GELLING AGENTS USED IN FOOD INDUSTRY

INTRODUCTION

Within the food industry, stabilisers, thickeners and gelling agents are often more simply referred to as food hydrocolloids. The hydrocolloids traditionally used in food thickening and gelling include, but are not limited to, the following: agar, alginates, arabic, carrageenan, cassia tora, carboxymethyl cellulose, gelatin, gellan, guar, karaya, konjac, locust bean gum, methyl cellulose, hydroxypropylmethyl cellulose, microcrystalline cellulose, pectin, starches, tara, tragacanth and xanthan.

Many of these ingredients are carbohydrates but at least one important hydrocolloid, gelatin, is a protein. Most are agricultural derivatives but some are biotechnology derived, and gelatin, of course, is an animal product.

Many, if not all, of the thickening and gelling agents for food are available in a wide range of differentiated grades. Starch is a good example. There are literally hundreds of different food starches based on different raw materials and production process conditions. A double derivatised, waxy maize starch is totally different from, for example, a pregelatinised potato starch. Cellulose derivatives, such as carboxymethyl cellulose, microcrystalline cellulose, methyl cellulose and hydroxypropylmethyl cellulose, come in a virtually limitless range of differentiated grades depending on the degree of substitution and other processing factors.

A large number of ‘new’ and ‘differentiated’ properties have been and continue to be developed for hydrocolloids that fall under an ‘umbrella category’; for example methyl cellulose, hydroxypropylmethyl cellulose and microcrystalline cellulose can be produced in a multitudeof grades to suit a wide range of specific functional needs. Xanthan is offered in different mesh sizes, rapidly hydrating, brine tolerant and/or as a clarified grade. New versions are constantly being developed and assure the specialty future of at least part of this market.

The following is a brief overview of the key functional properties for which these ingredients are used. Nutritional properties are relatively new and nutraceutical or health-enhancing properties are even more recent. Further work is sure to advance the use of hydrocolloids beyond modification of the rheology of foods.

Viscosity

Viscosity is probably one of the most widely used properties. In this respect, hydrocolloids are often used in systems where the oil or fat content has been reduced or eliminated through substitution with water. The hydrocolloid thickens water, which, in turn, replaces the fat or oil to give a product with similar properties to the full-fat food. A typical application for this function is reduced-fat salad dressings. In other cases, the thickened water simply adds body, texture and mouthfeel to a food such as table syrups, particularly low-calorie syrups.

Stability

If oil or fat is partially removed from a formulation and is replaced with thickened water, an emulsion is usually formed. Often the function of the hydrocolloid is to stabilise the emulsion, to prevent separation and, in the case of frozen foods, to control ice crystal formation. New technology and new ingredients have been developed specifically to address the problem of ice crystals in frozen foods, but hydrocolloids will continue to play a role. Virtually every ice cream product sold in retail outlets is stabilised with carrageenan, locust bean gum and/or guar gum. Low-fat salad dressings, discussed above, also benefit from emulsion-stabilising properties.

Suspension

If insoluble particles are included in the thickened product then separation and settling should be eliminated or at least minimised. Some hydrocolloids create solutions with a ‘yield point’ that will keep particles immobilised in suspension. Salad dressing is a good example of this and xanthan gum is the typical hydrocolloid to supply this functionality.

Gelation

One of the key texturising aspects of hydrocolloids is the ability to gel and solidify fluid products. For example, in gelled milk desserts, even low levels of carrageenan will form a solid milk gel. Other classic gelling agents are pectin, gelatin and agar. Many others, however, will form a gel under specific conditions. Certain grades of alginates form gels with calcium ions. Xanthan and locust bean gum do not gel individually but together they display synergy and form a strong cohesive gel. Methyl cellulose and hydroxypropylmethyl cellulose are unusual in forming solutions that reversibly thicken or gel when heated. The food industry has a myriad of gelling applications ranging from soft, elastic gels to hard and brittle gels.

Nutritional and nutraceutical

There is already a wide use of some hydrocolloids, arabic and guar gum, for example, as sources of soluble dietary fibre. Much research has been conducted in the nutraceutical benefits of hydrocolloids. Potential benefits range from cholesterol reduction to cancer risk prevention. Their use in weight loss programmes is already widespread and likely to expand further.

