Polyphenol- and Glucuronoxylan-Rich Fiber Extract from Birch (Betula sp.) Wood Regulates Colonic Barrier Function and Cell Proliferation in Healthy Rats.

Birch wood-derived fiber extracts containing glucuronoxylans (GX) and polyphenols show potential for various food technological applications. This study investigated the effect of two extracts, GXpoly and pureGX, differing in lignin content on colonic barrier function. Healthy rats were fed diets containing 10% GXpoly, pureGX, or cellulose for 4 weeks. Colon crypt depth was lower in the GX groups than in the control group, but in the proximal colon, the result was significant only in GXpoly. An artificial intelligence approach was established to measure the mucus content and goblet cells. In the distal colon, their amounts were higher in the control group than in the GX groups. All diets had a similar effect on the expression of the tight junction proteins occludin, claudin-1, and claudin-7. GXpoly enhanced the fecal IgA production. Our results suggest that GX-rich extracts could support the colonic barrier and work as functional food ingredients in the future.

Metabolic Fate of Lignin in Birch Glucuronoxylan Extracts as Dietary Fiber Studied in a Rat Model.

SCOPE: While previously considered inert, recent studies suggest lignin metabolism with unknown metabolic fates is occurring in the gastrointestinal tract of several animal models. This study focuses on analyzing the potential metabolites of lignin. METHODS AND RESULTS: The diets of rats include relatively pure birch glucuronoxylan (pureGX) with residual lignin or lignin-rich GX (GXpoly) in their diet. Nuclear magnetic spectroscopy of the lignin isolated from the GXpoly-fed rats fecal sample shows high alteration in chemical structure, whereas lignin-carbohydrate complexes (LCCs) are enriched in fecal samples from the pureGX group. Moreover, the increased syringyl-to-guaiacyl (S/G) ratio suggests that lignin G-units are predominantly metabolized based on pyrolysis gas chromatography-mass spectrometry (pyr-GC/MS). The presence of small phenolic metabolites identified in urine samples of the GXpoly group, for example, ferulic and sinapic acids, their sulfate and glucuronide derivatives, and 4-sulfobenzylalcohol, suggests that the small fragmented lignin metabolites in the large intestine enter the plasma, and are further processed in the liver. Finally, the relative abundances of polyphenol-degrading Enterorhabdus and Akkermansia in the gut microbiota are associated with lignin metabolism. CONCLUSION: These findings give further evidence to lignin metabolism in the gut of nonruminants and provide insight to the potential microbes and metabolic routes.

Correction: Gut microbiota can utilize prebiotic birch glucuronoxylan in production of short-chain fatty acids in rats.

Correction for 'Gut microbiota can utilize prebiotic birch glucuronoxylan in production of short-chain fatty acids in rats' by Emma Kynkäänniemi et al., Food Funct., 2022, 13, 3746-3759, DOI: 10.1039/D1FO03922A.

Gut microbiota can utilize prebiotic birch glucuronoxylan in production of short-chain fatty acids in rats.

Birch-derived glucuronoxylan (GX)-rich hemicellulose extract is an abundantly available by-product of the forest industry. It has multifunctional food stabilizing properties, and is rich in fiber and polyphenols. Here, we studied its effects on colonic metabolism and gut microbiota in healthy rats. Male and female Wistar rats (n = 42) were fed AIN-93G-based diets with 10% (w/w) of either cellulose (control), a polyphenol and GX-rich extract (GXpoly), or a highly purified GX-rich extract (pureGX) for four weeks. Both the GXpoly and pureGX diets resulted in changes on the gut microbiota, especially in a higher abundance of Bifidobacteriaceae than the cellulose containing diet (p < 0.001). This coincided with higher concentrations of microbial metabolites in the luminal contents of the GX-fed than control rats, such as total short-chain fatty acids (SCFAs) (p < 0.001), acetate (p < 0.001), and N-nitroso compounds (NOCs) (p = 0.001). The difference in the concentration of NOCs was not seen when adjusted with fecal weight. GX supplementation supported the normal growth of the rats. Our results indicate that GXpoly and pureGX can favorably affect colonic metabolism and the gut microbiota. They have high potential to be used as prebiotic stabilizers to support more ecologically sustainable food production.