Molecular features, antioxidant potential, and immunological expression assessment of thioredoxin-like protein 1 (TXNL1) in yellowtail clownfish (Amphiprion clarkii).

Thioredoxin-like protein 1 (TXNL1) is a redox-active protein belonging to the thioredoxin family, which mainly controls the redox status of cells. The TXNL1 gene from Amphiprion clarkii (AcTXNL1) was obtained from a pre-established transcriptome database. The AcTXNL1 is encoded with 289 amino acids and is predominantly localized in the cytoplasm and nucleus. The TXN domain of AcTXNL1 comprises a34CGPC37 motif with redox-reactive thiol (SH-) groups. The spatial distribution pattern of AcTXNL1 mRNA was examined in different tissues, and the muscle was identified as the highest expressed tissue. AcTXNL1 mRNA levels in the blood and gills were significantly increased in response to different immunostimulants. In vitro antioxidant capacity of the recombinant AcTXNL1 protein (rACTXNL1) was evaluated using the ABTS free radical-scavenging activity assay, cupric ion reducing antioxidant capacity assay, turbidimetric disulfide reduction assay, and DNA nicking protection assay. The potent antioxidant activity of rAcTXNL1 exhibited a concentration-dependent manner in all assays. Furthermore, in the cellular environment, overexpression of AcTXNL1 increased cell viability under H2O2 stress and reduced nitric oxide (NO) production induced by lipopolysaccharides (LPS). Collectively, the experimental results revealed that AcTXNL1 is an antioxidant and immunologically important gene in A. clarkii.

Nile tilapia skin (Oreochromis niloticus) for burn treatment: ultrastructural analysis and quantitative assessment of collagen.

Nile tilapia (Oreochromis niloticus) skin is a well-known biomaterial used as an occlusive dressing for burn treatment. It is also an inexpensive and important source of collagen. This study aims to describe the ultrastructural aspects of Nile tilapia skin, assess its collagen amount and organization, and compare quantitative methods of histochemical and immunohistochemical analysis (in all sterilization steps for use in burn dressings). One sample (0.5 × 0.5 cm) of ten different fish skins was divided in four groups: in natura skin (IN), chemical sterilization (CH), additional irradiation (30 kGy) (IR), and skins used in burn treatment (BT) to compare histochemical and immunohistochemical findings of collagen amount and describe ultrastructural aspects through scanning electron microscopy. The amount of type I collagen decreased during sterilization and clinical use owing to gradual reduction of immunostaining (anti-collagen-I) and decreasing fiber thickness of the collagen, when compared to type III (Picrosirius-red-polarized light). The collagen fibers were rearranged at each sterilization step, with a low collagen percentage and large structural disorganization in BT. The amount of type-I collagen was further reduced after BT (p < 0.05). Both the methods did not exhibit a quantified value difference (p = 0.247), and a positive correlation (r = 0.927; 95 % CI = 0.720-0.983) was observed between them, with concordance for collagen quantification in similar samples, presenting a low systematic error rate (Dalberg coefficient: 6.70). A significant amount of type-I collagen is still observed despite sterilization, although clinical application further reduces type I collagen. Its quantification can be performed both by immunohistochemistry and/or Picrosirius Red reliably.

Comprehensive assessment of Nile tilapia skin collagen sponges as hemostatic dressings.

Nile tilapia skin collagen sponge was fabricated by lyophilization and cross-linked with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide in the presence of N-hydroxysuccinimide (EDC/NHS). The physicochemical properties were examined. The EDC/NHS cross-linked collagen sponge presented an enhanced water absorption capacity. In addition, biocompatibility and hemostatic efficiency were evaluated by acute systemic toxicity assay, dermal irritation test, intradermal reaction test, sensitization test, cytotoxicity, blood clotting assay in vitro, and liver and femoral artery hemorrhage models in vivo. Results showed that the produced collagen sponges before and after EDC/NHS cross-linking had excellent biocompatibility. Furthermore, EDC/NHS cross-linking promoted fibroblast cells viability and proliferation reflected by the MTT reduction assay. Meanwhile, EDC/NHS cross-linked collagen sponge exhibited the best blood clotting ability and hemostatic efficiency in rat femoral artery hemorrhage model in comparison with non-crosslinked and commercial collagen sponges. Our results demonstrated that the fabricated collagen sponges could be used as perfect hemostatic dressings.

