Effects of Konjac Glucomannan and Inulin on the Gel Properties, Swallowing Characteristics, and In Vitro Digestion of Heat-Induced Silver Carp–Sea Cucumber Composite Gels for Dysphagia

In this study, we used silver carp (Hypophthalmichthys molitrix) and sea cucumber (Apostichopus japonicus) as the primary protein sources and supplemented them with konjac glucomannan (KGM) or inulin (INU) at concentrations of 0%, 0.5%, 1.0%, and 1.5% to evaluate the gelling properties, textural characteristics, rheological behaviors, and in vitro digestibility of the resulting composite gels. The gastrointestinal digestion behavior, structural changes, and functional characteristics of these gels under simulated adult and elderly physiological conditions were also systematically investigated to clarify how different physiological stages influence their digestive fate. The results showed that incorporating KGM or INU modified hydrogen bonding and protein–polysaccharide interactions within the gel network, thereby regulating the structural integrity and rheological properties of the composite gels. According to the International Dysphagia Diet Standardization Initiative (IDDSI) framework, the KGM/INU-modified gels successfully passed the prescribed tests and were classified as level 4 (pureed/extremely thick) and level 6 (soft and bite-sized) foods, confirming their suitability for dysphagia management. Compared with the control group, the 0.5% KGM group showed the most desirable texture profile, with significantly lower hardness, chewiness, and adhesiveness, and higher cohesiveness (p < 0.05), while the 1.0% INU group exhibited the greatest enhancement in gel strength and viscoelasticity, as evidenced by the highest storage modulus (G′) and loss modulus (G″) (p < 0.05). Moreover, both adult and elderly in vitro digestion models showed extensive proteolysis of the composite gels, together with reduced protein aggregation, a looser microstructure in the digesta, and enhanced antioxidant capacity. Notably, the elderly model generally showed higher digestibility than the adult model, accompanied by greater release of free amino acids and antioxidant constituents (p < 0.05). Overall, these findings indicate that KGM/INU-modified composite gels possess promising potential as texture-modified foods, while the two in vitro physiological models provide a valuable platform for evaluating their digestion-related properties. KGM/INU-modified composite gels thus provide a promising platform for developing texture-modified, nutritionally fortified foods suitable for elderly individuals with swallowing impairments and adults who require safe, readily digestible dietary options.