Consumption of breads containing in situ-produced arabinoxylan oligosaccharides alters gastrointestinal effects in healthy volunteers.

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.

A randomised, double-blind, placebo controlled cross-over study to determine the gastrointestinal effects of consumption of arabinoxylan-oligosaccharides enriched bread in healthy volunteers.

BACKGROUND: Prebiotics 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. METHODS: A 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. RESULTS: Consumption 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. CONCLUSIONS: AXOS-breads led to a potentially beneficial shift in fermentation end products and are well tolerated.

Enzymic degradability of hull-less barley flour alkali-solubilized arabinoxylan fractions by endoxylanases.

The impacts of the arabinose to xylose (A/X) ratio of arabinoxylans (AX) and the endoxylanase substrate specificity on the enzymic degradability of hull-less barley flour AX by endoxylanases were studied by using alkali-solubilized AX (AS-AX) fractions with different A/X ratio, on the one hand, and glycoside hydrolase family 10 and 11 endoxylanases of Aspergillus aculeatus (XAA) and Bacillus subtilis (XBS), respectively, on the other hand. AS-AX were obtained by saturated barium hydroxide treatment of hull-less barley flour water-unextractable AX. Fractionation of AS-AX by stepwise ethanol precipitation resulted in structurally different hull-less barley flour AS-AX fractions. Their A/X ratios increased with increasing ethanol concentration, and this increase in A/X ratio was reflected in their xylose substitution levels. For both XAA and XBS, the enzymic degradability of AX and apparent specific endoxylanase activity decreased with increasing A/X ratio of the AS-AX substrates, implying that both endoxylanases were sterically hindered by arabinose substituents. However, for all AS-AX fractions, hydrolysis end products of lower average degree of polymerization were obtained after incubation with XAA than with XBS, indicating that the former enzyme has a lower substrate specificity toward hull-less barley flour AS-AX than the latter. In addition, apparent specific endoxylanase activities indicated that XBS was approximately 2 times more sensitive to variations in the A/X ratio of AS-AX fractions than XAA. Furthermore, AS-AX with higher A/X ratio were relatively resistant to degradation by XBS.

Impact of inhibition sensitivity on endoxylanase functionality in wheat flour breadmaking.

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.

Effect of ingestion of dark chocolates with similar lipid composition and different cocoa content on antioxidant and lipid status in healthy humans.

The association between in vitro antioxidant capacity of dark chocolates with different cocoa percentage and the in vivo response on antioxidant status was investigated. In a randomized crossover design, 15 healthy volunteer consumed 100g of high antioxidants dark chocolate (HADC) or dark chocolate (DC). In vitro, HADC displayed a higher Total Antioxidant Capacity (TAC) than DC. In vivo, plasma TAC significantly peaked 2h after ingestion of both chocolates. TAC levels went back to zero 5h after DC ingestion whilst levels remained significantly higher for HADC. HADC induced a significantly higher urinary TAC in the 5-12h interval time than DC. No change was detected in urinary excretion of F2-isoprostanes. Plasma thiols and triacylglycerol (TG) levels significantly increased for both chocolate with a peak at 2h remaining significantly higher for DC after 5h respect to HADC. Results provide evidence of a direct association between antioxidant content of chocolate and the extent of in vivo response on plasma antioxidant capacity.