Extraction of Plant Material
Which is the Best Extractant?
Scientists have used many different solvents to extract plant material. To examine
which extractants would be the most useful, freeze dried and finely ground leaves
of two plants with known antimicrobial activity, Anthocleista grandiflora [32] and
Combretum erythrophyllum [22], were extracted with a series of extractants of vary-
ing polarity (methylene dichloride, acetone, ethanol, methanol, methanol/chloro-
form/water and water) at a 1 to 10 ratio of dry material to solvent in each case [33].
The following parameters were investigated with the different extractants: the
quantity extracted, the rate of extraction, the diversity of different compounds ex-
tracted, the diversity of inhibitory compounds extracted, the ease of subsequent
handling of the extracts, the toxicity of the solvent in the bioassay process, and the
potential health hazard of the extractants. The different solvents were compared by
grading on an arbitrary five-point weighted scale. As shown in Table 5.1, acetone
gave the best results with these plants with an arbitrary value of 102 followed by
methanol/chloroform/water (MCW, 81), methylene dichloride (MDC, 79), metha-
nol (MeOH, 71), ethanol (EtOH, 58) and water with 47 [33].
5.7 Extraction of Plant Material 103
Table 5.1 Comparison of extractants on different parameters based on a fivepoint
scale (0–4) and with different weights allocated to the different parameters
(A = results for A. grandiflora and C = results for C. erythrophyllum) [33].
Weight Acetone EtOH MeOH MCW MDC Water
Parameter A C A C A C A C A C A C
Quantity extracted 3 6 3 9 6 12 12 12 12 3 3 9 9
Rate of extraction 3 12 15 12 12 12 12 12 12 15 15 9 9
Number of compounds extracted 5 20 20 10 15 15 20 10 15 10 15 5 5
Number of inhibitors extracted 5 20 20 0 10 20 15 20 20 20 15 0 0
Toxicity in bioassay 4 16 16 8 8 0 0 8 8 8 8 16 16
Ease of removal 5 20 20 5 5 10 10 10 10 20 20 0 0
Hazardous to use 2 8 8 8 8 2 2 6 6 6 6 8 8
Total 102 102 52 64 71 71 78 83 79 79 47 47
Extraction Period and Efficiency
Very finely ground plant material suspended in an inert dosing vehicle mobilizes
from the rat peritoneal cavity into the blood almost as fast as if it had been injected
in a soluble form [34]. It may therefore be possible to shorten the extraction period
by grinding the leaves finer and by shaking at a very rapid rate for a short period.
The average diameter of the particles of the plants that we ground using a mill was
about 10 μm. After three 5-min extractions, 49% of the A. grandiflora and 38% of
the C. erythrophyllum dry mass was extracted [33]. These values were even higher
than values obtained after 24 h in a shaking machine with less finely ground mate-
rial. Four 5-min sequential extractions of very finely ground A. grandiflora shaken
with solvent at a high rate extracted 97% of the total antimicrobial activity
Which is the Best Extractant?
Scientists have used many different solvents to extract plant material. To examine
which extractants would be the most useful, freeze dried and finely ground leaves
of two plants with known antimicrobial activity, Anthocleista grandiflora [32] and
Combretum erythrophyllum [22], were extracted with a series of extractants of vary-
ing polarity (methylene dichloride, acetone, ethanol, methanol, methanol/chloro-
form/water and water) at a 1 to 10 ratio of dry material to solvent in each case [33].
The following parameters were investigated with the different extractants: the
quantity extracted, the rate of extraction, the diversity of different compounds ex-
tracted, the diversity of inhibitory compounds extracted, the ease of subsequent
handling of the extracts, the toxicity of the solvent in the bioassay process, and the
potential health hazard of the extractants. The different solvents were compared by
grading on an arbitrary five-point weighted scale. As shown in Table 5.1, acetone
gave the best results with these plants with an arbitrary value of 102 followed by
methanol/chloroform/water (MCW, 81), methylene dichloride (MDC, 79), metha-
nol (MeOH, 71), ethanol (EtOH, 58) and water with 47 [33].
5.7 Extraction of Plant Material 103
Table 5.1 Comparison of extractants on different parameters based on a fivepoint
scale (0–4) and with different weights allocated to the different parameters
(A = results for A. grandiflora and C = results for C. erythrophyllum) [33].
Weight Acetone EtOH MeOH MCW MDC Water
Parameter A C A C A C A C A C A C
Quantity extracted 3 6 3 9 6 12 12 12 12 3 3 9 9
Rate of extraction 3 12 15 12 12 12 12 12 12 15 15 9 9
Number of compounds extracted 5 20 20 10 15 15 20 10 15 10 15 5 5
Number of inhibitors extracted 5 20 20 0 10 20 15 20 20 20 15 0 0
Toxicity in bioassay 4 16 16 8 8 0 0 8 8 8 8 16 16
Ease of removal 5 20 20 5 5 10 10 10 10 20 20 0 0
Hazardous to use 2 8 8 8 8 2 2 6 6 6 6 8 8
Total 102 102 52 64 71 71 78 83 79 79 47 47
Extraction Period and Efficiency
Very finely ground plant material suspended in an inert dosing vehicle mobilizes
from the rat peritoneal cavity into the blood almost as fast as if it had been injected
in a soluble form [34]. It may therefore be possible to shorten the extraction period
by grinding the leaves finer and by shaking at a very rapid rate for a short period.
The average diameter of the particles of the plants that we ground using a mill was
about 10 μm. After three 5-min extractions, 49% of the A. grandiflora and 38% of
the C. erythrophyllum dry mass was extracted [33]. These values were even higher
than values obtained after 24 h in a shaking machine with less finely ground mate-
rial. Four 5-min sequential extractions of very finely ground A. grandiflora shaken
with solvent at a high rate extracted 97% of the total antimicrobial activity
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