Dear 

The water extract are dried by using freeze dryer, which is have no effect on the extract content. The use of rotary evaporator may affect the phenolic content especially if the compounds are not thermal stable, as many flavonoids. 

dear all thanks for your promptly response.

Dear Alsiding

How about gallic acid, is it thermal stable? one of the parameter that I checked is total phenolic content by using gallic acid standard as calibration curve. if you have any journal related on that, you can send to me too. thanks

Dear

According to your methodology, you will measure all phenolic content not only gallic acid. HPLC methodology is more specific to detect selected compounds with standard for each. However it is not necessary to have gallic acid in your extract to use it in spectrometry methodology. However many phenolic compounds are not thermal stable, when you don't have any idea about the specific compounds in your extract you have to be careful and not use any heating process may influence your assays.

Good luck

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 Dear Azlan,

          Freeze-drying of plant extract is a widely used drying method that is considered as the best possible drying technique. The extract is frozen and dried under vacuum conditions at low temperatures.

          You can use the freeze drying techniques to removes the solvent at a very Low processing temperature, the concentration takes place at the freezing point of the extract (e.g. -5ºC). All microbiological and chemical reactions have virtually stopped. There is no thermal damage to active components.

Dear Dr Fatma Aly

Thanks for your answer, actually I used freeze dryer to dry raw material which is dragon fruit peel before extraction. But I never try to use freeze dryer after extraction process. But if i used freeze drying technique to remove solvent content in my extraction sample, for sure my sample extraction will be frozen, mean i need to do further extraction, is it? please advise. I need solution(free solvent) from extraction to test Total phenolic content and mineral profile, my solvent extraction just ultra pure water. thanks