Corn starch, as a polysaccharide, is mainly composed of two parts: amylose and amylopectin.
Amylose typically accounts for 20%-30% of corn starch. It is a long-chain molecule composed of glucose units linearly linked by α-1,4 glycosidic bonds, with a degree of polymerization (DP) generally between 2000 and 6000. This relatively regular linear structure gives amylose a certain degree of extensibility in solution and weak intermolecular forces. After heating and gelatinizing, amylose molecules will change from an ordered crystalline state to a disordered dispersed state. Furthermore, during cooling, amylose molecules are prone to re-aggregation and aging, which affects the subsequent processing performance of the starch.
Amylopectin constitutes a large proportion of corn starch, approximately 70%-80%. It is a highly branched macromolecule, with its main chain also composed of glucose units linked by α-1,4 glycosidic bonds. At regular intervals (approximately every 20-30 glucose units), an α-1,6 glycosidic bond connects to a branch on the main chain, resulting in a degree of polymerization (DP) of 300,000-3,000,000. This highly branched structure gives amylopectin a complex spatial conformation, with molecules intertwined to form a relatively tight network structure, thus imparting high viscosity and stability to starch pastes. The branched structure of amylopectin hinders the close arrangement of molecules, making it difficult to crystallize; therefore, amylopectin has a relatively weak retrogradation tendency.
The ratio and structural differences between amylose and amylopectin have a crucial impact on the hydrolysis process of corn starch. Due to its linear structure, amylose is more easily hydrolyzed stepwise from the chain ends by hydrolytic enzymes, resulting in a relatively smooth hydrolysis process. Amylopectin, with its numerous branches and complex spatial structure, requires the synergistic action of multiple hydrolytic enzymes for complete hydrolysis. α-Amylase can randomly act on the α-1,4 glycosidic bonds within starch molecules, rapidly degrading them into smaller dextrin fragments, but its effect on α-1,6 glycosidic bonds is limited. Saccharifying enzymes, on the other hand, can act not only on α-1,4 glycosidic bonds but also slowly on α-1,6 glycosidic bonds, further hydrolyzing dextrin into glucose. Therefore, in the process of hydrolyzing corn starch to prepare glucose, it is necessary to rationally combine enzyme preparations and control reaction conditions to achieve effective hydrolysis of starches with different structures.
For more corn processing information, please visit the official website of Beijing Meckey Engineering Co.