Tuning casein coagulation and structure: Exploring the effects of ionic strength and glycerol

Casein-based materials offer a sustainable platform for advanced biomaterials, yet the impact of ionic strength on their macroscopic structure and properties remains largely unexplored. This study investigates the coagulation (and gelation) of sodium caseinate solutions (14-20 wt%) at the isoelectric point in citric acid-trisodium citrate buffers of varying strengths (30-300 mM). The results demonstrate that buffer strength significantly influences water content, compactness, mechanical strength, and optical properties of the formed hydrogels. Notably, samples coagulated in 100 mM buffer exhibited lower compactness and tensile strength, and greater opacity compared to those formed in 300 mM buffer. Treatment with glycerol, which also induces partial dehydration, proved valuable in preventing structural collapse during drying, enabling structural insights through scanning electron microscopy. Additionally, glycerol played a crucial role in enhancing the samples' rehydration capability. The study also revealed a hydroresponsive switchable opacity, a feature that could be leveraged for applications such as wound dressings that indicate exudate saturation. Furthermore, the ability to tune the mechanical properties and structural compactness could be useful for designing tissue engineering scaffolds and drug delivery carriers. These findings provide critical insights into tailoring casein-based biomaterials through controlled coagulation conditions.