Cross-linking effects of carbodiimide, oxidized chitosan oligosaccharide and glutaraldehyde on acellular dermal matrix of basa fish (Pangasius bocourti).

Basa acellular dermal matrix (BADM) has advantages in the preparation of oral prosthetic membranes. In order to prepare high-quality BADM, a suitable cross-linking agent is necessary. In this study, acellular dermal matrix was prepared from basa fish skin and then cross-linked with carbodiimide (EDC), oxidized chitosan oligosaccharide (OCOS) and glutaraldehyde (GA), respectively. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction analysis (XRD), histological staining, DNA electrophoresis and the limulus amoebocyte lysate chromogenic assay were used to detect the structure and properties of BADM. The compatibility of BADM was detected by implantation in vivo and cell experiments. The results showed that the majority of the cellular and DNA in BADM were removed. The endotoxin was not be detected. Furthermore, the structure of BADM was not destroyed. The mechanical and anti-degraded properties of BADM were promoted obviously after cross-linking. The thermal shrinkage temperatures of wet and dry EDC-BADM (BADM cross-linked by carbodiimide) were increased by 39.22 °C and 18.27 °C, respectively, compared with that of the uncross-linked BADM. In addition, the EDC-BADM had good biocompatibility and cytocompatibility. In conclusion, carbodiimide can improve the properties of BADM, which has potential application in the field of biomaterials.

Structural feature and self-assembly properties of type II collagens from the cartilages of skate and sturgeon.

Acid-soluble collagen (ASC) and pepsin-soluble collagen (PSC) were extracted and purified from the cartilages of skate and sturgeon. Their typical structure and physicochemical properties were evaluated by circular dichroism (CD), X-ray diffraction (XRD), and so on. Results showed that the extracted collagen was likely identified as collagen-II composed of three α-chains (135 kDa), with the typical peptide sequence of Gly-X-Y. It showed the collagen retained the native and intact triple helical structure, and its intensity ratio of the positive and negative absorption peaks (Rpn) was 0.19-0.25. In addition, the extracted collagen exhibited obvious self-assembly behavior with the concentration above 0.3 mg/mL, the adjustment of pH 7.4-7.6 and the NaCl concentration of 120 mmol/L. The critical aggregate mass concentrations of pepsin-soluble collagens from skate and sturgeon were 0.93 and 0.86 g/L, respectively. Therefore, collagens from skate and sturgeon cartilages have potential commercial application.

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.

The Protective Effect of Mycosporine-Like Amino Acids (MAAs) from Porphyra yezoensis in a Mouse Model of UV Irradiation-Induced Photoaging.

The objective of this research was to extract and prepare mycosporine-like amino acids (MAAs) and investigate the mechanism by which they act against UV-induced skin photoaging in Institute of Cancer Research (ICR ) mice. MAAs such as porphyra-334 and shinorine were extracted from Porphyra yezoensis, separated, and purified using column chromatography with SA-2 cation exchange resin. The effects of MAAs on the activity of endogenous antioxidant enzymes, namely total superoxide dismutase (T-SOD), glutathione peroxidase (GSH-Px), catalase (CAT), and malondialdehyde (MDA) were analyzed in mouse skin tissue. Pathological changes of skin tissue caused by ultraviolet radiation and the arrangement of collagen were observed by Hematoxylin-Eosin (HE) staining and scanning electron microscopy (SEM). Interleukin 1ß (IL-1ß), IL-6, and IL-10 were detected using the quantitative real-time reverse transcription-polymerase chain reaction (qPCR) and Enzyme Linked Immunosorbent Assay (ELISA). The concentration and expression of these proinflammatory cytokines was associated with the presence of nuclear factor (NF)-κB. The results show that MAA compounds from Porphyra yezoensis could suppress UV-induced photoaging of skin by inhibiting the reduction of endogenous antioxidant enzymes. Compared to the control group, the concentrations of SOD, GSH-Px, and CAT increased significantly in skin tissue homogenate following the external administration of MAAs (p < 0.05, p < 0.01), while the content of MDA decreased significantly (p < 0.05). Meanwhile, the administration of MAAs was associated with down-regulations in the concentration and mRNA expression of NF-κB, IL-1ß, IL-6, and IL-10. The results suggest that MAAs could protect skin from photodamage by increasing antioxidant enzyme activities and inhibiting inflammation.

Effects of three products from Antarctic krill on the nitrogen balance, growth, and antioxidation status of rats.

