Imino Acid Content Research Articles

Utilization of Blackmouth Catshark (Galeus melastomus) Skins as an Alternative Source of Gelatin: Extraction and Physicochemical Characterization in Comparison to Porcine Skin Gelatin

The present study investigated the potential use of blackmouth catshark (Galeus melastomus) skins for gelatin production by employing a combined alkaline and acidic process. The yield of dry gelatin was relatively high (13.95%), showing a high protein content (87.80%), but low moisture (10.64%), ash (1.34%) and lipid (0.03%) contents, on a wet weight basis. Fish skin gelatin showed better color properties (>L*, <+b* values) than porcine skin gelatin and exhibited similar gel strength (315.4 g) and higher viscosity (5.90 cP) than the latter (p < 0.05). Although the electrophoretic study revealed that fish skin gelatin was degraded to a lesser extent than its mammalian counterpart, the resulting fish skin gelatin gels melted at a significantly lower temperature (Tm = 21.5 °C), whereas the reverse process (i.e., gelling) also occurred at a lower temperature (Ts = 10.6 °C) and required more time (ts = 29.5 min) compared to porcine skin gelatin gels (Tm = 30.4 °C, Ts = 19.4 °C and ts = 20.7 min). These differences were attributed to the different imino acid content, which was greater in mammalian gelatin (p < 0.05). The results suggested that the skins from blackmouth catshark can be potentially used as an alternative raw material for gelatin production, which will fill the needs of more diverse cultures that do not consume pork- or cow-related products.

Comparison of Structural and Physicochemical Characteristics of Skin Collagen from Chum Salmon (Cold-Water Fish) and Nile Tilapia (Warm-Water Fish).

This study compared collagens from cold-water and warm-water fish for their structural, rheological, and functional properties, and explored their potential applications, aiming to realize the high-value utilization of marine biological resources. To this end, chum salmon skin collagen (CSSC) and Nile tilapia skin collagen (NTSC) were both successfully extracted. Collagens from the two species had different primary and secondary structures, with NTSC having a higher molecular weight, imino acid content, and α-helices and β-turns content. The denaturation temperatures were 12.01 °C for CSSC and 31.31 °C for NTSC. CSSC was dominated by viscous behavior and its structure varied with temperature, while NTSC was dominated by elastic behavior and its structure remained stable with temperature. Both collagens had good oil holding capacity, foaming capacity, and emulsifying activity, but NTSC had better water holding capacity and foaming and emulsifying stability. Their different properties make CSSC more suitable for the preservation of frozen and chilled foods and the production of sparkling beverages, and give NTSC greater potential in biofunctional materials and solid food processing.

Microencapsulation of Lactobacillus plantarum with Improved Survivability Using Pufferfish Skin Gelatin-Based Wall Materials.

To improve the survivability of probiotics, Lactobacillus plantarum was microencapsulated using pufferfish skin gelatin (PSG)-based wall materials by spray-drying. This work investigated the protective effect of three different pH-dependent proteins (sodium caseinate (SC), soy protein isolate (SPI), and whey protein isolate (WPI)) combined with PSG on L. plantarum. The experimental results of spray-drying with an inlet temperature of 120 °C and an outlet temperature of 80 °C, storage at 4 °C for 6 months, simulated digestion, and turbidity indicated that PSG/SC had better stability and encapsulation effects and was more suitable to encapsulate L. plantarum than PSG/SPI and PSG/WPI. The optimum preparation conditions for L. plantarum microcapsules were a PSG/SC mass ratio of 2:1, an SC concentration of 20 g/L, and a cell concentration of 10 g/L. The encapsulation efficiency of the obtained microcapsules was 95.0%, and the survival rate was 94.2% in simulated gastric fluid for 2 h and 98.0% in simulated intestinal fluid for 2 h. Amino acid composition analysis exhibited that the imino acid and aspartic acid contents of PSG were 27.98 and 26.16 g/100 g protein, respectively, which was much higher than commercial bovine gelatin. This characteristic was favorable to the high encapsulation efficiency and stability of microcapsules. In vitro release experiments showed that the PSG/SC microcapsules did not disintegrate in simulated gastric fluid for 2 h but could completely release in simulated intestinal fluid for 2 h, which can maintain the high survivability of L. plantarum in simulated digestion. In general, this study demonstrated that microcapsules using PSG/SC as wall materials can effectively improve the survivability of probiotics and have great potential for application in probiotic products.

