Mammalian Gelatin Research Articles

Mechanical Properties of Mammalian and Fish Gelatins as a Function of the Contents of α-Chain, β-Chain, and Low and High Molecular Weight Fractions

Small-strain oscillatory measurements and size-exclusion chromatography coupled to multiangle laser light scattering were used to study the mechanical properties and the molecular weight distribution, respectively, of acid porcine skin gelatins (type A), lime bovine bone gelatins (type B), and cold water fish gelatins, while principal component analysis (PCA) and partial least squares regression were used to relate the mechanical properties with the molecular weight distribution. The present study suggests a linear relationship between the mechanical properties and the fractions of low molecular weight (LMW) molecules, α-chains, β-chains, and high molecular weight (HMW) molecules. The Bloom value for mammalian gelatin was positively correlated with the fractions of α-chains, β-chains, and HMW molecules and negatively correlated with the fraction of LMW molecules. The dynamic storage modulus for cold water fish gelatin was positively correlated with the fractions of β-chains and HMW molecules and negatively correlated with the fractions of LMW molecules and α-chains.

Mechanical properties of mammalian and fish gelatins based on their weight average molecular weight and molecular weight distribution

Acid porcine skin gelatins (type A), lime bone gelatins (type B) and gelatin from different cold water fish species were compared on the basis of low deformation mechanical properties, Bloom value, weight average molecular weight, molecular weight distribution and isoelectric point. The dynamic storage modulus and Bloom value for all types of gelatin increased with increasing weight average molecular weight. Type A and type B gelatins with similar weight average molecular weight exhibited different dynamic storage modulus (G′) and different Bloom values. This is most probably due to a different molecular weight distribution as well as the presence of different hydrolytic fragments. The present study suggests that it may be possible to improve the mechanical properties by removing low molecular weight molecules from a gelatin sample. The Bloom values for gelatin from haddock, saithe and cod were determined to be 200, 150 and 100 g from a linear correlation between G′ and Bloom.

Instrumental texture profile analysis of gelatin gel extracted from grouper skin and commercial (bovine and porcine) gelatin gels

Mechanical compression was used to study the gelling characteristics of gelatin gels. Texture profile analysis (TPA) showed that the hardness of fish and mammalian gelatin increased significantly as the concentrations of gels increased. TPA attributes of 10% fish skin gel showed significant differences from those obtained from 20% and 30% gels. In bovine and porcine cases, such generic trends were not observed. Mechanical characteristics of 10% gels of gelatin from fish skin, determined from one cycle compression, were significantly lower than other sources of gelatin gels, while bovine and porcine gels did not show any significant differences. In the case of TPA, hardness of bovine gelatin gel was highest at 41 N for 10% gel, followed by porcine (30 N) then fish skin (5 N) gelatin gels. The gels prepared from different sources did not show any generic trends when all other mechanical attributes were considered.

황다랑어 복부 껍질로부터 추출한 gelatin의 물리화학적 특성

Physicochemical characteristics of gelatin extracted from abdominal skin of yellowfin tuna (Thunnus albacares), were investigated by comparing its proximate composition, pH, amino acid composition, viscoelastic properties, gel strength and SDS-PAGE patterns, with those of bovine and porcine gelatins. The effects of gelatin concentration, maturation time, heat and freeze treatments on the gel strength of yellowfin tuna abdominal skin gelatin were studied. Amounts of $\alpha$-chains, $\beta$- and $\gamma$-components of yellowfin tuna abdominal skin gelatin were higher than those of the two mammailan gelatins. Yellowfin tuna abdominal skin gelatin had the lowest imino acids (proline and hydroxyproline) content, which was consistent with that of other fishes. However, yellowfin tuna abdominal skin gelatin was highest in glycine, alanine, and lysine. The gel strengths of all gelatins were proportional to the concentration of gelatin, but yellowfin tuna abdominal skin gelatin exhibited the greatest gel strength at each concentration. Yellowfin tuna abdominal skin gelatin required a longer maturation time than the two mammalian gelatins to form a firm gel. Higher heating temperature decreased the gel strength of yellow fin tuna abdominal skin gelatin more than in the two mammalian gelatins. Freezing decreased the gel strength of bovine gelatin only slightly, but longer freezing times resulted in greater reductions in gel strength in the yellowfin tuna abdominal skin and porcine gelatins.