Assessment of Fatty Acid Desaturase (Fads2) Structure-Function Properties in Fish in the Context of Environmental Adaptations and as a Target for Genetic Engineering.

Fatty acid desaturase 2 (Fads2) is the key enzyme of long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis. Endogenous production of these biomolecules in vertebrates, if present, is insufficient to meet demand. Hence, LC-PUFA are considered as conditionally essential. At present, however, LC-PUFA are globally limited nutrients due to anthropogenic factors. Research attention has therefore been paid to finding ways to maximize endogenous LC-PUFA production, especially in production species, whereby deeper knowledge on molecular mechanisms of enzymatic steps involved is being generated. This review first briefly informs about the milestones in the history of LC-PUFA essentiality exploration before it focuses on the main aim-to highlight the fascinating Fads2 potential to play roles fundamental to adaptation to novel environmental conditions. Investigations are summarized to elucidate on the evolutionary history of fish Fads2, providing an explanation for the remarkable plasticity of this enzyme in fish. Furthermore, structural implications of Fads2 substrate specificity are discussed and some relevant studies performed on organisms other than fish are mentioned in cases when such studies have to date not been conducted on fish models. The importance of Fads2 in the context of growing aquaculture demand and dwindling LC-PUFA supply is depicted and a few remedies in the form of genetic engineering to improve endogenous production of these biomolecules are outlined.

Properties of collagen extracted from Amur sturgeon Acipenser schrenckii and assessment of collagen fibrils in vitro.

The objective of this study was to assess the nature of the collagens from the Amur sturgeon to determine its possibility as a potential collagen source for biomedical applications. From a sturgeon (1.22 kg), 6.0 g (dry wt) of skin collagen (SC), 4.1 g of swim bladder collagen (SBC), and 0.4 g of notochord collagen (NC) were obtained. SC and SBC were characterized as type I, and NC as type II collagen. Denaturation temperatures of SC, SBC, and NC were calculated as 28.5, 30.5, and 33.5 °C, respectively. Gene expression of the type I procollagen α2 chain of Amur sturgeon (ascol1a2) was specifically higher than ascol1a1 expression in the swim bladder, suggesting a unique composition of α chains in this organ. SC and SBC had better abilities of fibril formation with unique higher-order structures compared with porcine type I collagen. The maximum transition temperature (Tm) of reassembled fibrils formed in a buffer solution containing NaCl at 0 and 140 mM was 34.4 °C and 38.9 °C in SC, and 40.1 °C and 40.7 °C in SBC, respectively. These characteristic features suggested that sturgeon collagens could be used in the biomedical industries in future applications.

Bio-functional properties of sardine protein hydrolysates obtained by brewer's spent yeast and commercial proteases.

