Rheological properties of channel catfish (Ictalurus punctaus) gelatine from fish skins preserved by different methods

Gelatins were extracted from channel catfish skins preserved by different methods using 50 mmol/l acetic acid. Molecular weight distribution, gel strength and viscoelastic properties of gelatin samples were studied. Compared to gelatins from fresh and frozen skins, gelatin from dried channel catfish skin exhibited higher gel strength. This can be explained by the large α-chains content of gelatin from the dried skins. The gelling point and melting point of dried channel catfish skin gelatin solution were similar to those of fresh skin gelatin solution, but distinctly different from those of frozen skin gelatin. After maturation at low temperature, melting points of gelatins increased. But the melting point of frozen skin gelatin was still the highest among the three gelatin samples studied.     

Effect of microbial transglutaminase on the functional properties of megrim (Lepidorhombus boscii) skin gelatin

This paper examines the effect of a microbial transglutaminase (TGase) on the gelling and viscoelastic properties of a gelatin from megrim (Lepidorhombus boscii) skins. Although TGase extended the setting time of fish gelatin, it was found that melting temperature, gel strength and viscosity in solution at 60 °C were considerably increased by the covalent cross‐linking action of the enzyme, as observed by SDS‐PAGE and SEM. Increasing concentrations of TGase increased the elasticity and cohesiveness of gelatin gels but reduced gel strength and hardness. Partial inactivation of the enzyme was achieved thermally without negatively affecting the properties of the gelatin; whether or not gelatin is thermoreversible depends essentially on the degree of enzyme inactivation. © 2001 Society of Chemical Industry     

Dehydration of Pollock Skin Prior to Gelatin Production

ABSTRACT: Alaska pollock (Theragra chalcogramma) is the U.S.A.'s largest commercial fishery, with an annual catch of over 1 million tons. During pollock processing, the skins are discarded or made into fish meal, despite their value for gelatin production. The absence of gelatin-processing facilities in Alaska necessitates drying of the skins before transport to decrease the moisture content, but conventional hot-air drying is expensive. This study evaluated a less energy-intensive technology, the use of desiccants for reducing water weight in pollock skins prior to shipment. To ensure that the functional properties of gelatin obtained from dried pollock skins were not affected during desiccation, gelatins were prepared from each skin-drying treatment and compared with gelatin extracted from air-dried pollock skins. None of the desiccation treatments decreased the gel strength of pollock skin gelatin, nor were there major differences in gelling temperature or viscosity among the gelatin solutions. This suggests that pollock skins can be economically stabilized for transport to a gelatin-processing facility through the use of regenerable desiccants that are already common in the food industry. Practical Application: Pollock skins destined for gelatin production can be stabilized using chemical desiccants prior to shipment. The dehydration process does not harm the functional properties of gelatin, such as gel strength, gelling temperature, and viscosity. This research suggests that fish skins can be economically stabilized for transport to a gelatin-processing facility through the use of regenerable desiccants that are already common in the food industry.     

Rheological and physico‐chemical properties of gelatin extracted from the skin of a few species of freshwater carp

The physico‐chemical and rheological properties of gelatin from the skins of three different freshwater carp species, namely Catla catla, (catla) Cirrhinus mrigala (mrigal) and Labeo rohita (rohu), have been assessed and compared with that of gelatin from porcine skin. The average solids yield from the three species of carp varied in the range of 11.8–14.1%. The amino acid profile showed that the porcine gelatin had a higher proportion of imino acids and glycine than carp skins gelatin. The average molecular weight of carp skins gelatin as determined using a gel filtration technique was 233 kDa, while that of porcine skin gelatin was 282 kDa. The gelling temperature of carp skins gelatin was in the range of 6–15.7 °C, and the melting temperature was 17.9–23.7 °C as determined using a controlled stress rheometer. A higher gelling and melting temperature was observed for porcine skin gelatin.     

