Molecular and Lumped Products from Hydrothermal Liquefaction of Bovine Serum Albumin

We examined the decomposition of and product formation from a model protein, bovine serum albumin (BSA), under hydrothermal conditions. BSA forms smaller polypeptides as it decomposes, primarily via hydrolytic cleavage of the peptide bonds. It also forms insoluble aggregates in high yields at mild conditions, which subsequently decompose. There were no polypeptides (MW > 5 kDa) remaining after 5 min at 350 °C, but smaller peptides persisted in yields of about 15 wt %. The total yield of free amino acids was typically <3 wt % but nearly reached 6 wt % at 250 °C and 60 min. Glycine and glutamic acid were the most abundant amino acids in the aqueous-phase products. The yields of primary and secondary amines reached 50 wt % and generally increased with time and temperature. Up to 40 mol % of the nitrogen in the BSA appeared as NH₃ in the aqueous phase, and the NH₃ yields increased with both time and temperature. Biocrude yields increased with reaction severity until reaching a maximum of about 20 wt %. Cyclic dipeptides were the most abundant GC-elutable components in the biocrude.