Mechanisms of starch structural reorganization induced by freeze-thaw techniques under mild osmotic stress
Raphael Lucas Jacinto Almeida1, Newton Carlos Santos2, Iêda Letícia de Souza Ferreira1
1Department of Chemical Engineering, Federal University of Rio Grande do Norte, Campus Universitário Lagoa Nova, Av. Sen. Salgado Filho, 3000, Natal, RN, 59078-970, Brazil.
Abstract:
This study investigated the structural and physicochemical reorganization of potato starch induced by two freezing methods (fast/LN2 and slow/UF) coupled with mild osmotic stress thawing (0.2 M sucrose). Quantitative analysis revealed that osmotic thawing drove significant water migration, with mass loss reaching 8.34% (LN2O) and 14.67% (UFO), while water activity (Aw) progressively decreased from 0.982 (native) to 0.872 (UFO), confirming the establishment of an effective osmotic gradient. Slow freezing (UF) caused more severe granule fragmentation, reducing the median diameter (Dv50) by 37% (to 17.5 μm) vs. 23% for LN2 (21.5 μm), and a greater crystallinity loss (13% reduction to 28.74%). Crystallite size, estimated by the Scherrer equation, decreased progressively from 16.21 nm (native) to 10.81 nm (UFO), indicating fragmentation of crystalline domains. Thawing under osmotic stress (LN2O, UFO) synergistically increased molecular disaggregation, reducing the hydrodynamic radius of amylopectin by up to 8.6% (to 85.20 nm) and the IR 1047/1022 ratio by 9.6% (to 0.888). Rheological analysis revealed a transition from elastic-dominant behavior in native starch (G' = 419.82 Pa, tan δ = 0.39) to viscous-dominant behavior in osmotically thawed samples (LN2O: G': 108.15 Pa, tan δ: 2.98; UFO: G': 125.97 Pa, tan δ: 2.44), indicating severe network disruption. The dual treatment (UFO) led to the highest syneresis (94.5% after 5 cycles) and the lowest pasting viscosity (44% reduction in PV to 2550 mPa·s). These results demonstrate that thawing under mild osmotic stress is a critical factor amplifying freeze-induced damage, offering a route to tailor starch functionality through controlled physical restructuring.
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