A few studies conducted over the past few decades have demonstrated the health benefits of a diet rich in marine products, but limited studies have investigated the effects of different krill products on the nitrogen balance and their potential health benefits. In our study, after a 14-day acclimation period, 50 female Sprague-Dawley rats were randomly assigned to five groups, each of which was fed a different diet, for 28 days. We then evaluated the effect of krill protein complex (KPC), krill powder, and defatted krill powder on the nitrogen balance, growth, and antioxidant activity through analyses of MDA, CAT, GSH-Px, and T-SOD. An in vivo analysis suggested that the nitrogen retention rate, protein digestibility, and bioutilization of krill products were equal to those of casein. Moreover, the KPC diet resulted in the highest nitrogen intake and retention among the groups, and the biological value and net protein utilization obtained with KPC were higher than those obtained with defatted krill powder, which was consistent with the weight gains observed for these two groups. The hematological test also showed that KPC contributed to the production of functional proteins in the body. The antioxidant activity analysis indicated that higher GSH-Px and T-SOD activities were obtained with krill products and KPC, respectively, compared with casein. The results from this study suggested that krill proteins could promote growth and improve the antioxidant status of an organism. Although further studies on the safety of krill products for human consumption are needed, this work provides insights into the use of krill proteins as a potential substitute for other proteins and restructured foods.

Evaluating the efficacy of a ferrous-ion-chelating peptide from Alaska pollock frame for the improvement of iron nutritional status in rats.

This study aimed to investigate the effects of ferrous-ion-chelating peptides from Alaska pollock frames (APFP-Fe) on iron deficiency in anaemic rats. We hydrolysed the Alaska pollock frames to obtain a peptide with an average molecular weight of 822 Da. The bioavailability of APFP-Fe was tested using animal experiments. Wistar rats were randomly divided into six groups: an iron deficiency control group, a normal control group, and iron deficiency groups treated with ferrous sulfate (FeSO4) or low-, medium-, or high-dose APFP-Fe. Rats in the iron deficiency groups were fed an iron-deficient diet to establish the iron deficiency anaemia (IDA) model. After the model was established, different iron supplements were given to rats once per day via intragastric administration for 21 days. The results showed that APFP-Fe had restorative effects, returning the body weight, weight gain, height, and haematological parameters in IDA rats to normal levels. In addition, compared with FeSO4, APFP-Fe promoted significant weight gain and effectively improved haemoglobin, serum iron and transferrin levels, and recovery of the capacity of iron binding with transferrin, especially at the medium and high doses. These findings suggest that APFP-Fe is an effective source of iron for improving the iron nutritional status in IDA rats and shows promise as a new source of iron supplementation.

Physicochemical and Biocompatibility Properties of Type I Collagen from the Skin of Nile Tilapia (Oreochromis niloticus) for Biomedical Applications.

The aim of this study is to investigate the physicochemical properties, biosafety, and biocompatibility of the collagen extract from the skin of Nile tilapia, and evaluate its use as a potential material for biomedical applications. Two extraction methods were used to obtain acid-soluble collagen (ASC) and pepsin-soluble collagen (PSC) from tilapia skin. Amino acid composition, FTIR, and SDS-PAGE results showed that ASC and PSC were type I collagen. The molecular form of ASC and PSC is (α1)2α2. The FTIR spectra of ASC and PSC were similar, and the characteristic peaks corresponding to amide A, amide B, amide I, amide II, and amide III were 3323 cm-1, 2931 cm-1, 1677 cm-1, 1546 cm-1, and 1242 cm-1, respectively. Denaturation temperatures (Td) were 36.1 °C and 34.4 °C, respectively. SEM images showed the loose and porous structure of collagen, indicting its physical foundation for use in applications of biomedical materials. Negative results were obtained in an endotoxin test. Proliferation rates of osteoblastic (MC3T3E1) cells and fibroblast (L929) cells from mouse and human umbilical vein endothelial cells (HUVEC) were increased in the collagen-treated group compared with the controls. Furthermore, the acute systemic toxicity test showed no acute systemic toxicity of the ASC and PSC collagen sponges. These findings indicated that the collagen from Nile tilapia skin is highly biocompatible in nature and could be used as a suitable biomedical material.

Novel hard capsule prepared by tilapia (Oreochromis niloticus) scale gelatin and konjac glucomannan: Characterization, and in vitro dissolution.