DEVELOPMENT OF AN USER-FRIENDLY VIRTUAL ENVIRONMENT FOR DESIGN AND SIMULATION OF FOOD PROCESSING PLANTS: APPLICATION TO THE VALORIZATION PROCESS OF FISH SKINS TO OBTAIN GELATINES

ISHS IV International Symposium on Applications of Modelling as an Innovative Technology in the Agri-Food-Chain: Model-IT DEVELOPMENT OF AN USER-FRIENDLY VIRTUAL ENVIRONMENT FOR DESIGN AND SIMULATION OF FOOD PROCESSING PLANTS: APPLICATION TO THE VALORIZATION PROCESS OF FISH SKINS TO OBTAIN GELATINES

Cold water fish gelatin films: Effects of cross-linking on thermal, mechanical, barrier, and biodegradation properties

Gelatin was extracted from Alaska pollock ( Theragra chalcogramma) and Alaska pink salmon ( Oncorhynchus gorbuscha) skins and cast into films. The fish gelatin films’ tensile, thermal, water vapor permeability, oxygen permeability, and biodegradation properties were compared to those of bovine and porcine gelatin films. In addition, fish gelatin films were cross-linked with glutaraldehyde. Pollock and salmon gelatin films had comparable tensile properties, but had lower tensile strength and percent elongation than mammalian gelatin films. The lower strength and elongation might have been due to lower structural gelatin levels present in fish gelatin films. The addition of cross-linkers had little effect on tensile properties and melting temperatures of fish gelatin films. Pollock gelatin films had the lowest water vapor and oxygen permeability values, whereas mammalian gelatin films had the highest permeability values. Cross-linking resulted in lower water vapor permeability for salmon gelatin films and higher oxygen permeability for pollock gelatin films. However, all fish gelatin films had better water vapor and oxygen barrier properties than mammalian gelatin films. Also, fish gelatin films degraded faster than mammalian gelatin films.

Thermal characterisation of gelatin extracted from yellowfin tuna skin and commercial mammalian gelatin

Glass transition and other thermal characteristics of gelatin from different sources were studied by differential scanning calorimetry (DSC) and modulated DSC (MDSC). The initial glass transition temperatures of equilibrated gelatin samples at 11.3% relative humidity, determined from reversible heat flow thermogram of MDSC, were 23, 75 and 59°C, respectively, for tuna skin, bovine and porcine gelatin. When gelatin samples were equilibrated at higher relative humidity of 52.9%, glass transition temperature of fish skin and bovine gelatin decreased to −3 and 57°C, respectively. Further increase of equilibration relative humidity to 75.3% showed increased value in the case of tuna skin, whereas bovine and porcine did not show any significant change. DSC and MDSC results indicated that tuna gelatin showed lower glass transition compared to mammalian source gelatin equilibrated at the same constant relative humidity. In general glass transition measured by DSC was found lower than the values measured by MDSC. The results in this study showed that the degree of plasticization varied with the source of gelatin as well as their extraction methods.

Characterization of Edible Film Fabricated with Channel Catfish (Ictalurus punctatus) Gelatin Extract Using Selected Pretreatment Methods

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 degrees 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 degrees 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.

Nanostructural Characterization of Catfish Skin Gelatin Using Atomic Force Microscopy

To determine the nanostructure of gelatin from catfish (Ictalurus punctatus) skin, atomic force microscopy (AFM) was used to study gelatin aggregates. The gelatin was extracted at an optimized acid concentration after alkaline processing. First, the AFM imaging parameters were optimized to obtain high-quality images. Then height mode with a 2-dimensional plane, 3-dimensional topographical images, and error signal mode images, which removed slow variations in surface topography but highlighted the edges of sample features, were used to analyze the structure of particles. The results describe fish gelatin at a nanoscale level for the first time and are compared with AFM images of mammalian gelatins. Both annular pores with diameters averaging 118 nm and spherical aggregates with an average diameter of 267 nm were seen in the AFM images of fish gelatin. From the AFM images, we propose that the structures formed were determined by whether the solution penetrated into the gelatin molecules evenly or not during hydrolysis. A scheme for the formation of annular pores and spherical aggregates is proposed.

