According to the guidance notes the drying process of plant materials should be completed at the stage when there still remains 6 - 10 percent of moisture in the plant. Overdrying under e.g. 6 % seems to decrease the content of carotenoids, ascorbic acid and essential oils - according to the few references I have found. Thus evidence is very limited. Our own tests have shown a slight tendency to decreasing contents of phenolics.
I would be happy to get some new hints, experiences or explanations of this phenomenon!
Hello,
I have experience with EOs exaction. The literature recommends s short period drying of the plant material until 10% moisture content. I collected plant material in flowering season and dried it es recommended and them used Clevenger apparatus to get EO. 3 and 6 months later i distilled the material for its EO. The weight to weight ratio changed slightly increasing in 3 month period and den decreasing after 6 months but this difference was in 0.2%. The content of the oil changed more drastically. With more time and less moisture I had more heavier components and less lighter ones. I did not try to analyse the different moisture content for the same time period so take this findings with a grain of salt. Difference in carotenoid content and ascorbic acid content could arise through their natural decomposition over time. There is no reason for them to decreas with drying of the material. I do not expect them to evaporate so with less water their % should increase in plant material. There can be an impact of over-drying on the extraction process.
Phenolitic compounds, especially lower-weight ones can evaporate so you can lose some in drying process but mostly they degrade over time.
First no constants in phytocemicals persrntage due to environmental diversity and other conditions such as age of collected plant and time of collection. Also drying conditions affected volatile compound and may affect the composition of steroselective compunds. Their are several studies on age of plant , composition of phytocemicals, solvent of extraction method in marine alge which infected this environmental diversity and conditions variability
Thanks everybody for your reply! My problem relates to the normal convective drying process, which is still the most common method of preserving cultivated and wild plants for the later utilization as food or as a health promoting ingredients. The moisture content I mentioned means the weight loss in the d.m. determination at the end of the drying process. It is thus grams (of weight loss)/grams of dried material at the end of the drying process.
In the natural product business the management of the drying process is of importance. We should focus on determining the right ending point for drying of each product to be dried, if the overdrying really decreases the content of those valuable compounds we want to preserve. Question still remains open! Thanks especially to Mateo! Your thoughts gave me some new ideas.
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