Medicinal Plant ExtractsMedicinal Plant Extracts

THEORETICAL THEORETICAL FUNDAMENTALS OF FUNDAMENTALS OF

EXTRACTION PROCESS EXTRACTION PROCESS

Extraction - as the term is used pharmaceutically, involves the

separation of medicinally active portions of plant or animal tissues from the inactive or inert components by using selective solvents in standard extraction procedures.

The products so obtained from plants are relatively impure liquids, semisolids or powders intended only for oral or external use.

These include classes of preparations known as:

decoctions, infusions, tinctures, fluid extracts, pilular (semisolid) extracts powdered extracts.

Such preparations popularly have been called Galenicals, named after Galen, the second century Greek physician.

The purposes of standardized extraction procedures for crude drugs

are to attain the therapeutically desired portion and to eliminate the inert material by treatment with a selective solvent known as menstruum or extragent.

The extract thus obtained may be ready for use as a medicinal agent in the form of tinctures and fluid extracts, it may be further processed to be incorporated in any dosage form such as tablets or capsules, or it may be fractionated to isolate individual chemical entities.

Solid-phase extraction (SPE) is

a separation process by which compounds that are dissolved or suspended in a liquid mixture are separated from other compounds in the mixture according to their physical and chemical properties.

Molecular diffusion,

often called simply diffusion, is the thermal motion of all (liquid or gas) particles at temperatures above absolute zero.

The rate of this movement is a function of temperature, viscosity of the fluid and the size (mass) of the particles.

Diffusion explains the net flux of molecules from a region of higher concentration to one of lower concentration, but it is important to note that diffusion also occurs when there is no concentration gradient.

The result of diffusion is a gradual mixing of material.

In a phase with uniform temperature, absent external net forces acting on the particles, the diffusion process will eventually result in complete mixing.

Diffusive equilibrium is reached when the concentrations of the diffusing substance in the two compartments becomes equal.

Diffusion is part of the transport phenomena.

Of mass transport mechanisms, molecular diffusion is known as a slower one.

Molecular diffusion is characterized by coefficient of molecular diffusion D, which is derived from the equation of Einstein:

D= RT/6Nπrµ

D= RT/6N0πrµ

R - universal gas constant, is equal to 8.32 J / (mol • deg);

N0 - constant of Avogadro (6,06 • 1023);

T - absolute temperature, K;

µ - viscosity of solution, N • s/m2;

r - radius of Diffusing particles, m.

D= RT/6N0πrµ

Coefficient of molecular diffusion describes the ability of a given substance to penetrate due to diffusion in the stationary environment.

As seen from equation, they is increased with increasing of temperature and decreased with increasing viscosity of medium and particle size of molecules of BAS.

Layer of extragent is present about the wall of part of HRM. It called diffusion boundary layer, on the surface of slices of HRM.

This layer makes a great resistance to further transfer of extracted substances in the extragent.

Its thickness depends on the hydrodynamics of the process, especially rate of mixing during extraction. While higher of the mixing speed, the boundary layer is thinner.

Double-diffusive convection

is an important fluid dynamics topic that describes a form of convection driven by two different density gradients which have different rates of diffusion.

Convection in fluids is driven by density variation within them. These density variations may be caused by gradients in the composition of the fluid, or by differences in temperature (through thermal expansion).

Within the diffusion boundary layer transfer of substances are legally as the first law of free diffusion and can be expressed as the first law of Fiks: S=βF (C1-C2)τ/dS – amount of substances that was diffused, kg;β – coefficient of convective diffusion, m/s, which

is the greater than more intensive of mixing.F - surface of separation phases, m2.d - thickness of diffusion boundary layer, mτ - time of diffusion, s;

C1- C2 – difference of concentration of BAS, kg/m3.

Extraction process depends on many factors, most important of which:

hydrodynamic conditions surface of separation of phases difference of concentration duration of process viscosity of extragent temperature adding of surfactants, choice of extragent, porosity and the size of cavities between pieces of crushed

HRM influence of vibrations, pulsations, electric pulse discharge

in a liquid medium, strain and chop of raw in extragent.

In the presence of hydrodynamic conditions rate of the extraction is higher, because layer of stationary liquid is decreased, there are convection currents that promote transfer of substances. The difference of concentrations of BAS in HRM

(C1) and in extragent (C2) is drives the process of extraction.

During the extraction should aspire to the maximum gradient of concentration.

It is achieved by frequent changes of extragent (bismaceration instead maceration), a process extraction with opposite direction of HRM and extractant et al.

