Electrostatic hydrogels formed by gelatin and carrageenan induced by acidification: Rheological and structural characterization

The rheological, chemical and structural characteristics of electrostatic hydrogels formed by gelatin and carrageenan (Gel:Car) were studied in this work. Hydrogels were formed at 1:1, 1:2, 1:4, 1:8, 2:1, 4:1 and 8:1 protein:polysaccharide ratios. The influence of the ratio between the biopolymers on the rheological characteristics of hydrogels was evaluated. The hydrogels were characterized by large and small deformation, water holding capacity and microstructural analysis. All hydrogels showed viscoelastic characteristics, and the Burger model was appropriate to explain the viscoelastic behavior of hydrogels formed. The hydrogel that presented the best viscoelastic and mechanical characteristics was the 1:2 Gel:Car showing that good amount of carrageenan associated with slow acidification results the formation of more junction zones due to complementary interactions between the gelatin triple helix and the carrageenan double helix. When carrageenan (1:4 and 1:8) or gelatin (2:1, 4:1 and 8:1) was in excess there was a suppression of the gelatin structure modification significantly reducing the density of the junction zones negatively impacting the flexibility and hardness of these hydrogels. All samples showed a good water holding capacity, retaining between 80 % and 90 % of water in the interior, making these hydrogels an attractive material for food applications because they can improve food texture, increasing water retention capacity, which will produce greater durability of food. However, its structure and its mechanism of formation can also be explored in protecting active molecules in its structure or in the manufacture of new hydrogels through the slow acidification, such as in yogurt manufacturing.