Shear scission through extrusion diminishes inter-molecular interactions of starch molecules during storage

The starch retrogradation behavior of native and extruded maize, wheat and rice flours were compared to better understand the efficacy of extrusion to decrease the propensity of different starches to form inter-molecular interactions. In all flour pastes, the increase of the storage modulus (G′) during a 7-day storage (representing inter-molecular interactions) was diminished with extrusion, albeit this effect was not detectable in rice due to the low gel consistency. Furthermore, thermo-rheological analyses revealed two distinct mechanisms depending on the cereal source. In maize and wheat flours, AM fragmentation through extrusion (detected through HPSEC) decreased the residual G′ at 85 °C of 7-day stored gels, which represents AM-AM physical junction zones that build gel structure. On the other hand, the extrusion of rice flour, which contains starch with lower AM ratio, resulted in a marked AP fragmentation that decreased the relative G′ drop, representing inter-molecular interactions involving AP.