What are the Food Use of Hydrocolloids?
Gums are employed for an extensive array of applications. A few examples are:
as adhesives in bakery glazes;
binding agents in sausage;
bulking agents in dietetic foods;
crystallization inhibitors in ice creams and sugar syrups;
clarifying agents in beer and wine;
clouding agents in fruit juices;
coating agents in confectionery;
emulsifiers in salad dressings;
encapsulating agents in powdered fixed flavors;
film formers in sausage casings and other protective coatings;
flocculating agents in wine;
foam stabilizers in whipped toppings and beer;
gelling agents in puddings, desserts, aspics, and mousses;
mold-release agents in gum drops and jelly candies;
protective colloids in flavor emulsions;
stabilizers in beer and mayonnaise;
suspending agents in chocolate milk;
swelling agents in processed meats;
syneresis inhibitors in cheeses and frozen foods;
thickening agents in jams, pie fillings, sauces, and gravies;
and, whipping agents in toppings and icings.
It is important to note that the broad applications of gums are confined to their two main properties—to serve as thickening and gelling agents. The thickening ability, that is, viscosity production, is the key feature in the use of hydrocolloids as bodying, stabilizing, and emulsifying agents in foods. A few gums that have gelling abilities are helpful in foods where shape retention is needed before any application of pressure. The most widespread, gelled food item for consumption is gelatin dessert gel; additional recognized food gels are starch-based milk puddings, gelatin aspics, and pectin-gelled cranberry sauce.
Textures, Thickening, and Gelling
Hydrocolloids are classified as either thickening or gelling agents. Some common gel texture descriptors are:
Hard/Soft: How much force does it take to rupture the gel?
Brittle/Elastic or Springy: Does the gel break suddenly or deform? After the first bite, does the gel return to its original height?
Cohesive: Is the gel difficult to break up in the mouth? Does it stay together?
Gummy: Is the gel hard and cohesive?
Chewy: Is the gel both gummy and springy?
Adhesive: Does the gel adhere to the teeth or palate?
What are the Characteristics of Gels?
Important characteristics of gels are:
Thermo-reversible/Irreversible: Thermo-reversible gels melt when heated to a high enough temperature (with the exception of methylcellulose, which forms thermo-reversible gels that set when heated and melt when cooled). Thermo-irreversible gels will not melt when heated. Some gels are thermally reversible, but the melting temperature is so high that they don’t melt in practice (high-acyl gellan).
Tendency for Syneresis: Syneresis occurs when liquid weeps out of a gel over time, as happens in custards. Agar is prone to syneresis; water can be expelled merely by pressing on it. Some gels only experience syneresis after long periods of time. Many gels that are ruined by freezing (see freeze-thaw stability, below) tend to weep when thawed. Within a given hydrocolloid system, harder gels tend to weep more than softer ones.
Freeze-thaw stability: Gels that may be frozen and thawed repeatedly are called freeze-thaw stable. Many gels begin to degrade after freezing; only one freeze-thaw cycle is advised. When an unstable gel is frozen and later thawed, its texture and structural may be compromised by the physical changes. To offset this effect and promote freeze-thaw stability, a second thickening hydrocolloid may be added to the gel system.
Clarity: The addition of some hydrocolloids yield gels that are more transparent than others.
Flavor release: Flavor release describes how well a gel expresses the flavorings with which it has been made. Flavor release is determined by many gel texture properties. Gelatin, for example, is considered to have excellent flavor release mainly because it melts in the mouth, whereas alginate is said to have poor flavor release because it tends to lock up flavors.
Shear reversibility: Shear is a force in which parallel objects move in opposite directions in a “sliding” motion, such as in the action of scissors cutting or a razor shaving. Stirring produces a shear, as does blending. Very fast blenders are called high-shear blenders. A shear-reversible gel will reform after it has been broken by a shear force. Most gels are not shear reversible.
What is a Hydrocolloids?
A hydrocolloid is defined as a colloid system wherein the colloid particles are hydrophilic polymers dispersed in water. A hydrocolloid has colloid particles spread throughout water, and depending on the quantity of water available that can take place in different states, e.g., gel or sol (liquid). Hydrocolloids can be either irreversible (single-state) or reversible. For example, agar, a reversible hydrocolloid of seaweed extract, can exist in a gel and solid state, and alternate between states with the addition or elimination of heat.
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Other hydrocolloids are xanthan gum, gum arabic, guar gum, locust bean gum, cellulose derivatives as carboxymethyl cellulose, alginate and starch.
Other more specialist applications include adhesion, suspension, flocculation, foam stabilization and film formation. Foodstuffs are very complex materials and this together with the multifactorial functionality of the hydrocolloids has resulted in several different hydrocolloids being required; the most important of which are listed below.
