The inadequate management of fish processing waste or by-products is one of the major problems that fish industry has to face nowadays. The mismanagement of this raw material leads to economic loss and environmental problems. The demand for the use of these by-products has led to the development of several processes in order to recover biomolecules from fish by-products. An efficient way to add value to fish waste protein is protein hydrolysis. Protein hydrolysates improve the functional properties and allow the release of peptides of different sizes with several bioactivities such as antioxidant, antimicrobial, antihypertensive, anti-inflammatory, or antihyperglycemic among others. This paper reviews different methods for the production of protein hydrolysates as well as current research about several fish by-products protein hydrolysates bioactive properties, aiming the dual objective: adding value to these underutilized by-products and minimizing their negative impact on the environment.

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Enzymatic hydrolysis of proteins from low commercial value fish could be produced for uses like functional ingredients in a wide and always increasing zone of application in different food products. The objective of this work was to evaluate the functional properties and the amino acid profile of enzymatic hydrolysates from Bluewing searobin (Prionotus punctatus), using two microbial enzymes, Alcalase and Flavourzyme. The enzymatic hydrolysate obtained through the addition of the enzyme Alcalase reached the maximum solubility (42%) at pH 9, water holding capacity (WHC) of 2.4 g water g protein −1 , 4.5 g oil g protein −1 of oil holding capacity (OHC) and an emulsifying activity index (EAI) of 54 m 2 g solids −1 at pH 3. On the other hand, the hydrolysate obtained from Flavourzyme attained 38% of solubility at pH 9, 3.7 g water g protein −1 and 5.5 g oil g protein −1 for the holding capacities, and an EAI of 71 m 2 g solids −1 at pH 11. The hydrolysate with Flavourzyme produced best results for WHC, OHC, and EAI because it had solubility lower than the hydrolysate of Alcalase. The hydrolysate produced by Alcalase had a higher amino acid content compared with Flavourzyme's hydrolysate. However, both showed a good essential amino acid amounts. In general, these results indicate the potential utilization of the hydrolysate from Bluewing searobin in food formulations for the direct human consumption.

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22This study evaluated the effect of protein hydrolysate (PH) and clove essential oil (CEO) on 23 agar film properties and the shelf-life improvement of flounder fillets. Firstly, Argentine croaker 24 muscle protein was alkali-solubilised and recovered to obtain a stable substrate. This substrate 25 was hydrolysed to 20% degree of hydrolysis, by Alcalase (A20) and Protamex (P20). The 26 molecular weight (MW) distribution, amino acid and in vitro antimicrobial activity of these 27 hydrolysates were tested. Agar films were prepared with and without (control) incorporation of 28 PH (A20 hydrolysate) or CEO characterised by mechanical properties, water vapour 29 permeability, solubility and optical properties. The microbiological, physical and chemical 30properties of flounder fillets coated with these films were monitored during storage at 5°C for 31 15 days. Compared to P20, A20 hydrolysate possessed lower MW, higher hydrophobic amino 32 acid content and the most effective antimicrobial activity against selected pathogens, such as 33 Staphylococcus aureus, Yersinia enterocolitica, Aeromonas hydrophila, Debaryomyces hansenii 34and Listeria innocua. The presence of PH increased the water solubility, water vapour 35 permeability, elongation at break and yellowness of the films. The CEO films possessed less 36 transparency than PH films and control films, due to the presence of oil in the formulations. 37Fillets covered with PH and CEO films, especially the latter, presented lower total volatile bases 38and pH values, and delayed considerably the growth of H 2 S-producing microorganisms 39 compared to the control films. The CEO might be used as a natural biopreservative to extend the 40 flounder shelf-life. However, further studies are necessary, to assess the antimicrobial effect of 41 PH when used as food packaging. 42 43

In this work, chicken and fish peptides were obtained using the proteolytic enzymes α-Chymotrypsin and Flavourzyme. The muscle was hydrolyzed for 4 h, and the resulting peptides were evaluated. Hydrolysates were produced from Argentine croaker (Umbrina canosai) with a degree of hydrolysis (DH) of 25.9 and 27.6% and from chicken (Gallus domesticus) with DH of 17.8 and 20.6% for Flavourzyme and α-Chymotrypsin, respectively. Membrane ultrafiltration was used to separate fish and chicken hydrolysates from Flavourzyme and α-Chymotrypsin based on molecular weight cutoff of >1,000, <1,000 and >500, and <500 Da, to produce fractions (F1,000, F1,000-500, and F500) with antioxidant activity. Fish hydrolysates produced with Flavourzyme (FHF) and α-Chymotrypsin showed 60.8 and 50.9% of peptides with a molecular weight of <3 kDa in its composition, respectively. To chicken hydrolysates produced with Flavourzyme and α-Chymotrypsin (CHC) was observed 83 and 92.4% of peptides with a molecular weight of <3 kDa. The fraction that showed, in general, higher antioxidant potential was F1,000 from FHF. When added 40 mg/mL of FHF and CHC, 93 and 80% of lipid oxidation in ground beef homogenates was inhibited, respectively. The composition of amino acids indicated higher amino acids hydrophobic content and amino acids containing sulfuric residues for FHF, which showed antioxidant potential.

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