Extraction and characterisation of gelatine from Atlantic salmon (Salmo salar) skin

Gelatine was extracted from Atlantic salmon and Atlantic cod skin by the acid extraction process. After filtration and ion exchange treatment the extracts were colourless and free from fishy odour. In three separate experiments the average yields of gelatine from salmon and cod skins were 39.7% (+/-2.2%) and 44.8% (+/-0.2%) respectively, on a dry matter basis. Gelatine from salmon contained slightly more hydroxyproline and proline (16.6%) than cod gelatine (15.4%), whereas the content of serine was lower (4.6% versus 6.3%). Salmon gelatine expressed slightly higher gelling temperature (12 degrees C) than cod gelatine (10 degrees C), and higher initial gel strength. During storage at 10 degrees C, gel strengths were increased and more so with gels made from cod than from salmon gelatine. Hence, gels made from cod and salmon gelatines extracted at 56 degrees C achieved the same gel strength (195g) after 7days of storage. Gelatines extracted at a higher temperature (65 degrees C) gave lower gel strengths.     

Native fibrin gel networks observed by 3D microscopy, permeation and turbidity

Native fully hydrated fibrin gels formed at different fibrinogen and thrombin concentrations and at different ionic strengths were studied by confocal laser 3D microscopy, liquid permeation and turbidity. The gels were found to be composed of straight rod-like fiber elements that often came together at denser nodes. In gels formed at high fibrinogen concentrations, or with high amounts of thrombin, the spaces between the fibers decreased, indicating a decrease of gel porosity. The fiber strands were also shorter. Gel porosity decreased dramatically in gels formed at the high ionic strengths. Shorter fibers were observed and fiber swelling occurred at ionic strengths above 0.24. Quantitative parameters for gel porosity, fiber mass/length ratio and diameter were also derived by liquid permeation and turbidometric analyses of the gels. Permeation analysis showed that gel porosity (measured as Ks) decreased in gels formed at higher fibrin and thrombin concentrations in agreement with the porosity observed by microscopy. The turbidometric analysis showed good agreement with the permeation data for gels formed at various thrombin concentrations, but supported the permeation data more poorly in gels formed at different fibrinogen concentrations, especially above 2.5 mg/ml. Turbidometric analysis showed that the fiber mass/length ratio and diameter decreased in gels formed at ionic strength up to 0.24, as was seen in the permeation study. However, at higher ionic strengths swelling of the fibers was suggested from the gel turbidity data and this was also indicated by microscopy. These findings are discussed in relation to previous hydrodynamic and electron microscopic studies of fibrin gels.     

Sensory perception is related to the rate of change of volatile concentration in-nose during eating of model gels.

The relationship between perceived aroma and the volatile concentration measured in-nose was investigated during eating of a model food. Sensory ranking and time-intensity analysis (TI) were used to measure perceived aroma, while in-nose volatile concentration was monitored by atmospheric pressure ionization mass spectrometry, which produced time release data. A gelatine-sucrose gel with a range of gelatine concentrations (2-8% w/w) and flavoured with furfuryl acetate was used as the model food. Sensory scaling showed decreased flavour intensities and TI showed a decrease in the flavour perceived over time, as the gelatine concentration increased. Studies in model systems and in people demonstrated that the different rates of release observed for different gelatine concentrations were not due to binding of volatile to protein in the gel, nor to mucous membranes, but were due to different rates of gel breakdown in-mouth. There were no significant differences in the maximum in-nose volatile concentrations for the different gelatine concentrations, so the amount of volatile present did not correlate well with the sensory analysis. However, the rates of volatile release were different for the different gels and showed a good correlation with sensory data.     

Photon transmission study on swelling of kappa-carrageenan gels prepared in various concentrations

κ-Carrageenan gels prepared with various carrageenan concentrations in pure water were completely dried and then swelled in pure water. Photon transmission measurements were performed using a UV-Vis (UVV) spectrometer during the swelling of κ-carrageenan gels. Transmitted photon intensity, I_tr, increased exponentially as swelling time is increased for all gel samples. The behaviour of I_tr was interpreted by Monte-Carlo Simulation. The increase in I_tr was quantified by employing Li-Tanaka equation, from which time constants τ₁ and collective diffusion coefficients, D_o were determined for the gels in various carrageenan concentrations. Gravimetric and volumetric measurements were also carried out during swelling of gels. It is observed that gel with high carrageenan content possess more double helices and more lattice dislocations and swell slower than gels with low carrageenan content which may contain less double helices and less lattice imperfections. Increase in I_tr was interpreted by the homogeneous distribution of double helices in the carrageenan gel system.     