Agar
Alginate
Arabinoxylan
Carrageenan
Carboxymethylcellulose
Cellulose
Curdlan
Gelatin
Gellan
β-Glucan
Guar gum
Gum arabic
Locust bean gum
Pectin
Starch
Xanthan gum
What are the Sources of Hydrocolloids?
Many hydrocolloids are derived from natural sources, such as seaweed, seeds, roots, tree sap, fruit peels, etc. Many cultures have employed some of these naturally-derived hydrocolloids for thousands of years. Agar, for example, comes from seaweed, and is a traditional ingredient in Asia. Gelatin is produced by hydrolysis of proteins of bovine and fish origins, and pectin is extracted from citrus peel and apple pomace. Carrageenan, known as Irish moss, has been used in traditional Irish cooking for centuries. Gum arabic (tree sap), locust bean gum (seeds of the carob tree), and gelatin have also been used for thousands of years. Pectin, naturally occurring in fruits, has always been used to make jellies and jams.
Gelatin desserts like jelly or Jell-O are made from gelatin powder, another effective hydrocolloid. Hydrocolloids are employed in food mainly to influence texture or viscosity (e.g., a sauce). Hydrocolloid-based medical dressings are used for skin and wound treatment.
Some modern but still all-natural hydrocolloids, such as xanthan and gellan, are produced by bacteria. Other hydrocolloids are produced by modifying natural ingredients to create new compounds not found in nature. The most important of these are the cellulose-derived hydrocolloids: methylcellulose, hydroxypropylmethylcellulose, etc. These modified products, while not “all natural,” are still safe.
Since hydrocolloids are derived from natural sources, they are not uniform. Two samples of the same product might have different average molecular weights, and will therefore perform differently. Even the molecules within a given batch of hydrocolloids will vary in size. As a result, commercial manufacturers usually specify a range of weights. By carefully selecting hydrocolloids of different molecular weight, gum manufacturers can also develop products with specialized properties. Some hydrocolloids, such as carrageenan, are made of a mixture of similar but slightly different molecules. The ratios of the different types of molecule vary from batch to batch. Manufacturers blend these hydrocolloids to provide a consistent product, but often the blends will produce consistent results only for a specific application—the mixtures are standardized to do one particular thing very consistently. Many carrageenans, for instance, are standardized to gel milk at a certain strength. The variability in hydrocolloids is one reason that it is not only important to know the name of a hydrocolloid—for example, Alginate—but also its manufacturer and exact specifications, such as alginate, ISP Manugel GHB. When writing recipes, try to list the exact hydrocolloid used.
CONSIDERATIONS WHEN USING HYDROCOLLOIDS
Forming Gels
It is extremely important to understand when and why a hydrocolloid gels since this behavior typically determines which hydrocolloid is appropriate to use.
Heating and Cooling
Many hydrocolloids gel when cooled. Sometimes these gels can be melted again, such as gelatin, and sometimes they cannot, such as the pectin in a jam. Methylcellulose forms a gel when heated that melts on cooling. Some thermally reversible gels show temperature hysteresis, that is, the setting temperature of the gel is lower than the temperature needed to melt the gel. This property can be very important to a chef. For example, agar sets around 35°C but melts at around 90°C. The low set temperature makes agar easy to work with, and the high melt temperature allows agar preparations to be served hot. Thermally formed gels can also be slow set or snap set. Snap setting hydrocolloids, like gellan, gel instantly below their gelation temperature.
Calcium and Potassium
Some hydrocolloids form gels in the presence of positively charged ions, mainly calcium and potassium. In these instances, the positive ion fits into negatively charged areas in the hydrocolloid, allowing two hydrocolloid molecules to stick together in a structure similar to an egg-crate. In some cases, like alginates, these gels are not reversible; in others, like kappa carrageenan, thermo-reversible gels are formed. It is extremely important to control the amount of calcium in solution when dealing with calcium-dependent hydrocolloids. If too much calcium is present, the hydrocolloid will gel immediately, a process that is called pre-gelation.
Sometimes, the hydrocolloid simply will not hydrate in a recipe. In these cases, chemicals called sequestrants are added to these solutions to prevent pre-gelation and allow proper hydration. Sequestrants have the ability to bind with ions like calcium more effectively than hydrocolloids can. In many cases, the amount of calcium in tap water alone can cause pre-gelation of a hydrocolloid if not treated with sequestrants. Acidic solutions (low pH) also need more sequestrants than neutral solutions because many calcium impurities are more soluble and affect hydrocolloids more at low pH.
