Gum Arabic establishes prebiotic functionality in healthy human volunteers in a dose dependent manner

Abstract

The present study was undertaken to determine the prebiotic efficacy of gum arabic upon consumption by man for up to 4 weeks and, if any, to establish the dose-effect relationship. Human healthy volunteers consumed various daily doses (5, 10, 20, 40 g) of gum arabic (EmulGold) in water for up to 4 weeks. Daily consumption of water was taken as the negative control and that of 10 g inulin as the positive control. At 0, 1, 2 and 4 weeks quantification of bacterial numbers in stool samples was performed via real time-PCR techniques and questionnaires were filled in to account for potential drawbacks. The genera of Bifidobacteria and Lactobacilli were taken as potentially beneficial bacteria and those of Bacteroides, Clostridium difficile and Enterococci as potentially non-beneficial, this distinction was dependent on the issue of these numbers being or becoming out of balance in the host. Compared with the negative control the numbers of Bifidobacteria and Lactobacilli 4 weeks after consumption were significantly higher for gum arabic: the optimal dose being around 10 g. Moreover, at this dose the numbers of Bifidobacteria, Lactobacilli and Bacteroides were significantly higher for gum arabic than for inulin. No significant drawback was encountered during the study. It is concluded that gum arabic establishes prebiotic efficacy, at least as good as inulin. The optimal daily dose was found to be 10 g.

Full text

Gum arabic establishes prebiotic functionality in healthy human volunteers
in a dose-dependent manner
Wim Calame
1
*, Antje R. Weseler
2
, Christer Viebke
3
, Cal Flynn
4
and Andre
´
D. Siemensma
1
1
Kerry Group Nutrition Technical Center, Veluwezoom 62, 1327 AH Almere, The Netherlands
2
NutriScience BV, Oxfordlaan 70, 6229 EV Maastricht, The Netherlands
3
Kerry Ingredients, Veluwezoom 62, 1327 AH Almere, The Netherlands
4
Kerry Ingredients, Tralee Road, Listowel, Co. Kerry, Republic of Ireland, Ireland
(Received 5 November 2007 – Revised 13 March 2008 – Accepted 17 March 2008 – First published online 9 May 2008)
The present study was undertaken to determine the prebiotic efficacy of gum arabic upon consumption by man for up to 4 weeks and, if any, to
establish the dose–effect relationship. Human healthy volunteers consumed various daily doses (5, 10, 20, 40 g) of gum arabic (EmulGold
w
)in
water for up to 4 weeks. Daily consumption of water was taken as the negative control and that of 10 g inulin as the positive control. At 0, 1, 2 and
4 weeks quantification of bacterial numbers in stool samples was performed via real time-PCR techniques and questionnaires were filled in to
account for potential drawbacks. The genera of Bifidobacteria and Lactobacilli were taken as potentially beneficial bacteria and those of Bacter-
oides, Clostridium difficile and Enterococci as potentially non-beneficial, this distinction was dependent on the issue of these numbers being or
becoming out of balance in the host. Compared with the negative control the numbers of Bifidobacteria and Lactobacilli 4 weeks after consumption
were significantly higher for gum arabic: the optimal dose being around 10 g. Moreover, at this dose the numbers of Bifidobacteria, Lactobacilli
and Bacteroides were significantly higher for gum arabic than for inulin. No significant drawback was encountered during the study. It is concluded
that gum arabic establishes prebiotic efficacy, at least as good as inulin. The optimal daily dose was found to be 10 g.
Gum arabic: Prebiotic: Bifidobacteria: Lactobacilli
Gum arabic is a dried exudate of the acacia tree (Acacia sene-
gal or Acacia seyal), a tree commonly encountered in various
tropical and subtropical parts of the world, especially in
Africa. It is a heteropolysaccharide of high molecular weight
(approximately 350–850 kDa) containing galactose, rham-
nose, glucuronic acid and arabinose residues, but also minerals
like calcium, potassium and magnesium
(1)
. The total amount
of protein is limited to less than 3 %. Gum arabic is highly
soluble in water, concentrations up to 40 % are feasible with-
out a major impact on viscosity
(1)
, rendering it an attractive
candidate compound for various applications, like beverages.