Texture properties of high and low acyl mixed gellan gels

The strength, deformability, and firmness of high acyl (H) and low acyl (L) mixed gellan gels were studied by compression tests. The gels were prepared with total polymer concentrations of 0.5, 1.0, and 1.5% at H/L weight ratios of 25/75, 50/50, 75/25, and calcium concentrations 2–80 mM. The mixed gels were much more deformable, with failure normal strains ranging from 0.6 to 1.5, but had similar strength compared to low acyl gellan gels. Both H/L ratio and total polymer concentration affected the textural properties, but H/L ratio was a more important factor. Maximum synergistic interaction was observed at H/L=50/50. The mixed gels exhibited excellent texture properties compared to other common food gels.     

Charged acrylamide copolymer gels as media for weak alignment

The use of mechanically strained acrylamide/acrylate copolymers is reported as a new alignment medium for biomacromolecules. Compared to uncharged, strained polyacrylamide gels, the negative charges of the acrylamide/acrylate copolymer strongly alter the alignment tensor and lead to pronounced electroosmotic swelling. The swelling itself can be used to achieve anisotropic, mechanical strain. The method is demonstrated for the alignment of TipAS, a 17 kDa antibiotic resistance protein, as well as for human ubiquitin, where alignment tensors with an A_ZZ,NH of up to 60 Hz are achieved at a gel concentration of 2% (w/v). The alignment can be modulated by the variation of pH, ionic strength, and gel concentration. The high mechanical stability of the swollen gels makes it possible to obtain alignment at polymer concentrations of less than 1% (w/v).     

Viscoelastic properties of plasticized methylcellulose and chemically crosslinked methylcellulose

Films of methylcellulose (MC), poly(ethylene glycol)400 (PEG400) plasticized MC, and MC gels (MC crosslinked with glutaraldehyde (GA)) were prepared by casting from aqueous solutions. The swelling test has shown that the MC gels were insoluble in water and that their crosslinking density increased with increasing GA and HCl concentrations. The effect of the addition of PEG400 or GA to MC was investigated through dynamic mechanical analysis (DMA). The DMA analysis of PEG400/MC blends has shown that PEG400 was compatible with MC and was an effective plasticizer since the curves of tan δ against temperature exhibited single peaks (corresponding to a single glass transition temperature), which were displaced to lower values with increasing PEG400 content. The thermogravimetric analysis (TGA) indicated that the thermal stability of MC was not affected by the chemical crosslinking. The tensile strength was slightly increased through crosslinking while the elongation was slightly decreased. The presence of moisture in MC hydrogels decreased the tensile strength and enhanced the elongation while the addition of PEG400 decreased the tensile strength but sharply increased the elongation.     

Interpenetrating network formation in agarose--kappa-carrageenan gel composites

Thermal, mechanical, turbidity, and microscope evidence is provided which strongly suggests molecular interpenetrating network (IPN) formation by mixtures of the seaweed polysaccharides agarose and kappa-carrageenan. Over a range of ionic strength, and potassium content, there is no evidence for synergistic coupling of the networks, and simple phase separation (demixing) can definitely be ruled out. At low ionic strength, where the agarose gels first, differential scanning calorimetry evidence shows some influence of the carrageenan on the agarose ordering enthalpy, particularly at higher polymer concentrations. As the potassium level is increased, however, and the order of gelling is reversed, this effect disappears. Cure behavior for the systems at high ionic strength can be described as a simple summation of the pure component contributions. At low ionic strength, on the other hand, the modulus behavior is more complex, suggesting either a modification, in the mixture, of the kappa-carrageenan gelling parameters or a more complex modulus additivity rule.     