Acacia Gum (Gum Arabic)

Acacia gum, also known as gum arabic, is a natural gum exudate obtained from acacia trees in the ‘African sub-Sahelian zone’. The gum has a highly branched compact arabinogalactan structure which gives a low-viscosity solution together with a central protein fraction that provides good emulsification properties. The powder hydrates readily in water and concentrations up to 40–50% can be handled easily. Key food applications include a range of confectionery products, flavoured oil emulsions and capsules and health foods as a source of soluble fibre with prebiotic properties.

Acacia gum is a highly branched arabinogalactan polysaccharide with a high molecular weight developing a low viscosity in water. All molecules of acacia gum contain the same sugars: galactose, arabinose, rhamnose and glucuronic acids (Jurasek et al., 1993) partially neutralised with calcium, potassium, sodium and magnesium salts.

Acacia gum is not considered a thickening hydrocolloid when dissolved in water at low concentrations up to 30%. However, when used in sucrose or sugar-free systems at high levels of dry solids, acacia gum provides a unique texture to confectionery products. Acacia gum is used in a wide range of finished products including moulded candies, jujubes, pastilles with sucrose or polyols, for coated and non-coated chewy products, for sugar-free hard candies and in different tableting processes where binding properties are needed.

Moulded candies

For moulded candies made with sucrose, acacia gum is used at different levels depending upon the texture required. For a hard texture, acacia gum from A. senegal is used alone at high concentrations in the finished confectionery. A typical formula contains 35% acacia gum, 30% sucrose, 25% glucose and about 10% water plus flavouring and colouring. Because of the occasional shortage of acacia gum, modified starch has partially substituted the natural gum. And yet, compared to modified starch, it is recognised that hard candy made with acacia gum lasts longer in the mouth, does not stick to the teeth and provides a unique flavour release.

To produce moulded candies with a softer texture, acacia gum is used with other gelling agents, such as gelatine. The combination of the hard texture from acacia gum with the flexible, soft gel from gelatine gives a wine gum-type texture. A typical formula is based on 15% acacia gum from A. seyal or A. senegal with 5% gelatine, 24% sucrose, 44% glucose, colour and flavour, and the remaining part being 12% moisture.

Chewy confectionery

A chewy product is a slightly whipped, soft confection containing 74% sucrose and glucose, 5% hydrogenated vegetable fat, flavour and acid. Specific textures are obtained by including 1% gelatine for aeration and 1% gum from A. seyal for a long-lasting, cohesive chew. These chewy products can also be used as centres and then sugar coated.

Sugar-free hard candies

Because of the water-binding properties of acacia gum, the addition of a low level of 2–5% of gum in the formulation of a sugar-free hard candy, based on sorbitol, maltitol or mannitol, slightly increases the amount of residual water by 1–3% after cooking and, therefore, decreases the cooking temperature between 5 and 15◦C. Hygroscopicity of the candy is reduced, recrystallisation of polyols is avoided and wrapped sweets are not sticky.

Tableting

Tableting includes different techniques: direct compression, wet granulation and making lozenges which are a type of tablet. Agglomerated acacia gum from A. seyal and A. senegal is used as a binder in these different processes to make food and pharmaceutical products. For direct compression, purified and agglomerated acacia gum is mixed with the other powders having the same mesh size before filling the die. In wet granulation, a solution of acacia gum is added to the powders to make a slurry which is dried and sieved to produce a free-flowing material which is then compressed.

For lozenges, two binders are combined: acacia gum and gelatine are dissolved in water and used to bind the flavoured icing sugar. The paste is then sheeted, cut to shape and dried in an oven. The lozenges are usually flavoured with mint and have an old-fashioned traditional appearance with a rough surface.

Coating and panning

The most popular sugar-free product is polyol-coated chewing gum in which the gum base is used as a carrier for an active principle suitable for tooth health. Sorbitol, maltitol and xylitol can be used for hard coating. Each of these polyols has its own specific behavior in terms of stability, hygroscopicity, cooling effect, crunchiness and sweetness. Xylitol and maltitol are the main polyols used for panning sugar-free chewing gum.

Acacia gum is used in a hard-coating syrup containing about 65% polyol, 3% acacia gum, 1% titanium dioxide and 31% water. This is sprayed onto the surface of the chewing gum centre and then dried by air at 30◦C and 40% humidity. One role of acacia gum is to decrease the crystallization temperature of the polyol in order to apply the syrup at a lower temperature of 65–70◦C so as not to damage the shape of the chewing gum centres. Other benefits of including acacia gum in the coating syrup are improving resistance of the polyol layers and increasing shelf life by decreasing hygroscopicity.

