Gelatin Extraction Research Articles

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, MgCl 2, MgSO 4 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 Mg 2+ gave rise to the retaining of this bivalent cation in the resultant gelatin, which is detrimental to the gelatin quality.

Storage of dried fish skins on quality characteristics of extracted gelatin

Drying was evaluated as preservation method for storage of Dover sole ( Solea vulgaris) skins. Fish skins were air-dried by using ethanol, ethanol–glycerol mixture and marine salt, and stored at room temperature for 160 days. Gelatin extraction was carried out periodically during the storage time, and the quality of the resulting gelatin preparations was evaluated according to the molecular weight distribution, viscoelastic properties, gelling and melting temperatures and gel strength. All the drying methods used showed a similar effect on the gelatin quality characteristics evaluated. Although drying involved a slight decrease in viscoelastic properties as well as gelling and melting points, it was striking the great protein stability found throughout the storage period. Drying scarcely affected gel strength, which values did not show noticeable changes along the storage.

Extraction of gelatin from fish skins by high pressure treatment

High pressure, at 250 and 400 MPa, for 10 or 20 min, was applied at either of two stages: during pre-treatment in acid at 10 °C to facilitate destabilisation of acid labile crosslinks, or during extraction in water at 45 °C to accelerate collagen hydrolysis. The resulting gelatins were evaluated in terms of yield of extraction, molecular weight distribution by SDS-PAGE, and viscoelastic properties of gelatin newly dissolved and after overnight cold maturation. Pressure level and time of treatment induced noticeable changes in molecular weight distribution and consequently affected viscoelastic properties. The use of high pressure to extract gelatin from fish skins is a useful alternative to the conventional procedure. Its utility lies basically in that the longest phase of the treatment can be drastically shortened, thus making it possible to produce a gelatin of high gelling quality in only a few minutes.

Use of lactic acid for extraction of fish skin gelatin

The ability of lactic acid compared to acetic acid for Dover sole ( Solea vulgaris) skin swelling and the subsequent gelatin extraction was examined. The resultant gelatins were evaluated in terms of extraction yield, amino acid composition, molecular weight distribution, gel strength, viscoelastic properties, ability to refold into triple helical structures, and aggregation phenomena. Lactic acid (25 mM) proved to be an excellent substitute for acetic acid during the skin swelling process, as the gelatin preparation thus obtained presented quite similar properties to that prepared by using 50 mM acetic acid without the negative organoleptic properties of this acid. However, the application of 50 mM lactic acid gave rise to a highly hydrolysed gelatin, with lower folding ability, gel strength and viscoelastic properties than those obtained using 25 mM lactic acid or 50 mM acetic acid.

Highly porous silica networks derived from gelatin/siloxane hybrids prepared starting from sodium metasilicate

The formation of polymeric hybrid materials of siloxanes with gelatin (GE) starting from sodium metasilicate as the silica source, and their transformation into silica under different conditions have been studied. Gelatin/silicate hybrid nanocomposites were obtained by acid precipitation of mixed gelatin and sodium silicate solutions. Porous xerogels with large BET areas (452m2/g) constituted by closed packed microspheres (1μm diameter) containing residual gelatin in microporous domains were obtained after thorough extraction of gelatin with water from the nanocomposites. By calcination at 550°C the residual gelatin occluded in the micropores was eliminated and a highly microporous silica (BET area 834m2/g) with microspherical morphology was produced. Blanks were prepared in order to establish the role of GE in the process. Silica samples obtained under the same conditions but without gelatin also have large BET areas but they are mesoporous (40–100Å), presenting an irregular morphology on a micron scale. The morphological and textural differences between both silica types demonstrate the nanocomposite structure of the hybrids, making evident the templating role of gelatin in the formation of the silica network.

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.

