Multiscale insights into the role of water content in the extrusion-crosslinked starch

Water content is a key factor in the extrusion-crosslinking process, profoundly influencing the modification and structural properties of starch. The specific effects of water content have not been sufficiently emphasized in the extrusion-crosslinking process, limiting the high-value utilization of starch. This study elucidates the mechanisms of extrusion crosslinking under varying water contents through multiscale analysis, revealing that water content directly affects starch modification. As water content increases, starch crystallinity and molecular degree of order decrease, while the proportion of short-chain structures increases. Higher water content (≥45 %) improves starch melt fluidity and molecular chain mobility, promotes crosslinking, and results in starch gels with superior viscoelastic properties. However, excessive water content (85 %) decreases gel strength and crosslinking efficiency. Molecular simulations complemented the experimental results, showing that water modulates hydrogen bonding and starch molecular mobility. At 65 % moisture content, the crosslinking bonds exhibited the highest and narrowest peak, indicating a higher proportion of crosslinking bonds and greater bond stability. This multiscale analysis highlights the importance of combining molecular simulations and experimental methods to better understand the role of water in starch modification. These results provide insights into the optimization of starch processing and guidance for the sustainable use of starch applications.