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One major pepsinogen, PG-I, and two minor pepsinogens, PG-II and PG-III were purified from lizardfish stomach by ammonium sulfate precipitation and two chromatographic columns. The three purified PGs migrated as single bands in native-PAGE gels with molecular weights (MW) ranging from 36 to 38 kDa. Each PG was converted to pepsin (P) at pH 2.0, and the MW were determined as 32 kDa (for P-I), 31 kDa (for P-II) and 30 kDa (for P-III). The optimum pH and temperature of pepsins were 2.0-3.5, and 40-50 °C. All 3 pepsins were strongly inhibited by pepstatin A. Divalent cations slightly stimulated the pepsin activities, but ATP had no effect on the pepsins. Purified pepsins were effective in the hydrolysis of various proteins. K m and k cat of the three pepsins for hemoglobin hydrolysis were 107.64-276.61 µM and 18.30-32.68 s -1 , respectively. The new pepsins have potential for use in protein food procession and modification., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Impacts of 2-butanol and β-cyclodextrin (β-CD) at various ratios and treatment times on bitterness, physicochemical and functional properties of Alcalase salmon frame protein hydrolysate (ASF) were investigated. ASF treated with 2-butanol at a ratio of 1:4 (w/v) for 20 min (ASFB) or with β-CD at a ratio of 1:1 (w/w) for 30 min (ASF-C-1) had lower bitterness score than ASF (p < 0.05). Bitterness score of ASF (8.45) was reduced to the lowest score (1.32) when ASFB was subsequently treated with β-CD at a 1:1 ratio (w/w) for 30 min (ASFB-C-1). Surface hydrophobicity of all debittered samples was lower than that of ASF sample (p < 0.05). The level of aromatic amino acids-containing peptides was reduced in ASFB-C-1 as shown by gel permeation chromatography. ASFB-C-1 sample had higher overall-likeness score but lower antioxidant properties than ASF (p < 0.05). The desired antioxidant activity could be achieved via increasing the amount of protein hydrolysate without imparting undesirable taste., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Acid soluble collagen (ASC) and pepsin soluble collagen (PSC) were extracted from the swim bladders of yellowfin tuna (Thunnus albacares) with yields of 1.07% and 12.10%, respectively. Based on electrophoretic patterns, both ASC and PSC consisted of two α-chains (α1 and α2) and were characterised to be type I collagen. ASC had higher β-chains than PSC. Imino acid contents of ASC and PSC were 128 and 169 residues/1,000 residues, respectively. Fourier transform infrared (FTIR) spectra of both ASC and PSC were similar and revealed the presence of a triple helix. Both ASC and PSC had the highest solubility at acidic pHs. From zeta potential analysis, a net charge of zero was found at pH 6.05 and 5.93 for ASC and PSC, respectively. Tmax of ASC and PSC were 32.97 and 33.92°C, respectively. The swim bladders of yellowfin tuna could therefore serve as an alternative source of collagen for future applications., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Characteristics and gel properties of gelatin from seabass skin, as influenced by extraction conditions, were studied. Yields of gelatin extracted at 45 and 55 °C for various times were 51.6-57.3% and 62.0-66.4% (dry weight basis), respectively. All gelatins contained β-chain and α-chains as the predominant components and showed a high imino acid content (198-202 residues/1000 residues). Generally, the gel strength of gelatins decreased as the extraction temperature and time increased. Gelatin extracted at 45 °C for 3h exhibited the highest gel strength (369 g). Gelling and melting temperatures for seabass skin gelatin were 19.5-20.0 and 26.3-27.0 °C, respectively. All gelatins could be set at 25 °C within 30 min, however gelatins extracted at 45 °C had a shorter setting time than those extracted at 55 °C (P<0.05). Gelatin from seabass skin showed a higher gel strength than bovine gelatin and could be used as a potential replacement for land animal gelatins., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Chemical compositions and nutritive value of the edible portions including foot, mantle and viscera of Asian hard clam (Meretrix lusoria) harvested from the coast of Andaman Sea were determined. Proximate compositions varied with portions tested. Edible portions had moisture (76.23-84.22%) and protein (9.09-12.75%) as the major components. Carbohydrate (0.32-7.89%), fat (1.58-6.58%) and ash (1.23-2.58%) were also found at various levels, dependent upon portions. Myofibrillar proteins were observed as the major fraction in foot (40.54%) and mantle (31.65%), whilst non-protein nitrogen constituents were dominant in the viscera (36.85%). All portions contained a large amount of essential amino acids (167.66-187.63 mg/g sample), in which leucine (30.91-36.96 mg/g sample) and lysine (35.24-36.03 mg/g sample) were predominant. They were rich in polyunsaturated fatty acids (46.84-49.18% of total fatty acid) with high