One of the most promising applications linked with gum
arabic, due to its relative inaccessibility to the various
enzymes within the small intestines, concerns its use as pre-
biotic, being defined as a non-digestible food ingredient that
beneficially affects the host by selectively stimulating the
growth and/or activity of one or a limited number of bacteria
in the colon without stimulating that of unwanted bacteria, and
thus contributes to host well-being and health
(2,3)
. Various
studies mention its potential as a prebiotic agent. Wyatt
et al.
(4)
addressed the issue in one volunteer by applying
10 g gum arabic and noted an increase in the numbers of
Bacteroides and Bifidobacterium. In healthy human volunteers
Cherbut et al.
(5)
demonstrated that consumption of 10 and
15 g/d for 10 d yielded an increase in counts of both lactic
acid-producing bacteria and Bifidobacteria as determined in
faecal samples. Using in vitro techniques Michel et al.
(6)
as
well as May et al.
(7)
yielded conflicting results on the selec-
tive outgrowth of the unwanted Clostridium difficile. The
latter might be explained by a difference of the host providing
the faecal sample: man in the former and pigs in the latter.
Moreover, differences in the production of SCFA upon incu-
bation of various fibre sources were also encountered
(7)
.
The effect on the composition of SCFA in vitro
(7,8)
and
enhancement of gut membrane function underline the poten-
tial functionality of gum arabic on gastrointestinal health as
well. As demonstrated in experimental animal models, opti-
mizing the host resistance in the colon
(9,10)
represents another
biological function associated with the consumption of gum
arabic. Although a possible effect on lowering of the glycae-
mic index is also suggested, scientific proof is lacking yet.
All of these considerations render gum arabic a potentially
interesting compound for gastrointestinal health functionality.
Moreover, gum arabic is already used as a coating agent and it
is known to enhance the survival of probiotica under physio-
logical conditions in the gut
(11,12)
.
Since most of the studies mentioned earlier concern in vitro
and animal models, there is a lack in fundamental understan-
ding in the use of gum arabic in man. Especially the impact of
gum arabic consumption on the qualitative and quantitative
* Corresponding author: Dr Wim Calame, fax þ31 36 5233110, email wim.calame@kerrybioscience.com
British Journal of Nutrition (2008), 100, 1269–1275 doi:10.1017/S0007114508981447
q The Authors 2008
British Journal of Nutrition

composition of micro-organisms within the colon flora in
healthy man has not been evaluated over a relatively long
period of time. To assess the prebiotic potential during 4
weeks of consumption, gum arabic was compared with that
of a well-established compound, inulin
(13)
, and with water as
the negative control because the various doses of gum
arabic were dissolved in water. Therefore the aim of the pre-
sent study was to investigate a potential prebiotic functionality
by gum arabic, and if any, establish a dose–effect relationship
after a period of 4 weeks of daily consumption.
Methods
Material
Gum arabic (EmulGold
w
) was provided by Kerry Ingredients
(Cam, UK) in a spray-dried form as a water-soluble free-flow-
ing food-grade powder. EmulGold
w
consists of at least 80 %
soluble fibre and 3 % protein. Gum arabic has GRAS status
(E414, EU directive 95/2/EC); no recommended daily dose
has been established so far.
Inulin (Fibruline
w
Instant), kindly provided by Cosucra
(Warcoing, Belgium), is a fructo-oligosaccharide polymer
derived from the chicory root. It was also obtained as a
spray-dried powder and typically consists of at least 90 %
non-digestible fibre and a maximum of 10 % free fructose,
glucose and saccharose. The mean degree of polymerization
is 9. All test products were of food-grade standard.
Subjects and study design
The present study was performed as a randomized, double-
blinded, double-controlled trial with six parallel test groups.