Optimization of Extraction Conditions for Pollock Skin Gelatin

ABSTRACT: Seven potential variables, pretreatment temperature, pretreatment time, concentration of OH−, concentration of H+, extraction temperature, extraction time, and skin/water ratio, were investigated by a 27‐3 fractional factorial design to identify critical control factors for pollock skin gelatin extraction, and 3 responses, yield, gel strength, and viscosity, were evaluated. The results suggest that 4 variables, pretreatment temperature, concentration of OH−, concentration of H+, and extraction temperature, have significant effects on gelatin extraction, and these key factors were then selected for the subsequent optimization using response surface methodology with a 4‐factor, 5‐level central composite rotatable design. It suggests that a concentration of OH− at 0.25 mol/L, a concentration of H+ at 0.09 mol/L, a pretreatment temperature at 2°C, and an extraction temperature at 50°C, will give the highest values for the 3 responses. The predicted responses for these extraction conditions are that the yield will be 18%, gel strength will be 460 g, and viscosity will be 6.2 c P.

Isolation, Characterization, and Identification of Bacterial Contaminants in Semifinal Gelatin Extracts

Bacterial contamination of gelatin is of great concern. Indeed, this animal colloid has many industrial applications, mainly in food and pharmaceutical products. In a previous study (E. De Clerck and P. De Vos, Syst. Appl. Microbiol. 25:611-618), contamination of a gelatin production process with a variety of gram-positive and gram-negative bacteria was demonstrated. In this study, bacterial contamination of semifinal gelatin extracts from several production plants was examined. Since these extracts are subjected to harsh conditions during production and a final ultrahigh-temperature treatment, the bacterial load at this stage is expected to be greatly reduced. In total, 1,129 isolates were obtained from a total of 73 gelatin batches originating from six different production plants. Each of these batches was suspected of having bacterial contamination based on quality control testing at the production plant from which it originated. For characterization and identification of the 1,129 bacterial isolates, repetitive-element PCR was used to obtain manageable groups. Representative strains were identified by means of 16S rRNA gene sequencing, species-specific gyrB PCR, and gyrA and rpoB sequencing and were tested for gelatinase activity. The majority of isolates belonged to members of Bacillus or related endospore-forming genera. Representative strains were identified as Bacillus cereus, Bacillus coagulans, Bacillus fumarioli, Bacillus amyloliquefaciens, Bacillus licheniformis, Bacillus pumilus, Bacillus sonorensis, Bacillus subtilis, Bacillus gelatini, Bacillus thermoamylovorans, Anoxybacillus contaminans, Anoxybacillus flavithermus, Brevibacillus agri, Brevibacillus borstelensis, and Geobacillus stearothermophilus. The majority of these species include strains exhibiting gelatinase activity. Moreover, some of these species have known pathogenic properties. These findings are of great concern with regard to the safety and quality of gelatin and its applications.

Fourier transform infrared (FTIR) spectroscopic study of acid soluble collagen and gelatin from skins and bones of young and adult Nile perch ( Lates niloticus)

Fourier transform infrared (FTIR) spectroscopy was conducted on type A gelatins derived from skins and bones of young and adult Nile perch ( Lates niloticus) by a sequential extraction process. Spectra for gelatins were compared to each other and to that of acid soluble collagen from young Nile perch skins, in order to elucidate changes in protein secondary structure during collagen to gelatin transformation. The first gelatin extracts showed diminished amide III bands while the last gelatin extracts showed distinct amide III bands and their amide I bands consisted of a higher percent area of a component around 1690 cm −1. The differences suggested that the collagen to gelatin transition leads to loss of molecular order. The later gelatin extracts exhibited higher molecular order than earlier gelatin extracts, probably because the former contained surviving crosslinks or/and because renaturation of the low molecular weight gelatin fractions (later gelatin extracts) led to formation of more protein–protein linkages.

Modification of the properties of gelatin from skins of Baltic cod ( Gadus morhua) with transglutaminase

The aim of the investigations was to optimize the procedure of gelatin extraction from the skins of Baltic cod ( Gadus morhua) and to modify the properties of fish gelatin, using transglutaminase, to form gels at room temperature. A temperature of 45 °C and 30 min of extraction was established as optimal conditions for preparing gelatin from cod skins. Fish gelatin in 5% solutions formed gels at room temperature in the presence of transglutaminase (0.15–0.7 mg of enzyme protein/ml), depending on the reaction time. Transglutaminase was also active in crosslinking of fish gelatin at 4–5 °C. The deformation of gels obtained from 5% gelatin solutions after a 24-h incubation with transglutaminase, at concentration 0.25 mg/ml, measured at 6–8 °C, was the same as or slightly lower than in control samples (without enzyme). Fish gelatin gels, enzymatically crosslinked, did not melt after 30 min of heating in a boiling water bath.

