ABSTRACT
CONTENTS Introduction ....................................................................................... 50
What Are Foods? ..................................................................... 50 Sensory and Texture Tests ...................................................... 52 Why Use Rheological Testing for Foods? .............................. 52 Measurement of Rheological Functions: Bulk and
Interfacial ............................................................................ 54 Mechanical Characterization of Solids ............................................ 55
Determination of Stress-Strain Plots ...................................... 58 Compression Tests and Friction Effects ................................. 59 Analytical Solution for Friction .............................................. 62 Numerical Solution for Friction ............................................. 62 Bulk Rheology and Texture: Case Examples ......................... 63
Example 3.1: Why Is Low-Fat Cheddar Cheese Rubbery? ........................................................................ 64
Example 3.2: What Is a Stale Bagel? ................................. 65 Friction and Texture ................................................................ 67
Shearing of Spreadable Solids ......................................................... 68 Failures under Shear and Extension ...................................... 68 Friction of Spreadable Solids ................................................... 72 Bulk Rheology and Texture of Spreadable Solids ................. 77 Friction and Texture of Spreadable Solids ............................ 77
Adsorption on Surfaces by Emulsions ............................. 78 Motions of Particles in Dispersions .................................. 78 Release of Lubricants ......................................................... 78 Surface Morphology of Grain-Based Materials ............... 80
Pourable Fluids ................................................................................. 80 Case Example: Pourability of Gum Solutions ....................... 82
Summary ............................................................................................ 82 Acknowledgment .............................................................................. 84 References .......................................................................................... 84
Analysis of interactions among ingredients is a popular subject among food developers. Faced with product prototypes that are almost “right,” but fail in unforeseen characteristics of texture or flavor, it is easy to understand why a product developer would wish to know, why? Conversely, it would also be useful to understand the reasons for unforeseen successes, which also happen. Most foods are conventional, established substances. Consumers do not need to understand the chemistry in food systems in order to prepare and enjoy foods. The need to understand the science in food products rests with the producers of food products as new foods are developed, either to reduce the cost of production or to meet market demands. Unique challenges arise in developing new foods, given the stringent requirements to meet the sensory satisfaction and safety criteria. To face these challenges and to formulate the right balance of texture and flavor in food preparations, it is necessary to understand foods as materials that also need to be engineered and understood as any other engineered materials.