Türkiye Kıyılarında Dağılım Gösteren İstilacı Denizkestanesinden (Diadema setosum L., 1778) Kolajen Ekstraksiyonu ve Karakterizasyonu

In the present study, collagen was obtained from tissues of the invasive sea urchin (Diadema setosum) rapidly spread in the Mediterranean Sea. As a result, the yield of collagen isolated from sea urchin was determined to be 23.78±1.33% (dry weight). As a result of SDS-Page analysis, it was determined that it contains (α1)2α2, (Molecular Weight (MA) 124, 114 kDa) and ß chains (MA 245 kDa) similar to calfskin collagen. In the amino acid analysis of collagen, it was determined that the imino acid (proline+hydroxyproline) content was 196.1 residues/1000 residues. The functional bands of amide A (3301 cm-1), B (2924 cm-1), I (1643 cm-1), II (1550 cm-1), and III (1242 cm-1) functional bands were visualized in the FTIR spectrum. These results were like other collagen sources. Invasive sea urchin was used as a source of collagen for the first time in the present study. An alternative source of collagen to mammalian collagen, which is used commercially in many industries such as biomedicine, food and cosmetics, was isolated for the first time from D. setosum. It was proposed that marine collagen can be used as an alternative source of collagen and a functional component in areas including food, cosmetics, and pharmaceutical industries.

Gelatin extraction from chicken skin by conventional and Ohmic heating methods and comparison with commercial halal gelatins

Gelatin extraction from chicken skins using ohmic heating (OH) is a promising application in the food industry. In this study, the effects of OH parameters (electric field (5, 10, 15, and 20 V/cm) and extraction time (1, 3, and 5 h)) on the extraction yield, physicochemical, functional, rheological, thermal, and microstructural properties of chicken skin gelatin were investigated, as well as comparison with conventional extraction and commercial halal gelatins. Chicken skin gelatins obtained with OH-assisted extraction showed higher ash content resulting in more turbidity than commercial gelatins. OH parameters significantly increased the gelatin yield, and 1 h of OH treatment revealed the highest gel strength amongst the electric field applications, conventional extracted, and bovine gelatin. The melting and gelation temperatures of chicken skin gelatins were higher than bovine gelatin and OH treatment increased the thermal stability. The amino acid composition significantly changed with OH treatment, and total imino acid content, relating to the gelation properties, increased. Functional properties, water and oil binding, emulsifying, and foaming, of chicken skin gelatin were significantly higher than commercial gelatins, and OH treatment significantly increased these properties. Overall, OH extraction of gelatin from chicken skins could be a better option for less extraction time, higher extraction yield, better functionality, and higher thermal stability compared to conventional extraction. It was concluded that chicken skin gelatins extracted using OH have properties that can be an alternative to commercial gelatins, but further purification processes are required.

Structural and molecular characterization of collagen-type I extracted from lamb feet.

This study aimed to extract collagen-I from lamb feet (LF) and examine the effects of ultrasound treatment on the structural and molecular characteristics of the collagen. Compared to ultrasonic bath treatment and conventional extraction methods, ultrasonic probe (USP) treatment significantly increased the collagen content of the extract (p<0.05). The electrophoretic profiles confirmed the presence of α- and β-chains, indicating it as type I. Furthermore, X-ray diffraction, Fourier-transform infrared spectroscopy, and circular dichroism spectra analyses revealed that the extraction method did not adversely affect the triple helix structure of the collagen. Moreover, the fibrillar structure of the collagen samples was verified through scanning electron microscopy analyses. Notably, the LF collagen exhibited a high thermal denaturation temperature owing to its elevated imino acid content. The collagen samples exhibited high solubility in acidic pH but low solubility in high salt concentrations. The present findings signified that sonication with USP can effectively enhance the yield of collagen from LF without compromising its quality. PRACTICAL APPLICATION: This study showed that ultrasonication enhanced the collagen concentration without disturbing the integrity of lamb feet collagen. We expect that lamb feet collagen can be used for industrial processes and consumer products thanks to unique product properties.