The study protocol was approved by the Medical Ethics Com-
mittee of the University of Maastricht, The Netherlands (MEC
05-148) and conducted in accordance with the World Medical
Association Declaration of Helsinki. Healthy volunteers (n 54)
were initially selected according to specific inclusion criteria,
such as BMI between 19 and 27 kg/m
2
; normal blood cell
counts and normal non-fasted blood glucose concentrations;
absence of glucose and/or albumin in urine; no use of medi-
cation affecting gastrointestinal physiology, such as antimicro-
bial drugs; no use of specific supplements, functional foods or
other products claiming specific pro- and/or prebiotic effects
(yoghurts, etc.). Every volunteer was asked to sign the
Informed Consent Form. In total eighty-one subjects were
screened for the study of which fifty-one actually started.
At the onset of the trial three subjects dropped out due to
various personal reasons. Individuals were randomized over
the various groups.
Experimental procedures
Every volunteer was randomly assigned to one of the six
groups via Latin-square arrangement with date of entry as con-
trolling factor. Subjects consumed either 5, 10, 20 or 40 g
EmulGold
w
/d, water as a negative control or a dose of 10 g
Fibruline/d for 4 weeks.
Every product was dissolved in 250 ml water and consumed
at around 10.00 hours. The negative control consisted of
250 ml water without any addition. Volunteers were instructed
to maintain their usual eating habits throughout the entire
study period.
At the start of the study, as well as at 1, 2 and 4 weeks the
volunteers were asked to collect two fresh faecal samples of
approximately 10 – 15 ml in special tubes via a standardized
method and store them directly in the freezer (2 208C) or in
the fridge at 48C if they did not have access to a freezer.
They were asked to deliver the samples to the laboratory as
quickly as possible.
At weeks 0, 1, 2 and 4 volunteers were requested to rank
their well-being with respect to gastrointestinal drawbacks,
such as abdominal pain, intestinal bloating, flatulence,
nausea, borborygmi, diarrhoea and constipation. The respec-
tive ranks given were: 0 ¼ none, 1 ¼ mild, 2 ¼ moderate,
3 ¼ severe. Moreover, stool frequency and consistency were
also monitored and ranked as follows: 1 ¼ watery/diarrhoeal,
2 ¼ soft, 3 ¼ normal, 4 ¼ hard.
Microbial determination of frozen stool samples
The frozen samples were regularly collected and sent to the
appropriate microbiological laboratory (Laboratorium Pro
Health BV, Weert, The Netherlands). Quantification of the
various genera or species of bacteria, Bifidobacteria, Lactoba-
cilli, Bacteroides, C. difficile and Enterococci, was achieved
via real-time PCR with 16S ribosomal DNA-targeted
genus-specific primers
(14)
(Table 1) using the LightCycler
w
System (Roche Diagnostics, Mannheim, Germany). The used
primers showed a high PCR efficiency (96·5–100·1 %) and no
cross-reactivity with other micro-organisms
(14)
. Extraction of
Table 1. Primers used within the present study to quantify the various (groups of) bacteria by means
of real-time PCR
(Group of) bacteria identified Amino acid sequence Reference no.
(I) Bifidobacteria spp. (243 bp) Forward: 5
0
-TCGCGTC(C/T)GGTGTGAAAG-3
0
14
Reverse: 5
0
-CCACATCCAGC(A/G)TCCAC-3
0
(II) Lactobacilli spp. (341 bp) Forward: 5
0
-AGCAGTAGGGAATCTTCCA-3
0
14
Reverse: 5
0
-CACCGCTACACATGGAG-3
0
(III) Bacteroides spp. (140 bp) Forward: 5
0
-GGTGTCGGCTTAAGTGCCAT-3
0
14
Reverse: 5
0
-CGGA(C/T)GTAAGGGCCGTGC-3
0
(IV) Clostridium difficile (157 bp) Forward: 5
0
-TTGAGCGATTTACTTCGGTAAAGA-3
0
14
Reverse: 5
0
-CCATCCTGTACTGGCTCACCT-3
0
(V) Enterococci spp. (144 bp) Forward: 5
0
-CCCTTATTGTTAGTTGCCATCATT-3
0
14
Reverse: 5
0
-ACTCGTTGTACTTCCCATTGT-3
0
W. Calame et al.1270
British Journal of Nutrition

DNA from the respective faecal samples was done via
QIamp
w
DNA stool mini kit (Qiagen, Hilden, Germany).
