Journal of Ethnopharmacology 134 (2011) 775–780
Contents lists available at ScienceDirect
Journal of Ethnopharmacology
journal homepage: www.elsevier.com/locate/jethpharm
A comparative study of the antimicrobial and phytochemical properties between
outdoor grown and micropropagated Tulbaghia violacea Harv. plants
B. Ncube, V.N.P. Ngunge, J.F. Finnie, J. Van Staden ∗
Research Centre for Plant Growth and Development, School of Biological and Conservation Sciences,
University of KwaZulu-Natal Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa
a r t i c l e
i n f o
Article history:
Received 2 November 2010
Received in revised form 7 January 2011
Accepted 21 January 2011
Available online 1 February 2011
Keywords:
Antibacterial
Antifungal
Micropropagation
Phenolic compounds
Saponins
Tulbaghia violacea
a b s t r a c t
Aim of the study: The study aimed to compare the antimicrobial and phytochemical properties of in vitro
cultured and outdoor grown Tulbaghia violacea plants in the quest to validate the use of micropropagated
plants as alternatives to outdoor grown plants in traditional medicine. Tulbaghia violacea is used extensively in South African traditional medicine for HIV/AIDS patients and in the treatment of gastrointestinal
ailments, asthma, fever and tuberculosis.
Materials and methods: Extracts of micropropagated and outdoor grown Tulbaghia violacea plants were
evaluated for their antibacterial and antifungal activities against Bacillus subtilis, Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus and a fungus Candida albicans using microdilution methods.
Saponins and phenolic compounds including condensed tannins, gallotannins and flavonoids were
quantitatively determined using spectrophotometric methods. A qualitative test for saponins was also
carried out.
Results: The petroleum ether (PE) extracts of micropropagated plants and dichloromethane (DCM)
extracts of outdoor grown plants showed good antibacterial activity, each against two bacterial test
strains. PE extracts of micropropagated plants showed the best antibacterial activity with a minimum
inhibitory concentration (MIC) of 0.39 mg/ml against Bacillus subtilis. Good MIC (<1 mg/ml) and minimum fungicidal concentration (MFC) values of 0.78 mg/ml were only obtained in DCM extracts of outdoor
grown plants. MIC and MFC values for water and ethanol extracts of both micropropagated and outdoor
grown plants were similar and in the range 3.125–12.5 mg/ml. Total phenolics, gallotannins, flavonoids
and saponins were significantly higher in micropropagated plants than in outdoor grown ones. In all
cases, the amounts of phytochemical compounds in micropropagated plants were more than twice that
of outdoor grown plants except for condensed tannins.
Conclusion: The results form a good basis for the use of Tulbaghia violacea micropropagated plants as a
complement to the outdoor grown plants in traditional medicine.
© 2011 Elsevier Ireland Ltd. All rights reserved.
1. Introduction
Tulbaghia violacea Harv. (Alliaceae), bulbs and leaves are used
traditionally in the southern African region for the treatment of gastrointestinal ailments, asthma, fever, and tuberculosis (Hutchings
et al., 1996; Van Wyk and Wink, 2004). The freshly prepared herbal
Abbreviations:
ATCC, American type culture collection; BA, 6benzylaminopurine; CFU, colony forming unit; CTE, catechin equivalent; DCM,
dichloromethane; DE, diosgenin equivalent; EtOH, ethanol; GAE, gallic acid equivalent; INT, p-iodonitrotetrazolium chloride; LC, least concern; MIC, minimum
inhibitory concentration; MFC, minimum fungicidal concentration; MS, Murashige
and Skoog; NAA, a-naphthalene acetic acid; PE, petroleum ether; PGR, plant growth
regulators; YM, yeast malt.
∗ Corresponding author. Tel.: +27 33 2605130; fax: +27 33 2605897.
E-mail address: rcpgd@ukzn.ac.za (J. Van Staden).
