Abstract:The intact cotyledon cells were isolated from pinto beans and treated with dry heat at 120, 140, 160, 180 ℃ for 4 h. The crystalline structures of starch were analyzed by X-ray diffraction and differential scanning calorimeter, and the digestion kinetics were analyzed based on the first-order kinetic model.The results showed that compared with the pinto bean starch under the same heating treatment condition, the pinto bean cotyledon cell epidermis shrank, the volume decreased slightly, the shape tended to be spherical, and the polarized cross weakened slightly. The crystallinity of the pinto bean cotyledon cells decreased, but the X-ray diffraction patterns remained to be C type. The initial gelatinization temperature and enthalpy of gelatinization decreased by 0.41 ℃ and 4.61 J/g, respectively. In terms of digestibility, the digestion extent of pinto bean cotyledon cells treated at 180 ℃ was increased by 3.02% than that of untreated pinto bean cotyledon cells. However, the hydrolysis rate of cells at 360 min (~8%) was significantly lower than that of pinto bean starch (~60%), which might be due to starch granules were wrapped by the protein components in the cells that hinder the binding of α-amylase to intracellular starch, which leads to slow digestion rate of starch in pinto bean cotyledon cells in vitro.The results showed that the dry heat treatment of pinto bean cotyledon cells at 120 ℃~180 ℃ was an excellent processing method and the product with lowglycemic index could be obtained.