CHANGES IN THE AMINO ACID COMPOSITION OF GELATIN AFTER TREATMENT OF BOVINE COLLAGEN WITH ENZYME PREPARATION

Recently, more attention has been paid to the study of the amino acid composition of gelatins, which is associated with the quality of the corresponding gels as intermediates for human and animal nutrition. In a brief review, a modification of the general method of acid extraction of collagens for the preparation of gelatins using enzymes (such as papain, actinidin, and others) is considered and the corresponding changes in the amino acid composition of gelatins are discussed. It is clear that there are changes in the content of glycine in gelatins from any collagens, but in all cases the content of glycine is about a third of the content of all amino acids (as in the original collagens). It is important that the content of imino acids (the sum of proline and hydroxyproline, which largely determines the properties of gels) in gelatins from any collagens with the use of all the studied enzymes is much higher than without them. In addition, the content of imino acids in gelatin from the bovine skin of cows with the use of any enzymes is significantly higher than in gelatins from the skin of pigs and fish. This holds true for other key “proteinogenic” amino acids as well. The reverse trend is observed only for a few amino acids: serine, threonine, tyrosine, phenylalanine, the content of which is low in gelatins from any collagens.

Angiotensin-I-Converting Enzyme (ACE)-Inhibitory Peptides from the Collagens of Monkfish (Lophius litulon) Swim Bladders: Isolation, Characterization, Molecular Docking Analysis and Activity Evaluation.

The objective of this study was to isolate and characterize collagen and angiotensin-I-converting enzyme (ACE)-inhibitory (ACEi) peptides from the swim bladders of monkfish (Lophius litulon). Therefore, acid-soluble collagen (ASC-M) and pepsin-soluble collagen (PSC-M) with yields of 4.27 ± 0.22% and 9.54 ± 0.51%, respectively, were extracted from monkfish swim bladders using acid and enzyme methods. The ASC-M and PSC-M contained Gly (325.2 and 314.9 residues/1000 residues, respectively) as the major amino acid, but they had low imino acid content (192.5 and 188.6 residues/1000 residues, respectively) in comparison with collagen from calf skins (CSC) (216.6 residues/1000 residues). The sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) patterns and ultraviolet (UV) absorption spectrums of ASC-M and PSC-M illustrated that they were mainly composed of type I collagen. Subsequently, three ACEi peptides were isolated from a PSC-M hydrolysate prepared via a double-enzyme system (alcalase + neutrase) and identified as SEGPK (MHP6), FDGPY (MHP7) and SPGPW (MHP9), with molecular weights of 516.5, 597.6 and 542.6 Da, respectively. SEGPK, FDGPY and SPGPW displayed remarkable anti-ACE activity, with IC50 values of 0.63, 0.94 and 0.71 mg/mL, respectively. Additionally, a molecular docking assay demonstrated that the affinities of SEGPK, FDGPY and SPGPW with ACE were -7.3, -10.9 and -9.4 kcal/mol, respectively. The remarkable ACEi activity of SEGPK, FDGPY and SPGPW was due to their connection with the active pockets and/or sites of ACE via hydrogen bonding, hydrophobic interaction and electrostatic force. Moreover, SEGPK, FDGPY and SPGPW could protect HUVECs by controlling levels of nitric oxide (NO) and endothelin-1 (ET-1). Therefore, this work provides an effective means for the preparation of collagens and novel ACEi peptides from monkfish swim bladders, and the prepared ACEi peptides, including SEGPK, FDGPY and SPGPW, could serve as natural functional components in the development of health care products to control hypertension.

