Hot water -extracted birchwood glucuronoxylans (GX) are promising novel food hydrocolloids with unique emulsion stabilizing properties. Xylans are considered dietary fibers that are not digested in human gastrointestinal tract, but may produce health-promoting bacterial metabolites. However, very little is known about their gastrointestinal fate.

Depending on the isolation method, GX-rich hardwood extracts may contain varying amounts of lignin. Here, we compared the effects of pure GX from the BLN process and lignin-containing pressurized hot water -extracted (PHWE) GX on intestinal barrier function, gut microbiota composition, and microbial-derived metabolites in a rodent model. Female and male Wistar rats (n=42) were randomly divided into three groups and fed a diet containing 10% (w/w) of either cellulose (control group), PHWE GX, or BLN GX for 28 days. The rats were weighed weekly. At the end of the experiment, the fecal content of total N-nitroso compounds and short-chain fatty acids were analyzed. In addition, we characterized the bacterial composition, mucus layer, crypt structure, and tight-junction proteins.

The rats gained weight normally during the feeding period and no difference in body weight was observed between the diet groups. Thus GX did not have adverse effects on the growth or apparent well-being of rats. Bifidobacteriaceae, and to a lesser extent Lactobacillaceae were significantly enriched in the fecal microbiota of GX-fed rats compared to the control group (ca. 400 and 6 folds, respectively), suggesting a potent prebiotic effect. The abundance of sulfate-reducing bacteria including Peptostreptococcacea, Peptococcaceae and Desulfovibrionaceae, previously linked to negative gut health, were significantly reduced in the GX group. The amount of total N-nitroso compounds and nitrosyl iron compounds were higher in samples of GX-fed rats than of the control group. This also indicates that gut bacteria can utilize GX in formation of bacterial metabolites. The study brings new insights into whether industrially underutilized GX could be used as a healthy food ingredient. The transformation of wood into food may not only improve gut health, but also meet the demand for more sustainable food resources.

Maarit Lahtinen

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