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.

 BIBILOGRAPHY

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