NAZMA LIAQUAT

13-PHC-S15

NATURAL PRODUCTS

Natural product is a chemical compound or substance produced by a living organism, that is found in nature.

ExtractionExtraction is a mass transfer process of one or more components from one phase to another.

Goals;• High yield• high selectivity and purity• high sensitivity

These properties may differ in terms of importance depending on the process scale.

At the industrial scale yield and purity are the key properties.

When dealing with natural products, in most cases the sample to be extracted is a solid material, although in some cases liquid samples are used. The extracting solvent is usually a liquid, but it can also be a solid or asupercritical fluid.In order to understand how any extraction technique works, both the target compounds and the extraction solvent must be considered.

Therefore, knowledge of the properties of the solute, mainly its chemical properties, is important in order to understand the extraction process. Moreover, it isimportant to know the properties of the solvent medium in which the target material is to be dissolved during the extraction process. The interactionsbetween solute and solvent are determined by the vapor pressure of the solute, the solubility of the solute in the solvent, the hydrophobicity , and the acid/base properties of both solute and solvent.

Some of these properties only relate to the compound of interest (solute), while others concern the solvent used for the extraction process. Thecompatibility between solvent and solute is based on assessing the polarity of the molecular structure to predict their solubility and miscibility. As a generalrule, it is assumed that non-polar solutes are dissolved by non-polar solvents while polar solutes are dissolved by polar solvents.

For example, water dissolves glucose due to the attraction between the partially positively charged atom of the glucose molecule to the partially negatively charged atom of the water molecule while at the same time the partially negatively charged atom of the glucose molecule is attracted to the partially positively charged atom of the water molecule. If the target component from the raw material is freelyavailable and the polarity of the solvent and of the solute is compatible, the solvent dissolves the solute to form a homogenous solution.

Extraction mechanism

1. the solvent is transferred from the fluid phase to the solid surface and pervades it;

2. the solvent penetrates into the solid matrix by molecular diffusion;

3. the soluble material is solubilized by desorption from the matrix and solvation into the extraction solvent – the breakage of chemicals bonds may be required for the for desorption of target analytes from the solid matrix;

4. the solution containing the solutes returns to the surface of the solid bymolecular diffusion;5. the solution is transferred from the solid surface to the bulk fluid by natural of forced convection.

The extraction of a chemical component X from a phase A to a second phase B begins when the two phases come into contact. The two phases shouldtherefore not be miscible if they are both liquids.

Furthermore, phase A can be in the solid or semi-solid state. The distribution of X between the immiscible phases occurs as soon as it can be transferred from phase A to phase B and back from phase B to phase A. The solubilization limit is the equilibrium concentration between the phases.

The equilibrium can be represented as:

XA XB

Where ,XA is the component X in phase AAnd XB is the component X in phase B.

Conventional Extraction Techniques

The extraction method to be applied to a particular solid matrix depends on the raw material to be processed and on the product desired. There is no single and standard extraction method for obtaining bioactive compounds from naturalproducts, each one presenting advantages and disadvantages.

The most commonly usedconventional techniques are ;• Soaking extraction,• Soxhlet extraction, • Distillation.

Choosing one of them for extracting bioactive compounds fromnatural products depends on process conditions such as temperature, mechanical action and solvent type.

Soaking

In this process, the untreated or powdered plant material is placed in a container along with the solvent. The plant material stays in contact with the solvent for several hours or even days, during which the soluble material is transferred from the solid sample to the solvent. Usually some kind of agitation is provided to increase the mass transfer rate by increasing the turbulence.

Agitation devices are used to process fine particles. The dispersion of the particles in the liquid solvent by the agitation facilitates the contact of the solid with the solvent, accelerating the process by favoring the diffusion of the extracted components and avoiding super saturation in the immediate proximity of the surface of the solid to be extracted. However, care should be taken with excessive agitation, which may cause the disintegration of particle solids.

The most common is to perform the process under room temperature, but heat can be applied to improve the extraction efficiency. However, whenextracting thermosensitive compounds high temperatures should be avoided.

Drawbacks

Time consumingHigh energy demand product quality lossmass transfer rate decreases with time because solvent is continously enriched with solutes.