0378-8741/$ – see front matter © 2011 Elsevier Ireland Ltd. All rights reserved.
doi:10.1016/j.jep.2011.01.039
remedies are used as decoctions that are either taken orally or as
enemas (Hutchings et al., 1996). Due to the devastating effects and
the high prevalence rate of HIV/AIDS in South Africa, the search for
anti-HIV agents has stimulated the screening of medicinal plants
based on their ethnobotanical data (WHO, 1989; Motsei et al., 2003;
Klos et al., 2009). Tulbaghia violacea is one of these plants and has
shown promising antimicrobial activity against some medically
important pathogenic bacteria and fungi that cause opportunistic
infections in HIV/AIDS patients (McGaw et al., 2000; Gaidamashvili
and Van Staden, 2002; Motsei et al., 2003). The plant has undoubtedly found its traditional use among HIV/AIDS patients. Young
Tulbaghia violacea plants are eaten as vegetables (Hutchings et al.,
1996). Apart from the medicinal and nutritive value, the plant is also
used extensively as an ornamental in South Africa (Bryan, 2002).
As a result of the extensive use and increased demand for medicinal plants, both formal and informal markets for these plants have
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B. Ncube et al. / Journal of Ethnopharmacology 134 (2011) 775–780
grown tremendously in South Africa. Most of the plant material
traded is from wild harvested plant stock (Mander and Mckenzie,
2005) and this acute harvesting is leading to local plant extinction
(Mander, 1998).
The basic idea behind sustainable harvesting is that a biological resource should be harvested within the limits of its capacity
for self-renewal. Importantly, the use of Tulbaghia violacea in traditional medicine involves the destructive harvesting of the whole
plant. Despite the plant being listed under the National Red List of
South African plants as of least concern (LC) (Raimondo et al., 2009),
the emerging interest and research emphasis being placed on the
improvement and validation of traditional medicine increases the
demand for these plants. This pressure exerts ecological instability on the resource base, hence the need for alternative medicinal
sources.
Although conventional cultivation of medicinal plants is a logical conservation strategy, it is challenged by a number of factors
such as land availability, climate, season, water availability, diseases and pests, and slow growth of plants (Pierik, 1987; Arikat
et al., 2004). The development and adoption of tissue culture methods has provided a means for rapid propagation of a large number
of uniform plants while maintaining their genotypes (Bryan, 2002).
The technology also allows an opportunity for ethnopharmacological exploitation of cells, tissues, organs or entire plants at their
early stages of growth. Application of the technology in traditional
medicine may offer benefits that include avoidance of collection of
endangered wild medicinal plant species and rapid production of
pharmacological compounds irrespective of seasonal and climatic
conditions (Pierik, 1987; Arikat et al., 2004). The success of this
strategy, however, depends on the validation of micropropagated
plants through pharmacological screening on their suitability for
use in traditional medicine.
In view of the medicinal importance of Tulbaghia violacea, the
present investigation was undertaken to compare antimicrobial
and phytochemical properties of micropropagated and outdoor
grown Tulbaghia violacea plants in an effort to validate and promote
the use of micropropagated plants in traditional medicine.
2. Materials and methods
2.1. Plant material
Tulbaghia violacea Harv. seeds (Silverhill Seeds Nursery, Cape
Town) were surface sterilised and germinated for 30 days on onetenth strength of Murashige and Skoog (MS) medium (Murashige
and Skoog, 1962). The medium was supplemented with myoinositol (0.1 g/L), without plant growth regulators (PGRs) and
sucrose. The pH of the medium was adjusted to 5.8 and solidified with 8 g/L No. 1 bacteriological agar (Oxoid Ltd., England). The
medium was sterilised by autoclaving at 121 ◦ C for 20 min. The photoperiod of the growth room in which the cultures were placed was
16/8 h light/dark at 25 ± 2 ◦ C.
Hypocotyls derived from in vitro grown seedlings were surface
sterilised. These were cultured on full strength MS medium supplemented with sucrose (30 g/L), myo-inositol (0.1 g/L) and various
concentrations of PGRs in the range 0–1.5 mM for NAA and 0–12 mM
for BA. The pH of the medium was adjusted to 5.8 and solidified with
agar (8 g/L). The medium was sterilised by autoclaving at 121 ◦ C for
20 min. Cultures were grown under 24 h light conditions at 25 ± 2 ◦ C
for three months. The plantlets were subcultured onto a medium
containing 1.5 mM NAA and 12 mM BA for a period of two months
before being taken for analysis.
