Dried materials are  used mostly in phytochemicals fields because it can be stored in a freezer for years without significant degradation of phytochemicals.

Dear Dr. Bhuiyan

Some researchers responded differently in response to a question "Can i re-dry the sample to reduce the moisture content? posed by Ms. Norrashidah Mokhtar of Malaysia.

What are the disadvantages of using fresh or semi-dried plant material for obtaining crude extracts or pure chemicals?

My intention is to solicit responses from experts for the benefit of students and young researchers in the filed of phytochemistry, natural product chemistry  and other related fields of science.

Best wishes and good luck.

Dear Dr. Rao,

Actually samples (fresh, semi-dried and dried) depends on compounds of nature i.e which types of compounds you want to isolate. Usually researchers of phytochemists used dried samples for inhibiting degradation of compounds or for long time preservation and also used long time for their isolation experiments to safe its quality. In the case of fresh or semi-dried samples, you can't keep it long time preservation or moistures of samples which helps to grow unwanted fungus or others or your samples quality is destroyed or samples nature is totally changed. I think, this is the main reason to use dried samples. Important thing is what is the aim of your isolation?Some times, in fresh samples, you got one compound but the same samples when you dried, you donot get the same compounds.So, in this case, scientist used fresh samples. Please read the following article for your kind understanding. Thank

http://www.academicjournals.org/article/article1380034213_Laitonjam%20and%20Wangkheirakpam.pdf

It is usual to use fresh plants to extract essential oil, in other cases it is better to dry the sample to avoid degradation of some compounds and to avoid fungus or other microorganism grows.

To obtain reproducible results for bioactive compounds from plant sources, shade dried plant material is preferable/ advisable.

i am agreed with suggestion given by Olga Lock and M R Rathod. Because there are some essential oil which are volatille in nature and can be isolated from fresh sample while in other cases the shade dried plant materials are prefered.

If you are trying to do activity-directed isolation of foods for bioactive compounds, it is best to use fresh material, i.e. vegetables recently obtained. Obviously, dried materials may be used for isolation of bioactive constituents from herbs since this is their typical state of use found in commerce.

Dear all

Thank you all for your responses. What are the disadvantages of using fresh herbs/medicinal plants or their parts for extracting bioactive phytochemicals with the help of solvents?

The main "disadvange" is the enormous amount of water that you have to deal with. But this can be turned around if you do a polar extract first and then use a less polar solvent. For example, use ethanol/ether ( a good ether, with no peroxides, like methyl-t-buthyl ether) after extracting with ethanol. Evaporate the polar extract and finally freeze dry the remaining slurry. This fraction will provide very polar components, like glycosides. Some of these glycosides are active compounds. You might be surprised with the results. Of course, you have to use reverse chromatography to separate these components. Stay away from silica or alumina chromatography! The use of reverse chromatography will be of great advantage.

Agreed, @ Dr Mora.  The water content can be an issue, although not solely due to dilution.  Fresh plant samples don't stay that way!  During transport to the lab, fresh plant samples can begin to degrade, grow mold and bacteria, and some constituents evaporate or oxidize easily.  If you're using fresh, it really must be fresh.

If the whole plant is being used in the study rather than isolated constituents, water content can also have an effect on the concentration of the plant medicine.  This vacillates depending on ambient conditions (how wilted/fresh is the plant sample) and can change the outcome of one's study.  Dried/preserved material has less mass variation sample to sample and therefore contains a (slightly!) more predictable amount of the constituents you want per gram.

You WILL have different chemicals in different concentrations in the fresh sample than the dried, and must take this into account.  Plants like Anemone pulsatilla, for example, are useless prepared from a dried sample.  The constituents you'd want are simply not present in the dried material.

-JS

Agreed that fresh plant sources are difficult to handle due to moisture problem and fungal contamination, but what are the chances of insect infestation of dried plant material and its consequence on the bioactive compounds?

It is always better to extract dry material.

If the component of interest is volatile oil, then careful extraction of fresh is beneficial.

It depends on the end product which you are going to extract and also on the availability of the plant source. If it is to be used for the whole year and it is harvested once a year; it has to be dried otherwise it will get spoiled till the time of use. Sometimes few constituents are higher in fresh plant material, which gets degraded after drying. In this case fresh plant material immediate after harvesting needs to be used for extraction or else needs to preserved so that active compound is not degraded till the time of use.

To reduce chances of insect infestation, dry biomass should be stored without pulverization. As such biomass will be infested less as compared to pulverized biomass. It is advisable to pulverize the dry biomass at the time of preparation of extract.  

To avoid degradation by any means.

For extraction better to use the dry plant material. But in this case of studyinig of essential oil components better to use a fresh plant material

I think it may also increase the overall surface area and wetability for effective extraction.

I prefer dried sample. The water content in the sample may interact with the solvent, and affecting the extraction. If you are using fresh sample, it is hard for you to standardize your extraction protocol as the moisture content of your sample is not consistent.