A novel material for making capsules was prepared with tilapia scale gelatin and konjac glucomannan (KGM). Rheological behaviors of gelatin with KGM at different levels (0.1%, 0.15%, and 0.2%, w/w) were investigated. The highest values (P < 0.05) of gel strength (518.33 ± 6.17 g) and melting temperature (39.7 ± 0.11 °C) could be observed at the gelatin solution with 0.15% (w/w) KGM. The tensile strength (TS) and elongation at break (EAB) of the films increased with the increasing of KGM. The water contact angle was enhanced with the increasing of KGM, indicating the decrease of the film hydrophilicity. XRD and FTIR showed the interactions between gelatin and KGM. Gelatin solution with 0.15% KGM is suitable for preparing capsules. Drug dissolution test in vitro showed the shell rupture time is in range of 3-5 min, and 80% of the drugs were released within 10 min. Therefore, the composite materials made of tilapia scale gelatin and KGM can be utilized for hard capsules.

Discrimination of dried sea cucumber (Apostichopus japonicus) products from different geographical origins by sequential windowed acquisition of all theoretical fragment ion mass spectra (SWATH-MS)-based proteomic analysis and chemometrics.

The article reports on discrimination of dried sea cucumber Apostichopus japonicus (A. japonicus) products from different geographical regions in China (Xiapu, Jiaonan, Weihai, Yantai, Dalian). For this purpose, sequential window acquisition of all theoretical fragment ion mass spectra (SWATH-MS)-based proteomic analysis combined with chemometrics was evaluated. Proteome variations of A. japonicus samples determined by SWATH-MS using ultra-high performance liquid chromatography coupled to quadrupole time of flight mass spectrometer were mined by chemometric tools to clarify the correlation between protein quantitation data and geographical origin. A differentiating OPLS-DA model was constructed with 55 SWATH-MS quantified proteins. A. japonicus samples from five locations were clearly classified by the developed OPLS-DA model and 100% prediction accuracy was achieved in validation testing as well as real-life sample analysis. Seventeen proteins were identified as discriminatory biomarkers allowing geographical provenance. The proposed method might be applied in origin authentication of commercially dried A. japonicus products.

Functional Calcium Binding Peptides from Pacific Cod (Gadus macrocephalus) Bone: Calcium Bioavailability Enhancing Activity and Anti-Osteoporosis Effects in the Ovariectomy-Induced Osteoporosis Rat Model.

Calcium binding peptides from Pacific cod (Gadus macrocephalus) bone have attracted attention due to their potential effects on bone health. In this study, calcium binding peptides (CBP) were prepared from Pacific cod bone by trypsin and neutral protease. Ultraviolet spectra, circular dichroism (CD), and Fourier transform infrared spectroscopy (FTIR) revealed that carboxyl and amino groups in CBP could bind to Ca2+, and form the peptide-calcium complex (CBP-Ca). Single-pass intestinal perfusion (SPIP) experiments indicated that the intestinal calcium absorption was significantly enhanced (p < 0.01) in CBP-Ca treated Wistar rats. The anti-osteoporosis activity of CBP-Ca was investigated in the ovariectomized (OVX) Wistar rat model. The administration of CBP-Ca significantly (p < 0.01) improved the calcium bioavailability, trabecular bone structure, bone biomechanical properties, bone mineral density, and bone mineralization degree. CBP-Ca notably (p < 0.01) increased serum calcium, however, it remarkably (p < 0.01) reduced the levels of osteocalcin (OCN), bone alkaline phosphatase (BALP), tartrate-resistant acid phosphatase isoform 5b (TRAP5b), and C-telopeptide of type I collagen (CTX-1) in serum. Results suggested that the cod bone derived CBP could bind with calcium, improve the intestinal calcium absorption, calcium bioavailability, and serum calcium, then reduce the bone turnover rate, and thus ameliorate osteoporosis.

Physical properties and antioxidant activity of gelatin-sodium alginate edible films with tea polyphenols.