Outdoor grown Tulbaghia violacea plants (12 years old) were
collected in summer (December) from the University of KwaZuluNatal Botanical Garden, Pietermaritzburg, South Africa and a
voucher specimen (NCUBE 04 NU) deposited in the University of
KwaZulu-Natal Herbarium (NU), Pietermaritzburg. Whole plant
samples (bulbs and leaves), including those of micropropagated
plants were then dried at a constant temperature of 50 ◦ C in an
oven and ground into fine powders.
2.2. Preparation of plant extracts
The ground samples were sequentially extracted with 20 ml/g of
petroleum ether (PE), dichloromethane (DCM), 80% ethanol (EtOH)
and water in a sonication bath containing ice for 1 h. The crude
extracts were then filtered under vacuum through Whatman No. 1
filter paper and the organic extracts concentrated in vacuo at 35 ◦ C
using a rotary evaporator. The concentrated extracts were subsequently dried at room temperature under a stream of cold air. Water
extracts were freeze dried and kept in airtight containers.
2.3. Antibacterial activity
Minimum inhibitory concentrations (MIC) of extracts for
antibacterial activity were determined using the microdilution
bioassay as described by Eloff (1998). Overnight cultures (incubated
at 37 ◦ C in a water bath with an orbital shaker) of two Gram-positive
(Bacillus subtilis ATCC 6051 and Staphylococcus aureus ATCC 12600)
and two Gram-negative (Escherichia coli ATCC 11775 and Klebsiella
pneumoniae ATCC 13883) bacterial strains were diluted with sterile
Mueller–Hinton (MH) broth to give final inoculums of approximately 106 CFU/ml (colony forming units). The dried crude organic
plant extracts were resuspended in 70% ethanol to a concentration of 50 mg/ml while water extracts were dissolved in distilled
water to the same concentration. One hundred microlitres of each
extract were serially diluted two-fold with sterile distilled water
in a 96-well microtitre plate for each of the four bacterial strains.
A similar two-fold serial dilution of neomycin (Sigma–Aldrich,
Germany) (0.1 mg/ml) was used as a positive control against each
bacterium. One hundred microlitres of each bacterial culture were
added to each well. Water and 70% ethanol were included as negative and solvent controls, respectively. The plates were covered
with parafilm and incubated at 37 ◦ C for 24 h. Bacterial growth
was indicated by adding 50 ml of 0.2 mg/ml p-iodonitrotetrazolium
chloride (INT) (Sigma–Aldrich, Germany) and a further incubation
at 37 ◦ C for 24 h. Since the colourless tetrazolium salt is biologically
reduced to a red product due to the presence of active organisms,
the MIC values were recorded as the concentrations in the last wells
in which no colour change was observed after adding the INT indicator. Bacterial growth in the wells was indicated by a reddish-pink
colour. The assay was repeated twice with two replicates per assay.
2.4. Antifungal activity
A microdilution method as described by Eloff (1998) and modified for fungi (Masoko et al., 2007) was used to determine the
antifungal activity of the extracts against Candida albicans (ATCC
10231). An overnight fungal culture was prepared in yeast malt
(YM) broth. Four hundred microlitres of the overnight culture were
added to 4 ml of sterile saline and absorbance was read at 530 nm.
The absorbance was adjusted with sterile saline to match that of a
0.5 M McFarland standard solution. From this standardised fungal
stock, a 1:1000 dilution with sterile YM broth was prepared giving a
final inoculum of approximately 106 CFU/ml. Dried organic extracts
were resuspended in 70% ethanol to a concentration of 50 mg/ml
and water extracts were dissolved in water to the same concentration. One hundred microlitres of each extract were serially diluted
two-fold with sterile water in a 96-well microtitre plate. A similar two-fold dilution of amphotericin B (Sigma–Aldrich, Germany)
(2.5 mg/ml) was used as the positive control while water and 70%
B. Ncube et al. / Journal of Ethnopharmacology 134 (2011) 775–780
ethanol were used as negative and solvent controls, respectively.
One hundred microlitres of the dilute fungal culture were added
to each well. The plates were covered with parafilm and incubated
at 37 ◦ C for 24 h, after which 50 ml (0.2 mg/ml) INT were added and
incubated for a further 24 h at 37 ◦ C. The wells remained clear where
there was inhibition of fungal growth. MIC values were recorded as
the lowest concentrations that inhibited fungal growth after 48 h.