Comparing Efficiency of Green Methods for Surimi Skin and Bone Gelatin Extraction

Globally, the surimi processing industry produces a large amount of by-products in the form of head and viscera, skin, bones, scale, etc. The aim of this study was to assess the combined biomass of pink perch skin and bones obtained from the surimi industry as a potential source of raw material for gelatin production and identify a green method of gelatin extraction by comparing four green processes. Four green gelatin extraction processes were compared for their gelatin extraction efficiency. Among the four processes, process 1 and process 2 comprised of two-step extraction viz pre-treatment with NaCl and extraction with hot water. Process 3 and process 4 comprised of single-step wherein pre-treatment and extraction were done simultaneously with acidic water using acetic acid. The gelatin extraction efficiency was determined based on the yield and L-hydroxyproline content of the extracted gelatin. Further, the extracted gelatin was characterized for their proximate and amino acid composition. The acetic acid based single-step method was found to be more efficient in the extraction of gelatin than the NaCl pretreatment method. The gelatin extracted with this method had a higher yield (4.2%), protein content (79.6%), and imino acid (27.3%) content than the NaCl pretreatment method, which had 1.51% gelatin yield, 48.1% protein content, and 13.1% imino acid content. The results suggested that the single-step extraction method can be effectively utilized for the extraction of gelatin from pink perch skin and bones combined biomass. This study provides a method for the valorization of the surimi industry by-product into a high value product with potential application in various industries.

Swim Bladder of Farmed Totoaba macdonaldi: A Source of Value-Added Collagen

Finding strategies to use the swim bladder of farmed totoaba (Totoaba macdonaldi) is of the utmost need to reduce waste. Fish swim bladders are rich in collagen; hence, extracting collagen is a promising alternative with benefits for aquaculture of totoaba and the environment. The elemental biochemical composition of totoaba swim bladders, including their proximate and amino acid compositions, was determined. Pepsin-soluble collagen (PSC) was used to extract collagen from swim bladders, and its characteristics were analyzed. Alcalase and papain were used for the preparation of collagen hydrolysates. Swim bladders contained 95% protein, 2.4% fat, and 0.8% ash (on a dry basis). The essential amino acid content was low, but the functional amino acid content was high. The PSC yield was high, at 68% (dry weight). The amino acid composition profile, electrophoretic pattern, and structural integrity analyses of the isolated collagen suggested it is a typical type-I collagen with high purity. The denaturalization temperature was 32.5 °C, probably attributable to the imino acid content (205 residues/1000 residues). Papain-hydrolysates (≤3 kDa) of this collagen exhibited higher radical scavenging activity than Alcalase-hydrolysates. The swim bladder from the farmed totoaba could be an ideal source to produce high-quality type I collagen and may be considered an alternative to conventional collagen sources or bioactive peptides.

Extraction and Characterization of Pepsin- and Acid-Soluble Collagen from the Swim Bladders of Megalonibea fusca.

There is a growing demand for the identification of alternative sources of collagen not derived from land-dwelling animals. The present study explored the use of pepsin- and acid-based extraction protocols to isolate collagen from the swim bladders of Megalonibea fusca. After extraction, these acid-soluble collagen (ASC) and pepsin-soluble collagen (PSC) samples respectively were subjected to spectral analyses and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) characterization, revealing both to be comprised of type I collagen with a triple-helical structure. The imino acid content of these ASC and PSC samples was 195 and 199 residues per 1000 residues, respectively. Scanning electron microscopy demonstrated that samples of freeze-dried collagen exhibited a compact lamellar structure, while transmission electron microscopy and atomic force microscopy confirmed the ability of these collagens to undergo self-assembly into fibers. ASC samples exhibited a larger fiber diameter than the PSC samples. The solubility of both ASC and PSC was highest under acidic pH conditions. Neither ASC nor PSC caused any cytotoxicity when tested in vitro, which met one of the requirements for the biological evaluation of medical devices. Thus, collagen isolated from the swim bladders of Megalonibea fusca holds great promise as a potential alternative to mammalian collagen.

Physicochemical and Fibril Formation Properties of Pufferfish (Takifugu obscurus) Skin Collagen from Solvent Extraction in Different Conditions.

