Fecal fermentation characteristics of Rheum tanguticum polysaccharide and its effect on the modulation of gut microbial composition.

BACKGROUND: Rheum tanguticum is utilized as one of the well known traditional Chinese medicine for the treatment of gastrointestinal diseases. Recently, R. tanguticum polysaccharides (RP) have received increasing attention due to their diversely pharmacological activities. Usually, the pharmacological activities of polysaccharides are closely correlated to their metabolic properties from the stomach to the intestine. However, the digestive behavior and fecal fermentation characteristics of RP are unknown, which need to be fully investigated. METHODS: In this study, an in vitro simulated gastrointestinal model was carried out for the investigation of the digestive behavior and fecal fermentation characteristics of RP. The possible changes in physicochemical properties of RP, such as molecular weight, monosaccharide composition, reducing sugar released, chemical composition, pH value, and short chain fatty acids, were determined during in vitro simulated digestion and human fecal fermentation, and its effect on the modulation of gut microbial composition was also evaluated. RESULTS: The results revealed that RP was indigestible under the in vitro simulated digestion conditions according to its stabilities in physicochemical properties. Conversely, the indigestible RP (RPI) could be notably utilized by colonic microbiota in human feces after the in vitro fermentation, especially, at the initial fermentation stage (0-6 h). The fecal fermentation characteristics of RPI were revealed. Results showed that the content of reducing sugars obviously increased from 0.177 to 0.778 mg/mL at the initial stage of fermentation, and its molecular weight notably declined from 2.588 × 105 to 0.828 × 105 Da at the end stage of fermentation. Notably, the utilization of arabinose and galactose in RPI by colonic bacteria was faster than that of galacturonic acid. Besides, RPI could obviously modulate gut microbial composition via promoting the relative abundances of several beneficial bacteria, such as genera Bacteroides, Bifidobacterium, and Megamonas, resulting in the promoted production of several short-chain fatty acids, such as acetic, propionic, and butyric acids. CONCLUSIONS: Results from this study showed that RP was indigestible in the human upper gastrointestinal tract in vitro, but could be easily utilized by colonic microbiota in human feces at the initial stage of fermentation. RP could be used as potential prebiotics for the improvement of intestinal health.

In vitro digestive characteristics and microbial degradation of polysaccharides from lotus leaves and related effects on the modulation of intestinal microbiota.

Polysaccharides exist as one of the most abundant components in lotus leaves, which attract increasing attention owing to their promising health-promoting benefits. In this study, the digestive and microbial degradation characteristics of lotus leaf polysaccharides (LLP) were studied by using an in vitro gastrointestinal model. The results suggested that LLP was stable in the human upper gastrointestinal tract in vitro according to its digestive stabilities at different simulated digestion stages. Conversely, the indigestible LLP (LLPI) could be remarkably utilized by intestinal microbiota in human feces during in vitro fermentation, and its fermentability was 58.11% after the in vitro fermentation of 48 h. Indeed, the microbial degradation characteristics of LLPI during in vitro fermentation by human fecal inoculum were revealed. The results showed that the content of reducing sugars released from LLPI obviously increased from 0.498 to 2.176 mg/mL at the initial fermentation stage (0-6 h), and its molecular weight sharply decreased from 4.08 × 104 to 2.02 × 104 Da. Notably, the molar ratios of arabinose (Ara), galactose (Gal), and galacturonic acid (GalA) in LLPI decreased from 2.89 to 1.40, from 5.46 to 3.72, and from 21.24 to 18.71, respectively, suggesting that the utilization of arabinose and galactose in LLPI by intestinal microbiota was much faster than that of galacturonic acid at the initial fermentation stage. Additionally, LLPI could remarkably regulate gut microbial composition by increasing the abundances of several beneficial microbes, including Bacteroides, Bifidobacterium, Megamonas, and Collinsella, resulting in the promoted generation of several short-chain fatty acids, especially acetic, propionic, and butyric acids. The findings from the present study are beneficial to better understanding the digestive and microbial degradation characteristics of LLP, which indicate that LLP can be used as a potential prebiotic for the improvement of intestinal health.

Deep Eutectic Solvent-Assisted Extraction, Partially Structural Characterization, and Bioactivities of Acidic Polysaccharides from Lotus Leaves.

