Synthesis and Properties of Polyhydroxyalkanoates on Waste Fish Oil from the Production of Canned Sprats

The waste fish oil obtained from Baltic sprat waste in the production of canned sprats was studied as a sole carbon substrate for PHA synthesis by the wild-type strain Cupriavidus necator B-10646. Sprat oil contained a set of fatty acids with a chain length from C14 to C24, saturation factor 0.63, and provided bacterial growth and PHA synthesis. Bacteria metabolized fatty acids unevenly utilizing polyenoic acids and not using monoenoic and saturated acids. The bacterial biomass yield and the intracellular polymer concentration were 6.5 ± 0.5 g/L and 65 ± 5% by fed-batch culture in flasks. The synthesized PHAs were three-component copolymers with a predominance (97–98 mol.%) of 3-hydroxybutyrate monomers and small inclusions of 3-hydroxyvalerate and 3-hydroxyhexanoate; the ratio of monomers changed slightly depending on the sprat oil concentration. The series of samples had a temperature (Tmelt) of 158–165 °C, a molecular weight (Mw) of 540–760 kDa, and a degree of crystallinity (Cx) of 66–72%. For the first time, the waste fish oil from the production of sprats studied as a carbon substrate is a promising, affordable, and renewable substrate for PHA biosynthesis.