Preparation and characterisation of gelatine from the skin of harp seal ( Phoca groendlandica)

This paper describes a method for extraction of gelatine from the skin of harp seal at mild acid conditions and gives a chemical and physical comparison of this gelatine with other mammalian and cod-skin gelatines. As compared to the wet weight of unhaired skin, a recovery of 11% dry gelatine was achieved after acid treatment and a two step water extraction at 60 and 75 °C. The chemical and physical properties of the gelatine were similar to the properties of commercial gelatines made from bovine and porcine skin, but significantly different from the properties of Atlantic cod-skin gelatine. The results indicated that seal skin gelatine can be used as a substitute for standard commercial gelatines for food technology applications.

Development of a Sandwich Enzyme-Linked Immunosorbent Assay for the Detection of Egg Residues in Processed Foods

Chicken eggs are used extensively as an excellent source of dietary proteins. These proteins have many functional properties, making them valuable food ingredients. However, eggs are a frequent cause of food hypersensitivity, especially in children. Of major concern to food processors is the inadvertent cross-contact of food products with allergenic residues, which could result in potentially life-threatening reactions in those with a food allergy. The aim of the present study was to develop an enzyme-linked immunosorbent assay (ELISA) for the detection of undeclared egg residues in foods. Commercially purified ovalbumin (OVA) and dehydrated egg white solids were used as antigens to induce antibodies in rabbits and goats. Reference pasta standards and various food samples were extracted, then clarified by centrifugation. Goat anti-egg white antibodies were used as the capture reagent, nonspecific sites were blocked with gelatin, then standard and sample extracts were added. Rabbit anti-OVA antibodies were used as detector antibodies, followed by addition of commercial goat anti-rabbit IgG antibody labeled with alkaline phosphatase and subsequent substrate addition. Twenty brands of egg-free pasta (two lots each) were analyzed using the ELISA. Fourteen common pasta ingredients were also evaluated for cross-reactivity problems in the method. The detection limit of the assay was 1 ppm spray-dried whole egg. Fifty-five percent (22 samples) of the egg-free pasta samples tested positive for the presence of undeclared egg residues, with values ranging from 1 to >100,000 ppm. Minimal cross-reactivity was encountered in general, but portobello mushrooms and basil caused some minor matrix effects. This sandwich-type ELISA method can be used to detect undeclared egg residues in processed foods and to evaluate industrial clean-up operations.

Purification and characterization of angiotensin I converting enzyme (ACE) inhibitory peptides from Alaska pollack ( Theragra chalcogramma) skin

Proteolytic digestion of gelatin extracts from Alaska Pollack ( Theragra chalcogramma) skin brings about a high angiotensin I converting enzyme (ACE) inhibitory activity. Gelatin extracts were hydrolyzed by serial protease-treatments in the order of Alcalase, pronase E, and collagenase using a three-step recycling membrane reactor. Fragments arising from the third step were composed of peptides ranging from 0.9 to 1.9 kDa and responsible for ACE inhibitory activity. Catalytically active two peptides were separated by the consecutive chromatographic methods including gel filtration, ion-exchange chromatography, and reverse-phase high performance liquid chromatography. The isolated peptides were composed of Gly-Pro-Leu and Gly-Pro-Met and showed IC 50 values of 2.6 and 17.13 μM, respectively. These results suggested that Gly-Pro-Leu would be useful as a new antihypertensive agent.

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.

Coprothermobacter platensis sp. nov., a new anaerobic proteolytic thermophilic bacterium isolated from an anaerobic mesophilic sludge.

