Thermo-mechanical response of liquid-core beads as affected by alginate molecular structure

Core-shell hydrogel beads have recently drawn considerable attention to meet ever-changing consumer demand for exciting texture combined with functional properties. Still, the thermal processing of these types of beads remains insurmountable. In this paper, spherical liquid core gel beads were prepared from alginate with distinguishable Mw and M/G ratios and treated at temperatures varying from 60 to 121 °C. The core and the shell both had a precise response and influence towards heat. Improved mechanical properties were observed from beads up to 100 °C, figuring on hydrogels' network structure. High G-content and high molecular weight (Mw) contributed broadly up to a 50% increase in bursting force at high temperatures. Above the boiling point, beads started losing their original geometry since core materials diffused at an accelerated rate with a vapor pressure buildup. An irregular pattern of reduction in shell thickness, depending on crosslinking nature, was observed among alginate beads during heat treatment. A maximum 63.4% thickness reduction was recorded from low Mw alginate. Poorly constructed gel networks produced thermally vulnerable structures, predominantly by shorter chain length or higher M residue. Higher calcium concentration (up to a saturated crosslinking point) enhanced stability within the same alginate group. Heat treatment resulted in a compact shell microstructure with reduced pore size and a smoother surface. The water state and crosslinking of the chains were the decisive factors for the beads' thermo-mechanical response. Thus, a relationship was established between liquid-core beads' structural integrity, stability, and alginate's molecular composition concerning thermal treatment.