Water Vapor Permeability of Mammalian and Fish Gelatin Films

ABSTRACT:  Water vapor permeability of cold- and warm-water fish skin gelatins films was evaluated and compared with different types of mammalian gelatins. Alaskan pollock and salmon gelatins were extracted from frozen skins, others were obtained from commercial sources. Water vapor permeability of gelatin films was determined considering differences on percent relative humidity (%RH) at the film underside. Molecular weight distribution, amino acid composition, gel strength, viscoelastic properties, pH, and clarity were also determined for each gelatin. Water vapor permeability of cold-water fish gelatin films (0.93 gmm/m²hkPa) was significantly lower than warm-water fish and mammalian gelatin films (1.31 and 1.88 gmm/m²hkPa, respectively) at 25 °C, 0/80 %RH through 0.05-mm thickness films. This was related to increased hydrophobicity due to reduced amounts of proline and hydroxyproline in cold-water fish gelatins. As expected, gel strength and gel setting temperatures were lower for cold-water fish gelatin than either warm-water fish gelatins or mammalian gelatins. This study demonstrated significant differences in physical, chemical, and rheological properties between mammalian and fish gelatins. Lower water vapor permeability of fish gelatin films can be useful particularly for applications related to reducing water loss from encapsulated drugs and refrigerated or frozen food systems.     

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.     

Properties of Alaska Pollock Skin Gelatin: A Comparison with Tilapia and Pork Skin Gelatins

ABSTRACT:  The objective of this work was to compare the physiochemical and rheological properties of Alaska pollock skin gelatin (AG) to those obtained for tilapia and pork skin gelatins. Results were also obtained for some mixed gels containing AG and pork skin gelatin, or AG and tilapia gelatin. AG contained about 7% hydroxyproline (Hyp), which was lower than that of tilapia (∼11%) or pork skin gelatin (∼13%). Most of the protein fractions in AG were α chain, β chain, and other oligomers. The gel strength of AG was 98 gram-force at 10 °C, and increased at a greater rate than other gelatins with decreasing temperature. The gel melting point of AG was the lowest with the oil-drop method, while the viscosity of AG was the highest of the samples studied. The rheological properties of gelatins were determined using small amplitude oscillatory shear testing. G' was nearly independent of frequency for most of the gelatin gels, but AG gels showed a slight dependence on G' and a minimum in G". G' was found to be a power law function of concentration for all gelatins used: G'= k × Cⁿ. In rheological measurements, AG also showed the lowest gel melting temperature and sharpest melting region. Increasing gelatin concentration resulted in a higher melting temperature and a broader melting region for all gelatin gels. For both the AG-pork and AG-tilapia mixed gels, the gel melting temperatures decreased and melting regions narrowed as the AG fraction was increased.     

Physical, mechanical, and barrier properties of carp and mammalian skin gelatin films

Films of 0.11 to 0.13 mm thickness were prepared using gelatins from the skins of cultured freshwater carp species and mammalian gelatins viz., porcine and bovine skin gelatin. A comparative study was made on the physical, mechanical, and barrier properties of these films. The amino acid composition, gel strength, clarity, and gel setting point of the gelatins were also determined. Carp skin gelatins had a lower imino acid content (19.16% to 20.86%) than mammalian skin gelatins (22.91% to 23.7%). Grass carp gelatin had gel strength of 230.2 B that is comparable to the reported value for bovine skin gelatin (227.2 B). The bloom values of rohu and common carp skin gelatins were 188.6 B and 181.3 B, respectively, which were significantly lower than mammalian gelatins. Mammalian gels have significantly higher (P < 0.05) setting temperatures (23.7 to 24.2 °C) than carp skin gelatins. Tensile strength (TS) was lowest for films from common carp and rohu skin gelatin (490 and 497 kg/cm(2), respectively) and highest for porcine skin gelatin film. The degree of transparency (L*) was significantly higher for films from grass carp, bovine hide, and pork skin gelatin films. Carp skin gelatin films had significantly lower water vapor permeability (WVP) and oxygen permeability (OP) than mammalian skin gelatin films, which indicated that carp skin gelatin based films have superior barrier properties than mammalian skin gelatin films.     

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.     

Gelatins from three cultured freshwater fish skins obtained by liming process

The physico-chemical properties of gelatins from the skins of Red tilapia (Oreochromis nilotica), Walking catfish (Clarias batrachus) and Striped catfish (Pangasius sutchi fowler) obtained through a liming process for 14 days were evaluated. All the gelatins had very mild to undetectable fishy odour and had acceptable colour attributes, which were light yellowish to whitish. The highest gelatin yield (dry basis) was obtained from red tilapia (39.97%) skin and the bloom strength exceeded 300 g. The pH values of the gelatins were in the vicinity of 5.0. The viscosity (cp) was highest in striped catfish, followed by red tilapia and walking catfish. Their melting points were in the vicinity of 26 ± 1 °C. Turbidity was lowest in the red tilapia gelatin. Glycine, proline and alanine were the three highest amino acids found in all the gelatins obtained.     