BACKGROUND: The canned-sardine industry generates large amounts of protein-rich waste, which demands useful exploitation. This paper describes the potential use of muscle and viscera proteins from canned sardine by-products as substrate to obtain hydrolysates with biological and functional properties. Three enzymatic approaches, brewer's spent yeast (Bsy) proteases, Alcalase® and Neutrase® were applied to perform protein hydrolysis at the same proteolytic activity (1 U mL-1 ), using an enzyme/substrate ratio of 20% (v/v), at 50°C and for 7 h. Hydrolysis degree (DH), antioxidant and angiotensin I-converting enzyme inhibitory (ACE-I) activities, functional properties (i.e. solubility, emulsifying and foaming properties, water and oil binding capacity) and colour were investigated. RESULTS: All hydrolysates presented a high protein content [52.7-83.2% dry weight (DW)] and low fat content (0.9-3.9% DW). Alcalase® treatment of muscle and viscera proteins resulted in higher DH (7.5% and 8.6%, respectively) and higher biological activities (P < 0.05). All hydrolysates had excellent solubility and presented functional properties. Among viscera hydrolysates, treatment with Bsy proteases promoted higher emulsion (80.1 m2 g-1 ), foaming (79.2%) and oil binding capacity (5.8 g g-1 ) of viscera sardine proteins. CONCLUSION: Improved biological and functional properties were observed for sardine protein hydrolysates produced using the three enzymatic treatments tested. © 2017 Society of Chemical Industry.

Dietary fish protein hydrolysates containing bioactive motifs affect serum and adipose tissue fatty acid compositions, serum lipids, postprandial glucose regulation and growth in obese Zucker fa/fa rats.

The world's fisheries and aquaculture industries produce vast amounts of protein-containing by-products that can be enzymatically hydrolysed to smaller peptides and possibly be used as additives to functional foods and nutraceuticals targeted for patients with obesity-related metabolic disorders. To investigate the effects of fish protein hydrolysates on markers of metabolic disorders, obese Zucker fa/fa rats consumed diets with 75 % of protein from casein/whey (CAS) and 25 % from herring (HER) or salmon (SAL) protein hydrolysate from rest raw material, or 100 % protein from CAS for 4 weeks. The fatty acid compositions were similar in the experimental diets, and none of them contained any long-chain n-3 PUFA. Ratios of lysine:arginine and methionine:glycine were lower in HER and SAL diets when compared with CAS, and taurine was detected only in fish protein hydrolysate diets. Motifs with reported hypocholesterolemic or antidiabetic activities were identified in both fish protein hydrolysates. Rats fed HER diet had lower serum HDL-cholesterol and LDL-cholesterol, and higher serum TAG, MUFA and n-3:n-6 PUFA ratio compared with CAS-fed rats. SAL rats gained more weight and had better postprandial glucose regulation compared with CAS rats. Serum lipids and fatty acids were only marginally affected by SAL, but adipose tissue contained less total SFA and more total n-3 PUFA when compared with CAS. To conclude, diets containing hydrolysed rest raw material from herring or salmon proteins may affect growth, lipid metabolism, postprandial glucose regulation and fatty acid composition in serum and adipose tissue in obese Zucker rats.

Clupeiformes' Egg Envelope Proteins characterization: The case of Engraulis encrasicolus as a proxy for stock assessment through a novel molecular tool.

Zona radiata proteins are essential for ensuring bactericidal resistance, oocyte nutrients uptake and functional buoyancy, sperm binding and guidance to the micropyle, and protection to the growing oocyte or embryo from the physical environment. Such glycoproteins have been characterized in terms of molecular structure, protein composition and phylogenetics in several chordate models. Nevertheless, research on teleost has not been extensive. In Clupeiformes, one of the most biologically relevant and commercially important order which accounts for over 400 species and totally contributes to more than a quarter of the world fish catch, Egg Envelope Protein (EEP) information exist only for the Clupea pallasii and Engraulis japonicus species. The European anchovy, Engraulis encrasicolus, the target of a well-consolidated fishery in the Mediterranean Sea, has been ignored until now and the interest on the Otocephala superorder has been fragmentally limited to some Cypriniformes and Gonorynchiformes, as well. The aim of the present study was to fill the ZP protein-wise gap of knowledge afflicting the understanding of the European anchovy's reproductive process and to expand the background on Clupeiformes. We cloned the five Engraulis encrasicolus' zp genes and deduced their products, determined their tissue distribution, quantified their mRNA expression throughout the reproductive cycle and provided an insight into their evolution through phylogenetic tools. Furthermore, we proposed a multivariate statistics-based method to objectively infer and/or confirm the classification of Engraulis encrasicolus' sexual maturity stages by analyzing data of zp mRNAs' relative abundance.