The amount of PCR product within each amplification
cycle was determined via SYBR Green I fluorescence inten-
sity. For each bacterial group, or species as in the case of
C. difficile, standard curves were made by plotting threshold
cycles obtained after real-time PCR analyses of different
culture dilutions of bacterial strains representative for the
groups. This enabled direct comparison between the threshold
cycle and the 10-logarithm of the number of bacteria, as
established via plate counting
(15,16)
. From the precise
amount of faeces obtained the results were calculated and
given as log10 number of bacteria/g wet faeces.
Power analysis
Since to our knowledge no similar study has been conducted,
data from Kruse et al.
(13)
were used. The a has been set at
0·05 and the power (1 2 b) at 0·8, for a one-sided test. The
formula used for the power analysis
(17)
was:
n ¼
ðZ
a
þ Z
b
Þs
ffiffiffi
2
p
d
0

2
; ð1Þ
in which Z is the value to determine that a standard normal
deviate has certain probability of exceeding a specified
value; s is the standard deviation of the outcome variable,
assumed to be equal for both treatments; d
0
is the smallest
treatment effect which has to be detected with probability of
at least 1 2 b .
Calculation revealed that in this parallel study a number of
at least eight persons is needed, taking into account a drop-out
rate of one person per group.
Statistical analyses
Bacterial numbers were expressed as log10 numbers/g wet
faeces. The D values (log10 numbers at t
x
(x ¼ 1, 2 or 4)
minus log10 numbers at t
0
) per individual were calculated
and used for statistical evaluation. Since every group consisted
of different individual subjects (parallel test group design)
unpaired tests were applied for statistical analysis between
groups and paired tests within groups.
Initially, t tests were used to detect differences between
groups at various time intervals and between groups receiving
various doses. Subsequently, via ANOVA and multiple
regression
(18)
, the effect of the various doses of gum arabic
on the change in log10 number of bacteria over 4 weeks
was addressed. The formula used
(18)
was:
y ¼ a
1
ðXÞþa
2
ðX
2
Þþa
3
ðe
2X
Þþa
4
; ð2Þ
in which y ¼ D log10; X is the dose of gum arabic used; a
1–4
are coefficients.
Significance was obtained via t test and F test. The
software used for the statistical analyses was STATA version
8 (Stata Corp., College Station, TX, USA).
With respect to the adverse effects as experienced by the
volunteers the results were standardized between 1 (100 %
increase in occurrence) and 21 (100 % decrease in occurrence).
Throughout the study P values of 0·05 or lower were
considered to be significant.
Results
Compliance of volunteers
Table 2 provides information on baseline characteristics of
the various groups. There were no statistically significant
Table 2. Demographic baseline characteristics of the study population used for statistical analyses*
(Mean values and standard deviations)
Blood pressure
(mmHg)
Group Age (years) Systolic Diastolic Height (m) Weight (kg) BMI (kg/m
2
)
Water
Mean 30·6 124·3 70·3 1·83 78·7 23·2
SD 13·0 14·9 8·0 0·11 17·3 2·9
Arabic gum
5g
Mean 33·0 126·3 76·3 1·73 70·2 23·5
SD 13·8 11·6 6·8 0·09 8·3 2·6
10 g
Mean 29·7 124·8 74·7 1·78 71·5 22·5
SD 13·6 9·8 7·3 0·09 10·3 1·9
20 g
Mean 34·9 119·8 73·4 1·72 65·8 22·3
SD 15·2 11·4 7·3 0·08 7·4 2·2
40 g
Mean 28·8 112·8 66·7 1·70 61·9 21·4
SD 9·1 7·4 6·8 0·13 9·4 1·2
Inulin (10 g)
Mean 28·3 120·9 69·8 1·74 70·1 23·0
SD 12·3 14·7 6·8 0·08 10·5 2·0
Total
Mean 30·9 121·9 72·0 1·75 70·3 22·7
SD 12·8 12·3 7·5 0·10 11·8 2·2
* For details of subjects and procedures, see Methods.
