Home / Summaries / FPE 30306 / droplets-rubbery-liquids

Food structures, building blocks and food properties - Exercises

3 important questions on Food structures, building blocks and food properties - Exercises

Mayonnaise can be considered as a mixture of oil and water. Both components are liquids, though the final product is much thicker. Can you explain this observation?

The number of oil droplets is so large that they cannot move freely in the continuous water phase. The droplets are jammed, which leads to friction upon deformation and results in a high viscosity.

Bread can be considered as a mixture of protein (gluten), starch and water. Can you describe in what state (glass, rubber, crystalline) the biopolymers are in case of a fresh product and a stale product? Make a distinction between the crust and crumb.

Fresh product

Crust: low water content, solid, very brittle = glassy state
Crumb: high water content, starch is gelatinised due to baking = rubbery state

Staled product

Crust: upon storage, water migrates from the crumb to the crust, and this softens the crust. The crust changes to the rubbery state.
Crumb: the state in the crumb can crystalline (starch retrogradation that follow gelatinisation). Water is lost to the crust and the environment, and also the crystals will incorporate water. As a result, the crumb becomes firmer and crumblier.