A method for the recovery of medium-chain-length polyhydroxyalkanoate (MCL-PHA) from Pseudomonas putida KT2440 was developed using NaOH digestion. PHA purity was affected by several factors, including NaOH concentration, temperature, digestion time, and number of treatment cycles. PHA purity of about 85% was attained after 70 g/L biomass containing 66% PHA was treated with 0.2 N NaOH at 22°C±1°C for 2 h or with 0.1 N at 80°C for 15 min. However, sequential treatment of 0.2 N NaOH at 22°C±1°C for 2 h followed by 0.1 N NaOH at 80°C±1°C for 15 min produced PHA with a higher purity of 94.7% and a recovery efficiency of 88%. Under these conditions, digestion had a negligible effect on PHA molecular weight. Further treatment with lysozyme gave a purity of 98.6%. This is the first study to demonstrate that MCL-PHA of lower density and crystallinity than other classes of PHAs can be effectively recovered by alkaline digestion. This method is a greener alternative and lower safety risk than current industrial-scale solvent recovery processes.
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