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Abstract

Corn silk refers to the stigmas of Zea mays L. (Gramineae) from the female flowers of maize. Based on its flavonoid contents, it is medicinally used in the treatment of a number of diseases. Screening of plants against pathogenic bacteria is an important step to validate its medicinal properties. Therefore, the aim of this study was to investigate the antimicrobial activities of different solvent extracts, flavonoids of corn silk and compare the activities with standard antibiotic gentamycin. The petroleum ether (PECS), chloroform (CECS) and methanol (MECS) extracts (25 mg/mL) of corn silk were tested for their antimicrobial activity. Twelve pathogenic bacteria: Bacillus cereus, Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa, Enterobacter aerogenes, Salmonella typhi, Salmonella paratyphi, Escherichia coli, Shigella sonnei, Shigella flexneri, Proteus vulgaris, Proteus mirabilis and one yeast Candida albicans were used to investigate the antimicrobial activities of the extracts. Gentamycin (50 µg/mL) was used as reference antibiotic. Two isolated flavonoid glycosides (2.0 mg/mL) of corn silk were tested for their antimicrobial activity. The microbial growth inhibitory potential was determined by using the agar hole-plate diffusion method. PECS, MECS and flavonoids were active against eleven bacteria out of twelve bacteria. CECS was active only against five bacteria. No extracts and flavonoids were sensitive against Escherichia coli and Candid albicans. The results were compared with gentamycin, which was active against all the bacteria tested. Extracts and flavonoids showed significantly (p<0.05) higher sensitivity against a number of bacteria than gentamycin.
International Journal of Biotechnology for Wellness Industries, 2012, 1, 115-121 115
ISSN: 1927-3037/12 © 2012 Lifescience Global
Antimicrobial Activities of Extracts and Flavonoid Glycosides of
Corn Silk (Zea mays L)
Fazilatun Nessa*,a, Zhari Ismailb and Nornisah Mohamedb
aPharmaceutical and Medicinal Chemistry Department, Dubai Pharmacy College, P.O.BOX: 19099; Dubai -
United Arab Emirates
bSchool of Pharmaceutical Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia
Abstract: Corn silk refers to the stigmas of Zea mays L. (Gramineae) from the f emale flowers of maize. Based on its
flavonoid contents, it is medicinally used in the treatment of a number of diseases. Screening of plants against
pathogenic bacteria is an important step to validate its medicinal properties. Therefore, the aim of this study was to
investigate the antimicrobial activities of different solvent extracts, flavonoids of corn silk and compare the activities with
standard antibiotic gentamycin. The petroleum ether (PECS), chloroform (CECS) and methanol (MECS) extracts (25
mg/mL) of corn silk were tested for their antimicrobial activity. Twelve pathogenic bacteria: Bacillus cereus, Bacillus
subtilis, Staphylococcus aureus, Pseudomonas aeruginosa, Enterobacter aerogenes, Salmonella ty phi, Salmonella
paratyphi, Escherichia coli, Shigella sonnei, Shigella flexneri, Proteus vulgaris, Proteus mirabilis and one yeast Candid a
albicans were used to investigate the antimicrobial activities of the extracts. Gentamycin (50 µg/mL) was used as
reference antibiotic. Two isolated flavonoid glycosides (2.0 mg/mL) of corn silk were tested for their antimicrobial activity.
The microbial growth inhibitory potential was determined by using the agar hole-plate diffusion method. PECS, MECS
and flavonoids were active against eleven bacteria out of twelve bacteria. CECS was active only against five bacteria.
No extracts and flavonoids were sensitive against Escherichia coli and Candid albicans. The results were compared wit h
gentamycin, which was active against all the bacteria tested. Extr acts and flavonoids showed significantly (p<0.05)
higher sensitivity against a number of bacteria than gentamycin.
Keywords: Zea Mays, Corn silk, Plant extract, Flavonoid glycosides, Antimicrobial activity.