level of DHA (13.33-16.47 % of total fatty acids) and EPA (4.75-7.11% of total fatty acids). Cholesterol of 0.07-0.21% wet weight was detected. All portions were also rich in macro- (Na, K, Ca and Mg) and micro- (Fe, Zn, Cu and Cr) minerals. Therefore, Asian hard clam is an excellent source of several nutrients, which could be beneficial for the health of the consumers., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Acid soluble collagens (ASCs) from skin and swim bladder of seabass (Lates calcarifer) were isolated and comparatively characterised. Higher yield (28.5%) was obtained for ASC from swim bladder, compared with that from skin (15.8%). ASCs from both skin and swim bladder had the similar protein patterns and were identified to be type I. Both α- and β-chains constituted as major components. Fourier transform infrared (FTIR) spectra revealed that both ASCs were triple helix in structure. ASC from both sources contained glycine as the major amino acid with imino acids (proline and hydroxyproline) of 194-195 residues/1000 residues). Peptide maps of both ASCs digested by chymotrypsin and trypsin showed slight differences, suggesting some differences in their primary structure. The thermal transition temperature of swim bladder ASC (35.02°C) was slightly higher than its skin counterpart (33.33°C). Based on zeta potential analysis, ASCs from skin and swim bladder had a net charge of zero at pH 6.46 and 6.64, respectively. Therefore, both the skin and swim bladder of seabass could be used potentially for collagen extraction., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Proteolytic activity of viscera extract from hybrid catfish (Clarias macrocephalus × Clarias gariepinus) was studied. The optimal pH and temperature were 9.0 and 50°C, respectively, when toothed ponyfish (Gazza minuta) muscle was used as a substrate. When viscera extract from hybrid catfish was used for the production of protein hydrolysate from toothed ponyfish muscle, extract concentration, reaction time, and fish muscle/buffer ratio affected the hydrolysis and nitrogen recovery (NR) (p<0.05). Optimum conditions for toothed ponyfish muscle hydrolysis were 3.5% hybrid catfish viscera extract, 15 min reaction time and fish muscle/buffer ratio of 1:3 (w/v). High correlation between the degree of hydrolysis (DH) and NR (R(2)=0.974) was observed. Freeze-dried hydrolysate had a high protein content (89.02%, dry weight basis) and it was brownish yellow in colour (L(∗)=63.67, a(∗)=6.33, b(∗)=22.41). The protein hydrolysate contained a high amount of essential amino acids (48.22%) and had arginine and lysine as the dominant amino acids., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Acid soluble collagen (ASC) and pepsin soluble collagen (PSC) were extracted from scale of spotted golden goatfish (Parupeneus heptacanthus) with the yields of 0.46% and 1.20% (based on dry weight basis), respectively. Both ASC and PSC were characterised as type I collagen, containing α1 and α2 chains. β and γ components were also found in both collagens. Based on FTIR spectra, the limited digestion by pepsin did not disrupt the triple helical structure of collagen. ASC and PSC contained glycine (336-340 residues/1000 residues) as the major amino acid and had imino acids of 186-189 residues/1000 residues. Maximal transition temperatures (Tmax) were 41.58 and 41.01°C for ASC and PSC, respectively. From zeta potential analysis, net charge of zero was found at pH 4.96 and 5.39 for ASC and PSC, respectively. Both collagens exhibited high solubility in acidic pH (2-4) and were soluble in the presence of NaCl at concentration up to 20 and 30g/l for ASC and PSC, respectively., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Trypsin was purified to homogeneity from the viscera of hybrid catfish (Clarias macrocephalus×Clarias gariepinus) through ammonium sulphate fractionation and a series of chromatographies including Sephacryl S-200, Sephadex G-50 and DEAE-cellulose. It was purified to 47.6-fold with a yield of 12.7%. Based on native-PAGE, the purified trypsin showed a single band. The molecular weight of purified trypsin was estimated as 24kDa by size exclusion chromatography and SDS-PAGE. The optimum pH and temperature for N(α)-p-tosyl-l-arginine methyl ester hydrochloride (TAME) hydrolysis were 8.0 and 60°C, respectively. Trypsin was stable to heat treatment up to 50°C, and over a pH range of 6.0-11.0. Trypsin was stabilized by calcium ion. The trypsin activity was strongly inhibited by soybean trypsin inhibitor and N-p-tosyl-l-lysine chloromethyl ketone and partially inhibited by ethylenediaminetetraacetic acid. Activity decreased continuously as NaCl concentration (0-30%) increased. Apparent Km value of trypsin was 0.3mM and Kcat value was 92.1S(-1) for TAME. The N-terminal amino acid sequence of 20 residues of trypsin was IVGGYECQAHSQPPTVSLNA, which is highly homologous with trypsins from other species of fish., (Copyright © 2011 Elsevier Ltd. All rights reserved.)