Eco-Friendly Biopolymers: Eco-Friendly Biopolymers: Converting Waste Cooking Oil Into Simultaneous Production of Two Valuable Polyhydroxyalkanoates and Bacterial Alginate Through Microbial Conversion

Abstract

An obstacle to the commercial application of polyhydroxyalkanoates (PHAs) and a co-product exopolysaccharide, alginate, is their high production cost. In this study, waste cooking oil (WCO) was used as an inexpensive carbon source for biopolymer production by Pseudomonas mendocina PSU. The highest biomass of 4.60 ± 0.06 g/L and PHA concentration of 2.58 ± 0.03 g/L (accounting for about 54% DCW) were achieved with a productivity of 0.072 g/L/h under optimal conditions determined by response surface methodology. Additionally, a maximum alginate yield of 8.85 ± 0.24 g/L was obtained as the co-product. The WCO, which primarily contained oleic acid (C18:1), palmitic acid (C16:0), and linoleic acid (C18:2) influenced the monomer composition of the produced PHA. The results demonstrated the presence of both SCL-PHA monomers such as 3HB (3-hydroxybutyrate) and MCL-PHA monomers including 3HHx (3-hydroxyhexanoate), 3HO (3-hydroxyoctanoate), 3HD (3-hydroxydecanoate), and 3HDD (3-hydroxydodecanoate) in varying molar fractions. Moreover, an average molecular weight of approximately 10⁴ Da and a polydispersity index of 1.58 were determined in the produced PHA, consisting predominantly of 3HB (86 mol%) when the cells were grown in 2.0% (v/v) WCO. Furthermore, the melting temperature (T_m) and glass transition temperature (T_g) were around 157°C and −20°C, respectively. Additionally, the produced alginate from P. mendocina PSU exhibited functional acetyl groups, which are a distinguishing feature of bacterial alginate, and showed an apparent viscosity comparable to commercial alginate from brown seaweed. These biopolymer characteristics demonstrate strong potential for biomaterial applications, adding value to WCO and reducing overall production costs.