1. INTRODUCTION
Corn silk ascribed as stigmata of maize female
flowers of Zea mays L. (Gramineae), are fine soft
thread 10-20 cm long, commonly cultivated in warm
climates. It is medicinally used as a mild stimulant,
diuretic and demulcent, useful in acute and chronic
cystitis and in the bladder irritation of uric acid and
phosphatic gravel; has also been employed in
Gonorrhoea [1]. In Chinese medicine, corn silk is used
for oedema of various origin and for hepato-biliary
disease [2]. The medicinal properties of corn silk
supported by several authors as it exhibited antioxidant
activity [3-6], anti-diabetic activity [7, 8], antibiotic
activity towards corn earworm [9], resistance to insect
attacks [10] and antitumour activity [11]. Phytochemical
studies on corn silk revealed that it contained a number
of flavonoids, chlorogenic acid, p-coumaric, ferulic acid,
saponins, phytosterols, volatile oil, fixed oil, resin,
sugars, allantoin, tannin and minerals [12-16]. Since
one of the standard approaches for determining
potential medicinal use of plants and their chemical
constituents is to screen them for activity against a
wide range of viruses, bacteria and pathogenic fungi,
therefore, the present work was undertaken to further
*Address corresponding to this author at the Pharmaceutical and Medicinal
Chemistry Department, Dubai Pharmacy College, P.O.BOX: 19099; Dubai -
United Arab Emirates; Tel: +971-4-2120311; Fax: +97 1-4-2646740;
E-mail: nessa1995@yahoo.com
the study on the medicinal herb, corn silk, found in
Malaysia, and to establish fairly comprehensive data on
its chemical constituents and their antimicrobial
properties. In this investigation, phytochemical analysis
on corn silk resultant the isolation of two flavonoid
glycosides, therefore, the objectives of this study was
to investigate the antimicrobial activities of different
solvent extracts of corn silk and its flavonoid
glycosides, and to compare the activities with standard
antibiotic gentamycin.
2. MATERIALS AND METHODS
2.1. General Experimental Methods
Melting points were determined on a Gallenkamp
instrument and are uncorrected. FTIR spectra were
recorded on a Bomem Hartmann and Braun, MB-
Series instrument; UV spectra were recorded on a
Hitachi U-2000 spectrophotometer. ESI MS spectra
were obtained from a Finnigan LC-Q Classic, Ion Trap
Spectrometer. 1H and 13C NMR spectra were acquired
using Bruker Avance 300 MHz spectrometers equipped
with 5 mm bore gradient-pulse inverse probeheads.
Samples were dissolved in DMSO-d6 and chemical
shifts were recorded in δ (ppm) relative to that of TMS
(δ= 0.00 ppm).
2.2. Plant Materials
Freshly collected corn silks (Speicimen voucher No.
8765 for the Zea mays, The School of Biology,
116 International Journal of Biotechnology for Wellness Industries, 2012 V ol. 1, No. 2 Nessa et al.
Universiti Sains Malaysia), were oven dried (40oC) for 5
days, and then milled into powder. The powdered silks
(300 g) were then extracted first with petroleum ether
(60-80o), followed by chloroform and then finally with
methanol (2.5 liters each) in a Soxhlet extractor for 30
hours each. After removal of the solvents by vacuum
evaporation the percent of yield for pet-ether (PECS),
chloroform (CECS) and methanol (MECS) extracts was
about 1.1 %, 1.2 % and 6.5 %, respectively. All the
samples were freeze dried by using the Cole-Parmer
benchtop freeze dryer (Model LD-53, Kingston, NY)
before testing for antimicrobial studies.
2.3. Isolation of Flavonoid Glycosides from
Methanol Extract
The methanol extract (18 g) was stirred with 500 mL
of water and the contents were extracted with n-butanol
(3 x 300 mL). Dried butanol extract (3 g) was subjected
to column chromatography over Sephadex-LH-20 with
methanol as eluent. Fractions of 20 mL were collected.