To determine the fungicidal activity, 50 ml of sterile YM broth were
added to all the clear wells and further incubated at 37 ◦ C for 24 h
after which the minimum fungicidal concentrations (MFC) were
recorded as the last clear wells. The assay was repeated twice with
two replicates per assay.
2.5. Phenolic content determination
2.5.1. Preparation of extracts
Phenolic compounds were extracted from plant material as
described by Makkar (1999). Dried plant samples (2 g) were
extracted with 10 ml of 50% aqueous methanol by sonication on ice
for 20 min. The extracts were then filtered under vacuum through
Whatman No. 1 filter paper.
2.5.2. Determination of total phenolic compounds
The amounts of total phenolic compounds in plant samples
were determined using the Folin Ciocalteu (Folin C) assay for total
phenolics as described by Makkar (1999) with slight modification
(Ndhlala et al., 2007). Fifty microlitres of each extract from the plant
samples were transferred into test tubes into which 950 ml of distilled water were added followed by 1 N Folin C phenol reagent
(500 ml) and 2% sodium carbonate (2.5 ml). A blank that contained
aqueous methanol instead of plant extracts was also prepared.
The test mixtures were incubated for 40 min at room temperature
and the absorbance was read at 725 nm using a UV–vis spectrophotometer (Varian Cary 50, Australia). Each extract had three
replicates. Total phenolic concentrations were expressed as gallic
acid equivalents (GAE).
2.5.3. The butanol–HCl assay for condensed tannins
(proanthocyanidins)
Three millilitres of butanol–HCl reagent (95:5, v/v) were added
to 500 ml of each extract, followed by 100 ml ferric reagent (2%
ferric ammonium sulphate in 2 N HCl). The test combination was
mixed with a vortex and placed in a boiling water bath for 60 min.
Absorbance was then read at 550 nm using a UV–vis spectrophotometer against a blank prepared by mixing the extract (500 ml)
with butanol–HCl reagent (3 ml) and ferric reagent (100 ml), but
without heating. Each extract had three replicates. Condensed tannins (%) were calculated as leucocyanidin equivalents using the
formula developed by Porter et al. (1986).
2.5.4. Vanillin assay for flavonoids
Plant extracts (50 ml), were made up to 1 ml with methanol
in test tubes before adding 2.5 ml methanolic-HCl (95:5, v/v) and
2.5 ml vanillin reagent (1 g/100 ml acetic acid). Similar preparations
of a blank that contained methanol instead of plant extracts were
made. After 20 min at room temperature, absorbance was read at
500 nm using a UV–vis spectrophotometer. The flavonoid levels
were expressed as catechin equivalents (CTE) (Hagerman, 2002).
2.5.5. Rhodanine assay for gallotannins
Gallotannin contents from plant material were determined as
described by Makkar (1999). Plant extracts (50 ml) in test tubes
were made up to 1 ml with distilled water. One hundred microlitres
of 0.4 N sulphuric acid and 600 ml of rhodanine were added to the
diluted extracts. After 5 min, 200 ml of 0.5 N potassium hydroxide
was added followed by 4 ml of distilled water after a further 2.5 min.
777
The mixtures were left for a further 15 min at room temperature,
after which the absorbance at 520 nm was read using a UV–vis spectrophotometer against a blank that contained methanol instead of
sample. Each extract was evaluated in triplicates and gallotannin
concentrations were expressed as gallic acid equivalents (GAE).
2.6. Saponin content
2.6.1. Qualitative saponin detection
Ten millilitres of distilled water were added to 0.1 g of ground
samples in test tubes. The test tubes were corked and vigorously
shaken for 2 min. The appearance of stable and persistent foam on
the liquid surface for 15 min indicated the presence of saponins
(Tadhani and Subhash, 2006). The presence of saponins was confirmed by the formation of an emulsion upon addition of ten drops
of olive oil to the 2 ml aqueous extract.
2.6.2. Preparation of extracts for saponin quantification
Saponins were extracted from the plant material as described
by Makkar et al. (2007). The dried and ground plant samples were
defatted with hexane in a Soxhlet apparatus for 3 h. After airdrying, saponins were extracted twice from the defatted samples
(10 g) in 100 ml of 50% aqueous methanol by incubating at room
temperature overnight with continuous stirring. The extracts were
then centrifuged at 3000 × g for 10 min and the supernatant collected. The procedure was repeated with the original residue to
obtain a second supernatant. The first and second supernatants
were combined and filtered under vacuum through Whatman No.