Triple helical structure of acid-soluble collagen derived from Nile tilapia skin as affected by extraction temperature.

BACKGROUND: Fish skin has become a new source of collagen. It is usually extracted at low temperature. Increasing the extraction temperature can increase the collagen yield. However, high temperature might cause degradation of the triple helical structure of collagen, which is related to its functional biomaterial. This work thus aimed to investigate the effect of extraction temperature on the extraction efficiency and characteristics of acid-soluble collagen (ASC), particularly its triple helical structure. RESULTS: ASC was extracted at 5 ± 1, 15 ± 1 and 25 ± 1 °C for 0-24 h with 0.3 or 0.5 mol L(-1) acetic acid. The results showed that extraction with 0.5 mol L(-1) acetic acid gave a higher extraction efficiency than that in 0.3 mol L(-1) acetic acid (P < 0.5). Extraction at 25 ± 1 °C for 5 h with 0.5 mol L(-1) acetic acid gave a higher extraction efficiency (73.73 ± 1.28%), which is higher than that of 5 ± 1 °C by about 1.7-fold. All ASC obtained were identified as type I collagen and showed similar physicochemical properties. CONCLUSION: The results showed that extraction temperature strongly affected extraction efficiency. Extraction at 25 °C did not affect the triple helical structure, which was confirmed by the results of Fourier transform infrared, circular dichroism spectrum and collagen self-assembly. © 2015 Society of Chemical Industry.

A Review of Potential Marine-derived Hypotensive and Anti-obesity Peptides.

Bioactive peptides are food derived components, usually consisting of 3-20 amino acids, which are inactive when incorporated within their parent protein. Once liberated by enzymatic or chemical hydrolysis, during food processing and gastrointestinal transit, they can potentially provide an array of health benefits to the human body. Owing to an unprecedented increase in the worldwide incidence of obesity and hypertension, medical researchers are focusing on the hypotensive and anti-obesity properties of nutritionally derived bioactive peptides. The role of the renin-angiotensin system has long been established in the aetiology of metabolic diseases and hypertension. Targeting the renin-angiotensin system by inhibiting the activity of angiotensin-converting enzyme (ACE) and preventing the formation of angiotensin II can be a potential therapeutic approach to the treatment of hypertension and obesity. Fish-derived proteins and peptides can potentially be excellent sources of bioactive components, mainly as a source of ACE inhibitors. However, increased use of marine sources, poses an unsustainable burden on particular fish stocks, so, the underutilized fish species and by-products can be exploited for this purpose. This paper provides an overview of the techniques involved in the production, isolation, purification, and characterization of bioactive peptides from marine sources, as well as the evaluation of the ACE inhibitory (ACE-I) activity and bioavailability.

Two novel antioxidant nonapeptides from protein hydrolysate of skate (Raja porosa) muscle.

In the current study, the preparation conditions of neutrase hydrolysate (SMH) from skate (Raja porosa) muscle protein were optimized using orthogonal L9(3)4 tests, and R values indicated that pH was the most important factor affecting HO· scavenging activity of SMH. Under the optimum conditions of pH 7.0, enzymolysis temperature 60 °C, enzyme/substrate ratio (E/S) 2%, and enzymolysis time 5 h, EC50 of SMH on HO· was 2.14 ± 0.17 mg/mL. Using ultrafiltration, gel filtration chromatography, and RP-HPLC, two novel antioxidant nonapeptides (SP-A and SP-B) were isolated from SMH and their amino acid sequences were found to be APPTAYAQS (SP-A) and NWDMEKIWD (SP-B) with calculated molecular masses of 904.98 Da and 1236.38 Da, respectively. Both showed strong antioxidant activities. SP-A and SP-B exhibited good scavenging activities on HO· (EC50 0.390 and 0.176 mg/mL), DPPH· (EC50 0.614 and 0.289 mg/mL), and O2-· (EC50 0.215 and 0.132 mg/mL) in a dose-dependent manner. SP-B was also effective against lipid peroxidation in the model system. The aromatic (2Trp), acidic (2Asp and Glu), and basic (Lys) amino acid residues within the sequences of SP-B might account for its pronounced antioxidant activity. The results of this study suggested that protein hydrolysate and peptides from skate muscle might be effective as food additives for retarding lipid peroxidation occurring in foodstuffs.