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.     

Extraction and properties of gelatin from channel catfish (Ietalurus punetaus) skin

Response surface method was used to determine the optimum operating conditions for extracting the gelatin from channel catfish skin. The optimal conditions for maximum gel strength are 68.8 h for the time of treatment with calcium hydroxide solution, 43.2 °C for the extraction temperature, 5.73 h for the extraction time with hot water. The gelatin from channel catfish skin showed a high gel strength, 276±5 g. Compare to porcine skin gelatin, the gelatin from channel catfish skin has different amino acids composition and a lower thermo-stability.     

Study on the properties of gelatins from skin of carp (Cyprinus carpio) caught in winter and summer season

The objective of this work was to compare the physiochemical (molecular weight distribution and amino acid composition) and rheological (viscosity property, gel strength and melting point) properties of gelatins from skins of carp caught in winter to those obtained for the summer equivalents. Gelatins from winter and summer fish skins were extracted at 60, 70 and 80 °C. SDS-PAGE patterns for gelatins extracted under the same conditions showed that the degradation of gelatins from winter fish skins were more severe than that of the summer ones. The imino acid contents of the winter and summer gelatins extracted at 60 °C were very similar, showing 190 and 188 residues/1000 residues, respectively. The gelatins from summer fish presented higher melting points and gel strengths, as well as better viscosity properties than the winter equivalents (P < 0.05). The differences in the rheological properties between winter and summer gelatins may be explained by different thermostability of interstitial collagen molecules (from which gelatins were derived) in the two seasons.     

Effects of alkaline and acid pretreatment on the physical properties and nanostructures of the gelatin from channel catfish skins

The objective of this study was to illustrate the correlation between the physical properties and nanostructure of gelatins made of channel catfish (Ictalurus punctatus) skins. The gelatin samples were first pretreated with sodium hydroxide, acetic acid, or water, and then extracted with hot water before the measurement. Physical properties including the yield of protein, viscosity and textural properties were determined on gelatins obtained with different pretreatment conditions. The acid pretreatment group showed the highest gel strength and protein yield, and a reasonable viscosity. The water pretreatment group showed the lowest values for all of the physical properties. Four samples including water, 0.1 M acid and 0.25 and 1.0 M alkaline-pretreated groups’ nanostructures were then studied using atomic force microscopy (AFM). The AFM images showed that the acid-pretreated gelatin was composed of sponge-like aggregates, while the others showed separated individual aggregates. Annular pores were only found in the alkaline pretreatment group. There was no significant correlation between the diameters of the spherical aggregates and the physical properties; however, the different AFM patterns may relate to the gelatin's physical properties.     

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.     

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.     

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.     

斑点叉尾鮰鱼皮保藏方法

通过自然风干、烘干和盐渍3种不同的方法处理斑点叉尾鮰鱼皮,并在室温条件下分别保藏10、30、60和90 d。在鱼皮保藏结束后,利用差示扫描量热法定期测定鱼皮的收缩温度,提取鱼皮酸溶胶原并测定各胶原的红外光谱性质,利用SDS-PAGE电泳法测定胶原分子的分子质量分布,以此分析各种处理方法及保藏时间对鱼皮性质的影响。结果表明:风干处理后的鱼皮经保藏一段时间后,复水后的鱼皮和其酸溶胶原的特性与新鲜鱼皮及其酸溶胶原的特性最为接近,表明风干处理的效果最佳,从中提取所得酸溶胶原结构基本保持原有状态。     

Physicochemical Properties of Mammalian Gelatin in Relation to Membrane Process Requirement

In any of the membrane process application, understanding of the characteristics of the feed solution is essential in order to achieve desired level of separation performance. In this study, in an effort to substitute evaporation with membrane processes partially, experiments were carried out to investigate the physicochemical properties of gelatins, namely, molecular weight distribution, pH, viscosity, isoelectric point, and gel strength, which are, of foremost, important parameters in the characterization of gelatin. Two different mammalian gelatins, i.e. from bovine (type B) and porcine (type A) sources, were used in this study. The pH was significantly varied for all gelatins in the vicinity of 4.75–5.51 (±0.01). Experimental result revealed that both sources of mammalian gelatin contained components of different molecular weights with wide distribution ranging from 10 to 400 kDa. Analysis of the molecular weight distribution result also showed strong correlation between average molecular weight and gel strength of gelatin. The isoelectric points of gelatins from bovine were 4.60 ± 0.08 to 5.25 ± 0.43 and porcine gelatins were in the range of 7–9.3, which agreed well with the results obtained from other researchers. The high bloom strength mammalian gelatins were also significantly more viscous and thus, had a higher melting point.     