Effects of Ca, Cu, Al and La on pectin gel strength: implications for plant cell walls

Rheology of Ca-pectate gels is widely studied, but the behaviour of pectate gels formed by Cu, Al and La is largely unknown. It is well known that gel strength increases with increasing Ca concentration, and it is hypothesised that this would also be the case for other cations. Pectins are a critical component of plant cell walls, imparting various physicochemical properties. Furthermore, the mechanism of metal toxicity in plants is hypothesised to be, in the short term, related to metal interactions with cell wall pectin. This study investigated the influence of Ca, Cu, Al and La ion concentrations at pH 4 on the storage modulus as a function of frequency for metal-pectin gels prepared from pectin (1%) with a degree of esterification of 30%. Gels were formed in situ over 6 d in metal chloride solution adjusted daily to pH 4. Cation concentration was varied to develop a relationship between gel strength and cation concentration. At similar levels of cation saturation, gel strength increased in the order of La < Ca ? Al ? Cu. The swelling of the gels also varied between cations with Ca gels being the most swollen.     

Transport in C4 mesophyll chloroplasts. Characterization of the pyruvate carrier

1. Evidence is presented for high rates of carrier-mediated uptake of pyruvate into the stroma of intact mesophyll chloroplasts of the C₄ plant Digitaria sanguinalis, but not the chloroplasts of the C₃ plant Spinacea oleracea. Uptake of pyruvate in the dark with the C₄ mesophyll chloroplasts was followed using two techniques: uptake of [¹⁴C]pyruvate as determined by silicon oil centrifugal filtration and uptake as indicated by absorbance changes at 535 nm (shrinkage/swelling) after addition of 0.1 M pyruvate salts.

2. Uptake of the pyruvate anion by an electrogenic carrier is suggested to be the major mode of transport. Chloroplast swelling was observed in potassium pyruvate plus valinomycin and uptake of [¹⁴C]pyruvate was inhibited by membrane-permeant anions. Valinomycin reduced uptake in the absence of external potassium and the inhibition could be reversed by addition of external potassium.

3. Uptake of pyruvic acid (or a pyruvate ⁻/OH⁻ antiport) is ruled unlikely since [¹⁴C]pyruvate uptake was relatively independent of the pH gradient across the envelope and addition of pyruvate to chloroplasts did not result in an alkalization of the medium. The low rate of swelling observed in ammonium pyruvate may be due to non-mediated permeation of pyruvic acid, which is possible only at high pyruvate concentrations.

4. The concentration of pyruvate in the stroma increased with external concentration over the range tested (up to 40 mM) but the concentration ratio (internal/external) was always less than one. The steady-state concentration of [¹⁴C]pyruvate in the stroma was dependent on the ionic strength of the medium, with saturation at roughly I = 0.04 M, while accumulation of the membrane-permeant cation tetraphenylmethylphosphonium decreased with increasing ionic strength. This suggests that ionic strength modifies a membrane potential (inside negative) across the envelope and that pyruvate uptake responds to the magnitude and direction of that potential (−80 mV at low ionic strength).

5. Chloride and inorganic phosphate were potent inhibitors of [¹⁴C]pyruvate uptake. Of the sulfhydryl reagents tested, N-ethylmaleimide was not inhibitory while mersalyl completely blocked [¹⁴C]pyruvate uptake and swelling in potassium pyruvate plus valinomycin. Pyruvate uptake, as measured by valinomycin induced swelling in potassium pyruvate, was highly temperature sensitive, with an energy of activation of 39 kcal/mol above 9 °C.

6. Phenylpyruvate, -ketoisovalerate, -ketoisocaproate, -cyano-4-hydroxycinnamic acid and -cyanocinnamic acid inhibited [¹⁴C]pyruvate but not [¹⁴C]-acetate uptake in the dark and also reduced pyruvate metabolism by the chloroplasts in the light.     

Physico-Mechanical Properties of Chemically Treated Bacterial (Acetobacter xylinum) Cellulose Membrane

