Associative and segregative interactions between gelatin and low-methoxy pectin: Part 2—co-gelation in the presence of Ca

The effect of segregative interactions with gelatin (type B; pI=4.9; 0–10 wt%) on the networks formed by low-methoxy pectin on cooling in the presence of stoichiometric Ca²⁺ at pH 3.9 has been investigated by rheological measurements under low-amplitude oscillatory shear. Samples were prepared and loaded at 85 °C, cooled (1 °C/min) to 5 °C, held for 100 min, and re-heated (1 °C/min) to 85 °C, with measurement of storage and loss moduli (G′ and G″) at 10 rad s⁻¹ and 2% strain. The final values of G′ at 5 °C for mixtures prepared at the same pH without Ca²⁺ were virtually identical to those observed for the same concentrations (0.5–10.0 wt%) of gelatin alone, consistent with the conclusion from the preceding paper that electrostatic (associative) interactions between the two polymers become significant only at pH values below 3.9. Increases in moduli on cooling in the presence of Ca²⁺ occurred in two discrete steps, the first coincident with gelation of calcium pectinate alone and the second with gelation of gelatin. Both processes were fully reversible on heating, but displaced to higher temperature (by 10 °C), as was also observed for the individual components. The magnitude of the changes occurring over the temperature range of the gelatin sol–gel and gel–sol transitions demonstrates that the gelatin component forms a continuous network; survival of gel structure after completion of gelatin melting shows that the calcium pectinate network is also continuous (i.e. that the co-gel is bicontinuous). On progressive incorporation of NaCl (to induce phase separation before, or during, pectin gelation) the second melting process, coincident with loss of calcium pectinate gel structure, was progressively abolished, indicating conversion to a gelatin-continuous network with dispersed particles of calcium pectinate. These qualitative conclusions are supported by quantitative analyses reported in the following paper.     

Associative and segregative interactions between gelatin and low-methoxy pectin. Part 3. Quantitative analysis of co-gel moduli

The experimental moduli (G′ at 5 °C) reported in the preceding paper for gelatin–calcium pectinate co-gels (pH 3.9; 1.0 wt% pectin; stoichiometric Ca²⁺; 0–10 wt% gelatin) formed in the presence or absence of 1 M NaCl have been analysed using a single adjustable parameter, p, to characterise partition of solvent. The analysis of samples incorporating 1 M NaCl assumed complete segregation of calcium pectinate into dispersed particles in a continuous gelatin matrix, with p defined as the ratio of water/polymer in the gelatin phase divided by the corresponding ratio for the pectin phase. Relative phase volumes at each trial value of p were used to determine the polymer concentration in each phase, and the corresponding moduli were obtained from standard calibration curves. For solvent distributions where the calculated modulus of the continuous gelatin phase was higher than that of the dispersed calcium pectinate phase, co-gel moduli were derived using the Takayanagi isostrain model, and the isostress model was used for the converse situation. The p factors required to give perfect agreement with the moduli observed experimentally were tightly grouped around a single value (p=1.21) for all concentrations of gelatin studied, indicating that the assumption of complete segregation is reasonably valid. Calculated moduli for the gelatin phase were in good agreement with experimental values obtained by melting the gelatin network, centrifuging to sediment the dispersed calcium pectinate particles, and re-gelling the gelatin supernatant. The same p factor (1.21) was used to derive calculated moduli for co-gels formed in the absence of NaCl, where the mixed solutions remain monophasic, by application of the relationship proposed by Davies for bicontinuous composites. The modulus of the calcium pectinate gel, which is already present when the gelatin network forms, was calculated (i) on the assumption of dynamic cross-linking (i.e. using the concentration-dependence of G′ for calcium pectinate alone), and (ii) for permanent cross-linking (by application of deswelling theory). The experimental moduli moved from close agreement with the former model to close agreement with the latter as the gelatin concentration increased from 0 to 10 wt%, consistent with a progressive increase in the extent of rearrangement of the calcium pectinate network required to accommodate the compression introduced by gelation of gelatin.     

