Crystallization in food

In terms of molecular structure, there are three forms of powders: crystalline, amorphous, and the mixture of the two. Solid foods can either be amorphous (such as hard candies or milk powders) or crystalline (such as chocolate or ice cream).

Low molecular weight carbohydrates, such as lactose, glucose, sucrose, and organic acids and polyols, can either be in crystalline or amorphous states, depending on the processing conditions and presence of other components in the system.

In many food products, the crystalline structure within is important to product quality, texture, and stability. Crystallization determine product appearance, mechanical properties during handling, mouthfeel during consumption, and shelf stability.

The formulation, processing conditions, transport and storage conditions govern the crystalline microstructure in foods and thus, the shelf stability of these food products.

Crystallization is also important during the processing of certain food components, as a purification or separation step.

Crystals may promote a certain texture, as in products such as frozen foods (ice cream), grained sugar confections and fat-based products (e.g. butter, margarine and chocolate). In confectionery products such as fondants and creams, controlled crystallization results in the formation of a large number of fine crystals that give the desired texture.

The principle of crystallization is based on the limited solubility of a compound in a solvent at a certain temperature, pressure, etc. Crystallization involves the following steps.
*First, the liquid must attain a level of supersaturation or supercooling. This is accomplished through cooling or evaporation.
*Once a critical supersaturation has been exceeded, nucleation occurs. Nucleation involves the formation of the crystalline phase from supersaturated solutions can occur by either a spontaneous or a forced nucleation mechanism.
*Once nuclei form, they grow into product-sized crystals through incorporation of additional molecules into the crystal lattice. Crystallization continues until equilibrium is achieved between the liquid and crystalline. The balance being determined by the solubility (concentration) and the temperature. The driving force making the crystals grow is the concentration excess (supersaturation) of the solution above the equilibrium (saturation) level.
Crystallization in food