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Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions

Structurally Different Wheat-Derived Arabinoxylooligosaccharides Have Different Prebiotic and Fermentation Properties in Rats^1,2

³ Laboratory of Food Chemistry and Biochemistry and Leuven Food Science and Nutrition Research Centre, and ⁴ Laboratory for Livestock Physiology, Immunology and Genetics, and ⁵ Division of Mechatronics, Biostatistics and Sensors, Katholieke Universiteit Leuven, B-3001 Leuven, Belgium; ⁶ Laboratory of Microbial Ecology and Technology, Ghent University, B-9000 Ghent, Belgium; and ⁷ Laboratory of Aquatic Ecology and Evolutionary Biology, Katholieke Universiteit Leuven, B-3000 Leuven, Belgium

^* To whom correspondence should be addressed. E-mail: christophe.courtin{at}biw.kuleuven.be.

	ABSTRACT

TOP ABSTRACT Introduction Materials and Methods Results Discussion LITERATURE CITED

 
To evaluate the prebiotic potential and intestinal fermentation products of wheat bran-derived arabinoxylooligosaccharides (AXOS) in relation to their structure, 5 preparations with structurally different AXOS were included (4% wt:wt) in rat diets that mimicked the average Western human diet composition. Xylooligosaccharides (XOS), fructooligosaccharides (FOS), and inulin were used as references. The observed effects mainly depended on the average degree of polymerization (avDP) of the AXOS preparations. The AXOS and XOS preparations with a low avDP (3) resulted in increased colonic acetate and butyrate production and boosted bifidobacteria concentrations in the cecum, but did not significantly lower the concentrations of branched SCFA, which are considered to be markers of protein fermentation by intestinal microbiota. In contrast, an AXOS preparation with a higher avDP (61) effectively suppressed branched SCFA concentrations and thus tipped the balance away from protein fermentation. However, it neither increased colonic butyrate concentrations nor stimulated cecal bifidobacteria development. Two AXOS preparations with a similar avDP (12 and 15) but different average degrees of arabinose substitution (avDAS) (0.69 and 0.27) affected the measured intestinal characteristics similarly, suggesting that the influence of the avDAS was apparently limited and possibly overshadowed by that of the avDP. Among those tested, an AXOS preparation with an avDP of 5 and an avDAS of 0.27 exhibited the best combination of desirable effects on gut health characteristics. Compared with this optimal AXOS preparation, FOS and inulin resulted in similar bifidogenic effects with increased production of colonic acetate (inulin) but not of butyrate. These new insights into the structure-activity relation of AXOS open up new perspectives for the production and application of AXOS preparations with optimized prebiotic and fermentation properties.

	Introduction

TOP ABSTRACT Introduction Materials and Methods Results Discussion LITERATURE CITED

Prebiotics are compounds that cannot be utilized by enzymes of the upper gastrointestinal tract of healthy individuals but that are fermented selectively by some types of intestinal bacteria in the large intestine, thereby exerting a beneficial health effect on their host (4). Ingestion of prebiotics causes a shift in the composition of the intestinal bacterial population, typically characterized by a relative increase in Lactobacillus and Bifidobacterium species. This shift in the intestinal microbiota is associated with improved overall health (5,6), reduced gut infections (5,7), better absorption of minerals (5–8), and suppression of colon cancer initiation (6,7,9). The β-(2–1)-fructans inulin and fructooligosaccharides (FOS) are frequently used and well-studied prebiotics.

Fermentation of prebiotics by colonic bacteria gives rise to production of unbranched SCFA such as acetate, propionate, butyrate, and lactate. The presence of SCFA in the intestine lowers pH (10–12), increases bioavailability of calcium and magnesium (6,11), and inhibits the growth of potentially harmful bacteria (11,12). Among the SCFA, butyrate appears to be of greatest interest, because it is a preferred energy source for colonocytes (12–14), stimulates colon epithelial cells, thereby increasing their absorptive capacity (9), and inhibits the growth of colonic carcinoma cells in vitro (14) and in vivo (12,14,15). The cancer-suppressing properties of dietary fiber appear to correlate with their ability to generate butyric acid upon colonic fermentation (12,14,16).

