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Laboratory of Microbial Ecology and Technology, Faculty of Agricultural and Applied Biological Sciences, University Ghent, B-9000 Ghent, Belgium and * Laboratory of Intestinal Immunobiology, Division of Nutritional Sciences, University of Illinois at Urbana-Champaign, Urbana, IL 61801
2To whom correspondence should be addressed.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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30% during the supplementation period; this was due
mainly to a significant increase of acetic and propionic acids. Gas
analysis revealed that the methane concentration increased
significantly. Ammonium and sulfide concentrations were not influenced
by soygerm supplementation. Use of an electronic nose apparatus
indicated that odor concentrations decreased significantly during the
treatment period. The ß-glycosidic bonds of the phytoestrogenic
isoflavones were cleaved under the conditions prevailing in the large
intestine. The increased bacterial fermentation after addition of the
soygerm powder was paralleled by substantial metabolism of the free
isoflavones (genistein, daidzein and glycitein), resulting in recovery
of only 12–17% of the supplemented isoflavones.
KEY WORDS: • soy • isoflavones • gut microbiota • fermentation • culture system
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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,
Setchell, 1998
). Substantial evidence indicates that
isoflavones present in soy play an important role in the observed
effects. These naturally occurring plant chemicals have been shown to
compete effectively with endogenous mammalian estrogens in binding to
the estrogen receptor of mammalian cells, preventing
estrogen-stimulated growth of cancerous cells (Brzezinski and Debi 1999
, Molteni et al. 1995
). Other
isoflavone effects include inhibition of tyrosine protein kinases,
antioxidative activity and in vitro angiogenesis (Brandi 1997
, Kim et al. 1998
).
Isoflavones occur predominantly as biologically inactive
ß-glycosides in soybean (conjugated isoflavones) (Setchell 1998
). After ingestion, the glycosides genistin and daidzin are
hydrolyzed by bacteria to release the bioactive phytoestrogens
genistein and daidzein (free isoflavones). Daidzein can be metabolized
by bacteria in the large intestine to form the more estrogenic equol
and the nonestrogenic O-desmethylangolensin, whereas
genistein is metabolized to the nonestrogenic p-ethyl phenol
(Kurzer and Xu 1997
). These data indicate that the gut
microbiota play an important role in the generation of biologically
active isoflavones but at the same time in the inactivation of these
bioactive compounds after further bacterial fermentation, resulting in
a loss of their acclaimed beneficial effects.
Much of the research concerning the health-promoting effects of soy
products has focused on the putative role of one dietary ingredient
i.e. the isoflavones. However, soy is an important source of many other
nutrients including dietary fiber, oligosaccharides, proteins, trace
minerals and vitamins, which could influence the host’s well-being
(Slavin et al. 1999
). A particular role can be reserved
for the oligosaccharides, which could meet the standards of a
prebiotic. Prebiotics have been developed to promote the growth and
activity of beneficial microorganisms in the large intestine. A
prebiotic is a nondigestible food ingredient that affects the host
beneficially by selectively stimulating the growth and/or activity of
one or a limited number of bacteria in the colon that can improve the
health of the host (Gibson and Roberfroid 1995
).
Soy products contain characteristically high concentrations of the
-glycosidic galactooligosaccharides, raffinose and stachyose. These
type of sugars are not absorbed in the upper part of the
gastrointestinal tract or hydrolyzed by human digestive enzymes
(Suarez et al. 1999b
). Upon delivery to the colon, these
sugars are fermented by the colonic microbiota possessing
-galactosidase activity. Administration of soybean oligosaccharides
to an in vitro culture of human gut microbiota has been reported to be
bifidogenic (Hayakawa et al. 1990
). Therefore,
Gibson and Roberfroid (1995)
suggested a potential
prebiotic role for soybean oligosaccharides. Studies addressing this
hypothesis have not been published.
