Variation in characterization and probiotic activities of polysaccharides from litchi pulp fermented for different times

Unveiling biotransformation of free flavonoids into phenolic acids and Chromones alongside dynamic migration of bound Phenolics in Lactobacillus-fermented lychee pulp

Lactobacillus strains have emerged as promising probiotics for enhancing the bioactivities of plant-based foods associated with flavonoid biotransformation. Employing microbial fermentation and mass spectrometry, we explored flavonoid metabolism in lychee pulp fermented separately by Lactiplantibacillus plantarum and Limosilactobacillus fermentum. Two novel metabolites, 3,5,7-trihydroxychromone and catechol, were exclusively identified in L. plantarum-fermented pulp. Concomitant with consumption of catechin and quercetin glycosides, dihydroquercetin glycosides, 2,4-dihydroxybenzoic acid and p-hydroxyphenyllactic acid were synthesized by two strains through hydrogenation and fission of C-ring. Quantitative analysis revealed that bound phenolics were primarily located in water-insoluble polysaccharides in lychee pulp. Quercetin 3-O-rutinoside was partially liberated from water-insoluble polysaccharides and migrated to water-soluble polysaccharides during fermentation. Meanwhile, substantial accumulations in short-chain fatty acids (increased 1.45 to 3.08-fold) and viable strains (increased by 1.97 to 2.00 Log10 CFU/mL) were observed in fermentative pulp. These findings provide broader insight into microbial biotransformation of phenolics and possible guidance for personalized nutrition.

Comparison of different longan polysaccharides during gut Bacteroides fermentation

The bioactivity of polysaccharide was closely related to its fermentation utilization by gut Bacteroides, and its utilization degree was determined by various gut Bacteroides species and different polysaccharides characteristics. The effects of longan polysaccharide (LP) and LP treated by ultrasonic-assisted hydrogen peroxide for 8 h (DLP-8) on gut Bacteroides growth, and their fermentation utilization were compared. The results of LP and DLP-8 on the proliferation of six Bacteroides species showed that Bacteroides uniformis had the highest proliferation index. In fermentation by B. uniformis, DLP-8 (with a lower molecular weight), the viable count of which was higher than that of LP, was degraded more and especially utilized more glucose and glucuronic acid. The microstructure of the two polysaccharides changed differently during fermentation. Moreover, DLP-8 promoted greater short-chain fatty acids production than LP. These results indicated that the fermentation properties of DLP-8 by B. uniformis were superior to those of LP.

In vitro human gut microbiota fermentation of litchi pulp polysaccharides as affected by Lactobacillus pre-treatment

In this study, litchi polysaccharides were obtained from unfermented or fermented pulp by Lactobacillus fermentum (denoted as LP and LPF, respectively). The differences between LP and LPF in the colonic fermentation characteristics and modulatory of gut microbiota growth and metabolism were investigated with an in vitro fecal fermentation model. Results revealed that the strategies of gut bacteria metabolizing LP and LPF were different and LPF with lower molecular weight (Mw) was readily utilized by bacteria. The monosaccharide utilization sequence of each polysaccharide was Ara > Gla > GalA > GlcA ≈ Glu ≈ Man. Moreover, LPF promoted stronger proliferation of Bifidobacterium, Megamonas, Prevotella, and Bacteroides and higher SCFAs production (especially acetic and butyric acids) than LP. Correlation analysis further revealed that Mw could represent an essential structural feature of polysaccharides associated with its microbiota-regulating effect. Overall, Lactobacillus fermentation pre-treatment of litchi pulp promoted the fermentation characteristics and prebiotic activities of its polysaccharide.

Structural characterization and prebiotic activity of Bletilla striata polysaccharide prepared by one-step fermentation with Bacillus Licheniformis BJ2022

Bletilla striata polysaccharide (BP) is one of the main active ingredients in Orchidaceae plant Bletilla striata. BP has a high molecular weight, high viscosity, and complex diffusion, which is not conducive to the absorption and utilization of the human body. For the first time, we produced fermented Bletilla striata polysaccharide (FBP) with a low polymerization degree using Bacillus licheniformis BJ2022 one-step fermentation. FBP was a neutral polysaccharide with the molecular weight of 6790 Da. It was composed of glucose and mannose at a molar ratio of 1:2.7. The glycosidic bonds of FBP were composed of β-1,4-linked mannose, β-1,4-linked glucose and β-1,6-linked mannose according to methylation and NMR analysis. Compared with BP, FBP has a lower viscosity and higher solubility. The scanning electron microscopy results showed that the surface of FBP was porous and honeycomb-like. The rheology properties of FBP solution were close to non-Newtonian fluid. Using in vitro fermentation, we proved that FBP could regulate human gut microbiota and significantly increase the content of Bifidobacterium and Bacteroides. Our results suggested that Bacillus licheniformis fermentation significantly improved the physical and prebiotic properties of FBP. This study provides a new strategy for developing and utilizing Bletilla striata resources in China.

