NTRS410 Physical aspects of food preparation

Theoretically, a supersaturated solution cannot exist, and yet such solutions can be made, Explain how this is achieved.

A supersaturated solution is a true solution containing more solute than theoretically can be dissolved at that temperature, a situation created by cooling a heated saturated solution carefully. By carefully cooling down the solution it can be achieved.

Define true solution

A true solution is dispersion in which ions or molecules no larger than one millimicron are dissolved in a liquid, usually water.

Explain why it is possible to float a needle in water

Effect of surface tension, "A needle will float on the surface of the water, causing shallow deformation of the water's contour. Unless the needle is placed so that the entire length is in contact with the water at the same time, it will sink because its density is greater than that of the water. "

Why is the transition temperature of a glassy solid of importance in dried milk solids?

GLASSY STATE: A solid, inflexible physical state formed at an extremely cold temperature and with limited moisture in an amorphous solid; capable f changing to a rubbery or somewhat elastic physical state. GLASS TRANSITION: when the temp or proportion of water activity is increased, the material may begin to be somewhat more elastic or rubbery and exhibit reduced stiffness and viscosity. GLASS TRANSITION TEMPERATURE: temp at which an amorphous solid in the glassy state begins to transform to a less rigid state. The transition temperature is important in dried milk solids so that clumps of dried milk wont come to fruition. If the problem needs to be avoided they need to achieve and try to maintain a practical glass transition temperature.

Why is the hydrophilic nature of the solid particles in a sol of importance to the behavior of the sol?

Sols are colloidal systems in which a solid of colloidal dimensions is dispersed throughout a liquid. This means it solids stay throughout solution and don't go to the bottom like coarse suspensions. They are characterized as pourable/ able to flow slightly even though the solids (colloids) are in high concentration.

Define colloidal dispersion

Two-phase system containing at least one colloid (substance measuring between 0.001 and 1 millimicron in diameter). Colloidal dispersions contain molecules intermediate in size between the tiny substances capable of forming true solutions and the gross particles found in coarse suspensions

Define coarse suspension

it is a mixture of substances with particles larger than colloidal dimensions (greater than 1 millimicron) are part of systems formed in food preparation. They are influenced by gravity and tend to separate. Uncooked starch mixture and oatmeal flakes in in water are illustrations of coarse suspension