Utilization of Fish Processing By-Products in the Gelatin Industry

Since the bovine spongiform encephalopathy crisis, there has been a growing interest for finding an alternative source of raw materials for gelatin production. Gelatin produced from fish processing by-products is a potential alternative to mammalian gelatin. Fish processing generates solid wastes that can be as high as 50–80% of the original raw material. These wastes are an excellent raw material for preparation of high protein foods. About 30% of the wastes consists of skin and bone with a high collagen content. Fish gelatin can be obtained by hydrolysis of collagen the principal protein found in skin and bone. Fish skin and bone gelatin can be prepared with bloom strength similar to that obtained from mammalian sources. Fish gelatin has numerous applications, particularly, in the food, pharmaceutical, and photographic industries due to its unique chemical and physical properties. This review presents how fish processing by-products can be utilized in the manufacture of gelatin.

Influence of Transglutaminase‐Induced Cross‐Linking on Properties of Fish Gelatin Films

ABSTRACT: Fish gelatin (FG) is a potential alternative to current mammalian (beef and pork) gelatin. However, its physical and thermal properties limit its use in many applications. The treatment of microbial transglutaminase (MTGase) on FG could be a practical way to increase the use of FG films in various applications. Physical properties, barrier properties, and molecular weight change of FG films were measured. The viscosity of the MTGase‐treated FG solution significantly (P < 0.05) increased from 6.81 ± 0.65 cP to 35.04 ± 3.59 cP as the reaction time and concentration of MTGase increased. After employing 2% of MTGase into FG solution, the tensile strength increased from 48.03 ± 5.45 MPa to 68.00 ± 1.9 MPa, while percent elongation decreased from 13.1%± 2.90% to 1.47%± 0.05%. Oxygen barrier property was significantly (P < 0.05) increased from 7.24 ± 1.48 cc·m/m2·d to 17.69 ± 3.08 cc·m/m2·d, while water vapor permeability was not statistically (P < 0.05) different. The melting temperature (Tm) measured by differential scanning calorimetry increased from 124.78 ± 1.98 °C to 158.49 ± 2.68 °C as the enzyme reaction time increased. The color values of L*, a*, and b* were changed from 95.56 ± 0.09 to 95.50 ± 0.06, from −0.17 ± 0.01 to −0.23 ± 0.00, and from 3.17 ± 0.04 to 3.47 ± 0.09, respectively. The opacity significantly (P < 0.05) increased from 1.43%± 0.32% to 2.87%± 0.06%. SDS‐PAGE results showed that the molecular weight of fish gelatin films increased when the MTGase reaction takes place.

Characterizations of fish gelatin films added with gellan and κ-carrageenan

Fish gelatin is known to be inferior to mammalian gelatins. Gellan and κ-carrageenan were added to improve properties of the fish gelatin films. Initially, polysaccharides were added to make fish gelatin gels, and tested for the melting point. Mechanical, barrier, color and microstructure properties, as well as Fourier transform infrared (FTIR) and thermal analysis (DSC) of the modified fish gelatin films were evaluated. The addition of gellan and κ-carrageenan increased the melting point of fish gelatin gels, gellan being more effective. Polysaccharides modified fish gelatin films by increasing tensile strength and barrier against water vapor, but made films slightly darker. Scanning electron microscopy (SEM) microstructure analysis revealed that gellan eliminated cracks present in the film matrix resulting in a more uniform structure. FTIR and DSC analyses showed that both polysaccharides effectively interacted with fish gelatin, and moreover, gellan being more effective. Overall, addition of gellan up to 2 g/100 g of gelatin performed better in enhancing fish gelatin films properties.

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.