Fractions 5-10 (120 mL), was evaporated to a yellow
glass like solid mass, was recrystallized from methanol
to give compound I (12 mg). It showed one yellow-
orange spot at Rf 0.277 on silica gel plate [n-
butanol:acetic acid:water (BAW), 5:1:4, upper phase]
with NP-reagent. Fractions 21-25, was evaporated to
give compound II (14 mg), was recrytallized from
methanol to yellow powder. It showed one spot at Rf
0.295 on silica gel plate (BAW, 5:1:4) with NP-reagent.
Hydrolysis of I and II (1 mg each, separately) was
heated with 2N HCl (5 mL) for 3 hours at 100°C and
extracted with ethylacetate (3 x 10 mL). The organic
extract was washed with water and evaporated. The
aglycone obtained gave one spot. The aqueous portion
left was dried under high vacuum and the sugar
residue was chromatographed on TLC (BAW, 4:1:5,
upper phase) and identified as rhamnose (Rf 4.3) by
comparing with authentic sugar.
2.4. Spectral Data
Compound (I): M.p. 222-224 °C (decompose). FeCl3
test: (+); UV max (MeOH): 349, 270 (sh), 256 (sh), 212;
NaOMe 406, 264, 212; AlCl3 422, 276, 211; AlCl3/HCl
379, 278, 211; NaOAc 413, 270, 228; NaOAc/H3BO3
374, 263, 222 nm; IR bands (KBr disc): 3397, 1730,
1659, 1620, 1343, 1098, 809 cm–1; ESI-MS m/z (%):
M+ +1, 577 (100). 1H NMR (300 MHz, DMSO) and 13C
NMR (75 MHz, DMSO) spectral data are presented in
Table 1.
Compound (II): M.p. 193-195 °C. FeCl3 test: (+); UV
max (MeOH): 347, 270, 242 (sh), 211; NaOMe 412,
336 (sh), 280(sh), 259, 212; AlCl3 389, 365, 297 (sh),
279, 262 (sh), 235 (sh), 211; AlCl3/HCl 387, 361, 298
(sh), 279, 260 (sh), 235 (sh), 211; NaOAc 407, 279,
221; NaOAc/H3BO3 349, 270, 222 nm; IR bands (KBr
disc): 3444, 1726, 1642, 1623, 1346, 1198, 1088, 831
cm –1; ESI-MS m/z (%): M+ +1, 591 (100), 445 (46) and
315 (25). 1H NMR (300 MHz, DMSO) and 13C NMR (75
MHz, DMSO) spectral data are presented in Table 1.
2.5. Antimicrobial Screening
The microorganisms used in this study included four
gram-positive bacteria e.g. B. cereus, B. subtilis, Staph.
aureus, P. aeruginosa and eight gram-negative
bacteria e.g. Ent. aerogenes, S. typhi, S. paratyphi, E.
coli, S. sonnei, S. flexneri, Prot. vulgaris, Prot. mirabilis
and one yeast e.g. C. albicans, were obtained from the
stock culture of the Microbiology Laboratory of the
School of Pharmaceutical Sciences, Universiti Sains
Malaysia, Penang, Malaysia. Bacterial strains were
grown on nutrient agar and yeast strains in sabouroud
dextrose agar suspended in nutrient broth.
Subculturing was done once weekly.
