Techno-functional gelling mechanism and rheological properties of gelatin capsule-waste gel modified with kappa-carrageenan for future functional food applications

• Gelatin capsule waste was converted into food-grade functional hydrogels • κ-Carrageenan improved gel texture, strength, and elasticity of GCW gels. • SR-FTIR identified gelatin–carrageenan intermolecular interactions • Carrageenan increased gelling and melting temperatures of GCW gels • Optimized gels show potential for soft confectionery and elderly-friendly foods. Gelatin capsule production generates large amounts of waste. Repurposing this waste into hydrogels offers a sustainable solution. This study investigated the techno-functional gelling mechanism and rheological properties of gelatin waste gel with added carrageenan, aiming to enhance the gel’s potential for future functional food applications. Gelatin capsule waste (GCW) was substituted with carrageenan at different levels (0%, 10%, 20%, 30%, 40%, or 50% w/w). The texture profile analysis and gel strength increased with the addition of carrageenan, accompanied by changes in the spectra obtained from Synchrotron Radiation-based Fourier-Transform Infrared Spectroscopy (SR-FTIR), which identified intermolecular and intramolecular interactions between the gelatin and carrageenan. The rheological measurements revealed that the incorporation of carrageenan influenced the elastic modulus (G’) and loss modulus (G’’) of the substituted GCW gel, as observed from the temperature sweep, which coincided with the higher gelling and melting temperatures (p<0.05). The substituted GCW gels had a higher turbidity than the GCW gel without substitution, as confirmed by a decreased L* value. The water activity of the GCW gel remained stable with the addition of carrageenan. Based on the gel microstructure, the GCW gel had a looser gel network with larger voids, whereas the substituted gels had a finer network with smaller voids. However, there was a decrease in the overall likeness score for the gels substituted with carrageenan, especially at higher levels. In summary, the incorporation of carrageenan into GCW gel significantly influenced its rheological and textural properties. At an optimal substitution level, the GCW gel with carrageenan had strong potential as a functional material for food applications, particularly in soft confectionery.