# Preparation and Characterization of Casein–Soy Protein Hybrid Gels Cross-Linked by Transglutaminase

## TL;DR

This study blends casein with soy protein using an enzyme to create stronger, more water-retaining gels with better structure.

## Contribution

The novel approach uses transglutaminase to cross-link casein and soy protein, enhancing plant protein functionality.

## Key findings

- A 1:1 casein-to-soy protein ratio produced the strongest gels with optimal water retention and structure.
- Transglutaminase enabled covalent bonding, while hydrophobic and disulfide interactions stabilized the gel matrix.
- Hybrid gels showed improved network uniformity and immobilized water effectively in a porous matrix.

## Abstract

To enhance the gelling functionality of plant proteins, this study developed hybrid gels by blending casein with soy protein isolate (SPI) at various ratios using microbial transglutaminase (MTG) as a cross-linking catalyst. The gels were systematically characterized in terms of microstructure, water distribution, rheological and textural properties, secondary structure, and intermolecular interactions. Incorporation of casein significantly improved gel strength, water-holding capacity, and network uniformity. Notably, the 1:1 casein-to-SPI ratio yielded the highest performance, featuring extensive inter-protein cross-linking, an increased proportion of ordered secondary structures, and a finely porous matrix that effectively immobilized water. Mechanistically, MTG-catalyzed covalent bonding established the primary network scaffold, while hydrophobic interactions and disulfide bonds further stabilized the gel matrix. These findings demonstrate that MTG-induced Casein–SPI hybrid gels can enhance the functional properties of plant proteins and offer a viable strategy for designing sustainable protein-based food structures with tailored performance.