Tuna Skin Research Articles

Extraction and characterisation of gelatine from yellowfin tuna skin pretreated with a eutectic solvent

The accumulation and management of waste generated during the processing of seafood products is one of the major current challenges in the fishery industry. Among these residues, fish skin stands out for its high collagen content, from which high-quality gelatine can be obtained. However, conventional methods for gelatine extraction are time-consuming and complex processes that involve the use of strong acidic and alkaline solutions, leading to serious environmental concerns. This research studied the use of a eutectic solvent, formed by two safe and environmentally friendly compounds such as sodium acetate trihydrate and urea, to pretreat the skin of yellowfin tuna before the extraction of gelatine. Two different times of pretreatment were tested, and the subsequent extraction was carried out in warm water, resulting in much higher yields of gelatine (0.3 g/g wet fish skin) than previous studies. Additionally, using FT-IR analysis and amino acid profiling, it was observed that the pretreatment time did not significantly affect the structure or composition of the gelatine. However, some variation was found in its molecular weight distribution and therefore in its rheological properties: with an increase in the pretreatment time, both the molecular weight and the storage modulus of the gel also increased, as well as the gelation and melting temperatures. This contribution offers a simplified process that reduces environmental impact and provides the opportunity to tailor the final product.

Particle size analysis of yellowfin tuna (Thunnus albacares) skin collagen powder using papain-soluble collagen method with varying NaCl concentrations: an experimental laboratory

ABSTRACTIntroduction: The skin of yellowfin tuna (Thunnus albacares) contains high protein, which could potentially be a halal collagen product. Collagen extraction using the papain-soluble collagen method has the advantage of producing a higher collagen yield compared to the acid method. Particle size, one of the physical properties of collagen, plays a crucial role in its efficacy in dentistry. This study aims to analyze the particle size of collagen powder synthesized from Thunnus albacares skin using the papain-soluble collagen method, with varying concentrations of NaCl. Methods: Type of research is an experimental laboratory. Thunnus albacares skin was synthesized by chopping, cleaning, and soaking in a 0.1 M NaOH solution. The extraction process used the enzyme papain and 0.5 M of acetic acid. Samples were divided into four groups, each with different concentrations of NaCL: 0, no NaCL;, 0.9 M NaCl, 1.3 M NaCl, and 1.7 M NaCl. After centrifugation, the samples were freeze-dried. The particle size of collagen powder was measured using a Particle Size Analyzer test tool. The data collected was then analyzed using the Mann-Whitney test. Results: Particle size distributions are as follows: K group (3.36 nm), P1 (1.842 nm), P2 (3.36 nm), and P3 (10.12 nm). There is a significant difference in groups K-P1 and P3, P1-P2 and P3, and P2-P3 (p<0.05). However, there is no significant difference in groups K-P2 (p>0.05). Conclusion: Particle size of this research produced nano-sized collagen powder, with the lowest particle size observed in the 0.9 M NaCl group, measuring at 1.842 nm. The particle size increased in the group without NaCl and in the 1.3 M NaCl group at 3.36 nm, and reached the highest value in the 1.7 M NaCl group at 10.12 nm.

Structural, Functional, and Bioactive Properties of Sulfated Polysaccharides from Skipjack Tuna Skin as a Function of Drying Techniques.

The study aims to investigate the impact of various drying techniques on the quality of sulfated polysaccharides (SP) extracted from Skipjack tuna (Katsuwonus pelamis) skin. Three drying methods, namely microwave drying (M-KPP), freeze-drying (F-KPP), and hot air drying (HA-KPP), are examined. The chemical and monosaccharide compositions of SP are significantly affected by the drying methods. The extraction yields for M-KPP, F-KPP, and HA-KPP are 3.30%, 3.11%, and 2.50%, respectively (P<0.05). Additionally, HA-KPP, with 10.67% moisture content, exhibits the lowest moisture level among the dried samples (P<0.05). Furthermore, the structural properties of SP remain consistent across different drying methods, as indicated by FTIR, XRD, and DSC analyses. F-KPP demonstrates the highest antioxidant properties. The functional and antimicrobial activities of SP are significantly influenced by the drying technique, with hot air drying resulting in increased foaming capacity and microwave drying showing enhanced antimicrobial activity. In conclusion, the findings demonstrate that the functionality and bioactivity of SP from tuna skin are greatly influenced by the drying technique employed, suggesting that the selection of the optimal method should be tailored to the desired properties of the SPs and given careful consideration.