Emulsions

Acacia gum is used as an emulsifier and stabiliser in preparing oil-in-water emulsions. Acacia gum is not considered an actual emulsifier which contains a lipophilic and hydrophilic part in its molecule. Acacia gum is a water-soluble polysaccharide. However, it is possible to give it a hydrophilic–lipophilic balance value. The protein contained in the AGP fraction of the molecule gives surface-active behaviour to the molecule and allows formation of a colloidal film around the oil droplets.

Encapsulation

Encapsulation is a general term that includes many different techniques using different carriers including acacia gum (Risch, 1995). The main reasons for encapsulating an active principle are:

• protection against oxidation, water migration or internal reactions;
• production of a water-dispersible, free-flowing powder;
• production of a controlled release powder;
• reduction of hygroscopicity or reduction of dust pollution.

The encapsulation process is generally classified into two groups:

• Matrix encapsulation. The dispersion of oil droplets inside the matrix in which acacia gum may be used. Such a system allows 10–30% oil content in the carrier. The matrix system is normally produced by spray drying.
• Membrane encapsulation. The formation of membrane around a ‘big’ oil droplet from 20 to 500 μm in size. Such a system allows encapsulation of up to 90–95% oil.

Processes used to form the membrane system are mainly:

• complex coacervation where acacia gum could be involved, or
• extrusion where the membrane could be gelatine, agar or alginate.
• 
  

Agar

Agar is a seaweed hydrocolloid, or phycocolloid, with a long history of use as a gelling, thickening and stabilising food additive. Agar is considered to have been discovered in the mid-seventeenth century in Japan, 200 years before it was introduced to the West.

Agar is widely used for solid culture media in microbiology. Although this application is credited to Robert Koch, it is now accepted that his wife, Angelina, first suggested the use of this material. She had learnt of the use of agar-agar in jams and jellies from a Dutch immigrant returning from Java. This gelling agent melted at higher temperatures than gelatine and enabled the jellies to tolerate the hot and humid climate conditions. Subsequently, Koch and his assistant Hesse perfected the extraction of agar for use in microbiological plates leading to Koch’s discovery of the tuberculosis bacillus and the promotion of agar for microbiological media in general.

Agar has been recognised as a polysaccharide since its introduction into Europe in the middle of the nineteenth century. Initially, it was assigned a linear galactan configuration, but later small quantities of sulphate were identified within the macromolecule. The sulphate content of agar is below 4.5% which is very low compared to that of carrageenans, another group of polysaccharides which are obtained from red seaweeds, Rhodophyceae. Typically, the sulphate content of agar is 1.5–2.5%, in contrast to the ester sulphate content of kappa, iota and lambda carrageenans of 22, 32 and 37%, respectively.

Gelation

The ability to form reversible gels by simply cooling hot, aqueous solutions is the most important property of agar. This gel-forming ability has led to the large number of practical applications where agar is used as a food additive or in other applications in microbiology, biochemistry or molecular biology, as well as in industrial applications.

Agar is insoluble in coldwater but hydrates to form random coils in boilingwater. Gelation depends exclusively on the formation of hydrogen bonds, where the random coils associate to form single helices and double helices. These left-handed threefold helices are stabilised by the presence of water molecules bound inside the double helical cavity and exterior hydroxyl groups allow aggregation of up to 10 000 of these helices to form microdomains of spherical microgels. Following the phase separation process, the microgels aggregate to form gels on cooling below 30–40◦C.

This transition occurs at higher temperatures with increasing agar concentration and decreasing cooling rate. For example, the gelling temperature for Gelidium agar increases from 32 to 38◦C and melting temperature rises from 86 to 89◦C as the concentration increases from 0.5 to 2.0%. The gelation process of agar: random coils associate on cooling to form helices followed by further aggregation of the helices to give the aggregated structures of agar gels.

