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Protein hydrolysates from two forms of salmon frames named “chunk” and “mince” were produced and characterized. Both samples were subjected to hydrolysis using alcalase and papain at 1%–3% (w/w protein) for 0–240 min. Hydrolysate prepared with either protease at 3% for 180 min had the solid yield of 24.05%–26.39%. Hydrolysates contained 79.20%–82.01% proteins, 6.03%–6.34% fat, 9.81%–11.09% ash, and 4.02%–5.80% moisture. Amino acid profile showed that all hydrolysates had glutamic acid/glutamine (113.45–117.56 mg/g sample), glycine (77.86–86.18 mg/g sample), aspartic acid/asparagine (76.04–78.67 mg/g sample), lysine (61.97–65.99 mg/g sample), and leucine (54.30–57.31 mg/g sample) as the predominant amino acids. The size distributions determined by gel filtration chromatography varied, depending on proteases and the form of frame used for the hydrolysis. Different hydrolysates showed varying antioxidant capacities. Thus, protein hydrolysates from salmon frame could be used as a nutritive supplement in the protein deficient foods. Practical applications Frames of salmon are by‐products from salmon fish processing industries. The frames contained the remaining meat, hence they can be used for the preparation of protein hydrolysates. Generally, hydrolysates from fish by‐products have been regarded as a promising food supplement, because they are rich in amino acids. Additionally, hydrolysates possess antioxidant activity, which is of health benefit. To produce the hydrolysate with less time consumption, the use of frame chunk instead of minced frame can be of better choice. Thus, frame of salmon, especially in chunk form, could be used as a raw material for production of protein hydrolysate using alcalase. The hydrolysate produced from salmon frame could serve as an alternative nutritive supplement to tackle the nutrition inadequacies in foods.

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Extraction Clown featherback skinFreeze-drying -82.08% total collagen recovery -27.64% yield of ASC -44.63% yield of PSC -330-333 residues/1000 residues of glycine -201-202 residues/1000 residues of imino acid -type I, comprising (α1) 2 α2-heterotrimer -T max = 35.23-36.28 °C -pI = 5.54-5.68 Salt precipitation Dialysis Characteristics of collagen Collagen ExtractionGraphical Abstract and PSC were 27.64 and 44.63% (dry weight basis) with total collagen recovery of 29 82.08%. Both collagens contained glycine as the major amino acid with relatively 30 high content of proline, hydroxyproline and glutamic acid/glutamine. Nevertheless, 31 they had the low content of cysteine, histidine and tryrosine. The collagen was 32 characterised as type I, comprising (α1) 2 α2-heterotrimer. Pepsin-aided process did not 33 affect triple-helical structure of PSC as determined by FTIR spectra. Thermal 34 transition temperature of ASC (36.28 °C) was slightly higher than that of PSC (35.23 35 °C). However, no differences in isoelectirc point (5.54-5.68) between ASC and PSC 36 was observed. Therefore, collagen from the skin of clown featherback could be 37 successfully extracted for further applications. 38 39

Characteristics and gel properties of gelatin from frog skin as influenced by extraction temperatures (45−75 °C) were investigated. Yield of gelatin increased as the extraction temperature increased (P < 0.05). All gelatins contained α-and β-chains as the predominant components and showed a high imino acid content (215 residues/1000 residues). Fourier transform infrared (FTIR) spectra indicated that all gelatin samples had major peaks in amide regions. Gelatin extracted at 55 °C exhibited the highest gel strength (P < 0.05), which was similar to that of commercial bovine gelatin (P > 0.05). Gelling and melting temperatures of frog skin gelatin were 23.47−24.87 and 33.22−34.66 °C, respectively. Gels became more yellowish with increasing extraction temperatures (P < 0.05). All gelatin gels were sponge or 35 coral-like in structure but varied in patterns as visualized by scanning electron microscopy 36 (SEM). Gelatin from frog skin could be used as a replacement for land animal counterpart.

Gelatin was extracted from the skin of seabass (Lutes calcarifer) with different average sizes (2, 4 and 6 kg/fish), termed G2, G4 and G6, respectively and their characteristics and functional properties were determined. Yields of G2, G4 and G6 were 38.22, 40.50 and 43.48% (based on dry weight), respectively. G2 contained cc-chains as dominant component, whilst G4 and G6 comprised alpha-, beta- and gamma-chains with a larger content of high MW cross-links. All gelatins had the similar imino acid (hydroxyproline and proline) content. Net charge of G2, G4 and G6 became zero at pH of 6.73, 6.41 and 7.12, respectively. Amongst all gelatin samples, G6 exhibited the highest gel strength (321.5g) (p < 0.05), but had the lowest turbidity (p < 0.05). Gels of G6 sample had the lower L*-value but higher a*-, b*- and Delta E*-value, compared with others. Gelling and melting temperatures of all gelatins were 17.09-19.01 and 26.92-28.85 degrees C, respectively. Furthermore, all gelatins were able to set at room temperature, regardless of size of seabass used. G6 had the shorter setting time at room temperature than others. Therefore, size of seabass, in which skin was used for gelatin extraction, had the impact on yield, composition and properties of resulting gelatin. (C) 2014 Elsevier B.V. All rights reserved

Protein hydrolysates were obtained from salmon frame using Alcalase or Flavourzyme at 3% (w/w protein) for 180 min. Protein hydrolysates prepared using Alcalase (HA) and Flavourzyme (HF) had DH and yield of 25.1-26.9% and 28.5-32.3 g/100 g sample, respectively. HF showed lower bitterness score (5.78) than that of HA (8.68) (P \ 0.05). When HA and HF were further subjected to debittering with 2-butanol or isopropanol, the recovery of 77.88-81.60% was obtained (P \ 0.05). HF and HA debittered with 2-butanol possessed less bitterness score, 3.60 and 3.77, respectively (P \ 0.05). Surface hydrophobicity of 81.4 and 124.8 was attained when HF and HA were debittered with 2-butanol (P \ 0.05). Selected debittered hydrolysates, produced using Flavourzyme, followed by fractionation using 2-butanol (HF-B) contained glutamic acid/glutamine (15.14 g/100 g), aspartic acid/asparagine (10.07 g/100 g) and glycine (9.30 g/100 g) as the predominant amino acids. HF-B had the decreased ABTS radical scavenging activity and metal chelating activity. A 280 of peptides separated by gel filtration was lowered to some extent and coincided with the lower bitterness score and surface hydrophobicity. Thus, debittered protein hydrolysate from salmon frame could serve as a nutritive ingredient at high levels in health promoting foods.