The microbial growth inhibitory potential of the
extracts was determined by using the agar hole-plate
diffusion method [17]. For preparation of inocula, few
colonies were mixed with sterile 0.8% nutrient broth
solution and compared the turbidity with that of
standard 0.5 McFarland solutions, which was
equivalent to 106-108 CFU/ml. The inoculum was added
to molten agar and the media was thoroughly shaken
to disperse the microorganisms. Different organic
solvent extracts of corn silk (25 mg/ml) and the isolated
compound (2.0 mg/ml) were prepared in 10% DMSO
[17]. Holes (7 mm diameter) were made in the solidified
media by punching with a sterile cork borer, then 70 µL
of the plant extract solution was introduced in each
hole. For positive control, 70 µL of standard antibiotic
gentamycin solution (50 µg/ml) was introduced into the
wells. A blank was also run, consisting of holes with 70
µL of the solvent only (10% DMSO). This was done to
check for sterility and any growth inhibitory potential of
the solvent. All plates were left at room temperature for
2 hr to allow the diffusion process to take place. Then
the plates were incubated at 25 °C for 3 days for
fungus and at 37 °C for 24 hr for the bacteria. All
determinations were performed in triplicate. Zones of
inhibition were measured after the incubation period
from the edge of each well. All the results are
expressed as mean ± standard deviation (S.D.). The
data were subjected to a one-way analysis of variance
(ANOVA) and Tukey’s test (p<0.05) was performed to
Antimicrobial Activities of Extracts and Flavonoid Glycosides International Journal of Biotechnology for Wellness Industries, 2012 Vol. 1, No. 2 117
determine the significance of the difference between
means.
3. RESULTS AND DISCUSSION
3.1. Structure Determination of Isolated
Compounds
Compound (I) is a yellow powder, decomposed at
222-224 °C. Its molecular formula C27H28O14 was
confirmed by ESI-MS positive ions spectrum (577). Its
UV spectral data exhibited characteristics for flavone
nucleus. The bathochromic shift of band I (57 nm) with
aluminum chloride and hypsochromic shift of band I (43
nm) with addition of hydrochloric acid but bathochromic
shift (30 nm) relative to methanol indicated the
presence of 5-OH with ortho-dihydroxyl group in its B
ring. It was supported by the formation of boric acid
complex [18]. The bathochromic shift of band I (57 nm)
with increased intensity on addition of sodium
Table 1: Summary of Spectral Data of 1H-NMR and 13C-NMR of Flavonoid Glycosides (I and II) of Corn Silk
Maysin (I)
Maysin-3-methyl ether (II)
Position
1H NMR
δ (DMSO- d6) ppm
13C
δ (DMSO- d6) ppm
1H NMR
δ (DMSO- d6) ppm
13C
δ (DMSO- d6) ppm
C2
-
164.53
-
164.30
C3
6.70 (1H, s)
103.53
6.92 (1H, s)
104.40
C4
-
182.93
-
183.10
C5
13.81 (1H, s, -OH)
162.07
13.81 (1H, s, -OH)
162.10
C6
-
108.37
-
108.30
C7
-
163.06
-
164.20
C8
6.49 (1H, s)
93.86
6.54 (1H, s)
94.00
C9
-
157.33
-
157.30
C10
-
103.76
-
103.80
C1
-
122.13
-
122.10
C2
7.42 (2H, overlapped)
114.15
7.57 (2H, overlapped)
110.90
C3
-
146.62
-
148.92
C4
-
150.62
-
151.60
C5
6.89 (1H, d, J = 8.14 Hz)
116.94
6.93 (1H, d, J = 8.2 Hz)
116.60
C6
7.42 (2H, overlapped)
119.86
7.57 (2H, overlapped)
121.2
C1′′
5.30 (1H, d, J = 10 Hz)
72.03
5.30 (1H, d, J = 10 Hz)
72.0
C2′′
4.83 (1H, d, J = 10 Hz)
78.90
4.83 (1H, d, J = 10 Hz)
78.40
C3′′
4.40 (1H, br)
78.96
4.46 (1H, br)
78.90
C4′′
-
206.90
-
206.90
C5′′
3.9 (1H, br)
76.26
4.17, (1H, br q, J = 5.1 Hz)
76.20
C6′′
(-CH3)
1.29 (3H, d, J = 6 Hz)
18.16
1.30 (3H, d, J = 6 Hz)
18.17
C1′′′
5.24 (1H, d, J = 10 Hz)
100.09
5.24 (1H, d, J = 10 Hz)
100.0
C2′′′
3.77 (1H, s)
70.99
3.70 (1H, s)
71.0
C3′′′
3.0 (2H, complex)
70.99
3.0 – 3.5 (2H, complex)
71.0
C4′′′
3.0 (2H, complex)
74.14
3.0 – 3.5 (2H, complex)
74.10
C5′′′
2.4 (1H, complex)
69.70
2.4 (1H, complex)
69.70
C6′′′
(-CH3)
0.67 (3H, d, J = 5.9 Hz)
19.83
0.66 (3H, d, J = 5.8 Hz)
19.80
3-OCH3
-
-
3.99 (3H, s)