Lotus leaves are often discarded as byproducts in the lotus industry. Polysaccharides are regarded as one of the essentially bioactive components in lotus leaves. Therefore, in order to promote the application of lotus leaves in the functional food industry, the deep eutectic solvent (DES) assisted extraction of polysaccharides from lotus leaves (LLPs) was optimized, and structural and biological properties of LLPs extracted by DES and hot water were further investigated. At the optimal extraction conditions (water content of 61.0% in DES, extraction temperature of 92 °C, liquid-solid ratio of 31.0 mL/g and extraction time of 126 min), the maximum extraction yield (5.38%) was obtained. Furthermore, LLP-D extracted by DES and LLP-W extracted by hot water possessed the same sugar residues, such as 1,4-α-D-GalAp, 1,4-α-D-GalAMep, 1,3,6-ß-D-Galp, 1,4-ß-D-Galp, 1,5-α-L-Araf, and 1,2-α-L-Rhap, suggesting the presence of homogalacturonan (HG), rhamnogalacturonan I and arabinogalactan in both LLP-W and LLP-D. Notably, LLP-D was much richer in HG fraction than that of LLP-W, suggesting that the DES could assist to specifically extract HG from lotus leaves. Additionally, the lower molecular weight and higher content of uronic acids were observed in LLP-D, which might contribute to its much stronger in vitro antioxidant, hypoglycemic, and immunomodulatory effects. These findings suggest that the optimized DES assisted extraction method can be a potential approach for specific extraction of acidic polysaccharides with good bioactivities from lotus leaves for applications in the functional food industry.

Polysaccharides from dandelion (Taraxacum mongolicum) leaves: Insights into innovative drying techniques on their structural characteristics and biological activities.

The aim of this study was to well understand the impacts of innovative drying techniques (radio frequency drying and microwave drying) and traditional drying techniques (vacuum drying, freezing drying, and hot air drying) on the structural characteristics and bioactivities of polysaccharides from dandelion leaves (DLPs). Five different DLPs were obtained from dandelion leaves dried by abovementioned drying techniques. Results showed that the structural characteristics and bioactivities of DLPs varied with different drying techniques. The molecular weights, apparent viscosities, molar ratios of constituent monosaccharide, contents of uronic acids, and contents of bonded polyphenolics in DLPs obtained by different drying techniques had noticeable variations, while the types of constituent monosaccharides and the major glycosidic linkages in DLPs were similar. In addition, results showed that DLPs, especially DLP-RF obtained by the radio frequency drying, exhibited remarkable antioxidant activities (ABTS, DPPH, and NO radical scavenging activities), excellent in vitro antiglycation activity, and obvious in vitro inhibitory activity on α-glucosidase. Results from this study suggest that the radio frequency drying can be used as a potential drying technique before extracting DLPs for applications in the functional food and medicine industries.

Carboxymethylation of Qingke ß-glucans and their physicochemical properties and biological activities.

In this study, the response surface methodology was used to optimize the reaction conditions of carboxymethylated modification of Qingke ß-glucans (QG), and effects of different degrees of carboxymethylation (high, medium, and low) on their structural characteristics, in vitro antioxidant activities, and in vitro hypolipidemic activities were studied. The optimal reaction conditions of carboxymethylated Qingke ß-glucans (QG-Cs) with high degree of carboxymethylation (DC = 0.90) were as follows: reaction temperature of 62.1 °C, reaction time of 3.29 h, and concentration of chloroacetic acid of 1.75 mol/L. Results demonstrated that the carboxymethylated modification significantly affected the solubilities, molar ratios of constituent monosaccharides, molecular weights, and apparent viscosities of QG. Indeed, the QG-Cs exhibited much higher antioxidant activities (reducing powers, NO, and DPPH radical scavenging activities), in vitro binding properties (fat, bile acid, and cholesterol binding capacities), and pancreatic lipase inhibition activities than that of QG. Furthermore, results showed that bioactivities of QG-Cs were closely correlated to their carboxymethyl groups. Results suggested that the carboxymethylated modification could be an efficient method for enhancing bioactivities of QG, and QG-Cs had good potential applications in bio-pharmaceutical industry.

Comparison of structural characteristics and bioactivities of polysaccharides from loquat leaves prepared by different drying techniques.

In the present study, freeze drying, hot-air drying, vacuum drying, and microwave drying at the microwave powers of 400, 600, and 800 W, respectively, were utilized to dry loquat leaves for evaluating the effects of different drying techniques on the physicochemical structures and bioactivities of polysaccharides extracted from loquat leaves (LLPs). Results demonstrated that the physicochemical structures and bioactivities of LLPs significantly affected by different drying techniques. The degrees of esterification, molar ratios of constituent monosaccharides, contents of uronic acids, apparent viscosities, and molecular weights of LLPs were varied by different drying techniques. Additionally, LLPs, particularly LLP-M4 which extracted from loquat leaves prepared by microwave drying at the power of 400 W, exerted remarkable in vitro binding capacities, strong inhibitory effects on α-amylase and α-glucosidase, and obvious antioxidant activities. Results indicated that the microwave drying could be an efficient drying technique before extraction of bioactive LLPs, and LLPs had great potential applications in the functional food and pharmaceutical industries.