Characterization of gelation time and texture of gelatin and gelatin–polysaccharide mixed gels

The effects of cooling rate, holding temperature, pH and polysaccharide concentration on gelation characteristics of gelatin and gelatin–polysaccharide mixtures were investigated using a mechanical rheometer which monitored the evolution of G′ and G″. At low holding temperatures of 0 and 4 °C, elastic gelatin gels were formed whereas a higher holding temperature of 10 °C produced less elastic gels. At slow cooling rates of 1 and 2 °C/min, gelling was observed during the cooling phase in which the temperature was decreased from room temperature to the holding temperature. On the other hand, at higher cooling rates of 4 and 8 °C/min, no gelation was observed during the cooling phase. Good gelling behavior similar to that of commercial Strawberry Jell-O^® Gelatin Dessert was observed for mixtures of 1.5 and 15 g sucrose in 100 ml 0.01 M citrate buffer containing 0.0029–0.0066 g low-acyl gellan. Also, these mixed gels were stronger than Strawberry Jell-O^® Gelatin Desserts as evidenced by higher G′ and gel strength values. At a very low gellan content of 0.0029 g, increasing pH from 4.2 to 4.4 led to a decrease in the temperature at the onset of gelation, G′ at the end of cooling, holding and melting as well as an increase in gel strength. The gelation time was found to decrease to about 40 min for gelatin/sucrose dispersions in the presence of 0.0029 g gellan at pH 4.2 whereas the corresponding time at pH 4.4 was higher (79 min). In general, the gelation time of gelatin/sucrose dispersions decreased by a factor of 2 to 3 in the presence of low-acyl gellan. The addition of low-acyl gellan resulted in an increase in the gelation rate constant from 157.4 to 291 Pa. There was an optimum low-acyl gellan content for minimum gelation time, this optimum being pH dependent. Addition of guar gum also led to a decrease in gelation time to 73 min with a corresponding increase in the gelation rate constant to 211 Pa/min though these values were not sensitive to guar gum content in the range of 0.008–0.05 g. The melting temperature of gelatin/sucrose/gellan as well as gelatin/sucrose/guar mixtures did not differ significantly from that of pure gelatin or Strawberry Jell-O^® Gelatin Desserts. At pH 4.2, the melting rate constant was highest at a low-acyl gellan content of 0.0029 g whereas the rate constant was insensitive to low-acyl gellan content at pH 4.4. Addition of guar did not seem to affect the melting temperature or the melting rate constant.     

酶解马铃薯泥对馕质构和风味的影响

将不同比例的马铃薯泥(MP)、α-淀粉酶酶解马铃薯泥(α-AMP)和β-淀粉酶酶解马铃薯泥(β-AMP)分别与小麦粉复配制作馕,对比分析了不同类型马铃薯泥对馕质构和风味的影响.结果表明,随着MP或α-AMP添加量增加,馕内部的气孔逐渐减少,其质构品质变差;而添加β-AMP的馕内部保留了均匀气孔,添加10％或15％β-A...     

Gelation behaviour of gelatin and alginate mixtures

Mixtures of alginate and gelatin were studied by rheology as a function of different parameters, such as temperature, biopolymer concentrations, calcium concentration and ionic strength. In particular conditions, the formation of a mixed gel of alginate and gelatin is obtained. A slow release of calcium ions leads first to an irreversible alginate gel and cooling results in a reversible gelatin gel. Depending on experimental conditions, non-linear behaviours upon gelation of alginate occur and a collapse of alginate gel is directly observable by rheology. These trends are favoured between 35 and 45 °C, by a high total biopolymer concentration or a high calcium concentration and ionic strength. Different mechanisms could be responsible for this collapse, such as a competition between alginate gelation and phase separation in the biopolymer mixture or an over-association of alginate chains at high Ca²⁺ concentration, favoured by the presence of gelatin.     

