Solvent-free extraction of polyhydroxyalkanoates from wet biomass using mechanical cell disruption

Abstract

• High pressure homogenization enables direct use of dense cultivation broth. • High yields 88 – 95 % and purity > 96 % were achieved. • No initial separation and drying or organic solvents are required. • Molecular weight of the PHA was not significantly affected. • Nitrogen content of the product was reduced by Alcalase and surfactant treatment. Polyhydroxyalkanoates (PHAs) have great potential as bio-based and biodegradable alternatives to fossil-based plastics. Despite many efforts to optimize the production process, one of the main areas that need to be improved is downstream processing. PHAs are commonly extracted using solvents which require a high demand of energy for recycling and are potentially harmful to the environment and health. Alternative methods using chemical digestion also use large amounts of chemicals and may impact the polymer’s molecular weight. In this study, a mechanical PHA recovery method based on high pressure homogenization is tested and applied to obtain poly(3-hydroxybutyrate) [P(3HB)] and poly(3-hydroxybutyrate- co -3-hydroxyhexanoate) [P(3HB- co -3HHx)] in yields close to 100 % at purities above 95 %. For this purpose, the process was analyzed regarding the impact of homogenization pressure and passes at different cell densities and optimized by adding purification steps to the protocol further improving the PHAs quality. Even without additional purification, high purities of >85 % were obtained, making high pressure homogenization suitable for lower quality PHA alone or as a pretreatment step when especially high purities are desired or the PHA content is only intermediate. Further assaying protein in the supernatant might serve as a control to evaluate cell disruption. Additionally, we did not observe signs of micronization of the PHA. This simple methodology is suitable for process integration to the production site.

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