Soxhlet ExtractionAdvantages

Simplicity

low cost

Apparatus

A schematic representation of a Soxhletextractor1: Stirrer bar 2: Still pot (the still pot should not be overfilled and the volume of solvent in the still pot should be 3 to 4 times the volume of the soxhletchamber) 3: Distillation path 4: Thimble5: Solid 6: Siphon top 7: Siphon exit 8:Expansion adapter 9: Condenser 10:Cooling water in 11: Cooling water out

Operation;

The solvent is heated to reflux. The solvent vapourtravels up a distillation arm, and floods into the chamber housing the thimble of solid. The condenser ensures that any solvent vapour cools, and drips back down into the chamber housing the solid material. The chamber containing the solid material slowly fills with warm solvent. Some of the desired compound dissolves in the warm solvent.

Some of the desired compound dissolves in the warm solvent. When the Soxhlet chamber is almost full, the chamber is emptied by the siphon. The solvent is returned to the distillation flask. The thimble ensures that the rapid motion of the solvent does not transport any solid material to the still pot. This cycle may be allowed to repeat many times, over hours or days.During each cycle, a portion of the non-volatile compound dissolves in the solvent. After many cycles the desired compound is concentrated in the distillation flask.

The advantage of this system is that instead of many portions of warm solvent being passed through the sample, just one batch of solvent is recycled.After extraction the solvent is removed, typically by means of a rotary evaporator, yielding the extracted compound. The non-soluble portion of the extracted solid remains in the thimble, and is usually discarded.

Several solvents have been used for the extraction of active components from plants. Soxhlet has been specifically applied to extract vegetable oil. In theseapplications hexane has been the most commonly used solvent. Different types of bioactive compounds have been isolated using this method with hexane assolvent. Hexane has a boiling point of approximately 65 1C, i.e. it should enable the application of Soxhletextraction to any compound with a boilingpoint above 65 1C. Hexane is also an excellent solvent for oil because of the high oil solubility in this solvent and also because oil can be easily recoveredby distillation.

Drawback;

The main drawback for the use of hexane is its high toxicity. As a result, other solvents have been used to substitute hexane in oil recovery including some polarity alcohols such as isopropanol and ethanol, another option is to use water at pH 12

Focused Microwave assisted SoxhletExtraction (FMASE)

Ultrasound assisted Soxhlet Extraction (UASE)

FMASE;

In FMASE systems the extractor design is the same of a conventional Soxhlet apparatus and the solvent is heated by conventional means (an electricaljacket, for instance). The microwave irradiation is focused only in the part of the extraction vessel containing the sample and is directed to affect both the solvent and the sample. Of course the effect of microwaves on both will depend on their nature and characteristics.

FMASE

UASE;

The application of ultrasound directed to the sample and solvent causes the formation of bubbles that collapse the cell structure and therefore facilitate the extraction process.The application of ultrasound combined to Soxhletreduces the number of cycles needed for exhaustive extraction of fats from oleaginous seeds as sunflower,rapeseed and soyabean

Distillation with water/steam;

Soxhlet is not applicable to highly volatile components, but only tocomponents that have a boiling point below the solvent boiling point. For highly volatile compounds distillation is the preferred alternative. Water andsteam distillation are used for the extraction of several volatile bioactive components from plants.

The product of this process is known as volatile oilor essential oil. It is the most widely used method at industrial scale for the processing of natural products when the target compounds are volatile.This technique simply involves vaporizing or liberating the volatile compounds from the solid matrix at high temperatures using water and/orsteam as extracting agent.The water/steam heats the solid matrix, which releases the volatile compounds present in it.

These are vaporized taking vaporization heat from the steam, and then are transported to the steam through diffusion. The resulting vapor phase is then cooled and condensed prior to separating water and the organic phase based on their mutual immiscibility. The volatile oil constitutes the upper phase in the decanter, while the bottom phase is constituted of water containing some hydrolyzed compounds, known as hydrosol. The compounds present in hydrosol usually confer to it a pleasant aroma; therefore, it can be used in the formulation oflotions, soaps etc

Variants of distillation with water/steam process;

Direct steam distillation

Hydrodistillation (water distillattion)

Dry steam distillation

NEW TECHNIQUES OF EXTRACTION

MICROWAVE ASSISTED EXTRACTIONULTRASOUND ASSISTED EXTRACTION ACCELERATED LIQUID EXTRACTION SUPER CRITICAL FLUID EXTRACTION

Microwave Assisted Extraction

Microwaves heating principle;

Microwaves are electromagnetic waves made up of two oscillating perpendicular fields:electrical field and magnetic field.They can be used as information carriers or as energy vectors. The direct action of waves on a material which is able to absorb a part of electromagnetic energy, transform it into heat.

Ionic conduction is the mechanism by which electromagnetic field is developed.