Active edible films were prepared by incorporating tea polyphenols (TP) into gelatin and sodium alginate. The effects of 0.4%-2.0% TP (w/w, TP/gelatin) on physical, antioxidant, and morphological properties of gelatin-sodium alginate films were evaluated. Tensile strength (Ts), contact angle (CA), and cross-linking degree showed an enhanced trend as TP concentration in the film increased, whereas elongation at break (EAB) and water vapor permeability (WVP) possessed a decline trend. The light transmittance of the film was decreased by the incorporation of TP. Antioxidant capacity was improved by increasing TP content in the films. For DPPH and ABTS radical, the films with 2.0% TP possessed the highest values of 90.62 ±â€¯2.48% and 53.36 ±â€¯1.06 Trolox (mg Trolox equivalent/g film), respectively. Fourier transform infrared spectroscopy analyses (FTIR) indicated the interactions existed between gelatin­sodium alginate and TP. Smooth and continuous surface and dense internal structure of the films with TP were observed by scanning electron microscopy (SEM). Thus, incorporating TP into gelatin and sodium alginate film solution was an effective method in order to improve physical properties and antioxidant activity of the films. Gelatin-sodium alginate films with TP could be used as an edible film for food packaging applications.

Interactions of quercetin, curcumin, epigallocatechin gallate and folic acid with gelatin.

Some small bioactive molecules from food show the potential health benefits, but with poor chemical stability and bioavailability. The interactions between small molecules and gelatin were investigated. Fluorescence experiments demonstrated that the bimolecular quenching constants (kq) of complexes (gelatin-quercetin, gelatin-curcumin, gelatin-epigallocatechin gallate, gelatin-folic acid) were 3.7 × 1012 L·mol-1·s-1, 1.4 × 1012 L·mol-1·s-1, 2.7 × 1012 L·mol-1·s-1 and 8.5 × 1012 L·mol-1·s-1, indicating that fluorescence quenching did not arise from a dynamical mechanism, but from gelatin-small molecules binding. Furthermore, the affinity with gelatin was ranked in the order of folic acid > quercetin > epigallocatechin gallate > curcumin. Fluorescence spectroscopy, ultraviolet and visible absorption spectroscopy, FTIR and circular dichroism showed that the interactions between small molecules and gelatin did not significantly alter the conformation and secondary structure of gelatin. Non-covalent interactions may result in the binding of gelatin with small molecules. The interactions were considered to be through two modes: (1) small molecules bound within the hydrophobic pockets of gelatin; (2) small molecules surrounded the gelatin molecule mainly through hydrogen bonds and hydrophobic interactions.

Effects of cross-linking on mechanical, biological properties and biodegradation behavior of Nile tilapia skin collagen sponge as a biomedical material.

The objective of this study was to explore the effects of dehydrothermal treatment (DHT) and glutaraldehyde (GTA) cross-linking on mechanical, biological properties and biodegradation behavior of Nile tilapia skin collagen sponge fabricated by freeze-drying technology. It was found that the GTA cross-linked collagen sponge exhibited a higher degree of cross-linking in comparison with DHT. The extent of increased tensile strength as well as hygroscopicity indicated that GTA cross-linking was superior to DHT in mechanical properties and liquid absorption, which was attributed to different cross-linking mechanisms. Hygroscopicity assay indicated that cross-linking could improve stability of collagen in solutions. No obvious changes in porosity and blood coagulation time were observed whether cross-linking or not. Results from collagenase biodegradation assay in vitro illustrated that GTA-treated collagen sponge was more resistant to collagenase biodegradation, while DHT exhibited negligible resistance. In addition, photochemical stability of collagen sponge was studied by Fourier transforms infrared spectroscopy (FTIR), which indicated that both cross-linking treatments could not change the backbone structure of collagen. Furthermore, the microstructure of collagen sponge was stable after cross-linking. The highly porous and interconnected structure of collagen sponge was helpful to the absorption of wound exudates, supplement of oxygen and cell proliferation, accompanied with good blood compatibility, which indicated that our fabricated collagen sponge could be applied in biomedical materials field as wound dressings.

A novel calcium-binding peptide from Antarctic krill protein hydrolysates and identification of binding sites of calcium-peptide complex.

Trypsin was used for preparing peptides with high calcium-binding capacity from Antarctic krill. Hydroxyapatite chromatography (HAC), size-exclusion chromatography (SEC), and reversed phase high performance liquid chromatography (RP-HPLC) were used to capture and purify calcium-binding peptides. The peptide sequence was determined to be VLGYIQIR (N- to C-terminal, MW = 960.58 Da), using LTQ Orbitrap XL. According to the results of FTIR and mass spectrometry, chelating site of calcium ions may possibly involve the carbonal or amino groups of Gln, Ile and Arg residues. Molecular dynamic simulation showed the conformation of peptide was markedly varied, and the distance between calcium ion and Gln and Ile residues was changing all the time. However, the distance between calcium ion and carboxyl oxygen of arginine residues was not changed significantly from 2 ns to 100 ns. Identified peptide can be used as a novel calcium supplement.