The selective stimulation by prebiotics of certain colonic bacteria proceeds, in some cases, together with the suppression of protein fermentation in the colon (17–19). Reduced protein fermentation in the colon is desired, because the amino acid degradation pathways in bacteria result in the production of potentially toxic catabolites such as ammonia, other amines, phenols, indoles, and thiols, some of which have been implicated in bowel cancer (18–21) and exacerbation of ulcerative colitis (22). In this context, reduced concentrations of the branched SCFA isobutyrate and isovalerate, formed during the catabolism of branched chain amino acids (20,21,23), are desired, because they are indicators of microbial protein fermentation in the gut.

Preparations of xylooligosaccharides (XOS; i.e. oligosaccharides consisting of β-(1–4)-linked D-xylopyranosyl units) with predominance of oligosaccharides with an average degree of polymerization (avDP) of 2–3 (xylobiose and xylotriose), caused a significant increase in the concentrations of bifidobacteria and SCFA in the cecum and feces of rats (10,24) and mice (25) and also in human feces (26–28). Such xylobiose-rich XOS preparations also suppressed early symptoms of chemically induced colon carcinogenesis in rats (24). A preparation consisting predominantly of arabinoxylooligosaccharides (AXOS) with an avDP of 3–6 (arabinosylxylobiose, arabinosylxylotriose, arabinosylxylotetraose, and diarabinosylxylotetraose) increased the concentrations of bifidobacteria in the intestines of rats and mice (29). In addition, an AXOS preparation with an avDP of 15 increased bifidobacterial counts in the cecum of chickens to a much higher extent than did FOS (30). However, so far, the influence of the avDP and the avDAS on the prebiotic potential of AXOS has not, to our knowledge, been studied systematically. Against this background, the aim of the present study was to investigate the structure-activity relation of AXOS through evaluation of changes in microbiota and fermentation metabolites in the cecum and colon of rats following administration of structurally different AXOS.

	Materials and Methods

TOP ABSTRACT Introduction Materials and Methods Results Discussion LITERATURE CITED

 
Materials and chemicals

Wheat pentosan concentrate (WPC) [described by Courtin and Delcour (31)] was from Pfeifer and Langen and wheat bran was from Dossche Mills and Bakeries. XOS was the oligosaccharide preparation Xylooligo-95P (Suntory). This product consists predominantly of xylobiose, xylotriose, and xylotetraose (32). The FOS preparation was Orafti P95 (avDP = 4) and the inulin preparation was Orafti HP (avDP = 25).

Enzyme preparations used were heat-stable -amylase (Termamyl 120L, Novozymes), bacterial protease (Neutrase 0.8L, Novozymes), a glycosyl hydrolase family 11 Bacillus subtilis endoxylanase (Grindamyl H640, Danisco), and a glycosyl hydrolase family 10 endoxylanase from Aspergillus aculeatus (Shearzyme 500L, Novozymes). Endoxylanase activity was determined as described by Swennen et al. (33). One unit of enzyme activity (EU) was the amount of enzyme required to yield an absorbance of 1.0 at 590 nm under the assay conditions (40°C, pH 4.7, 10 min). Units of amylase and protease activity (EU) were as defined by the suppliers.

All chemicals, bovine serum albumin, and reagents were of at least analytical grade and supplied by Sigma-Aldrich.

Preparation of AXOS compounds

    Preparation of AXOS with avDP of 61 and avDAS of 0.58 (AXOS-61–0.58). WPC was solubilized in deionized water (1:10 wt:v) and silica was added as an aqueous suspension (20% wt:v) until a silica:protein ratio of 7:1 was achieved. The pH of the mixture was adjusted to 4.8 using 0.1 mol/L HCl. After 30 min of stirring, the suspension was Büchner filtered and the residue discarded. Ethanol (95% v:v) was added to the filtrate with continuous stirring to a final concentration of 65% (v:v) and after additional stirring (30 min), settling (24 h, 4°C), and centrifugation (10,000 x g; 30 min, 4°C), the obtained residue was dissolved in deionized water and lyophilized. The obtained residue was dissolved in deionized water, lyophilized and sieved (250 µm).