56.80
118 International Journal of Biotechnology for Wellness Industries, 2012 V ol. 1, No. 2 Nessa et al.
methoxide indicated the presence of free hydroxyl
group at C-4 position. The presence of free hydroxyl
group confirmed from its bathochromic shift of band II
(14 nm) with sodium acetate. Its 1H NMR spectrum was
assigned with the literature reported by Elliger et al.
[12]. The signal at δ 6.70 (1H, s) was assigned for H-3,
was a characteristic for flavone. The A ring protons
appeared at δ 6.49 (1H, s) accounted for H-8,
suggested the substitution at C-6 position. Its B ring
protons appeared at δ 6.89 (1H, d, J = 8.14) and δ 7.42
(as overlapped signal integrating for two protons) were
accounted for H-5 and H-2/H-6 respectively.
Hydrolysis of I with 2N HCl (100°C, 3 hr), yielded the
sugar rhamnose, was identified by comparing with
authentic sugar using thin-layer chromatography, which
indicated that it was a terminal sugar. The
characteristic signal at δ 0.67 (3H, d, J = 5.9 Hz) for the
methyl group of rhamnose, once again confirmed the
presence of this sugar. The resistance to hydrolysis of
the remaining aglycone revealed the presence of other
sugar, which might attach at C-6 as the
deoxyhexosulose. It was consistent with observation of
a non-flavonoid IR band for C=O at 1726 cm-1 as well
as the 13C NMR signal appearing at 206.9 ppm which
indicated the presence of an aliphatic ketone. The
other signal for sugar moieties was confirmed from the
reported data for this compound [12]. The 13C NMR
spectral data (Table 1) was also consistent with Snook
et al. [13]. Based on the above data, the compound I
was identified as 2′′-O-α-L-rhamnosyl-6-C-(6-deoxy-
xylo-hexos-4-ulosyl)-luteolin or namely maysin (I).
Compound (II) a yellow powder, m.p. 193-195 °C.
It’s molecular formula C28H30O14 was confirmed by ESI-
MS positive spectrum (M++H, 591). Its IR spectrum
showed strong absorption band at 1726 cm-1 indicated
the presence of an aliphatic ketone (C=O). Its UV
spectrum changes with various additives showed
typical flavonoid absorption and gave characteristics
shift for the basic luteolin structure. A bathochromic
shift of band I of 65 nm with increase of intensity with
sodium methoxide and band II of 9 nm with sodium
acetate were observed, suggesting the presence of a
free hydroxyl group at C-4 and C-7 positions. The UV
spectrum exhibited a bathochromic shift of band I of 42
nm with aluminum chloride and no change of
absorption band in presence of hydrochloric acid
indicated the absence of orthodihydroxyl groups in its
B-ring and presence of a chelated hydroxyl group at C-
5 position. This was further supported by the chemical
shift at δ 13.81 ppm in its 1H NMR spectrum. In the 1H
NMR spectrum, a chemical shift at δ 6.92 (1H, s)
indicates the characteristic olefinic proton of a flavone.
The signal at δ 6.93 (1H, d, J = 8.2 Hz) and 7.57 ppm
(as overlapped signals integrating for two protons),
which accounted for H-5, H-6 and H-2 for its B-ring
protons respectively, clearly suggestive of oxygenation
at C-3 and C-4. Its only one proton of the A ring was
evident at δ 6.54 (1H, s), can positioned at either C-6 or
C-8. The 1H NMR data for apigenin 6-C-glucoside and
apigenin 8-C-glucoside [12] showed that the chemical
shift for H-6 is at 6.29 ppm and for H-8 is at 6.56 ppm.