Bacterial cellulose obtained through fermentation by the Acetobacter xylinum is of superior functional quality in comparison to plant cellulose. Various alkali treatment methods were used to process bio-chemically complex pellicle into a clean cellulose membrane/sheet. The effect of potassium hydroxide, sodium carbonate and potassium carbonate was found to be milder on the final cellulose product in contrast to the widely used sodium hydroxide treatment. These novel treatment methods also caused improvement in the tensile strength of the membranes in comparison to sodium hydroxide. The overall quality of the 0.1 M sodium carbonate- and potassium carbonate-treated cellulose was superior, as the membranes displayed maximum tensile strength and elongation next to the native membrane. The low tensile strength of sodium hydroxide-treated membrane is attributed to its higher swelling characteristics in alkali. Further, the low swelling property of sodium carbonate- and potassium carbonate-treated membranes resulted in their high oxygen transmission rates (low oxygen barrier). Hunter lab colour parameters were determined to assess the effect of different alkali treatments on the colour characteristics of the membranes. Further, based on the high mechanical strength and comparatively low oxygen transmission rates, the processed cellulose membranes may find application as a bio- packaging material for controlled atmosphere packaging, where hydrophilic membranes with high oxygen barrier and water vapour permeation are desirable.     

The effects of culture medium rigidity on adventitious bud production and tissue vitrification in needle cultures of Sitka spruce [Picea sitchensis (Bong.) Carr.]

Adventitious bud formation on Sitka spruce [ Picca sitchensis (Bong.) Carr.] needle explants was strongly dependent upon the rigidity of the culture medium. In general, of organogenesis was greatest on weak gels and poorest on more rigid gels resulting from increased medium pH or agar strength. There was a significant interaction between agar strength and pH, with the optimum pH for organogenesis declining with increasing agar strength. Poor organogenesis at high agar concentrations was not due to toxic impurities since increased adventitious bud production could be stimulated by decreasing the medium pH whilst maintaining a high agar strength and an agar washing treatment had no significant effect. Although high levels of organogenesis could be sustained on weak gels the resultant adventitious shoots often showed severe vitrification. The frequency of shoots showing vitrification could be reduced by growing the tissues on harder media but this resulted in reduced shoot elongation. Vitrification of needle tissues did not stimulate the formation of adventitious buds in the absence of cytokinins.     

Thermally induced protein gelation: gelation and rheological characterization of highly concentrated ovalbumin and soybean protein gels

In order to optimize the use of proteins as functional ingredients in foods, one needs more insight into the effects of environmental conditions (pH, ionic strength, and temperature) on the functional properties of protein. This paper summarizes the results of an extensive study on heat-induced gelation of ovalbumin (egg-white protein) and soybean protein in the concentration range from 10 to 35 g/100 g. It was the aim of the study to relate the rheological properties of thermally induced protein gels to the microstructure of the gel and the physicochemical properties of the constituent protein. The gelling behavior of the protein was quantified with rheological techniques, and the physical properties of the gels were determined, at small and large deformations. From the swelling/dissolving behavior of the gels in various media, the nature of the crosslinks was determined qualitatively. The microstructure of the gels was determined with electron microscopy. Nmr-spectroscopy was applied in order to elucidate changes in conformation during heating. It was found that the formation of a continuous covalently crosslinked network is not a prerequisite for thermally-induced protein gelation. The properties of a gel strongly depend on the pH at which the gel is formed. When heat-set at high pH(pH～10), a homogeneous, strong, and almost transparent gel is formed, consisting of flexible crosslinked protein gels. Heat-setting at low pH (pH 5) leads to the formation of a heterogeneous and weak gel, which easily exudes water. This gel consists of crosslinked aggregated protein. The ionic strength of the solvent in which the protein is dissolved and heat-set has a much lower effect on gel properties.     

Swelling behavior and controlled release of theophylline and sulfamethoxazole drugs in beta-lactoglobulin protein gels obtained by phase separation in water/ethanol mixture

Physically cross-linked beta-lactoglobulin (BLG) protein gels containing theophylline and sulfamethoxazole low molecular weight drugs were prepared in 50% ethanol solution at pH 8 and two protein concentrations (6 and 7% (w/v)). Swelling behavior of cylindrical gels showed that, irrespective of the hydrated or dehydrated state of the gel, the rate of swelling was the highest in water. When the gels were exposed to water, they first showed a swelling phase in which their weight increased 3 and 30 times for hydrated and dehydrated gels, respectively, due to absorption of water, followed by a dissolution phase. The absorption of solvent was however considerably reduced when the gels were exposed to aqueous buffer solutions. The release behavior of both theophylline and sulfamethoxazole drugs from BLG gels was achieved in a time window ranging from 6 to 24 h. The drug release depended mainly on the solubility of the drugs and the physical state of the gel (hydrated or dry form). Analysis of drug release profiles using the model of Peppas showed that diffusion through hydrated gels was governed by a Fickian process whereas diffusion through dehydrated gels was governed partly by the swelling capacities of the gel but also by the structural rearrangements inside the network occurring during dehydration step. By a judicious selection of protein concentration, hydrated or dehydrated gel state, drug release may be modulated to be engineered suitable for pharmaceutical as well as cosmetics and food applications.     