Effects of Concentration,Bloom Degree,and pH on Gelatin Melting and Gelling Temperatures Using Small Amplitude Oscillatory Rheology

Concentration, gel strength (Bloom), and pH effects on both melting and gelling temperatures of gelatin were studied using small amplitude oscillatory rheology. Temperature sweeps were applied to gelatin gel samples for heating and cooling at fixed frequencies. Results showed that melting temperatures were higher than gelling temperatures, and both increased with increasing concentration at pH from 3 to 6 for all gel strength. For constant gelatin concentration and pH, as gel strength increased, melting temperatures decreased, whereas gelling temperatures increased. A mathematical model was obtained which correlates melting and gelling temperatures, respectively, with pH and concentration at fixed Bloom degrees. All gelatin gels showed storage modulus higher (2 to 10 kPa) than loss modulus (50 to 500 Pa).     

Extraction of Gelatin from Megrim (Lepidorhombus boscii) Skins with Several Organic Acids

ABSTRACT: Light-colored, dry collagen was obtained and, after dissolving in warm water, turned into soluble gelatin. The type of acid used influenced the gelatin viscoelastic and gelling properties. Acetic- and propionic-acid extracts produced the gelatins with the highest elastic modulus, viscous modulus, melting temperature, and gel strength, especially when skins were previously treated with dilute NaOH. After such treatment, lactic acid was also shown to be suitable for collagen or gelatin extraction. The lowest degree of turbidity was achieved by using citric acid, whereas propionic acid led to the most turbid gelatin. No improvements of rheological properties were observed when acid concentration for extraction was increased above 0.05 M.     

Structural and mechanical properties of fish gelatin as a function of extraction conditions

The effect of 18 different extraction conditions on yield, weight average molecular weight, dynamic storage modulus, gelling and melting temperature, and helix recovery was studied. Gelatins were extracted from saithe (Pollachius virens) skins with an average yield of 8.9 ± 0.8% (average ± S.D.; n = 54), on a wet weight basis. High weight average molecular weight gelatins extracted at room temperature exhibit higher resulting dynamic storage modulus, higher gelling and melting temperatures and more helix formation compared to highly hydrolyzed gelatins extracted under harsher conditions. The storage modulus was increased 5 times compared to commercial cold water fish gelatin. The highest gelling and melting temperatures observed for 5% (w/v) fish gelatin were 8 °C and 16 °C, respectively. The present study suggests that the dynamic storage modulus, gelling and melting temperatures and helix content are related and increase with increasing weight average molecular weight up to about 250 kg/mol. The dynamic storage modulus correlates with the helix concentration according to the previously published correlation between dynamic storage modulus and helix concentration, which has been defined as the master curve for gelatin.     

Characteristics and chemical composition of skins gelatin from cobia (Rachycentron canadum)

Gelatin was obtained from cobia (Rachycentron canadum) skins, which is an important commercial species for marine fish aquaculture, and it was compared with gelatin from croaker (Micropogonias furnieri) skins, using the same extraction methodology (alkaline/acid pre-treatments). Cobia skins gelatin showed values of protein yield, gelatin yield, gel strength, melting point, gelling point and viscosity higher than the values found from croaker skins gelatin. The values of turbidity and Hue angle for cobia and croaker gelatins were 403 and 74 NTU, and 84.8° and 87.3°, respectively. Spectra in the infrared region had the major absorption band in the amide region for both gelatins, but it showed some differences in the spectra. The proline and hydroxyproline contents from cobia skins gelatin (205 residues/1000 residues) was higher than from croaker skins gelatin (188 residues/1000 residues). SDS-PAGE of both gelatins showed a similar molecular weight distribution to that of standard collagen type I. Therefore, cobia skins could be used as a potential marine source of gelatin obtainment for application in diversified industrial fields.     