    Preparation of AXOS with avDP of 12 and avDAS of 0.69 (AXOS-12–0.69). WPC was treated with silica as described for the preparation of AXOS-61–0.58. The recovered filtrate was further incubated at 30°C for 24 h with the A. aculeatus endoxylanase (29 EU/g WPC). After inactivation of the enzyme by boiling (30 min), the obtained solution was cooled. Ethanol (95% v:v) was added under continuous stirring to a final concentration of 65% (v:v) and after additional stirring (30 min), settling (24 h, 4°C), and centrifugation (10,000 x g; 30 min, 4°C), the precipitated material was removed. Ethanol (95% v:v) was added to the supernatant under continuous stirring to a final concentration of 80% (v:v), and after additional stirring (30 min), settling (24 h, 4°C), and centrifugation (10,000 x g; 30 min, 4°C), the obtained residue was dissolved in deionized water and lyophilized. The obtained material was filtered through a 250-µm sieve.

    Preparation of AXOS with avDP of 15 and avDAS of 0.27 (AXOS-15–0.27). The production of this AXOS preparation was based on a procedure described by Swennen et al. (33). Briefly, wheat bran in water (1:7 w:v) was treated with Termamyl 120L (120 EU/kg wheat bran, 90 min, 90°C) and Neutrase 0.8L (32 EU/kg wheat bran, 4 h, 50°C, pH 6.0). After boiling (20 min) and filtering the suspension, the destarched and deproteinized wheat bran (DDWB) was washed with water and resuspended in deionized water (1:14 w:v). The suspension was incubated under continuous stirring with the B. subtilis endoxylanase at 1.4 EU/g DDWB (10 h, 50°C) and for another 10 h at 50°C after adding a 2nd dose of the endoxylanase (1.1 EU/g DDWB). After inactivation of the enzyme by boiling (30 min), the solution was concentrated to 20% dry matter in a falling film evaporator and finally spray-dried.

    Preparation of AXOS with avDP of 5 and avDAS of 0.27 (AXOS-5–0.27). AXOS-5–0.27 was prepared by incubating a solution (1:10 w:v) of AXOS-15–0.27 at 30°C during 60 min with the A. aculeatus endoxylanase at 75 EU/g AXOS-15–0.27. After inactivation of the enzyme by boiling (30 min), the solution was lyophilized and the obtained material was filtered through a 250-µm sieve.

    Preparation of AXOS with avDP of 3 and avDAS of 0.26 (AXOS-3–0.26). Wheat bran was destarched and deproteinized as described for the preparation of AXOS-15–0.27. The resulting material was incubated with continuous stirring for 10 h at 50°C with the B. subtilis endoxylanase at 1.2 EU/g DDWB and for another 10 h at 50°C after adding the A. aculeatus endoxylanase (21 EU/g DDWB). After inactivation of the enzymes by boiling (30 min), the solution was concentrated to 20% dry matter in a falling film evaporator and finally spray-dried.

Characterization of the isolated preparations

Moisture and ash contents were analyzed according to AACCI methods 44–19 and 08–01, respectively (34). Protein contents were determined according to a Dumas combustion method, using an automated Dumas protein analysis system (EAS varioMax N/CN, Elt), an adaptation of the AOAC official method for protein determination (35) and using 5.7 as the nitrogen protein conversion factor.

Total and reducing end sugar contents were determined by GC analysis as described earlier (33). The avDP and avDAS of AXOS were calculated using formulae 1 and 2, respectively. The total AXOS content was calculated using formula 3.

(Formula 1)

(Formula 2)

(Formula 3)

The correction for the percent galactose in formulae 1–3 is only for WPC-derived material, because WPC contains soluble arabinogalactan peptides (0.7 is the fixed arabinose:galactose ratio in arabinogalactan peptides) (36). DDWB no longer contains such material as a result of the purification.

