| Summary: | Food security can be improved by reducing post-harvest losses in sustainable food product chains. About 50% of fish is lost during filleting, including significant levels of high quality protein (10–23% (w/w)), which may be a source for biofunctional peptides. The fish processing waste protein hydrolysate can be a potential solution for minimizing the environmental issues related to marine processing products, and act as an alternative to producing value added fish processing by products. The main aim of this study was to investigate the physicochemical properties of fish processing waste streams from Atlantic Mackerel (Scomber scombrus) and mixed fish by membrane separation. Protein hydrolysates of Atlantic Mackerel (Scomber scombrus) and mixed fish from fish waste streams were prepared by enzymatic hydrolysis using pepsin and pancreatin and measured for their antioxidant and functional properties. The chemical composition (moisture, protein, total lipids and ash) of the Atlantic mackerel and Nile Perch (Lates niloticus) fish fillets (FF) compared to fish waste (FW) was also investigated. Protein fractions from the fish waste samples were separated by using the TFF cogent μscale ultrafiltration system from Millipore, and parameters including transmembrane pressure (TMP) on flux excursion, protein performance scalability, mass transfer analysis, as well as hold up volume were studied. The mechanism of antioxidant activity was studied by DPPH, FRAP, FTC and TBARS assays. It was demonstrated that fish waste water protein hydrolysate especially for Atlantic Mackerel showed good antioxidant activities by the Ferric Thiocyanate (FTC) and Thiobarbituric acid Reactive substances (TBARS) methods and compared well with other antioxidants (BHA, ascorbic acid and trolox). There was significant difference (p < 0.05) between samples and negative control (no antioxidant). DPPH scavenging activity increased with the extract concentration in the range of 1.5-26 %. In FRAP assay, both sample showed that there was an increase in absorbance with an increase in concentration. Structural and thermodynamic changes in fish waste samples were also determined by FT-Raman spectroscopy, differential scanning calorimetry (DSC) and small deformation rheology respectively. The DSC thermograms from the samples indicated that fish waste samples may be comparable. Moreover in fish waste sample hydrolysates, the same trends were obtained in 10 kDa AM and MF fractions. Fish waste samples especially hydrolysed fish waste samples, showed different protein denaturation transition peaks, indicating that enzymatic hydrolysis can affect the thermodynamic and functional properties of protein samples. Similarly, the rheological properties were different for different fish samples (AM and MF) with AM showing higher G’ or elastic modulus values (p < 0.05). The proteins in mackerel and mixed fish waste stream were characterised by FT-Raman spectroscopy and showed significant differences in their respective spectra and most of the assigned peaks (p < 0.05).
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