Using AFM and force spectroscopy to determine pectin structure and (bio) functionality

Pectin is an integral component of non-graminaceous plant cell walls. It is believed to form an interconnected network structure independent of the cellulose-xyloglucan network structure. Pectin gels are often used as a model for the pectin network structure within the plant cell wall. Atomic force microscopy studies of calcium-induced gel precursors, and fragments released from gels, suggest that association leads to a branched fibrous structure within the gels. Enzymatic de-esterification of high-methoxyl pectin in the presence of calcium ions can induce gelation of the pectin. Thus pectin gel networks may provide a model for a self-assembled network structure within the middle lamella region of the plant cell wall. The pectin network in plant cell walls is a source of soluble and insoluble fibre. In addition to the health benefits associated with the dietary fibre aspects of pectin new health claims are emerging. Recently published in vitro and in vivo animal studies, and human studies, suggest that oral consumption of a modified form of pectin may have anti-cancer properties. These studies suggest that the modified pectin may act on a range of cancers at several stages of progression of the cancer. It has been hypothesised that this generic action is due to the modification allowing release of bioactive fragment(s) which are claimed to bind specifically to and inhibit the action of the mammalian lectin galectin 3 (Gal3). Gal3 is a key regulator of cellular homeostasis and plays important roles in several stages of cancer metastasis. Studies using force spectroscopy, flow cytometry and fluorescence microscopy suggest that the bioactive fragments of pectin may be pectin-derived galactans.     

Phase separation in gelatin/dextran and gelatin/maltodextrin mixtures

Phase separation mechanisms and kinetics in quiescent and shear conditions were studied using small-angle light scattering, optical polarimetry and confocal laser scanning microscopy in the gelatin/maltodextrin and gelatin/dextran systems. In the former system the temperature quench caused phase separation, which was studied in the gelled and liquid states, whereas in the latter system phase separation was triggered by the conformational ordering of the gelatin molecules and could only be studied when the system gelled. In both systems the different phase separation mechanisms of nucleation and growth and spinodal decomposition were identified from the different behaviour of structure function measured by light scattering. In the liquid state coarsening of the microstructure occurred by droplet coalescence that was accelerated by hydrodynamic effects when the droplets reached a certain size. Gelation hindered, but did not prevent coarsening. Reduced coarsening rates were measured in the gelled systems. In most cases the phase separation kinetics were faster than the gelation kinetics, and the system rapidly evolved into the late stages of phase separation that were characterised by a well-defined morphology with sharp interfaces. For sufficiently rapid ordering kinetics, corresponding to deep quenches, in the gelatin/dextran systems, however, it was possible to trap the microstructure in the early stages of phase separation while the interfaces were still diffuse. When the phase-separated liquid gelatin/maltodextrin system was sheared, coarsening was accelerated at low shear rates due to increased rates of droplet coalescence. At higher shear rates, stable elongated structures were formed. At one particular shear rate (approximately 1 s⁻¹), the rates of break-up and coalescence were balanced and a monodisperse size distribution of elongated droplets was formed.     

Physicochemical properties of gelatin gels from walleye pollock (Theragra chalcogramma) skin cross-linked by gallic acid and rutin

