# Exopolysaccharides from Cyanobacteria: Strategies for Bioprocess Development
## 3 Cyanobacterial Bioprocess (Cyano-EPS) Development
### Downstream Processes and Cyano-EPS Global Market
The second extraction strategy focuses on polysaccharides designed as a sheath (or CPS) and concerns the main extraction protocols described in the literature. Numerous cyanobacteria such as _Nostoc_ genus form macroscopic colonies embedded in extracellular polysaccharides protecting them from environment [108]. Even if these polysaccharides do not have covalent linkages with the cyanobacteria cell wall, they interact strongly with it, which requires specific processes to dissociate them. Note that in numerous publications, authors include sheath and capsular polysaccharides as a unique fraction. These processes present some differences but can be resumed by collecting biomass using centrifugation and the extraction of EPS using hot distilled water (50-121 \({}^{\circ}\)C) in varying times (0.5-6 h). In other protocols, the extraction is achieved by differential sucrose gradient centrifugation of cyanobacterial biomass or after re-suspending it in a low ionic strength buffer at 100 \({}^{\circ}\)C [22; 105; 108]. After the extraction, the suspension is filtered through a filter paper, of 0.2 \(\upmu\)m membrane or centrifuged to collect the permeate or the supernatant. The retentate or the pellets are extracted again several times using the same process to deplete the biomass (up to 5-6 times). Note that with this extraction numerous non-polysaccharide compounds and notably proteins are co-extracted needing a purification supplementary step. Another way to start is by a 50 \({}^{\circ}\)C concentration under vacuum (not always  
Figure 1: Process flow chart for the extraction of EPS from cyanobacteria. necessary or done) followed by an optional protein extraction using the Sevag method or another. Then, an alcoholic (isopropanol or ethanol (2-3 _v/v_)) precipitation of polysaccharides is applied. Finally polysaccharides are freeze- or oven-dried [10; 14; 90; 105]. Sometimes, the lipids and pigments of the biomass can be previously extracted using an organic solvent such as hexane, acetone, ethanol, or other [14; 92]. This kind of process may be improved using microwave or ultrasound treatments as applied to _Arthospira_ biomass [109; 110]. Finally, the last class of extracellular polysaccharides is that of capsular polysaccharide needing stronger conditions for their extraction. Often considered as EPS in literature, their extraction implies the use of alkaline treatments of biomass such as a reflux in NaOH 0.1 M for 5 h at 90 \({}^{\circ}\)C [111]. The polysaccharides are precipitated using two volumes of isopropanol and dissolved in Milli-Q water. A second precipitation with alcohol is performed to increase their purity level. In their excellent review entitled << Exocellular polysaccharides from cyanobacteria and their possible applications >> published in FEMS Microbiology Letters in 1998, [PERSON] and [PERSON] [108] were very careful considering the industrial exploitation of EPS from cyanobacteria despite their potential. Cyanobacterial EPS have to compete with cheaper hydrocolloids from seaweeds, terrestrial plants, and non-photosynthetic bacteria, wherein some have authorizations for their use in food. What is the situation 21 years later? The number of publications focusing on the rheological and biological potential of these biopolymers increases dramatically [10; 105; 112; 101; 22] but is not correlated with the arrival on the market of EPS from cyanobacteria. Currently and to our knowledge, only four EPS from Cyanobacteria are commercially available and exploited in niche markets mainly in the cosmetic and nutraceutical area. They are Spirulan, Immulan, Nostoflan, and Emulcyan extracted from respectively _Arthospira platensis_, _Aphanotece halophyta_, _Nostoc flagelliforme_, and _Phormidium_[113; 114; 115; 22].