Properties of a commercial κ-carrageenan food ingredient and its durable superabsorbent hydrogels

Physical kappa-carrageenan-based hydrogels are often prepared from dilute aqueous kappa-carrageenan (kappa-carrageenan) solutions at the presence of metallic ions or by mixing these solutions with proteins and other polysaccharides. The kappa-carrageenan hydrogels have been used for technological purposes; however, there are no reports about the properties of a commercial GENUGEL (R) kappa-carrageenan produced by the CP Kelco. The flame atomic absorption spectrometry shows that the commercial kappa-carrageenan comprises a high content of metallic ions (K+ = 216.1 g kg(-1), Na+ = 6.3 g kg(-1) and Ca2+ = 12.5 g kg(-1)). The X-ray photoelectron spectroscopy (XPS) indicates the presence of sodium, calcium, and potassium atoms on the as-received kappa-carrageenan and its physical hydrogel surfaces. XPS supports the occurrence of a low protein content onto the sample surfaces, as well. The metallic level (especially for K+) in the commercial kappa-carrageenan plays an essential role in the preparation of durable hydrogels. These materials are prepared by cooling aqueous kappa-carrageenan solutions at 4.0 and 5.0 wt%. The gelation temperature is determined by measuring G' & G '' as a function of the temperature. The gelation behavior depends on the kappa-carrageenan concentration, as well as the metallic content in the commercial sample. Scanning electron microscopy shows that hydrogels have porous and smooth surfaces. The dried materials swell from 2400 to 3100%, while the disintegration/dissolution test confirms that the samples present high stability in distilled water throughout 14 days. These hydrogels are superabsorbent materials and can be applied in agriculture as soil conditioners.