The aim of our study was to investigate the effects of a soygerm powder on the fermentative capacity of the simulated microbiota of the colon. Furthermore, the capacity of this intestinal microbiota to metabolize the phytoestrogens present in the soygerm powder was evaluated.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The Simulator of the Human Intestinal Microbial Ecosystem
(SHIME)3
consists of five double-jacketed vessels maintained at
a temperature of 37°C. Each vessel simulates a particular part of the
gastrointestinal microbial ecosystem (Table 1
). The first two vessels work according to a fill-and-draw system,
whereas the last three are continuously stirred tank reactors with a
total retention time of 76 h. The suspensions are mixed
continuously by means of magnetic stirrers (Labinco L22, Vel, Leuven,
Belgium). pH controllers (pH controller R301, Consort, Turnhout,
Belgium) maintain the pH in the last three vessels between fixed limits
by the addition of 0.1 mol/L HCl or 0.1 mol/L NaOH (Table 1)
. There was
no gas exchange between the different vessels and the headspace of the
culture system was flushed twice a day for 15 min with
O2/free N2 to ensure
anaerobic conditions. A detailed scheme of the reactor set-up is
provided in Figure 1
. At the beginning of the experiment, the last three vessels were
inoculated with a pooled fecal sample of five volunteers (Molly et al. 1993
). Aliquots (10 g) of freshly voided fecal samples
were diluted and homogenized with 100 mL sterilized phosphate buffer
(0.1 mol/L, pH 7.0), containing 1 g/L sodium thioglycolate as reducing
agent. After removal of the particulate material by centrifugation (1
min, 500 x g), the supernatants were pooled and 50 mL
was introduced into the last three vessels. The microbial inoculum was
stabilized over a period of 3 wk by the addition of 200 mL of a
carbohydrate-based medium containing arabinogalactan (1 g/L),
pectin (2 g/L), xylan (1 g/L), starch (3 g/L), glucose (0.4 g/L) and
mucin (4 g/L) to the first vessel of the culture system three times a
day (Molly et al. 1994
). The pH of the feed was
gradually decreased to 2, simulating stomach acidification. The passage
of food in the small intestine was simulated in the next vessel by the
addition of 100 mL simulated pancreatic and bile liquid [6 g/L oxgall
(Difco, Bierbeek, Belgium), 0.9 g/L pancreatin (Sigma, Bornem, Belgium)
and 12.6 g/L NaHCO3]. Steady-state
conditions were assessed by monitoring the concentration of
short-chain fatty acids (SCFA). After the initial stabilization
period of 3 wk, the microbial communities present in the last three
vessels of the culture system were fed the carbohydrate-based
medium. During this control period of 14 d, bacterial populations
were characterized using plate counts of selected fecal marker
organisms (Table 2
), and the production of fermentation metabolites (SCFA, ammonium,
H2S, and gases) was monitored. During the
treatment period of 14 d, 2.5 g/d of a soygerm powder (SOYLIFE,
Soylife Nederland BV, Giessen, The Netherlands, Table 3
) was added to the carbohydrate-based medium. The effect of this
supplementation on the simulated microbial communities of the large
intestine was studied by means of the previously mentioned parameters
(selected fecal marker organisms and fermentation metabolites).
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Five subjects participated in this study. They were all healthy males with a mean age of 25 ± 2 y. They all reported to have no gastrointestinal problems or a recent history of antibiotic usage. Informed consent was obtained in writing.
Microbiological analyses.
The bacterial groups analyzed and the media used are indicated in Table 2
. These media have been used successfully by Molly et al. (1994)
to select for these bacterial maker organisms. Liquid
samples were withdrawn from the culture system and diluted serially in
physiologic solution (8.5 g/L NaCl). Three plates were inoculated with
a 0.1-mL sample of three dilutions, and incubated at 37°C using
conditions given in Table 2
. Anaerobic incubation of plates was
performed in jars with a gas atmosphere (84% N2, 8%
CO2, and 8% H2) adjusted by the Anoxomat 8000
system (Mart, Sint-Genesius-Rode, Belgium).
SCFA determination.
Liquid samples were collected and frozen at -20°C for subsequent
analysis. The SCFA were extracted from the samples with diethyl ether
and determined with a Di200 gas chromatograph (GC; Shimadzu,
’s-Hertogenbosch, The Netherlands). The GC was equipped with a
capillary free fatty acid packed column [EC-1000 Econo-Cap column
(Alltech, Laarne, Belgium), 25 m x 0.53 mm; film thickness
1.2 µm], a flame ionization detector and a Delsi
Nermag 31 integrator (Thermo Separation Products, Wilrijk, Belgium).
Nitrogen was used as the carrier gas at a flow rate of 20 mL/min. The
column temperature was set at 130°C and the temperature of the
injector and detector was set at 195°C (Nollet et al. 1998
).
Ammonium determination.
Liquid samples were frozen at -20°C for subsequent analysis. Using a
1026 Kjeltec Auto Distillation (FOSS Benelux, Amersfoort, The
Netherlands), ammonium in the sample was liberated as ammonia by the
addition of an alkali (MgO). The released ammonia was distilled from
the sample into a boric acid solution (Bremner and Keeney 1965
). The solution was back-titrated using a 665 Dosimat
(Metrohm, Berchem, Belgium) and 686 Titroprocessor (Metrohm).
