Starch-based hydrogels produced by high-pressure processing (HPP): The effect of high pressure on volume changes

The transformation of a solution into a gel, known as the sol-gel transition, can be observed in a variety of systems, such as colloidal suspensions, polymers, and biomolecules. Among them, starch, a plant-derived polysaccharide, undergoes sol-gel transition when subjected to different processing conditions, displaying intriguing rheological characteristics. This work aimed to investigate the mechanism of pressure-inducted gelatinization, with a particular focus on the impact of high pressure on volume changes. The investigation was carried out using different starches, namely rice, corn, and wheat dissolved in water at a constant concentration of 20 % w/w. The starch solutions underwent HPP, and the treatment conditions used were high pressures in the range of 500-700 MPa and holding times between 5 min and 15 min. The volume changes were assessed by using differential scanning calorimetry (DSC) and microscopy techniques. The results obtained showed that, regardless of the starch source and the evaluation method used, the volume changes, related to the partial molar volume of a polymer in a solvent, had negative values (-12.63 - -35.83 mL/mol) and decreased with increasing the pressure level. As a result, it can be suggested that when the amorphous and crystalline regions of the granules were hydrated under pressure, producing the swelling of starch granules, the partial volume of starch decreased due to molecular-level rearrangements or interactions occurring within the starch granules during the sol-gel transition. This study provides valuable insights into the fundamental mechanisms of pressure-induced starch gelatinization, which could pave the development of more stable, functional, and efficient products where controlled texture and consistency are critical.