Nearly all the gelling, thickening and emulsifying ingredients are obtained from plant materials, only gelatin is made from animal collagen (pork, cattle, chicken, fish). Nearly all these agents with the ability to alter the texture of foods do so by similar mechanisms but to different degrees: in all cases very large molecules (usually made up from many interconnected sugar molecules) alter the way in which water molecules can move around. In a typical liquid, the water molecules are fairly free to move around but in the presence of these huge molecules the movement of the water molecules is more restricted and as a result the liquid can thicken, solidify or form a jelly, depending on the type and amount of gelling agent, temperature and composition of the liquid.
The most familiar gelling agents probably are gelatin, agar and carrageenan (commonly called vegetarian gelatin). Familiar thickening agents in the home kitchen are corn flour (gravy thickener) and pectin (in jam sugar). In addition there are several other gelling and thickening ingredients with interesting properties giving a range of slightly different food textures. In fact, here we follow the footsteps of some high-end Michelin-starred cuisines where professional chefs often take advantage of these ingredients.
Gelatin is different from all other gelling agents as it is made from animal collagen. Collagen consists of well-ordered polymeric chains of proteins (see Figure 1). Collagen is the most abundant protein in the human body in connective tissues (tendons, ligaments, skin, cartilage, blood vessels) varying from rigid to compliant structures. Its role is to give a certain elasticity to tissues and ensure smooth operation of joints in living creatures. Isolating collagen and heating it breaks down the ordered polymeric chains into a conglomerate of disordered chaotic polymeric chains.
In this form (now called gelatin) it can take up large quantities of water molecules. The two main building blocks of gelatin are aspartic acid and lysine (see Figure 2). Both of these molecules have several polar (‘sticky’) groups that can interact with (hold on to) water molecules.
Figure 3 illustrates how water molecules attach to the polar groups and thus get taken up in the polymeric network. This process is called swelling.
Gelatin is a gelling agent (E441) which can also be used to stabilise foams and mousses (see recipes and cooking videos). It is available in sheet and powder form.
Gelatin-based jellies melt around 35°C (ca. body temperature), so need to be set in the fridge (at temperatures below 15°C); it takes several hours to set.
The low melting point of gelatin-based jellies is the most beneficial aspect with regard to ease of swallowing (these jellies literally melt in the mouth / throat and have a particularly smooth texture). In addition gelatin does not distort the flavour of foods. Gelatin-based jellies last usually for several days in the fridge before they start leaking liquid (water) / separating. Presence of sugar, acids or alcohol may slightly alter the firmness of set. Gelatin-based jellies cannot be frozen and thawed. Gelatin works with just about all liquids (with the exception of raw pineapple and papaya juice, both contain enzymes that prevent the gelatin from setting the liquid – the same mechanism that helps making sticky saliva less sticky when munching on pineapple junks). Gelatin is a particularly robust and forgiving gelling agent. Powdered gelatin is most convenient to precisely adjust the wanted firmness of set. This is of practical importance because wobbly, softly set gelatin-based jellies have viscoelastic properties that make them good lubricants for other foods.
Using gelatin (powder and sheets) to produce jellies is demonstrated in our cooking videos and there is a collection of recipes for gelatin-based jellies in the Maxfacts cookbook alongside a number of further recipes making use of gelatin for the production of smooth and slippery foods (such as mousses).
Thickeners and gelling agents from plant materials
A wide variety of thickening and gelling agents is obtained from a wide range of plant materials, many of which are very large, complicated concatenated poly-sugar molecules (polysaccharides). Many of these agents have long-standing traditional uses in cuisines all over the world. Figure 4 shows four representatives of plant-derived food thickeners and gelling agents together with their basic chemical building blocks.
Corn (or potato) starch, arrow root
These are all commonly used ingredients in western cuisines for thickening of sauces and soups. They need to be suspended in some liquid and the suspension slowly added to the boiling liquid while stirring well. They tend to form lumps unless vigorously stirred but permit very good control of adjustment to a particular degree of thickness for many different liquids (provided the liquid can be heated to boiling point). All of the above may be less suitable as thickening agents when dealing with dry mouth problems owing to the resulting texture.
Figure 5 illustrates how all of the thickening and gelling agents derived from polymeric sugars (such as starch in corn flour) in principle can attract and accommodate large quantities of water molecules in between the polymer chains. Since the basic building blocks of all these polymers vary slightly, also the resulting properties and interactions with water molecules will vary slightly. That, in turn, is very useful as a wide selection of thickeners and gelling agents thus gives us a very finely tuned handle on the texture of foods. This is vital when catering for the needs of people with dysphagia (maxillofacial patients and others) as many will have a narrowly defined window of manageable textures (and temperatures) of foods.
Pectin is obtained from various fruits and plants (for example apples and peel of citrus fruit; see Figure 4). It is a well-known household gelling agent (E440) widely used in jam making, or in the production of jelly beans. Its gelling effect requires high sugar content in a (at least) slightly acidic environment, perfect for jam making. Pectin produces stable jellies that can be frozen and thawed.
Guar gum is made from guar beans (E412; see Figure 4). It is a stabiliser and thickener, widely used in commercial foods. It works similarly to starch in corn or potato flour (see Figure 5) but is a more powerful thickening agent that only requires small quantities to be added to a liquid. It may be a more suitable thickener for those afflicted by dry mouth. Guar gum can also act as a gelling agent but only in the presence of calcium ions (such as in dairy products).
