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.     

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.     

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.     

鲢鱼皮明胶-海藻酸钠复合膜的制备与性能

鲢鱼皮明胶膜因具有安全性高和来源丰富等优点受到广泛关注。然而鲢鱼皮明胶膜的力学性能和阻隔性能 较差,若作为食品包装膜将会受到限制。为了改善鲢鱼皮明胶膜的性能,将海藻酸钠与鲢鱼皮明胶共混制成复合 膜。结果发现,制成的复合膜外观透亮,有阻隔紫外线和油脂的性质;当添加体积分数为20%的海藻酸钠时,复合 膜的水溶性和水蒸气透过率达到最小,抗拉强度达到最大。说明复合膜的阻隔性能和力学性能都优于鲢鱼皮明胶 膜。对膜的傅里叶变换红外光谱图和X射线衍射图进行分析,表明鲢鱼皮明胶和海藻酸钠存在较强的相互作用,这 可能是复合膜性能发生变化的主要原因。     

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.     

Extraction and functional properties of gelatin from the skin of cuttlefish (Sepia officinalis) using smooth hound crude acid protease-aided process

The characteristics and functional properties of gelatin from skin cuttlefish (Sepia officinalis) were investigated and compared to those of halal bovine gelatin (HBG). The gelatin extraction efficiency was improved by an acid-swelling process in the presence of smooth hound crude acid protease extract (SHCAP). The yields of gelatins from cuttlefish skin after 48 h with acid and with crude acid protease (15 units/g alkaline-treated skin) were 2.21% and 7.84%, respectively. The gelatin from skin cuttlefish had high protein (91.35%) but low fat (0.28%) contents. Compared to HBG, the cuttlefish-skin gelatin (CSG) has different amino acids composition than halal bovine gelatin. CSG contained slightly low hydroxyproline and proline (180‰) than HBG (219‰), whereas the content of serine was higher (49‰ versus 29‰). The gel strength of the gelatin gel from CSG (181 g) was lower than that of HBG (259 g) (p < 0.05) possibly due to lower hydroxyproline content. Cuttlefish-skin gelatin exhibited a similar emulsifying activity but greater emulsifying and foam stability than the halal bovine gelatin (p < 0.05). Foam formation ability, foam stability and water-holding capacity of CSG were slightly lower than those of the HBG, but fat-binding capacity was higher in the cuttlefish gelatin.     

Rheological Properties of Fish Gelatins

ABSTRACT: The rheological properties of fish gelatins (cod, megrim, tuna, and tilapia) and conventional gelatin (bovine and porcine) were compared. The different fish gelatins had from low to high viscosity values. They also had from low to high gel strength values. However, they had lower melting and gelling temperatures than gels from conventional gelatins. Cold-water fish gelatins were more different from conventional gelatins than warm water fish gelatins reflecting the different amino acid composition, as cold-water fish gelatins are low in imino acids. Binary blends of cod and other fish or conventional gelatins seemed to be completely compatible.     

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 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.     

Characterization of Fish-Skin Gelatin Gels and Films Containing the Antimicrobial Enzyme Lysozyme

ABSTRACT:  Fish skins are rich in collagen and can be used to produce food-grade gelatin. Films cast from fish-skin gelatins are stable at room temperature and can act as a barrier when applied to foods. Lysozyme is a food-safe, antimicrobial enzyme that can also produce gels and films. When cold-water, fish-skin gelatin is enhanced with lysozyme, the resulting film has antimicrobial properties. The objective of this study was to characterize the effect on strength and barrier properties of lysozyme-enhanced fish-skin gelatin gels and films, and evaluate their activity against potential spoilage bacteria. Solutions containing 6.67% fish-skin gelatin were formulated to contain varying levels of hen-egg-white lysozyme. Gels were evaluated for strength, clarity, and viscoelastic properties. Films were evaluated for water activity, water vapor permeability, and antimicrobial barrier capabilities. Fish-skin gels containing 0.1% and 0.01% lysozyme had pH (4.8) and gelling-temperatures (2.1 °C) similar to lysozyme-free fish-skin gelatin controls. However, gel strength decreased (up to 20%). Turbidities of gels, with or without lysozyme, were comparable at all concentrations. Films cast with gelatin containing lysozyme demonstrated similar water vapor permeabilities and water activities. Lysozyme was still detectable in most fish gelatin films. More antimicrobial activity was retained in films cast with higher lysozyme concentrations and in films where lysozyme was added after the gelatin had been initially heated. These results suggest that fish-skin gelatin gels and films, when formulated with lysozyme, may provide a unique, functional barrier to increase the shelf life of food products.     

