Molecular mechanisms of antifreeze activity in wheat bran arabinoxylan: The role of fine structure in modulating water-ice dynamic changes

The relationship between the low-temperature protective properties and fine structure of wheat bran arabinoxylan (WBAX) remains unclear. This study used xylanase at concentrations of 0%, 2%, and 4% to prepare WBAX (WBAX-0, WBAX-2, and WBAX-4), revealing the molecular mechanism by which the fine structure of WBAX modulates water-ice dynamic change to exert antifreeze activity. Results of structural characterization showed that xylanase altered the molecular chain length (from long to short), molecular weight (mw, reduced from 479.29 to 285.84 kDa), and the Z -average particle size (reduced from 1180.00 to 466.15 nm) of WBAX. This was accompanied by an increased exposure of hydrophilic groups and the disappearance of porous structure. Results of the interaction between WBAX and water-ice revealed that the antifreeze activity of WBAX does not change linearly with enzymatic hydrolysis, but is regulated by different dominant mechanisms. Of these, WBAX-0 and WBAX-4 exhibited exceptional antifreeze activity, with ice crystal contents of 8.76% and 7.99%, and mean grain size of 35.50% and 22.82%, respectively. This is attributed to the high molecular weight (479.29 kDa), long-chain structure, and porous structure of WBAX-0, enabling its antifreeze activity through steric hindrance and water holding capacity. In contrast, WBAX-4 had more hydroxyl groups capable of forming hydrogen bonds with water, enhancing its hydrophilicity and water solubility, thus preventing water from freezing into ice crystals. In summary, this study confirms that the antifreeze activity of WBAX depends on water-ice dynamic changes regulated by its fine structure, providing guidance for the application of WBAX as a cryoprotectant