice to assess sourness, and consommé to assess umaminess.  As you will find, all five qualities may be elicited from the tip of the tongue. 

 

THE SENSE OF SMELL

The immense diversity of flavours we associate with foods are primarily derived from the volatile compounds (released into the air) that are released in the oral cavity when food or liquids are chewed and swallowed.  The scientific importance of the sense of smell was recently highlighted when Axel and Buck were awarded the 2004 Nobel Prize in Medicine for their work on olfactory receptors (ORs) and organisation of the olfactory system. There are approximately 1,000 genes for ORs in the mammalian genome making it the largest family of G-protein coupled receptors, but in humans on only approximately 36% of the genes remaining functional.  If the volatile compound has a structure recognized by the receptor, the a signal is sent to the processing regions of the brain and we perceive an aroma quality (e.g., rose, caramel, cut grass).  There are two routes to activate the sense of smell, orthonasal and retronasal. First, orthonasal, this is active sniffing or the act of breathing through the nose.  Think about walking past a bakery and the aromas that are coming from it – you are not eating the baked goods, but you can smell them. Second, retronasal, this is when the volatile compounds released from the food in the mouth take a passage to the nose at the back of the mouth, top of the throat.  Both are used when you are tasting beer or wine, the assessor will first actively sniff the product before placing in the mouth, then when in the mouth close the lips and breath through the nose. Retronasal is associated with the flavour of the food or beverage as the food is in your mouth and the senses of taste and somatosensory (see below) are involved, as well as the sense of smell.

A simple experiment demonstrates the influence the sense of smell has on flavour perception; if you taste a grated apple and onion it is very easy to distinguish between the two, yet with your nose plugged (index finger and thumb pinching your nostrils closed) it is near impossible.  When the nose is plugged, there is no airflow over the olfactory epithelium effectively removing aroma from the overall flavour and we must distinguish between the two samples by taste and texture attributes alone. 

 

SOMATOSENSORY COMPONENTS OF FLAVOUR

Irritant and textural sensations are also perceptual components of flavour.

CHEMICAL IRRITATION

Free endings of individual nerve fibers innervating both the oral and nasal mucosa have sensory receptors that respond to both heat and cold both of which evoke thermal and pain sensations.  The oro-nasal nerve fibers are not independent sensory systems, but a component of the pain and temperature fibers that occur throughout the body.  Our mouth and nose (and other mucus membrane regions) are particularly sensitive to certain chemical irritants due to a porous skin surface allowing chemicals to diffuse through the protective barrier to the nerve endings beneath.  A common feature of oro-nasal chemical irritation is the delayed response of sensation relative to that of taste or smell, due to the time taken for the chemicals to diffuse through tight junctions or epithelium to engage receptors on the nerve fibers- think about eating a chilli pepper and the time taken for the heat (and pain) to build.

There are a number of chemicals that are capable of activating irritant sensations and different adjectives to describe the sensations; the burn of chili pepper, the warmth of ethanol, the tingle of CO₂, the pungency of wasabi.  While there is not diversity of flavours we associate with the sense of smell, what we experience from chemical irritants often adds to the complexity of flavour.

PHYSICAL TEXTURE

The importance of texture in flavour perception should not be underestimated.  Our mouth contains nerve endings that respond to touch, pressure, and vibration and we have muscles, tendons, and joints that convey information on chewing foods to flavour processing areas of the brain.  The first bite and manipulations of the food are the most important in assessment of texture.  When you bite into fresh bread, the first few jaw movements collapse the food structure and provide information about the quality and flavour of the bread.  As the process of chewing continues the texture of the food changes as particle size of the food is reduced and a bolus suitable for swallowing is formed with the addition of saliva.  The thought of eating entirely puréed foods would not only modify the pleasure of eating but also cause problems identifying the foods you eat as texture conveys important characterizing information.

THE OTHER SENSES: SIGHT AND HEARING

Both sight and hearing are involved in flavour perception.  You have heard the saying ‘you first taste with your eyes’, to an extent it is true, sight sets up expectation and expectation can be persuasive!  Think about an orange flavour in a red jelly, 9 out of 10 people will pick the flavour as strawberry or raspberry – a flavour we associate with red coloured fruit.

Finally hearing, which is very much associated with the perceived quality of food.  Think about a wilted celery stick, it lacks the crispness (basically sound) expected and makes the celery stick less liked even though the taste and smell components are identical to a crisp celery stick.  The same situation will occur with potato crisp, if they lack the crispness and noise expected when eating, they are less liked.