Structural and chemical requirements for hydroxychlorobiphenyls to uncouple rat liver mitochondria and potentiation of uncoupling with aroclor 1254

Rat hepatic mitochondrial permeability and succinate + valinomycin-dependent swelling were studied in the presence of hydroxy derivatives of polychlorinated biphenyls (PCBOHs), Aroclor 1254 (ARO) and combinations of both. PCBOHs with two or more chlorines and pKas greater than 8.0 (PCBOH I) induced passive swelling in a potassium acetate-sucrose medium (pH 7.2), maximally stimulated succinate respiration, and suppressed ADP-stimulated H+ uptake. Mono- and certain dichlorinated biphenylols with similar high pKas (PCBOH II) were ineffective. Para-hydroxy PCBs with chlorines substituted in the 3,5 positions and with pKas near 6.8 (PCBOH III) inhibited succinate + valinomycin swelling and ADP-stimulated H+ and oxygen uptake. The efficacy of both PCBOH I and III derivatives required the presence of a hydroxyl moiety and increased directly with the degree of chlorination. Coplanarity was not a determining factor for PCBOH I compounds. ARO activated succinate + valinomycin swelling at low concentrations (3-25 nmol/mg protein) but inhibited at higher concentrations (greater than 40 nmol/mg). Activating concentrations of ARO potentiated the influence of PCBOHs on mitochondria. The uncoupling effects of the PCBOHs and ARO involved permeability changes of the inner membrane, respiratory inhibition, or combinations of both.     

Polyphenoloxidases immobilized in organic gels: Properties and applications in the detoxification of aromatic compounds

Gelatine gels originate from water in oil microemulsions in which the ternary system consists of isooctane/ sulfosuccinic acid bis [2-ethyl hexyl] ester/water; the solubilization of gelatin in the water pool of these microemulsions transforms them into viscous gels in which it is possible to cosolubilize various reactive molecules. These gels were used to immobilize two phenoloxidases, a laccase from Trametes versicolor and a tyrosinase from mushroom. The best balance between gel retention and catalytic activity was reached at a gelatine concentration of 2.5% (w/v) in the case of tyrosinase, while laccase immobilization was independent of gelatine concentration. Both enzymes kept the same optimum pH as the corresponding soluble controls, while a partial loss of activity was observed when they were immobilized. Immobilized enzymes showed an increased stability when incubated for several days at 4 degrees C with a very low release from the gels in the incubation solutions. The immobilization of tyrosinase and of laccase enhanced stability to thermal inactivation. Furthermore, gel-entrapped tyrosinase was almost completely preserved from proteolysis: more than 80% of the activity was maintained, while only 25% of the soluble control activity was detected after the same proteolytic treatments. A column packed with gel-immobilized tyrosinase was used to demonstrate that enzymes immobilized with this technique may be reused several times in the same reaction without loosing their efficiency. Finally, gel-entrapped tyrosinase and laccase were capable of removing naturally occurring and xeno-biotic aromatic compounds from aqueous suspensions with different degrees of efficiency. (c) 1995 John Wiley & Sons, Inc.     

Bio‐antifelting of wool based on mild methanolic potassium hydroxide pretreatment

Covalently bound lipids cover the wool surface and make enzymatic degradation of wool scales very difficult. In this paper, methanolic potassium hydroxide (MPH) pretreatment was used prior to enzymatic treatment of wool with protease, aiming at hydrolyzing the outmost lipids on the wool surface and promoting the subsequent proteolytic reaction. The efficacy of lipid removal from the fiber surface and the properties of the protease‐treated wool were evaluated. The results indicated that mild MPH pretreatment with 0.10 mol/L MPH for 10 min improved the wettability of the wool without adverse impacts on its mechanical properties. The wetting time and area shrinkage of the wool fabric reached 0.5 s and 5.6%, respectively, and the strength loss was within the acceptable range. Pretreatment with high concentrations of MPH for longer times led to significant damage to the wool fibers and caused heavy strength loss, without improving the antifelting properties after protease treatment. Thus, the combination of mild MPH and protease treatments endowed the wool with desirable properties in contrast to the treatment with protease alone.     

