Insight into the role of linear chains with and without branches in the structure and digestibility of rice starch gel during short-term and long-term retrogradation

The chain structures of starch are crucial in determining the gel retrogradation process. The roles of linear chains with and without branches in the structure and digestibility of rice starch (RS) gel during short-term (0-24 h) and long-term (1-14 d) retrogradation were investigated. The linear chains (LC) were generated by pullulanase (PUL) modification, and the linear chains with few branches (LCFB) were generated by further transglucosidase (PULTG) modification. At the same retrogradation time, the gel strength was PULTG > RS > PUL, the digestible starch content was RS > PUL > PULTG, and the digestion rate was PUL > RS > PULTG. The short-term and longterm retrogradation of RS gel tended to be stable after 12 h and 7 d, respectively. The LC and LCFB with high fluidity facilitated easier rearrangement, shortening the short-term retrogradation stability time to 6 h, but did not change the long-term retrogradation. The branches on LCFB enhanced intermolecular interactions to form more microcrystals and improve the crystal stability, resulting in the improvement of gel strength and the reduction of digestibility. Therefore, the LCFB was conducive to the rapid formation of starch gel with high strength and low digestibility, while maintaining exceptional comprehensive quality during storage.