Food applications

The most important advantages for agar in different food applications derive from the characteristic firm texture and heat tolerance of the gels, stability in acidic conditions and limited reactivity to other food components. The key properties are listed below:

• The large gelling capacity enables agar to be used at very lowconcentrations. The threshold concentration for gelation is 0.2% and levels in food products are typically between 0.5% and 2.0%.
• The large gel hysteresis, the difference between setting and melting temperatures, is much greater than that of any other reversible gelling agent, so that liquid solutions may be held at 40◦C before setting and, once gelled, products remain stable up to 80◦C.
• Agar forms gels over a wide pH range. The neutral polymer chain confers good resistance to acid hydrolysis at the normal pH values found in foods, such as in fruit products. However, agar can be hydrolysed by acid at high temperatures, so for pH values below 5, it is recommended that the pH of the food is lowered just before cooling to form the gel.
• No counter ions are needed for gelation and, hence, there is no characteristic metallic taste in the final products as found with alginates or carrageenan, which makes agar a very good product for delicately flavoured foods. Also, variations in the levels of cations in the food product do not produce a change in the textural properties of the gel.
• In cultured foods, such as yogurt, agar does not inhibit the growth of inoculated bacteria.
• It has good compatibility with other polysaccharides and proteins at normal use levels. This enables agar to give consistent gelled dairy desserts and avoid textural variations which can result from differences in milk quality.
• It does not require a minimum sugar solids level for gelation and so it can be used for low-sugar jams and jellies where reduced sugar levels and/or high intensity sweeteners may be employed. In some cases, high sugar concentrations assist the association of the agar network and gel strength increases.
• Agar now has 350 years of safe use in food. It has a high soluble fibre content that is not metabolised in humans and so it does not add calories to foods.

This combination of benefits results in agar maintaining its position as the hydrocolloid of choice in a number of specific food applications, particularly where firm, short-textured gels with good heat stability and good moisture stabilisation are required:

• Water gels, such as water dessert jellies, vegetable, meat and fish aspics and artificial caviar.
• Confectionery including sweets and candies, fruit jellies, nougat, candy fillings, piping gels, jellies and jams.
• Bakery products, such as icings and glazes for pastries, cakes and doughnuts.

Carrageenan

For centuries, red seaweeds (Rhodophyceae) have been harvested and used as foods in the Far East and Europe. There are many different species of red seaweeds but they all contain naturally occurring polysaccharides that fill the voids within the cellulose structure of the plant. This family of natural polysaccharides includes carrageenan, furcellaran and agar.

Carrageenan extracted from seaweed is not assimilated by the human body, providing only fibre with no nutritional value, but it does provide unique functional characteristics that can be used to gel, thicken and stabilise food products and food systems. Multiple commercial red seaweed species provide a sub-family of carrageenan extracts, with differences in composition and molecular conformation, which lead to a wide spectrum of rheological profiles, gel properties and textures, molecular charge densities and interactions with other gums and proteins.

Carrageenans have a backbone of galactose but differ in the proportion and location of ester sulphate groups and the proportion of 3,6-anhydrogalactose. There are three primary types. Kappa carrageenan and iota carrageenan form thermally reversible gels, which range in texture from firm and brittle to soft and elastic. Lambda carrageenan is non-gelling. Kappa carrageenan interacts synergistically with other gums to modify further the gel texture, for example with polymannans such as locust bean gum and konjac. A specific interaction between kappa carrageenan and kappa casein is widely used to stabilise dairy products.

Water gelling applications

Water dessert gels and cake glazes are some of the more traditional uses of carrageenan. These products are based on the firm, brittle gel properties of kappa carrageenan with the texture modified as necessary for elasticity, cohesiveness and syneresis control using iota carrageenan or other gums, such as locust bean gum or konjac. Recent improvements in the combinations used for these applications have resulted in vegetarian products which have a similar appearance and texture to traditional gelatin products while giving additional 

benefits of fast setting and stability at ambient temperatures.

Gelatine

Through the years, mankind discovered that gelatine is a multifunctional protein molecule, used as an ingredient for the food, pharmaceutical and photographic industries in a wide range of applications.

The photographic industry initiated research on gelatine. The manufacturing processes were also found to have a large impact on gelatine characteristics. Research by Ames (1952) clearly made the distinction between two major manufacturing processes: the acid or A-type process, where the raw materials are pre-treated in acid, and the alkaline or B-type (basic) process, where the raw materials are pre-treated in an alkaline solution.

The basic characteristics of gelatine, such as gel strength, viscosity and isoelectric point (IEP), are mainly determined by which process is used. Gel strength is primarily determined by the proportion of proline and hydroxyproline present in the total amino acids. A high content of these two amino acids indicates a high gelling power. Viscosity is primarily determined by the molecular weight distribution of the gelatine. A high molecular weight is linked to a high viscosity. The alkaline process results in IEP values between 4.5 and 5.5, and the IEP from an acid process can vary from 6 to 9.5. These three characteristics are important in determining the appropriate type of gelatine required for a particular application.

