As liquid egg white is whisked, air bubbles are incorporated. An emulsion may be oil-in-water (o/w) in which case small oil droplets are dispersed through water, e.g., milk, or water-in-oil (w/o) in which case small water droplets are dispersed through oil, e.g., butter.įoams are composed of small bubbles of gas (usually air) dispersed in a liquid, e.g., egg white foam. A stable emulsion is formed when two immiscible liquids are held stable by a third substance, called an emulsifying agent. If left to stand, the oil will form a separate layer on top of the water, e.g., traditional French dressing. When water and oil are shaken together, they form an emulsion. One liquid (the dispersed phase) is dispersed in the other (the continuous phase), i.e., material that keep fat globules in water droplet or water droplet in fat are emulsifiers. This loss of liquid is known as syneresis.Īn emulsion is a mixture of two or more immiscible (they will not mix together) liquids. If a gel is allowed to stand for a time, it starts to ‘weep’. Agar is a polysaccharide extracted from seaweed which is capable of forming gels. However, for it to gel there must be at least 50% sugar and conditions should be acidic. Pectin, a form of carbohydrate found in fruits, is used in the production of jam to help it set. Other types of gel are formed with pectin and agar. If corn flour is mixed with water and heated, the starch granules absorb water until they rupture, the starch then disperses in the water and the mixture becomes more viscous and forms a gel on cooling. As the solution cools, protein molecules unwind forming a network that traps water and forms a gel. When a jelly is made, gelatin is dispersed into a liquid and heated to form a sol. Gravy, stirred custard and other thick sauces are some of the examples of sols. Types of Colloidal System in Food :Ī sol can be defined as a colloidal dispersion in which a solid is the dispersed phase and liquid is the continuous phase. An emulsifying agent may be used to help the oil and water phases to mix permanently. Food colloid contains hydrocolloid that gives stability and rheological properties of food components. They may also become unstable when frozen or heated, especially if they contain an emulsion of fat and water.įunctions of Colloidal Systems in Food Products :Ĭolloidal systems give structure texture and mouth-feel to many different food products, for example – Jam, ice cream, mayonnaise. Most colloids are stable, but the two phases may separate over a period of time because of an increase in temperature or by physical force. The detailed classification of colloidal systems in food is given in Table 2.1. Emulsion and foam again can be categorised into solid emulsion/foam and liquid emulsion/foam.Ĭolloids are formed when one substance is dispersed through another, e.g., sols (a solid is dispersed in a liquid), gels (a liquid held in a solid network, e.g., jam or jelly), emulsions (oily and watery liquids mixed together, e.g., milk and butter), foams (bubbles of gas trapped in a liquid, e.g., whisked egg white or whipped cream), solid foam (bubbles of gas trapped in a solid, e.g., meringue, cake, bread). Colloidal systems in foods can be classified into different groups based on the states of matter constituting the two phases. For this reason, most manufactured foods can be considered as food colloids and many contain hydrocolloids that are added to control stability and rheological properties.įood hydrocolloids are high molecular weight hydrophilic biopolymers used in food products to control their texture, flavor and shelf life. Air bubbles (disperse phase) are trapped in the egg white (continuous phase) resulting in a foam.Ĭolloidal dispersion is a two phase system in which the particles in the dispersed phase are between 1 and 100 nm in diameter. The substance which is dispersed is known as the disperse phase and is suspended in the continuous phase. A colloidal system may be solid, liquid, or gaseous. There are many types of colloidal systems depending on the state of the two substances mixed together.Ī colloidal system consists of two separate phases: a dispersed phase (or internal phase) and a continuous phase (or dispersion medium). Colloids are formed when one substance is dispersed through another, but does not combine to form a solution. Classification and Function of Colloidal Systems in Food:Ī colloid is a type of chemical mixture where one substance is dispersed evenly throughout another. Classification and Functions of Colloidal Systems in Food 2. In this article we will discuss about:- 1.
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