Novel Rice Bran Polysaccharide Demonstrates Prebiotic Potential in Fermentation Study

A newly isolated heteropolysaccharide derived from rice processing byproducts has exhibited notable prebiotic activity and structural stability during laboratory investigations, according to findings published by agricultural and nutritional researchers. The novel carbohydrate, designated as rice bran polysaccharide, demonstrated an ability to alter microbial communities during in vitro human fecal fermentation experiments by stimulating the growth of beneficial gut bacteria while suppressing common intestinal pathogens. Utilizing a combination of advanced chromatographic, spectroscopic, and thermal techniques, the investigative team elucidated the fine primary structure and conformational properties of the biopolymer. The analytical data revealed a relatively low molecular weight carbohydrate predominantly assembled from glucose units linked through specific glycosidic bonds. Rather than relying on animal models or direct clinical interventions in patients, the researchers implemented a controlled anaerobic benchtop model to evaluate how human intestinal microbiota metabolize this specific fraction over twenty-four hours. The resulting observations provide detailed structural benchmarks and empirical evidence highlighting the value of rice bran fractions as functional food ingredients.

The material under investigation originated from japonica rice milling streams collected at a specialized agricultural cooperative in the Songjiang District of Shanghai. Sourced specifically from the secondary discharge outlet where aleurone layers are removed to produce fine bran, the raw feedstock represented the byproduct of a multi-stage light milling system utilizing three sand-rollers and one iron-roller. To ensure representative composition and experimental reproducibility across subsequent extractions, samples gathered from three distinct production batches were blended in equal proportions. Compositional analysis of this pooled raw bran indicated a matrix containing 15.14 percent crude protein, 14.40 percent crude fat, 27.76 percent starch, 30.87 percent total dietary fiber, and 8.50 percent ash. To isolate the target polysaccharide, defatted rice bran was subjected to hot water extraction at ninety degrees Celsius for two successive two-hour cycles using a liquid-to-solid ratio of fifteen to one. The aqueous extract was treated with alpha-amylase to digest co-extracted starches, followed by protein degradation using papain combined with the Sevag chloroform-butanol solvent precipitation protocol. After multiple graded ethanol precipitation steps, the soluble biopolymer was dialyzed across a two-kilodalton cutoff membrane and freeze-dried.

Quantitative chemical profiling of the purified rice bran polysaccharide established that carbohydrates constitute the overwhelming bulk of the isolated fraction. Phenol-sulfuric acid assays recorded a total sugar content of 75.28 plus or minus 2.15 percent, accompanied by an uronic acid content of 5.28 plus or minus 0.36 percent determined through sulfuric acid-carbazole colorimetry. Residual protein measured 2.04 plus or minus 0.31 percent via Coomassie Brilliant Blue G-250 testing, while total polyphenols were present at a minor concentration of 1.25 plus or minus 0.25 milligrams per gram using Folin-Ciocalteu reagent. Colorimetric tests confirmed the complete absence of sulfate groups and flavonoid moieties within the purified sample. Importantly, the polysaccharide yielded a negative iodine-potassium iodide reaction, confirming that enzymatic digestion and ethanol fractionation successfully eliminated residual starch contaminants. The low content of uronic acids and polyphenols indicated that the resulting preparation was predominantly a neutral, non-starch polysaccharide free from major non-carbohydrate impurities that could otherwise confound structural or biological assays.

Molecular weight determination carried out via high-performance gel permeation chromatography coupled with refractive index detection yielded an average molecular weight of approximately 3.72 kilodaltons, or 3720 daltons, calibrated against dextran standards. This value highlights the low molecular weight nature of the isolated polysaccharide compared to previously documented cereal and fungal polysaccharides, which frequently exceed dozens or hundreds of kilodaltons. Monosaccharide composition analysis performed through high-performance anion-exchange chromatography with pulsed amperometric detection following trifluoroacetic acid hydrolysis demonstrated that the polymer is a heteropolysaccharide comprised of six distinct monosaccharide residues. Glucose represented the dominant building block at 82.93 molar percent, followed by arabinose at 6.95 percent, galactose at 5.15 percent, galacturonic acid at 2.13 percent, xylose at 2.07 percent, and glucuronic acid at 0.78 percent. This pronounced predominance of neutral glucosyl residues aligned closely with methylation analysis benchmarks, validating the analytical precision of the monosaccharide profiling and confirming that glucose serves as the primary structural component of the molecular chain.