Characterization of collagen and its hydrolysate from southern bluefin tuna skin and their potencies as DPP-IV inhibitors

Collagen-derived peptides have been gaining interest due to their potential to act as DPP-IV inhibitors, which are considered to have antidiabetic effects. This study focused on extracting type I collagen from discarded southern bluefin tuna skin, confirming its structure and properties, and then measuring the ability of its hydrolysates to act as DPP-IV inhibitors. First, type I collagen was purified from southern bluefin tuna skin, and the constituent subunit was found to contain the α3(I) chain. Next, enzymatic hydrolysates were prepared, and their DPP-IV inhibitory activity measurements were examined and compared. Collagenase hydrolysate showed the highest DPP-IV inhibitory activity (71.8 ± 0.3 %), and considering digestive degradation, collagenase-pepsin-trypsin hydrolysate was prepared and separated into fractions via anion exchange chromatography, cartridge column, and HPLC. Notably, the 70 % methanol eluted fraction separated via cartridge column was found to have an IC50 of 0.26 ± 0.01 mg/ml. Subsequently, a novel peptide GPSGGGYDV with the highest DPP-IV inhibitory activity (IC50 value 82±0.0 µM) was purified from this fraction and found to be a competitive inhibitor of DPP-IV. This is the first study to investigate the DPP-IV inhibitory potential of type I collagen hydrolysate from southern bluefin tuna.

Karakteristik Mutu Sabun Cair Alami Komposit Dengan Penambahan Kolagen Kulit Ikan Tuna (Thunnus albacores)

This study aims to analyze the quality of natural liquid soap extracts of cucumber (Cucumis sativus L.) and lime (Citrus aurantifolia S.) with the addition of tuna skin collagen (Thunnus albacores), describe the level of preference (hedonic) of panelists towards natural liquid soap and determine the selected product. This study consisted of two stages: the preliminary, which aims to obtain collagen. The main résearch aims to determine the formula of natural liquid soap with collagen concentration treatment of 1%, 3%, and 5% and characterize the quality of natural liquid soap. The parameters tested included collagen yield and chemical characteristics, which were analyzed descriptively, the hedonic value of soap, which was analyzed using Kruskal Wallis, and viscosity of liquid soap designed with RAL and analyzed with ANOVA and Duncan. The selected product was determined using Bayes' test, which was then tested for pH, foam stability, free fatty acids, and Total Plate Count (TPC), which were analyzed descriptively. The results showed that collagen yield is 5,021%, protein content is 76,89%, water content is 4,05%, fat content is 0,57%, and ash content is 0,20%. The results of the Kruskal Wallis test show that natural liquid soap with the addition of collagen has a significant effect on aroma, viscosity, and appearance but has no effect on the impression during its use, the imression after use, and the amount of foam. The ANOVA test shows that collagen has a significant effect on the viscosity of natural liquid soap. The characteristics of the selected natural liquid soap pH 7,41, foam stability 83,33%, free fatty acids 2,5%, and ALT 3,4×103, all of which meet the requirements of SNI (1996).

Ultrasound-Mediated Technique for Facilitating Collagen Recovery from Yellowfin (Thunnus albacares) Skin: Insight into the Structure, Functional and Antioxidant Specification

ABSTRACT The highest yield (34%) and imino acid (18.7%) of collagen were obtained from yellowfin tuna (Thunnus albacares) skin using 20 min ultrasound. The collagen was identified as type I collagen according to the results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and its structure remained intact, proved by ultraviolet spectroscopy (UV) and fourier transform infrared spectroscopy (FTIR). Collagen solubility was superior in acidic and low salt environments. Ultrasound cavitation for 20 min improved collagens’ emulsifying (EAI: 78.8 m2/g and ESI: 110.3 min) and foam properties (FA: 151.8% and FS: 133.3%) and water holding capacity (51.9%) by enhancing internal hydrophobic interactions and surface hydrophobicity. 20 min ultrasound resulted in desirable DPPH (61.1%) and ABTS (53.1%) radical scavenging and ferric-reducing antioxidant power (0.078 ABS).

