Deproteinization and controlled starch prehydrolysis in intact pulse cotyledon cells regulates starch retrogradation and digestion.

Intact pulse cotyledon cells are known for their intact cellular structure and dense protein matrix, leading to slower starch digestibility. However, the retrogradation and digestibility of retrograded intracellular starch has rarely been investigated, and our preliminary results indicated the difficulty of intracellular starch retrogradation. To test mechanistic principles of intracellular starch retrogradation, intact pulse cells were extracted and treated with protease followed by pancreatic α-amylase (0-20 min) and pullulanase (24 h) prehydrolysis, and then controlled retrogradation (4 °C, 5 d). Protein hydrolysis had little effect on starch retrogradation and digestibility, showing no change in the crystallinity, retrogradation enthalpy change and extent of digestion, compared to the cooked sample. Meanwhile, additional 5 min of α-amylase hydrolysis maximized the retrogradation of intracellular starch likely by producing perfect chain length for retrogradation, which then exhibited the lowest digestion rate and extent (0.0172 min-1 and 29.8 %). Further increasing α-amylase hydrolysis reduced crystallinity and enthalpy, leading to decreased retrogradation and increased digestibility. These findings shed new light on the mechanism underlying intracellular starch retrogradation and the extending application of retrograded starch with low propensity to negatively affect texture.