Synergy, 1+1=3
Hydrocolloids do not act like most ingredients. In general, do not expect to be able to mix two hydrocolloids without changing their properties. When two liquids of the same viscosity made with different hydrocolloids are mixed, the viscosity often does not stay the same, but increases. The hydrocolloids have a synergistic increase in viscosity. This effect is used by manufacturers to save money, because they can use a smaller quantity of hydrocolloid in a synergistic system. Another example of synergy is when xanthan gum and locust bean gum, normally non-gelling thickeners, are mixed. Surprisingly, they form a gel. This is called synergistic gelation. Sometimes, hydrocolloids will show synergism with a particular non-hydrocolloid ingredient. For instance, carrageenan plus milk gels at half the concentration of carrageenan plus water.
As a rule of thumb, gelling hydrocolloids and thickening hydrocolloids can often be mixed to get the benefits of both (locust bean gum can be added to kappa carrageenan to give it a better texture, for example) without synergistic effects that will damage a recipe. Charged and uncharged hydrocolloids can also often be mixed without incident, like methylcellulose and alginate.
HYDRATION
For a hydrocolloid to work properly, it must be hydrated and dissolved in solution. When a recipe fails, the problem is frequently improper hydration. Hydration procedures vary from hydrocolloid to hydrocolloid, but there are some important general rules. Hydrocolloids added to water tend to swell as they unfold into solution. The swelling causes particles to clump together forming lumps that are very difficult to dissolve. This phenomenon is familiar to chefs who use starch as a thickener (lumps in the gravy). Many hydrocolloids are even more lump-forming than starch. The trick to hydrating hydrocolloids is to get good dispersion –keep the hydrocolloid particles separated before they start to swell, hydrate, and cause lumps. Industrially, hydrocolloids are often mixed with a non-solvent, like alcohol or corn syrup, or an easily dissolved powder like sugar. This pre-mix helps the hydrocolloid particles get away from each other while they hydrate.
In general, hydrocolloids like to be hydrated in pure water. Large concentrations of sugar, salt, starch, alcohol, or anything that competes with the hydrocolloid for water can hinder hydration. Sometimes a hydrocolloid will not hydrate in a recipe. Alginates, for instance, will not hydrate in acidic liquids. In these cases, the hydrocolloid can be pre-hydrated in pure water, and the resulting solution can usually be added to the recipe without a problem. It is a good practice to add hydrocolloid as early in a recipe as possible.
Correct Recipe Formulations and Measuring
Hydrocolloids are usually specified in percent by weight. One kilogram of 2% alginate solution contains 980 g of water and 20 g of alginate. However, to make a 2% alginate solution, most chefs will add 20 g of alginate to 1000 g of water. Although this mix is technically incorrect (this is a 1.96% solution), the effect of the small additional hydrocolloid is negligible, and this method is easier to calculate. To get consistent results, it is important to use the same method every time. Most hydrocolloid work requires accurate measurement. A scale accurate to 0.1 g is essential; in some cases, it is helpful to have a scale accurate to .01 g.
Quick Hydration Tips
A chef’s best friend in hydration is the blender, and it’s worth it to get a good one. Blenders use high shear to beat particles away from each other and achieve good dispersion throughout a mixture.
Here’s a good technique: Add liquid to the blender, then select a speed that forms a vortex in the liquid without a lot of splashing. Slowly sprinkle the hydrocolloid in the center of the vortex until it is thoroughly dispersed. Continue blending on high until the mixture is hydrated.
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REFERENCES:
Davidson, R. L. 1980. Handbook of water-soluble gums and resins. New York: McGraw-Hill.
Dickinson, E. and P. Walstra. 1993. Food colloids and polymers, stability and mechanical properties. Cambridge: Royal Society of Chemistry.
Glicksman, M. 1969. Gum technology in the food industry. New York and London: Academic Press.
Glicksman, M. 1983. Food hydrocolloids, vols. 1, 2, 3. Boca Raton: CRC Press Inc. Harris, P. 1990. Food gels. New York: Elsevier Science Publishing Co.
Hoefler, A. C. 2004. Hydrocolloids: Practical guides for the food industry. St. Paul, MN: American Association of Cereal Chemists.
Hollingworth, C. S. 2010. Food hydrocolloids: Characteristics, properties and structures. New York: Nova Science Publishers, Inc.
Imeson, A. 1992. Thickeners and gelling agents for food. London: Blackie Academic and Professional.
Laaman, T. R. 2010. Hydrocolloids in food processing. Oxford: Willey-Blackwell (IFT Press).
Mantel, C. L. 1947. The water soluble gums. New York: Reinhold Publishing Corp.
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Helpful article. Thank you for sharing.
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