The role of salt washing of fish skins in chemical and rheological properties of gelatin extracted

Dover sole (Solea vulgaris) skins were washed with different salt solutions previous to gelatin extraction by a mild acid pre-treatment. The effects of NaCl, KCl, MgCl₂, MgSO₄ and no-salt washing on the mineral content, yield of extraction, molecular weight distribution, gel strength, aggregation phenomena and viscoelastic properties of gelatin newly dissolved and after overnight cold maturation were evaluated. Skin washing with NaCl and KCl induced noticeable changes in molecular weight distribution, and consequently in gel strength and rheological properties, especially when compared with unsalted gelatin preparations. However, salts containing Mg²⁺ gave rise to the retaining of this bivalent cation in the resultant gelatin, which is detrimental to the gelatin quality.     

Preparation and characterisation of gelatins from the skins of sin croaker (Johnius dussumieri) and shortfin scad (Decapterus macrosoma)

Gelatins were prepared from the skins of the tropical fish, sin croaker (Johnius dussumeiri) and shortfin scad (Decapterus macrosoma). Visual appearance, colour, pH, bloom strength, viscoelasticity, melting point and amino acid profiles of the fish gelatins were evaluated. Shortfin scad gelatin had higher melting and gelling temperatures than those of sin croaker gelatin. The bloom strengths of gelatins from sin croaker and from shortfin scad were 125 and 177 g, respectively, compared to 240 g for commercial bovine gelatin. The pH values were significantly different between the solutions of the two fish gelatins. The elastic modulus (G′) of the fish gelatin gels increased by more than 10-fold and the viscous modulus (G″) of fish gelatin solution increased sixfold after holding at 5 °C for 2 h. These viscoelastic properties of bovine gelatin only increased by less than twice.     

大目金枪鱼皮明胶的理化性质及结构分析

以大目金枪鱼皮为原料制备明胶,对所得明胶的凝胶强度、胶凝温度、熔化温度、氨基酸组成、十二烷基硫酸钠-聚丙烯酰氨凝胶电泳（sodium dodecyl sulfate-polyacrylamide gel electrophoresis,SDS-PAGE）、光谱学特性等理化性质及结构特性进行研究,并与猪皮明胶进行比较。结果表明,金枪鱼皮明胶的凝胶强度为403?g,胶凝温度和熔化温度分别为21.5?℃和28.8?℃,略低于猪皮明胶;氨基酸分析结果表明,金枪鱼皮明胶中亚氨基酸质量分数为19.09%,低于猪皮明胶的22.82%,可以解释金枪鱼皮明胶凝胶特性、胶凝温度和熔化温度低于猪皮明胶的原因。SDS-PAGE电泳结果显示,金枪鱼皮明胶的小分子组分质量分数仅为6.67%,说明预处理及热水提胶过程并没有破坏明胶中亚基的完整性。金枪鱼皮明胶的紫外光谱与红外光谱谱图均与猪皮明胶相似,进一步说明实验所制得的产物为高质量明胶。     

Characterization of fish gelatin from surimi processing wastes: Thermal analysis and effect of transglutaminase on gel properties

Fish gelatin extraction from wastes of fish Herring species (Tenualosa ilisha) was carried out by a series of pretreatment with 0.2 M Ca(OH)₂ followed by 0.1 M citric acid and final water extraction at 50 °C for 3 h. The resulting fish gelatin preparation was evaluated for its dynamic viscoelastic properties, gelling and melting temperatures and gel strength. The gelling and melting temperatures of gelatin samples (at 6.67%, w/v) were obtained from differential scanning calorimetry and rheological studies. The melting temperature of extracted fish gelatin (EFG) obtained ranged from 16.2 to 16.7 °C compared to that of commercial fish gelatin gel (CFG), from 23.7 to 25.6 °C and halal bovine gelatin (HBG), from 26.5 to 28.7 °C. On the other hand, gelling temperatures of EFG, CFG and HBG ranged from 5.1 to 5.2 °C, 11.9 to 17.46 °C, and 12.6 to 19.33 °C, respectively. EFG gave gels with a considerably lower G′ values than CFG and HBG. The bloom strength of EFG gels at 6.67% (w/v) was 69.03 g which was much lower than HBG (336.2 g) and CFG (435.9 g). Enzyme transglutaminase was added in the amounts of 0.5, 1.0, 3.0 and 5.0 mg/g gelatin to modify the gel properties of the extracted fish gelatin. The modified EFG gels obtained had higher gel strengths of 101.1 g and 90.56 g with added transglutaminase of 1.0 and 3.0 mg/g, respectively. However with addition of 5.0 mg/g enzyme the gel strength increased only up to 75.06 g. SDS-PAGE of extracted gelatin gel showed protein band intensities for α1-chains and 53 kDa but in gels added with higher concentration of transglutaminase, these protein band intensities seemed to disappear.     