Gelatin gels were cross-linked by gallic acid and rutin. The gel strength, viscoelastic properties, thermal stability, swelling property, ultrastructure, X-ray diffraction patterns and FTIR spectra were determined to evaluate the physicochemical properties of the modified gels. The gel strength increased with increasing gallic acid concentration up to 20 mg/g dry gelatin, and then decreased at further elevated gallic acid concentration, while it continuously increased with increasing levels of rutin. Either cross-linking agent could enhance the elastic modulus (G′) and the viscous modulus (G″) of hydrogels, but the gelling and melting points didn’t show a notable improvement. Rutin boosted the thermal stability of xerogels, but decreased the equilibrium swelling ratio significantly, while as for gallic acid, there were no obvious effects on the thermal stability and equilibrium swelling ratio of xerogels. Scanning electron microscopy (SEM) was applied to observe the ultrastructure changes of the modified xerogels suggesting that gelatin xerogel at rutin concentration of 8 mg/g dry gelatin showed the highest cross-linking density. X-ray diffraction revealed that both gallic acid and rutin could enter the spacing of polypeptide chains of gelatin to reinforce the intermolecular interaction. And FTIR spectra verified that gallic acid and rutin molecules mainly interacted with skeletal C–N–C group and carboxyl group of gelatin molecules in the formation of gels. The results suggested that rutin was a better cross-linking agent for gelatin, and gels treated with rutin could be found with different physicochemical properties.     

Improvement and modification of whey protein gel texture using polysaccharides

Whey proteins (WP) and polysaccharides are two gelling biopolymers used in the food industry for their wide range of rheological and textural properties. Mixed gels containing more than one gelling agent are usually classified into three types: interpenetrating, coupled, and phase-separated networks. Large deformation behavior of whey protein gels mixed with polysaccharides is presented. pH, and the concentration and nature of the cations added in the system, affect both protein and polysaccharide gels. These factors will also modify the mixing behavior of protein-polysaccharide solutions. The effect of cations and pH are respectively explained using WP/κ-carrageenan and WP/pectin systems. Under the conditions studied, two types of mixed systems were obtained: one with two gelling biopolymers (WP/κ-carrageenan), and the other where protein is the only gelling biopolymer (WP/pectin). Conditions favoring incompatibility can lead to spherical inclusions of whey protein.     

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.     

Texture and structure of high-pressure-frozen gellan gum gel

To determine the effects of sucrose and high-pressure-freezing, unsubstituted form-gellan gum gels with 0, 5, 10 or 20% sucrose were frozen at 0.1–686 MPa and −20 °C. Gels were frozen during pressurization at 0.1, 100, 600–686 MPa. However, at 200–500 MPa, gels did not freeze but froze during pressure release (pressure-shift-freezing). On pressure release, a sharp rise in sample temperature was observed for the samples between 200 and 500 MPa. This was a consequence of the exothermic freezing event. Thus, appearance and structure of gels frozen at 200–500 MPa were better than other treated samples due to quick freezing. However, when gels were frozen at 0.1–686 MPa, rupture stress decreased remarkably and strain increased. Texture of pressure-shift-frozen gel was somewhat better than that of gels frozen in freezers (−20, −30 or −80 °C) at atmospheric pressure. Consequently pressure-shift-freezing was more effective. It was found that the addition of sucrose to gels was effective in improving the quality of frozen gellan gum gels.     

Gel texture and chain structure of amylomaltase-modified starches compared to gelatin

Amylomaltase (AM) (4-α-d-glucanotransferase; E.C. 2.4.1.25) from Thermus thermophilus was used to modify starches from various botanical sources including potato, high amylose potato (HAP), maize, waxy maize, wheat and pea, as well as a chemical oxidized potato starch (Gelamyl 120). Amylopectin chain length distribution, textural properties of gels and molecular weight of 51 enzyme and 7 non-enzyme-modified starches (parent samples) were analyzed. Textural data were compared with the textural properties of gelatin gels. Modifying starch with AM caused broadening of the amylopectin chain length distribution, creating a unimodal distribution. The increase in longer chains was supposedly a combined effect of amylose to amylopectin chain transfer and transfer of cluster units within the amylopectin molecules.Exploratory principal component analysis (PCA) data analysis revealed that the data were composed of two components explaining 94.2% of the total variation. Parent starches formed a cluster separated from that of the AM-modified starches.Extended AM treatments reduced the apparent molecular weight and the gel texture without changing the amylopectin chain length distribution. However, the gel texture was typically increased as compared to the parent starch. AM-modified HAP gels were about twice as hard as gelatin gels at identical concentration, whereas gels of pea starch were comparable to gelatin gels. Modifying Gelamyl 120 and waxy maize with AM did not change the textural properties. Branching enzyme (BE) (1,4-α-d-glucan branching enzyme; EC 2.4.1.18) from Rhodothermus obamensis was used in just one modification and in combination with AM. The combined AM/BE modification of pea starch resulted in starches with shorter amylopectin chains and pastes unable to form gel network even at concentration as high as 12.0% (w/w). The PCA model of all gel texture data gave suggestive evidence for starch structural features being important for generating a gelatin-like texture.     

