Figure 1
Comparison of different PHA isolation methods (update and extensive expansion of [14])
| Recovery method | Method suitable for strains / types of PHA: | Time expenditure | Throughput of chemicals | Scalability to industrial scale? | Recovery yields | Product purity | Reduction of molar mass | Selected references |
|---|---|---|---|---|---|---|---|---|
| Organic solvents | ||||||||
| Chloroform extraction | All strains | Medium | High | No | High | High | Medium | [17] |
| Combined application of chloroform and aqueous NaOCl solution | All strains | Medium | High | No | High | High | Medium | [19] |
| “Agroferm method” based on cyclic carbonates) | All strains | Medium | Medium | Yes | Medium | High | High | [28] |
| Brazilian “PHB/ISA method” using fusel alcohols | All strains | High | Extraction solvents available in-house | Yes | High | Low/ Medium | High | [31] |
| Extraction with lactic acid esters | All strains | Medium/ High | High | Yes | Low/ Medium | Medium | High | [65] |
| Ethanol extraction | Mutant strains, mcl-PHA producers. For scl-PHA: in pressurized vessels | Medium | Low- Medium (easily recyclable solvent) | Yes | Low | Low/ Medium | High | [32] |
| GBL extraction | All strains | Medium | High | No | Low | Medium | Low | [23] |
| Cyclohexanone extraction | All strains | Medium | High | Yes | Medium | Medium | Low | [23] |
| Dimethyl carbonate (DMC) | All strains | Low | Medium | To be tested | Medium | High | Medium | [26, 35, 63, 64] |
| 1,2-propylene carbonate | All strains | Low | Low- Medium (easily recyclable solvent) | Yes | Medium | High | Medium | |
| Acetone under reflux | Pseudomonads (mcl-PHA producers) Fractionation of low crystalline scl-PHA fractions | Medium | Medium (easily recyclable solvent) | No | High | High | Low | [18, 29] [22] |
| Acetone under elevated temperature and pressure | All strains | Low | Medium (easily recyclable solvent) | Adequate equipment to be developed; data only for lab-scale | High | High | Low | [22] |
| Ethyl acetate | All strains | Medium | Medium (easily recyclable solvent) | To be tested | High | Medium | Medium-High | [24, 33] |
| Supercritical solvents | ||||||||
| Supercritical sCO2 | Tested only for restricted number of strains; scl-PHA and mcl-PHA | Medium | High (addition of modifiers needed) | No | Low | Low | Low | [37, 39, 40] |
| Ionic liquids | ||||||||
| C2mim][MeO(H)PO2] | All strains | Low | High | To be tested | Medium | Medium | Low | [43, 44] |
| Biocatalytic and biological digestion of non-PHA cell mass | ||||||||
| Digestion of non- PHA cell material by enzyme cocktails (“ICI process”) | All strains | Low | High | Yes | High | Low | No | [45, 46] |
| Biological digestion of non-PHA biomass by Tenebrio molitor and excretion of PHA granules with feces | All non-toxic microbes | High | No | Doubtful | High | Medium | Low | [57, 58, 59] |
| Chemical digestion of non-PHA cell mass | ||||||||
| Alkaline (NaOH) digestion of non-PHA cell material | Rec. E. coli; wild type strains with high contents of PHA like A. vinelandii | Low | Low | Yes | Medium | High | Depends on incubation time and temperature | [62] |
| Combined SDS/ hypochlorite treatment | All strains | Medium | Medium | Yes | High | High | Negligible (depends on hypochlorite concentration) | [47, 63] |
| Hypochlorite digestion of non-PHA cell material | All strains | Medium | Medium | No | Medium | Medium | Medium-High | [48] |
| Switchable anionic surfactants (NH-4laurate) | All strains | Medium | Medium | Yes | Medium | High | Low | [26, 50] |
| Mechanical and osmotic disrupture of cells | ||||||||
| Mechanical disintegration of PHA-rich cells (High-pressure homogenization, ultrasonication, vortexing, bead mills) | All strains (Ultrasonication for fragile strains like Haloferax mediterranei or rec. E. coli) | Low | No | Yes | Medium | Low | No | [14] |
| Cell disruption in hypotonic medium | Tested for highly osmophilic strains like Haloferax mediterranei or Halopiger aswanensis | Low | No | Yes | High | Medium | No | [52, 53, 54, 55] |