Effect of microbial transglutaminase on gel properties and film characteristics of gelatin from lizardfish (Saurida spp.) scales

The addition of microbial transglutaminase (MTGase) generally increased the gel strength of lizardfish (Saurida spp.) scale gelatin gels (P≤0.05) with an increase in gel strength with the addition of MTGase up to 0.5% (w/v). The texture profile analysis compression tests of lizardfish scale gelatin gel with and without MTGase were studied to determine their effects on gel characteristics. MTGase added to the gels decreased the band intensity of the β- and α-components with increasing concentrations of enzyme. Gel microstructures with various concentration of MTGase showed denser strands in the gels with enzyme compared with the looser stands in non-enzyme-treated gel samples. Films cast from lizardfish scale gelatin with and without 0.5% MTGase and bovine gelatin films were transparent and flexible. The lizardfish gelatin films were all slightly yellowish while the bovine gelatin films were clearer. The L value of bovine gelatin films had the highest value (P≤0.05) whereas lizardfish scale gelatin films with and without enzyme were not significantly different (P>0.05) for L, a, and b values and ΔE. The film's mechanical properties included tensile strength (TS) and elongation at break (E) were not significantly different (P > 0.05) for E and the films of lizardfish scale gelatin showed higher TS than the films without enzyme added (P ≤ 0.05). The water vapor permeability of films from lizardfish scale gelatin with and without 0.5% MTGase and bovine gelatin films were 21.0 ± 0.17, 26.3 ± 0.79, and 25.8 ± 0.09 g·mm/m(2)·d·kPa, respectively, while the oxygen transmission rate of all 3 types of films were less than 50 cc O(2)/m(2)·d.     

Gelation, oxygen permeability, and mechanical properties of mammalian and fish gelatin films

The objective of this study was to evaluate the gelation, thermal, mechanical, and oxygen permeability properties of different mammalian, warm- and cold-water fish gelatin solutions and films. Mammalian gelatin solutions had the highest gel set temperatures, followed by warm-water fish and then cold-water fish gelatin solutions. These differences were related to concentrations of imino acids present in each gelatin, with mammalian gelatin having the highest and cold-water fish gelatin having the lowest concentrations. Mammalian and warm-water fish gelatin films contained helical structures, whereas cold-water fish gelatin films were amorphous. This was due to the films being dried at room temperature (23 °C), which was below or near the gelation temperatures of mammalian and warm-water fish gelatin solutions and well above the gelation temperature of cold-water fish gelatin solutions. Tensile strength, percent elongation, and puncture deformation were highest in mammalian gelatin films, followed by warm-water fish gelatin film and then by cold-water fish gelatin films. Oxygen permeability values of cold-water fish gelatin films were significantly lower than those for mammalian gelatin films. These differences were most likely due to higher moisture sorption in mammalian gelatin films, leading to higher oxygen diffusivity.     

Properties of Gelatin Film from Horse Mackerel (Trachurus japonicus) Scale

Optimal conditions for extracting gelatin and preparing gelatin film from horse mackerel scale, such as extraction temperature and time, as well as the protein concentration of film‐forming solutions were investigated. Yields of extracted gelatin at 70 °C, 80 °C, and 90 °C for 15 min to 3 h were 1.08% to 3.45%, depending on the extraction conditions. Among the various extraction times and temperatures, the film from gelatin extracted at 70 °C for 1 h showed the highest tensile strength and elongation at break. Horse mackerel scale gelatin film showed the greatly low water vapor permeability (WVP) compared with mammalian or fish gelatin films, maybe due to its containing a slightly higher level of hydrophobic amino acids (total 653 residues per 1000 residues) than that of mammalian, cold‐water fish and warm‐water fish gelatins. Gelatin films from different preparation conditions showed excellent UV barrier properties at wavelength of 200 nm, although the films were transparent at visible wavelength. As a consequence, it can be suggested that gelatin film from horse mackerel scale extracted at 70 °C for 1 h can be applied to food packaging material due to its lowest WVP value and excellent UV barrier properties.     