H2S analysis.
The H2S concentration was determined by the addition of 5
mL of liquid samples to 0.4 mL of a solution containing
dimethyl-p-phenylenediamine
(p-aminodimethyl aniline) and ferric chloride
(Trüper and Schlegel 1964
). The methylene blue dye
produced was measured at 670 nm with a UVIKON930 spectrophotometer
(BRS, Brussels, Belgium).
Gas analysis.
Before flushing, the headspace of vessels 3, 4 and 5 was sampled (1 mL)
and analyzed for CO2 and CH4. A 20-mL sample
was collected to determine the concentration of H2. The
concentrations of CO2 and CH4 were determined
with an Intersmat IGC 120MB gas chromatograph (Thermo Separation
Products) connected to a Hewlett-Packard 3396A integrator (HP
Benelux, Brussels, Belgium). The GC was equipped with a dual-column
arrangement consisting of an in-series connected Porapak (50–80
mesh), a molecular sieve (60–80 mesh) and a catharometer. The column
temperature was set at 30°C and the flow rate of the carrier gas (He)
was fixed at 10 mL/min. The percentage of H2 was determined
using an Exhaled Hydrogen Monitor (GMI, Renfrew, Scotland) equipped
with a H2-sensitive three-electrode electrochemical
cell (Nollet et al. 1998
).
Further analysis of the gases present in the headspace was done using
the FOX3000 electronic nose (Alpha M.O.S., Toulouse, France). The
electronic nose consists of two measuring chambers each with six
different metal oxide sensors. Each chamber is equipped with two extra
sensors for measuring temperature and humidity. Each sensor consists of
a 50-µm layer of a metal oxide film deposited on a
ceramic film and displays a high sensitivity toward a broad range of
volatile chemical compounds (Table 4
). A mass-flow controller regulates the rate (150 mL/min) with which
humidified air flows continuously over the sensors. The injection time
or the sampling time was set at 15 s. The headspaces of SHIME
vessels (2 mL) were diluted in 2 L of dry air (Messer, Machelen,
Belgium) before injection. The measurement principle of an electronic
nose is based on the change in electrical resistance of the sensors
when volatile compounds are present. The metal oxide sensors are
semiconductors and are therefore gas sensitive. Oxygen present in the
air is chemisorbed on vacancies in the lattice of the bulk material and
removes electrons from the conducting band as follows:
 |
In the presence of a gas or a fragrant molecule (F), this
chemisorbed oxygen (O-) reacts irreversibly to
produce combined molecules (FO) as follows:
 |
The liberated electrons reduce the potential barrier of the
oxide grains, which decreases the electron mobility. As a consequence,
the electrical resistance of the sensors drops when a gas sample with
volatile organic compounds passes the sensors. The type of sensor and
the percentage of change of a sensor’s resistance after the injection
of a sample are an indication of the type and concentration of certain
organic compounds in the gas sample (Maricou et al. 1998
). The odor intensity can be estimated by the sensoric odor
perception (SOP) value, which is calculated according to the following
formula:
 |
where R0,i is the baseline resistance of sensor i; Ri is the resistance between the gas and sensor i; and Volume is the volume of gas analyzed.
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The concentration of glycosylated (genistin, daidzin and glycitin) and
free isoflavones (genistein, daidzein and glycitein) was determined by
HPLC (Wang and Murphy 1994
). All samples were analyzed
in triplicate.
Statistical analysis.
Samples were taken on d 7, 10 and 14 of the control and treatment
periods. ANOVA was performed on the data with the statistical software
SPSS 7.5 (SPSS, Chicago, IL). A P-value 
0.05 was
considered to be significant. All values are reported as means ± SD.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The SHIME reactor system was subjected to a control period of
14 d to establish a microbial community after inoculation of the
last three reactor vessels with a pooled fecal sample. During the
treatment period of 14 d, the addition of 2.5 g/d of soygerm
powder to the SHIME resulted in a rise in the concentrations of all
analyzed bacterial groups, especially in vessel 3 (Table 5
). An increase of >2 log10 units was observed for
the Lactobacillus population in vessel 3 (P
0.05). A microbial ecosystem could not establish itself in
vessel 1 or 2 because of the short retention time and the fill-and-draw
principle. Hence, vessels 1 and 2 were not sampled.
