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The pressurized liquid extraction (PLE) technique was used to obtain protein extracts with antioxidant capacity from salmon muscle remains, heads, viscera, skin, and tailfins. A protein recovery percentage ≈28% was obtained for all samples except for viscera, which was ≈92%. These values represented an increase of 1.5-4.8-fold compared to stirring extraction (control). Different SDS-PAGE profiles in control and PLE extracts revealed that extraction conditions affected the protein molecular weight distribution of the obtained extracts. Both TEAC (Trolox equivalent antioxidant capacity) and ORAC (oxygen radical antioxidant capacity) assays showed an outstanding antioxidant activity for viscera PLE extract. Through liquid chromatography coupled with electrospray ionization triple time-of-flight (nanoESI qQTOF) mass spectrometry, 137 and 67 peptides were identified in control and PLE extracts from salmon viscera, respectively None of these peptides was found among the antioxidant peptides inputted in the BIOPEP-UMP database. However, bioinformatics analysis showed several antioxidant small peptides encrypted in amino acid sequences of viscera extracts, especially GPP (glycine-proline-proline) and GAA (glycine-alanine-alanine) for PLE extracts. Further research on the relationship between antioxidant activity and specific peptides from salmon viscera PLE extracts is required. In addition, the salmon side streams studied presented non-toxic levels of As, Hg, Cd, and Pb, as well as the absence of mycotoxins or related metabolites. Overall, these results confirm the feasible use of farmed salmon processing side streams as alternative sources of protein and bioactive compounds for human consumption.

In the present work, we provide insight into electrostatic interactions and phase behaviors in mixtures of myofibrillar protein (MP) and κ-carrageenan (KC) of various pHs (8.0-3.0) and biopolymer weight ratios [R, from 1:1 to 20:1; total concentration=0.05% (w/w)] through turbidimetric analysis, dynamic light scattering (DLS) and zeta potential analysis, and optical microscopy. At R=1: 1, critical pH values (i.e., pH c , pH Φ1 , and pH Φ2 ), which indicate phase transitions interrelated to the formation of soluble or insoluble MP-KC complexes, were observed at pH7.6, 6.8, and 3.6, respectively. As the ratio increased, the pH max shifted from 4.9 to 5.8. A similar trend was observed for the isoelectric point of MP-KC mixtures, as determined by zeta potential measurements. The maximum interaction indicated by the highest turbidity occurred at pH max =5.3, at a ratio of 5:1, whereas pH c remained constant during acidification. The changes in electrostatic interactions and transformations of phase behaviors accompanying the complex formation and disassociation processes were further supported by particle size distribution analysis and optical microscopic observations of MP-KC mixtures (R=1:1) at different pH values. This work fills the previous lack of studies on phase behaviors of surimi protein and colloidal polysaccharide in liquid system, and lay the foundation to provide a new way to solve problems of interactions between protein and polysaccharide during the processing of surimi products., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

This study systematically explored the effect of HEPES, Tris and sodium phosphate (PB) buffers on the xanthine oxidase (XO) inhibitory activity of tuna protein hydrolysate (TPH, containing over 90% of constituents with molecular weight below 5kDa). The greatest XO inhibition by TPH was observed in HEPES buffer. The optimal HEPES concentration was 100mmol/L. Tryptophan fluorescence and circular dichroism measurements revealed the comparable stability of XO and TPH in the three buffers. The buffers did not alter the majority of XO or TPH structure but induced slight modifications to specific domains (e.g. Trp residues on α-helices) and certain rearrangements (e.g. XO unfolding or refolding). HEPES buffer exerted stronger interactions with XO or TPH, causing a lower α-helical content in XO and consequently a lower XO catalytic activity but greater XO inhibition, compared to Tris and PB buffers., (Copyright © 2017 Elsevier Ltd. All rights reserved.)