Maxfacts

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Taste, texture and temperature

Contents

  1. Taste
  2. Texture
  3. Temperature

Our experience of eating is a complex mixture of contributions from different senses (taste and smell), the texture and temperature of foods, habits and social situations, our sense of (visual) aesthetics, sensual pleasures, as well as the clever ways in which nature runs our appetite in order to ensure that our bodies get the necessary nutrition. Concentrating on our sense of taste and the texture and temperature of food and drink is therefore a massive simplification but is helpful to gain some understanding of the interplay of food and drink with eating / swallowing. This is important to understand the normal functions, what happens when they are compromised and, hence, how one can best mitigate such difficulties by all kinds of practical tricks and how the modification of texture and temperature of foods enables oral food intake even in difficult circumstances.

Taste

Taste information is sensed in small structures, called taste buds, distributed over the tongue (see Figure 1).

Figure 1: Distribution of taste buds over the tongue.

A few more taste buds are found in the area of the soft palate and the cheeks. For many years it was believed that different areas of the tongue are responsible for sensing different tastes. This is incorrect, there are no special regions of the tongue that are tuned to sense a particular taste: all types of tastes are registered in all areas of the tongue.

Similar to the complicated process of swallowing or the highly regulated production and complex properties of saliva, also the story of tasting is a rather complicated one. Figure 2 summarizes the process where everything works as it should.

Figure 2: The various different components and agents that break down food such that it can interact with taste receptor cells in the taste buds. The components in saliva that help with chewing and swallowing are the same that also help to expose very small food particles to the taste receptor cells. The little green symbol “Toxin” signifies essentially bitter tastes (see text).

If we put food in the mouth, it usually needs to be chewed in order to break it down into smaller bits. However, the mechanical work of literally grinding down solid food into smaller bits is not the only process that needs to run smoothly. The action of saliva is not only required to enable the formation of a smooth and soft bolus that is easy to swallow, saliva also acts as a solvent that facilitates tasting. This explains well why people suffering from dry mouth usually report distorted or diminished taste.

Some of the active components in saliva help to produce microscopically small food particles that can access the taste receptor cells via the taste pores of the taste buds. This mechanism also works when eating soft or liquid foods that do not require chewing. Once the small food particles have passed the taste pore they will stimulate the taste receptor cells in the taste bud. The taste receptor cells, when stimulated, send taste signals to the brain and ultimately it is the brain that provides us with the perception and impression of taste. The various taste receptor cells are highly specialised and only register particular types of basic tastes.

Taste receptor cells are equipped with specialised protein molecules (or complexes of more than one protein) which specialise in recognising specific taste agents. We have five, more probably six (or even more), distinct basic taste receptors as shown in Figure 3.

Figure 3: The six basic tastes as identified by various receptor protein complexes (as far as currently known – there may be another basic taste "starchy"). A basic taste “fat” is not traditionally included in the basic set of distinguishable tastes but there is convincing and growing evidence that this is a taste in its own right. The abbreviations CD36, GPRI20, GPR40, T1R1, T1R3 and T1R2 are all short names / laboratory jargon of biochemists to identify specific proteins or protein families that are known to be involved as taste receptor proteins.

A group of proteins (CD36, GPR120, GPR40) have recently been identified as highly likely to be sensing a taste “fatty”. Savoury / umami taste is carried by an amino acid, glutamic acid, and its Na+ salt. Glutamic acid is, for example found in soy sauce, roast meats or roast mushrooms. The role of umami / savoury taste is to stimulate the appetite so that we wish to eat protein and nourish the body. Umami is sensed by a complex of two proteins, T1R1 + T1R3.

The protein complex T1R2 + T1R3 is responsible for sensing sweet taste. The most likely biologically useful role of this taste receptor is to give us an appetite for carbohydrates to curb acute hunger pangs and provide a quick energy boost.

A group of ca. 30 different T2R proteins all sense bitter taste. The little green label “Toxin” for bitter taste in Figure 3 refers to our evolutionary history. We have so many different taste receptors for bitter taste because avoiding eating toxic or rotten foods was crucially important for our species to survive; most toxic or rotten foods would tend to come with a bitter taste.

The taste receptors register “their” special taste agents by sensing common structural features in say, a range of different kinds of sugar molecules, all of which will then stimulate a response from those taste receptors with special features to recognise these typical sugar structural units, resulting in a signal “sweet” transmitted to (and from) the brain.

The two tastes salty and sour are triggered by Na+ (and a few other) ions and by H+ ions, respectively. Seemingly these two tastes are the simplest, their presence is well established but it is currently not known how exactly these two tastes are being sensed. There are suggestions that the mechanisms for tasting salty and sour do not require taste receptor protein complexes but may simply be due to flow of Na+ and / or H+ ions across cell membranes.