Characterization and evaluation of antioxidant properties of skipjack (Katsuwonus pelamis) tuna skin gelatin Hydrolysate

The present society is extremely conscious of the lifestyle-related ailments and the serious consequences that result from an unhealthy diet and lifestyle. A holistic approach to incorporating nutraceuticals into one's lifestyle has become the current trend. Protein hydrolysates with antioxidant potential have gained critical commercial importance. Protein hydrolysates are produced from food industrial remnants in order to reduce production costs and achieve sustainable resource management. The food industry generates a greater proportion of waste from fisheries, and with the consistent requisite for fish-based products, utilisation of remnants remains a critical concern. Fish hydrolysates have been discovered to have exceptional physical, chemical, and functional properties. It is noteworthy that fish hydrolysates have strong antioxidant properties against reactive oxygen species. In the current research, gelatin prepared from the processing waste of skipjack tuna (Katsuwonus pelamis) skin were hydrolysed by proteolytic enzyme papain. The obtained gelatin hydrolysate showed ~33% degree of hydrolysis (DH). The surface-active properties of Skipjack tuna skin gelatin hydrolysate (SSGH) revealed pronounced foaming and emulsion properties at low protein concentrations. SSGH demonstrated higher antioxidant efficacy by in vitro antioxidant assays. In conclusion, the resulting hydrolysates demonstrated remarkable antioxidant potential, as well as great development prospects for a variety of applications. Further studies with regard to isolation, purification and identification of and peptide sequences improve the quality of functional foods.

Physicochemic characteristics and antibacterial activity of solid soap with additional of collagen from tuna skin (Thunnus sp.)

Collagen is a long-chain protein compound composed of the amino acids alanine, arginine, lysine, glycine, proline, and hiroxyproline and from fishery waste, like a fish skin. This Research aims to determine the physical and chemical characteristics as well as the antibacterial activity of solid soap with the addition of tuna skin collagen and uses an experimental method (experimental) with several treatments of adding collagen. The results showed that the physical and chemical characteristics of solid soap were stability foam stability from 16.55 mm to 84.61 mm, water content ranging from 21.66 - 27.79%, pH 10.69 - 11.78, and free alkaline 1.22 - 1.92, Antibacterial activity against Staphylococcus aureus, was found in sample A2 with a diamater inhibitory zone is of 20.5 mm (very strong).

Community Partnership Program of Making Liquid Organic Fertilizer from Fish Waste in Pedungan Village, Denpasar

The concept of implementing Blue Economy is highly expected in this activity. The implementation of Zero Waste of Community Partnership Program conducted at Ni Wayan Sarimi’s household industry turned waste into Liquid Organic Fertilizer. The purpose is to provide Liquid Organic Fertilizer Manufacturing Technology in managing tuna skin waste. The method began with partner’s application to Service Team, doing examination and interview by the team to find out the partner’s problems. The team conducted Counseling related to Liquid Organic Fertilizer Production, Packaging, and Marketing and did practicing three (3) times. The results include making Liquid Organic Fertilizer properly, having new products with good packaging to be sold, publishing activities on Electronic Media or Journals, and uploading activities videos on YouTube.

Evaluation of the Physicochemical and Techno-functional Properties of Gelatin Extracted from Fish Processing Waste

The current research was completed at the Indian Council of Agricultural Research - Central Institute of Fisheries Technology (ICAR-CIFT), Cochin, Kerala, India from August 2021 to August 2022 as a modified thermal extraction protocol for deriving gelatin from processing waste of skipjack tuna (Katsuwonus pelamis) skin. The study evaluated the effect of chemical composition and molecular weight contributing to the techno-functional attributes of the resulting gelatin. In the present study, we followed warm water-coupled NaCl pre-treatment to reduce the lipid content of the extracted gelatin. The extracted gelatin was characterized for Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The amount of gelatin extracted from the fish skin was 9.30±0.22%. The protein pattern of extracted gelatin on SDS-PAGE was identical to commercial grade gelatin, which implies the purity of extracted gelatin is comparable to that of commercial one. The physicochemical and functional properties were evaluated and pose remarkable techno-functional properties. Therefore, fish processing skin waste of skipjack tuna could be effectively exploited for the preparation of commercial gelatin. The extraction protocol remains environment friendly and this approach remains optimal for food technological applications. The effective exploration contributed to nutritional benefits, technological, functional, and biological functionalities for a large fraction of applications in the area of food technology, nutraceuticals, pharmaceutics, and numerous others as a future line of research.