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The SCFA, acetic, propionic and butyric acids, comprised >90% of the
total fatty acid production. The other SCFA were the sum of the
concentrations of isobutyric, isovaleric and valeric acids. The
addition of soygerm powder led to an overall increase of the fatty acid
concentration. The total concentration in vessel 3 was significantly
higher (P 0.05) during the supplementation period
and this was due mainly to a significant increase in the concentration
of acetic and propionic acids (P 0.05). The
percentage increase of the total SCFA production amounted to 32, 24 and
24% for vessel 3, 4 and 5, respectively (Table 6
). Methane production increased significantly (P 0.05) in the last two reactor vessels concomitant with the addition of
the soygerm powder (Table 7
). Supplementation of the soygerm powder did not influence ammonium and
sulfide production. Supplementation of the soygerm powder had no
significant effect on the concentration of H2 and
CO2 (Table 7)
.
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0.05) reduced the SOP value in the headspace of all three reactor
vessels as measured by the FOX3000 electronic nose (Table 8
). The percentage of change of electrical resistance for the 12 FOX3000
sensors was plotted in a radar plot to distinguish qualitatively the
odor profiles of the headspace in the reactor vessels before and during
the addition of the soygerm powder. During the supplementation period,
significant decreases (P 0.05) of the electrical
resistance were observed for sensors 1, 3, 4 and 6, and sensors 4 and 6
for vessels 3 and 4, respectively. When the headspace of vessel 5 was
analyzed, the resistance dropped significantly for all sensors, except
5 and 10, during the treatment (Fig. 2
).
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). The free isoflavones comprised solely daidzein.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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, Zhang et al. 1999
). During a 2-wk period, the soygerm powder was
supplemented to the SHIME, an in vitro model simulating the colonic
microbial ecosystem of healthy adults, to determine the effect of the
soygerm powder on the microbial ecosystem. A second aim was to
determine to what extent the microbial ecosystem metabolizes the
isoflavones present in this soygerm powder.
A growing body of scientific publications indicates that dietary
modulation, by ingestion of prebiotics, may shift the microbial
ecosystem toward higher concentrations of lactic acid–producing
bacteria, which may be beneficial for the host (Fooks et al. 1999
, Fuller and Gibson 1997
, Roberfroid 1998
). Criteria that allow classifying a food ingredient as a
prebiotic include the following (Gibson 1999
): it must
neither be hydrolyzed nor absorbed in the upper part of the
gastrointestinal tract; it must be selectively fermented by one or a
limited number of potentially beneficial bacteria in the colon; it must
alter the composition of the colonic microbiota toward a healthier
composition; and it must preferably induce effects that are beneficial
to the host’s health.
The oligosaccharides present in the soygerm powder consist mainly of
the nondigestible raffinose (13 g/kg) and stachyose (87 g/kg)
oligosaccharides, which therefore serve as substrates for bacterial
fermentation (Suarez et al. 1999b
). Moreover, use of the
SHIME in vitro model, which lacks resorption of the small intestine,
implied that all nutrients present in the soygerm powder were
considered as colonic foods. During the treatment period, the
concentration of all bacterial groups increased and the strongest
increase was observed for Lactobacillus sp. An increase in
lactic acid bacteria is often driven by a decrease in luminal pH
because the capacity to thrive in low pH environments gives these
bacteria a selective advantage over other intestinal bacteria
(Sghir et al. 1998
). Gibson (1999)
stated
that lowering of the gut pH by metabolic products may be one of the
most important mechanisms by which a prebiotic can improve colonic
health. The pH drop in a microniche could select for lactic
acid-producing bacteria in this environment, possibly excluding
long-term colonization by invasive pathogens (Gibson and Wang 1994
). In our in vitro model, however, the colon vessels
are pH controlled, allowing nonacid-resistant microorganisms to
develop. The pH in the colon compartments of our system was set at the
lower limit of the pH interval, and the amount of base dosed to
maintain this pH (data not shown) increased during supplementation of
the soygerm powder, giving the lactic acid–producing bacteria a slight
growth advantage over the other microorganisms. Furthermore, it is now
recognized that the classical culture-based methods give a biased
view of the gut microbiota composition. Use of molecular approaches has
indicated that 60–80% of the gut microbiota have not been cultivated
and that the contribution of some species may not have been estimated
correctly (Langendijk et al. 1995
, Suau et al. 1999
). Moreover, molecular techniques are more sensitive than
culture-based techniques, making it plausible that we missed
changes in bacterial populations. However, we contend that the plate
counts obtained remain indicative of relative major trends in microbial
changes, although they do not necessarily represent absolute changes in
the complex microbial ecosystem of the colon. The knowledge gained via
the application of molecular techniques and the limited information
obtained with plate counts emphasize that the use of accurate methods
for monitoring microbial ecosystems is essential to understand the true
effect of a dietary strategy that aims at modulating the gut
microbiota.
