Thermal, Mechanical, and Molecular Relaxation Properties of Frozen Sucrose and Fructose Solutions Containing Hydrocolloids

Model frozen systems formulated with 20wt% sucrose or fructose and with the addition of 0.3 or 0.5wt% of xanthan gum (XG), guar gum (GG), locust bean gum (LBG), or a 50wt% mixture of XG and LBG were studied by differential scanning calorimetry, dynamic mechanical analysis, and ¹H-pulsed nuclear magnetic resonance. Melting onset of either the sucrose or fructose model systems was not affected by the addition of hydrocolloids. As expected, ice content was lower in fructose than in sucrose systems. Addition of hydrocolloids had no effect on ice content, except when the blend of XG and LBG was added to the fructose system, where ice content was significantly diminished. Hydrocolloids decreased molecular mobility for both frozen sucrose or fructose solutions, especially for the addition of XG/LBG blend. Relaxation times and storage modulus of the frozen systems with added hydrocolloids were significantly lower than the control frozen sugar solutions.     

Structural properties of pectin-gelatin gels. Part II: effect of sucrose/glucose syrup

Small deformation dynamic oscillation and bright field microscopy were used to examine the structural properties of single and mixed high methoxy pectin and gelatin systems in the presence of sucrose/glucose syrup blends. Co-solute concentrated (≥78%) systems of the polysaccharide form rubbery structures which are readily transformed into glassy consistencies according to the time-temperature superposition principle. Increasing amounts of co-solute in the gelatin samples induce changes in viscoelasticity from that of conventional hydrogels to mechanical traces that cover much of the plateau region and the beginning of the glass transition area. Furthermore, manipulation of the protein/ sugar ratio can result in strong crystalline matrices, or viscoelastic solutions where the co-solute forms the continuous phase and the gelatin inclusions can undertake a conformational transition. The properties of the single components were used to rationalise the phase behaviour of their mixtures. Upon triggering the gelation of pectin, mixtures can be made where either gelatin or both components form a continuous phase. Results are discussed in the light of evidence obtained from the ethylene glycol work in Part I.     

Phase separation in dextran/locust bean gum mixtures

Dextran/locust bean gum (LBG) mixtures have been prepared and investigated with respect to their phase separation behaviour. These systems exhibited phase separation at 20 °C, the upper phase, itself biphasic, being enriched with locust bean gum but also containing dextran, whereas the lower phase contained only dextran. This lower phase was a liquid. The upper phase, which did not flow, was characterized by means of rheological dynamic measurements. Clearly, its behaviour was typical of a gel, the three-dimensional structure of which can be ascribed to self-association of LBG chains owing to the very high concentration of the galactomannan in this upper phase. The self-association of the galactomannan was confirmed by fluorescence microscopy carried out on mixtures containing fluorescein isothiocyanate (FITC)-labelled dextran. The rheological behaviour of a concentrated LBG solution was also investigated as a function of time, clearly showing progressive formation of a weak gel structure.     

Steady-state and pulsed NMR studies of gelation in aqueous agarose

Steady-state and pulsed NMR techniques have been used to investigate molecular motion in sols and gels of agarose. In passing through the sol–gel transition, the molecular mobility of water molecules is reduced only by a small amount, whereas motion of the polymer chains is greatly attenuated. The results are discused in terms of the network theory of gelation, with references to the role of water in the process and the nature of the “junction zones” between polymer chains. T₂ and line-width measurements are dominated by exchange broadening. The effects of exchange rate and differences in relaxation time between the exchanging sites are discussed. The temperature hysteresis behavior of agarose gels has been investigated and the effects of “ageing” correlated with changes in nuclear relaxation times. The synergistic increase in gel strength obtained on adding locust bean gum (LBG) to agarose has been investigated. The results indicate that LBG does not form double-helix junctions and may decrease rates of gelation by steric effects. At high agarose concentration, the LBG remains mainly in solution in interstitial water, but at low agarose concentration, it is suggested that the LBG can link gel aggregates together into a self-supporting structure, producing a synergistic increase in gel strength. Comparisons have been made between the nature of the agarose–LBG interaction and agarose–cellulose interactions in biological systems.     