SUMMARY

Flavour is fun – my daughter Hannah and I experiment with Jelly Belly candies – close your eyes, your partner in the flavour experiment places the Jelly Belly in your mouth.  Next, try to identify the flavour.  Or if you are by yourself,  you can block your nose with thumb and index finger, place the Jelly Belly in your mouth, use the sense of taste first, what do you experience?  Then release your nostrils, breath out through them and experience the flavour of the Jelly Belly. 

Flavour is complex, but every day, chefs, product developers and occasional cooks manage to use the knowledge they have to produce foods we all consume. While an in depth understanding is not essential to produce foods, it is an interesting topic area and understanding how the senses work together to produce flavour may help you produce new and interesting versions of foods you like.

A recipe for disaster. Creating a food supply for our appetite

I authored this article, it first appeared Twitter @Conversation in 2012

For all but the past 10,000 years, hominin species (2 legged primates) on the human evolutionary tract have been hunter-gatherers, and over millions of years of natural selection our senses were developed and refined to help us navigate the local environment.  Of critical importance was the ability to make correct food choices, and the sense of taste informed the hunter gatherer about the suitability of food for consumption. When a potential food was placed in the mouth the 5 taste primaries informed on essential nutrients and toxins: sweet elicited by sugars reflecting carbohydrate; umami elicited by glutamic and other amino acids reflecting protein content; salt elicited by sodium and other ions (Na+) reflecting mineral content; sour elicited by free hydrogen ions (H+) reflecting excessive acidity; and bitter reflecting potential toxins in foods.   In concert with the taste quality is a hedonic response and sweet, salty and umami qualities are appetitive and encourage consumption, whereas excessive sour and bitter are aversive and promote rejection of the food.  Decisions on whether to swallow or spit the food were critical to preservation of life. Appetitive responses to foods that contained fats, salt and sugars ensured these biologically prized yet scarce nutrients were consumed.

So, over millions of years of evolution, the sense of taste guided the hunter gatherer to essential nutrients and away from potential toxins.  Then approximately 10,000 years ago, the Neolithic revolution was underway and included human mastery of agriculture and animal husbandry meaning a secure food supply, thereby ending the need for hunter-gathering.  Civilisations were established around a secure food supply.

Arguably in the past 50 years there has been more change in the food supply than any other 50 year period with the establishment of fast food empires, multinational food companies, hyper-supermarkets, and a food supply heavily based on our appetitive response; in westernised societies we live in a vastly different environment to our hunter-gatherer forebears.  Our appetitive response is now a relic of evolution, and there has not been enough time since the Neolithic revolution for any adjustment to the human genome. 

Food companies, quite rightly, produce foods that appeal to our appetitive desires.  But, driven by appetite we now consume excess quantities of energy, fats, salts and sugars which lead to diseases of civilisation including obesity, hypertension and related pathologies.  One answer is to produce foods that are appetitive and nutritious, yet contain low concentrations of fats, salts and sugars.  While such strategies have the potential for significant health benefits, it will not be easy and the following example with salt (sodium) illustrates.

Sodium, in the form of manufactured sodium chloride (salt), is found in abundance in the modern diet, and excessive sodium consumption is linked to hypertension, cardiovascular disease and other diseases. Predicted health gains with a modest 15% reduction in dietary salt may avert 8.5 million cardiovascular related deaths worldwide over 10 years making salt reduction a priority for food industries and governments alike. In Westernised societies approximately 75% of our dietary salt intake is from manufactured foods, therefore pressure is on food companies to reduce the level of salt added to foods. 

While salt has certain functionality in foods, palatability and consumer acceptance is the most commonly cited constraint to salt reduction by the food industry. Large reductions in salt content of foods often result in declines in palatability and consumer acceptance of those foods.  The bliss point region represents the intensity of saltiness and the concentration of sodium at which the optimal level of liking occurs.  For example, salt added to a food at low concentrations may result in the food not being salty enough to be perceived and therefore too bland to be liked, while a higher concentration will increase liking until an optimal level of liking is reached.  However, further increases in salt concentration will result in the food becoming too salty, and liking will then decrease. The challenge remains, how can salt be removed while maintaining consumer liking and acceptance of a product. (For a review on the effects salt has on flavour please see Liem et al 2011).  

The food environment has changed significantly over the past 50 years and this has coincided with increased prevalence of diet related diseases.  Our appetitive response to certain nutrients aided the hunter gather survive by making appropriate food choice, but we now have a secure food supply and our appetite is leading us down a path to disease states rather than survival.  As the food supply has been refined in response to drivers of appetite we have created a food environment that promotes obesity, hypertension, certain cancers.  The challenge is to develop a food supply that meets not only our nutritional needs, but also fulfils our hedonic requirements.

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