What is a Hydrocolloid?
Hydrocolloids, or gums, are substances consisting of hydrophilic, long-chain and high molecular weight molecules often with colloidal properties. In water-based systems, they can take on different states, like gel or sol, and their primary purpose is of thickening and/or gelation. Hydrocolloids often exhibit related secondary functions, such as emulsifying, whipping, suspending, and encapsulating. They are generally polysaccharides, but gelatin (a protein) is included because its functionality and behavior in food systems is very similar to that of a polysaccharide-based gum.
Where Do They Come From ?
Hydrocolloids have been used since at least as far back in time as ancient Egypt and have been part of the human diet for several thousand years. They are produced from seeds, roots, red and brown seaweed extracts, tree sap, fruit peels, and animal extracts. There are microbiological hydrocolloids which are produced by the fermentation of bacterias; like Xantham and gellan gums, and there are also cellulose derivatives, like methylcellulose.
Types of Structure
Hydrocolloids can have linear or branched molecules. The linear type is the most abundant in nature and are composed of one long sugar chain with side chains. These side chains can be composed of single or multiple sugar units, or they can be as simple, as carboxyl or sulfate groups. The branched type, is composed of many branches joined together in a bushy shape and typically display lower viscosities(thinner) than the linear type of the same size. The branched hydrocolloids are compact, acting like tennis balls, while the linear type act like a tangle of spaghetti moving through the solution, taking up more space. Whether its a linear or a branched type, the side units coming off the backbone greatly influence the properties of the hydrocolloid and determine whether the gum is a thickening or gelling agent.
Functions and Properties
Hydrocolloids are added to various food systems for a variety of reasons.
- Influence the texture
- Increase the stability
- Reduce fat or calories in a food product.
"Texture" usually refers to that of a finished food product. The hydrocolloid could provide extra body and "mouth feel" to a beverage or give a gel structure to a milk-based product, like a pudding.
To "Stabilize" a food product, refers to the prevention of physical changes in the product resulting from the separation of its components, for example; a vinaigrette or salad dressing. Also, the handling and processing conditionsof a product, such as high temperatures, can prevent a pie filling from melting and running when subjected to the heat of an oven.
Fat replacement or reduction is when fat or oil is removed from a formula and replaced with water. The texture of the water must be altered to better imitate the texture contributed by the missing fat or oil. This can be done with food gums.
The addition of the hydrocolloid to the main ingredient and the act of diffusing in equally keeps the hydrocolloid particles as far way from each other. Keeping them from prematurely absorbing water, swelling, then "clumping" assures proper hydration and maximum thickening(gelation). Shearing is a necessary step in preventing this and will aid in dissolution.
Once dispersed properly, it must absorb water and swell to fully activate its gelation potential. Some hydration will occur during the shear, but many of the products must be heated and brought to specific temperatures to reach optimum hydration and gelation efficiency.
When a recipe fails, it's usually due to improper hydration. The trick to hydrating is to get good dispersion. A good technique to hydrate food gums is to add the liquid to a blender, and put to a speed to where a vortex is formed. Slowly sprinkle the hydrocolloid into the vortex until it is thoroughly dispersed. The concept of dispersion is getting the hydrocolloid particles as far away from each other before they start to absorb water and swell.
<u>Further Reading/Research:</u> Hydrocolloids: Practical Guides for the Food Industry (Eagan Press Handbook Series), Andrew C. Hoefler Modern Gastronomy A to Z, Alicia Foundation ElBullitaller