Biochemical characterisation and assessment of fibril-forming ability of collagens extracted from Bester sturgeon Huso huso × Acipenser ruthenus.

Collagens purified from Bester sturgeon organs were characterised biochemically, and their fibril-forming abilities and fibril morphologies formed in vitro clarified. Yields of collagens were 2.1%, 11.9%, 0.4%, 18.1%, 0.4%, 0.8% and 0.03% (collagen dry weight/tissue wet weight) from scales, skin, muscle, swim bladder, digestive tract, notochord and snout cartilage, respectively. Using SDS-PAGE and amino acid composition analyses, collagens from scales, skin, muscle, the swim bladder and digestive tract were characterised as type I, and collagens from the notochord and snout cartilage as type II. Denaturation temperatures of the collagens, measured using circular dichroism, were 29.6, 26.8, 29.0, 32.9, 31.6 and 36.3 °C in scales, skin, muscle, swim bladder, digestive tract, and notochord, respectively. For fibril formation, swim bladder and skin collagen showed a more rapid rate of increase in turbidity, a shorter time to attain the maximum turbidity, and formed thicker fibrils compared with porcine tendon type I collagen.

Purification and characterization of parvalbumin isotypes from grass carp (Ctenopharyngodon idella).

The prevalence of fish allergy is rapidly increasing because of a growing fish consumption driven mainly by a positive image of the fish and health relationship. The purpose of this study was to characterize parvalbumin isotypes from grass carp (Ctenopharyngodon idella), one of the most frequently consumed freshwater fish in China. Three parvalbumin isotypes were purified using consecutive gel filtration and reverse-phase chromatography and denoted as PVI, PVII, and PVIII. The molecular weights of the isotypes were determined to be 11.968, 11.430, and 11.512 kDa, respectively. PVI showed 74% matched amino acids sequence with PV isotype 4a from Danio rerio, while PVII and PVIII showed 46% matched amino acids sequence with PV isotypes from Hypophthalmichthys molitrix. PVII is the dominant allergen, but it was liable to gastrointestinal enzymes as PVIII; however, PVI was resistant to pepsin digestion. A further study is to characterize the epitopes of PVII, the dominant allergen.

Nutritive value of diets containing fish silage for juvenile Litopenaeus vannamei (Bonne, 1931).

BACKGROUND: Fish wastes has been used for many years as an alternative in feeds for aquaculture. In the present study weight gain of juvenile white shrimp Litopenaeus vannamei fed diets including fish waste silage (WS), fish waste silage with soybean meal SBM (WS + S) or fish waste meal (WM) was compared. A conventional acidic silage process was applied to obtain from wastes (skin, heads, bones and viscera) of snapper (Lutjanus spp.), grunt (Haemulon plumieri), and grouper (Epinephelus spp.) an ingredient rich in protein. RESULTS: After 3 days ensilage more than 90% protein was hydrolysed. Waste material processed at pH 3.8 lost about 24% tryptophan. Butylated hydroxytoluene (BHT) prevented lipid oxidation, as shown after 45 days with malonaldehyde production. Shrimp fed WS + S diet gained 0.7 g per week higher than those fed WS and WM diets with 0.3 g per week (P < 0.05). CONCLUSION: WS processed with formic acid under conditions of low pH is beneficial for the white shrimp L. vannamei. It sustained reasonable weight gain combined with soybean meal in practical diets. On the other hand, BHT addition was beneficial in preventing oxidative action during silage preparation.