Structural elucidation and physicochemical properties of litchi polysaccharide with the promoting effect on exopolysaccharide production by Weissella confusa

Exopolysaccharide (EPS), as a secondary metabolite of microorganisms, has been commonly used in the dairy industry to replace the traditional stabilizers. However, the EPS production by microorganism is generally low, which limits its application. A litchi polysaccharide (Lzp2-2) with the promoting effect on EPS production by Weissella confusa was purified. The SEM and FT-IR analysis indicated that Lzp2-2 displayed a compact netlike structure and typical bands of carbohydrates. The structure of Lzp2-2 was further elucidated, which was comprised of a major backbone structure [→3)-β-D-Galp-(1→6)-β-D-Galp-(1 → 6)-β-D-Galp-(1 → 3)-β-D-Glcp-(1 → 6)-α-D-Glcp-(1 → 3)-α-D-Glcp-(1→] linked with two side chains [α-L-Araf-(1 → 5)-α-L-Araf-(1→, and β-D-Glcp-(1 → or α-L-Araf-(1→] at the O-3 and O-6) of β-D-Galp-(1→, respectively. Finally, Lzp2-2 was applied as an additive to the medium of yoghurt fermented by W. confusa. The results indicated Lzp2-2 not only promoted the EPS production to improve the viscosity, texture and mouthfeel of yoghurt, but also facilitated the generation of other secondary metabolites (volatile organic compounds), thus elevating the flavor of yoghurt.

Recent advances in polysaccharide biomodification by microbial fermentation: production, properties, bioactivities, and mechanisms

Polysaccharides are natural chemical compounds that are extensively employed in the food and pharmaceutical industries. They exhibit a wide range of physical and biological properties. These properties are commonly improved by using chemical and physical methods. However, with the advancement of biotechnology and increased demand for green, clean, and safe products, polysaccharide modification via microbial fermentation has gained importance in improving their physicochemical and biological activities. The physicochemical and structural characteristics, biological activity, and modification mechanisms of microbially fermented polysaccharides were reviewed and summarized in this study. Polysaccharide modifications were categorized and discussed in terms of strains and fermentation techniques. The effects of microbial fermentation on the physicochemical characteristics of polysaccharides were highlighted. The impact of modification of polysaccharides on their antioxidant, immune, hypoglycemic, and other activities, as well as probiotic digestive enhancement, were also discussed. Finally, we investigated a potential enzyme-based process for polysaccharide modification via microbial fermentation. Modification of polysaccharides via microbial fermentation has significant value and application potential.

Lychee pulp phenolics fermented by mixed lactic acid bacteria strains promote the metabolism of human gut microbiota fermentation in vitro

Lychee pulp phenolics possess excellent biological activities, however, changes in phenolic substances after microbial treatments are unknown. Herein, lychee pulp was fermented by Lactobacillus plantarum, Lactobacillus rhamnosus, and a mixed strain of the two, followed by an investigation of the products' colonic fermentation. In comparison to single-strain fermentation, mixed-strain fermentation significantly increased catechin and quercetin. In addition, lychee phenolics fermented by mixed strains were more conducive to the growth of gut microbiota. The results of HPLC-DAD showed that colonic fermentation further promoted the release of lychee phenolics. There was a notable increase in the content of gallic acid and quercetin, while multiple phenolics were degraded. Quercetin-3-O-rutinose-7-O-α-L-rhamnoside (QRR) and rutin were catabolized into quercetin by gut microbiota, and 4-hydroxybenzoic acid was produced from the metabolism of QRR and procyanidin B2. Lychee phenolics fermented by mixed lactic acid bacteria were easily metabolized and transformed by gut microbiota. These findings indicate that lychee pulp fermented by mixed lactic acid bacteria possesses probiotic potential, which is of great significance for the development of functional probiotic products.

Purification, Characterization and Bioactivity of Different Molecular-Weight Fractions of Polysaccharide Extracted from Litchi Pulp

Litchi polysaccharides are a kind of macromolecular polymers with various biological activities and a wide range of molecular weights. In this study, two separate fractions, with average molecular weights of 378.67 kDa (67.33%) and 16.96 kDa (6.95%), which were referred to as LP1 and LP2, respectively, were separated using an ultrafiltration membrane. Their physicochemical properties, and immunomodulatory and prebiotic activity were compared. The results revealed that LP2 contained more neutral sugar, arabinose, galactose and rhamnose, but less uronic acid, protein, mannose and glucose than LP1. Compared with LP1, LP2 possessed higher solubility and lower apparent viscosity. LP2 exhibited stronger stimulation on macrophage secretion of NO, TNF-α and IL-6, as well as better proliferation of Lactobacillus plantarum, Leuconostoc mesenteroides, Lactobacillus casei and Bifidobacterium adolescentis. These results suggest that an ultrafiltration membrane might be used to prepare a highly-active polysaccharide fraction from litchi pulp that may be used for food or drug development.