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Recrystallization of ice crystals during storage of frozen food, cells, or medical samples causes serious damage to the stored material. To mitigate this damage, additives such as κ-carrageenan, a polysaccharide derived from algae, can be employed. Experimental results demonstrated that κ-carrageenan strongly inhibits ice recrystallization and alters the ice crystal morphology, suggesting ice-binding properties. However, a binding of κ-carrageenan to ice crystals has not yet been shown, and the underlying mechanism of its recrystallization inhibition activity remains unclear. In this study, molecular dynamics simulations using different κ-carrageenan molecules and ice planes were performed to shed light on this. The results revealed that κ-carrageenan is able to interact with the basal plane and primary and secondary prism planes, but the binding appears to be reversible, at least for the investigated molecular sizes. In addition, the formation of a double helix did not affect the binding affinity. Hydrogen bond formation and the integration of κ-carrageenan's oxygen atoms into the ice lattice structure facilitate the interaction with the ice crystal. These findings provide further insights into the recrystallization inhibition of polysaccharides and foster the tailored design of effective freeze-protection molecules.

Recrystallization is considered the main damaging mechanism during the frozen storage of biologic materials. In this study, furcellaran, a polysaccharide related to κ-carrageenan, was studied for its concentration-dependent effect on ice crystal growth and recrystallization. The structure and sulfate content of the utilized furcellaran was analyzed by 1 H nuclear magnetic resonance spectroscopy, ion chromatography, and high-performance size-exclusion chromatography. Additionally, the rheological properties of furcellaran solutions were investigated. Our findings demonstrate that furcellaran inhibits ice growth as effectively as κ-carrageenan. Furthermore, the rheological properties change with increasing furcellaran concentration, resulting in a gel-like consistency at 5 g/L, which coincides with decreased recrystallization inhibition activity and larger crystals. This suggests that gel formation or a gel-like consistency has to be avoided for optimal recrystallization inhibition activity.