To find the total phenol content, i have seen some researchers using dry samples and others fresh samples!! Which one is right? Should we use dry or fresh sample?
It depends on the aim of your work. Are you interested in providing a description of how many polyphenols can be ingested eating a fresh apple or drinking a cup of tea?
Extracting phenolics is an art!
Indeed it is a matter of what you want to study, and additionaly if you have a clear applied aim, of the realistic possibilities in the final application.
Another question is dried sample yes, but dried how? Some drying procedures (hot air!) result in oxidation and in irreversible binding of polyphenols to other molecules in the plant sample.
If fresh, per definition the sample is not stable (and my not be available all through the year). In extraction, you will have to be careful to avoid oxidation. If costs is not a question, freeze-drying is often the prefered method for stabilization.
We discussed this actually in a recent publication (Bureau et al., JAFC 60 (2012) 3551.
Also consider the possible artefacts in the total phenol assays of Folin-Ciocalteu: interference of other reducing agents such as ascorbic acid, variation of the response with oxidatin (typically it increases with slight oxidation, then decrease).
Thank you both Renato and Catherine,
We are studying the effects of total phenols on preference of mango by the orintial fruit fly. We shade dry the sample and then powder it in a blender. This powder is extacted with 80% Methanol (Known volume) and then the extarct is used for total phenol estimation.
If i use fresh samples won't water interfere the results??
Please suggest any best method to do this work. It would be of great help.
Catherine, can i please have the publication mentioned in your answer. It can be sent to [email protected]. Please dont mind. It would really help us in our research.
Dear Vivek,
If you extract from fresh magoes, you have to take in account the water from the mangoes into the 80% methanol, i.e. start from more concnetrated methanol (one single extraction or repeated until no more compound is extracted?). 80% methanol is a good concentration to start; my experience is that we often get best yields with a bit more water.
Greetings Mr. Vivek,
I agree with the answers given by Mr. Renato and Ms. Catherine. It all depends on the aim of your experiment. Some researchers prefer to address the total phenols content in terms of fresh sample as to simulate the daily intake of fresh samples. Nowadays, we have capsules and tablets made from herbs/functional fruits (either oven dried, freeze dried or sprayed dried) by manufacturers. Thus the total phenolic acid in these capsules/tablets will be calculated based on thier dry mass as to simulate the daily intake of these pills.
And of course, the values of TPC for both fresh and dried samples (same weight and extracted using the same protocols) WON'T be the same. Dried samples might give a higher reading as the water content in fresh sample will 'dilute' the phenolic acids.
All the best for your research yeah :-)
Thanks a lot Catherine. Your answers were really helpful. But, how can i pre-determine the water content of mangoes. I mean, each mango sample would have different water content. I have to determine the water content for each sample!!!?? and the water content changes from season to season, species to species!!! Can't i just shade dry all the sample at ones and powder them under liquid nitrogen and then extract the total phenol content!!! Please guide me with this. Thank you again Dr. Catherine. :)
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