Gum arabic as prebiotic compound in man 1271
British Journal of Nutrition

differences in these characteristics between the various groups.
Subjects’ compliance to the protocol was assessed on the basis
of the test product intake as recorded in the study diaries.
In all test groups compliance was found to be very high:
97·0–99·6 %.
Quantification of bacterial numbers over 4 weeks
of intervention
The actual numbers of the various groups of bacteria at the
start and at the end of the period are listed in Table 3.
There were no significant differences observed in the initial
number of the various bacteria between the different groups
of volunteers. Analyses were done on the difference in the
10-logarithmic number at 4 weeks to that at the start. Only
in the volunteers who consumed gum arabic was a significant
change in these bacterial numbers observed. At a dose of 10 g
a significant increase in Bifidobacteria, Lactobacilli and Bac-
teroides was noted. A decrease in numbers was found for Lac-
tobacilli at a dose of 20 g and for Bacteroides at a dose of 40 g.
Bifidobacteria spp.
The change in numbers of Bifidobacteria within the faeces
followed a dose-dependent effect (Table 4). The increase in the
numbers of Bifidobacteria in subjects having consumed 10 g
gum arabic/d was significantly (P, 0·01) higher than in those
who consumed 0 g gum arabic (water, negative control): approxi-
mately 40 fold difference in outgrowth. Moreover, at a dose
of 10 g this increase was also significantly (P,0·05) higher for
gum arabic than for inulin: an approximately 10-fold difference.
Higher doses of gum arabic did not lead to an additional effect.
Using the regression model the optimal dose with respect
to the highest number of bacteria was found to be around
10 g gum arabic.
Lactobacilli spp.
After consuming 10 g gum arabic/d for 4 weeks the increase in
the number of Lactobacilli was significantly (P, 0·05) higher
than observed at 0 g gum arabic (water, negative control): an
approximately 6-fold difference in numbers. Interestingly,
consumption of 10 g gum arabic yielded a significantly
(P, 0·03) higher increase in numbers than that observed for
10 g inulin: approximately 7-fold (Table 4).
An optimum dose of EmulGold
w
with respect to the num-
bers of Lactobacilli was established at about 5– 10 g.
Bacteroides spp.
No differences in the D numbers of Bacteroides were detected
between volunteers consuming gum arabic for 4 weeks and
those consuming water, except at a dose of 10 g at which
approximately a 2-fold increase was found. Interestingly,
intake of 10 g gum arabic yielded a significantly (P, 0·01)
higher increase in counts than that of 10 g inulin (approxi-
mately 2·5-fold; Table 4).
Relatively large changes in numbers of Bacteroides were
found at doses of 5 and 10 g gum arabic. As was observed
with the Lactobacilli the number of Bacteroides declined at
higher doses, this difference being significant (P, 0·01).
