# Influences of pH on Gelling and Digestion–Fermentation Properties of Fish Gelatin–Polysaccharide Hydrogels

## TL;DR

This study explores how pH affects the structure and digestion of fish gelatin-based gels mixed with polysaccharides, revealing how these materials could be used to create healthier food products.

## Contribution

The novel contribution is the systematic evaluation of pH effects on gelation and gut microbiota interactions in fish gelatin-polysaccharide hydrogels.

## Key findings

- Gel strength and hardness increased at pH 4–6 but decreased at higher pH due to structural changes.
- FG–XG showed better digestion enhancement than FG–κC at higher pH levels.
- FG–κC promoted beneficial gut bacteria like Lachnospiraceae and Bacteroides more than FG–XG.

## Abstract

This study systematically evaluated the effects of pH (4–10) on the gelation properties, structural characteristics, and in vitro digestion–fermentation behavior of fish gelatin (FG, 6% (w/v)) hydrogels combined with either xanthan gum (XG, 0.07% (w/v)) or κ-carrageenan (κC, 0.07% (w/v)). The results revealed that the gel strength, hardness, and chewiness of the composite gels initially increased (pH 4–6) and subsequently decreased with rising pH levels. This trend correlated with the formation of a dense gel network structure. Furthermore, as pH increased, in vitro digestibility showed a similar pH-dependent trend, with FG–XG demonstrating superior enhancement compared to FG–κC. The addition of XG and κC resulted in increased gas production and a decreased pH during fermentation. Intestinal microbiota analysis revealed that both FG–XG and FG–κC improved the abundances of Proteobacteria and Bacteroidete while reducing Firmicutes. Compared to FG–XG and FG, FG–κC promoted higher levels of the genera Lachnospiraceae and Bacteroides, suggesting a more favorable impact on intestinal health. These findings provide valuable insights into the pH-responsive functional properties of FG-based hydrogels and their potential applications in designing novel food matrices with enhanced nutritional and probiotic attributes.