Modification of gelatin from tuna skins by green tea polyphenols

This paper presents the result of study on the effect of modifying conditions on properties and structure of tuna skin gelatin by using green tea polyphenols. The results showed that gelatin modified by green tea polyphenols changed its gel strength, degree of cross-linking, molecular weight and gel structure. The appropriate parameters to modify gelatin by using green tea polyphenols which indicated the best mechanical properties were determined as follows: temperature of 40oC in 40 minutes, polyphenol content of 20 mg/g gelatin and gelatin solution of 20%. As a result, modified gelatin showed a decrease in solubility, an increase in cross-linking degree (16.7%), molecular weight (55÷72 kDa) as well as a larger protein structure in comparison with the natural gelatin. The IR spectrograph of the modified gelatin did not show any evidence of forming new functional groups, only an apparent change in the absorption of infrared spectroscopy at the peak of the amide B region was found. The dried modified gelatin became insoluble in hot water.

Antioxidant Activity and Potential Bioactive Peptides from Skin Protein Hydrolysate of Yellowfin Tuna (&lt;I&gt;Thunnus albacares&lt;/I&gt;)

Highlight Research Immersion of tuna skin using NaHCO3 at low temperatures effectively reduces the fat content. The DH value, MW, and amino acid composition are in line with the antioxidant activity of tuna skin hydrolysate. The ABTS method showed the highest antioxidant activity in tuna skin hydrolysate. FPH of tuna skin shows functional group characteristics and amino acid composition that are similar to collagen hydrolysate products. FPH of tuna skin has the potential as a source of antioxidants, ACE inhibitors, and antifibrinolytics. Abstract The tuna fillet industry produces abundant skin by-products with high protein, which has the potential as a raw material for fish protein hydrolysate (FPH) for a source of bioactive peptides. Exploration of bioactive peptides from fish skin is generally from hydrolyzed gelatin and collagen. The study aimed to produce FPH directly from tuna skin as an antioxidant and identify potential bioactive peptides. The research began by defatting using multiple concentrations of NaHCO3 and immersion times. The defatted fish skin was produced as FPH by enzymatic hydrolysis method using different papain enzyme concentrations and hydrolysis times. The selected treatments were assessed for antioxidant activity and bioactive peptides. The results showed that the defatting process using a 0.50% NaHCO3 for 30 minutes generated the highest reducing fat content in value was 80.53%. Using papain enzyme gave a significant effect on the DH of FPH, with value was 29.72-67.64%. Therefore, FPH obtained from different concentrations for 4 hours was chosen to characterize the antioxidant activity and bioactive peptide. Hydrolysis using 5% enzyme papain showed the highest antioxidant activity of DPPH, ABTS, and reducing power with values of 0.965 mg/mL, 0.495 mg/mL, and 0.415 absorbances, respectively. FPH possesses a molecular weight of 10.15-48.50 kDa. Functional groups detected were amides A, B, I, II, and III. Glycine, proline, and arginine became amino acids dominant of FPH. Based on the diversity of biopeptide compounds, several biological function candidates were detected, namely antioxidants, ACE inhibitors, and antifibrinolytics which have the potential to be used as nutraceutical products.

In silico and in vitro assessment of yellowfin tuna skin (Thunnus albacares) hydrolysate antioxidation effect