Comparing these with the signal at 6.54 ppm for
compound II suggested the presence of a C-8 proton
and substitution at C-6 in the A-ring. A three-proton
singlet at δ 3.99 was attributed to a methoxyl group,
which was evident at C-3 position, was confirmed from
its UV spectrum [18]. Identification of the sugar
attached at C-6 as the deoxyhexosulose was
consistent with observation of a non-flavonoid IR band
for C=O at 1726 cm-1 as well as the 13C NMR signal
appearing at 204.4 ppm which indicated the presence
of an aliphatic ketone [12]. Attachment of rhamnose to
the C-6 sugar residue and not directly to a flavone
oxygen was established from its LC-MS spectral data
as well as hydrolysis. Treatment of II with 2N HCl
(100°C, 3 hr) yielded rhamnose, identified by thin layer
chromagraphy and by comparison with authenthic
sugar (Rf 4.3, B.A.W., 4:1:5). Its identification was
supported by the rhamnosyl CH3 group at 0.66 ppm
(3H, d, J = 5.8 Hz), suggested it was a terminal sugar
moiety. Based on the above data the structure of
compound II was concluded as maysin-3-methyl ether.
The structure of II was further supported by its ESI-MS
spectrum. The spectrum showed peaks at 591 (M+),
445 (M+ + H – rhamnose) and 315 (M+ + H – rhamnose
deoxyhexosulose), once again confirmed the
structure as maysin-3-methyl ether. The 13C NMR
chemical shifts (Table 1) were also consistent with
those reported literature [13]. Based on the above data,
the compound II was assigned as 2′′-O-α-L-rhamnosyl-
6-C-(6-deoxy-xylo-hexos-4-ulosyl)-luteolin-3-methyl
ether or namely maysin-3-methyl ether, previously
isolated from this plant [12, 13]. The structures of the
two isolated flavone glycosides were shown in Figure
1.
3.2. Antimicrobial Activities of Different Organic
Solvent Extracts of Corn silk
Evaluation of antimicrobial activities against four
gram-positive bacteria, eight gram-negative bacteria
and one yeast were carried out separately with the pet-
ether (PECS), chloroform (CECS) and methanol
(MECS) extracts (25 mg/mL) of corn silk. Gentamycin
Antimicrobial Activities of Extracts and Flavonoid Glycosides International Journal of Biotechnology for Wellness Industries, 2012 Vol. 1, No. 2 119
6'''
5'''
4'''
3'''
2'''
1'''
6''
5''
4'' 3'' 2''
1''
H
H
O
O
H
CH3
O
H
HO
O
H
CH3
H
OH
OH
OH
H
O
HO
OH O
OCH3
OH
Compound I Compound II
Figure 1: Structures of the isolated compounds I (maysin) and II (maysin-3-methyl ether) from the n-butanol fraction of
methanol extract of corn silk.
(50 µg/mL) was used as reference antibiotic. The
results are shown in Table 2. PECS and MECS were
sensitive against eleven bacteria out of twelve bacteria.
CECS was sensitive only against five bacteria. No
extracts was sensitive against E. coli and C. albicans.
The results were compared with gentamycin, which
was sensitive against all the bacteria tested. PECS (25
mg/mL) showed significantly (p<0.05) higher sensitivity
against some bacteria than gentamycin (50 µg/ml),
except against P. aeruginosa, Ent. aerogenes, S. typhi.
And towards S. paratyphi, S. sonnei and S. flexner it
showed insignificant (p<0.05) activity in comparison
with gentamycin.
Similarly MECS showed comparatively higher
activity in comparison to gentamycin against eight
bacteria and the results were significant (p<0.05),
Table 2. Antimicrobial Activity of Different Organic Solvent Extracts of Corn Silk
1Zone of Inhibition (mm ± S.D.)
