Evaluation of potential processing routes for the purification of polyhydroxyalkanoates (PHAs) from oilseed rape (canola)

Polyhydroxyalkanoates (PHAs) are a family of biodegradable thermoplastics with a wide range of applications. PHAs are currently produced by fermentation but high production costs make them expensive. Recent advances in genetic engineering have enabled the production of PHAs in agriculturally important crops, most notably oilseed rape. This could potentially be a more cost effective method. This thesis investigates the processing of oilseed rape containing PHAs. An ultra scale down process was developed to simulate a commercial oilseed processing plant. The concentration and state of PHA in oilseed rape was found to affect the volume of oil produced. This may be of critical importance when processing oilseed material containing PHB at large scale, since the potential state and final concentration of PHB in transgenic rapeseed is not yet known. The study was not intended to be quantitatively predictive but was a means to foresee potential problems which could not be determined by a theoretical paper study. Potential routes for separation of rapeseed meal and PHB following oil extraction were considered. Physical properties of rapeseed and PHB investigated included size, density and viscosity. They were used to enable selection of preliminary extraction equipment for separation of meal from PHB. The best property for separation of PHB and rapeseed meal was found to be density since density differences between meal and PHB were significant. Further investigation using a scale-down centrifugation system showed that a threefold purification factor for concentrating PHB from rapeseed meal was possible. Chemical methods of separating PHB and rapeseed meal were investigated. Solubilisation of the protein fraction of rapeseed meal using sodium hydroxide allowed a high percentage of protein to be removed from the meal without any detrimental effect on PHB molecular weight. Using the information obtained from the microprocess, physical and chemical studies, different schemes for the extraction of PHB from meal were discussed. Solvent extraction was also briefly reviewed. A number of different processes were proposed as potential processing routes for the purification of PHAs from transgenic oilseed rape.