Similarly, it is well established that stimulating the various taste receptors sends taste signals to the brain via taste neurons (see Figure 2). However, it is not at all clear how our rich and subtle experiences of taste (and smell) arise from just sensing six basic taste varieties.

The sense of taste can be compromised in many different ways. For example, medication (in particular chemotherapy drugs and some antibiotics) can cause bad and/or distorted taste perception. Radiotherapy can cause damage to taste buds and salivary glands and alter or diminish taste, as can dry mouth as a symptom of other underlying conditions. Neurological conditions as well as damage by surgery to nerves essential for transmitting taste information to/from the brain can impair taste; and even the normal process of ageing will gradually reduce our taste acuity as we get older.

The latter is a reason why usually specially prepared (commercial) soft foods for elderly people are not suitable for oral and maxillofacial patients: these foods are usually fairly strongly seasoned, to account for lacking taste acuity in many elderly people.

This short account of what we know about the working of our sense of taste hints at a wide range of possibilities to maximise the taste experience in situations where our sense of taste may be severely compromised.

Texture

The reality for many maxillofacial patients is that they will encounter some kind of short- or longer-term difficulties with eating, sometimes these are permanent problems.

The good news is that this does not mean that anybody has to give up on their favourite tastes and flavours, but some compromise regarding the food texture may be necessary: almost all flavours and tastes can be prepared in a very wide range of textures at different temperatures. There should be some suitable preparations for almost everybody!

The best way to think about this wide field of possible textures of foods is to abandon our traditional and often fairly narrow-minded views of meals such as breakfast / lunch / dinner over the day, or starter / main course / dessert making up a typical meal. These ideas are just a reflection of western food traditions and are not a law written in stone; why not to have pea soup for breakfast if that works! Your care and support team, the speech and language therapist or dietitian, will give you some general basic recommendations for food that is safe for you to eat, their recommendations will be mainly defined by the texture of foods.

The textures (and temperature) of foods are the organisational principle of the Maxfacts cookbook too. Whatever combination of texture / temperature works for you at a given point in time will usually allow you to prepare a well-balanced and varied diet in that particular texture. Below we briefly describe the different categories of food textures most relevant for people afflicted by some kind of eating difficulty. It needs to be remembered that there are many different dysphagia problems and not all recommendations will be suitable for all conditions. For example, some people will experience difficulties swallowing liquids and, accordingly, will benefit from tricks that make liquids ‘less liquid’; others may only be able to swallow liquids and will thus be interested in the wide range of liquid foods one can prepare.

Foams

Foams are sometimes called “tasty air”, which is a fairly good description. Foams are highly dispersed liquids obtained after vigorous whipping, stabilised by some thickener and/or emulsifier. Foams a can be produced from most liquids and are best when made from strongly flavoured liquids. There is no need to swallow a foam but it will still provide taste stimulation in the mouth. The main use of foams in a care setting (outside the high-end Michelin star cuisines – no joke!) is in intensive and palliative care, often trying to provide some gustatory stimulation for neurological patients who literally will have to re-learn how to taste and swallow (for example, after a massive stroke, or when slowly waking up from a long coma).

For maxillofacial patients foams can have several useful roles, given that there is no need to swallow foams. Foams can be a tailor-made tasty way to keep the mouth moist. If somebody completely depends on a feeding tube for taking up enough nutrition, then any taste stimulation is completely missing. This lack of stimulation may be responsible for a lack of “drive” to return to oral feeding (given that taste triggers our appetites). Using foams to provide taste stimulation (and hence motivation to try and eat) can be helpful in the process of returning to food by mouth. For those who can and try to eat but suffer from insufficient saliva production, foams can be a useful appetiser that triggers / boosts saliva production before eating a meal. This usually also works for people with a diminished sense of taste if their sense of smell is working: much of the flavour of a foam is noticed by its smell rather than its taste.

Liquids

Equipped with a reasonable household blender and using some suitable dilution, almost all (solid) foods can be liquidised. In order to produce a completely smooth liquid texture, the liquid needs to be passed through a fine-meshed sieve before serving (or further processing / cooking). Liquid foods can be prepared across all savoury and sweet tastes, and over a wide range of temperatures. There are degrees of thickness liquid foods can take (some people may find slightly thicker but still drinkable foods more satisfying as a meal).

When having to rely on a liquid diet, by necessity the foods are diluted and it may be a challenge to eat enough to ensure provision of all necessary nutrients. Many liquid foods, in particular when dairy based, can easily be enriched with supplements and/or by using rich diluting agents, such as concentrated stock or cream.