Texture profile and turbidity of gellan/gelatin mixed gels

The effect of gellan (1.6–0.2%) to gelatin (0–1.4%) ratio and calcium ion concentration (0–30 mM) on the textural properties and turbidity of gellan/gelatin mixed gels was examined using instrumental Texture Profile Analysis (TPA) and spectrophotometry. Hardness of the mixed gels decreased as the proportion of gellan decreased. Hardness increased with increasing calcium ions until calcium concentration reached a critical level, after which further increases in calcium resulted in a reduction of hardness. Brittleness, springiness and cohesiveness were very sensitive to low levels of added calcium (0–10 mM), but less sensitive to higher calcium concentrations and gellan/gelatin ratio. In general, the addition of calcium ions caused gels to be more brittle and less cohesive and springy. Decreasing gellan to gelatin ratio caused an increase in gel turbidity at lower calcium ion levels (2–4 mM) and a decrease in turbidity at high calcium levels (20–30 mM). Maximum turbidity was observed in 0.6% gellan–1.0% gelatin gels without added calcium. The results of this study suggested a weak positive interaction between gellan and gelatin when no calcium was added, whereas at higher calcium levels gellan formed a continuous network and gelatin a discontinuous phase.     

Phase behaviour of gelatin/polydextrose mixtures at high levels of solids

This investigation focuses on understanding the phase behaviour of gelatin when mixed with polydextrose (co-solute) primarily at high solid concentrations. The experimental work was carried out using small deformation dynamic oscillation in shear, modulated differential scanning calorimetry, Fourier transform infrared spectroscopy, wide angle X-ray diffraction and environmental scanning electron microscopy. A progression in the mechanical strength and thermal stability of the gelatin network was observed with the addition of polydextrose to the system. Combined thermomechanical and microscopy evidence argues for the development of phase separation phenomenon between protein and co-solute in high-solid preparations, where gelatin maintains helical conformation to provide network integrity as well as glassy consistency at subzero temperature. At the high solids regime, glassy consistency was treated with theoretical frameworks from the synthetic polymer research to pinpoint the glass transition temperature of the system.     

Characteristics and chemical composition of skins gelatin from cobia (Rachycentron canadum)

Gelatin was obtained from cobia (Rachycentron canadum) skins, which is an important commercial species for marine fish aquaculture, and it was compared with gelatin from croaker (Micropogonias furnieri) skins, using the same extraction methodology (alkaline/acid pre-treatments). Cobia skins gelatin showed values of protein yield, gelatin yield, gel strength, melting point, gelling point and viscosity higher than the values found from croaker skins gelatin. The values of turbidity and Hue angle for cobia and croaker gelatins were 403 and 74 NTU, and 84.8° and 87.3°, respectively. Spectra in the infrared region had the major absorption band in the amide region for both gelatins, but it showed some differences in the spectra. The proline and hydroxyproline contents from cobia skins gelatin (205 residues/1000 residues) was higher than from croaker skins gelatin (188 residues/1000 residues). SDS-PAGE of both gelatins showed a similar molecular weight distribution to that of standard collagen type I. Therefore, cobia skins could be used as a potential marine source of gelatin obtainment for application in diversified industrial fields.     

