Process of crystallization

Crystallization is an example of a separation process in which mass is transferred from a liquid solution, whose composition is generally mixed, to a pure solid crystal. Butter, margarine, ice cream, sugar, and chocolate all contain different types of crystals, although they all contain fat crystals. Ice cream has fat crystals, ice crystals, and sometimes lactose crystals. Key elements in the candy making process are in sugar's physical properties. Specifically, its solubility with its effect on the water's boiling point.

Crystallization occurs in two major steps.
*Nucleation: The appearance of a crystalline phase from either a supercooled liquid or a supersaturated solvent. The solute molecules or atoms dispersed in the solvent start to gather into clusters.
*Crystal growth: The increase in the size of particles and leads to a crystal state.

Nucleation involves formation of a crystalline state from the supersaturated liquid state. Once nuclei form, they grow into product-sized crystals through incorporation of additional molecules into the crystal lattice. This is called spontaneous nucleation.

Seed crystals are small crystals, generally of the solute, which then grow by deposition on them of further solute from the solution. This growth continues until the solution concentration falls to the saturation line. Below the saturation curve there is no crystal growth, crystals instead dissolve.

Controlling crystallization to obtain the desired crystal content, size distribution, shape, and polymorph is key to manufacturing products with desired functionality and shelf life. The crystalline phase plays such a large role in appearance, texture, spreadability, and flavor release in many food products including chocolate, margarine, butter, and shortening..
Process of crystallization

What is retrogradation?

Retrogradation is another important property of starch. Retrogradation refers to the occurrence where starch reverts or retrogrades to a more crystalline structure upon cooling.

In most products, retrogradation causes deterioration of quality and therefore retrogradation has to be avoided.

Both amylose and amylopectin may participate in a textural change that makes them somewhat more ‘gritty’ with time.

In particular it appears that retrogradation is the recrystallization of the amylopectin where the amylose molecules clump together and separate from the sol or gel, thus destroying the semi-elastic network on which its properties depend.

Retrogradation is more likely to occur in a high amylose starch. Starches with a very high amylose content undergo retrogradation less readily than those with a lower amylose content and such starches are commercially available to food manufacturers,.

This occurrence is noted in baked products that become ‘stale’ no longer ‘fresh’ tasting or ‘fresh’ handling.  It is also observed in leftover, long-grain rice.

Moreover, the term retrogradation can also be used to describe changes occurring during cooling from gelatinization temperatures as well as changes occurring during long-term storage.
What is retrogradation?

Crystallization in foods

The process of forming crystals from solution is known as crystallization. It is important unit operation for separation of solids in dissolved form in a solution by making used of the principles of saturation solubility, temperature or solubility and temperature.

Crystallization is a term that describes several different phenomenon related to the formation of a crystalline lattice structure.

Crystallization is often a four step process that includes:
*Generation of a supersaturated state
*Nucleation – formation of nuclei
*Propagation – crystal growth
*Maturation – crystal perfection or continued growth

The liquid phase remaining after the formation of the crystals is called ‘mother liquor’.

In the food industry, crystallization may serve for the recovery of crystalline products – (sugar, glucose, lactose, citric acid, salt), for the removal of certain undesirable components or for modification of certain food products in order to obtain a desirable structure.

Several materials may also crystallize during food processing.

Crystallization of triglycerides 

Crystallization of triglycerides is a complex phenomenon characterized by fairly slow growth rates and polymorphic transitions of their crystallized phases.

The crystallization of triglycerides is also complicated by the presence of minor components frequently contained in them. For examples, milk fat consists of 95-98% triglycerides but also contained diglycerides, free fatty acids, monoglyceride, phospholipids and sterols as minor components.

Crystallization of sucrose
Crystallization is the final step in the recovery of sugar from sugar cane or sugar beet. Also called ‘sugar boiling’, sugar crystallization of sugar is a complex process requiring precise control, skill and experience.

Crystallization process is used as a unit operation for separation of solids from the liquids or as a process tool for processing certain foods item.

In the separation process, in some cases the solids are the desired products, whereas in others liquid is the desired product.
Crystallization in foods

Crystallization of sugar

Crystallization of sugar
Crystallization of sugar can be a problem in a variety of products. For example, the crystallization of lactose in a glassy state will make nonfat milk difficult to disperse.

If too great an amount of milk solids are added to a frozen dessert, a gritty texture results due to the lactose crystals.

Crystallization of sugar is a major factor in the candy manufacturing industry.

Candies can be divided into two groups crystalline and non-crystalline. Crystalline candies include fudge, fondant and any other candies that have crystals as an important structural component.

Divinity is a crystalline candy but is a special case as crystals are dispersed in foam.

Non-crystalline candies include caramels, brittles, taffies, marshmallows and gum drops.

Marshmallows and gum drops are also special classes of candies as they contain a gelling substance.

Crystallization is a complex process with many interrelated factors. The nature of the crystallizing substance is important for crystallization.

The rate of crystallization is the speed at which nuclei grow into crystals. This rate is dependent upon the concentration of the soluble in the solution, as a more concentrated syrup will crystallize rapidly than a less concentrated syrup.

At higher temperature the rate of crystallization is slow and becomes more rapid at a lower temperature. Agitation distributes the crystal forming nuclei and hastens crystallization.

Impurities in the solution usually delay crystallization and in some cases such as caramels may prevent crystal formation.

Fat and protein decrease the number and size of crystals.
Crystallization of sugar