Comparison of water gel desserts from fish skin and pork gelatins using instrumental measurements

ABSTRACT:  The objective of this study was to compare water gel desserts from various gelatins using instrumental measurements. The puncture test and texture profile analysis (TPA) with compression were determined at 25% and 75% deformation; the melting properties were determined rheologically by monitoring the change of storage modulus (G') with increasing temperature. The measurements with 25% deformation were always nondestructive, while measurements with 75% deformation were mostly destructive. Desserts made from Alaska pollock gelatin (AG) or gelatin mixtures containing AG were more resistant to the destruction caused by the large deformation than tilapia gelatin and pork gelatins. In addition, the gel dessert made from AG melted at a lower temperature than those from tilapia skin gelatin and pork gelatins, while desserts made from gelatin mixtures reflected the melting properties of the separate gelatins.     

Chemical compositions and characterisation of skin gelatin from farmed giant catfish (Pangasianodon gigas)

Gelatin was extracted from the skin of farmed giant catfish (Pangasianodon gigas) with a yield of 20.1 g/100 g skin sample on the basis of wet weight. The chemical composition and properties of gelatin were characterised. The gelatin had high protein (89.1 g/100 g) but low fat (0.75 g/100 g) content and contained a high number of imino acids (proline and hydroxyproline) (211 residues per 1000 residues). Giant catfish skin gelatin had a slightly different amino acid composition than calf skin gelatin. The bloom strength of the gelatin gel from giant catfish skin gelatin (153 g) was greater than that of calf skin gelatin (135 g) (P < 0.05). Viscosity, foam capacity and foam stability of gelatin from giant catfish skins were in general greater than those of the gelatin from calf skin tested. SDS-PAGE of giant catfish skin gelatin showed a high band intensity for the major protein components, especially, α-, β- and γ-components and was similar to that of standard calf skin collagen type I.     

Extraction and Physicochemical Characterization of Greater Lizardfish (Saurida tumbil) Skin and Bone Gelatin

ABSTRACT:  Type A gelatins were extracted from skins and bones of lizardfish and analyzed to determine their functional and chemical properties. Lizardfish skin gelatin had ash content of 2.2 ± 0.3% while bone gelatin had ash content of 12.2 ± 0.2%. Gel strength was 159.1 ± 14 and 135 ± 7.9 g, respectively, for skin and bone gelatins compared to 224.3 ± 7.7 g for porcine gelatin. Gelatin from skin exhibited higher viscosity and lower setting time than bone. Skin gelatin had higher imino acid content than bone gelatin. The total imino acid content was 21.71% and 19.83% for skin and bone, respectively. Both skin and bone gelatins contained more α chains than β and γ components. Both bone and skin gelatins also contained low molecular weight (< α) peptides. The differences in functional properties between the skin and bone gelatins appeared to be related to differences in amino acid composition and molecular weight distribution of the gelatins.     

用差示扫描量热法分析明胶品质

通过对明胶凝胶强度和明胶相变时焓变值的测定,研究明胶的凝胶强度与其相焓值的关系,试图找出明胶品质与相变的内在联系.利用差示扫描量热法(DSC法)分别对5种明胶凝胶和溶液的相变参数进行测定,结果表明:降温时,明胶溶液的焓变值与其凝胶强度间存在指数关系;升温时,明胶凝胶的焓变值与其凝胶强度存在指数关系;溶化并降温时,明胶凝胶的焓变值与相变起始温度存在线性关系,与明胶凝胶强度存在极度显著的线性关系.结果表明,利用差示扫描量热法法测定明胶凝胶的相变焓值,同样可以准确表征明胶的品质,并且样品用量极小.     

Effects of concentration on nanostructural images and physical properties of gelatin from channel catfish skins

Physical properties are crucial to gelatin utilization and the physical properties are determined by structure. Therefore, it is important to investigate the nanostructure and physical properties of gelatin over the full range of concentrations which are widely applied in research and industry. Nanostructure of gelatin can be investigated by atomic force microscopy (AFM). However, it is hard to obtain reliable AFM images of gelatin with high concentrations (1–6.67%). In this study, methods for imaging gelatin with high concentration were explored and developed, which mainly included six steps. Then the relationships among concentration, nanostructure and physical property of gelatin extracted from channel catfish skins (Ictalurus punctatus) were studied. The high-resolution AFM images show fibril structure in gelatins with concentrations from 1% to 6.67%. However, in low concentrations (<1%), most nanostructures of gelatin were spherical aggregates and fibril structure only existed occasionally. Correspondingly, there were no significant differences of gel strength, texture profile and viscosity among several groups of gelatin when the concentration was lower than 1%, in contrast, these properties changed dramatically when the concentration was greater than 1%. It indicates that there must be some close relationships among concentration, nanostructure and physical property of gelatin. The illustration of nanoscale transition would help us understand the macroscale changes of physical properties.