Deacetylation-regulated dual thermal transitions and two-stage melting in KGM/κ-carrageenan composites.

Konjac glucomannan (KGM) and κ-carrageenan (κ-Car) are widely used hydrocolloids with strong gel-forming properties. Our previous work suggested that KGM promotes κ-Car coil-helix transition via a chain conformational-entropy-related mechanism, yet how deacetylation-induced changes in KGM structure regulate this effect remains unclear. Here, KGM with graded degrees of deacetylation was investigated in κ-Car composite gels using rheology, micro-DSC, variable-temperature NMR, AFM, and SAXS. Results show that KGM'S gelation-promotion effect is tightly regulated by chain flexibility versus aggregation propensity. Mildly deacetylated KGM (degree of deacetylation, DD around 48%) retains flexible chains that enhance κ-Car helix formation, yielding a single gelation transition. With increasing deacetylation (DD around 60-76%), local deacetylated KGM self-association weakens cooperativity, producing two thermally distinguishable gelation and melting events. At high deacetylation around 87%, aggregated DK domains form, and DK-assisted ordering is strongly weakened. These findings provide structural insight into tuning hydrogel behavior through controlled polysaccharide modification.