ABSTRACT
I. Introduction............................................................................................................................ 64 II. Emulsions............................................................................................................................... 64 III. Lipid-Based Emulsifiers......................................................................................................... 66
A. Molecular Characteristics............................................................................................... 66 B. Functional Properties ..................................................................................................... 66
1. Critical Micelle Concentration................................................................................ 66 2. Cloud Point ............................................................................................................. 67 3. Solubilization .......................................................................................................... 67 4. Surface Activity and Droplet Stabilization............................................................. 68
C. Ingredient Selection ....................................................................................................... 68 1. Bancroft’s Rule ....................................................................................................... 68 2. Hydrophile-Lipophile Balance ............................................................................... 69 3. Molecular Geometry and Phase Inversion Temperature ........................................ 70 4. Other Factors........................................................................................................... 71
IV. Biopolymers........................................................................................................................... 72 A. Molecular Characteristics............................................................................................... 72 B. Functional Properties ..................................................................................................... 73
1. Emulsification ......................................................................................................... 73 2. Thickening and Stabilization .................................................................................. 74 3. Gelation................................................................................................................... 75
C. Ingredient Selection ....................................................................................................... 77 V. Emulsion Formation............................................................................................................... 77
A. Physical Principles of Emulsion Formation .................................................................. 79 B. Role of Emulsifiers ........................................................................................................ 80 C. Homogenization Devices ............................................................................................... 80
1. High-Speed Blenders .............................................................................................. 80 2. Colloid Mills ........................................................................................................... 81 3. High-Pressure Value Homogenizers....................................................................... 81 4. Ultrasonic Homogenizers........................................................................................ 81 5. Microfluidization..................................................................................................... 82 6. Membrane Homogenizers ....................................................................................... 82 7. Energy Efficiency of Homogenization ................................................................... 82 8. Choosing a Homogenizer ....................................................................................... 82
D. Factors That Determine Droplet Size ............................................................................ 83
83 A. Droplet-Droplet Interactions ........................................................................................ 83
1. van der Waals Interactions .................................................................................... 84 2. Electrostatic Interactions........................................................................................ 84 3. Hydrophobic Interactions ...................................................................................... 85 4. Short-Range Forces ............................................................................................... 85 5. Overall Interaction Potential.................................................................................. 85
B. Mechanisms of Emulsion Instability ............................................................................ 87 1. Creaming and Sedimentation ................................................................................ 87 2. Flocculation and Coalescence ............................................................................... 88 3. Partial Coalescence................................................................................................ 90 4. Ostwald Ripening .................................................................................................. 91 5. Phase Inversion...................................................................................................... 91 6. Chemical and Biochemical Stability ..................................................................... 92
VII. Characterization of Emulsion Properties .............................................................................. 92 A. Dispersed Phase Volume Fraction................................................................................ 92 B. Droplet Size Distribution.............................................................................................. 93 C. Microstructure............................................................................................................... 94 D. Physical State................................................................................................................ 94 E. Creaming and Sedimentation Profiles .......................................................................... 94 F. Emulsion Rheology ...................................................................................................... 95 G. Interfacial Properties ..................................................................................................... 95
References ....................................................................................................................................... 96
Many natural and processed foods exist either partly or wholly as emulsions, or have been in an emulsified state at some time during their existence [1-7]. Milk is the most common example of a naturally occurring food emulsion [8]. Mayonnaise, salad dressing, cream, ice cream, butter, and margarine are all examples of manufactured food emulsions. Powdered coffee whiteners, sauces, and many desserts are examples of foods that were emulsions at one stage during their production but subsequently were converted into another form. The bulk physicochemical properties of food emulsions, such as appearance, texture, and stability, depend ultimately on the type of molecules the food contains and their interactions with one another. Food emulsions contain a variety of ingredients, including water, lipids, surfactants, proteins, carbohydrates, minerals, preservatives, colors, and flavors [5]. By a combination of covalent and physical interactions, these ingredients form the individual phases and structural components that give the final product its characteristic physicochemical properties [9]. It is the role of food scientists to untangle the complex relationship between the molecular, structural, and bulk properties of foods, so that foods with improved properties can be created in a more systematic fashion.
