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The degradation of sodium alginate by human gut microbiota was found to be retarded via calcium cross-linking in our previous study. We hypothesized that the guluronic acid block (GB) on the alginate molecule might be the key structural region affecting alginate degradation by the gut microbiota when cross-linked with calcium. This study aims to prove this hypothesis by studying the structural features of the cross-linked GB on its in vitro fecal fermentation behaviors concerning the aspects of total carbohydrate contents, monosaccharide contents, short-chain fatty acids production, calcium state variations, and structural variations. Herein, GB isolated from sodium alginate was cross-linked under ranges of molar ratios of [Ca 2+ ]/[-COOH] that further restricted the degradation by gut microbiota similar to the cross-linked alginates. First, total carbohydrate contents, short-chain fatty acids production, monosaccharides contents, and calcium state analyses confirmed that the degradation of GB by gut microbiota was restricted by calcium cross-linking. Furthermore, the tracking analysis of structural variations during in vitro fermentation revealed that the "granules" structure could further restrict degradation by the gut microbiota, leaving more cross-linked GB fragments surviving in comparison to the "networks" structure. In addition, Bacteroides xylanisolvens showed a significant positive correlation to the "cross-linking porosity ( R = 0.825, p < 0.001), which supported our previous findings on fermentation behaviors of cross-linked alginate. Together, guluronic acid blocks are the key structural regions that retard the degradation of sodium alginate by the gut microbiota when cross-linked with calcium.

Hexadecyltrimethylammonium bromide complexed alginate-Ca 2+ microgels (C/AMGs) were developed as emulsifiers, which shown remarkably improved emulsifying performance than non-complexed alginate-Ca 2+ microgels (AMGs) in previous study. This work focus on the impact of deformability on the emulsifying performance of C/AMGs. By regulating alginate concentration (1.0-4.0 wt%), microgels with different deformability were prepared. Deformability was proved to have great influence on the emulsifying performance of C/AMGs, which was evaluated by Langmuir trough measurements, emulsion appearance, centrifugation stability, digestive behavior, and oxidative stability. Particle size and SEM images indicated microgels prepared with lower alginate concentration are more deformable. C/AMGs (2.0 wt%) exhibits the best emulsifying performance, which could be ascribed to the appreciated deformability and mechanical strength. Digestive behavior and oxidative stability of alginate-Ca 2+ microgel (2.0 wt%) stabilized emulsions were further investigated. Compared with alginate-Ca 2+ microgel (2.0 wt%) stabilized emulsions, C/AMGs (2.0 wt%) stabilized emulsions shown delayed lipid digestion and lower POV. Results of this work supporting that Mickering mechanism have potential in fabricating functional emulsions based on natural polysaccharides., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

Slow fermentable dietary fibers can be utilized by human gut microbiota in the distal region of the colon and thus exert a sufficient short-chain fatty acids (SCFAs) supplement in the distal region of the human colon. Alginate (Alg) based microgels are widely fabricated and used to control their digestion by digestive enzymes releasing active substances site-specifically. Herein, sodium alginate microgels with gradient calcium-ion (Ca 2+ ) cross-linking densities were developed, restricting their degradation by gut microbiota. Alg microgels were prepared using high-speed shearing after Alg was cross-linked with 10, 40, and 60 mmol/L Ca 2+ , respectively (named 10-Alg, 40-Alg, and 60-Alg). The fluorescence and atomic force microscopic results showed that the 40-Alg particle has the densest structure among the three cross-linked Alg. In vitro human fecal fermentation results revealed that the Ca 2+ cross-linking exerted more restricting effects than delaying effects on the fermentation of Alg, and the 40-Alg exhibited the slowest fermentation rate and the least fermentation extent, by characterizing the residual total carbohydrate content, residual monosaccharide content, pH, and total short-chain fatty acids. The 16S rRNA gene sequencing results indicated that cross-linking structures shaped a high specifical Bacteroides-type microbial community and that OTU205 (Bacteroides&#95;xylanisolvens) highly correlated to the cross-linking density (R = 0.65, p = 0.047). In sum, Ca 2+ cross-linking generated a dense and compact structure of sodium alginate that facilitated a more restricted fermentation property and specificity-targeting microbial community structure in comparison to the original sodium alginate., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

In this research, sodium alginate (ALG) microgels were prepared with different ALG concentrations, and physicochemical and emulsifying profiles of these hydrophilic microgels were comparatively analyzed. Results showed that these microgels possessed different size, hardness, and surface charge. All these microgels could stabilize an oil-in-water emulsion through the Mickering mechanisms, and smaller microgels had better emulsifying capacity. The surface hydrophobicity and interfacial tension of the microgels had no exact effects on their emulsifying behaviors. Compared with the harder microgels (prepared with high ALG concentration, e. g. 4 mg/mL), the emulsifying capacities of the softer ones (prepared with low ALG concentration, e.g. 1 mg/mL) were more sensitive to the high salt concentration (200 mM NaCl) but stable under acidic environment (pH 2.0). Our research would afford a new strategy for the manufacture and application of the novel polysaccharide-based emulsifiers. [ABSTRACT FROM AUTHOR]

It has been a great challenge of using natural polysaccharides to stabilize food emulsions, due to their poor amphiphilicity. In this study, a novel strategy of using polysaccharide to stabilize O/W emulsions was developed, through in situ crosslinking of sodium alginate on oil-water interface. During the emulsifying process, the acetic acid migrated across the interface, and induced the released of calcium ions, which immediately crosslinked the sodium alginate on interface. Results showed that the oil droplets were encapsulated in the integral polysaccharide shells. The droplet size of the emulsions located in the range from 20 to 200 μm. The concentration of sodium alginate and HAc, as well as the mixing rates were showed to be positively related with the thickness of the shell. However, excess calcium ions would disintegrate the shell structure. Additionally, the interfacial crosslinked sodium alginate stabilized emulsions exhibited excellent physical stability under centrifugating and freeze-thawing. [Display omitted] • Emulsions based on in situ crosslinking of alginate were manufactured. • Oil droplets were encapsulated in the integral polysaccharide shells. • Influence of different factors on shell thickness of oil droplets was evaluated. • In situ crosslinking of alginate endow emulsions with excellent physical stability. [ABSTRACT FROM AUTHOR]