RHEOLOGY OF GELATIN/CHITOSAN SOLUTIONS AT DIFFERENT pH

New biopolymer-based films has been developed in recent years, as consequence of a search for sustainable materials. Due to their characteristics such as biocompatibility, biodegradability, chemical functionalization capacity, among others, these materials can be applied in different areas, including food packaging. Thus, the objective of this study was to study the rheological characteristics of solutions of blends of two biopolymers, gelatin and chitosan, at different pH. A medium molecular weight chitosan (CH) solution was prepared by dissolving 2 g of chitosan in 98 g of a 2% acetic acid solution, at 40 °C for 12 hours. A pigskin gelatin (GE) solution was prepared by dissolving 4 g of gelatin in 96 g of water, at 55 °C for 30 minutes. These solutions were mixed adequately to prepare a solution with 2:1 ratio of GE:CH, at 50 °C for 2 hours. Then, solutions with different pH (3.5, 4.0, 4.5, 5.0, 5.5, and 6.0) were obtained by adding 5M acetic acid or 1.5M NaOH solutions. These solutions were analyzed, using a rheometer (AR2000 Advanced Rheometer; TA Instruments, New Castle, DE, USA), in a temperature sweeping mode (60 °C to 5 °C and 5 °C to 60 °C, at 2 °C/min), performed in duplicate. The solutions at pH= 3.5 presented the lowest Tsol-gel (8.2 ºC) and Tgel-sol (12.5 ºC), while the highest values were observed at pH= 6.0 (24.5 and 27.4 ºC, respectively). This behavior was consequence of interactions between the charged functional groups of both biopolymers, and their variation according to pH, thus affecting their viscoelastic properties.