The factors 132 and 150 in the formulae above reflect the molecular mass of anhydropentose sugars and pentose sugars, respectively. As the anhydroxylose and anhydroarabinose units in AXOS are hydrated upon hydrolysis, a correction for this molecular mass shift must be incorporated into the calculations.

Rat trial design

The changes in microbiota and fermentation metabolites in the cecum and colon of rats following administration of structurally different AXOS were evaluated in a completely randomized controlled trial. Ninety 6-wk-old male rats (Wistar, Elevage Janvier) were housed in stainless steel wire-bottom cages (2 rats per cage) in an environmentally controlled room (22°C) with a 14-/10-h light/dark cycle. For 6 d, rats consumed ad libitum water and pellets (10 mm) of a basic diet (Table 1). The basic diet, mimicking the average Western human diet composition, was prepared and analyzed by Ssniff Spezialdiäten. The diet was designed and produced following the general feed standards for laboratory animals and met all nutrient requirements for rats (37). Furthermore, the diet was formulated to allow a margin of safety for strain and individual differences. After 6 d of adaptation, the rats were randomly assigned to 1 of 9 different treatment groups (10 rats per group). All groups were given free access to pellets (10 mm) of basic diet to which the dosages of AXOS, XOS, FOS, or inulin were added (Table 2). For the oligosaccharide-containing diets, the starch in the basic diet was replaced with the appropriate amount of oligosaccharide preparation.

The above experimental protocol was approved by the Ethical Committee on Animal Experiments of the Katholieke Universiteit Leuven.

SCFA analysis

For measurement of nonbranched and branched SCFA, the following were added to vials containing individual intestinal (cecal or colonic) samples (2.0 g, fresh weight): 0.5 mL 9.2 mol/L sulfuric acid, 0.4 mL of 0.75% (v:v) 2-methylhexanoic acid (internal standard), 0.4 g NaCl, and 2.0 mL diethyl ether. After shaking the vials for 2 min, they were centrifuged (3000 x g; 3 min) and the diethyl ether phases containing the organic acids (1.0 µL) analyzed as described earlier (38).

Ammonium analysis

Ammonium ions in cecal samples were liberated as ammonia by addition of magnesium oxide (0.4 g/g fresh weight of sample). Released ammonia was distilled from the sample into a boric acid solution (20.0 g/L) using a 1062 Kjeltec Auto Distillation apparatus (FOSS Benelux). Ammonia was determined by titration using a 665 Dosimat (Metrohm) and 686 Titroprocessor (Metrohm). Colonic ammonium ion concentrations could not be measured due to the lack of a sample.

Microbiological analyses by quantitative PCR

The concentrations of total bacteria, lactobacilli, and bifidobacteria in the cecum were measured by quantitative PCR. Extraction of metagenomic DNA from cecal samples was performed using the QIAamp DNA Stool Mini kit (Qiagen) according to the manufacturer's instructions and starting from a 0.2-g (fresh weight) sample. DNA amplification was performed in triplicate in 25-µL reaction mixtures of the qPCR Core kit for SYBR Green I as described by the supplier (Eurogentec) in MicroAmp Optical 96-well reaction plates with optical caps (PE Applied Biosystems) using an ABI Prism SDS7000 instrument (PE Applied Biosystems). For the detection of the number of copies of the 16S ribosomal RNA genes from total bacteria, the following PCR program, using 0.3 µmol/L of both 338f (39) and 518r (40) as the forward and reverse primers, respectively, was performed: 50°C for 2 min, 95°C for 10 min, followed by 40 cycles of 94°C for 1 min, 53°C for 1 min, and 60°C for 2 min. By analogy, the number of copies of 16S ribosomal RNA genes from Bifidobacterium and lactobacilli was detected using 0.3 µmol/L of the primers 243f/243r and LactoF/LactoR (41), respectively, and the following thermal protocol: 50°C for 2 min, 95°C for 10 min, followed by 40 cycles of 94°C for 20 s, 58°C for 30 s, and 60°C for 1 min. Standard curves for quantification of bifidobacteria were constructed based on real-time PCR amplification using 6 different dilutions of DNA extracted from a culture of Bifidobacterium breve (strain LMG11042), and from Lactobacillus brevis (strain LMG12023) for quantification of total bacteria and lactobacilli. Real-time PCR data obtained were plotted against the standard curve and corrected for efficiency of DNA extraction using a factor consisting of the mean DNA concentration of all samples divided by the DNA concentration of the individual experimental sample. Colonic bacterial concentrations could not be measured due to the lack of a sample.

