Development of a stable hydrogel network based on agar–kappa-carrageenan blend cross-linked with genipin

Blend of food hydrocolloids, viz. agar and kappa-carrageeenan (agar/kC), was treated with the natural cross-linker genipin in aqueous medium to impart functional stability. The genipin-fixed blend exhibited remarkable stability in the wide range of pH 1–12, as well as in Ringer's solution. Ratios of the hydrocolloids and genipin in the blend as well as in the cross-linked product were optimized (agar/kC 25:75 and agar/kC/genipin 25:75:0.8, w/w) on the basis of swelling properties. Compatibilities of unmodified blend (agar/kC) and the cross-linked blend product in aqueous solution were studied by measuring apparent and intrinsic viscosities and UV absorptions. Properties of agar/kC blend and the genipin cross-linked blend in solid state were evaluated by bulk and true density, pore volume, porosity, thermogravimetric analysis (TGA), swelling ability, X-ray diffraction, degradation rate in vitro, optical microscopy, scanning electron microscopy (SEM) and rheological measurements. The cross-linked blend exhibited higher viscosity, thermal stability and swelling ability as well as low weight loss ratio compared to those of the un-modified blend. The presence of genipin in the cross-linked polymer network was confirmed by MS/MS analysis. This genipin cross-linked blend presents an immense potential for food applications and in other pH-specific applications as well.