Clostridium difficile
No differences in the numbers of C. difficile at the start and
at 4 weeks were encountered between the various groups
(Table 4). However, the variation in numbers per time-
point was relatively large, especially after consumption
of higher doses of gum arabic, but also at the start of the inter-
vention. No significant differences were identified, not only
between water and the various doses of gum arabic, but also
Table 3. The 10-logarithmic numbers of bacteria within the various groups at the start (week 0) and at the end (week 4) of the study†
(Mean values and standard deviations)
Bifidobacteria Lactobacilli Bacteroides Clostridium difficile Enterococci
Week 0 Week 4 Week 0 Week 4 Week 0 Week 4 Week 0 Week 4 Week 0 Week 4
Water
Mean 8·90 8·49 7·83 7·63 8·91 8·89 8·87 8·15 8·88 8·07
SD 1·25 1·20 0·57 0·51 0·45 0·56 0·90 1·44 1·02 1·42
Gum arabic
5g
Mean 7·77 7·75 7·39 7·68 8·72 9·08 8·47 8·72 7·65 7·56
SD 0·64 0·94 0·59 0·62 0·48 0·27 0·99 0·90 0·46 0·53
10 g
Mean 7·87 9·09** 7·13 7·70* 8·66 8·97** 8·21 8·60 8·08 7·64
SD 1·06 1·17 0·61 0·70 0·36 0·38 1·38 2·24 0·77 0·72
20 g
Mean 8·54 8·93 7·69 7·17** 8·89 8·78 8·35 7·22 8·12 8·34
SD 1·47 1·13 0·93 0·79 0·59 0·66 1·03 2·45 1·07 1·36
40 g
Mean 8·21 9·09 7·91 7·44 9·10 8·86* 8·82 7·86 8·33 8·37
SD 1·61 1·36 1·27 0·89 0·51 0·58 1·24 2·17 1·69 1·50
Inulin (10 g)
Mean 8·39 8·67 8·00 7·71 8·92 8·81 8·94 8·77 8·43 8·13
SD 1·04 1·08 0·93 0·33 0·54 0·17 0·57 1·42 1·04 0·5
Mean values were significantly different from those of week 0 (paired t testing (one-sided)): *P, 0·05, **P, 0·01.
† For details of subjects and procedures, see Methods.
W. Calame et al.1272
British Journal of Nutrition

between inulin and gum arabic. There was no dose-depen-
dency in the changes of bacterial numbers after 4 weeks of
intervention.
Enterococci spp.
In general, during the 4 weeks of intervention a non-signifi-
cant reduction in bacterial numbers was encountered,
especially in the water group (Table 4). Statistically significant
differences in the numbers of bacteria between the various test
groups were not encountered. A potential dose-dependency in
the outcome for gum arabic was not seen.
Potential drawbacks associated with the intake of gum arabic
for 4 weeks
Stool frequency and stool consistency were monitored
throughout the study and various gastrointestinal symptoms
were assessed via questionnaire: consistency of faeces,
abdominal pain, nausea, borborygmi, colic cramps, bloating,
flatulence, diarrhoea and constipation. Overall, all subjects
tolerated the 4 weeks of consumption of gum arabic even at
the highest dose of 40 g/d very well. Changes in the reported
gastrointestinal symptoms were minimal and not significant
during the intervention period as compared to subjects who
consumed the negative or positive control. As an example of
the discomfort the change in the intensity of diarrhoea is
given in Fig. 1. The values below 0 represent those people
who listed diarrhoea at the previous measurement. Evidently,
the 4 weeks of consumption of all investigated compounds and
doses did not result in a substantial diarrhoeal incidence.
Discussion
The results of the present study clearly demonstrate that con-
sumption of gum arabic (EmulGold
w
) at a dose of 10 g/d for 4
weeks is associated with higher numbers of Bifidobacteria and
Lactobacilli as compared with that of water (negative control).
When compared with the intake of 10 g inulin (positive con-
trol) the numbers of Bifidobacteria, Lactobacilli and Bacter-
oides were found to be significantly higher after gum arabic
intake. The effect on numbers of other bacteria was not signifi-
cantly different from that of water or inulin. It is concluded
that gum arabic, by yielding higher numbers of beneficial
bacteria without stimulation of unwanted bacteria, can be
considered a prebiotic fibre with functionality at least as
good as inulin.
An important issue within the prebiotic topic is the balance
in the floral composition. The issue of beneficial to the host
(or not) is associated with numbers of bacteria in the colon
being out of balance. Species such as Bifidobacteria and Lac-
tobacilli are well recognized for their health-improving
characteristics (e.g. increase in the colonization resistance or
production of SCFA
(19,20)
) and are therefore widely used as
probiotics. Moreover, groups of bacteria in the colon consist
of various species potentially beneficial or non-beneficial.