Gelatine is obtained by hydrolysis of the collagen that is contained in animal connective tissues. Commercially, skins or bones of different animal species, such as beef, pork, fish and poultry, form the main raw material for gelatine production. These raw materials are collected from animals approved for human consumption by ante- and post-mortem veterinary inspection. Skins can be frozen if there is a long delay between sourcing and eventual use in the gelatine manufacturing process. Some raw materials, mainly bones, are pre-treated by grinding, degreasing and drying before they are used in gelatine production.

Sugar confectionery

In the early days of sugar confectionery, products were made by skilled craftsman working empirically and the science of sugar confectionery came later. The link with more scientific technology for the production of cough sweets and similar products in the pharmaceutical industry was a big step in understanding the basic aspects of sugar confectionery.

The sugar confectionery market offers a wide variety of products around the world. Cultural differences, habits and eating customs can be completely different, so apparently identical sugar confectionery products can have a completely different taste and texture. A good example is the famous gummy bear.

A German gummy bear, with a hard texture, resembles the appearance of a British jelly baby, which has a very soft texture. These are different from the soft Asian gummy bear which has unusual exotic flavours. This means that there is no standard reference for sugar confectionery, but similar basic principles are applied throughout the industry.

Gelatine is one of the most versatile texturising ingredients for sugar confectionery and is perfectly adaptable to most industrial sugar confectionery processes as a result of a number of features:

• the thermo-reversible gel allows confectionery products to be re-melted for easy recyclingand rework of finished products,
• solutions are low viscosity and easy to deposit without tailing,
• it is a protein with good whipping and emulsifying properties,
• it is fully compatible with many other texturising agents,
• strong water binding prevents the finished product from drying out,
• different mesh sizes from 8 mesh (2.35 mm) up to 60 mesh (0.25 mm) allow combination with other ingredients of the same particle size and processing is easy.

Gelatine sugar confectionery products can be divided into two classes: jelly confectionery and aerated confectionery. Jelly confectionery is characterised by the formation of a gel after depositing into starch and cooling down to ambient temperature. Aerated confectionery is made by the introduction of air into the liquid phase and the amount of air is characteristic of the aerated product.

Jelly confectionery

These products are usually called jellies. Occasionally, they are also referred to as gums, although the name ‘gum’ is generally reserved for products made with modified starch. Sometimes modified starch is combined with gelatine, for example in a so-called wine gum.

Variations in texture will be obtained when using gelatine of different gel strengths at the same concentration. Higher gel strength gelatine gives harder textures. Sugar and glucose syrup are the bulking agents in the recipe and are responsible for the sweet taste and the shelf life of the product. Citric acid is used to lower the pH to about 3.2, which will enhance the typical acid fruit flavour.

The gelatine solution is made in a separate tank. Solutions of gelatine up to maximum 40% can be made; at higher concentrations, part of the gelatine will not be dissolved. Gelatine dissolves rapidly in hot water (80–90◦C) and can be kept for 4–6 h maximum at 50–60◦C without significant degradation.

Aerated confectionery

In aerated confectionery, gelatine gives the air cell wall the required mechanical resistance to avoid deformation. The basic principles and the recipes are very similar to jelly confectionery. The big difference is that air is introduced in the gel mass, which results in a mass with densities that can vary from 1.0 to 0.25. The aeration can be done with a planetary beater or a continuous beater under pressure. It is the final density which determines the texture and type of finished product. Four main types can be defined:

• Chewy candy: density 1.0–0.9
• Aerated jelly candy: density 0.9–0.8
• Deposited marshmallow: 0.55–0.5
• Extruded marshmallow: 0.30–0.25

Gellan Gum

Gellan gum is a fermentation polysaccharide produced by the microorganism Sphingomonas elodea (previously identified as Pseudomonas elodea, but later reclassified). CP Kelco found this organism when it undertook a worldwide screening program to discover interesting and useful new gums that could be made by fermentation. At the time of its discovery, gellan gum was thought to be a ‘universal’ gelling agent. The fact that gellan gum gel textures can range from soft and elastic to hard and brittle is unusual. Adding to this appeal, gellan gum can form gels using both monovalent and divalent cations. Gellan gum can be used at very low use levels, and its gels show excellent thermal stability. With its unique combination of properties, it is easy to understand why gellan gum has high appeal to the food industry.