Effect of high-pressure/high-temperature processing on chemical pectin conversions in relation to fruit and vegetable texture

Heat sterilization of plant derived food products entails considerable organoleptic and nutritional quality losses. For instance, texture loss of fruits and vegetables occurs, next to turgor pressure losses, mainly due to chemical changes in the cell-wall pectic polysaccharides. High-pressure sterilization, i.e. the combination of high temperature (?90 °C) with high pressure (?500 MPa), could present a positive alternative assuring safety while minimizing quality losses. In this study, the potential of high-pressure sterilization in preserving fruit and vegetable texture was evaluated by investigating the effect of combined high-pressure/high-temperature (HP/HT) treatments on two texture related chemical pectin conversions in model sytems. First, a protocol was developed to perform reproducible kinetic studies at HP/HT under constant processing conditions. Subsequently, apple pectin solutions at pH 6.5 were subjected to different HP/HT combinations (500, 600 and 700 MPa/90, 110 and 115 °C) and the extent of chemical demethoxylation and β-eliminative depolymerization was determined. At atmospheric pressure, both zero-order reaction rate constants increased with increasing temperature. At all temperatures, demethoxylation showed a higher rate constant than β-elimination. However, a temperature rise resulted in a stronger acceleration of β-elimination than of demethoxylation. When combining high temperature with high pressure, β-elimination was retarded or even stopped, whereas demethoxylation was stimulated. These results are very promising in the context of the texture preservation of high-pressure sterilized fruits and vegetables, as β-elimination is accepted to be one of the main causes of thermal softening and low methoxylated pectin can enhance tissue strength by forming cross-links with calcium ions present.     

Preparation of gelatin microparticles using water-in-water (w/w) emulsification technique

Gelatin microparticles were prepared using water-in-water (w/w) emulsification technique, in which aqueous solutions of gelatin and polypropylene glycol (PEG) were employed as dispersed phase and continuous phase, respectively. The effect of gelatin and PEG concentrations on the size of gelatin microparticles were evaluated. The size of the gelatin microparticles decreased with the increase in PEG concentration and increased with the increase in gelatin concentration. The gelatin microparticles obtained through this process were nearly perfect spheres with smooth surface. The gelatin microparticles, both un-crosslinked and crosslinked, were found to be fully amorphous in nature. The un-crosslinked gelatin microparticles were found to swell instantaneously (within 10 s) whereas the crosslinked ones were quite resistant to water uptake.     

磁性明胶复合微球的制备和性质

研究了明胶改性新途径，制备了内含四氧化三铁晶粒，外壳为明胶的纳米级明胶复合微球。     

Nano-biomaterials application: Morphology and physical properties of bacterial cellulose/gelatin composites via crosslinking

Nano-scale bacterial cellulose (BC) provides a fine structural network; therefore, this study investigated alkaline treated BC/gelatin composites (ATBC/G) crosslinked with transglutaminase (ATBC/G/T), genipin (ATBC/G/G), or EDC (ATBC/G/E), to improve the mechanical strength and hydrophilic property of BC composites. The ATBC/G composites displayed increased gelatin content, moduli, and hardness with increased gelatin concentrations in the immersion solution. EDC most effectively improved the mechanical properties of ATBC/G composites. Gelatin entering ATBC network, fills the empty spaces and connects to the 3D structure of ATBC. The ATBC/G/E composites maintain a network structure under 10% gelatin concentrations because gelatin tightly attaches to the ATBC surface. The ATBC/G composite exhibited analogical crystal morphology of ATBC, however, increased gelatin concentrations in addition to the EDC treatment decreased crystallinity in the composites. The FTIR spectrograph of the ATBC/G composites revealed the OH groups of the composites tended to increase. Therefore, gelatin crosslinking disrupted the crystallization formed from the hydrogen bonds between cellulose molecules. Crosslinking can also enhance the rehydration ratio.