Improvement of gel strength and melting point of fish gelatin by addition of coenhancers using response surface methodology.

UNLABELLED: Fish gelatin is a potential alternative to mammalian gelatin. However, poor gel strength and low melting point limit its applications. The study was aimed at improving these properties by adding coenhancers in the range obtained from response surface methodology (RSM) by using Box-Behnken design. Three different coenhancers, MgSO4, sucrose, and transglutaminase were used as the independent variables for improving the gel strength and melting point of gelatin extracted from Tiger-toothed croaker (Otolithes ruber). Addition of coenhancers at different combinations resulted gel strength and melting point in the range of 150.5 to 240.5 g and 19.5 to 22.5 °C, respectively. The optimal concentrations of coenhancers for predicted maximum gel strength (242.8 g) obtained by RSM were 0.23 M MgSO4, 12.60% sucrose (w/v), and 5.92 mg/g transglutaminase and for predicted maximum melting point (22.57 °C), the values were 0.24 M MgSO4, 10.44% sucrose (w/v), and 5.72 mg/g transglutaminase. By addition of coenhancers at these optimal concentrations in verification experiments, the gel strength and melting point were improved from 170 to 240.89 g and 20.3 to 22.7 °C, respectively. These experimental values agreed well with the predicted values demonstrating the fitness of the models. Results from the present study clearly revealed that the addition of coenhancers at a particular combination can improve the gel strength and melting point of fish gelatin to enhance its range of applications. PRACTICAL APPLICATION: There is a growing interest in the use of fish gelatin as an alternative to mammalian gelatin. However, poor gel strength and low melting point of fish gelatin have limited its commercial applications. The gel strength and melting point of fish gelatin can be increased by incorporation of coenhancers such as magnesium sulphate, sucrose, and transglutaminase. Results of this work help to produce the fish gelatin suitable for wide range of applications in the food industry.

Preparation of reactive oxygen scavenging peptides from tilapia (Oreochromis niloticus) skin gelatin: optimization using response surface methodology.

Gelatin extracted from tilapia skin was hydrolyzed with Properase E. Response surface methodology (RSM) was applied to optimize the hydrolysis condition (temperature [T], enzyme-to-substrate ratio [E/S], pH and reaction time [t]), to obtain the hydrolysate with the highest hydroxyl radical (•OH) scavenging activity. The optimum conditions obtained were T of 44.2 °C, E/S of 2.2%, pH of 9.2, and t of 3.4 h. The predicted •OH scavenging activity of the hydrolysate under the optimum conditions was 60.7%, and the actually experimental scavenging activity was 60.8%. The hydrolysate was fractionated by ultrafiltration, and 4 fractions were collected. The fraction TSGH4 (MW<2000 Da) showed the strongest •OH scavenging activity with the highest yield. Furthermore, reactive oxygen species (ROS) scavenging activities of TSGH4 with different concentrations were investigated in 5 model systems, including superoxide anion radical (•O2), •OH, hydrogen peroxide (H2O2), peroxynitrite (ONOO-), and nitric oxide (NO•), compared with reduced glutathione (GSH). The results showed that TSGH4 significantly scavenged these ROS, and could be used as a functional ingredient in medicine and food industries.

Channel catfish (Ictalurus punctatus) muscle protein isolate performance processed under different acid and alkali pH values.

