Fabrication of soy protein isolate/κ-carrageenan hydrogels for release control of hydrophilic compounds: Flax lignans

A suitable carrier for flax lignans using Soybean protein isolated (SPI) - κ-carrageenan (KC) hydrogels was developed. The effects of KC concentration on the stability of hydrogels were investigated, as well as water holding capacity (WHC), syneresis and morphological changes. A solid-like gel network and viscoelasticity of composite hydrogels were confirmed by rheological behavior test. Scanning electron microscopy (SEM) displayed a dense and uniform structure for hydrogels with the optimum KC concentration (0.6 %). Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC) curves suggested lignan might interact with SPI and KC by hydrogen bonding or hydrophobic effects. The release of flax lignans in hydrogels was followed with Fick diffusion in simulated gastric fluids (SGF) and non-Fickian diffusion in simulated intestinal fluids (SIF), respectively. The cumulative release rate of flax lignan in complex gels (46.00 %) was lower than that of pure SPI hydrogels (77.43 %) at the end of digestion. The results indicated that KC protected the protein by hindering the accession of digestive enzymes into the hydrogels, thus resulting in a reduction of gel matrix erosion and lignan release during digestion. These findings shield a light on SPI-KC hydrogels as carriers for water-soluble bioactive compounds in food and pharmaceutical industries.