Various types of methylcellulose exist, they are all obtained from plant fibres (cellulose), often from the cotton plant (E461; see Figure 4). Methylcellulose is a gelling agent and potent foam stabiliser. Depending on the particular fraction used, firm gels form at elevated temperatures (ca. 50-80°C), set rapidly and melt in the mouth. At room temperature small quantities of pre-swelled methylcellulose added to a liquid (together with some thickener such as xanthan gum, see below), combined with vigorous whisking of the liquid, produce stable foams (‘tasty air’). Such foams can act as appetisers that do not require active swallowing but can provide taste stimulation from many different strongly flavoured liquids.
Thickeners and gelling agents from algae and sea weeds
A range of algae and sea weeds are a rich resource for the isolation of (mostly) different gelling agents. Figure 6 shows three selected examples together with their chemical signatures. As they also consist of polymeric sugar molecules they work in similar ways to all the other related agents (see Figure 5).
Agar is obtained from seaweed, a gelling agent (E406). It is usually sold in powder form in many supermarkets and Asian food stores (traditional ingredient in Asian cuisine).
Agar-based jellies are produced by heating it in the liquid to nearly boiling point, the jelly then sets rapidly on cooling. Agar produces firm, slightly brittle jellies that can be cut into shape at room temperature. The jellies are fairly stable at higher temperatures, so can be gentle re-heated and served hot. Agar-based jellies cannot be frozen and thawed. Agar jellies do not keep well but start leaking water after a short while.
Carrageenan is obtained from red algae (Irish moss), a gelling agent (E407, E407a). It is the usual vegetarian alternative to gelatin. Carrageenan has been used for centuries in China, Ireland and Scotland (for example, according to some local Scottish traditions seaweed is boiled in milk, strained, flavouring (whisky…) added to the liquid and set aside to cool, yielding a variety of milk jelly).
Different fractions of carrageenan exist (Iota – gives soft gels, requires presence of calcium ions to work, so naturally works well with dairy products; Kappa – gives firm gels but requires presence of potassium ions to work (usually already added to commercial ‘vegetarian gelatin’; Lambda – acts as a thickener for dairy products, this fraction is usually not contained in ‘vegetarian gelatin’).
Carrageenan-based jellies cannot be heated but can be frozen and thawed. Especially jellies made with the Iota fraction have interesting mouthfeel properties: they tend to slightly liquefy when shaken, stirred or chewed (a bit like ketchup) and in this way give the impression of a silky texture in the mouth and may ease swallowing. The Kappa fraction gives a silky mouthfeel similar to that of tofu. Carrageenan jellies set rapidly on cooling but only work with liquids that can be heated to boiling point.
The use of carrageenan to produce jellies is not quite as robust as the use of gelatin and the firmness of set is slightly more difficult to predict but carrageenan-based jellies broaden the range of properties beyond those based on gelatin (and, of course, may be more acceptable to vegetarians and are halal and kosher as well). We demonstrate the use of carrageenan in our cooking videos.
Alginates are obtained from brown algae, they are a range of gelling and gum-forming agents (E400-E404). You may have come across sodium alginate as the main ingredient in some well-known heart-burn remedies. Alginates are commonly used as food thickeners in the food industry. As gelling agents they yield firm, brittle and heat-stable jellies. Alginates are popular in so called molecular cuisine where one can use their properties to prepare unusual foods and food textures, such as wobbly jelly spheres containing a liquid core.
Thickeners and gelling agents from fermentation processes
Some of the most powerful thickening and gelling agents, widely used in the food industry as well as in high-end gastronomy, are obtained as a by-product of bacterial sugar fermentation. Figure 7 shows two representatives of this class of texture modifying agents, well worth to try out at home, they are easy to use!
Gellan gum is a by-product of sugar fermentation (E418), a powerful gelling agent that is widely used in the food industry. Small concentrations of gellan gum form typically elastic jellies that are particularly good at releasing flavours. Robust whisking of these jellies produces so called liquid gels – liquids that are perfectly smooth and can be poured but still maintain most of the properties of a gel rather than a simple liquid. These unusual food textures are definitely under-researched as far as their potential benefits for dysphagia sufferers are concerned. Gellan-based jellies are easy to cut once set and thus are particularly suitable as slippery ‘finger food’.
Xanthan gum is another by-product of fermentation (E415), a powerful thickener and stabiliser. It works with a very wide range of hot and cold liquids. Small quantities of xanthan gum swell liquids to a jelly-like consistency (fluid gels) maintaining the viscosity even when heated. Xanthan-based gels typically have a pleasant mouth feel because xanthan gum can also act as an emulsifier (widely exploited, for example in the preparation of commercial ice cream). In addition, xanthan gum can stabilise many food preparations, for example foams.
Lecithin represents a group of compounds usually extracted from egg yolks or soy beans (E322). Lecithin is a highly effective emulsifier, it belongs to a class of compounds with so called amphiphilic properties, that is these compounds are attracted both by water and by fatty compounds (more specifically, these are all phospholipids). Because of this dual attraction of lecithin to otherwise immiscible phases, emulsifiers such as lecithin give foods a particularly silky and comfortable texture (and help paint particles to remain suspended in wall paint, or prevent commercial salad cream from splitting while sitting on the shelf in the supermarket, etc.). The resulting lubricating property of lecithin, together with its similarity to some components of natural saliva, is fully explained in our detailed pages about lubrication of foods. With lecithin being a natural component of egg yolks, egg yolks can easily be used as a natural emulsifying agent in home cooking (think of proper homemade custard or baked custards / flans; recipes can be found in the Maxfacts cookbook and we demonstrate the preparation of custard and baked custard in cooking videos).
Lecithin powders can be used with a wide range of hot or cold liquids and purees and may also be used to stabilise foams. In order to produce a stable emulsion, lecithin must first be dissolved in the water phase, and the fatty / oily phase is added step by step in small quantities while whisking the mixture constantly (the secret of making mayonnaise…).