During the supplementation period, the fermentative capacity of the
microbial community was increased and this led to a general rise in
SCFA. The strongest increase was observed in vessel 3, indicating high
carbohydrate fermentation. A rise of the SCFA concentration is a
positive property because these acids, especially butyric acid, are the
main energy source for colonocytes and influence colonic function by
stimulating water and sodium absorption and modulating motility
(Cherbut et al. 1997
). Furthermore, butyric acid induces
differentiation, stimulates apoptosis of cancerous cells in vitro and
thus arrests the development of cancer (Scheppach et al. 1995
). During the supplementation of the soygerm powder, no
effect on ammonium and hydrogen sulfide concentrations was observed.
Ammonia can alter the morphology and intermediary metabolism of
intestinal cells, increase DNA synthesis and promote tumorigenesis
(Ichikawa and Sakata 1998
). Hydrogen sulfide selectively
inhibits butyric acid oxidation in colonocytes and this may play a
pathogenic role in inflammatory bowel diseases such as ulcerative
colitis [see reviews by Pitcher and Cummings (1996)
and
Roediger et al. (1997)
]. Hence, increases in the
concentration of these compounds are considered to be potentially
harmful for the host. Quantitative gas analyses revealed that the
methane concentration increased significantly in the last two colon
compartments during the supplementation period. Production of methane
by the colonic microbiota is important because it permits a more
complete fermentation in that the removal of hydrogen is energetically
more favorable for fermentation (Christl et al. 1992
).
Although clinical relevance is not clear, the prevalence of
methanogenesis is inversely related to the prevalence of bowel cancer.
Long-term methanogenic conditions in the intestine can eventually
result in out-competition of the potentially harmful
sulfate-reducing bacteria (Gibson et al. 1988
).
Second, there is some evidence that methanogenic persons suffer less
from gas symptoms. Excessive gas production, primarily hydrogen gas, is
an important cause for irritable bowel syndrome. This common
gastrointestinal disorder causes abdominal pain, distention, flatulence
and borborygmus. These symptoms may be reduced in methanogenic persons
because the oxidation of hydrogen gas to methane gas reduces the volume
of gas to 25% (Florin and Jabbar 1994
). Moreover,
pulmonary excretion of methane may also be less limited by intestinal
blood flow because methane is more soluble than hydrogen (Florin and Woods 1995
).
Many of the putrefactive compounds (such as sulfur-containing
compounds, indoles, aliphatic amines and phenols) generated by
bacterial fermentation in the colon are responsible for the malodor of
flatus and feces (Hussein et al. 1999
). Because of its
offensive odor, rectal gas has been a topic of scientific interest for
many years. Furthermore, there have been allusions to the possibility
that malodorous breath gases may originate from the gut. In a recent
study, Suarez et al. (1999a)
showed that the predominant
sulfur gas causing the persistent malodor of breath after garlic
consumption originated from the gut. The authors suggested that if
these intestinal gases were the major cause of malodorous breath, a
reduction of the breath concentration of these gases would presumably
require manipulation of the diet and/or gut microbiota. Furthermore,
phenolic and indolic compounds have been linked to a variety of disease
states in humans, including initiation of cancer, malabsorption and
anemia (Macfarlane and Macfarlane 1997
). During our
study, we investigated the odor intensity and pattern generated by the
microbial community by means of an electronic nose. This apparatus has
been used in the past to measure the concentration of volatile organic
compounds (Maricou et al. 1998
). Our data revealed that
during the addition of the soygerm powder, the amount of odor decreased
significantly. In the headspace of vessels 3 and 4, the decreased
amount of odor was due to a significantly decreased response of the
electrical sensors 1, 3, 4 and 6. Nearly all sensors showed a low
response when the headspace of vessel 5 was analyzed. Low electrical
response of the sensors 1, 3, 4 and 6 was caused by a concentration
decrease of certain gaseous compounds. To determine which classes of
compounds were reduced in concentration during the soygerm powder
treatment, the FOX pattern of a range of pure volatile organic
compounds was determined. Sensors 1, 3, 4 and 6 were very sensitive to
skatol, indol and phenol (data not shown). These compounds can be
recovered in a large concentration in the distal part of the colon and
originate from bacterial metabolism of aromatic amino acids
(Macfarlane and Macfarlane 1997
). To our knowledge, this
is the first study in which the odor produced by the gut microbiota was
monitored. Taking into account that compounds produced by intestinal
microorganisms can be responsible for malodorous breath and various
diseases, the capacity of the soygerm powder to reduce the
concentration of odoriferous compounds is an interesting feature.
