Expression of Results
Authors have used different ways of expressing the biological activity of plant ex-
tracts based on the technique used. Initially the agar diffusion method led to re-
sults being expressed in the width of the inhibition zone. Later the MIC values of
5.10 Expression of Results 107
Fig. 5.1 Bioautography of acetone leaf extracts of eight Combretum species
sprayed with Enterococcus faecalis, incubated, and then sprayed with tetrazolium
violet. White areas indicate the presence of antibacterial compounds.
Fig. 5.2 Antioxidant activity of acetone leaf extracts of several Combretum
species determined by spraying with methanolic DPPH solution. White areas
indicate the presence of antioxidant compounds in extracts.
extracts were determined. Both of these techniques gave information on the activ-
ity of the extracts and were used to isolate biologically active components or evalu-
ate whether the ethnobotanical use of plants could be justified. These techniques
gave little quantitative information about the plants. We proposed that the quantity
of material extracted from 1 g of dried plant material be divided by the MIC value
to give the total activity of the plant. The unit is mL g–1, and indicates the largest
volume to which the biologically active compounds in 1 g can be diluted and still
inhibit the growth of bacteria. If the results of other bioassays are also expressed in
relative quantity of activity present in plants investigated, the most promising
plants to use in rural areas for traditional health care can be identified [44].
This technique can also be of great value in bioassay-guided fractionation if the
total activity of a fraction is expressed in milliliters per fraction by dividing the
mass in milligrams by the MIC in mg mL–1. This volume indicates to what level
that fraction can be diluted and still inhibit growth of the test organism. By follow-
ing this approach, any loss of activity is soon detected and it ensures that minor bi-
ologically active compounds are not isolated in the mistaken belief that they are
major active components [37].
Authors have used different ways of expressing the biological activity of plant ex-
tracts based on the technique used. Initially the agar diffusion method led to re-
sults being expressed in the width of the inhibition zone. Later the MIC values of
5.10 Expression of Results 107
Fig. 5.1 Bioautography of acetone leaf extracts of eight Combretum species
sprayed with Enterococcus faecalis, incubated, and then sprayed with tetrazolium
violet. White areas indicate the presence of antibacterial compounds.
Fig. 5.2 Antioxidant activity of acetone leaf extracts of several Combretum
species determined by spraying with methanolic DPPH solution. White areas
indicate the presence of antioxidant compounds in extracts.
extracts were determined. Both of these techniques gave information on the activ-
ity of the extracts and were used to isolate biologically active components or evalu-
ate whether the ethnobotanical use of plants could be justified. These techniques
gave little quantitative information about the plants. We proposed that the quantity
of material extracted from 1 g of dried plant material be divided by the MIC value
to give the total activity of the plant. The unit is mL g–1, and indicates the largest
volume to which the biologically active compounds in 1 g can be diluted and still
inhibit the growth of bacteria. If the results of other bioassays are also expressed in
relative quantity of activity present in plants investigated, the most promising
plants to use in rural areas for traditional health care can be identified [44].
This technique can also be of great value in bioassay-guided fractionation if the
total activity of a fraction is expressed in milliliters per fraction by dividing the
mass in milligrams by the MIC in mg mL–1. This volume indicates to what level
that fraction can be diluted and still inhibit growth of the test organism. By follow-
ing this approach, any loss of activity is soon detected and it ensures that minor bi-
ologically active compounds are not isolated in the mistaken belief that they are
major active components [37].
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