Optimization of Gelatin Extraction from Silver Carp Skin

ABSTRACT:  Fish skins are a by-product of the fish processing industry that can be successfully processed into gelatin. This study was designed to optimize the extraction process to obtain the highest yield, gel strength, and viscosity for gelatin production from silver carp skin. A fractional factorial design (2 levels, resolution III, 2^9-5) was chosen to screen 9 parameters to determine the most significant ones. Those found to be significant were optimized to determine the maximum value for 3 dependent variables mentioned above. The hydroxyproline content and hydroxyproline/protein ratio of the skin were 1.7% and 6.5%, respectively. The protein content of the skin was 26%. The hydroxyproline content of the gelatin for the sample giving the highest hydroxyproline/protein ratio was 10.9%. This sample was arbitrarily called pure gelatin and the purity of the remaining samples was between 71.8% and 97%. The highest protein and gelatin recovery was 78.1% and 98.8% of the total available, respectively. The latter, gelatin recovery, is proposed to be used instead of protein yield. Four variables were determined as significant in screening and these variables were studied by a central composite rotatable design (4-factor and 5-level with 6 central points) to model the system and response surface methodology was used for optimization. The optimum extraction conditions were 50 °C for the extraction temperature, 0.1 N HCl for the acid concentration, 45 min for the acid pretreatment time, and finally 4 : 1 (v/w) for the water/skin ratio. The predicted responses for these extraction conditions were 630 g gel strength, 6.3 cP viscosity, and 80.8% gelatin recovery. The data suggest that silver carp skin gelatin is similar to those of fish gelatins currently being exploited commercially.     

Texture Profile Analysis and Functional Properties of Gelatin from the Skin of Three Species of Fresh Water Fish

The texture profile analysis and functional properties of gelatin from fresh water fish (carps) and porcine skin were measured. Texture profile analysis revealed that the porcine gelatin showed significantly higher values for hardness, springiness, cohesiveness, gumminess, and chewiness than carp skin gelatin (p < 0.05). The bloom strength of gelatin from a porcine source was higher (466.40 g) than carp skin. The solubility profile of gelatin from carps and porcine as function of sodium chloride concentration indicated a maximum solubility at 0.3 M. The relationship between emulsion capacity values and concentration of proteins were found to be inversed in all of the gelatin samples.     

Preparation and characterisation of chicken skin gelatin as an alternative to mammalian gelatin

The aims of this study were to report for the first time, the extraction and physico-chemical properties of chicken skin gelatin compared to bovine gelatin. Extracted chicken skin gelatin 6.67% (w/v) had a higher bloom value (355 ± 1.48 g) than bovine gelatin (259 ± 0.71 g). The dynamic viscoelastic profile of chicken gelatin exhibited higher viscous and elastic modulus values compared to bovine gelatin for a range of concentrations and frequencies. Thermal properties studied by differential scanning calorimetry (DSC) showed that the melting temperature of 6.67%, chicken skin gelatin was significantly greater (p < 0.05) than that of bovine gelatin, indicating lower stability of bovine gelatin compared to chicken skin gelatin. Results obtained in this study showed that Gly (33.70%), Pro (13.42%), H.Pro (12.13%) and Ala (10.08%) were the most dominant amino acids in chicken skin gelatin which contributed to the higher gel strength and stability. Raman spectra of chicken skin and bovine gelatin were similar and displayed typical protein spectra. Chicken gelatin showed strong hydrogen bonding compared to bovine gelatin as the tyrosine doublet ratio (I₈₅₅/I₈₃₀) of chicken gelatin was significantly lower than that of bovine gelatin. Significantly, the alpha helix and β-sheet type structures were higher for chicken skin gelatin compared with bovine gelatin. The average molecular weight of chicken gelatin was 285,000 Da. These findings, obtained for the first time for chicken skin gelatin, show that it has high potential for application as an alternative to commercial gelatin.     

Sea bream bones and scales as a source of gelatin and ACE inhibitory peptides

Sea bream scales and bones were used as sources of gelatin. Scales gave a higher gelatin yield than bones pretreated with HCl or Alcalase. Demineralization with EDTA was effective especially in the case of scale gelatin that showed the lowest ash content. The pretreatment of bones with HCl led to an increase in the removal of minerals. The gel strength and viscoelastic properties of sea bream scale gelatins were higher than those of bone gelatins, and only slight differences were found between gelatin extracted from bones pretreated with HCl or Alcalase, although the amino acid profile was similar in the three gelatins. The gel strength of scale gelatins was higher than that of a commercial bovine gelatin used for comparative purpose (Bloom 200–220). When the scales gelatin was hydrolyzed with Esperase, a high ACE-inhibitory activity was found in the peptide fraction below 3 kDa, and the amount of this peptide fraction required to inhibit 50% of the ACE activity (IC₅₀) was around 60 μg/mL.     

