Hydrocolloids
Pages 1-6
DOI: https://doi.org/10.1094/1891127381.001
ISBN: 1-891127-38-1
Abstract
Topics Covered
- Water "Organizing"
- Effects of Hydrocolloid Structure
- Gum Combinations
- Formulating with Gums
Introduction to Chapter
Hydrocolloids, or gums, are substances consisting of hydrophilic, long-chain, high molecular weight molecules, usually with colloidal properties, that in water-based systems produce gels, i.e, highly viscous suspensions or solutions with low dry-substance content. In addition to their primary purpose 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 is very similar to that of the polysaccharide-based gums.
Hydrocolloids have been used since at least as far back in time as ancient Egypt. The exudate of a plant in the genus Acanthus found in that region was used as an adhesive in the wrapping of mummies and as a medium for water-based paints. Many hydrocolloids have been part of the human diet for several thousand years. For example, locust bean gum (LBG) was known as “Saint John's bread” and is still called by that name in several European countries.
Over time, many useful, natural plant exudates were discovered and designated “gums,” including rubber, rosin, chicle (“chewing” gum), and other resinous materials. Eventually, the nomenclature for these natural materials became very confused, and it has been only during the last 50 years that an effort has been made to clarify the terminology. In this book, “gums” refers only to the water-soluble type. The water-insoluble (but oil-or organic solvent-soluble) materials are referred to as “resins.”
“Hydrocolloid,” a contraction of hydrophilic colloid, is the more scientific name for gums. Hydrocolloids are not really colloids, because they are truly water soluble. They are polymers of colloidal size (10-1,000Å) and exhibit certain of the colloidal properties, such as the ability to remain suspended in water under the influence of gravity.
Hydrocolloids can have linear or branched molecules (Fig. 1-1). The linear type (such as cellulose, amylose, alginates, and pectin) are the most abundant in nature and have sugar units that repeat over the entire length of the polymer. They usually have side units, which can be composed of single or multiple sugar units, or they can be as simple as carboxyl groups, sulfate groups, or a methyl ether group. Generally, these side units greatly influence the properties of the hydrocolloid. Most hydrocolloids occur naturally, but there are also several natural hydrocolloids that have been chemically modified, such as carboxymethyl cellulose (CMC), also known as cellulose gum, and propylene glycol alginate.
Throughout this book, different types of classification systems based on chemical, functional, and physical properties are mentioned. In Table 1-1, hydrocolloids are classified by source and by structure and charge characteristics.