Statistical analysis

The rat trial was performed according to a completely randomized controlled design. Because the response variables were not normally distributed based on a Kolmogorov-Smirnov test, the effect of the diets on different characteristics was analyzed by a nonparametric 1-way ANOVA at the 95% CI with the SAS software 8.1 (SAS Institute). Hereto, the original response variables were transformed into their ranks and a classical 1-way ANOVA was performed on those ranks. The model for the statistical analysis was

with the overall mean, the main effect of diet i, the response (rank) for the jth rat following diet i, and the error term. A Tukey multiple comparisons procedure was used to find differences (P < 0.05) among the different diets. Values in the text are medians, except for feed intakes and body weights, which are expressed as means ± SD.

	Results

TOP ABSTRACT Introduction Materials and Methods Results Discussion LITERATURE CITED

 
    Properties of AXOS. Table 2 lists the properties of the different preparations in terms of total AXOS content, avDP, and avDAS. All preparations were at least 70% pure in terms of AXOS content. Their avDP ranged from 3 to 61 and their avDAS from 0.26 to 0.69.

    Feed intakes and body weights. Feed intakes during wk 1 and 2 of the treatment period were 21.0 ± 1.2 and 21.2 ± 1.4 g per rat per day, respectively. Body weights of the rats at the start of the treatment were 252 ± 8.7 g and reached 311 ± 13.4 g and 360 ± 19.0 g after 1 and 2 wk of treatment, respectively (data not shown). Body weights and feed intakes did not differ among the groups.

    Fermentation products. Cecal concentrations of acetate, propionate, and butyrate did not differ significantly from the control group in any of the treatment groups, but there were differences among the treated groups (Fig. 1). The AXOS-61–0.58 group had a higher cecal acetate concentration than the AXOS-3–0.26, inulin, and FOS groups and a higher propionate concentration than the AXOS-15–0.27, AXOS-5–0.27, and FOS groups. The colon acetate concentration was significantly higher in rats fed the diets containing AXOS-5–0.27, AXOS-3–0.26, XOS, or inulin than in the control group (Fig. 2A), whereas propionate concentrations did not differ among the groups (Fig. 2B). The colonic butyrate concentration was significantly greater by more than 100% in the AXOS-5–0.27, AXOS-3–0.26, and XOS groups compared with the control group (Fig. 2C).

View larger version (13K): [in this window] [in a new window]   FIGURE 1  Effect of different oligosaccharides on the concentrations of acetate (A), propionate (B), butyrate (C), and branched SCFA (the sum of isovalerate and isobutyrate concentrations) (D) in the cecum of rats fed diets containing structurally different wheat-derived AXOS for 14 d. Data are expressed per gram dry weight intestinal sample. The box represents the 25th and 75th quartiles; the median is the square in the box; the whiskers are at the minimum and maximum values. Medians (n = 10) without a common letter differ, P < 0.05.

View larger version (14K): [in this window] [in a new window]   FIGURE 2  Effect of different oligosaccharides on the concentrations of acetate (A), propionate (B), butyrate (C), and branched SCFA (the sum of isovalerate and isobutyrate concentrations) (D) in the colon of rats fed diets containing structurally different wheat-derived AXOS for 14 d. Data are expressed per gram dry weight intestinal sample. The box represents the 25th and 75th quartiles; the median is the square in the box; the whiskers are at the minimum and maximum values. Medians (n = 10) without a common letter differ, P < 0.05.

