In vitro study of selected physiological and physicochemical properties of fish protein hydrolysates from 4 Australian fish species

Fish by-products from different fish species may be utilized to produce compounds possessing physiological and physical functional properties. A simple extraction process involving use of endogenous proteases and/or addition of exogenous enzyme preparation resulted in proteinaceous hydrolysates. The extracts from Salmon, Flathead, Silver warehou and Barramundi by-products were evaluated for selected physiological and physical properties. Fish by-products were subjected to four different treatments, with or without the addition of acid fungal protease (AFP). The peptides produced in fish protein hydrolysate (FPH) were examined for bioactive properties based on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging and angiotensin I-converting enzyme (ACE) inhibitory activities. Furthermore, dried FPHs were also examined for properties such as colour, solubility, heat stability, emulsion activity, and rheological properties. Time and addition of AFP to FPHs, influenced the degree of hydrolysis (DH), DPPH scavenging and ACE inhibition activities. Salmon FPH treated with AFP showed the highest DH (43.86 %) and ACE inhibitory activity (95.50 %). High antioxidant activity was observed for Flathead and Barramundi FPHs with DPPH scavenging activity of 45.86 % and 43.03%, respectively. The solubility of dried FPHs ranged from 93 to 100% and increased with decreased DH. Emulsifying capacity of FPH for Barramundi was the highest, whereas FPH for Silver warehou showed the highest emulsion stability. Heat induced the gelation of Barramundi and Silver warehou FPHs but not for Salmon and Flathead FPHs. These results have implications for the use of protein hydrolysate from fish by-products in food formulation technology and serve as important sources of bioactive compounds.