Mass spectrometric detection of marker peptides in tryptic digests of gelatin: A new method to differentiate between bovine and porcine gelatin

Gelatin is a mixture of polypeptides obtained by hydrolysis of collagen primarily from bovine and porcine skin and bones. The similarity between different gelatins makes it difficult to trace their species origin. In this work, a new method for differentiation between bovine and porcine gelatin was developed based on detection and identification of marker peptides in digested gelatins. Sequence alignment analysis indicates that bovine and porcine Type I collagen contain differential sequences. The gelatins were digested by trypsin, and the resulting peptides were analyzed by high performance liquid chromatography/tandem mass spectrometry (HPLC–MS/MS). The marker peptides specific for bovine and porcine were successfully detected in the digested bovine and porcine gelatin, respectively. Comparative analysis indicated that more marker peptides could be detected in gelatin with a higher mean molecular weight. It was found that proline hydroxylation was a key factor affecting the peptide identification. For peptides such as GPPGSAGSPGK and GPPGSAGAPGK detected in digested bovine and porcine gelatin, respectively, the sequence should be verified manually since the mass shift caused by proline hydroxylation can be confused with the mass difference between Ser and Ala residues. The results indicate that detection of marker peptides in the digested gelatin sample using HPLC–MS/MS is an effective method to differentiate between bovine and porcine gelatin.     

Characterization of edible film fabricated with channel catfish (Ictalurus punctatus) gelatin extract using selected pretreatment methods

ABSTRACT:  Farm-raised catfish are important to the economy of the southeastern states in the United States, and catfish processing produces about 55% of by-products for inexpensive sale. Therefore, the utilization of catfish by-products is of great interest to the catfish industry. The objectives of this research were to determine the optimum pretreatment method to extract catfish gelatin for edible film application, and to characterize physical, mechanical, and barrier properties of edible films fabricated with catfish skin gelatin. Catfish skins obtained from a local plant were treated with 6 selected pretreatment methods. The main extraction was performed with deionized water at 50 °C after pretreatment. The gelatin yield was calculated and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was performed to characterize molecular weight (MW) profile. Color, tensile strength (TS), elongation, and water barrier property were determined to characterize the fabricated catfish gelatin films. From the results of gelatin yield, color, SDS-PAGE, as well as mechanical and barrier properties of the film, the pretreatment method with 0.25 M NaOH and 0.09 M acetic acid, followed by extraction at 50 °C for 3 h, was determined as the optimum extraction method. The catfish gelatin exhibited higher MW fractions than commercial mammalian gelatin. The catfish gelatin extracts possessed film-forming properties determined by TS, elongation, and water vapor permeability (WVP) comparable to those of commercial mammalian gelatin. The selected formula for catfish gelatin film was determined as 1% gelatin and 20% glycerol, resulting in greatest TS and lowest WVP.     

Comparative study on characteristics of gelatin from the skins of brownbanded bamboo shark and blacktip shark as affected by extraction conditions

Gelatins from the skins of brownbanded bamboo shark (BBS; Chiloscyllium punctatum) and blacktip shark (BTS; Carcharhinus limbatus) were extracted using the distilled water at different temperatures (45, 60 and 75 °C) and times (6 and 12 h). Yields of gelatin from the skins of BBS and BTS were 19.06–22.81% and 21.17–24.76% (based on wet weight), respectively. Gelatins from both species extracted at 45 °C for 6 h exhibited the highest bloom strength (206–214 g), which was higher than that of commercial bovine bone gelatin (197 g) (p < 0.05). Gelatin gels from BBS skin could set at room temperature (25–26 °C) within 24 min. However, gelatin gels from BTS skin was not able to set within 3 h at the same temperature. Scanning electron microscopic study showed that gelatin gel from BBS skin presented the thicker strand than those from BTS skin and bovine bone. Cross-linked components (β- and γ-chains) and α-chains were more degraded with increasing extraction temperatures, especially at 75 °C. Gelatin from BTS skin was more susceptible to hydrolysis than that from BBS skin. Fourier transform infrared (FTIR) study revealed that the major absorption bands of gelatin from the skins of both sharks shifted to a higher wavenumber, compared with their corresponding acid soluble collagen (ASC). Therefore, gelatins from the skin of BBS has a potential to replace mammalian for gelatin, due to its similarity in bloom strength and setting behavior to the commercial bovine bone gelatin.