One example is the Bacteroides group. An interesting
finding within this study was the increase in log10 numbers
of Bacteroides by gum arabic. As with any group of bacteria,
Bacteroides consists of beneficial and non-beneficial members.
Recently manuscripts have been published stating the bene-
ficial impact of members of this group on gut health
(21,22)
.
Therefore, research into the contribution of the individual
members within bacterial groups might reveal the really
health-improving properties.
With respect to the bacterial development, within 4 weeks
the present study demonstrated that the most optimal dose of
gum arabic to achieve prebiotic efficacy lies around 5 – 10 g.
Table 4. The change in 10-logarithmic numbers of bacteria during 4 weeks of consumption of various doses of gum arabic, 10 g inulin or water†
(Mean values and standard deviations)
Bifidobacteria Lactobacilli Bacteroides Clostridium difficile Enterococci
Mean
SD Mean SD Mean SD Mean SD Mean SD
Water 2 0·41 0·98 2 0·20 0·82 2 0·02 0·39 2 0·72 1·11 2 0·81 1·36
Gum arabic
5g 2 0·01 1·15 0·29 1·09 0·36 0·61 0·25 1·66 2 0·28 0·83
10 g 1·22 1·03** 0·57 0·70* 0·31 0·29* 0·40 3·12 2 0·45 0·98
20 g 0·39 1·17 2 0·52 0·35 2 0·11 0·47 2 1·13 2·41 2 0·22 1·59
40 g 0·89 1·18* 2 0·47 0·77 2 0·24 0·17 2 0·97 1·82 0·04 2·56
Inulin (10 g) 0·28 1·24 2 0·29 0·97 2 0·12 0·43 2 0·18 1·58 2 0·31 1·24
Mean values were significantly different from those of water (t testing (one-sided)): *P, 0·05, **P, 0·01.
† For details of subjects and procedures, see Methods.
Fig. 1. Mean change in intensity (in arbitrary units (AU)) of diarrhoea in the
various test groups during the intervention as reported via questionnaires.
Positive values correspond with improving stool consistency whereas negative
values correspond with worsening, leading to less consistency. –V –, Water;
B, 10 g inulin; O, 5 g EmulGold
w
; £ , 10 g EmulGold
w
; *, 20 g EmulGold
w
;
--V- -, 40 g EmulGold
w
.
Gum arabic as prebiotic compound in man 1273
British Journal of Nutrition

Interestingly, at higher doses the numbers generally decreased.
For Bifidobacteria the numbers remain at the same level as
obtained at 10 g, reaching a plateau level. The present finding
suggests that Bifidobacteria are able to utilize gum arabic up
to doses of 40 g whereas the other bacteria have more diffi-
culty in metabolizing gum arabic at higher doses. This
might be explained by competition for substrate
(23)
: at high
doses other bacterial strains have easier access to the substrate
and subsequently, less becomes available for the ones deter-
mined within the present study. The enzyme systems within
Bifidobacteria might be more adapted to degrade gum arabic
than those of other micro-organisms. Another option is the
composition within the various layers of microflora present
in the gastrointestinal tract and subsequent utilization of
substrate able to degrade the prebiotic at higher doses: sur-
face-associated v. mucosa-associated flora
(24,25)
. It might be
speculated that at higher doses, bacteria present in the
mucosa layer are able to degrade the compounds more sub-
stantially than at lower doses, simply because they have
easier access. To what extent release of compounds by specific
gut bacteria as a result of gum arabic fermentation has an
impact on the outgrowth of others remains to be seen.
In the present study a real-time PCR assay was used to quan-
tify the number of relevant bacteria in the faecal slurry represen-
ting the bacteria in the lumen of the gut. There are various
limiting factors in this approach: not only the correlation in the
number and composition of bacteria between a faecal slurry
sample and the gut lumen, but also the validity of the primers
used: how reliable is the binding of the used amino acid array
to specific DNA in the stool. As reported
(14)
, the correlation
between DNA and threshold cycles as well as the correlation
between bacterially spiked faecal samples and signal were sig-
nificant. Moreover, in the present study internal validation
using multiple analyses within a sample as well as spiking
faecal samples with a known inoculum have been performed
and showed statistically reliable results (data not shown).
