Mechanism of brittleness deterioration of pork meatballs induced by freeze-thaw cycles based on ice crystals and molecular conformation

This study investigated the mechanism behind the gradual disappearance of the unique brittle texture of pork meatballs during multiple freeze-thaw (FT) cycles. The results showed that meatball brittleness decreased with increasing numbers of FT cycles. However, unexpected partial recovery occurred at FT3 and FT5, with the water holding capacity decreasing (74 %/81 %), and the fractal dimension (1.4502/1.6592) and size (76.9 mu m2/414.7 mu m2) of ice crystals increasing. During the FT cycles, tiny ice crystals and salt-ion crystals remaining from the previous FT process gradually increased in size under the influence of the Ostwald effect. By FT3, the ice crystals had transformed from relatively regular spheres to irregular dendritic structures, which pierced and disrupted the three-dimensional gel network, triggering new protein cross-linking driven by ionic bonding and hydrophobic interactions. By FT5, after multiple degradations and re-aggregations, the proteins formed heterogeneous aggregates with heavy chains of actin and myosin as the main components, bound by hydrogen and disulfide bonds, which was a partial reversion to the degree of cross-linking of the gelatinized network structure of the meatballs. This study revealed the effects of changes in the ice crystal state, protein aggregation morphology, and molecular conformation on the brittleness of meatballs during FT cycles, providing a theoretical foundation for developing freezing protection technologies.