The amount of BAS which are diffused through conventional layer is directly proportional to the time of extraction.

Excessive times of extraction process leads to the pollution of extracts by macromolecular associates.

While long extraction undesirable processes should be under the influence of enzymes.

It is reasonable to stop the process of extraction at some point because obtaining of more quantities of extracted substances dos not cover costs of extragent (alcohol, ether).

ViscosityLess viscous solutions have a greater diffusion

capacity. To reduce the viscosity while extraction by vegetable

oils resorted to heating.

Liquefied gases: carbon dioxide CO2, propane, butane, liquid ammonia and others are promised in this respect. Liquid carbon dioxide is the most commonly used because it is chemically indifferent to the large number of active substances. Its viscosity is in 14 times smaller than the viscosity of water and in 5 - than the viscosity of ethanol.

Raising of the temperature made faster the extraction process.

But:

heating is possible only for aqueous extracts because while heating loss of BAS are increased, and thus harm and danger of working with them are increased too.

While using hot water starch is polymerized, extracts in this case become mucous.

Porosity of materials – is the size of the cavities inside the plant tissue. Porosity of materials makes better extraction because the more internal juice is formed while swelling.The size of cavities between pieces of crushed

material affects the speed of extraction.

These characteristics of HRM cause its absorption capacity.

Influence of vibration, pulsation, shredding

Using the methods of extraction, in which there are vibration, pulsation, crushing and deformation in the medium of extraction allowed to increase speed and completeness of the extraction of raw materials.

Requirements to extragent to ensure complete of extraction of BAS and maximum speed of extraction1. selectivity (maximum dissolving medicines and

minimal – ballast substances), 2. chemical and pharmaceutical indifference, 3. low toxicity and flammable, 4. availability, be affordable,5. penetrate into the pores of the HRM and through

walls of cell, to provide high resolution of wet, 6. prevent the development of microflora in the

infusion, 7. have a low boiling point, easily recover.

Water is one of the most suitable extragents. It has several advantages: 1. Well penetrates through the cell membrane,

impermeable to hydrophobic substances;

2. Water dissolves and extracts substance better than other liquids;

3. Pharmacologically indifferent;

4. Very common;

5. Combustible and explosion proof;

6. Available at cost.

Water, as extragent has some negative properties:

1. Can not dissolve and can not extracts hydrophobic substances;

2. Has not antiseptic properties, resulting in water extractions can develop micro-organisms;

3. Due to water is hydrolytic cleavage of many substances, especially while high temperature;

4. Enzymes can be split medicines in the aquatic environment.

Characteristic of alcohol as extragent: 1. Is the solvent of many compounds not extracted

by water, such as fats, alkaloids, chlorophyll, glycosides, essential oils, resins and others;

2. Has antiseptic properties (alcohol in aqueous solutions with concentration above 20 % do not develop bacteria);

3. The stronger alcohol, hydrolytic processes are the less possible in its environmental.

4. Alcohol inactivate enzymes; Quite volatile, so alcohol extract is easy densities

and dried to a powdery substance.

Disadvantages of alcohol:

1. Is limited product, is solded by pharmaceutical production according to the law;

2. Much heavier than water. Penetrates through the cells walls and subtracts the water in proteins and mucous substances, converts them to sediments that clog cells pores, and therefore impairs the diffusion. Whether a lower concentration of alcohol, the easier it gets inside cells;

3. Is not pharmacologically indifferent, has both the local and general effect, which should be considered in the production of infusions;

4. Flammable.

Extragents are used in the manufacture of herbal medicines

Acetone With water and organic solvents mixed in any ratio. Used as extragent for the alkaloids, resins, oils and others.

Ethyl ether mixed in all proportions with acetone, alcohol, ether, fatty oils and essential oils.

Chloroform is a good solvent for alkaloids, glycosides, oils, oils and more. Dyhloretan is used for extracting glycosides. Methylene chloride used for the extraction of hydrophobic substances

(glycosides, alkaloids, etc.).. Methanol, methyl or wood alcohol. Mixed with water in all proportions.

Strong poison. Use within 10 ml of substance causes atrophy of the optic nerve dose of 15 - 20 ml lethal.

Vegetable oil. Often used peach, almond and sunflower oil. Fatty oils are mixed with ether, chloroform, gasoline, mineral and essential oils.

Liquefied gases: carbon dioxide, propane, butane, liquid ammonia, chladone are promising for the extraction is proposed recently. Liquid carbon dioxide good extracts ether oils, fatty oils and other hydrophobic substances. Extraction by liquefied gases is conducted under vacuum.