Acid-solubilized (ASC) and pepsin-solubilized collagen (PSC) extracted at 4 °C (ASC-4 and PSC-4), 12 °C (ASC-12 and PSC-12), and 20 °C (ASC-20 and PSC-20) from the skin of farmed pufferfish (Takifugu obscurus) was characterized by SDS-polyacrylamide gel electrophoresis (SDS-PAGE), Fourier-transform infrared spectroscopy (FTIR), and fibril-forming tests. The results indicate that extraction at 12 °C can effectively improve the extraction efficiency of natural collagen compared with extraction at 4 °C. However, extraction at 20 °C results in a decrease in molecular integrity, thus, inducing the resultant collagen to degrade or even lose fibril-forming ability. Transmission electron microscope (TEM) images revealed that ASC-4, PSC-4, ASC-12, and PSC-12 can assemble into fibrils with D-periodicities, and ASC-20 associated into molecular aggregates alongside partial D-banded fibrils, while no well-defined fibrils were observed in PSC-20. Scanning electron microscope (SEM) analysis confirmed the well-defined fibril morphologies of ASC-4, PSC-4, ASC-12, and PSC-12 with imino acid contents between 190.0 and 197.8 residues/1000 residues. The denaturation temperature of ASC-4, PSC-4, ASC-12 and PSC-12 was 30.0, 27.6, 25.9 and 22.7 °C, respectively. This study indicates that ASC and PSC extracted at 4 °C and 12 °C could be alternatives to terrestrial collagens for industrial applications.

Gelatins and antioxidant peptides from Skipjack tuna (Katsuwonus pelamis) skins: Purification, characterization, and cytoprotection on ultraviolet-A injured human skin fibroblasts

For full use of Skipjack tuna (Katsuwonus pelamis) canning by-products, gelatins (STG) were extracted from tuna skins using acid (STG-A), enzyme (STG-E) and hot water (STG-H) methods with yields of 65.30 ± 1.56%, 39.83 ± 1.61%, and 50.97 ± 1.44%, respectively. Due to the high imino acid contents (228, 216, and 213 residues/1000 residues for STG-A, STG-E, and STG-H, respectively), STG-A showed the highest transparency and gel strength properties. Amino acid analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), ultraviolet (UV) and Fourier transform infrared spectroscopy (FTIR) analysis confirmed that STG-A, STG-E, and STG-H kept the main structure of type I collagen, but enzyme and hot water extraction methods showed much stronger hydrolysis ability on α and β chains. Moreover, neutrase hydrolysate (STG-AH) of STG-A showed the highest 1,1-diphenyl-2-picrylhydrazyl radical (DPPH•) scavenging activity and the fraction STG-AH-І (<3.5 kDa) from STG-AH prepared by ultrafiltration could significantly protect human skin fibroblasts (HSFBs) against ultraviolet-A (UVA) injury. Furthermore, nineteen peptides with high antioxidant activity were purified from STG-AH-І and identified. These results suggested that STG-AH and its derived antioxidant peptides could serve as potential ingredients applied in health benefiting products for preventing UVA injury.

Extracted pepsin of trout waste and ultrasound-promoted method for green recovery of fish collagen

Collagen type I is a prominent protein in animal tissues. This structural protein can be commercially derived from fish processing waste without any health risk. The current study aimed to investigate the efficacy of rainbow trout pepsin and the ultrasound-promoted method on collagen recovery. Pepsin extract was purified from rainbow trout stomach in order to use in collagen extraction from wasted yellowfin skin through ultrasound technique in five durations (0, 5, 10, 15, and 20 min). The 15 min ultrasound treated pepsin soluble collagen indicated the highest recovery yield (23.8%) as well as the highest imino acid content (18.2%). The structure of type I collagen was observed in the SDS-PAGE pattern of collagens and no structural change occurred during the extraction process. The presence of the helical structure in collagen samples was confirmed by UV and FTIR spectra. The ultrasound cavitation advanced the viscosity of collagens and resulted in excellent solubility in acidic environments and lower salt concentrations. Ultrasound-treated samples suggested superior water holding capacity along with emulsifying, and foam attributes. The improved gel strength of collagens was parallel with increasing the time of ultrasound up to 15 min. Free radicals scavenging ability and ferric reducing power of collagens were positively stimulated by increasing the time of the ultrasound up to 15 min. Therefore, this study contributes to the development of green technology and the promotion of by-product utilization for collagen recovery as a potential practical protein in biomaterial, wound dressing, drug delivery, food, and cosmetics products.