Physicochemical,rheological, and molecular characterization of colloidal gelatin produced from Common carp by‐products using microwave and ultrasound‐assisted extraction

The effects of ultrasound‐assisted extraction (UAE) and microwave‐assisted extraction (MAE) methods on molecular and physicochemical characteristics of the resultant gelatin were examined. Before extraction procedure, we investigated the optimum pH for swelling of Common carp by‐products, which is an important pretreatment for gelatin production. The highest swelling yield was achieved at pH 13 among pH 1–14 with unit intervals. Results indicated that the UAE gelatin has a higher gel strength, viscosity, melting point, and gelling point. The power and time of sonication showed a reverse relation with these characteristics. In addition, as the time of microwave heating was raised, the gel strength, viscosity, melting point, and gelling point were decreased. The FT‐IR spectra showed similar peaks but the Amide B in UAE gelatin slightly vanished. The electrophoretic pattern also revealed the higher gel strength and viscosity of UAE gelatin due to the higher intensity of α and β chains compared to MAE gelatin. It can be concluded from all of the results of this study that the produced gelatin using these procedures can be a good source of gelatin in food and drug industries.     

Changes in functional properties of shark (Isurus oxyrinchus) cartilage gelatin produced by different drying methods

Fish gelatins extracted from shark ( Isurus oxyrinchus ) cartilage were dried by three different methods: freeze drying, hot-air drying and spray drying; and their functional properties were investigated. Freeze-dried gelatin was found to have the strongest gel strength, while gelatins made at high temperatures formed weaker gels. The 135-kPa gel strength of freeze-dried gelatin was relatively high. While foam formation ability of the freeze-dried gelatin was the highest, its foam stability was the lowest. In addition, spray-dried gelatin had the best emulsion capacities. Dynamic viscoelastic properties of shark cartilage gelatins prepared by these drying methods were closely correlated with their gel strength. Elasticity modulus ( G '; Pa) and loss modulus ( G "; Pa) of the freeze-dried gelatin had higher values than those prepared by hot-air drying and spray drying; viscoelastic properties of the freeze-dried gelatin were maintained longer than those of other drying methods.     

Extracting Conditions for Megrim (Lepidorhombus boscii) Skin Collagen Affect Functional Properties of the Resulting Gelatin

Various procedures for extracting collagen and/or gelatin from megrim skins were compared on the basis of gelatin functional properties. It was possible to prepare a dry powder of soluble collagen with good viscoelastic and gelling properties, which can be converted into gelatin by dissolving at temperatures above 45 °C. Physical properties of gelatins are influenced more by extracting conditions than by imino acid composition. A high-quality, readily-dissolved gelatin was obtained from megrim skins using a pretreatment of the skins with NaCl and dilute NaOH, then swelling with 0.05 M acetic acid followed by an extraction step in water at 45 °C.     