Channel catfish (Ictalurus punctatus) muscle was subjected to 6 protein extraction and precipitation techniques using acid solubilization (pH 2.0, 2.5, and 3.0) or alkaline solubilization (pH 10.5, 11.0, 11.5) followed by precipitation at pH 5.5. The catfish protein isolate was compared with ground defatted white muscle. Alkali-processed catfish showed increased gel rigidity, gel strength, and gel flexibility compared to acid-processed catfish, which exhibited inconsistent functional performance, increasing and decreasing gel rigidity, gel strength, and gel flexibility. The gel rigidity (G') at pH 3.0 in the absence of salt had the highest G' of the acid treatments and was not significantly different from the alkaline-treated catfish muscle (P>0.05). However in the presence of added salt pH treatment it had the lowest G' and was different from alkaline treatments (P<0.05) during break force testing. These results show that pH-shift processing of channel catfish muscle provides highly functional isolates with a potentially broad range of applications. This range of applications is possible due to the modification of the textural properties of catfish muscle protein produced using different acidic or alkaline pH solubility treatments.

Fish gelatin.

Gelatin is a multifunctional ingredient used in foods, pharmaceuticals, cosmetics, and photographic films as a gelling agent, stabilizer, thickener, emulsifier, and film former. As a thermoreversible hydrocolloid with a narrower gap between its melting and gelling temperatures, both of which are below human body temperature, gelatin provides unique advantages over carbohydrate-based gelling agents. Gelatin is mostly produced from pig skin, and cattle hides and bones. Some alternative raw materials have recently gained attention from both researchers and the industry not just because they overcome religious concerns shared by Jews and Muslims but also because they provide, in some cases, technological advantages over mammalian gelatins. Fish skins from a number of fish species are among the other sources that have been comprehensively studied as sources for gelatin production. Fish skins have a significant potential for the production of high-quality gelatin with different melting and gelling temperatures over a much wider range than mammalian gelatins, yet still have a sufficiently high gel strength and viscosity. Gelatin quality is industrially determined by gel strength, viscosity, melting or gelling temperatures, the water content, and microbiological safety. For gelatin manufacturers, yield from a particular raw material is also important. Recent experimental studies have shown that these quality parameters vary greatly depending on the biochemical characteristics of the raw materials, the manufacturing processes applied, and the experimental settings used for quality control tests. In this review, the gelatin quality achieved from different fish species is reviewed along with the experimental procedures used to determine gelatin quality. In addition, the chemical structure of collagen and gelatin, the collagen-gelatin conversion, the gelation process, and the gelatin market are discussed.

Collagens from the skin of arabesque greenling (Pleurogrammus azonus) solubilized with the aid of acetic acid and pepsin from albacore tuna (Thunnus alalunga) stomach.

BACKGROUND: Due to the low extraction efficiency of collagen from fish skin by the typical acid solubilization process, pepsin has been widely used to aid further extraction of collagen from the residue. The aim of this study was to characterize collagen from the skin of arabesque greenling extracted with the aid of albacore tuna pepsin, in comparison with collagen obtained from the acid solubilization process. RESULTS: Acid-solubilized collagen (ASC) from the skin of arabesque greenling was extracted with acetic acid. Pepsin-solubilized collagen (PSC) was further extracted from the skin residue with the aid of pepsin from albacore tuna. The yields of ASC and PSC were 303 and 140 g kg(-1) (dry weight), respectively. Both collagens contained alpha- and beta-chains as their major components and were characterized as type I collagen. Both collagens contained glycine as a major amino acid and had imino acid content of 157-159 residues per 1000 residues. The degradation induced by lysyl endopeptidase and V8-protease was more pronounced in PSC compared with ASC. Maximal transition temperatures of both collagens were in the range of 15.4-15.7 degrees C. Fourier transform infrared spectra revealed some differences in molecular order between ASC and PSC. Nevertheless, the triple-helical structure of PSC was still predominant. Based on zeta-potential, pI of ASC and PSC was estimated to be 6.31 and 6.38, respectively. CONCLUSION: Isolation of collagens from the skin of arabesque greenling could be achieved by acid or albacore tuna pepsin solubilization. However, there was a slight difference in properties between ASC and PSC.