Spectroscopic and thermal profiling further elucidated the physical stability and functional groupings of the biopolymer. Fourier-transform infrared spectroscopy revealed characteristic polysaccharide absorption peaks, notably a broad hydroxyl stretching band at approximately 3280 reciprocal centimeters and asymmetric carbon-hydrogen stretching at 2925 reciprocal centimeters. Absorption bands situated at 840 and 930 reciprocal centimeters indicated the presence of alpha-glycosidic bonds, alongside pyranose ring vibrations near 1020 reciprocal centimeters and weak signals associated with beta-glycosidic configurations. Differential scanning calorimetry demonstrated an initial endothermic peak between 100 and 120 degrees Celsius corresponding to moisture loss, but showed no melting or cleavage transitions across the 30 to 200 degrees Celsius range. Complementary thermogravimetric analysis revealed that substantial thermal decomposition and mass loss only took place between 200 and 300 degrees Celsius, recording a degradation onset temperature of 273 degrees Celsius. X-ray diffraction patterns displayed broad, rounded diffuse reflections centered at eighteen degrees two-theta, confirming that the biopolymer possesses minimal crystallinity and exists in an amorphous state.

Microscopic and conformational analyses provided further insights into the physical state and macromolecular organization of the polysaccharide chains. Congo red complexation tests demonstrated that the maximum absorption wavelength of the dye-polysaccharide solution increased gradually under low sodium hydroxide concentrations and plateaued without undergoing the characteristic bathochromic decline that signifies the collapse of an organized triple-helix structure, thereby establishing that the polymer exists as a flexible single chain rather than a triple-helical conformer. Scanning electron microscopy showed that the dry polysaccharide forms an uneven, flake-like morphology characterized by aggregated irregular fragments with rough exterior surfaces, providing an expansive specific surface area. Atomic force microscopy scans conducted on mica surfaces revealed unevenly distributed granular aggregates and island-like protrusions ranging in height from negative 1.1 to positive 2.3 nanometers. These aggregated surface features were attributed to strong intra- and intermolecular non-covalent forces, particularly extensive hydrogen bonding and van der Waals interactions occurring among hydroxyl substituents along the polysaccharide chains.

Detailed linkage configurations and sequential connectivity were established through gas chromatography-mass spectrometry methylation analysis combined with one-dimensional and two-dimensional nuclear magnetic resonance spectroscopy. Methylation assays identified eleven distinct glycosidic linkages, with non-reducing terminal glucose, 1,4-linked glucose, and 1,4,6-linked glucose representing the predominant species at relative molar percentages of 17.95 percent, 49.11 percent, and 13.04 percent, respectively. The remaining linkages included terminal arabinose, 1,5-arabinose, 1,4-xylose, 1,3-mannose, 1,6-glucose, 1,3,4-xylose, 1,3,4-glucose, and 1,3,6-galactose. Proton and carbon-13 nuclear magnetic resonance spectra, analyzed alongside homonuclear chemical shift correlation, heteronuclear single quantum coherence, heteronuclear multiple bond correlation, and nuclear Overhauser effect spectroscopy, resolved seven major sugar residue spin systems. Inter-residue cross-peaks demonstrated that the main structural backbone is predominantly constructed from repeating 1,4-linked alpha-D-glucopyranosyl and 1,4,6-linked alpha-D-glucopyranosyl residues, with side branches composed primarily of terminal alpha-D-glucopyranosyl units attached to the main chain at the oxygen-six position.