The effect of phase viscosity ratio on the rheology of liquid two phase gelatin-locust bean gum systems

The rheological behaviour of liquid two phase gelatin–locust bean gum (LBG) systems, comprising of (a) liquid LBG enriched continuous phase, and (b) flow-deformable gelatin-enriched dispersed particles seems to be determined, at the same phase composition, by phase viscosity ratio (μ). In the μ range from 0.03 to 0.21, viscosity dropped to values noticeably lower (13–40 times) than those of the corresponding LBG solution. Decrease in the viscosity of the mixtures was not observed at μ=0.5–0.6, corresponding that to the maximum energy scatter inside the droplets, in agreement with Mason’s conception of droplet deformation and disruption of liquid Newtonian emulsions.     

Phase equilibria and gelation in gelatin/maltodextrin systems — Part III: phase separation in mixed gels

Co-gels of potato maltodextrin Paselli SA-6 with gelatin were prepared by rapid quenching of mixed solutions from 90°C. At fixed setting temperature and fixed concentration of gelatin, the time required to form a self-supporting network showed an initial steady decrease with increasing concentration of SA-6 (as expected from polymer exclusion), but then increased dramatically before again decreasing. The interpretation of this behaviour as phase inversion from a gelatin-continuous network with SA-6 inclusions to a (more slowly-forming) SA-6 network with gelatin inclusions was confirmed by differential scanning calorimetry (showing both components melting separately, with no evidence of specific interaction), mechanical spectroscopy (showing that the mixed gel network was destroyed completely by melting of the gelatin component at low concentrations of SA-6, but only weakened at SA-6 concentrations above the inversion point) and by light microscopy (showing the expected changes in distribution of the two polymers).

In similar studies using the faster-gelling potato maltodextrin Paselli SA-2, microscopy and gel-melting profiles again showed phase-inversion from a gelatin-continuous network at low concentrations of SA-2 to a maltodextrin-continuous network at higher concentrations. Inversion, however, occurred at a lower concentration of maltodextrin than in the gelatin/SA-6 systems, and the accompanying change in gelation rate was confined to a sharp decrease in the dependence of gel-time on SA-2 concentration.     

Comparison of the glutamate-, arginine- and lysine-dependent acid resistance systems in Escherichia coli O157:H7

AIMS: The objective of this study was to investigate the effect of growing conditions on the glutamate-, arginine- and lysine-dependent acid resistance (AR) systems of Escherichia coli O157:H7. METHODS AND RESULTS: Seven E. coli O157:H7 strains were grown in five different media at neutral or acidic pH under aerobic or anaerobic conditions, and the survival rate after acid shocks (pH 2.0, 1 h, 37 degrees C) in the presence of glutamate, arginine and lysine was determined. Six strains induced the glutamate-dependent AR at stationary phase, and maximal survival were observed (> or =10%) when grown in pH 5- Luria-Bertani media with glucose (LBG) and in pH 4.5-anaerobic media. The arginine- and lysine-dependent systems were also present, but were only induced if cells had grown in LBG. For strain ATCC 43895, the minimum glutamate concentration that resulted in at least 10% survival rate was 10 micromol l(-1), but it required at least 10-fold more arginine and lysine. CONCLUSIONS: The lysine-dependent AR system could be as important as the arginine-mediated one, but the contribution of both systems to E. coli O157:H7 overall AR response might be minor compared with the glutamate-dependent system. SIGNIFICANCE AND IMPACT OF THE STUDY: Under typical environmental conditions, the glutamate-dependent AR system might be solely responsible for protecting cells against acidic pH.     

