Extraction procedure optimization and the characteristics of dissolved extracellular organic matter (dEOM) and bound extracellular organic matter (bEOM) from Chlorella pyrenoidosa.

The influence of extracellular organic matter (EOM) on membrane fouling is important for algae cultivation and harvest. Therefore, a deep understanding of EOM and a systematic extraction process are necessary. In this study, EOM from Chlorella pyrenoidosa was thoroughly studied by using different methods to stratify it into dEOM and bEOM. Among these methods, the centrifugation method was optimized for dEOM extraction, and the heating and NaOH methods were optimized for bEOM extraction. In addition, dEOM and bEOM were compared by using analytical methods to obtain their protein and polysaccharide contents, dissolved organic carbon (DOC) contents, specific UV absorbances (SUVA), zeta potentials, FTIR spectra, EEM fluorescence spectra, hydrophobicities and molecular weights. The dEOM and bEOM both primarily consisted of proteins and polysaccharides and carried negative charges with relatively low SUVAs. The protein/polysaccharide ratios in the bEOM were 6.35 (control), 12.54 (heating) and 7.54 (NaOH) mg mg(-1), which were greater than the ratio of the dEOM (2.93 mg mg(-1)). Furthermore, the hydrophobicity analysis indicated that the bEOM had higher hydrophobic fraction content than the dEOM. However, both types of EOM were more hydrophilic in terms of the DOC. Finally, size fraction analysis indicated that high-MW (>100 kDa) and low-MW fractions (<1 kDa) were the primary components in EOMs. Specifically, a greater high-MW fraction was observed in the bEOM, which primarily consisted of DOC and proteins. In contrast with the proteins, the polysaccharides of the dEOM and bEOM were primarily distributed in the hydrophilic and low-MW fractions. Using comparative analysis, centrifugation at 10,000×g for 10 min was chosen as the best method for extracting dEOM. In contrast, heating at 70°C for 20 min was the best method for extracting bEOM.