Isolation and identification of calcium-chelating peptides from Pacific cod skin gelatin and their binding properties with calcium.

A calcium-chelating peptide is considered to have the ability to improve calcium absorption. In this study, Pacific cod skin gelatin hydrolysates treated with trypsin for 120 min exhibited higher calcium-chelating activity. Sequential chromatography, involving hydroxyapatite affinity chromatography and reversed phase high performance liquid chromatography, was used for the purification of calcium-chelating peptides. Two novel peptides with the typical characteristics of collagen were sequenced as GDKGESGEAGER and GEKGEGGHR based on LC-HRMS/MS, which showed a high affinity to calcium. Calcium-peptide complexation was further characterized by ESI-MS (MS and MS/MS) and FTIR spectroscopy. The results showed that the complexation of the two peptides with calcium was conducted mainly at the ratio of 1 : 1. The amino terminal group and the peptide bond of the peptide backbone as well as the amino group of the lysine side chain and the carboxylate of the glutamate side chain were the possible calcium binding sites for the two peptides. Meanwhile, several amino acid side chain groups, including the hydroxyl (Ser) and carboxylate (Asp) of GDKGESGEAGER and the imine (His) of GEKGEGGHR, were crucial in the complexation. The arginine residue in GEKGEGGHR also participated in the calcium coordination. Additionally, several active fragments with calcium-chelating activity were obtained using MS/MS spectra, including GDKGESGEAGE, GEAGER, GEK, EKG and KGE. This study suggests that gelatin-derived peptides have the potential to be used as a calcium-chelating ingredient to combat calcium deficiency.

Nile tilapia skin collagen sponge modified with chemical cross-linkers as a biomedical hemostatic material.

Nile tilapia skin collagen sponges were fabricated by freeze-drying technology and modified with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide in the presence of N-hydroxysuccinimide (EDC/NHS), genipin+PBS, genipin+ethanol, tea polyphenol (TP), nordihydroguaiaretic acid (NDGA) and diphenyl phosphoryl azide (DPPA). Physicochemical and biological properties, micromorphology and compatibility before and after modification were investigated to evaluate collagen sponge as a hemostatic biomedical material. The mechanical property of collagen sponges strengthened after cross-linking. The elongation at break of cross-linked collagen sponges decreased except for EDC/NHS, which was close to that of non-crosslinked. The collagen sponge cross-linked with EDC/NHS exhibited the highest hygroscopicity in comparison with other cross-linkers. The resistance to collagenase biodegradation of collagen sponges after cross-linking strengthened significantly except for NDGA. Collagen sponges cross-linked with EDC/NHS, TP and NDGA maintained high porosity (97-98%), similar to non-crosslinked (98.42%). Collagen sponges could shorten the blood coagulation time. From the variations of the FTIR spectrum pattern and SEM, DPPA could change the secondary structure of collagen and destroy the spongy structure of collagen sponge, which was not suitable for the cross-linking of collagen sponge. Whereas, EDC/NHS was recognized as a perfect cross-linker owing to its excellent properties and porous microstructure. All fabricated collagen sponges were recognized to be biocompatible by the hemolysis assay in vitro. Therefore, collagen sponge modified with EDC/NHS could be used as a perfect biomedical hemostatic material.

The structure property and endothelial protective activity of fucoidan from Laminaria japonica.

Four antithrombotic fucoidan fractions F1, F2, LF1, and LF2 with different monosaccharide composition, molecular weight, and degree of sulfation and sulfate position were prepared from Laminaria japonica by hot water extraction and radical degradation. Their endothelial protective activity and possible action mechanism were studied using both cell- and rat-based models systematically. By comparison, the low molecular weight (LMW) fucoidan LF1 and LF2 were more potent than the medium molecular weight (MMW) fucoidan F1 and F2 in endothelial protection, down-regulation of von Willebrand Factor, CD31 and CD51 expressing endothelial microparticles in adrenalin-induced arterial endothelial injury rats and human umbilical vein endothelial cell system. However, the highly sulfated fucoidan fractions F2 and LF2 were better at inducing FGFR1c-expressing BaF3 cell proliferation in the presence of FGF-1, -2, -7, -8, -9 or -10. These results indicated that the chemical property of fucoidan was correlated to its specific biological activity tested. Therefore, defying fucoidan's monosaccharide composition, molecular weight, and degree of sulfation might be important in developing it into a medicine.

