**5.3. Characterizing fat components in emulsions**

Water in oil (W/O) emulsions have continuous phase made up of combinations of fats and oils. Butter and margarines, for example, are solid in the refrigerator (around 5°C) and almost liquid above 40°C. Unfortunately, when butter is removed from the refrigerator, there are some problems. Temperature sweep tests at a fixed frequency and strain rate can allow these products to be characterized as a function of temperature and specific melting point. This can help determine the combination of fats and oils required or fat substitute to obtain optimized spreading and texture.

Products containing more crystallizing fat melt a bit slower than products containing more oil. Softening of fresh cheese products rely on a larger extent on dispersion of the product in saliva, although the product consistency reduces considerably as a result of the melting of fat under mouth temperature. A completely molten fresh cheese will be has much more residual thickness in the mouth than margarine.

As for emulsions with plastic rheology, spreading does not tend to change the emulsion structure dramatically unless the volume fraction of the dispersed phase is very large and spreading induces coalescence of the emulsion droplets. Low-fat spreads may coalesce unless the water droplets are structured with biopolymers to retard re-coalescence under shear.

Processing in the mouth will result in more dramatic microstructural changes. First, consider the behavior of a food emulsion in the mouth during mastication when it is eaten pure, i.e., not on bread. In this situation, a typical food emulsion undergoes a chain of events, although some stages may occur simultaneously or may be unnecessary for a specific food emulsion.

The breakup of a food emulsion can be very important for flavor release. For soluble flavors, in both the lipid and the water phases, diffusion should be fast enough to allow the flavors to move from the product to the saliva within the typical residence time in the mouth.

For studying ice cream formulations using different types of fat, rheology provides informa‐ tion to analyze the effect of each fat studied in the ice cream structure [42, 43].
