Food Biochemistry and Food Processing (2 edition)

BLBS102-c40 BLBS102-Simpson March 21, 2012 14:23 Trim: 276mm X 219mm Printer Name: Yet to Come

40 Separation Technology in Food Processing 767

separation process affected by a fluid involving the transfer of

solutes from a solid matrix to a solvent. It is an operation ex-

tensively used to recover many important high-value food com-

ponents such as oil from oilseeds, protein from soybean meal,

phytochemicals from plants, etc. Solid–liquid extraction is also

used to remove undesirable contaminants or toxins from food

materials.

Liquid–Liquid Extraction, e.g., Two-Phase

Aqueous Extraction

Liquid–liquid extraction separates a dissolved component from

its solvent by transfer to a second solvent, mutually nonmisci-

ble with the carrier solvent. The liquid–liquid extraction as a

technology has been used in the antibiotics industry for several

decades and now is recognized as a potentially usefully separa-

tion step in protein recovery on a commercial production.

Supercritical Fluid Extraction

Supercritical CO 2 fluid extraction is mostly for high value-added

products that are sensitive to heat, light, and oxygen. The extrac-

tion process is implemented in a supercritical region where the

extraction fluid (e.g., CO 2 ) has liquid-like densities and solvating

strengths but retains the penetrating properties of a gas.

Distillation

Distillation is a physical separation process used to separate the

components of a solution (mixture) that contains more compo-

nents in the liquid mixture, by the distribution of gas and liquid

in each phase. The principle of separation is based on the dif-

ferences in composition between a liquid mixture and the vapor

formed from it, because each substance in the mixture has its

own unique boiling point.

Chromatographic Methods

Chromatography is a separation technique based on the uneven

distribution of analytes between a stationary (usually a solid) and

a mobile phase (either a liquid or a gas). Chromatography can be

conducted in two or three dimensions. Two-dimensional chro-

matography, for example paper chromatography, is almost solely

used for analytical purposes. Column chromatography separa-

tion is the most common form of chromatography used in the

food processing field for further purification of high value-added

components. Many variations exist on the basic chromatography

methods. Some well-established methods are listed below.

Liquid–Solid Absorption Chromatography

(e.g., Hydroxyapatite)

In absorption, molecules in a fluid phase concentrate on a solid

surface without any chemical change. Physical surface forces

from the solid phase attract and hold certain molecules (sub-

strate) from the fluid surrounding the surface.

Affinity Chromatography

Affinity chromatography exploits the natural, biospecific inter-

actions that occur between biological molecules. These inter-

actions are very specific and because of this affinity separation

process are very high resolution methods for the purification of

food products such as proteins. Affinity chromatography has a

gel surface that is covered with molecules (ligand) binding a

particular molecule or a family of molecules in the sample.

Size-Exclusion Chromatography

Size-exclusion chromatography, also known as gel permeation

chromatography when organic solvents are used, is used to

control the pore size of the stationary phase so as to separate

molecules according to their hydrodynamic volume and molec-

ular size.

Ion-Exchange Chromatography

Ion-exchange chromatography and a related technique called

ion-exclusion chromatography are based on differences in the

electric charge density of their molecules during charge–charge

interaction of molecules. It is a variation of absorption chro-

matography in which the solid adsorbent has charged groups

chemically linked to an inert support. Ion-exchange chromatog-

raphy is usually used for recovery and purification of amino

acids, antibiotics, proteins, and living cells.

Hydrophobic Interaction Chromatography

Hydrophobic interaction chromatography is based on a mild ad-

sorption process, and separates solutes by exploiting differences

in their hydrophobicity.

Reverse Phase Chromatography

Reverse phase chromatography is based on the similar principles

of hydrophobic interaction chromatography. The difference is

that the solid support is highly hydrophobic in reverse phase

chromatography, which allows the mobile phase to be aqueous.

ENGINEERING ASPECTS OF

SEPARATION PROCESSES

Much of the recent process development for the separation of

valuable components from natural materials has been directed

toward high value-added products. For the recovery of valuable

components from raw materials, applications of separation tech-

nologies to recover major or minor components from agricul-

tural commodities is usually a solid–liquid contacting operation.

As research moves into commercial production, there is a great

need to develop scalable and cost-effective methods of separa-

tion technologies. The successful and effective development of

separation technologies is a critical issue in the chain of value-

added processing of agricultural materials such as developments

in functional food ingredients, nutrients, and nutraceuticals.