Using water as a solvent for extraction, two processes were used as described below:
1. Fresh leaves of the plant collected and instantly extracted with hot water.
2. Leaves were collected, then sun drying carried out, followed by extraction with water.
Among the above two methods, the concentration of active ingredient was found to be appreciably higher in process 1.
Following process 2, the yield was very low. Solvent was hot water in both cases.
Does it has something to do with the use of fresh leaves and drying leaves in the sun. Heat is applied in both the cases but results are different. Suggestions are welcome.
The difference in the yield may occur due to sun drying. The active constituent may have degraded due to sun drying. Also due to drying the darkening of the leaves takes place, which may be due to oxidation of pigments or polymerization of certain polyphenols. The extraction of those color pigments and polymers after drying may get enhanced compared to the active constituent. The fresh leaves have certain moisture content in it which may help the active constituent get extracted easily.
Direct sun drying is not recommended for drying of plant tissue, as it will lead to damage and oxidation of some compounds. Drying of plant tissue using freeze dryer after grinding would help to protect the compounds and enable the storage of plant material for a period of time until use
It may be difficult to grind fresh plant tissue without drying, and there is also a good chance that active constituents might degrade due to enzymatic, fungal or bacterial action if extraction is not carried out immediately. Freeze-drying in or near the field may be impractical. Although not ideal, drying material in the shade is better than sun-drying, and use of an air-circulating stove at not more than 40 °C is better still.
Hot air oven with circulating air is preferable as suggested by Bruce Kennedy Cassels but question is deviating . topic is about percentage of yield i am not sure but i think its due high quantities of proteins, carbohydrates, chloroplast and other nutritive matter in fresh leaf when compared to dry one
In some cases, when plant material is dried (air circulating stove or freeze drying) complex compounds as proteins, starch, etc can encapsulate the active metabolites reducing yield. For example, when I analysed glycoalkaloids in fresh and freeze dried potato tubers, using the same NMKL official method, the reduction of glycoalkaloids recovery in freeze dried material was higher than 50%. With dried tissue you can extract twice or more to increase yield.
In some species extraction yield in dried tissues (freezed-dried) is believed to be lower than in fresh ones, even though freezing allows compounds to remain stable.
As it was mentioned above, sun drying may carry on degradation of several internal compounds.
I would rather recommend trying to compare the results of the extractions in the same kind of tissue if possible.
Sunlight is very hard to control. It can lead to temperatures that are not recommended for drying plant materials depending upon climatic and meterological conditions. Also, sunlight can provoke thermally or ultrviolet light-induced reactions of phytoconstituents exhibiting active chromophores.
Also, you have mentioned sunlight, not ambient (or plant surface) temperature at which drying was performed. Some phytoconstituents, such as artemisinin, are present in freshly harvested Artemisia annua leaves, but inadequate drying at temperatures that are not high enough to deactivate enzymes will lead to low or no yield of this substance in dry leaf materials.
Given the initial result, I would recommend drying under more controlled conditions in the lab in future comparisons of yields.
I have worked on different extraction methods for plant powder in same solvents and have found significant difference in the yield.
I do agree with the suggestions about loss of phytochemicals during drying process. Also presence of primary metabolites in extent in the fresh samples.
If you are focusing on some particular component from the plant then do go for quantitation of the same from extract obtained from bith fresh and dried sample. and do let us know the results.
There is lot of difference in the yield. In wet / fresh tissues, due to water content, yield is reduced, whereas, in case of dry tissue, the yield is normally high. If you determine extractive value, you will find the difference.
yes . there will be difference in the water soluble costituents when extracted with fresh leaves compared to dried leaves.The solvent water can better penetrate the fresh leaves and good digestion takes place to yield higher constituents. In case of dried leaves water solvent penetration will be less and less yield.Whereas with organic solvents the converse is true.i.e. Dried leaves yield higher constituents with organic solvents.
Yes solubility will be different in different mode of extraction. As each mode of extraction has different physical conditions. The solubility also depends on the nature of sample.
When water is solvent, fresh leaves give higher yield due to quick extraction as the constituents are already solubilized in the water pre-existing in leaves. Dry leaves are good for organic solvent extraction.
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