In fact, the therapeutic efficacy of a part or its parts is due the presence of specific active chemical constituent.  A plant may contain several compounds of different phytochemical class like alkaloids, steroids, terpenoids, polyphenolics, glycosides, etc. Each of them have different pharmacological action. when total crude extract  is used for a specific ailments, there will be a synergistic action or some constituents may retard the efficacy of the main compound responsible of therapeutic action against the ailment. Using the purified bioactive compound  of proven curative efficacy in prescribed and safe dose  will certainly be more effective than the crude extract. Another that claim that such using such pure individual compound may exert some side effects as well. 

The extract from plants , seeds ,leaves and any part of plant were count more compounds eg. phenoles , flavonids ,steroids and etc...It was very active for microbial 

The extract  need more step for any compound purification.  

It really depends on the extract and pure compound. Generally the pure compound will work at lower mg/mL as there is less other material present. However, a given antibiotic compound within a crude mixture may work more effectively in the presence of other compounds due to additive or even synergistic effects. Conversely, you may miss seeing antiseptic activity in an extract if there is antagonism with other components. Even established pure antibiotics will be affected by other compounds. In the attached publication, we tested commercial antibiotics in the presence/absence of crude plant extracts and found (in some combinations) that the affect was much greater than the sum of the activity of the antibiotic or the extract separately ie synergistic activity. 

Sorry, the publication did not add. Here it is this time.

Article Interactive antimicrobial and toxicity profiles of conventio...

If such a compound has highest bioactivity, purest compound will have higher activity. If in mixture other compounds are more potent, you might observe contrary effect. However, there is also a chance that there will be some synergistic effects, improving the efficiency of a combination.

Here are three publications (two reviews and a paper) that deal with the topic - synergy and antagonism of constituents in crude extracts. Hope they help!

Purified compound and Crude extract may have different activity. In some cases a similar group of purified compounds have more activity. There are possibility of pure compound be inactive. Some formulations of algal crude extract  have more activity than the purified compound. In the same there are chances for your pure compound is more active than crude. You have to prove it in wet lab. We cannot predict.

Dear All,

Thank you very much for your kind opinions. I have tried conducted the assay using each fractions that I purified from the preparative TLC. It doesn't seems like inhibit much compare to the one I have done with crude extracts. I'm not sure whether is it due to the low concentration. I used 5mg/mL for the purified ones. But the crude I'm using 50mg/mL. Is this problem here? Thanks

Candace Lee you are right the low concentration will effect the inhibition. But when it is inhibit in lower concentration there comes the drug potential.You can compare with similar concentration of crude and purified compound.Then only you can come to a conclusion.

Not always, some times crude extracts are more effective than purified compounds, since they have number of phyto-chemicals, due the synergistic effect activity of crude extract may high or some times activity of pure compound is more because concentration of the active compound would be more compared to crude extract, the effect of crude extract or pure bio-active compound is purely depend on nature of compound.

Dear Candace Lee. Unfortunately you did not tell what kind of assay method that you used. The antimicrobial assay that you use for determination of  antimicrobial activity of your sample have a significant influence to the results. If you used a diffusion based method, and your sample have a poor diffusion ability through the medium, you cannot detect the activity of your sample. The dilution based method is more reliable in the above case.

You can try bioautography method of evaluation to check the antimicrobial activity of crude extract and purified compound, it will give ultimate result for your question.

From herbal or medicinal plants dried powder, we need to consider that our herbal or crude is sensitive for high temperature or not. If so ,cool extraction, perculation and maceration, are the best to keep compound safe. If its background is ok for high temperature, sohxlet and ASE extraction are good for that. CO2  supercritical fluid is a non organic solvent using.

I agree with Andria Agusta. If you can specify the activity that you perusing, I will advise you to used the bioguarded  isolation assay. where you following your active compunds from plant extract until you get  pure compound. You can easily fractionate extract by using different ratio of mobile system. 

Some bioactive compound is more active than the extract that is our luck, my experience I got the single active compound, depending on its structure, usually aromatic ring with hydroxy, polyphenol side chain bringing its active. Some of my colleque has isolated the single compound from the active extract,following the activity, unfortunately it was inactive. We need to see the structure to predict  biological activity, sometimes. We can test another biological activity for the non active compound, it may useful.

Hi Dr. Andria, I'm using well diffusion method but I actually modified the method. My fungi doesn't have spores, therefore I have to grow it sideways by culturing the plug few cms beside the well with extract. I tried to use the dilution base as well but the blank solvent inhibits the growth of the fungi as well. Thats the reason I tried to use well diffusion method. But when I tested with crude it works well. 

Dr Thippeswamy, I couldn't use bioautography method for the evaluation of the antifungal properties because the fungi that I use have no spores. I couldn't spray on the plate as well. The only way I can use is to grow the fungi is using its plug. 

Well, if the solvent also produce inhibition in broth dilution method, alternatively you can use agar dilution method. Also the used of solvent in the assay must be carefully selected. DMSO with max. 5% (if possible below than this) in the final concentration did not inhibit most of microbial growth.

Bioactivity-guided fractionation is the best method for isolating biologically active compounds from the active crude extract. generally the isolated compound is more active than the crude extracts if there is no synergistic effect among the isolated compounds as it is the case in most essential oils. TLc-bioautography gives quick results about the number of active compounds in the extract if you have an optimal solvent system for resolving the crude drugs into its components.

Perform Bioactivity guided fractionation of crude extract. It is better way to isolate the potent compounds from extracts.

crude extracts is the first step to purify your compound. if you target a compound in the crude extracts which already is known use standard compound or inetrnational library. if it is unknown you need NMR.

Yes, commonly purified compound showed good effect. Then there is chance to develop as drug.

Synergistic action of more compounds in crude extracts has chance to get more potency to crude extract.

If it is in crude form, you cannot estimate the exact inhibition activity of your compound on particular bacteria/fungus. Because, crude sample will have many compounds in it. So along with your desired compound some other compound may show inhibition. 

And, crude sample may show more activity (if your crude sample contains inducer of your inhibitor).

Some pure compound yes, it's active, but some  of them, inactive, depending on compounds and the structure relationship between functional groups and the targeting site of the compounds / microbial/ diseases react to it. Another thing is synergistic between compounds in crude extracts, they work together, help and support each other, but then when we do purification and following to their bioactivity until the end of isolation to pure compound, it's inactive, and maybe fortunately active, most of my work they were quite active. Toxicity is one thing we should consider of the purified compound.