淀粉适度降解后可拓展其应用范围，与常规化学与酶法降解手段相比，物理方法如超声波处理具有绿色、方便和易操作的特点。该研究以糊化态普通玉米淀粉为对象，研究了直-支淀粉混合体系在超声场中的降解过程与规律。超声处理30 min后，普通玉米淀粉的分子量由1.68×107 g/mol降至8.33×105 g/mol，呈现先快后慢的降解趋势。结果表明：淀粉分子的超声降解过程具有尺寸“决定性”，即大分子更易被降解，所以超声处理的初始阶段支链淀粉分子的降解速率高于直链淀粉，当其尺寸达到一致时降解趋于同步。基于超声对淀粉的“中间降解”规律和大分子更易被降解的特性，发现淀粉分子Fb3链最先断裂，随着处理时间的延长Fb2链断裂导致Fa链比例增加。另外，直链淀粉α-1,4糖苷键的断裂导致Fb2和Fb3组分增加。1H NMR结果表明淀粉分子的α-1,4-糖苷键与α-1,6-糖苷键均发生断裂，但α-1,6-糖苷键断裂更显著。综上所述，超声对糊化态直-支淀粉体系的降解具有选择性，作为物理改性的手段应用于淀粉工业中具有重要意义。

The appropriate degradation of starch can expand its application range. In comparison to traditional chemical and enzymatic degradation techniques, physical methods like ultrasonic treatment are environmentally friendly, user-friendly, and easy processing. This research investigated the degradation process and mechanism of the amylose-amylopectin mixed system in ultrasonic irradiation using gelatinized normal corn starch as the subject. The molecular weight of normal corn starch was decreased from1.68×107 g/mol to 8.33×105 g/mol after treating with ultrasound for 30 min. The results revealed a "size-dependent" degradation mechanism for the starch molecules, with the larger molecules were more easily degraded. Consequently, the degradation rate of amylopectin molecules was higher than that of amylose during the initial phase of ultrasonic treatment. Based on the above degradation mechanism, results revealed that the initial breakage site was in the Fb3 chain, transitioning to the degradation of the Fb2 chain with increased ultrasonic treatment duration，which increased of the Fa chain. Both of the α-1,4- and α-1,6-glycosidic bonds in Fb3 and Fb2 chains were disrupted in ultrasonic treatment，and the α-1,6-glycosidic bonds was more likely to break. Meanwhile, the increase in Fb2 and Fb3 components was due to the breakdown of α-1,4 glycosidic bonds in the amylose. The 1H NMR results showed that both the α -1,4-glycosidic bond and the α -1,6-glycosidic bond of starch molecules were disrupted, but the disruption of the α -1,6-glycosidic bond was more significant. In summary, ultrasound show a selective degradation mechanism in the treatment of gelatinized starches. The application of ultrasound in the starch industry has important practical significance.