Organic solvents should be avoided.

But in order to use the appropriate solvent it is necessary to know the target phytocompounds.

In my opinion the green extraction protocol requires the maximization of extraction yield with the maximum extract concentration. The best way to obtain such objective is with multiple stage counter-current solid-liquid extraction. In the paper http://dx.doi.org/10.1016/j.compchemeng.2016.03.004 you can find a mathematical model for the process simulation and how to obtain the equilibrium properties required in a given solvent-solutes-solids system. In this paper the experimental validation was developed with an environmental friendly solvent: ethanol. In the paper http://dx.doi.org/10.1016/j.jfoodeng.2016.07.020 you can find the mass transfer analysis during the transient period of solid-liquid extraction.

"Green" is merely a buzzword which was coined in the 1980s to denote environmentally friendly processes in scientific magazines/newspapers. The choice from the list of 1 to 8 will depend on the nature of problem and what needs to be extracted. We should not over-generalize techniques as good or bad. Let us pick up supercritical fluid extraction, that is commonly based on CO2. It can also environmentally unfriendly depending on the perspective. Some people used nitrous oxide for supercritical fluid extraction. The results were horrible in terms of a major accident. It turned out to be a powerful oxidizing agent. Ionic liquids were hot in the late 1990s, but they are pretty toxic too.

How to make those 8 different techniques by changing, improving and optimisation to green extraction techniques... There are always some alternative approach to handle these natural product.

Think about deep eutectic solvents.

regards,

GB

Good question by Dr. Preethanuj Preethalayam. Green approach to extraction of phytochemicals is one that is environmentally friendly. I agree with Dr. M. Farooq Wahab

I believe that deep eutectic solvents could be an alternative for simple solvent extraction.

In agreement with Prof. Farooq the most important fact is the optimization of the used protocol: maximize the yield with the minimum solvent as possible, including the solvent recycle. In any case it is necessary the mechanistic modeling of process. A good discussion aim proposed by Prof. Preethalayam.

The main problem is while taking extraction...that contains chlorophyll...we have to minimise this drawback. If it is possible to use reusable solvent in an optimised way.. it includes amount of solvent, temperature, nature of the vessel, time taken for extraction etc. I agree with the suggestions given by Angel and Farooq. But the inhalation of most of the solvent creating problem...not only with researchers but also our environment. So we need a optimised system for the extraction procedure.. it will deviate with the nature of natural product we take. We can find a better solution by discussion..

Extractions with all solvent that are carcinogenic such as benzene, formaldehyde etc. can not be termed green extraction.

Superheated water extraction technique.

I agree with Benzeggouta. But by heating about 200 degree or above it will decompose some of the phytochemicals or may rearrange by them selves. The method is green but it has some demerit.

Until and unless we don't define the scientific problem and target phytochemicals, discussing the best green extraction method is akin to arguing on the classical problem of "How many angels can land on the head of a pin." According to Wikipedia this question "has also been linked to the fall of Constantinople, with the imagery of scholars debating about minutiae while the Turks besieged the city."

https://en.wikipedia.org/wiki/How_many_angels_can_dance_on_the_head_of_a_pin%3F

If anyone knows the proper technique for handling natural product without any harm to phytochemicals which are going to isolate, please share those things with my question. It surely will help me and others who have some concern over the health and environment. If someone thought it has no meaning in discussing it, I am totally disagree with that.

Dear Preethalayam, My point is not to discourage questions but generic questions rarely have answers. Which is the most beautiful place on Earth? There might be hundred of correct answers. The term phytochemical is so wide and there are so many compounds in plants. Until and unless you say that you wish to extract a certain class of phytochemicals, only then chemists can suggest which extraction procedure is most suitable.

Dear Farooq, I understood what you mean. But, for a person who works in natural product chemistry have to deal with so many types of plants and their different parts. If someone suggesting good method that is applicable to all type of natural product, is really good. Because a person handling some particular species may not no other type of plants. So it is good if some one propose good techniques for some perticular plant part because normally we have to deal with so many types of plants and their different parts.

The methods described above by respectable participants were mostly possible in laboratory but when we talk about extraction at industrial level, it comes to be much more difficult. Whether or not we have to adopt a method which should be green or environment friendly. This is achieve by S.M.A.R.T selection of extraction method and very intelligent plant engineering. For example, If we wish to prepare Ivy extract with 10% hedericoside C content, we have choice to use methanol or ethanol : Water system, which one the green choice, of course ethanol. Than comes its vapor also should not escape in environment, what should be the plant design, complete close system. Final product should be vacuum dries in such a way to ensure residual solvent keep remain with in limit. By this no interaction with environment, no residual impurity in product i.e. extract. And so process will be greeeeeeeeennnn

Thank you Professor Aqib. This type of answer I need. This is not only for me but also for those who interested in natural product and their isolation.

You are welcome. Brain storming help us a lot to learn.

Organic solvents should be avoided.

But in order to use the appropriate solvent it is necessary to know the target phytocompounds.

I agree Jelena, but in order to avoid organic solvent, we need alternative solvent system. Because most of the phytochemicals are soluble in organic solvent. Water and alcohol are most user friendly and green. But the problem is, this can be used only for polar compounds. For non polar to nearest to polar need alternative green solvent system.

A few comments above I mentioned a deep eutectic solvents. Some of them can be used for extraction of nonpolar compounds (check my papers).

The use of DESs is very promissing some of them are non-toxic and can be even used for drug delivery.

best regards,

GB

Green extraction protocol means an extraction protocol using solvents that are harmless to environment. Ethyl lactate and d-limonene are some such benign solvents.

Thank you all for valuable suggestions....

Dear Preethalayam ;

The green method is a way to minimize damage to the environment. For example method with minimum amount of acid used in extraction solvent or the use of organic acid instead of inorganic acid. However, the use of a new method such as ultrasound is the best green method which is due to less consumed solvent and thereby very lower consumption of acid.

Best regards

Thank you all for your information

Try to use natural things and non conventional methods.

Directly we are tacking plant material and using some suitable solvents like either or benzene or chloroform and extracting with soxhlet apparatus 10-15 cycles