Gel Formation Mechanism and Application in Dysphagia: Based on Peach Matrix-Soy Protein Interactions

With the global population aging, the prevalence of dysphagia is facing increasing challenges, creating an urgent need for innovative, safe-to-swallow, and nutrient-rich foods. To address these dietary requirements, functional gels composed of soy protein isolate (SPI) and peach-derived polysaccharides are developed, offering a promising solution for people with dysphagia. This dissertation systematically explores the mechanisms of gel formation and their practical applications from three stages: the development of peach pulp-SPI composite gels, the characterization of pectin fraction-SPI gels, and the optimization of SPI-to-pectin ratios for 3D food printing. Firstly, three peach varieties, namely, Meirui (MR), Yangshan (YS), and Cons758 (Cons), were selected and compounded with SPI to develop dysphagia-friendly composite gels. Correlation analysis between peach pulp properties and gel characteristics revealed that MR-SPI gels exhibited the best cohesiveness, gel strength, and water retention, meeting IDDSI Level 5 requirements for minced/ moist foods. These properties were attributed to dense three-dimensional network structures formed through strong electrostatic interactions and hydrogen bonding between SPI and the polysaccharides in the peach matrix. Notably, pectin composition and degree of methoxylation (DM), played a key role in determining texture, rheology, and structural stability of gels. Secondly, further research focused on the structural analysis of pectin fractions, namely, water-soluble pectin (WSP), chelator-soluble pectin (CSP), and sodium carbonate-soluble pectin (NSP), extracted from MR peach pulp. Due to the low DM and high linearity, CSP played an important role in forming dense and stable gels, which could be explained by the enhanced electrostatic interactions and hydrogen bonding between CSP and SPI. In contrast, based on the high DM and rich in RG-I and RG-II regions, WSP could improve the particle dispersion, which resulted in less compact networks. Meanwhile, NSP, with abundant branching and high polydispersity, contributed to flexible and highly viscous structures. Rheological analyses confirmed that the CSP-SPI gel formed uniform and continuous gel networks, while molecular docking further verified the strong binding affinity of CSP to β-conglycinin (7S) subunit of SPI, reinforcing the gel stability. At last, CSP-SPI gels were applied as 3D food printing inks using a mingling strategy to optimize gel properties. A series of SPI-to-CSP ratios (1:9 to 9:1, w/w) were analyzed, and the 7:3 (S7C3) formulation was identified as the most effective, balancing viscosity, mechanical strength, and extrusion performance. Additionally, the S7C3 gels demonstrated excellent printability and shape retention, attributed to dense and elastic network structures formed through hydrophobic interactions and physical entanglements. Elemental mapping (SEM-EDX) further revealed that carbon, oxygen, and nitrogen dominated the gel framework, while calcium ions contributed to additional cross-linking and improved the gel rigidity and stability. In conclusion, this research provides a new insight into the application of fruit pulp and SPI for the development of functional gels as innovative 3D printing inks for dysphagia-friendly foods. The interaction mechanism between peach-derived polysaccharides and SPI was deeply studied, which revealed the key role of CSP in achieving superior gelation properties. By leveraging the structural and functional characteristics of plant-based polysaccharides and proteins, these findings offer valuable insights into the development of texture-modified foods for people with diverse dietary needs.