Optimization of gelatine extraction from grass carp (Catenopharyngodon idella) fish skin by response surface methodology

To establish the optimum gelatine extraction conditions from grass carp fish skin, response surface methodology (RSM) was adopted in this study. The effects of concentration of HCl (%, A), pre-treatment time (h, B), extraction temperature ( degrees C, C) and extraction time (h, D) were studied. The responses were yield (%) and gel strength (g). A=1.19%, B=24 h, C=52.61 degrees C and D=5.12h were determined as the optimum conditions while the predicted responses were 19.83% yield and 267 g gel strength. Gelling and melting points were 19.5 degrees C and 26.8 degrees C, respectively. Moreover, grass carp gelatine showed high contents of imino acids (proline and hydroxyproline) 19.47%. RSM provided a powerful tool to optimize the extraction parameters and the results may be adapted for industrial extraction of gelatine from grass carp fish skins.     

Effect of calcium concentration on textural properties of high and low acyl mixed gellan gels

Textural properties of 1% low and high acyl gellan gels and their mixtures were studied using compression tests and the microcentrifuge-microfiltration based water holding capacity (WHC) method. Low acyl (1% LA), high acyl (1% HA) gels and mixtures of 1% 25/75 LA/HA, 50/50 LA/HA, 75/25 LA/HA gels with calcium concentrations ranging from 2 to 80 mM were studied. HA or mixed gels with a lower LA/HA ratio had a greater WHC and failure strain than that of LA or mixed gels with a higher LA/HA ratio. Gellan gels with a higher LA/HA ratio had a larger initial Young's modulus. Our study also indicates that a higher LA/HA ratio does not necessarily result in a gel with a larger failure stress, although LA gels are generally firmer than HA gels. Gel strength and WHC of HA and LA/HA mixtures may reflect both stabilization and destabilization effects of glycerate groups positioned at one of the glucose residues in each repeating tetrasaccharide unit of HA gels.     

Effect of hydrophobic modification on rheological and swelling features during chemical gelation of aqueous polysaccharides

Rheological characteristics during chemical gelation with the cross-linker ethylene glycol diglycidyl ether (EGDE) of semidilute aqueous solutions of hydroxyethylcellulose (HEC) and of two hydrophobically modified analogues (HM-1-HEC and HM-2-HEC) are reported. In addition, rheological features of gelling samples (dextran and its hydrophobically modified analogue (HM-dextran)) of a different structure have been examined. Some swelling experiments on these gels in the postgel region are also reported. The gelation time of the hydroxyethylcellulose systems decreased with increasing cross-linker concentration, and incorporation of hydrophobic units of HEC resulted in a slower gelation. The time of gelation for the dextran system was only slightly affected by the incorporation of hydrophobic groups (HM-dextran). At the gel point, a power law frequency dependence of the dynamic storage modulus (G' proportional to omegan') and loss modulus (G' proportional to omegan') was observed for all gelling systems with n' = n' = n. The attachment of hydrophobic moieties on the dextran chains had virtually no impact on the value of n (n = 0.77), and the percolation model describes the incipient dextran gels. By increasing the number of hydrophobic groups of the HEC polymer, the value of n for the corresponding incipient gel drops significantly, and the value of the gel strength parameter increases strongly. Incorporation of hydrophobic units in the HEC chains promotes the formation of stronger incipient gels because of the contribution from the hydrophobic association effect. The frequency dependence of the complex viscosity reveals that all the investigated gels become more solidlike in the postgel domain. Far into the postgel region, the hydrophobicity of HEC plays a minor role for the strength of the gel network, whereas the values of the complex viscosity are significantly higher for HM-dextran than for the corresponding dextran gel. The swelling experiments on HEC, HM-1-HEC, and HM-2-HEC systems disclose that the degree of swelling of the postgels in water is quite different, depending on the relative distance from the gel point at which the cross-linker reaction is quenched. At a given distance from the gel point, the swelling of the HEC gel is less pronounced than for the corresponding hydrophobically modified samples. At this stage, the swelling of the HM-dextran gel is stronger than for the dextran gel.