A new anaerobic, proteolytic, moderately thermophilic bacterium, strain 3RT, was isolated from a methanogenic mesophilic reactor treating protein-rich wastewater. The cells were Gram-negative, non-spore-forming, non-motile rods. The DNA base composition was 43 mol% G + C. The optimum pH and temperature for growth were 7.0 and 55 degrees C respectively. The bacterium fermented gelatin, casein, bovine albumin, peptone and yeast extract. Glucose, fructose, sucrose, maltose and starch were poorly fermented. The major fermentation products from glucose were acetate, CO2 and H2 and, from gelatin, propionate was also detected. Growth on glucose was stimulated by thiosulfate, which was reduced to sulfide. Sulfate and nitrate were not reduced. 16S rRNA gene analysis revealed that the isolated bacterial strain was phylogenetically related to Coprothermobacter proteolyticus (96.3% sequence similarity), the only known species within the genus. DNA-DNA hybridization analysis demonstrated a very low level of homology, indicating that the isolated strain and C. proteolyticus were not related at species level. Therefore, it is proposed to classify the described strain in the genus Coprothermobacter as a new species, Coprothermobacter platensis. The type strain of C. platensis is strain 3RT (= DSM 11748T).

D-Amino Acids in Non-gelling Components of Gelatin

As a possible cause of the non-gelling property of the sol fraction of gelatin, we considered that higher D-amino acid content should result in decreased formation of helices. The sol fractions ivere extracted from gelatin gels and hydrolyzed to amino acid mixtures. The rates of reaction with D-amino acid oxidase (D-AOX) were recorded for thehydrolyzates. For a comparison, residual gels were also treated similarly. The sol fractions always gave higher results than the residual gels for the three types of gelatin examined. The result also showed that the rates obtained from the sol fractions were in the order: limed ossein > limed hide > acid pigskin.To examine the reliability of this procedure the D-form content for each amino acid in the sol from the limed hide gelatin was compared with that of the residual gel. The contents in the sol were higher than those in the residue for most of the amino acids which racemized. The results indicate that the increased racemization of amino acids on the extraction of gelatin from raw materials is a cause of the non-gelling property.

A hyperthermophilic sulfur-reducing archaebacterium, Thermococcus sp. DT1331, isolated from a deep-sea hydrothermal vent.

A hyperthermophilic archaebacterium was isolated from a deep-sea black smoker chimney (depth, 760 m) at the Minami-ensei Knoll (28 degrees 23'N, 127 degrees 38'E). The strain, designated DT1331, was a coccoid shaped bacterium about 0.5 to 1.0 microns in diameter. The cells were surrounded by a cell envelope. The temperature for growth was between 55 degrees C and 93 degrees C with an optimum 80 degrees C. The growth occurred from pH 4.5 to 8.5 and the optimum pH was 6.0. DT1331 required 1% to 5% NaCl for growth and cell lysis was observed below 1% NaCl concentration. The strain was an anaerobic chemoorganotroph requiring elemental sulfur obligately. Organic substrates used included tryptone, peptone, soytone, casein, gelatin, and yeast extract. Under the optimal conditions, DT1331 had a generation time of 50 min and could reach densities of about 1.5 x 10(8) cells/ml. DT1331 was resistant to ampicillin, chloramphenicol, erythromycin, kanamycin, streptomycin, and tetracycline, which was one of the common characteristics of archaebacteria. The G+C content of DT1331 was 52.3 mol%. Analysis of the 16S rRNA gene by restriction enzymes coincided with those of Thermococcus celer, indicating that this strain belonged to the genus Thermococcus.

Thermococcus profundus sp. nov., A New Hyperthermophilic Archaeon Isolated from a Deep-sea Hydrothermal Vent