The soygerm powder used in this study is being marketed as a product
containing a naturally high level of ß-glycosidic isoflavones. Once
the isoflavone moiety is hydrolyzed from the sugar residue by bacterial
enzymes, the free isoflavone can exert estrogenic effects locally (on
colonocytes) or on other tissues (after resorption in the bloodstream).
Gut microbiota play important roles in further isoflavone metabolism
and bioavailability (Xu et al. 1995
). In our study, we
did not aim to identify the metabolites generated by the
microorganisms, but rather to confirm that the bacteria were able to
hydrolyze the conjugated isoflavones. Therefore, the concentration of
isoflavones was determined 1 and 2 wk after the initiation of the
treatment. The isoflavones were released in neither vessel 1 or 2,
simulating the stomach and small intestine, respectively. The
concentration of isoflavones (conjugated and free) in the three last
vessels of the SHIME ranged between 12 and 17% of the concentration
that could be expected, on the basis of the amount of soygerm powder
added daily to the reactor and the concentration of conjugated
isoflavones present in the powder (Table 3)
. The data are consistent
with the literature and indicate that isoflavones are not only
hydrolyzed but also extensively metabolized (Chang and Nair 1995
, Xu et al. 1995
). Although Zhang et al. (1999)
indicated that genistein and glycitein are more
resistant to bacterial breakdown than daidzein, we recovered only
daidzein. It is known that there is considerable interindividual
variation of isoflavone metabolism. Zhang et al. (1999)
hypothesized that isoflavone metabolism may be influenced by the
dietary pattern because diet has an effect on the gut microbial
population and its metabolizing capacity. The extent to which the host
can benefit from the positive effects of free isoflavones is determined
by the competition between resorption of free isoflavones by the host
and further metabolism and inactivation of these compounds by the
intestinal microbiota. The kinetics of isoflavone metabolism by the
microbial ecosystem is a point that merits more thorough research.
This study indicates that the consumption of soygerm powder may
influence the gut microbiota in a beneficial way. The concentration of
SCFA increased, whereas concentrations of the putative harmful
metabolites (NH4+ and
H2S) were not affected. Gas analyses revealed
that methanogenesis was stimulated significantly and that the odor
produced by the microbiota decreased. The microbial community of the
large intestine, as simulated by the SHIME, was able to hydrolyze
conjugated isoflavones and to transform the free isoflavones. Because
of the limited experimental set-up, we cannot draw firm conclusions
concerning the effect of soygerm powder on the host health. This is the
first study indicating the ability of soygerm powder to have a positive
influence on the fermentation balance in the large intestine, but these
results are to be confirmed in larger and better-designed in vitro
experiments. The limitations associated with in vitro systems
(Minekus et al. 1999
) also should trigger further
research to study the beneficial effects of soygerm powder consumption
in vivo.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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3 Abbreviations used: GC, gas chromatography; SCFA, short-chain fatty acids; SHIME, Simulator of the Human Intestinal Microbial Ecosystem; SOP, sensoric odor perception.
Manuscript received March 30, 2000. Initial review completed May 11, 2000. Revision accepted July 12, 2000.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
1. Ball G.F.M. Fat Soluble Vitamin Assays in Food Analyses 1988:64–75 and 234–258 Elsevier Applied Science London, UK.
2. Brandi M. L. Natural and synthetic isoflavones in the prevention and treatment of chronic diseases. Calcif. Tissue Int. 1997;61:S5-S8
3. Bremner J. M., Keeney R. D. Steam distillation methods for determination of ammonium, nitrate and glycine. Anal. Chem. Acta 1965;32:485-495
4. Brzezinski A., Debi A. Phytoestrogens: the "natural" selective estrogen receptor modulators?. Eur. J. Obstet. Gynaecol 1999;85:47-51
5. Chang Y. C., Nair M. Metabolism of daidzein and genistein by intestinal bacteria. J. Nat. Prod. 1995;58:1892-1896[Medline]
6. Cherbut C., Aubé A. C., Blottière H. M., Galmiche J. P. Effects of short-chain fatty acids on gastrointestinal motility. Scand. J. Gastroenterol. 1997;32:52-57[Medline]
7. Christl S. U., Murgatroyd P. R., Gibson G. R., Cummings J. H. Production, metabolism and excretion of hydrogen in the large intestine. Gastroenterology 1992;102:1269-1277[Medline]
8. Florin T.H.J., Jabbar I. A. A possible role for bile acid in the control of methanogenesis and the accumulation of hydrogen gas in the colon. J. Gastroenterol. Hepatol. 1994;9:112-117[Medline]
9.