Effects of early enteral nutrition supplemented with collagen peptides on post-burn inflammatory responses in a mouse model.

The effect of early enteral nutrition (EN) supplemented with Alaska pollock skin-derived collagen peptides (CPs) on post-burn inflammatory responses was investigated in a mouse model. Male blab/c mice were randomly assigned to four groups: a sham burn (SB) group, a control group (burn + EN + glycine, BE), a positive control group (burn + EN + glutamine, BEG) and a treatment group (burn + EN + CPs, BEC). Burn-induced increases of serum endotoxin level, and systemic and intestinal concentration of TNF-α and IL-6 were attenuated in BEG and BEC at post-burn day (PBD) 1, 3 and 7 (p < 0.05 vs. BE). Notably, BEC revealed a prominent decrease of the serum endotoxin level, TNF-α and IL-6 as compared to BEG at PBD 7 (p < 0.05). Furthermore, EN supplemented with CPs diminished the phosphorylation of intestinal NF-κB p65 and simultaneously down-regulated the mRNA expression of TNF-α and IL-6 in small intestine (p < 0.05 vs. BE). Also, it demonstrated a comparable effect with glutamine in ameliorating post-burn inflammatory responses in mice with burns. Therefore, CPs could be considered as a potential immunonutrient supplement in EN to improve post-burn outcomes in burn patients.

Effects of heat treatment on the gel properties of the body wall of sea cucumber (Apostichopus japonicus).

The sensory texture of sea cucumber (Apostichopus japonicus) was dramatically affected by heat treatment. In this study, sea cucumbers were heated under different thermal conditions (HSC), and divided into five groups (HSC-80, HSC-90, HSC-100, HSC-110, and HSC-120) according to the heating temperature (from 80 to 120 °C). The changes in texture, moisture, gel structure, and biochemical parameters of the HSC were investigated. With increasing heating time (from 10 to 80 min), the hardness and gel structure changed slightly, and the water activity decreased as the proportion of T21 increased by 133.33, 55.56, and 59.09% in the HSC-80, HSC-90, and HSC-100 groups, respectively. This indicated that moderate heating conditions (below 100 °C) caused gelation of sea cucumbers in HSC-80, HSC-90, and HSC-100 groups. However, as the water activity increased, the hardness declined rapidly by 2.56 and 2.7% in the HSC-110 and HSC-120 groups, with heating time increased from 10 to 80 min. Meanwhile, free hydroxyproline and ammonia nitrogen contents increased by 81.24 and 63.16% in the HSC-110 group; and by 63.09 and 54.99% in the HSC-120 group, as the gel structure of the sea cucumbers decomposed in these two groups. These results demonstrated that, severe heat treatment (above 100 °C) destroyed the chemical bonds, triggered the disintegration of collagen fibers and the gel structure of sea cucumbers, and transformed the migration and distribution of moisture, finally causing the deterioration of the sensory texture of the sea cucumbers.

Characterization of acid- and pepsin-soluble collagen extracted from the skin of Nile tilapia (Oreochromis niloticus).

Acid-soluble (ASC) and pepsin-soluble (PSC) collagen were extracted from the skin of Nile tilapia (Oreochromis niloticus), purified and physicochemically examined. Amino acid content analyses revealed that glycine accounted for approximately one-third of the total amino acid residues. The proline and hydroxyproline contents of Nile tilapia ASC and PSC were 189 residues and 205 residues/1000 residues, respectively, and the rate of proline hydroxylation was found to be 41.8% and 42.0%, respectively. Denaturation temperatures (Td), as measured by an Ubbelohde viscometer, were 35.2°C and 34.5°C, respectively, 6°C lower than that of the type I collagen found in calf skin. In this study, we measured the intrinsic viscosity, circular dichroism (CD) and, X-ray diffraction (XRD), and employed Fourier transform infrared spectroscopy (FTIR) analyses to confirm that the ASC and PSC samples from Nile tilapia skin were native and undenatured, and therefore, maintained their original, intact triple helical structure. Our SDS-PAGE results showed that the extracted ASC and PSC peptides were in their native molecular form; (α1)2α2 (type I collagen). Furthermore, the loose, fibrous, and porous structures, shown in the cross-sections of ASC and PSC, indicate that Nile tilapia skin collagen represents a powerful physical foundation for further use in biomaterial applications.