Microorganisms
Pet-ether
Extract (PECS)
(25 mg/ml)
Chloroform
Extract (CECS)
(25 (mg/ml)
Methanol
Extract (MECS)
(25 mg/ml)
Gentamycin
(50 µg/ml)
Bacillus cereus
12.17 ± 0.22
10.98 ± 0.12
10.66 ± 0.31
8.00 ± 0.13
Bacillus subtilis
*11.16 ± 0.07
*11.08 ± 0.18
*11.27 ± 0.12
8.08 ± 0.11
Staphylococcus aureus
10.45 ± 0.22
4.58 ± 0.58
*8.61 ± 0.37
*8.00 ± 0.24
Pseudomonas aeruginosa
8.37 ± 0.13
0
10.15 ± 0.15
11.23 ± 0.21
Enterobacter aerogenes
8.61 ± 0.25
7.01 ± 0.12
11.46 ± 0.10
10.00 ± 0.01
Salmonella typhi
9.75 ± 0.19
0
11.33 ± 0.21
13.04 ± 0.19
Salmonella paratyphi
*8.5 + 0.17
0
*7.47 + 0.43
*8.01 ± 0.15
Escherichia coli
0
0
0
5.07 ± 0.06
Shigella sonnei
*10.45 ± 0.25
8.43 + 0.38
*10.55 ± 0.13
*9.98 ± 0.20
Shigella flexneri
5.94 ± 0.24
0
7.12 ± 0.09
6.01 ± 0.13
Proteus vulgaris
10.18 ± 0.21
0
*8.01 ± 0.11
*8.00 ± 0.02
Proteus mirabilis
11.22 ± 0.17
0
6.59 ± 0.35
8.03 ± 0.07
Candida albicans
0
0
0
0
1Values are means of three readings (± S.D.). *Values are not significant within the row (p<0.05).
120 International Journal of Biotechnology for Wellness Industries, 2012 V ol. 1, No. 2 Nessa et al.
except towards Staph. aureus, S. paratyphi and S.
sonnei, where it showed insignificant (p<0.05) result
against these bacteria. In comparison to sensitivity of
CECS and gentamycin against the tested bacteria, it
was observed that CECS showed poor sensitivity
against gram-negative bacteria comparatively than
gram-positive bacteria. Only it exerted higher sensitivity
towards B. cereus and B. subtilis than gentamycin, and
towards Ent. aerogenes and S. sonnei it showed lower
activity than gentamycin (p<0.05).
Phytochemical investigation on PECS revealed the
presence of phytosterol, e.g. stigmasterol and β-
sitosterol, and mixtures of fatty acids, e.g. dodecanoic
acid, tetradecanoic acid, hexadecanoic acid and
octadecanoic acid [15]. MECS contained a number of
flavonoids such as maysin, quercetin and maysin-3-
methyl ether [12-16]. Therefore, the different chemical
constituents of the extracts could be contributed for
their different ranges of antimicrobial activity.
3.3. Antimicrobial Activities of Isolated Flavonoid
Glycosides of Corn Silk
Two flavonoid glycosides (compound I and II) were
isolated from n-butanol fraction of methanol extract of
corn silk. The chemical structures of the compounds
were elucidated as maysin (I) and maysin-3-methyl
ether (II) by means of different analytical methods such
as UV, IR, NMR and MS (ESI) analyses and by
comparison with those reported literature for the
compounds [12, 13, 18]. The antimicrobial studies of
maysin (I) and maysin-3-methyl ether (II) were studied
against twelve bacteria and one yeast. The results are
given in Table 3. The sensitivity of the compounds (2.0
mg/mL) towards bacteria was compared with that of
standard gentamycin (50 µg/mL). Flavonoid glycosides
showed wider range of activity towards gram-positive
and gram-negative bacteria. Comparatively, compound
I exerted highest antibacterial activity towards gram
positive bacteria than II. In comparison with
gentamycin, compound I showed significantly (p<0.05)
higher activity against the tested bacteria except
towards Ent. aerogenes, S. paratyphi and P. mirabilis
where it exerted statistically (p<0.05) similar activity
with gentamycin. Towards P. aeruginosa, it showed
lower activity than gentamycin.