Rheological properties of gelatin from silver carp skin compared to commercially available gelatins from different sources

Gelatin is used as a functional ingredient in many foods, pharmaceuticals, and cosmetics as a stabilizing, thickening, and gelling agent. The rheological properties of gelatins are important in the potential functionality of gelatin. This study is designed to determine the rheological properties of gelatin extracted from the skins of silver carp (Hypophthalmichthys molitrix Valenciennes 1844). The extracted gelatin is compared with commercially available gelatins from different sources. The results indicate that the stress-strain relationship of gelatin gels remained in the linear region over a broad range of strains and stresses and gave similar elastic moduli at varying frequency, stress, and strain levels. One exception was a commercial high molecular weight fish skin gelatin that gave a lower elastic modulus indicating that its gel strength was low compared to the other gelatin samples studied. Gel strength varied between 220 and 1230 g while viscosity varied between 4.53 and 6.91 cP among the samples. Melting and gelling temperatures varied between 14.2 and 32.3 °C and 3.2 and 25.4 °C, respectively. Texture profile analysis was done at 2 deformation levels, 25% and 75%, and the results correlated well with gel strength. The correlations between hardness, cohesiveness, and gumminess and gel strength were 0.98, 0.82, and 0.99, respectively, at 25% deformation but lower at 75% deformation. The results suggest that rheological measurements might be used to quickly estimate gel strength using less material. In addition, the silver carp skin gelatin seemed to be of equal quality to some of the commercial gelatins.     

Seasonal differences in the properties of gelatins extracted from skin of silver carp (Hypophthalmichthys molitrix)

The gelatins were extracted from skins of silver carp (Hypophthalmichthys molitrix) caught in winter and summer, respectively. The physicochemical (molecular weight distribution and melting point) and rheological characteristics (viscosity property), as well as functional properties (emulsifying capacity and stability) of the gelatin from winter silver carp skin were compared with those of the summer equivalent. The results showed the properties of the summer gelatin were superior to those of the winter one, showing higher viscosity, emulsion stability, melting point and lower concentration for gelling. The summer gelatin has slightly denser strands of the gel microstructure which was observed by scanning electron microscopy (SEM). Different properties of gelatins from skin of silver carp may be attributed to the big discrepancy of the environmental temperature in the two seasons.     

Improving the physical properties of fish gelatin by high hydrostatic pressure (HHP) and ultrasonication (US)

In this study, it was aimed to improve the physical properties of fish gelatin by using high hydrostatic pressure (HHP) and ultrasonication (US). Gelatin solutions were exposed to different pressures and ultrasonication separately and gelled afterwards. The physicochemical measurements based on gel strength, turbidity and rheology experiments showed that HHP treatment on fish and bovine gelatin stabilized the gelatin network by organising the structure and reducing the free volume. Both processing methods (HHP and US) increased the gel strength significantly (P < 0.05) compared with non-treated samples. Fourier-transform infrared spectroscopy (FTIR) results indicated that conformations of amino acids changed after the treatments. Furthermore, US treatment was shown to destroy the gelatin network, change the gelation mechanism and decreased the degree of aggregation. Both treatments improved the gel characteristics as gel strength, gelling and melting temperatures of the fish gelatin. At the end, the best combination for fish gelatin among HHP and US treatments was found as 400 MPa–10 °C–15 min pressurisation.     

Visco‐Elastic and Flow Properties of Gelatin from the Bone of Freshwater Fish (Cirrhinus mrigala)

The average yield of gelatin from the bone of freshwater fish (Cirrhinus mrigala) was 6.13%. The fluorescence spectra revealed maximum emission at 303 nm indicating the exposure of chromophores to bulk solvent. The amino acid profile of gelatin revealed a higher proportion of glycine and imino acids. The bloom strength of gelled gelatin was 159.8 g. The average molecular weight of fish bone gelatin was 281 kDa as determined by gel filtration technique. The dynamic oscillatory test of gelatin solution as a function of time and temperature revealed gelling and melting temperatures of 8.0 °C and 17.0 °C, respectively. The flow behavior of gelatin solution as a function of concentrations and temperatures revealed non‐Newtonian behavior with pseudo‐plastic phenomenon. The Herschel–Bulkley and Casson models were found suitable to study the flow behavior. The emulsion capacity (EC) of gelatin was inversely proportional to its concentration.