What is the reason explaining that the higher percentage contents of total polyphenols and total flavonoids significantly in dried mint leaves compared to the fresh ones?
Why does drying increase the biological activities (antioxidant and anti-inflammation) of total polyphenols and total flavonoids in plant leaf extract?
Also check https://www.researchgate.net/publication/281687611_Effects_of_drying_process_on_total_phenolics_antioxidant_activity_and_flavonoid_contents_of_common_mediterranean_herbs
Hi. The full details are available in the following article:
https://res.mdpi.com/d_attachment/sustainability/sustainability-12-08586/article_deploy/sustainability-12-08586-v2.pdf
I hope that the following papers could be useful. Good luck
https://doi.org/10.5897/JMPR11.916
https://doi.org/10.1007/s11694-016-9372-6
https://doi.org/10.1016/j.heliyon.2021.e06678
https://doi.org/10.15666/aeer/1302_583595
I used two methods in drying lemon pulp, freeze drying and solar drying not sun drying. Heat reduces water content and enzymatic catalysis, resulting in less decomposition of phenolic compounds. Furthermore, freeze drying method yielded the closest values with respect to colour values, total phenol content and antioxidant capacity to those of fresh samples when compared to the another one.
Depending on the level of oxidation, heat exposure, drying time, applied pretreatments etc., tissue damages in plant materials (including cell wall collapse, capillary and vacuole rupture) may occur. And again depending on the process and its conditions, these changes (which are normally accepted as unfavourable) may enhance the extraction yield of the bioactive materials from the plant tissue. The more detailed explanations can be found in the following papers. Good luck.
Article Influence of Carbonic Maceration Pre-treatment on Functional...
Article Improvements in drying characteristics and quality parameter...
Very simple! Evaporation of water increases the concentration of the available phenols in the sample.
The answer is not so simple, since the concentration of the specific phenols analyzed by HPLC and calculated be mg/g dry weight of the sample. Water is not concerned. We also found that the enzymatic reaction during slow drying like that occurs in tea leaves, but not by heat -shock before drying. in green tea leaves.
In my understanding, there might be some syntheses to generate new phenolic compound, or in other word, the transformation of one phenolic compound to another one with higher antioxidant capacity. Also, the plant cell wall can adosrb some soluble phenolic compounds once the vacuole disrupts during drying, thus helping retain the phenolics. Moreover, the affiliation between bound phenolics and cell wall could be affected by drying, resulting in the release of phenolics from cell wall. More fundamental studies are needed to find more experiemntal evidences.
Dear Dr. Yang Tao:
Thank you for your interesting answer. My plant is perilla tea leaf. I should explore for more information.
Zou B, Wu J, Yu Y, Xiao G, Xu Y. Evolution of the antioxidant capacity and phenolic contents of persimmon during fermentation. Food Sci Biotechnol. 2017 May 29;26(3):563-571. reported that.
"The changes in antioxidant capacity and phenolics of persimmon during alcoholic fermentation, acetification, and short aging were investigated. An increase in the antioxidant activity was observed when persimmon was transformed from puree to vinegar."
They showed that alcoholic and acetic fermentation can improve the antioxidant capacity of persimmon fruit.
Dear Prof. I also found an increase in polyphenolic components in redried tobacco leaves. In addition to tissue damage and polyphenols interconversion that might enhance the measured polyphenols content, I wonder if it is also possible that glycosides and esters would be decomposed into phenolics during heat exposure?
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