1 filter paper. Methanol from the filtrate was evaporated from
the solution under vacuum at 40 ◦ C to remain with the saponin
sample in the aqueous phase. The aqueous phase was then centrifuged at 3000 × g for 10 min to remove water insoluble materials.
The aqueous phase was then transferred into a separating funnel
and extracted three times with an equal volume of chloroform to
remove pigments. The concentrated saponins in the aqueous solution were then extracted twice with an equal volume of n-butanol.
The n-butanol was evaporated under vacuum at 45 ◦ C. The dried
fractions containing saponins were dissolved in 10 ml of distilled
water and freeze-dried.
2.6.3. Quantitative determination of total saponins
Total saponin content was determined using a spectrophotometric method as described by Hiai et al. (1976) with modifications.
The crude saponin extracts were dissolved in 50% aqueous
methanol to a concentration of 10 mg/ml. From this, aliquots of
250 ml (in triplicate) of each sample were transferred into test tubes
into which an equal volume of vanillin reagent (8 g/100 ml ethanol)
was added followed by 2.5 ml of 72% (v/v) sulphuric acid. The mixture was mixed with a vortex and placed in a water bath adjusted
at 60 ◦ C for 10 min. The tubes were cooled in an ice-cold water
bath for 3–4 min and absorbance was measured at 544 nm using
a UV–vis spectrophotometer against a blank that contained 50%
aqueous methanol instead of sample extract. The saponin concentrations were expressed as diosgenin equivalents (DE) calculated
from a standard curve.
2.6.4. Quantitative determination of total steroidal saponins
Total steroidal saponins were determined following the method
by Baccou et al. (1977). Crude saponin extracts were dissolved
in 50% aqueous methanol (0.1 mg/ml) from which 300 ml aliquots
(corresponding to a sapogenin content of between 1 and 40 mg)
were transferred into test tubes and placed in a boiling water
bath at 100 ◦ C in order to remove methanol. After cooling, 2 ml of
ethyl acetate were added followed by 1 ml of anisaldehyde–ethyl
acetate reagent (0.5:95.5, v/v) and 1 ml sulphuric acid–ethyl acetate
reagent (50:50, v/v). The test combination was mixed with a vortex
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B. Ncube et al. / Journal of Ethnopharmacology 134 (2011) 775–780
and incubated in a water bath at 60 ◦ C for 20 min. After cooling for
10 min in a water bath at room temperature, absorbance was measured at 430 nm using a UV–vis spectrophotometer against a blank
that contained ethyl acetate instead of sample. Each extract was
evaluated in triplicate and steroidal saponin concentrations were
expressed as diosgenin equivalents (DE) calculated from a standard
curve.
2.7. Statistical analysis
Data on phytochemical evaluation was subjected to one way
analysis of variance (ANOVA) using SPSS software for Windows
(SPSS® , version 15.0, Chicago, USA). Where there was statistical significance (P ≤ 0.05), the means were further separated using least
significant difference (LSD).
3. Results and discussion
3.1. Antimicrobial activity
The antibacterial MIC values and antifungal MIC and MFC values
of Tulbaghia violacea extracts are presented in Table 1. Only MIC and
MFC values less than 1 mg/ml were considered sufficiently active
for crude extracts (Aligiannis et al., 2001). The best antibacterial
activity was shown by the PE extracts of micropropagated plants
with an MIC value of 0.39 mg/ml compared to 0.78 mg/ml from the
DCM extracts of the outdoor grown plants against Bacillus subtilis.
Petroleum ether extracts of micropropagated plants showed good
activity (MIC < 1 mg/ml) against Bacillus subtilis and Klebsiella pneumoniae while DCM extracts were active from the outdoor grown
plants against Bacillus subtilis and Staphylococcus aureus. Although
HIV/AIDS has relatively minimal ethnobotanical treatments, the
good MIC values shown by Tulbaghia violacea against these bacterial
strains provides prospects for the treatment of such ailments since
the plant is used traditionally among HIV/AIDS patients. None of the
extracts showed good activity against Escherichia coli. This is surprising due to the plant’s widespread use in traditional medicine in
the treatment of gastrointestinal ailments (Hutchings et al., 1996)
which may be caused by Escherichia coli. Petroleum ether extracts
of micropropagated plants, however, showed promising activity
(1.56 mg/ml) although slightly higher than 1 mg/ml. Manipulation
of the culture environment may possibly result in the accumulation of high enough levels of bioactive compound(s) in these
plants.
