MECHANICAL AND RHEOLOGICAL STUDY ON GELATIN HYDROGEL FOR MIXED GEL APPLICATION

Hydrogels are three-dimensional reticulated hydrophilic polymer networks capable of retaining a large amount of water in their structures due to carboxylate groups enabling this cross-linking. They have a broad range of applications mainly used for pharmaceutical products. Recently, these systems have been applied in the aqueous phase of mixed systems of the bigel type, mainly destined for food products. Gelatin is a biopolymer highly used in producing hydrogels due to being readily soluble in water and to its gelling capacity and biocompatibility. This study focuses on understanding the behavior of hydrogels formulated with gelatin concentrations of 7%, 8.5%, and 10% and evaluating the mechanical and rheological properties of the structures obtained. The hydrogel was prepared through the dispersion of the biopolymer in deionized water containing 0.1% sodium azide; the system was stirred (300 rpm) and heated (65 ºC) for 15 minutes; after the production, the samples were kept in a BOD incubator for 24 h and 25 ºC to ensure the complete gelation. Rheological measurements on static and oscillatory modes were made and the mechanical properties of compression tested, concerning texture profile analysis (TPA). The results showed that different concentrations significantly influenced on the hydrogel structure. All the gelatin hydrogels showed shear behavior characteristics of non-Newtonian fluids. There was a slight difference in apparent viscosity between the concentrations of 8.5% and 10% of the biopolymer (p>0.05). Thereby, for 8.5% and 10% gelatin at 300 s−1 (ƞ300), the apparent viscosity was higher, 1.26 Pa.s and 1.54 Pa.s, respectively, compared to the 7% sample, which was 0.66 Pa.s. The stress sweep test indicated that the Oscillatory Strain Limit (OSL) value remained stable, with a strain at 10% for all samples. Thus, the results showed that, within the tested experimental range (0.1 to 10 Hz), all samples exhibited a gel-like behavior - more similar to a solid than a liquid. Therefore, deformations can be essentially elastic and recoverable. Concerning the frequency, all samples were independent of frequency (G'>G") and showed a characteristic of stronger gels (G'/G">10). In order to evaluate the structure resistance to thermal changes, the temperature sweep was measured, and it was observed that the gelatin hydrogel was an unstable system to apply high temperatures. At around 40 ºC, the system was unstructured; the decrease in G' can be related to the transformation of the gel state into a liquid state. The firmness and cohesiveness were statistically significant (p<0.05). The hydrogel with a gelatin concentration of 10% was the most resistant system to compression, with a firmness of 53.81 N, while the gelatin concentration of 7% had a firmness of 22.41 N. The hydrogel with 8.5% biopolymer presented similar characteristics to the 10% concentration, with the advantage of using less material amount, resulting in lower costs and additives. Therefore, the gelatin concentration of 8.5% is advised to obtain a firm, viscous and stable hydrogel.