BackgroundPrebiotics are food ingredients, usually non-digestible oligosaccharides, that are selectively fermented by populations of beneficial gut bacteria. Endoxylanases, altering the naturally present cereal arabinoxylans, are commonly used in the bread industry to improve dough and bread characteristics. Recently, an in situ method has been developed to produce arabinoxylan-oligosaccharides (AXOS) at high levels in breads through the use of a thermophilic endoxylanase. AXOS have demonstrated potentially prebiotic properties in that they have been observed to lead to beneficial shifts in the microbiota in vitro and in murine, poultry and human studies.MethodsA double-blind, placebo controlled human intervention study was undertaken with 40 healthy adult volunteers to assess the impact of consumption of breads with in situ produced AXOS (containing 2.2 g AXOS) compared to non-endoxylanase treated breads. Volatile fatty acid concentrations in faeces were assessed and fluorescence in situ hybridisation was used to assess changes in gut microbial groups. Secretory immunoglobulin A (sIgA) levels in saliva were also measured.ResultsConsumption of AXOS-enriched breads led to increased faecal butyrate and a trend for reduced iso-valerate and fatty acids associated with protein fermentation. Faecal levels of bifidobacteria increased following initial control breads and remained elevated throughout the study. Lactobacilli levels were elevated following both placebo and AXOS-breads. No changes in salivary secretory IgA levels were observed during the study. Furthermore, no adverse effects on gastrointestinal symptoms were reported during AXOS-bread intake.ConclusionsAXOS-breads led to a potentially beneficial shift in fermentation end products and are well tolerated.

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Arabinoxylan oligosaccharides (AXOS) are studied as food compounds with prebiotic potential. Here, the impact of consumption of breads with in situ-produced AXOS on intestinal fermentation and overall gastrointestinal characteristics was evaluated in a completely randomized, double-blind, controlled, cross-over study. Twenty-seven healthy volunteers consumed 180 g of wheat/rye bread with or without in situ-produced AXOS (WR(+) and WR(-), respectively) daily for 3 wk. Consumption of WR(+) corresponded to an AXOS intake of ~2.14 g/d. Refined wheat flour bread without AXOS (W(-)) (180 g/d) was provided during the 3-wk run-in and wash-out periods. At the end of each treatment period, participants collected urine for 48 h as well as a feces sample. Additionally, all participants completed a questionnaire about stool characteristics and gastrointestinal symptoms during the last week of each period. Urinary phenol and p-cresol excretions were significantly lower after WR(+) intake compared to WR(-). Consumption of WR(+) significantly increased fecal total SCFA concentrations compared to intake of W(-). The effect of WR(+) intake was most pronounced on butyrate, with levels 70% higher than after consumption of W(-) in the run-in or wash-out period. Consumption of WR(+) tended to selectively increase the fecal levels of bifidobacteria (P = 0.06) relative to consumption of W(-). Stool frequency increased significantly after intake of WR(+) compared to WR(-). In conclusion, consumption of breads with in situ-produced AXOS may favorably modulate intestinal fermentation and overall gastrointestinal properties in healthy humans.

Cereal Chem. 81(5):576-581A new procedure was developed for the isolation of highly purified water-extractable arabinoxylan (WE-AX) from hull-less barley flour. It included inactivation of endogenous enzymes, removal of proteins with silica gel, and removing β-glucans, arabinogalactan-peptides, and starch fragments by enzyme or solvent precipitation steps. WE-AX recovered by this isolation procedure represented, on average, 47% of all WE-AX present in hull-less barley flour. Purified WE-AX from flour of different hull-less European barley cultivars contained 84.9-91.8% AX and showed small structural differences. The apparent peak molecular weight of the purified WE-AX was 730,000-250,000, and the arabinose-to-xylose ratio was 0.55-0.63. Proton nuclear magnetic resonance spectroscopy showed that the levels of un-, O-2 mono-, O-3 mono-, and O-2,O-3 disubstituted xylose residues were 59.1-64.7%, 8.2-10.0%, 5.7-10.6%, and 17.6-23.1%, respectively, and the ratio of di-to monosubstituted xylose was 0.90-1.54. Both O-3 mono-and disubstituted xylose residues occurred isolated or next to disubstituted xylose residues in the WE-AX chain.

A Bacillus subtilis endoxylanase (XBS(i)) sensitive to inhibition by Triticum aestivum L. endoxylanase inhibitor (TAXI) and a mutant thereof (XBS(ni)), uninhibited by TAXI, were used in straight-dough breadmaking to assess the importance of endoxylanase inhibition sensitivity on endoxylanase functionality in the process. With two European wheat flours, the loaf volume improving effect of XBS(ni) at much lower enzyme dosages was substantially larger than that brought about by XBS(i). This coincided with differences in arabinoxylan (AX) hydrolysis. Although XBS(ni) had a lower substrate selectivity for water-unextractable arabinoxylan (WU-AX) than XBS(i), the former solubilized significantly more WU-AX than XBS(i). Because of inhibition, XBS(i) solubilized most of the WU-AX during mixing, whereas, with XBS(ni), the rate of solubilization decreased less with increasing processing time than that with XBS(i). During fermentation and baking and at the highest dosage (600 U/kg of flour of XBS(i) and 60 U/kg of flour of XBS(ni)), XBS(ni) induced a stronger degradation of enzymically solubilized and water-extractable AX than XBS(i). Taken together, the data clearly demonstrate that endoxylanases, which in vitro are inhibited by endoxylanase inhibitors and still are active in the breadmaking process, as demonstrated by their functional (bread volume) enhancing effect, gradually lose their activity in the process.