Conversion of fat-containing waste from the margarine manufacturing process into bacterial polyhydroxyalkanoates

A fat-containing waste produced from the margarine manufacturing process was tested as a low cost carbon source for cultivation of different polyhydroxyalkanoates (PHAs) producing bacterial strains, including Cupriavidus necator, Comamonas testosteroni and several Pseudomonas strains. The margarine waste was mainly composed of free fatty acids (76wt.%), namely mystiric, oleic, linoleic and stearic acids. In preliminary shake flask experiments, several strains were able to grow on the margarine waste, but C. necator reached the highest PHA content in the biomass (69wt.%). This strain was selected for batch bioreactor experiments, wherein it reached a cell dry weight of 11.2g/L with a polymer content of 56wt.%. The culture produced 6.4g/L of polyhydroxybutyrate, P3(HB), within 20h of cultivation, which corresponds to a volumetric productivity of 0.33gPHA/Lh. The P3(HB) polymer produced by C. necator from the margarine waste had a melting point of 173.4°C, a glass transition temperature of 7.9°C and a crystallinity of 56.6%. Although the bioprocess needs to be optimized, the margarine waste was shown to be a promising substrate for P(3HB) production by C. necator, resulting in a polymer with physical and chemical properties similar to bacterial P(3HB) synthesized from other feedstocks.