It depends on which compounds you want to extract. Some are heat sensitive, hence duration of drying might take different effects.

Drying at 50 C for a long time would lead to degradation or isomerization of pigments/phytochemicals. I believe, it is better to go for freeze drying. Or drying in N2 atmosphere. 

The longer time it takes - more is the chance of modifications and degradation - go for a quicker process.

thank you.

Dear Fairuz Iman

To me your question is not clear. Do you want to dry the plant material before aqueous/solvent extraction or the plant crude extract before separating the compounds from the extract?

Best wishes.

Dear Iman

You may check the following interesting link.

Good luck.

https://www.researchgate.net/post/How_long_time_i_can_keep_a_plant_extract_by_refrigerator_or_by_freezer_at-20_C?tpr_view=914fcf5a-5d61-4c38-8f97-2a2a34c60571_2

thank you. i was referring to the step of drying the plant material before the aqueous/solvent extraction. if i dry the extracts in 50 degree incubator for more than 3 days for determination of the antibacterial and immunomodulatory activity of the extracts, how can it influence the research outcome? 

Dear Fairuz Iman

If your material is bark or root or wood or seed sun drying and if the material is leaf or flower or inflorescence or buds shade drying the material before powdering and extracting it is preferable. You can also think of extracting the fresh material.

You can have a look at the following thread.

Good luck.

https://www.researchgate.net/post/Which_do_you_recommend_fresh_or_semi-dry_or_dry_biomass_tissue_for_an_aqueous_solvent_extract_or_for_extracting_isolating_separating_phytochemicals