Aqueous size-exclusion chromatographic method for the quantification of cyanobacterial native glycogen

Cyanobacterial glycogen has gained interest as a valuable biomass feedstock for biofuel production. However, an ideal method for native glycogen quantification has not been developed. Here, we have proposed a simple methodology that enables the quantitative determination of cyanobacterial glycogen concentration with high repeatability using aqueous size-exclusion chromatography with a differential refractive index detector (SEC/RID). Our SEC/RID system also allows size distributions for native glycogen based on hydrodynamic volumes (Vh), which is proportional to the product of the molecular mass (M) and intrinsic viscosity [η], obtained by universal calibration using linear homopolymers of known M with Mark–Houwink–Sakurada parameters. The universal calibration curve achieved a broad linear range (Vh parameter [η]M = 2 × 102–8 × 108 mL g−1) with a high correlation coefficient (R2 = 0.9942), because the developed system is equipped with an OHpak SB-806M HQ aqueous column containing four types of polyhydroxy methacrylate-based particles with different particle and pore sizes. Based on the SEC/RID system, response of molecular size distribution of glycogen in microalgae to the cultivation condition was first observed. Our established SEC/RID method has several advantages over conventional techniques, including the simultaneous quantitative and size distribution analyses of glycogen, and represents a potentially useful tool to elucidate the relationship between structural properties and the roles of glycogen in metabolism.