Optimising enzymatic conditions of monkfish (Lophius vomerinus) heads hydrolysis towards potential waste biomass valorisation

Enzymatic protein hydrolysis of fish processing by-products offers an alternative option to valorise this raw material. Monkfish heads originating from fish processors presents such an opportunity, as the heads constitute a significant portion of the total fish (approximately 30%) and are currently processed into relatively low-value fish meal or even discarded. In this study, the reaction conditions for enzymatic protein hydrolysis of monkfish heads were optimised by varying the reaction pH and temperature using the Alcalase proteolytic enzyme. A mixed 2-factor, 3-level factorial design was employed to determine significant factors and interactions and was followed by response surface optimisation to determine optimal enzymatic hydrolysis conditions, which were shown to occur at 62 °C and a pH of 8.2. In addition, proximate analysis of the raw material and functional property characterisation of both the aqueous fish protein hydrolysate (FPH) phase and the insoluble sediments were performed to maximise the possibility of total raw material utilisation. Both the FPH and sediment displayed functional and bioactive properties, including emulsion stabilisation, fat absorption and antioxidant activity; only the FPH displayed foaming capacity, while the sediment displayed a reasonable emulsion activity index. In addition, high levels of essential amino acids (EAA) were found in the sediment (49.5% of the total amino acids), and all EAA were present (except tryptophan, which was not analysed for), which confirmed the high quality of the protein contained in the sediment. Overall, this work successfully optimised hydrolysis conditions for the Alcalase/monkfish system and confirmed the potential of enzymatic protein hydrolysis as an upgrading strategy to better utilise monkfish processing by-products.