Sensory texture based on rheological properties: Applications in model foods and cheese

A series of gels were used as model foods to understand relationships among rheological properties and sensory texture. Fracture stress was the best predictor of sensory fracture force and particle breakdown, whereas a measure of the nonlinear region was a better predictor of sensory deformation. INTRODUCTION Food texture is a complex property involving a constant evaluation of the rheological and tactile properties during oral processing. To understand the role of rheological properties in food texture, we developed a series of four model food gels (polyacrylamide, alginate, agarose and agar) that allowed for precise manipulation and measurement of mechanical properties. All four gels can be made from aqueous solutions with polymer concentrations similar to what is found in foods. Polyacrylamide gels were used as a starting point because they show linear elasticity that is independent of strain level and rate, and can be modeled based on rubber elasticity. With that in mind, gel firmness/hardness could be increased by addition of more polymer or increased crosslinking. The three other gels were made with polysaccharides and all showed non-linear viscoelastic behavior. Alginate gels were investigated because they are food-grade and, because calcium interacting with uronic acids of the polymer chains causes crosslinks, the addition of different amounts of calcium provides a way to compare with the covalently cross-linked polyacrylamide gel. Agarose and agar gels are formed by noncovalent association among strands (physical gels) and thereby contrast with the covalently linked polyacrylamide gels (chemical gels). Agar gels are also food grade and were evaluated by a trained sensory panel in addition to mechanical analysis. RHEOLOGICAL CHARACTERIZATION To investigate important mechanical properties of food gels and the impact they likely contribute to overall product texture, a few critical conditions must be considered, namely extent and speed of compression and shear. Ignoring the breakdown contributions from thermal and enzymatic factors, oral processing is mainly dominated by a chewing action. This process of destruction can occur at varying rates, but ultimately a large gel is reduced to many smaller pieces that are conducive with swallowing. Rheologically, mastication is a complex set of actions involving shear and compressive stresses. Each of these stresses may occur at varying speeds. As the stresses are applied to the sample, it undergoes a strain. Understanding the stress and strain relationship permits computation of important mechanical properties, like viscoelastic moduli and fracture properties. To begin to fundamentally describe the mastication process, instrumentation is used to subject the gel to either a shear or compressive type of load. With respect to the condition of shear, rheometry permits the measurement of viscoelastic moduli (G' Sensory texture based on rheological properties: Applications in model foods and cheese E. Allen Foegeding and Christopher R. Daubert Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University,