Compared to DCM, PE is a non-polar solvent and accordingly
extracts less polar compounds than DCM. The observed activity
from the two extracts in different plants indicates that the activity
in micropropagated plants is due to non-polar compound(s) compared to the less polar compound(s) in outdoor grown plants. Most
of these phytochemical compounds are produced in response to
external stimuli (Derita et al., 2009) such as light, moisture stress
and temperature among other factors. It is possible therefore, that
the consistent exposure to constant temperature and photoperiod,
and media compositional balance in micropropagated plants, might
have favoured the production of particular compound(s), and hence
the increase in the bioactivity.
In terms of the antifungal activity, greater than 1 mg/ml MIC
and MFC values were recorded in all extracts of micropropagated
plants as compared to the outdoor grown plants (Table 1). Only
DCM extracts of outdoor grown plants showed noteworthy fungicidal activity (0.78 mg/ml). The results are, however, consistent with
those found in previous studies using outdoor grown plants against
the same fungus (Motsei et al., 2003). Candida albicans is more
resistant to plant extracts (Heisey and Gorham, 1992; Buwa and
Van Staden, 2006), and the good fungicidal activity demonstrated
by Tulbaghia violacea offers promising prospects for the treatment
of candidiasis. Particularly interesting were the stable MIC and
MFC values (1.56 mg/ml) shown by the PE extracts of micropropagated plants, although they were slightly higher than 1 mg/ml.
The concentration of the bioactive compound(s) in these extracts,
if identified, can possibly be further increased to effective levels by
manipulating the plants’ culture environment. However, antifungal activities of EtOH and water extracts were the same for both
outdoor grown and micropropagated plants.
The extract yields (%) and total activity of the plants from different extracting solvents are shown in Table 2. Although the
yields of micropropagated plants were lower than the outdoor
grown ones in most of the extracts, their antimicrobial activities were fairly comparable. A comparison of the total activity
of the corresponding extracts between the outdoor grown and
micropropagated plants reveals that micropropagated plants had
more concentrated active compounds in the PE extracts than the
outdoor grown ones. For example, the yield (1.52%: equivalent
to 15.2 mg/g) and MIC value (0.39 mg/ml) of the PE extracts of
micropropagated plants against Bacillus subtilis gives a total activity of 39 ml/g (15.2 mg/0.39 mg/ml) (Eloff, 2004) compared to the
PE extracts of the outdoor grown plants with a total activity of
11.4 ml/g (17.8 mg/1.56 mg/ml) against the same bacterium. The
same PE extracts of the micropropagated plants showed good activity against Klebsiella pneumoniae with a total activity of 19.5 ml/g
compared to 11.4 ml/g from the outdoor grown plants, despite the
fact that the outdoor grown plants had higher extract yield than the
micropropagated ones. Total activity (ml/g) indicates the degree to
which the active compound(s) in one gram of plant material can
be diluted and still inhibit the growth of the tested microorganism
(Eloff, 2000). The DCM extracts of the outdoor grown plants on the
other hand, were the only active ones compared to those of the
micropropagated plants, with total activities of 11.9 ml/g against
Bacillus subtilis and Staphylococcus aureus, respectively, compared
to 4.2 ml/g from the micropropagated plants against the same
bacterial strains. The DCM extracts of the outdoor grown plants
were the only extracts that showed good fungicidal activity and
had a total activity of 11.9 ml/g compared to 2.1 mg/g from the
DCM extracts of micropropagated plants. This indicates that gram
for gram; micropropagated plants had more concentrated active
compound(s) of the less polar class (PE extractable) while the outdoor grown plants have more concentrated active compound(s)
extractable by DCM. This, however, suggests some differences in
the chemical profile composition of the two plant samples. Results
of the antimicrobial and total activity of the two plant samples
indicate that the PE extracts of micropropagated plants can supplement outdoor grown ones in the traditional medicinal use of
Tulbaghia violacea, particularly in the treatment of Bacillus subtilis
and Klebsiella pneumoniae related ailments.