The protein hydrolysate that contains bioactive peptides of yellowfin tuna (Thunnus albacares) skin collagen with antioxidant activity has been successfully studied by using in silico and in vitro assays. We found that using the in silico assessment, the antioxidant peptides can be found from the precursor (type I α1 and α2 collagen of yellowfin tuna). Applying papain as a protease will also provide the greatest degree of hydrolysis for antioxidative peptides. The highest peptide rank peptides sequence such as Pro-Trp-Gly (PWG), Pro-His-Gly (PHG), His-Leu (HL), Ile-Arg (IR), Ala-His (AH), Glu-Leu (EL) that predicted using papain in silico. Molecular docking analysis showed all peptides derived from yellowfin tuna have hindered the substrate to access the active site of myeloperoxidase (MPO). Interestingly, the substitution of the amino acid from His (PHG, 7.1 kcal/mol) to Trp (PWG, 8.0 kcal/mol) has increased the affinity of the peptide towards MPO. They have antioxidative activities used in silico approach to MPO enzyme. We also confirm the in vitro assays for the protein hydrolysate after proteolysis using papain. The concentration and hydrolysis time will give influence the degree of hydrolysis, and antioxidant activities (P < 0.05). In conclusion, hydrolysate protein of type I α1 and α2 collagen from yellowfin tuna produced by papain hydrolysis has the potential to be used in food, active packaging material until health applications..

Bionic gradient flexible fish skin acts as a passive dynamic micro-roughness to drag reduction

Fish skin has a unique biological feature that hard fish scales are embedded in a flexible dermis layer and covered by a viscoelasticity mucus or compliant epidermis layer. Therefore, the entire fish skin system can act as a dynamic resilient energy-absorbing coating with micro-roughness to absorb external turbulent pulsations. The microscopic morphology, arrangement of fish scales, and mechanical characteristics of tuna skin inspired the extraction and fabrication of the bionic gradient flexible fish skin (BGFFS) model. First, BGFFS was fabricated by the three-dimensional (3D) printing method, spraying and casting process. Then, the 3D morphology of the bionic fish skin was characterized. The results indicated that the BGFFS exhibited good morphology of fish scales and spatial gradient mechanical properties like fish skin. Moreover, the experimental results in a circulating water tunnel showed that the BGFFS had excellent drag reduction performance in a turbulent flow. When the Reynolds (Re) number was 6.8 × 104, the maximum drag reduction ratio could reach 13.8 %. The drag reduction mechanism was analyzed by the computational fluid dynamics (CFD) method, and the energy-absorbing effect of the BGFFS was measured by the polyvinylidene fluoride (PVDF) piezoelectric film. In this experiment, the maximum voltage signal reached 0.448 V. The drag reduction mechanism of the BGFFS was that the rolling friction caused by vortexes replaced sliding friction. In the meantime, the BGFFS could absorb the micro disturbances in a turbulent flow. These findings can serve as a foundation for an in-depth analysis of the hydrodynamic performance of fish as well as a new inspiration for drag reduction and antifouling.

Effects of edible coatings of chitosan - fish skin gelatine containing black tea extract on quality of minimally processed papaya during refrigerated storage

Papaya fruit is a climacteric fruit that undergoes physical and chemical changes very quickly during storage. The edible coating is one method that can extend the shelf life of minimally processed fruit such as papaya. To improve the effect of edible the mechanical properties and functional value of edible coatings, black tea was added. The research aims to evaluate the application of edible coating from fish gelatin-chitosan enriched with black to the physicochemical characterization of the minimally processed papaya.The research was conducted through the extraction of tuna skin gelatin using the acid-base method. Furthermore, the preparation of edible coating solutions based on chitosan, gelatin, glycerol, and black tea with different concentrations of 0%, 5%, 10%, and 15%. The edible coating solution that has been obtained is then applied to minimally processed papaya fruit and stored for 1, 4, 7, and 10 days to determine the effect of edible coating on the physical, chemical and microbiological characteristics of papaya fruit.The results showed that the addition of black tea extract concentrations of 0%, 5%, 10%, and 15% had no significant effect on the color change of the resulting solution (p > 0.05), while the viscosity and pH occurred during the addition of the concentration to the coating solution which could eat (p < 0.05). Edible coating can suppress the decrease in weight loss and papaya texture. The chemical properties of minimally processed papaya such as pH, total dissolved solids, total titrated acid, antioxidant activity, and total carotenoids increased due to the ripening process and the effect of dissolved substances contained in the edible layer during storage. Total plate count (TPC) showed that edible coating treatment with the addition of black tea extract was able to suppress microbial growth during storage.