Ammonium ion concentrations in the cecum were significantly lower than in control for all treatment groups fed oligosaccharide preparations, except for the AXOS-12–0.69 group (Fig. 3). Decreased ammonium ion concentrations can result from either reduced protein fermentation or increased assimilation of ammonium ions by carbohydrate fermenting bacteria (23).

View larger version (12K): [in this window] [in a new window]   FIGURE 3  Effect of different oligosaccharides on the concentration of ammonium ions in the cecum of rats fed diets containing structurally different wheat-derived AXOS for 14 d. Data are expressed per gram dry weight intestinal sample. The box represents the 25th and 75th quartiles; the median is the square in the box; the whiskers are at the minimum and maximum values. Medians (n = 10) without a common letter differ, P < 0.05.

View larger version (11K): [in this window] [in a new window]   FIGURE 4  Effect of different oligosaccharides on the concentration of bifidobacteria in the cecum of rats fed diets containing structurally different wheat-derived AXOS for 14 d. Data are expressed per gram dry weight intestinal sample. The box represents the 25th and 75th quartiles; the median is the square in the box; the whiskers are at the minimum and maximum values. Medians (n = 10) without a common letter differ, P < 0.05.

	Discussion

TOP ABSTRACT Introduction Materials and Methods Results Discussion LITERATURE CITED

The present study clearly demonstrates that mainly the avDP, but not, or to a limited extent, the avDAS of AXOS preparations determine the effects they produce in the intestines of rats (Fig. 5). The avDP clearly influenced the bifidogenic potency, because the addition of AXOS and XOS preparations with a rather low avDP (5) increased bifidobacteria concentrations, whereas the addition of AXOS with a higher avDP (12) did not stimulate bifidobacteria development. The difference in bifidogenic effect between larger and smaller AX(OS) compounds is consistent with some earlier observations. Wheat flour AX did not affect bifidobacteria, bacteroids, or clostridia population levels in an in vitro continuous fermentation system mimicking the human gastrointestinal tract, whereas xylanase-pretreated wheat flour AX clearly increased the bifidobacteria concentration and decreased the concentrations of bacteroides and clostridia (43). No remarkable changes in the fecal microbiota occurred at the bacterial group level after the addition of maize AX to the diet of healthy human volunteers (44). In contrast, several studies reported wheat bran AXOS exerted bifidogenic effects in vitro (29,45) and in vivo (29,30). These studies collectively suggest that AX is not, or is only poorly, bifidogenic, whereas its hydrolysis products XOS and AXOS stimulate bifidobacterial growth. In contrast to the above-mentioned studies and the present results, Hughes et al. (46) in in vitro batch fermentation experiments observed that high-molecular mass AX fractions (with molecular masses between 354 and 66 kDa) significantly increased bifidobacteria counts. Also in these experiments, the bifidogenic effect clearly increased with decreasing molecular mass (46).

View larger version (10K): [in this window] [in a new window]   FIGURE 5  Schematic representation of the influence of the avDP on the prebiotic and fermentation properties of AXOS. Acetate and butyrate are based on measurements in the colon, branched SCFA, ammonium ions, and bifidobacteria are based on measurements in the cecum.

The influence of the avDAS on the bifidogenic potency was not clear from the present results. Two couples of AXOS preparations with a similar avDP, but different avDAS could be compared. AXOS-12–0.69 and AXOS-15–0.27 did not significantly increase the cecal bifidobacteria concentration, despite a positive trend for the AXOS-15–0.27 group. XOS and AXOS-3–0.26 both increased the cecal bifidobacteria concentration by 1 log unit. The fermentation products formed were similar in nature and abundance when comparing preparations with similar avDP. The AXOS-12–0.69 preparation did not affect any of the measured characteristics except that it reduced the concentrations of branched SCFA in the cecum, whereas AXOS-15–0.27 reduced cecal ammonium ion as well as branched SCFA concentrations. As outlined above, regretfully, colonic ammonium ion concentrations could not be measured. Based on the similarity between cecal and colonic branched SCFA concentrations (Figs. 1D and 2D), however, results are expected to be similar to cecal ammonium ion concentrations. The fact that the observed effects of AXOS preparations with a similar avDP but different avDAS were similar suggested that the influence of the avDAS was small in the range studied.