To assess biological activity, the researchers conducted in vitro fecal fermentation experiments utilizing pooled stool samples collected from six healthy human volunteers aged 20 to 30 years who had not consumed antibiotics, probiotics, or related medications for at least three months. The anaerobic culture system compared the novel polysaccharide against both a blank negative control medium containing no added carbohydrate substrate and a positive control formulated with commercial fructo-oligosaccharides. Over twenty-four hours of incubation at thirty-seven degrees Celsius, total carbohydrate consumption rose steadily, reaching 38.70 plus or minus 1.36 percent for the rice bran biopolymer compared to 42.36 plus or minus 1.67 percent for the fructo-oligosaccharides. Concurrently, microbial metabolism induced a substantial drop in culture medium pH, decreasing from an initial neutral-alkaline value of 8.18 down to 4.59 in the polysaccharide group, representing a net acidification of 3.59 pH units. This acidification occurred most rapidly during the initial six hours of fermentation, driven by the microbial generation of organic acid metabolites.

Chromatographic quantification of metabolic end-products revealed that short-chain fatty acids accumulated substantially during the fermentation of the rice bran polysaccharide. Gas chromatography-mass spectrometry measurements showed that acetic acid, propionic acid, and n-butyric acid constituted more than 95 percent of all detected volatile fatty acids across the culture period. By twenty-four hours, the concentrations of acetic acid, propionic acid, and n-valeric acid in the polysaccharide-supplemented vessels reached 2.08-fold, 2.12-fold, and 2.32-fold of the concentrations measured in the substrate-free blank group, mirroring the rapid drop in medium pH. High-throughput sequencing of the bacterial 16S ribosomal RNA gene variable three to four region yielded over 1.77 million quality-filtered reads across experimental groups. Alpha-diversity assessments revealed that exposure to the rice bran polysaccharide significantly lowered community richness and diversity indices, specifically the Chao1, abundance-based coverage estimator, and Shannon metrics, while increasing the Simpson dominance index, reflecting the selective proliferation of specialized bacterial taxa capable of rapidly utilizing the carbohydrate substrate in an increasingly acidic environment.

Taxonomic community profiling demonstrated marked restructuring of bacterial populations across multiple phylogenetic levels following twenty-four hours of polysaccharide fermentation. At the phylum level, the ratio of Firmicutes to Bacteroidetes decreased from 5.439 in the blank control to 3.925 in the polysaccharide treatment, accompanied by an overall increase in Bacteroidetes abundance and a sharp reduction in Proteobacteria. Genus-level analyses showed dramatic increases in core beneficial microbes, with Bifidobacterium expanding 10.32-fold and Lactobacillus increasing 9.24-fold relative to blank controls, alongside noticeable enrichment of Bacteroides. Conversely, potentially pathogenic and dysbiosis-associated genera were substantially curtailed; the relative abundance of Escherichia-Shigella dropped from 39.51 percent in the blank medium to 12.57 percent in the polysaccharide group, while Fusobacterium abundance declined markedly. Statistical correlation analysis connected these taxonomic shifts with elevated production of acetic, propionic, and butyric acids. While these benchtop findings demonstrate clear prebiotic potential in a closed laboratory system, the authors emphasize that in vitro batch cultures cannot fully capture the dynamic absorption, peristalsis, and mucosal immunology of a living human gastrointestinal tract.

Subject of Research: Structural characterization and in vitro prebiotic activity of a novel rice bran polysaccharide

Article Title: Structural characterization and prebiotic activity of a novel polysaccharide from rice bran

Article References: Chen, B., Xia, W., Liu, H., Wang, C., He, H., Qiao, Y., & Wang, X. (2026). Structural characterization and prebiotic activity of a novel polysaccharide from rice bran. Frontiers in Nutrition, 13, Article 1943700. https://doi.org/10.3389/fnut.2026.1943700

Image Credits: AI Generated

DOI: 10.3389/fnut.2026.1943700

Keywords: rice bran, polysaccharides, prebiotic activity, gut microbiota, short-chain fatty acids, fecal fermentation, Bifidobacterium, Lactobacillus, heteropolysaccharides, molecular weight, monosaccharide composition, methylation analysis, nuclear magnetic resonance, thermal stability, Escherichia-Shigella, Bacteroides, in vitro fermentation, acetic acid