Deciphering Biosynthesis Mechanism and Solution Properties of Cyclic Amylopectin

Abstract

A novel cyclic amylopectin (CA) was synthesized from waxy corn starch (WCS) using Bacillus stearothermophilus branching enzyme (BstBE), providing insights into its biosynthesis mechanism and solution properties. During the first 4 h, BstBE partially cyclized WCS, producing 68.20% CA with a significantly reduced molecular weight (MW), from 8.98 × 10⁶ to 3.19 × 10⁴ g/mol and a lower polymer dispersity index (PDI), decreasing from 1.97 to 1.12. This resulted in a uniform CA structure with shorter chain lengths, particularly increasing DP 3–13, especially DP 7–9. Over the subsequent 4–12 h, the PDI slightly increased to 1.18 as the CA content decreased to 50.48%, with an increase in small ring structures (DP 6–12) of CA, suggesting both ring-opening and ring-downsizing due to continued enzyme catalysis. These results propose a two-stage reaction model: initial cyclization followed bybranching and secondary cyclization. CA exhibited excellent solution properties, with BE-4 and BE-12 samples demonstrating high solubility (≥65 g/100 mL), low viscosity (<0.01 Pa·s), and over 90% light transmittance after 14 days at 4 °C, highlighting its broad application potential.