3.2. Phenolic composition
The total phenolic compounds, flavonoid, gallotannin and
condensed tannin contents of both outdoor grown and micropropagated plants are presented in Table 3. Micropropagated
plants showed higher total phenolic, flavonoid and gallotannin
concentrations compared to the outdoor grown plants. Particularly interesting to note was the markedly high levels of the
flavonoids in micropropagated plants (15.3 ± 1.5 mg CTE/g) compared to those that are outdoor grown (0.44 ± 0.03 mg CTE/g dry
matter). Flavonoids are reported to have multiple biological effects
including antioxidant (Rice-Evans et al., 1997; Tapas et al., 2008),
hepatoprotective (Tapas et al., 2008), and antimicrobial activities
(Tapiero et al., 2002; Makkar et al., 2007). In medicinal plants,
the plant’s ability to concentrate bioactive compounds in high
amounts within a limited period of time, makes it more preferable
to use. The high levels of phenolic compounds in micropropa-
B. Ncube et al. / Journal of Ethnopharmacology 134 (2011) 775–780
779
Table 1
Antimicrobial activity of Tulbaghia violacea extracts expressed as MIC (mg/ml) against bacteria and MIC (mg/ml) and MFC (mg/ml) against Candida albicans.
Sample
Extract
Yield (%)
Antibacterial MIC (mg/ml)
Antifungal
Bacteria
Candida albicans
Bs
Ec
Kp
Sa
MIC (mg/ml)
MFC (mg/ml)
3.125
0.78
12.5
12.5
0.39
0.78
3.125
12.5
6.25
0.78
6.25
12.5
1.56
3.125
3.125
3.125
1.56
3.125
3.125
12.5
1.56
6.25
6.25
12.5
Tulbaghia violacea
(outdoor grown)
PE
DCM
EtOH
Water
1.78
0.93
26.1
17.95
1.56
0.78a
6.25
>12.5
3.125
3.125
3.125
12.5
1.56
1.56
12.5
12.5
Tulbaghia violacea
(micropropagated)
PE
DCM
EtOH
Water
1.52
1.31
19.98
14.05
0.39
3.125
12.5
>12.5
1.56
3.125
3.125
12.5
0.78
3.125
12.5
3.125
0.098
3.13
1.56
1.56
–
–
–
–
–
–
0.15
9.80
Neomycin (mg/ml)a
b
Amphotericin B (mg/ml)
MIC, minimum inhibitory concentration; MFC, minimum fungicidal concentration; Bs., Bacillus subtilis; Sa., Staphylococcus aureus; Ec., Escherichia coli; Kp., Klebsiella pneumoniae; PE, petroleum ether; DCM, dichloromethane; EtOH, 80% ethanol. Values boldly written are considered very active (1 ≤ mg/ml).
a
Positive control for the antibacterial assay.
b
Positive control for the antifungal assay.
Table 2
Extract yields (%) and total antibacterial and antifungal activity (ml/g) of Tulbaghia violacea extracts.
Sample
Extract
Yield (%)
Total activity (ml/g)
Total activity
Bacteria
Candida albicans
Bs
Ec
Kp
Sa
(ml/g)
(ml/g)
Tulbaghia violacea
(outdoor grown)
PE
DCM
EtOH
Water
1.78
0.93
26.1
17.95
11.4
11.9
41.76
>14.4
5.7
3.0
83.5
14.4
11.4
6.0
20.9
14.4
5.7
11.9
20.9
14.4
45.6
11.9
83.5
14.4
2.8
11.9
41.76
14.4
Tulbaghia violacea
(micropropagated)
PE
DCM
EtOH
Water
1.52
1.31
19.98
14.05
39.0
4.2
16.0
>11.2
9.7
4.2
63.9
11.2
19.5
4.2
16.0
45.0
9.7
4.2
63.9
45.0
9.7
4.2
63.9
11.2
9.7
2.1
32.0
11.2
Bs., Bacillus subtilis; Sa., Staphylococcus aureus; Ec., Escherichia coli; Kp., Klebsiella pneumoniae; PE, petroleum ether; DCM, dichloromethane; EtOH, 80% ethanol. Values boldly
written represent total activity of extracts that were active.
gated plants observed in this study, demonstrate that these plants
have the capacity to produce large quantities of these secondary
metabolites and thus, have potential to be exploited commercially to accumulate these valuable compounds for their medicinal
benefits. The biosynthesis and accumulation of plant secondary
metabolites depend on exogenous factors, but the plant’s intrinsic
factors, developmental stage and tissue differentiation determine
the site of synthesis (Treutter, 2001; Mirdehghan and Rahemi,
2007). Accordingly, based on the results obtained in this study, it
therefore, follows that the physiological and/or environmental conditions are more favourable for phenolic compound production in
micropropagated than in outdoor grown plants. Nevertheless, both
types of plants accumulate sufficient quantities of various non polar
metabolites to effect some good antimicrobial activities.