Summary A hyperthermophilic coccoid archaeum of 1–2 μn in diameter, designated as strain DT5432, was isolated from a deep-sea hydrothermal vent system (depth, 1,395 m) at the Middle Okinawa Trough (27°33′N, 126°58′E). This organism was an anaerobic chemoorganotroph obligately requiring elemental sulfur and 1–6% NaCl. H 2 S was formed during growth. The strain was motile due to a polar tuft of flagella. The cells were surrounded by a thick cell envelope of 40 to 45 nm in width. Organic substrates utilized included tryptone, peptone, casein, gelatin and yeast extract. Growth of this organism was observed on a synthetic medium containing pyruvate, maltose or starch. The temperature range for growth was between 50 and 90 °C with an optimum at 80 °C. Growth was observed between pH 4.5 and 8.5. Under optimal conditions DT5432 had a generation time of 50 min and could reach densities of 8 × 10 8 cells/ml. The G+C content of DT5432 was 52.5 mol%. A partial nucleotide sequence of the 16S rRNA gene indicated that it belonged to the genus Thermococcus . The strain did not show significant DNA homology with Thermococcus celer and Thermococcus stetteri . On the basis of morphological, physiological and genetic differences with previously described organisms, we propose that DT5432 be designated as a new species with the name Thermococcus profundus .

Determination of the hydrogen isotopic composition of bone collagen and correction for hydrogen exchange

The hydrogen isotopic measurement (δD) of the non-exchangeable hydrogens in herbivore bone collagen has potential for paleoclimate research. We have developed the methodology for extracting the hydrogen from collagen for isotopic analysis and for correcting the δD results for hydrogen exchange. Preparations of whole bone powders, demineralized bone, or gelatin extracts from fresh bone samples all give reliable δD results and have isotopic results, yields, and proportions of exchangeable hydrogens consistent with that expected for collagen. Gelatin extraction for removal of contaminants remains a valuable option for the study of fossil bone samples. Vacuum preheating under good vacuum at 150°C for two days for whole bone powders and at 100°C for one day for gelatins is an important step to remove all adsorbed water before samples are oxidized for isotopic analysis. Of the remaining hydrogens released following oxidation, 20.5% in whole bone powders and 23.1% in gelatin extracts exchange with laboratory atmospheric water vapor within 48 hours. The δD results can be corrected for this exchange and for minor effects of sample preparation by using a calibration bone standard to determine the δD value of laboratory water vapor.

Ammonification of complexes prepared from gelatin and aqueous extracts of leaves and freshly-fallen litter of trees on different soil types

The rates of decomposition of polyphenol-gelatin complexes were studied in two sets of experiments. In the first set, ammonification rates of complexes formed from aqueous extracts of green, pre-dehiscent leaves and from aqueous extracts of freshly-fallen litter of a range of tree species and one shrub were determined using a standard soil inoculum and the unspecialized microflora of distilled water. The second set of experiments investigated the rates of ammonification of complexes prepared from green, pre-dehiscent leaves of a smaller range of species, using inocula prepared from the soils beneath the trees from which the leaves had been collected and with the medium buffered to the appropriate soil pH. The quantity of polyphenol-gelatin complex formed differed between species, within species between green pre-dehiscent leaves and freshly-fallen litter, and in the case of birch, sycamore, oak, and hybrid larch, within species between sites. Aqueous extracts of both green, pre-dehiscent leaves and fresh litter of elm, ash, and beech did not form precipitates with gelatin. Six of the 14 complexes formed from aqueous extracts of green, pre-dehiscent leaves were ammonified to some extent by the unspecialized microflora in unsterilized distilled H 2O, which suggests that the complexes have a relatively low resistance to ammonification. Complexes formed from leaves of hybrid larch at Grizedale forest, Sitka spruce, western hemlock, and grand fir, released no more mineral N with the soil inoculum than with microbial inhibitors, which suggests that those complexes are very resistant to ammonification. Complexes formed from aqueous extracts of freshly-fallen litter released more N in the presence of the soil inoculum than did complexes formed from aqueous extracts of green, pre-dehiscent leaves of the same species. In general, the release of mineral N from the complexes was fitted well by double exponential regressions, with R 2 values between 68 and 94%. From these regressions, the time taken for half of the N in a complex to be released ranged from 2 days (complex prepared from leaves of sycamore on a brown earth of high base status) to 56 weeks (complex prepared from leaves of birch growing on a brown podzolic soil). The regressions showed that complexes prepared from green, pre-dehiscent needles of western hemlock, Norway spruce, and Sitka spruce would never release 50% of their N in the experimental conditions.