Rheology-texture relationship

The next section, structure-rheology-texture relationships, deals with the quantification and modeling of the structure and the mechanical properties of lipid networks, and then examines cocoa butter and milkfat within this general framework. The chapter on milkfat focuses on the effects of the minor components contained in native milkfat on structure formation and final mechanical properties. This section also contains a chapter on the use of fluorescence depolarization spectroscopy as a tool to determine microviscosity and structural order in lipid systems and an overview of the texture of fat systems. 

The crystallization behavior of milk fat is complex, owing, in large part, to its complicated composition. By manipulating composition and crystallization conditions, milk fat and dairy products with unique structures and mechanical properties can be designed. Understanding the relationships between composition, crystallization, structure, rheology and texture is a powerful tool in this regard. 

Methods of objective measurement of cereal foam structures are reviewed, including image analysis, confocal microscopy and x-ray tomography. The analysis of foam structures and their relationship with mechanical and rheological properties is described, and also the relationships between these structures and sensory descriptors such as crispness, crunchiness and texture. The size, shape and anisotropy of bubbles and their cell walls in foams are seen as critical in determining their fracture properties and sensory perception of crispness. Techniques for measuring crispness using acoustic emission and force-deformation profiles are discussed. 

Rheology is the study of flow of matter and deformation and these techniques are based on their stress and strain relationship and show behavior intermediate between that of solids and liquids. The rheological measurements of foodstuffs can be based on either empirical or fundamental methods. In the empirical test, the properties of a material are related to a simple system such as Newtonian fluids or Hookian solids. The Warner-Bratzler technique is an empirical test for evaluating the texture of food materials. Empirical tests are easy to perform as any convenient geometry of the sample can be used. The relationship measures the way in which rheological properties (viscosity, elastic modulus) vary under a... 

It can be concluded from the above discussion that a combination of microscopy, sensory analysis and rheological properties (obtained under high and low deformation) using statistical evaluation methods can provide a correlation between sensory perception (as evaluated by expert panels) and the various characteristics of the gel. The relationship between microstructure and texture is important in optimizing the properties of food products as well as in the development of new products with the desirable properties. Modern techniques of microscopy (such as freeze fracture) can be applied to study the microstructure of gels. The viscoelastic properties of gels, which can be studied using oscillatory techniques (under various conditions of applied strain and frequency) can be correlated to the microstructure. 

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