Measurement of Temperature-dependent Ice Fraction in Frozen Foods

Ice fraction was measured for solutions containing glucose, sucrose, gelatin, and egg albumin at various concentrations at temperatures from 0 to -20°C. For glucose and sucrose solutions, the ice fraction was accurately measured from phase diagram, which could be interpreted by solution thermodynamics with two parameters. The ice fractions of these sample solutions increased with decreases in both temperature and concentration. Because of the limited applicability of the phase diagram method only to systems with low molecular weight materials, the DSC method was also used for ice fraction measurement. The DSC method, corrected for temperature-dependent latent heat of ice and corrected with Pham’s equation, provided a good approximation for ice fractions with general applicability. The DSC method was used to measure the ice fractions of gelatin and egg albumin gels as a function of solute concentration. The freezing point and bound water of gelatin and egg albumin gels were described as a function of concentration. Effects of the differences in molecular structure on ice fraction were analyzed for various carbohydrate solutions at the same concentration. The ice fraction proved to be strongly dependent on the colligative properties of the solution with nonideal behavior.     

The influence of LBG addition to carrageenan on the mechanical stability of the gel and the fermentative activity of immobilized propionic acid bacteria

In the first part of the experiments, the mechanical properties of 1%, 2% and 3% carrageenan and 1%, 2% and 3% carrageenan/locust bean gum (LBG) gels stored in various concentrations of propionic and acetic acids and their mixtures were examined. The stability of these materials was measured by uniaxial compression between two parallel plates using the Instron Universal Testing Machine. A mathematical model explaining the dependence of the destroying force on the storage time was chosen for data analysis. Using this model, the average rate of gel deterioration was calculated. The structural properties of the examined gels were most influenced by the highest concentration of propionic and acetic acids and their mixtures (1% acetic acid and 2% propionic acid). The addition of LBG to carrageenan decreased the gel destroying force and increased its resistance to acids. In the second part of the experiments, the Propionibacterium freudenreichii subsp. shermanii NCFB 1081 and NCFB 566 were immobilized in a living state in 1%, 2% and 3% carrageenan and 1%, 2% and 3% carrageenan/LBG gels. The ammonia consumption, glucose utilization, production of propionic and acetic acids and the biosynthesis of vitamin B₁₂ were examined. An increase in the productivity of propionic acid and a significant decrease in the vitamin B₁₂ produced in the biosynthesis were observed when immobilized cells were used. The immobilization of cells enhanced the productivity of propionic acid by up to 40% compared to free cells. The best results were obtained for the second and third applications of immobilized cells in all concentrations of carrageenan gels and 2% and 3% carrageenan/LBG gels The results showed that carrageenan/LBG is a better support material for the immobilization of propionic acid bacteria than the pure carrageenan.     

Temperature—composition phase diagram and gel properties of the gelatin—starch—water system

The gelatin-starch-water system has been studied at different temperatures, at a total biopolymer concentration of 5.0 wt%. The weight ratios (W) of gelatin/ starch used were 9:1, 8:2.4. 2:8, 1:9, with pH values between 5.82 (at W = 9:1) and 6.50 (at W = 1:9). The systems were characterized rheologically and by turbidity measurements to construct a phase diagram in the temperature (T) and composition (W) variables. The T-W quadrant consists of three regions: a singlephase solutions region (A) and regions of complete and incomplete phase separation (B and C, respectively). The system in region C is a gel. Region B, lying between A and C, corresponds to two co-existing liquid phases. The transition from A to C (obtained by cooling the system at constant W) involves crossing region B. The properties of the resulting gels depend on the rate of this intersection. Gels formed on rapid cooling have an even distribution of turbidity, whereas slow cooling gives two gel layers of different turbidity. The gelation temperature and gel strength of the mixed systems are dominated by the gelatin component, with no indication of network formation by starch.     

Phase state of aqueous gelatin-polysaccharide (1)-polysaccharide (2) systems

Optical microscopy, ultracentrifugation, phase analysis and turbidimetric titration methods were used to study phase state and phase equilibria of quaternary water-gelatin-pectin-dextran system in the absence of salts and at pH higher than the isoionic point. It was found that these systems are two-phase ones, contrary to the single-phase behaviour of the ternary water-gelatin-pectin and water-gelatin-dextran systems under the same conditions. The observed phase separation is the result of incompatibility of gelatin with pectin, dextran molecules being distributed practically uniformly between coexisting phases. This phenomenon is rather typical for many water-gelatin-polysaccharide-1-polysaccharide-2 systems under the conditions when all the pairs of biopolymers are compatible. The high compatibility of gelatin with pectin or dextran in the ternary systems under given conditions is due to the formation of weakly bonded interpolymer complexes. The incompatibility of gelatin with pectin in the presence of dextran can be explained by the blockage of the reactive gelatin groups due to their competitive interactions with dextran.     