Maysin-3-methyl ether (II) showed comparatively
lower activity than I, it seems the presence of methoxyl
substitution on C-3 position slightly decreases the
sensitivity towards bacteria. Wang et al. [19] reported
that the presence of phenolic hydroxyl groups was
essential for higher antibacterial activity. In comparison
the antibacterial activity of II and gentamycin, it exerted
little higher activity than gentamycin towards B. cereus,
Table 3: Antimicrobial Activity of Flavonoid Glycosides (I and II) of Corn Silk
1Zone of inhibition (mm ± S.D.)
Microorganisms
Maysin (I)
(2.0 mg/mL)
Maysin-3-
methyl ether (II)
(2.0 mg/mL)
Gentamycin
(50 µg/mL)
Bacillus cereus
17.45 ± 0.24
11.17 ± 0.11
8.00 ± 0.13
Bacillus subtilis
13.15 ± 0.29
10.12 ± 0.15
8.08 ± 0.11
Staphylococcus aureus
11.3 2 ± 0.14
*8.07 ± 0.18
*8.00 ± 0.24
Pseudomonas aeruginosa
8.6 7 ± 0.19
7.17 ± 0.14
11.23 ± 0.21
Enterobacter aerogenes
*10.18 ± 0.17
*10.19 ± 0.15
*10.00 ± 0.01
Salmonella typhi
*9.92 ± 0.27
*9.25 ± 0.16
13.04 ± 0.19
Salmonella paratyphi
*8.16 ± 0.11
7.01 ± 0.21
*8.01 ± 0.15
Escherichia coli
0
0
5.07 ± 0.06
Shigella sonnei
15.23 ± 0.23
12.15 ± 0.25
9.98 ± 0.20
Shigella flexneri
8.22 ± 0.16
7.11 ± 0.09
6.01 ± 0.13
Proteus vulgaris
*13.01 ± 0.18
*12.45 ± 0.21
8.00 ± 0.02
Proteus mirabilis
*8.25 ± 0.19
6.55 ± 0.11
*8.03 ± 0.07
Candida albicans
0
0
0
1Values are means of three readings (± S.D.). *Values are not significant within the row (p<0.05).
Antimicrobial Activities of Extracts and Flavonoid Glycosides International Journal of Biotechnology for Wellness Industries, 2012 Vol. 1, No. 2 121
B. subtilis, S. sonnei and P. vulgaris and the results
were significant (p<0.05). The activity towards Ent.
aerogenes and Staph. aureus was insignificant
(p<0.05) with gentamycin and towards other bacteria,
gentamycin showed higher activity than II. Both
compounds were not sensitive against E. coli and C.
albicans.
4. CONCLUSION
From the results of antimicrobial activities of
different solvent extracts of corn silk, it can be seen
that extracts exhibited wider range of antimicrobial
activity, petroleum ether and methanol extracts were
more active than chloroform extracts. The different in
activities of extracts can be ascribed for their different
chemical constituents. Therefore, it can be concluded
that extracts of corn silk can protect the body from
different disease condition related to the pathogenic
organisms.
ACKNOWLEDGEMENT
The authors are grateful to Dr. Pazilah Ibrahim of
the School of Pharmaceutical Sciences, Universiti
Sains Malaysia (Penang, Malaysia), for providing the
laboratory facilities to carry out the microbial studies.
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Received on 01-01-2012 Accepted on 28-04-2012 Published on 15-06-2012
DOI: http://dx.doi.org/10.6000/1927-3037/2012.01.02.02
© 2012 Nessa et al.; Licensee Lifescience Global.
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