Collecting, Drying, and Storage of Plant Material
Any fungal contamination on leaves leads to large differences in the chemical com-
position and biological activity of leaf extracts. Any plant material with visible fun-
gal growth or insect attack is therefore discarded. We do not collect material that is
wet or before dew has dried off completely, and collected material is dried as quick-
ly as possible.
Collecting plant material in nature poses difficulties with regard to drying under
controlled conditions but we follow guidelines to facilitate the process. We never
store material even for short periods in plastic containers. We use paper bags to
collect the leaves and within a short period spread leaves out on paper in a dust-free
environment in the shade. When large quantities of material are collected this is
more difficult and we then use open-mesh (c. 5 mm) bags that are used to sell
oranges and other fruit. We fill bags about half full with plant material and then
suspend them from strings in a room at room temperature in the shade for approx.
10 days until there is no mass change.
In most cases scientists have used dried material for extraction of biologically ac-
tive compounds. This makes sense because during drying, membranes of plant or-
ganelles containing different secondary compounds are destroyed, making extrac-
tion more efficient. Labile compounds may, however, be destroyed during the dry-
ing process or if hydrolase enzymes are released when vacuolar membranes are
broken during the drying process. Artifacts may be formed during drying, and this
is a major disadvantage in plant metabolic studies. This process is probably unim-
portant in the investigation of biologically active compounds because the artifact
may be the active compound useful in ethnomedicine. For practical reasons, tradi-
tional healers and especially traders in traditional medicine use predominantly
dried material. The difficulty with using fresh leaves is that it is tedious to remove
water from an extract. When bulbs or corms are used, it takes a long time to dry the
bulbs and undesirable changes may occur if bulbs are cut into slices and then dried.
The drying process has a major effect on the antibacterial activity of Combretum
erythrophyllum leaves. Freeze drying led to lower activity than other drying proce-
dures, probably because volatile antibacterial compounds were lost. Slow drying at
very low temperatures yielded the highest activity (IE Angeh, personal communi-
cation).
One would expect that there would be differences in biological activity and
chemical composition between dried and fresh material after extraction. When
fresh Acacia leaves were extracted, it led to a higher yield but lower antibacterial ac-
tivity than dried leaf extracts [29]. When bulbous material is extracted the water
content of the material should be brought into consideration in determining the
composition of the extractant. If, say, 70% acetone is used, the water content of the
plant material should be taken into consideration to ensure that reproducible re-
sults are obtained [30].
Storage conditions may also affect the activity and chemical constituents of plant
material. It appears that plant material stored in a dry condition in the dark does
102 5 Plant Extracts Used to Manage Bacterial, Fungal, and Parasitic Infections in Southern Africa
not lose any biological activity over a long period. Leaves of C. erythrophyllum col-
lected in the same area and stored in herbaria for up to 92 years did not lose any
antibacterial activity and the chemical composition was very similar to that of re-
cently collected material [31].
Any fungal contamination on leaves leads to large differences in the chemical com-
position and biological activity of leaf extracts. Any plant material with visible fun-
gal growth or insect attack is therefore discarded. We do not collect material that is
wet or before dew has dried off completely, and collected material is dried as quick-
ly as possible.
Collecting plant material in nature poses difficulties with regard to drying under
controlled conditions but we follow guidelines to facilitate the process. We never
store material even for short periods in plastic containers. We use paper bags to
collect the leaves and within a short period spread leaves out on paper in a dust-free
environment in the shade. When large quantities of material are collected this is
more difficult and we then use open-mesh (c. 5 mm) bags that are used to sell
oranges and other fruit. We fill bags about half full with plant material and then
suspend them from strings in a room at room temperature in the shade for approx.
10 days until there is no mass change.
In most cases scientists have used dried material for extraction of biologically ac-
tive compounds. This makes sense because during drying, membranes of plant or-
ganelles containing different secondary compounds are destroyed, making extrac-
tion more efficient. Labile compounds may, however, be destroyed during the dry-
ing process or if hydrolase enzymes are released when vacuolar membranes are
broken during the drying process. Artifacts may be formed during drying, and this
is a major disadvantage in plant metabolic studies. This process is probably unim-
portant in the investigation of biologically active compounds because the artifact
may be the active compound useful in ethnomedicine. For practical reasons, tradi-
tional healers and especially traders in traditional medicine use predominantly
dried material. The difficulty with using fresh leaves is that it is tedious to remove
water from an extract. When bulbs or corms are used, it takes a long time to dry the
bulbs and undesirable changes may occur if bulbs are cut into slices and then dried.
The drying process has a major effect on the antibacterial activity of Combretum
erythrophyllum leaves. Freeze drying led to lower activity than other drying proce-
dures, probably because volatile antibacterial compounds were lost. Slow drying at
very low temperatures yielded the highest activity (IE Angeh, personal communi-
cation).
One would expect that there would be differences in biological activity and
chemical composition between dried and fresh material after extraction. When
fresh Acacia leaves were extracted, it led to a higher yield but lower antibacterial ac-
tivity than dried leaf extracts [29]. When bulbous material is extracted the water
content of the material should be brought into consideration in determining the
composition of the extractant. If, say, 70% acetone is used, the water content of the
plant material should be taken into consideration to ensure that reproducible re-
sults are obtained [30].
Storage conditions may also affect the activity and chemical constituents of plant
material. It appears that plant material stored in a dry condition in the dark does
102 5 Plant Extracts Used to Manage Bacterial, Fungal, and Parasitic Infections in Southern Africa
not lose any biological activity over a long period. Leaves of C. erythrophyllum col-
lected in the same area and stored in herbaria for up to 92 years did not lose any
antibacterial activity and the chemical composition was very similar to that of re-
cently collected material [31].
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