Polyhydroxyalkanoate production from food waste : feeding strategy and fermentation scale- up for biodegradable plastics

Abstract

Polyhydroxyalkanoates (PHAs) are biodegradable microbial polyesters with strong potential as sustainable alternatives to petroleum-derived plastics. Oil-derived substrates, including free fatty acids, triglycerides, and waste cooking oil (WCO), are attractive feedstocks due to their high degree of reduction and favorable theoretical yields; however, their utilization remains limited by challenges in substrate accessibility, compositional variability, and process scalability. This work investigates the influence of substrate type and lipid composition on PHA production using Pseudomonas putida as a model medium-chain-length PHA (mcl- PHA) producer. A systematic experimental approach assessed the effects of various carbon sources--free fatty acids, triglycerides, and complex oils--on biomass formation and PHA accumulation. Co-substrate supplementation strategies were also examined to assess their impact on fermentation performance. The results show that substrate type strongly affects both growth and PHA accumulation. Free fatty acids supported higher biomass formation than triglycerides, indicating that hydrolysis and substrate accessibility are key limiting factors. Among the substrates tested, oleic acid yielded the highest biomass (5.75 g/L), while palmitic acid resulted in the highest intracellular PHA content (51.6 wt percent), reflecting more efficient carbon allocation toward storage. In contrast, linoleic acid exhibited reduced performance, suggesting metabolic constraints associated with increased unsaturation. Complex substrates such as WCO and hydrolyzed WCO (HWCO) provided balanced performance, supporting both growth and polymer accumulation. Scale-up studies demonstrated that oxygen transfer, substrate delivery, and inoculum strategy are critical parameters in oil-based fermentation systems. In a 2 L bioreactor, the optimized process achieved a maximum PHA titer of 52.40 g/L, confirming the feasibility of scaling oil-based PHA production under controlled conditions. A twostage fermentation strategy further improved performance by separating biomass growth from PHA accumulation. Overall, this work demonstrates that substrate type and composition are key determinants of PHA production from oil-derived feedstocks. The findings provide practical insights for the development and scale-up of sustainable PHA bioprocesses using low-cost, waste-derived substrates.