Quantitative assessment of extraction methods for bound extracellular polymeric substances (B-EPSs) produced by Microcystis sp. and Scenedesmus sp.

Extracellular polymeric substances (EPSs) play a significant role in the growth and survival of microorganisms. They have been applied in various fields, such as animal feed, pharmaceuticals and cosmetics, due to their physicochemical characteristics (e.g., high contents of polysaccharides and proteins, properties of antivirus, antitumor and antioxidant). However, lack of standard evaluation methods for efficient extraction restricts further investigation on the characteristics or functions of EPSs and their commercial applications. In this study, the Bound-EPS (B-EPS) Extraction Efficiency Evaluation Model (B-E-4 Model) was developed to assess various extraction methods for two microalgae (i.e., the prokaryotic Microcystis sp. and the eukaryotic Scenedesmus sp.), including heating, centrifugation, ultrasound, ethylenediaminetetraacetic acid, cation-exchange resin or sodium hydroxide. The evaluation parameter k, was introduced to represent the extraction yields of B-EPSs, which was normalized to the per unit mass of released intracellular organics. This study revealed that heating at 70 degrees C for 10 min led to the highest extraction efficiency for both Microcystis sp. and Scenedesmus sp., with k values of 12.34 +/- 1.48 and 6.02 +/- 0.14, respectively. Moreover, model predictions for cell rupture were in close agreement with the results of flow cytometry analysis obtained in this study and the literature. Moreover, to test the applicability of B-E-4 Model established in this study, it was utilized to evaluate the extraction efficiencies of various methods applied in a previous study on the microalgae Neocystis mucosa SX, and cation-exchange resin treating for 6 h was found to be the optimal method. The B-E-4 model developed in this study was proven to be a powerful tool for optimizing the microalgal B-EPS extraction procedures.