Phytochemicals are natural chemicals that are produced by plants. They are non-nutritive but are needed by plants for purposes such as disease and pathogen defence and control. Studies have shown that phytochemicals are important in human health. This is because they display different biological activities such as anti-oxidant, anti-inflammatory, anti-cancer and anti-bacterial activities. Most of these biochemicals are ingested in food such as fruits, vegetables and whole grains. This is why people are advised to eat more fruits and vegetables so that they can prevent many health conditions such as cancer, diabetes, high blood pressure and cell ageing. Main phytochemicals falls under two broad categories which are flavonoids and caretonoids. However some important phytochemicals, especially ones in traditional medicinal plants, are not available to people as they do not eat these plants. Ways in which these phytochemicals can be extracted from the said plants thus have to be devised to make the chemicals available for use.
Phytochemical extraction techniques follow a more or less standard protocol. A typical phytochemical extraction procedure is as follows
Homogenisation: This is where plant tissues and cells are disrupted so that they release the chemicals. This is mainly done using pestle and mortar under liquid nitrogen. Plant tissues can also be air dried usually at room temperature in a well aerated room temperatures and then the dry tissue is crushed using pestle and mortar. The disruption gives the samples more surface area for extraction.
Extraction: Then follows what can be referred to as the actual extraction. This is where the homogenised plant tissue is immersed in a solvent. Different solvents can be used depending on the kind of phytochemicals that are targeted for extraction. Solvents differ in polarity, just like phytochemicals. There are three polarity strengths of solvents and they are polar, medium-polar and non-polar. Polar solvents will extract polar chemicals and the same is true for non-polar solvents. Polar solvents include methanol, ethanol and water, medium-polar solvents examples are ethyl acetate, acetone and dichloromethane and non-polar solvents include toluene, chloroform and hexane. Thus in a sample, different solvents can be mixed for extraction or they can be used in sequence in the same sample material.
Extraction efficiency can be aided by what is referred to as different extraction methods; the most simple and easy to use of these methods are maceration, hydro distillation using steam and soxhlet extraction. In maceration, the homogenised plant sample is soaked in a solvent in a closed container and it is left at room temperature. The solvent is then decanted and filtered to remove debris. In hydro distillation the plant sample, which can be dry or wet, is placed in a flask and immersed in water. The flask is then connected to a condenser and heated. The distillate is collected in a tube that is connected to the condenser. It comes out as a mixture of oils and water and they are collected separately. Hydrodistillation is good for extraction of volatile phytochemicals. For soxhlet extraction, the homogenised plant sample is placed in a cellulose thimble in an extraction chamber. The chamber is then placed on top of a collection flask which is placed beneath a condenser. A solvent of choice is then added to the sample which gets heated up under reflux. The condensed solvent with extracts is collected in the flask underneath. There are other extraction methods that can be used such as sublimation, percolation, ultrasound-assisted extraction and so on that are not discussed in this article.
After extraction, to concentrate the extracts, the extract is left open at room temperature, ideally in a fume hood to evaporate the solvent. Then afterwards a measured volume of solvent can be used to dissolve the extract to required working concentrations. The extract is then used for metabolic profiling and also tested for different biological activities or any other analysis as required.
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