Dessert gels

In dessert gels, low-acyl gellan gum creates a firm, brittle texture with excellent clarity and heat stability. Because it is highly efficient at forming gels, the gellan gum use level is very low, with typical use levels for dessert gels ranging from 0.15 to 0.35%. Gellan gum also provides particularly good flavor release compared to other gums. However, the brittle texture of low-acyl gels is not typical of common dessert gels. Therefore, low-acyl gellan gum is often blended with other gelling agents to provide softer, more elastic textures. A blend of low-acyl gellan gum with xanthan gum and locust bean gum, targeted for a dessert gel 

texture, is commercially available.

Drinking jellies

Drinking jellies are formulated in a similar way to dessert gels, but lower levels of gelling agents are used to create a very soft gel. There are different types and textures of drinking jellies, depending on how they will be consumed. Some drinking jellies are soft enough to be sucked through a straw. Others will be crushed and squeezed out of a pouch. In many Asian countries, drinking jellies are consumed simply for their interesting textures.

Increasingly, however, gellan gum drinking gels are being formulated to provide enhanced nutrition or nutraceutical benefits. Sports gels are an example of such a product. They are typically packaged in pouches with tear-off tops for consumption while exercising. The gelled contents provide water and nutrients without spilling and the juicy gel bits slide down the throat without leaving a sticky coating.

Pectin

Pectin is a natural constituent of all land plants where, together with cellulose, it plays a key role in the cell wall structure. It comprises a group of polysaccharides rich in galacturonic acid units and, to a lesser extent, various neutral sugars. Pectin extracted from plants has been used as a gelling agent in food for many years. In fact, the invention of using pectin as a gelling agent dates from the 1820s when the Frenchman Henri Braconnot prepared a synthetic jelly with alkali-extracted pectin. However, the first recorded commercial production of pectin extract was in Germany in 1908, after which the process spread to the US, where Robert Douglas obtained a patent in 1913.

The centre of production is currently located in Europe and citrus-producing countries such as Mexico and Brazil. Historically, apple pomace was the major pectin source, but in recent years, an increasing use of citrus peel has taken place. An additional but much less important source of pectin is sugar beet pulp. In recent years, new application opportunities have emerged and pectin is no longer just a gelling agent but also used as a stabiliser and thickener.

Pectin raw materials presently used in industrial processes include apple pomace, citrus peel – comprising lime, lemon and orange – and, to a lesser extent, sugar beet pulp. Citrus peel and apple pomace are by-products of the fruit juice industry and sugar beet pulp of the refined sugar industry. Both wet and dry citrus peels are used for pectin production, whereas mainly dry apple pomace is used. Apple pomace must be dried immediately in order to prevent disintegration into a thick mash from which it is uneconomic to extract pectin.

Gelation

The prime physicochemical property of pectin is its ability to gel and gel strength generally increases with increased molecular weight. HM pectin gels in acidic conditions and in the presence of sugar, whereas LM pectin may gel over a broader pH range and lower concentration of sugar but requires the presence of cations which, when referring to food, is generally calcium. Accordingly, one refers to sugar and calcium gelling, respectively.

Pectin is used as a gelling, thickening and stabilising agent in foods and, to a lesser extent, in pharmaceuticals. Basically, pectin is used to control water in products and help to create the desired texture. The traditional and major application is as a gelling agent in jams and jellies which utilises the ability of HM pectin to form gels at low pH and high sugar levels and the ability of LM pectin to form gels at low sugar levels in the presence of calcium. One of the attractive features is that the pH at which pectin has optimal stability matches the natural pH of fruit preserves.

Confectionery

Pectin fruit jellies are delicate confectionery products with a low water content of around 20%. Recommended pectins are shown in Table 13.8. Normally, the jellies are prepared from combinations of sugar and glucose syrup, flavoured with synthetic flavours and acidified with citric acid. However, the jellies may also contain fruit pulp or juice. Pectin is used in the concentration range 1–3%.

Pectin provides a superior texture and flavour release compared to other gelling agents but may be troublesome to handle during processing due to gel formation at high temperatures (∼70◦C) and because of its sensitivity to pH and soluble solids content. In order to gelHMpectin, acid must be added to reduce the pH from 4.1 to 3.5. The acid must be added as a solution (maximum 50% w/v), otherwise pre-gelation will occur around each acid crystal and make the jelly grainy.