Although the present results suggest only a weak influence of the avDAS on the bifidogenic potential and the fermentation products, several other studies reported an influence of the avDAS on AX and AXOS fermentability. After in vitro fermentation of rye AX fractions with different avDAS (ranging from 0.52 to 0.74), unfermentable residues with an avDAS of 1.1 were obtained, regardless of the substrate (49). This suggests that the unfermented AX with high avDAS has a structure that is highly resistant to hydrolysis and fermentation and so remains unutilized by colonic microbiota (49). Similar results were obtained in an in vivo study with pigs. Comparison of different rye milling fractions showed the fecal digestibility to be highest for endosperm AX (avDAS = 0.76) and aleurone AX (avDAS = 0.42), whereas pericarp/testa AX (avDAS = 1.04) is virtually not degraded through colonic fermentation (42). Taken together with the data of the present study, the literature data suggest that the avDAS has a marked negative impact only on intestinal fermentability at relatively high values of 1.0.

Among the AXOS preparations tested, AXOS-5–0.27 exhibited the best combination of desirable effects on gut health characteristics in terms of increased acetate and butyrate concentrations in the colon, reduced intestinal protein fermentation (as deduced from reduced branched SCFA and ammonium ion concentrations in the cecum), and increased concentrations of bifidobacteria in the cecum. Compared with the most optimal AXOS-based oligosaccharide preparation (AXOS-5–0.27), the fructan-based oligosaccharides FOS and inulin resulted in similar bifidogenic effects, yet they caused increased production of only colonic acetate (inulin) and not of butyrate. Inulin was not effective at reducing the cecal concentrations of branched SCFA.

In conclusion, in vivo evaluation of structurally different AXOS shows that the AXOS structure has a strong influence on the prebiotic potential and the formed fermentation products. In general, smaller AXOS result in higher increases in intestinal butyrate concentrations and a significant bifidogenic effect, whereas larger compounds mainly lead to lower branched SCFA concentrations. The influence of the avDAS seemed to be limited in the range studied. These new insights into the structure-activity relation of AXOS open up new perspectives for the production and application of AXOS preparations with optimized prebiotic and fermentation properties.

	ACKNOWLEDGMENTS

 
We thank Ellen Van Gysegem (Laboratory of Microbial Ecology and Technology, Ghent University) for excellent technical assistance.

	FOOTNOTES

 
¹ Supported by the framework of research projects GOA/03/10 and IDO/03/005 financed by the Research Fund Katholieke Universiteit Leuven and of the Strategisch Basis-Onderzoek project "IMPAXOS" from the Flemish Instituut voor de aanmoediging van Innovatie door Wetenschap en Technologie in Vlaanderen (Brussels, Belgium). It is also part of the Methusalem Programme "Food for the Future" at the Katholieke Universiteit Leuven. B. De Ketelaere is an industrial research fellow sponsored by the ‘Industrieel Onderzoeksfonds’ (Belgium).

² Author disclosures: V. Van Craeyveld, K. Swennen, E. Dornez, T. Van de Wiele, M. Marzorati, W. Verstraete, Y. Delaedt, O. Onagbesan, E. Decuypere, J. Buyse, B. De Ketelaere, W. F. Broekaert, J. A. Delcour, and C. M. Courtin, no conflicts of interest.

⁸ Abbreviations used: avDAS, average degree of arabinose substitution; avDP, average degree of polymerization; AX, arabinoxylan; AXOS, arabinoxylooligosaccharide; DDWB, destarched and deproteinized wheat bran; EU, enzyme activity unit; FOS, fructooligosaccharide; WPC, wheat pentosan concentrate; XOS, xylooligosaccharide.

Manuscript received 16 June 2008. Initial review completed 27 June 2008. Revision accepted 21 September 2008.

	LITERATURE CITED

TOP ABSTRACT Introduction Materials and Methods Results Discussion LITERATURE CITED

 

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