Combined Effects of Defatted Hydrolyzed Collagen from Salmon Skin and Vitamin C on Proliferation and Migration of Human Fibroblast Cell

Skin injury causes fibroblast dysfunction and lowers collagen production. Safe, functional ingredients such as vitamin C (Vit C) and fish hydrolyzed collagen (HC) have been used to alleviate this problem. Defatted HC from salmon (Oncorhynchus nerka) skin could be a potential functional ingredient with skin nourishment activity. This study aimed to investigate the combined effects of HC and Vit C on the proliferation and migration of human dermal fibroblast (HDF). Molecular weight ranging from 102 Da to 10,175 Da and high imino acid content were found in HC. HC (0–800 µg/mL) or vitamin C (Vit C) (0.01–100 µg/mL) was applied for HDF treatment. Higher cell proliferation was found by adding HC at 50 µg/mL or Vit C at 0.01 µg/mL compared to the control and those treated with both compounds at other levels (p &lt; 0.05). Cells treated with HC (50 µg/mL) combined with Vit C (0.01 µg/mL) (HC+Vit C) showed higher proliferation, migration, and lamellipodia formation of HDF cells than those treated with HC or Vit C alone. Moreover, all the samples tested could stimulate the proliferation and migration of HDF cells via FAK/Akt and ERK/p38 MAPK signaling pathways. Thus, HC combined with Vit C could be a promising functional ingredient for skin nourishment and would healing.

Comprehensive physical and chemical characterization highlights the uniqueness of enzymatic gelatin in terms of surface properties

Abstract To shorten the long process of conventional alkaline extraction of gelatin, an enzyme-aided method was demonstrated, which was simpler, more effective, and environmental friendly. The main properties of enzymatic gelatin and conventional alkaline gelatin were comprehensively analyzed, including rheological properties, foaming properties, emulsifying properties, water absorption capacity, and thermal stability. It was found that enzymatic gelatin exhibits neutral isoelectric points of 7.4–7.8, higher imino acid content (21.85%, on average), and excellent emulsifying properties, thermal stability, and foaming properties (181%, on average), but lower water absorption properties (5.8 g‧g−1, on average). These findings would be beneficial for the future applications of enzymatic gelatin.

Gelatin From Cartilage of Siberian Sturgeon (Acipenser baerii): Preparation, Characterization, and Protective Function on Ultraviolet-A-Injured Human Skin Fibroblasts

For full use of the by-products during Siberian sturgeon (Acipenser baerii) processing, gelatin was extracted from the cartilages using the hot water method, and its physico-chemical properties and protective function on ultraviolet-A injured human skin fibroblasts (HFSBs) were measured. Using single-factor and orthogonal experiments, the conditions for extracting gelatin from Siberian sturgeon cartilage were optimized as extraction time of 7 h, pH 9, material-to-liquid ratio (g/ml) of 1:5, and temperature of 45°C. The prepared gelatin (TCG) with a yield of 28.8 ± 1.53% had Gly (307 residues/1,000 residues) as the major amino acid and contained a lower amount (214 residues/1,000 residues) of imino acids than that (227 residues/1,000 residues) of pigskin gelatin (PSG). Sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE), ultraviolet spectrum, and infrared spectroscopy analysis indicated that TCG had the main spectral characteristics of fish gelatin and contained α chains (α1 and α2 chains) and β chain of type I collagen, but its structural stability was lower than that of PSG due to its low content of imino acids, which induced the smaller molecular bands observed in the SDS-PAGE pattern. TCG exhibited lower water content, gel strength, emulsion stability index, foam capacity, foam stability, and water-holding capacity but higher ash content, transmittance, emulsion activity index, and fat-binding capacity (P &amp;lt; 0.05). Moreover, TCG could significantly protect HFSBs against ultraviolet-A injury by enhancing the activity of superoxide dismutase, catalase, and glutathione peroxidase to scavenge excess reactive oxygen species and decrease the content of malondialdehyde. Therefore, gelatin from Siberian sturgeon cartilages could act as promising candidates when applied in health-promoting products against ultraviolet-A injury.