When producing non-fruit flavoured pectin jellies, for flavours such as toffee and peppermint, the pH working range must be 4.0–4.5 as the neutral flavours are more compatible with this range. For this type of application, certain amidated LM pectin types can be used. For aerated confectionery products such as fruitflavoured marshmallows, which have a soluble solids content of approximately 80%, HM pectin confers texture and stabilises the foam in the product. Amidated LM pectin may also be used.

Starch

Chefs or food scientists often make a classic choice when they are developing their latest innovative creation: they know exactly how they are going to delight the consumer and where to source all the ingredients in order to do this. Alternatively, they go to their store shelves and see what they have in stock and work out how to create their latest innovation from the materials at hand. The former is exciting and potentially unlimited where their creativity can produce totally new solutions by combining the latest and best materials. 

The latter has the same potential but it is more about being innovative and creative with existing ingredients and obtaining value by pushing the limits of the functionality of these already-available raw materials. Both of these two routes are the purpose and expected delivery of this chapter on starch, a truly flexible and functional thickening and gelling agent.

Gelling starches

At the other extreme, starches can act as gelling agents. Here, the starch granules have broken down and the amylose and amylopectin chains are free in solution and can associate to form a gel. The type of interactions, chain length and interaction with other ingredients has an effect on the gel properties. There are no discrete starch granules and the free starch polymers are dissolved within the continuous phase.

In hot solutions these polymers have a certain degree of freedom to move around and that allows them to start to interact with each other and to create associative networks. It is, in fact, during the cooling phase that these interactions increase and a stronger gelling network is formed. Care should be taken when these are created. Generally with fairly rapid cooling a gelled network is formed but if the cooling is done more slowly, or if there is a higher concentration of starch or low levels of other ingredients that can interact, a process called retrogradation can occur where the starch polymers align to give small, discrete, insoluble particles. This precipitate is generally undesirable for gelling and thickening but important for other food properties such as the creation of insoluble fibrous starch material.

Starches with a higher amylose content are more likely to gel or retrograde but these processes can be avoided by using the 100% amylopectin starches. This shows the two extremes that can be achieved and takes us to the next important step: how to achieve the required thickening or gelling characteristics.

Confectionery

The confectionery market is at the furthest end of the spectrum in the journey from thickening through to gelling and it is in the area of sugar confectionery that there are the most applications for the gelling properties of starches.Within this category there are a number of subdivisions that need to be considered.

Moulded confections

In moulded confections, the end-product tends to be a relatively clear, highly elastic confection that has been formed by pouring a molten solution into a mould which is then cooled and often dried to reduce the moisture content to the desired level. The gelling properties for this product can be achieved by the use of starches. Success has been achieved with a whole range of starches but it is those with a higher amylose content that have proven most effective. In many cases, the goal has been to replace other hydrocolloids, such as gelatin, to allow vegetarian products to be produced in a cost-effective way.

Initially all the ingredients are blended, heated and hydrated. Here, it is important that the starch dissolves and mixes easily and retains fluidity at the high temperatures used in moulding. This fluid mix is poured into moulds and then it must gel rapidly and give an elastic texture. There is always a balance between fluidity at high temperatures and forming good gels at cooler temperatures. In many cases, a further drying step is required to achieve the moisture content before the product is ready to pack. One of the major issues for these products is to retain stable characteristics throughout the shelf life. By careful selection of starches these gelled products have been developed.

Chewy confections

The same approach is taken for chewable products that need to be gelled and also stretch. Again the higher amylose starches are suitable. After moulding the product is stretched in preparation for the final forming and packing so the product must remain elastic for part of this period. In the final form they should not be too sticky to touch but should easily soften when chewed in the mouth.

Xanthan Gum

Xanthan gum is a high-molecular-weight extracellular polysaccharide secreted by the microorganism Xanthomonas campestris and is produced commercially in a fermentation process. It is soluble in cold water and has a very wide range of applications. It was first discovered in the 1960s and commercialised in the 1970s. With an annual sales volume of approximately 46 000 metric tonnes, xanthan gum applications are split approximately 50/50 between food and non-food. Non-food includes oil field, personal care, pharmaceutical and home care. Typical food applications include sauces and dressings, baked goods, beverages, desserts and ice creams. The total textural ingredients market for food is currently estimated to be worth 2.8 billion US dollars and xanthan gum represents approximately 11% of this.