Florin T.H.J., Woods H. J. Inhibition of methanogenesis by human bile. Gut 1995;37:418-421
10. Fooks L. J., Fuller R., Gibson G. R. Prebiotics, probiotics and human gut microbiology. Int. Dairy J. 1999;9:53-61
11. Fuller R., Gibson G. R. Modification of the intestinal microflora using probiotics and prebiotics. Scand. J. Gastroenterol. 1997;32:28-31[Medline]
12. Gibson G. R. Dietary modulation of the human gut microflora using the prebiotics oligofructose and inulin. J. Nutr. 1999;129:1438S-1441S
13. Gibson G. R., Macfarlane G. T., Cummings J. H. Occurrence of sulphate-reducing bacteria in human faeces and the relationship of dissimilatory sulphate reduction to methanogenesis. J. Appl. Bacteriol. 1988;65:103-111[Medline]
14. Gibson G. R., Roberfroid M. B. Dietary modulation of the human colonic microbiota: introducing the concept of prebiotics. J. Nutr. 1995;125:1401-1412
15. Gibson G. R., Wang X. Regulatory effects of bifidobacteria on the growth of other colonic bacteria. J. Appl. Bacteriol. 1994;77:412-420[Medline]
16. Hayakawa K., Mizutani J., Wada K., Masai T., Yoshihara I., Mitsuoka T. Effect of soybean oligosaccharides on human fecal flora. Microb. Ecol. Health Dis. 1990;3:293-303
17. Hussein H. S., Flickinger E. A., Fahey G. C. Petfood applications of inulin and oligofructose. J. Nutr. 1999;129:1454S-1456S[Medline]
18.
Ichikawa H., Sakata T. Stimulation of epithelial cell proliferation of isolated distal colon of rats by continuous colonic infusion of ammonia or short-chain fatty acids is nonadditive. J. Nutr. 1998;128:843-847
19. Ireland P. A., Dziedzic S. Z., Kearsley M. W. Saponin content of soya and some commercial soya products by means of high-performance liquid-chromatography of the sapogenins. J. Sci. Food Agric. 1984;37:694-698
20. Kim H. K., Peterson T. G., Barnes S. Mechanism of action of the soy isoflavone genistein: emerging role of its effects via transforming growth factor ß signaling pathways. Am. J. Clin. Nutr. 1998;68:1418S-1425S[Abstract]
21. Kurzer M., Xu X. Dietary phytoestrogens. Annu. Rev. Nutr. 1997;17:353-381[Medline]
22. Langendijk P. S., Schut F., Jansen G. J., Raangs G., Kamphuis G. R., Wilkinson M. H. F., Welling G. W. Quantitative fluorescence in situ hybridisation of Bifidobacterium spp. with genus-specific 16S rRNA-targeted probes and its application in fecal samples. Appl. Environ. Microbiol. 1995;61:3069-3075[Abstract]
23. Macfarlane G. T., Macfarlane S. Human colonic microbiota: ecology, physiology and metabolic potential of intestinal bacteria. Scand. J. Gastroenterol. 1997;32:3-9
24. Maricou H., Pereira D., Verschuere L., Philips S., Verstraete W. Measurement of some volatile compounds by means of the electronic nose. Water Air Soil Pollut 1998;107:423-442
25.