Impact of extraction condition on the yield and molecular characteristics of collagen from Asian bullfrog (Rana tigerina) skin

The present study is the first report on collagen extraction as acid-soluble collagen (ASC) and pepsin-soluble collagen (PSC), which could maximize the exploitation of Asian bullfrog (Rana tigerina) skin as an alternative collagen material in food and pharmaceutical fields. Extraction methods for ASC and PSC from Asian bullfrog skin were developed using different concentrations of acetic acid (0.50, 0.75, and 1.00 M) and pepsin (1.00, 2.00, and 3.00% [w/w]). PSCs exhibited a higher extraction yield (22.59%–28.30%) and recovery (22.48%–31.12%) than ASCs. An electrophoretic study revealed that collagens possessed type I collagen. ASC with 0.75 M acetic acid (ASC-0.75) and PSC with 3.00% (w/w) pepsin (PSC-3.00) were selected and analysed on their solubility, molecular characteristics, and amino acid composition. A better solubility with a higher isoelectric point was observed for PSC-3.00 than ASC-0.75. Fourier transform infrared- and circular dichroism-spectra revealed a high-interacted compact structure with a triple helical-structure of the collagen peptides, respectively. A similar amino acid profile with a high imino acid content was observed. Therefore, collagens from Asian bullfrog skin were successfully extracted, where the optimized conditions provided a high yield with less adverse effects on collagen properties and molecular characteristics.

Physicochemical properties of gelatin produced from Nile tilapia skin using chemical and fermentation pretreatments

In this study, we aimed to verify the effectiveness of fermentation as a pretreatment in Nile tilapia (Oreochromis niloticus) skin gelatin production and to assess its effects on the extracted gelatin. Chemical-gelatin (CG) and fermentation-gelatin (FG) were extracted using hot water from tilapia skin after immersion in chemical reagents (sodium hydroxide and butanol) and after fermentation with Bacillus velezensis FEL-BM21, respectively. FG presented a higher recovery (27.40%), yield (49.99%), and imino acid (proline and hydroxyproline) content (177.17 ± 0.35 residues/1000 residues) than CG, but had a lower molecular weight. Fourier transform infrared and circular dichroism spectroscopy confirmed that the collagen was denatured, and scanning electron microscopy revealed that FG had a more continuous filamentous structure than CG. Furthermore, except for transmittance (66.19% at 450 nm and 86.36% at 620 nm), FG exhibited higher gel strength (492.81 g), gelling point (28.93 °C), and melting point (18.33 °C) than CG. These findings suggest that fermentation can be used to treat gelatin raw materials without negatively affecting the structure of gelatin. Moreover, fermentation has potential industrial applications as an alternative to chemical treatment.

Structural and emulsion stabilization comparison of four gelatins from two freshwater and two marine fish skins

This study analyzed the structural and emulsion stabilization properties of two freshwater and two marine fish skin gelatins: Chinese longsnout catfish skin gelatin (CLCSG), silver carp skin gelatin (SCSG), salmon skin gelatin (SSG), and Alaska pollack skin gelatin (APSG). Their gel strengths (Bloom values) were: 361 ± 1 (SCSG) > 253 ± 4 (CLCSG) > 69 ± 1 (SSG) > 36 ± 2 (APSG). Higher molecular weights and α/β subunit contents of gelatins might induce higher gel strengths. Both creaming and droplet stability were completely the same to the contents of imino acids, β-sheet percentages, and β-turn percentages, whereas they were completely the opposite to random coil percentages. The emulsion stabilization mechanisms involved an “fish skin source – protein chemical composition – protein secondary structure – protein functional properties – emulsion stability” route. This study provided useful knowledges for gelatin science and for the comprehensive utilization of aquatic by-products in gelatin industry.