Mechanism action of thickeners and their application in food processing(1)

Thickeners are used to thicken, gel, emulsify and stabilise food products, improving their quality and appearance and providing them with a rich taste. Thickeners are available from a wide range of sources and are added at low levels, and have become important food additives in foods such as meat products, dairy products and pasta products.

01. Mechanism of action of thickeners

Thickeners can change the rheological ability of the food system, i.e. the flow characteristic viscosity and the mechanical solid characteristic texture. Studies have confirmed that changes in texture or viscosity of food systems contribute to changes in their organoleptic properties. In general, thickeners tend to form webs or colloids with more hydrophilic groups in solution, which are heterogeneous groups of long-chain polymers (polysaccharides and proteins) and therefore improve the viscosity and texture of food products. The main properties of thickeners are thickening, gelling, emulsification, stabilisation and control of crystal growth of ice and sugar.

1.1 The thickening process

The thickening process involves the non-specific entanglement of conformationally disordered chains in structured gelling. The viscosity of polysaccharide dispersions arises mainly from the physical entanglement of conformationally disordered, unconformably curled chains. In low concentration dispersions, the individual molecules of the thickening agent are free to move and do not exhibit a thickening effect. In highly concentrated systems these molecules begin to come into contact with each other and therefore the movement of the molecules is restricted.

The degree of thickening varies depending on the type of thickener, e.g. at high concentrations giving low viscosity and at concentrations below 1% giving high viscosity. Common thickeners are starch, xanthan gum, guar gum, acacia bean gum, carrageenan, gum arabic and cellulose derivatives.

1.2 The gelation process

1.2.1 Gel formation

Gels are forms of matter that are intermediate between solids and liquids and show mechanical rigidity, giving food products viscoelasticity and exhibiting the properties of both liquids and solids. The textural properties of the gel (elastic or brittle, chewy or creamy) vary depending on the type of thickener, and the sensory properties of the food (opacity, mouthfeel or flavour) will also vary accordingly.

Knowledge of the gelling conditions of a particular thickener dispersion, the properties of the resulting gel and the texture it imparts, is a very important aspect of designing a particular food formulation. Gel formation involves the joining of irregularly dispersed polymer chain segments in the dispersion, resulting in a three-dimensional network containing the solvent in the voids. The relevant region known as the joining zone can be formed by two or more polymer chains.