Understanding the characteristics of fluid gels

Hydrocolloids such as polysaccharide are widely used to improve quality and texture of food products. Because of their broad range of functional properties, they are often used as thickening and gelling agents or for stabilizing dispersions and solutions. Due to specific molecular structure and physico-chemical properties, they can form a three-dimensional network of cross-links. Through aggregation of polymer chains via intermolecular interaction (e.g. hydrogen bonds, electrostatic interaction), they form hydrogels while cooling under quiescent conditions, i.e. without disturbing the gelation process of network formation. Agarose, for instance, a strongly gelling polysaccharide forms firm and brittle gels. However, these viscoelastic behaviors can be altered by manipulating the processing conditions namely by shear. For example, gelation under shear leads to microgel particles with a shear rate dependent size and large surface area, which in turn leads to completely different rheological properties and texture. The resulting micro gel particles slide past each other, as the water on their surfaces acts as lubricant between the gel particles. Such fluid gels are shown to play an important role in texture modification of foods and beverages for dysphagia patients. Moreover, they provide a well-defined, creaminess and a pleasurable smooth mouthfeel and thus can be used as fat replacer. Understanding the underlying gelling mechanism as well as the link between macro-and microscopic properties of the fluid gels and the respective structure at the molecular level is a prerequisite for tailoring texture in food and structure-based design of foods for dysphagia patients but also for low-fat food products.