An important characteristic of the present study was the
huge variation in bacterial numbers, not only during the
study but also at the start. Especially in the group of volun-
teers consuming 10 g gum arabic the individual variation
within the numbers of C. difficile was extreme: more than
five log numbers. A clear relation between the initial
number of bacteria in the stool and the net increase during
intervention has been recognized before
(26,27)
and was obvious
from the present study as well (Fig. 2). Fig. 2 reveals a signifi-
cantly (P, 0·01) negative correlation between the log10
number of C. difficile at the start and the rate of change in
numbers after 4 weeks of gum arabic consumption. At
low numbers of bacteria at the start the room for a decrease
is limited and numbers can only increase, whereas this situa-
tion is reversed for high numbers at the start. At the intake
of the study no evaluation of the numbers of bacteria in
the stool of the volunteers was performed. However, by chec-
king the diet per volunteer, those people who were expected
to have a high number of lactic acid bacteria due to yoghurt
consumption were excluded from the trial. Room for
change in the number of bacteria over time should be achie-
vable by the intervention. Apparently the inclusion criteria
should be optimized in the sense that volunteers with either
very low or very high numbers at the start should be taken
out to minimize bias.
At present there are only a few studies documenting rela-
tively long-lasting prebiotic effects in man by gums in general.
With respect to the prebiotic behaviour of gum arabic, other
gums demonstrate similar physiological effects upon con-
sumption. Partially hydrolysed guar gum in combination
with fructo-oligosaccharides (6·6 and 3·4 g/d respectively)
over 21 d yielded a significant increase in Bifidobacteria, but
not in Lactobacilli, Bacteroides, Clostridia and Entero-
cocci
(28)
. Moreover, partially hydrolysed guar seems to play
a role in the reduction of inflammatory bowel syndrome as
well
(29)
. In vitro research using bacteria isolated from the
human colon demonstrated that gum arabic is rapidly utilized
by these micro-organisms, more than any other tested com-
pound
(30)
. Not only by increasing the numbers of bacteria is
the application of fibres well known, but also by stimulating
the physiology of bacteria and thereby affecting the release
of specific compounds, such as SCFA
(31)
, and the reduction
of compounds with known carcinogenic properties
(32)
.
The results of the present study demonstrate that gum arabic
(EmulGold
w
) bears prebiotic efficacy within a dose range
similar to or lower than inulin, as established via the quantitat-
ive development of bacteria in stool samples. Taking into
account its functional properties within food matrices this
compound will be an attractive ingredient for the functional
food segment. To what extent it will also exhibit other physio-
logically relevant properties remains open for further studies.
Acknowledgements
The technical support of Dr Inge Verkooijen (NutriScience,
Maastricht, The Netherlands) and Dr Neil Bourke (Kerry
Bioscience, Almere, The Netherlands) is gratefully acknow-
ledged. W. C. was the principal investigator for this study
and responsible for the design, statistics, evaluation of the
data and writing of the various drafts of the manuscript.
A. R. W. contributed significantly to the design of the study,
the carrying out of the experiment, interpretation and critical
reading of the manuscript. C. V. and C. F. were responsible
for the delivery of the various products to be tested in the
volunteers and contributed in critical reviewing of the manu-
script. A. D. S. was involved in the design of the study, theor-
etical contributions and critical reading of the manuscript. All
authors approved the publishing of the final version of the
Fig. 2. Relationship between the number of Clostridium difficile at the
start of the intervention and the change in numbers 4 weeks later. Every
point is one individual, all data pooled. Equation of the regression line:
y ¼ 2 0·916x þ 7·50, P, 0·01.
W. Calame et al.1274
British Journal of Nutrition

manuscript. None of the authors had a financial or personal
conflict of interest in relation to this study.
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