Nile perch (Lates niloticus), typically found in lakes and rivers in north-east and Central Africa, is industrially processed (smoking, portioning and filleting) in many African and European countries, resulting in large quantities of by-products, namely skin and trimmings. Some of these by-products are composted at local production sites, as they are rich in nutrients such as N, P and Ca, or used to prepare fish silage to be incorporated into animal feed. In importing countries, the main destination is the production of fishmeal and fish oil. Considering that such raw materials may have up to 20% (fresh weight) of protein, another alternative lies in the production of enzymatic fish protein hydrolysates (FPHs), composed by a mixture of non-hydrolysed protein, free amino acids, and peptides with bioactive properties.
Therefore, this study aimed to investigate the potential of FPHs derived from Nile perch trimmings, using an optimised procedure with four different hydrolysis systems: Alcalase in a single step (A), Protana in a single step (P), Alcalase+Protana in a single step (AP) and Alcalase followed by Protana in a two-step process (A_P). The chemical composition and biological activities were carried out on all FPHs, by using well validated methods.
The protein and fat contents (dry weight) in prepared FPHs were between 70-87% and 2.0-3.6%, respectively. The results indicated that the combination of Alcalase and Protana—whether in a single- or two-stage process—significantly improved protein yield (79.7% for FPH_AP and 80.8% for FPH_A_P) and degree of hydrolysis (34.1% and 45.2% for FPH_AP and FPH_A_P, respectively), resulting in peptides with lower molecular weights. Furthermore, hydrolysates produced with the combined enzymes exhibited significantly higher antioxidant and metal-chelating activities compared to those prepared using Alcalase or Protana alone. Additionally, the fractionation of FPH_AP and FPH_A_P enabled the concentration of peptides with molecular weights below 1 kDa, increasing DPPH radical scavenging activity, copper chelating activity and ACE inhibitory activity (166%, 38% and 34%, respectively).
These findings indicate that the four FPHs prepared in this study, exhibit important bioactive and technological properties being valuable sources of nutritional compounds and bioactive peptides. Nevertheless, those obtained with Alcalase and Protana (FPH_AP and FPH_A_P) have greater potential for promising applications in food and nutraceuticals as well in tailor-made feeds.
Acknowledgments: This work was developed within the scope of the “BLUE BIOECONOMY INNOVATION PACT” (Project No. C644915664-00000026) funded by NextGenerationEU, under the incentive of “Agenda for Business Innovation” of the recovery and resilience plan (PRR) and also supported by Portuguese Foundation for Science and Technology (projects: UIDB/04077/2020, UIDB/ 04423/2020 and UIDP/04423/2020) and by project “INNOECOFOOD”, under the EU Horizon 2024 Research and Innovation program, grant agreement No.101136739.