Reduced Proteolysis of Secreted Gelatin and Yps1-Mediated α-Factor Leader Processing in a Pichia pastoris kex2 Disruptant

Heterologous proteins secreted by yeast and fungal expression hosts are occasionally degraded at basic amino acids. We cloned Pichia pastoris homologs of the Saccharomyces cerevisiae basic residue-specific endoproteases Kex2 and Yps1 to evaluate their involvement in the degradation of a secreted mammalian gelatin. Disruption of the P. pastoris KEX2 gene prevented proteolysis of the foreign protein at specific monoarginylic sites. The S. cerevisiae alpha-factor preproleader used to direct high-level gelatin secretion was correctly processed at its dibasic site in the absence of the prototypical proprotein convertase Kex2. Disruption of the YPS1 gene had no effect on gelatin degradation or processing of the alpha-factor propeptide. When both the KEX2 and YPS1 genes were disrupted, correct precursor maturation no longer occurred. The different substrate specificities of both proteases and their mutual redundancy for propeptide processing indicate that P. pastoris kex2 and yps1 single-gene disruptants can be used for the alpha-factor leader-directed secretion of heterologous proteins otherwise degraded at basic residues.

Extracting optimization and physical properties of yellowfin tuna ( Thunnus albacares) skin gelatin compared to mammalian gelatins

This work is to optimize gelatin extraction from dorsal skin of yellowfin tuna ( Thunnus albacares) using response surface methodology, and to compare physical properties of yellowfin tuna skin gelatin with those of two mammalian skin gelatins (bovine and porcine). Central composite design was adopted in gelatin processing for extracting optimization. Concentration of NaOH ( X 1), treatment time ( X 2), extraction temperature ( X 3) and extraction time ( X 4) were chosen for independent variables. Dependent variables were gel strength ( Y 1) and gelatin content ( Y 2). Optimal conditions were X 1=1.89(%), X 2=2.87 (days), X 3=58.15 (° C) and X 4=4.72 (h), and predicted values of multiple response optimal conditions were Y 1=429.1 (Bloom) and Y 2=89.7 (%). In order to investigate physical properties of yellowfin tuna skin gelatin, gel strength, gelling and melting points, and dynamic viscoelastic properties were measured. The gel strength of yellowfin tuna skin gelatin (426 Bloom) was higher than bovine and porcine gelatins (216 Bloom and 295 Bloom, respectively), while gelling and melting points were lower. Dynamic viscoelastic properties of yellowfin tuna skin gelatin did not change at 20 °C, but increase at 10 °C as a similar pattern with mammalian gelatins.

Physical behaviour of fish gelatin-κ-carrageenan mixtures

Fish gelatin is a possible alternative to, but not directly exchangeable with, mammalian gelatin due to low gel strength and low gelling and melting temperature. A possible approach to overcome these differences could be to mix fish gelatin and marine polysaccharides leading to systems with improved gel strength, gelling and melting temperature. Mixtures of fish gelatin and κ-carrageenan resulted in solutions and gels with varying degree of turbidity, depending on the concentration of polymers, pH, ionic strength and the nature of the added salt. The turbidity is most probably a result of phase separation in the system and was followed by measuring the optical density. Complexes of fish gelatin and κ-carrageenan at 60 °C were probably stabilised by electrostatic interactions, and the solutions were highly turbid. At room temperature and at 4 °C the turbidity of the mixed systems was much lower, and could be due to altered gel morphology. The system is believed to segregate when carrageenan adapts the ordered conformation and forms a gel network. Compression measurements revealed a considerable increase in Young's modulus when mixed solutions were allowed to gel at 4 °C compared to gelling at room temperature.