Table 3
Total phenolic, flavonoid, gallotannin, condensed tannin, total saponin and steroidal
saponin contents in micropropagated and outdoor grown Tulbaghia violacea
extracts. Values represent the means ± standard error (n = 3).
Total phenolics (mg GAE/ml)
Flavonoids (mg CTE/ml)
Gallotannins (mg GAE/ml)
Condensed tannins (% LCE/g)
Total saponins (mg DE/ml)
Total steroidal saponins (mg DE/ml)
Micropropagated
Outdoor grown
3.56
15.3
4.03
0.72
25.14
10.03
0.45
0.44
2.32
0.84
8.94
3.77
±
±
±
±
±
±
0.06a
1.5a
0.24a
0.22b
0.74a
0.58a
±
±
±
±
±
±
0.021b
0.03b
0.02b
0.078a
0.11b
0.43b
Values in a row with different letters are significantly different at P ≤ 0.05. GAE,
gallic acid equivalents; CTE, catechin equivalents; LCE, leucocyanidin equivalents;
DE, diosgenin equivalent.
3.3. Saponin composition
The qualitative froth test for the presence of saponins was positive for both types of plant material. Table 3 represents total
saponins and total steroidal saponins in micropropagated and outdoor grown Tulbaghia violacea plants. As was the trend with the
phenolic content, saponins and steroidal saponins were significantly higher in micropropagated plants than in the outdoor grown
ones. Saponins, particularly steroidal saponins have been reported
in Tulbaghia violacea (Burton, 1990). The results obtained in this
study agree with these previous findings. However, the markedly
high saponin content obtained in micropropagated plants compared to the outdoor grown plants is an indication that in vitro
culture conditions are favourable for the production of plant secondary metabolites.
Saponins are reported to have antimicrobial activity (Bader et al.,
2000), anti-inflammatory (Navarro et al., 2001) and haemolytic
(Oda et al., 2000) properties. This markedly high saponin composition recorded in micropropagated plants shows their promising
pharmacological potential as sources of bioactive molecules.
Manipulation of the culture environment may be effective in
increasing accumulation of these compounds.
4. Conclusions
The antibacterial results exhibited by micropropagated Tulbaghia violacea plants in comparison with the outdoor grown ones
were fairly comparable. Although micropropagated plants did not
780
B. Ncube et al. / Journal of Ethnopharmacology 134 (2011) 775–780
show good antifungal activity compared to the outdoor grown
plants, their PE extracts appeared to contain some active antifungal
compound(s). However, the concentration(s) of the compound(s)
might have been lower than those required to effect good activity. Micropropagated plants of Tulbaghia violacea may be used as
alternative sources of treatments of some ailments caused by bacteria in traditional medicine and have a promising potential to
produce better activity. The generally high total phenolics, gallotannin, flavonoid and saponin contents recorded in micropropagated
plants in contrast to those grown outdoors, makes them potential
sources for the production of secondary metabolites for medicinal
purposes. The fact that micropropagated plants produce secondary
metabolites at an early stage of growth provides an opportunity for rapid production of pharmacological compounds that can
be utilised for medicinal purposes. Although the yields of polar
extracts (water and EtOH) of the outdoor grown plants were higher
than those from the micropropagated ones, the later yielded high
levels of the screened polar compounds (phenolics and saponins)
in this study. This may, however, indicate the presence of other
polar compounds in these extracts, such as carbohydrates. Further
synergistic studies to determine the biological activity of all the
combined extracts are required to give an overall picture of the
whole extracts.
Acknowledgements
The National Research Foundation (NRF), Pretoria and the University of KwaZulu-Natal are gratefully acknowledged for financial
assistance.
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