Messina M. J. Legumes and soybeans: overview of their nutritional profiles and health effects. Am. J. Clin. Nutr. 1999;70:439S-450S
26. Minekus M., Smeets-Peeters M., Bernalier A., Marol-Bonnin S., Havenaar R., Marteau P., Alric M., Fonty G., Huis in ’t Veld J. H. A computer-controlled system to simulate conditions of the large intestine with peristaltic mixing, water absorption and absorption of fermentation products. Appl. Microbiol. Biotechnol. 1999;53:108-114[Medline]
27. Molly K., Vande Woestyne M., De Smet I., Verstraete W. Validation of the simulator of the human intestinal microbial ecosystem (SHIME) reactor using microorganism-associated activities. Microb. Ecol. Health Dis. 1994;7:191-200
28. Molly K., Vande Woestyne M., Verstraete W. Development of a 5-step multi-chamber reactor as a simulation of the human intestinal microbial ecosystem. Appl. Microbiol. Biotechnol. 1993;39:254-258[Medline]
29. Molteni A., Brizio-Molteni L., Persky V. In vitro hormonal effects of soybean isoflavones. J. Nutr. 1995;125:751S-756S
30. Nollet L., Mbanzamihigo L., Demeyer D., Verstraete W. Effect of the addition of Peptostreptococcus productus ATCC 35244 on reductive acetogenesis in the ruminal ecosystem after inhibition of methanogenesis by cell-free supernatant of Lactobacillus plantarum 80. Anim. Feed Sci. Technol. 1998;71:49-66
31.
Pitcher M. C., Cummings J. H. Hydrogen sulphide: a bacterial toxin in ulcerative colitis?. Gut 1996;39:1-4
32. Roberfroid M. B. Prebiotics and synbiotics: concepts and nutritional properties. Br. J. Nutr. 1998;80:S197-S202[Medline]
33. Roediger W. E., Moore J., Babidge W. Colonic sulfide in pathogenesis and treatment of ulcerative colitis. Dig. Dis. Sci. 1997;42:1571-1579[Medline]
34. Scheppach W., Bartram H. P., Richter F. Role of short-chain fatty acids in the prevention of colorectal cancer. Eur. J. Cancer 1995;:1077-1080
35. Setchell K.D.R. Phytoestrogens: the biochemistry, physiology, and implications for human health of soy isoflavones. Am. J. Clin. Nutr. 1998;68:1333S-1346S[Abstract]
36. Sghir A., Chow J. M., Mackie R. I. Continuous culture selection of bifidobacteria and lactobacilli from human faecal samples using fructooligosaccharide as selective substrate. J. Appl. Microbiol. 1998;85:769-777[Medline]
37.
Slavin J. L., Martini M. C., Jacobs D. R., Marquart L. Plausible mechanisms for the protectiveness of whole grains. Am. J. Clin. Nutr. 1999;70:459S-463S
38. Song T., Barua K., Buseman G., Murphy P. A. Soy isoflavones analysis: quality control and a new internal standard. Am. J. Clin. Nutr. 1998;68:1474S-1479S[Abstract]
39. Suarez F., Springfield J., Furne J., Levitt M. Differentiation of mouth versus gut as site of origin of odoriferous breath gases after garlic ingestion. Am. J. Physiol. 1999a;39:G425-G430
40.
Suarez F. L., Springfield J., Furne J. K., Lohrmann T. T., Kerr P. S., Levitt M. D. Gas production in humans ingesting a soybean flour derived from beans naturally low in oligosaccharides. Am. J. Clin. Nutr. 1999b;69:135-139
41.
Suau A., Bonnet R., Sutren M., Godon J. J., Gibson G. R., Collins M. D., Dore J. Direct analysis of genes encoding 16S rRNA from complex communities reveals many novel molecular species within the human gut. Appl. Environ. Microbiol. 1999;65:4799-4807
42. Trüper H. G., Schlegel H. G. Sulphur metabolism in Thiorhodaceae I. Quantitiative measurements on growing cells of Chromation okenii. Antonie Leeuwenhoek 1964;30:225-238
43. Wang H. J., Murphy P. A. Isoflavone content in commercial soybean foods. J. Agric. Food Chem. 1994;42:1666-1673
44.
Watanabe S., Yamaguchi M., Sobue T., Takahashi T., Miura T., Arai Y., Mazur W., Wahala K., Adlercreutz H. Pharmacokinetics of soybean isoflavones in plasma, urine and feces of men after ingestion of 60 g baked soybean powder (kinako). J. Nutr. 1998;128:1710-1715
45. Xu X., Harris K. S., Wang H. J., Murphy P. A., Hendrich S. Bioavailability of soybean isoflavones depends upon gut microflora in women. J. Nutr. 1995;125:2307-2315
46.
Zhang Y., Wang G. J., Song T. T., Murphy P. A., Hendrich S. Urinary disposition of the soybean isoflavones daidzein, genistein and glycitein differs among humans with moderate isoflavone degradation activity. J. Nutr. 1999;129:957-962
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). During the treatment period, 2.5 g/d of soygerm
powder was added to the SHIME medium. SD are not
represented to improve interpretability of the plots. Significant
differences between the control period and the treatment period are
indicated next to the angular data: *P