Physical and rheological properties of fish gelatin compared to mammalian gelatin

This study comprises characterisation of fish gelatin (FG) from cold water fish species, including rheological and optical rotation measurements. SEC-MALLS analysis revealed that fish gelatin is heterogeneous in molecular compositions and that it mainly contains α- and β-chains. Fish gelatin gave gels with a considerably lower storage modulus, G′, gelling (4–5 °C) and melting temperature (12–13 °C) compared to mammalian gelatin gels. This is probably due the lower content of proline and hydroxyproline in fish gelatin. Recording the storage modulus for 10 (w/w)% FG at various ionic strengths showed that G′ increased at low ionic strengths, while decreasing at medium to high salt concentrations. This suggests that electrostatic interactions are important in the stabilisation of the gelatin gel network. This suggestion was further supported by a partly reversible lowering of the gel modulus by the neutralisation of the carboxyl and amino groups at low and high pH, respectively. Optical rotation experiments clearly showed the importance of the amount of Pro and Hyp present in the gelatin. The degree of chain segment ordering at the gelling temperature in fish gelatin (at 5 °C) and mammalian gelatin (20 °C) was almost identical. This clearly showed the importance of the content of imino acids for the formation of some ordered structures and stabilisation of the gelatin gel network.

Rheological characterisation of gelatins from mammalian and marine sources

The aim of this work is to examine different blends of mammalian and fish gelatins and to investigate how the properties of the single component gels are altered in blends. Small deformation rheological measurements have been used to characterise the gelling and melting temperatures and the gel modulus. Both tropical and cold water fish samples were studied. Results so far indicate that in mammalian/fish mixtures, no significant difference in melting point from the single mammalian system is seen for the warm water fish blends. The modulus also remains relatively constant for all combinations studied. With the cold water fish blends however, both the modulus and gel melting temperature of the cod gelatin is lowered considerably in the presence of a small concentration of mammalian gelatin. At higher concentrations, mixtures show behaviour similar to mammalian gelatins. Concurrent with this work, an analysis of (a) the concentration vs. modulus behaviour of the single systems and (b) concentration vs. melting temperature has been carried out.

Reactivity of the immunoglobulin E in bovine gelatin-sensitive children to gelatins from various animals.

It has been reported that most children who showed anaphylaxis to measles, mumps and rubella vaccines containing bovine gelatin as a stabilizer have anti-bovine gelatin IgE. The present study was designed to investigate the reactivity of IgE in bovine gelatin-sensitive children to gelatins from various animals, and the antigenic cross-reactivity between the gelatins. Serum samples taken from 10 children who showed anaphylaxis to vaccines containing bovine gelatin were used in this study. The level of anti-bovine gelatin IgE in these serum samples ranged from 11.0 to 251 Ua/ml. The IgE in most of the children reacted to kangaroo and mouse gelatins, to which they had had little or no exposure as a food or a vaccine stabilizer. The IgE binding to kangaroo and mouse gelatins was completely inhibited by bovine gelatin, whereas reciprocal inhibition was not complete, indicating that antigenic cross-reactivity is present between the mammalian gelatins. Only one child had strong IgE reactivity to fish gelatins, and this reactivity was not inhibited by bovine gelatin, indicating that no antigenic cross-reactivity exists between bovine and fish gelatins. Most of the children who displayed sensitivity to bovine gelatin showed IgE reactivity to other mammalian gelatins. This reactivity may be due primarily to the antigenic cross-reactivity between mammalian gelatins.

Investigation of viscosity and gelation properties of different mammalian and fish gelatins

An easy-to-use method has been established to investigate important process parameters of gelatin solutions: viscosity, gelation temperature and gelation process. The measurement of these parameters is exemplified on several mammalian gelatins and is used to investigate the differences between mammalian and fish gelatins in solution. Hydrodynamic radii have been determined in addition by photon correlation spectroscopy. A series of mammalian gelatins of different Bloom numbers (from hydrolyzed to Bloom 300 gelatins) has been investigated. Gelation temperature, solution viscosity and hydrodynamic radius increase with increasing Bloom number. The activation energy of the gelation process is found to decrease with increasing Bloom number. Three fish gelatin samples have been investigated by the same technique. The fish gelatins show rather low gelation temperature, but relatively high solution viscosities. They do not correlate with any of the investigated mammalian gelatins. These fish gelatins therefore provide a type of gelatin with different technological properties compared to the mammalian gelatins. This could enlarge the already broad field of gelatin applications even further. The fish gelatins can find use in applications where high solution viscosity without gel formation is desired.