Liquid foods include preparations such as custard (which many praise as excellent lubricating agent for all kinds of foods) as a representative of foods with a particularly silky consistency owing to the emulsifying properties of egg yolk. Adding egg yolk to other liquid foods may be useful, not just because of its emulsifying properties but also because egg yolk is an excellent source of protein.

Completely smooth liquids have a second role in the kitchen as starting materials for the preparation of jellies. Essentially all liquids can be made into jellies, savoury and sweet. In addition, smooth liquids also serve as starting materials for preparing very soft, very smooth foods such as mousses (which are usually stabilised by a little gelatin).

Jellies

Preparation of a jelly starts with a smooth liquid or thin smooth puree, across a wide range of savoury or sweet starting materials. Jellies are particularly easy to swallow due to their slipperiness (especially when made with ordinary gelatin, these jellies melt at approximately body temperature). Jellies are, in a sense, liquids in disguise and can be a good way to take in enough fluid by mouth when swallowing liquids is difficult or impossible.

Wobbly, that is softly set, jellies can be useful and tasty lubricants to help eating when suffering from dry mouth.

There are many different gelling and thickening agents, all of which have slightly different properties and thus produce jellies with a range of different properties. When made with some gelling agents other than gelatin, for example the resulting jelly will be a little more brittle but could be heated to provide a warm meal.

The crucial ingredient for making jellies (apart from the gelling agent) is water. Accordingly, many jellies are predominantly water based. However, dairy such as milk or cream contain enough water to make dairy-based jellies. If you have problems swallowing liquids but thoroughly miss your cuppa, making tea or coffee jellies provides an alternative. And if there is reason to celebrate with a bit of a tipple, jellies can also be made with (somewhat diluted) alcohol, for example wine, port or G & T.

Soft foods (without chunks and bits)

This is a wide selection of foods, savoury and sweet, that do not need chewing. The category includes traditional pureed foods as well as foods made from purees and liquids such mousses and flans / set custards. As with liquid foods, in order to prepare a perfectly smooth consistency without chunks and bits, it will be necessary to pass the purees through a fine-meshed sieve before serving or further processing. Basic purees are convenient and versatile starting materials for many different dishes; they can usually be frozen and are a compact storage form for having a quick-start meal at hand at all times.

Pureed foods may be easier to eat when combined with sauces or other lubricants. Set custards and flans benefit from the in-built lubricating effect of egg yolk. Mousses are usually stabilised with gelatin and thus also have some degree of in-built slipperiness. Mousses and flans have textures that many people find comfortable to eat. The preferred degrees of compactness of purees will be individually different, will likely change over time and will depend on temperature and specific foods.

Soft foods (with chunks and bits)

This is the only category of foods in our selection where different textures of foods are mixed. We are still dealing with soft foods which will only require a minimum effort with chewing or no chewing. A typical example of such foods would be small chunks of well cooked, soft carrot in a thick and creamy cheese sauce.

Having two different textures combined in one food gives more parameters to adjust and it is important to get the mix of textures right for individual needs and preferences – and these may vary widely. Some may prefer small soft bits in plenty of nearly liquid sauce, while others will prefer a more uniform overall texture of tiny “bits” and thick “sauce”.

For some people this category of mixed textures will be a stepping stone on the way back to “ordinary” foods. For others with reduced sensation in the oral cavity and/or of the tongue a suitably adjusted mixture of food textures can help with processing and moving food during the oral phase of swallowing and with forming a bolus that will trigger the natural swallowing reflex, rather than having to wash food down.

Temperature

The temperature of the foods we eat has a major impact on our taste and smell, and more generally overall eating, experience. The colder the food is the less we will be able to smell it. This may be an advantage for those people who are put off from eating by the smell of food. Frozen foods, in particular smooth ice creams, are more tolerable to eat with a sore mouth than foods at higher temperatures. More generally, many people find that foods that are difficult to eat at higher temperatures tend to be easier to eat when cold or frozen. Some people can take advantage of temperature contrast which is thought to help with triggering the swallowing reflex: taking a small mouthful of warm vegetable soup, followed by a small mouthful of, say goats’ cheese ice cream, and so on can make for a more pleasant, less stressful eating experience. Being patient and keeping food in the mouth for a little while before swallowing will not only help with mixing it with saliva and enhancing the taste perception in this way, it will also increase the ability to smell the food as the temperature of cold foods increases when kept in the mouth.

It is probably best to consider the temperature of foods as a freely adjustable parameter, optimised according to needs and preferences. We are not aware of any law saying that mushroom soup must be eaten piping hot…

There are many tried and tested recipes and suggestions for foods in sometimes unconventional textures and temperatures in the Maxfacts cookbook. In addition, we demonstrate some possibly less familiar (but commonly straightforward) preparations in cooking videos.

Further reading: Oral food