Integrated Biorefining Approach for the Production of Polyhydroxyalkanoates from Enzymatically Hydrolyzed Rapeseed Meal under Nitrogen-Limited Conditions

Rapeseed meal (RSM) is an ideal candidate for biorefining due to its abundance, low cost, and valorizable factions, including protein and lignocellulose. High levels of residual nitrogen have hampered the application of RSM in fermentations where nitrogen-limitation is required, such as the production of polyhydroxyalkanoate (PHA) by Pseudomonas putida. A comprehensive multifactorial study using central composite design was conducted on enzyme hydrolysis of untreated and post-protein extraction RSM. It was found that a combination of protein extraction and enzyme hydrolysis was crucial in producing a fermentation medium with a high carbon to nitrogen ratio from RSM (36–38 g glucose-C g N–1). Significant PHA accumulation in P. putida KT2440 was achieved with said medium in shake flask (8.18–9.34%). Furthermore, process scalability was addressed, and the medium was shown to be viable at a 1.5 l bioreactor-scale. Through this work the importance of integrated biorefining is demonstrated, as omitting either the enzyme hydrolysis or protein extraction would compromise the scheme. In addition to potentially improving the economics of biomass valorization, integrated biorefining widens the range of biomass applications. This study has achieved the largest PHA accumulation to date for RSM as the sole carbon and nitrogen source and presents important insights for the use of high-nitrogen wastes in nitrogen-limiting applications.