Assessment System and Optimization of the Thermal Extraction Methods for Extracellular Polymeric Substances (EPS) from Microcystis

Extracellular polymeric substances (EPS) play crucial roles in the growth and survival of microorganisms. However, the lack of effective evaluation for extraction methods has limited further investigations and applications of EPS. This study established a quantitative assessment system for algal EPS thermal extraction methods based on extraction yield, cell integrity, and EPS chemical properties. An extraction efficiency parameter (ε) was introduced to quantify the relationship between EPS yield and cell rupture. Thermal treatment proved to be an effective approach for algal EPS extraction. Using the proposed evaluation system, the extraction methods for EPS of Microcystis were compared and optimized, including the following treatments: NaOH, NaCl, and buffer solutions (borate, phosphate, Tris-HCl). The results demonstrated that heating at 55 °C for 30 min with borate buffer achieved the highest extraction efficiency for EPS, with an ε value of 11.06 ± 1.13. In contrast, NaOH treatment at 60 °C for 30 min resulted in 30.4% cell rupture and the lowest ε value (9.7 ± 0.81). Furthermore, the modeled cell rupture rates aligned with flow cytometry and three-dimensional fluorescence spectroscopy analyses. The EPS extraction evaluation system developed in this study was empirically validated as a robust tool for optimizing extraction protocols for algal EPS.