Pelatihan Pembuatan Keripik dari Limbah Kulit Ikan Tuna kepada Kelompok Perempuan Binaan Lembaga Natural Aceh

PT. Sure Pacific Tuna and PT. Aceh Lampulo Jaya Bahari are 2 frozen tuna fish processing companies that produce fish skin waste, and have not been utilized economically. The majority of people work as fishermen and some groups of women work to process oysters into crackers. Utilization of tuna skin waste will provide many good impacts for the community because besides that it can also increase income for the company, besides that it can add entrepreneurial insight for participants and provide additional income for families. The targets of this activity are housewives, fishermen who generally also work as oyster seekers who also process oysters into crackers so that they have no difficulty understanding the process of making crackers. The results of this activity are very satisfactory because the participants of the activity can understand the process of processing tuna skin to be chips and able to process chips independently.

Photoaging induced by long-term exposure to UV irradiation and amelioration by Skipjack tuna skin hydrolysates: Targeting inhibition of MAPK and NF-κB signaling hyperactivation

• Hydrolysates from Skipjack tuna (STH), rich of GADGSVTR, ameliorated photoaging. • STH reversed the imbalance of oxidative stress and inflammatory response. • STH restored the pathological impairment of photoaging skin. • STH targeted the hyperactivation of MAPK and NF-κB signaling pathways. Excessive and long-term exposure of skin to UV irradiation induces the photoaging and previous reports have revealed the roles of oxidative stress and inflammation response in photoaging progression, which provides the potential targets for photoaging intervention. Herein, the low molecular weight hydrolysates obtained from Skipjack tuna skin (STH) were used to evaluate the ameliorating effects on photoaging and the action mechanism was further explored. Pathologically, STH significantly recovered the barrier functions and restored the impaired architectures of photoaging skin. Biochemically, the antioxidant capacity was remarkably elevated and the inflammatory cytokines were significantly reduced in photoaging skin when STH was simultaneously administrated. Moreover, the abnormalities in epidermal hyperplasia and dermal loss were dramatically improved, along with the significant increase of procollagen type Ⅰ expression and inhibition of MMP-1 activity ( P < 0.05). Furthermore, STH mitigated the phosphorylation levels of p38, JNK, ERK, IκB and p65 in photoaging skin, which strongly indicated that STH synergistically intervened the photoaging progression in SD rats via cascading modulation on the hyperactivation of MAPK and NF-κB signaling pathways. Overall, these data prove the desirable protection of STH against photoaging process and can be used as functional ingredients in cosmeceutical foods.

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.

Membrane fractionation of gelatins extracted from skin of yellowfin tuna (Thunnus albacares): effect on molecular sizes and gelling properties of fractions

ABSTRACT Membrane separation technologies allow the implementation of environmentally friendly and cost-effective processes to separate fine particles and molecules. Fractionation process of proteins from tuna skin gelatin was performed in four consecutive filtration steps using four membranes with pore diameters of 800 nm, 100 nm, 50 nm, and 20 nm. The retentates obtained from all membranes exhibited a similar protein size distribution. Gel strength and gelling and melting temperatures did not differ significantly among the tuna skin gelatin and the four retentates (p > .05). The permeate from the 20 nm pore diameter membrane exhibited significantly lower gelling properties than the other fractions (p < .05). The retentates of the four membranes presented gel strength values between 228 and 440 g. Gelling and melting temperatures from retentates and tuna skin gelatin ranged from 10.0 to 13.4°C and 18.0 to 20.6°C, respectively.

Impact of ultrasound on extractability of native collagen from tuna by-product and its ultrastructure and physicochemical attributes

The effect of ultrasound treatment (300 W; 0, 5, 10, 15, 20 and 25 min) on the extractability of acid soluble collagen from yellowfin tuna skin and its structural, physicochemical and functional properties were investigated. Ultrasound treatments significantly increased collagen extraction yield from the tuna skin up to 2.7 times, compared to the conventional extraction with acetic acid. The level of proline, hydroxyproline and thermal stability of collagens increased by applying ultrasound while their native triple-stranded helical structure was well-preserved, as revealed by X-ray diffraction and FTIR spectroscopy. However, ultrasound treatment reduced the particle size of the collagens which increased their pH and salt induced solubility. The water holding capacity and the emulsifying properties of ultrasound treated collagens were also higher than those produced with the conventional method. Altogether, the results suggested that ultrasonication can be a promising assistant technology for improving native collagen extraction efficiency from tuna skin and its functionality but its duration should be carefully optimized.