The resistance of the solution to this flow ofions and the collisions between molecules because the direction of ions changesas many times as the field changes sign will result in friction and, thus, heat thesolution

The treatment of plant material with microwave irradiation duringextraction can result in enhanced recovery of secondary metabolites and aroma compounds

Extraction of sensitive compounds

Nitrogen protected microwave assisted extraction (NPMAE)

Vaccum microwave assisted extraction (VMAE)

NPMAE

Oxidation of the active compounds during the extraction process can be prevented by using a pressurized inert gas, such as nitrogen, in a closed system. In nitrogen-protected microwave assisted extraction (NPMAE), the plant sample is introduced into the vessel with a certain volume of solvent.First, the air in the flask is pumped out by a vacuum pump until a certain degree of vacuum is obtained. Then the vessel is filled with nitrogen from the gas cylinder. This technique has been employed in the extraction of ascorbic acid from guava, yellow pepper, green pepper.

VMAE

The boiling point of the extraction solvent under vacuum is lower than at ambient pressure. Thus, the solvent can be kept boiling at lower temperature

which is good for mixing the sample with the solvent and extracting thermosensitive compounds while preventing their degradation. Furthermore, the air in the extraction system is mostly pumpedout, so oxidation of oxygen-sensitive compounds is avoided or reduced.

COMPOUNDS PLANT SAMPLES EXTRACTION TECHNIQUES

FLAVONIODS Hippophae Rhamnoides

FMAE

ISOFLAVONE SOYBEAN MAE

TRITERPENOIDS OLIVE LEAVES MAE

ASCORBIC ACID GUAVA AND PEPPERS

NPMAE

ULTRASOUND ASSISTED EXTRACTION

Ultrasound wave passes through medium, it induces a longitudinal displacement of those molecules, acting as a piston on the surface, resulting from a succession of compression.The molecules that form the liquid are temporarily dislodged from their original position and during the compression cycle they can collidewith the surrounding molecules

As a result negative pressure will be exerted, pulling the molecules apart. The extent of the negativepressure depends on the nature and purity of the liquid. At a sufficiently high power, the attraction forces between them might be exceeded, generating a voidin the liquid. The voids created into the

medium are the cavitation bubbles

The size of these bubbles reach a critical point they collapse during a compression cycle and, since heating is more rapid than thermal. The creating hotspots are able to accelerate dramatically the chemical reactivity of the medium. When these bubbles collapse onto the surface of a solid material, the high pressure and temperature released generate shock waves towards the solid surface.

Ultrasound in food extractionMATRIX PROCESSING TARGET

COMPOUNDS

FRUITS AND VEGETABLES

CITRUS PEEL UAE FLAVONOIDS

ORANGE PEEL UAE POLYPHENOLS

TOMATO UAE LYCOPEN

HERBS AND SPICES

CARAWAY SEEDS UAE CARVONE AND LIMONENE

ROSEMARY UAE ANTIOXIDANTS

RED AND WHITE WINE UAE VOLATILECOMPOUNDS

BRANDIES AND OAKEXTRACTS

UAE VOLATILE COMPOUNDS

Accelerated liquid extraction

Types;

Static accelerated solvent extraction (Static ASE) Dynamic accelerated solvent extraction (Dynamic ASE)

Steps in static ASE

Steps in dynamic ASE

Dynamic extraction time

Super critical fluid extraction (SFE)

A technique based on the use of solvents at temperatures and pressures above their criticalpoints. SFE can be a fast, efficient, and clean method for the extraction of natural products from several matrices.

Supercritical fluid extraction is commonly carried out considering two basic steps: (1) extraction of soluble substances from the matrix by the supercriticalfluid and (2) separation or fractionation of the extracted compounds from thesupercritical solvent after the expansion

SFE has been used in different fields such as the food, pharmaceutical, chemical, and fuel industries. Due to the absence of toxic residue in

the final product, among other advantages, supercritical fluids are especially useful forextraction in two situations:(a) extracting valuable bioactive compounds suchas flavors, colorants, and other biomolecules or (b) removing undesirable compounds such as organic pollutants, toxins, and pesticides

The extraction plant uses an extraction column in which the extraction is performed in countercurrent mode.

Countercurrent extraction (CC-SFE) is performed introducing the sample in the system from the top of the column and the pressurized solvent from the bottom; in this process, the components distribute between the solventand the liquid sample which flows countercurrent through the separation column.

Bioactive components obtained from SFE

Fatty acids , essential oils , antioxidants etc