Effect of extrusion with hydrocolloid-starch molecular interactions on retrogradation and in vitro digestibility of chestnut starch and processing properties of chestnut flour

Controlling the retrogradation properties and digestibility of starch has become an ideal objective in the field of food science. In this study, the synergistic effects of extrusion treatment (ET) and xanthan gum (XG)/hydrox-ypropyl methylcellulose (HPMC) addition on the retrogradation properties and in vitro digestibility of chestnut starch (CS) were investigated. Furthermore, their effects on the processing properties of chestnut flour (CF) were discussed. The results showed that the retrogradation properties and digestibility of CS were simultaneously slowed down under ET with XG/HPMC addition. Due to the barrier and encapsulation effects of hydrocolloids, the entanglement and aggregation behavior of starch chains were hindered during extrusion, which reduced the single/double helix and its stacking into long-range ordered structure, resulting in the increases of anti-retrogradation rate (AR) and resistant starch (RS) content. Interestingly, the AR and RS content of CS treated with ET and 5% XG addition at day 21 were as high as 36.19% and 16.99%, respectively. Besides, the results also showed that the processing properties of CF could be controlled by ET with XG/HPMC addition including the decreases in oil absorption index, peak viscosity and dynamic modulus, and the increases in freeze-thaw stability, water absorption index and water solubility index. Overall, this study had significance for the simultaneously manipulating and improving the quality of chestnut-based foods.