Hydrolysis Patterns of Different Crystalline Raw Starches by a Novel Cold-adapted α-Amylase

Objective: AmyZ1, a cold-adapted α-amylase derived from the deep-sea bacterium Pontibacillus sp. ZY, exhibits biocatalytic activity at 30~35 ℃. The hydrolytic behavior of low-temperature α-amylase on A-type crystalline starch (waxy maize starch, WMS) and B-type crystalline starch (potato starch, PS) was investigated in this study, using porcine pancreatic α-amylase (PPA) as a control. Methods: Hydrolysis products were analyzed using anionic high-performance liquid chromatography (HPAEC), and the physicochemical properties of starch granules were examined through scanning electron microscopy (SEM), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). Results: At pH7, the hydrolysis rates of WMS at 35 ℃ (AmyZ1) and 37 ℃ (PPA) were 42.36% and 23.28%, respectively. For PS, the hydrolysis rates were 18.34% for AmyZ1 and 17.09% for PPA, demonstrating that AmyZ1 exhibits a stronger hydrolytic ability for both types of starch. Chromatographic analysis revealed that AmyZ1 hydrolysates contained higher concentrations of maltotriose (G3, 24.60%) and maltotetraose (G4, 10.13%). The properties of residual starch particles after hydrolysis indicated pores on the surface of starch particles, and hydrolysis of WMS with AmyZ1 produced denser pores, which were more suitable for preparing porous starch. In addition, hydrolysis also reduced the long-range order and gelatinization enthalpy of starch, with AmyZ1 causing a more significant decrease than PPA. Hydrolysis of WMS by AmyZ1 and PPA reduced starch crystallinity from 35.9% to 25.6% and 33.6%, respectively, consistent with the hydrolysis rate results. Conclusion: A-type starch is easily hydrolyzed by both AmyZ1 and PPA, and the starch crystalline regions are hydrolyzed more effectively by AmyZ1. It contained more G3 and G4 in enzymatic hydrolysate. This might be due to the stronger ability of AmyZ1 to hydrolyze the crystalline regions and the difference in enzyme cleavage sites. The research results would provide a theoretical basis for AmyZ1 to directly hydrolyze starch granules at low temperatures.