Comparison of the morphologies of a flotable and non-flotable strain of Saccharomyces cerevisiae

In previous paper, Saccharomyces cerevisiae LBG H620 and DAM 2155 were compared regarding their ability to float. LBG H620 did not float at all; cells' surface properties indicated that the yeast LBG H620 has a high surface hydrophilicity and a high electrokinetic potential; yeast DSM 2155 possesses high hydrophobicity and a low electrokinetic potential [Tybussek et al. (1994) J Appl Microbiol Biotechnol 41:13–22]. In the present paper, the morphologies of these two yeast strains are compared. Strain LBG H620 formed only single or dudding cells, strain DSM 2155 formed cell aggregates, their size depending on the cultivation condiotions: in the presence of adequate substrate concentration cell aggregates were formed, and during substrate limitation single cell dominated. During rerspiratory growth rather small spherical aggregates and during respiratory/fermentative growth long-strain aggregates were observed *** DIRECT SUPPORT *** AG903053 00004     

Incorporation of DMSO and dextran-40 into a gelatin/alginate hydrogel for controlled assembled cell cryopreservation

A new cell cryopreservation strategy for cell-assembling constructs was proposed. With this strategy, different concentrations of dimethysulfoxide (DMSO) and dextran-40 were directly incorporated into the cell/gelatin/alginate systems, prototyped according to a predesigned structure, cryopreserved at −80 °C for 10 days and followed a thawing process at 17 °C. The rheological properties, bonding water contents and melting points of the gelatin/alginate hydrogel systems were changed with the addition of different amounts of DMSO. The microscopy analysis, (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrasodium bromide (MTT) and hematoxylin and eosin (HE) staining indicated that the cell numbers were progressively in a selected DMSO concentration range. With DMSO 5% (v/v) alone, the metabolic rate in the construct attained (81.3 ± 5.7)%. A synergistic effect was achieved with the combination of the DMSO/gelatin/alginate and dextran-40/gelatin/alginate hydrogel systems. These results indicated that the inclusion of DMSO and dextran-40 in the hydrogel could effectively enhance the cell preservation effects. This cryopreservation strategy holds the ability to be widely used in organ manufacturing techniques.     

Phase separation and gel formation in kinetically trapped gelatin/maltodextrin gels

The kinetics of phase separation and gel formation of gelatin/maltodextrin mixtures have been studied using confocal laser scanning microscopy (CLSM), transmission electron microscopy (TEM), stereological image analysis and rheology. The quantified microstructural parameters were the volume-weighted mean volume and the interfacial area. The temperature of phase separation was defined as the temperature where the first signs of phase separation were observed in CLSM. The gelatin concentration varied between 4 (wt.) and 5% and the maltodextrin concentration varied between 2 and 6%. Maltodextrin was labelled covalently with RITC to improve the contrast between the gelatin phase and the maltodextrin phase. The solutions were cooled from 60 to 10 degrees C, and the cooling rates used were 0.4, 1 and 3 degrees C/min. All systems were found to be gelatin continuous under the experimental conditions used. The results showed that the temperature of phase separation (TPS) increased both with the gelatin concentration and the maltodextrin concentration, but particularly with the former. The size of the maltodextrin inclusions increased with TPS, and the interfacial area decreased with increasing TPS. The diameter of the maltodextrin inclusions varied between 1.6 and 8.5 microm at 1 degrees C/min. The size of the maltodextrin inclusions was found to increase with decreasing cooling rate and was largest at 0.4 degrees C/min. The TPS was compared with the gelation temperature (Tgel) at three different concentrations of gelatin and maltodextrin (4/3, 4/5, 5/5%). CLSM micrographs and TEM micrographs showed that these three concentrations of gelatin and maltodextrin had different microstructures. At a TPS above Tgel (5/5%), the phase separation proceeded faster than the gel formation and the microstructure had few, large maltodextrin inclusions and a clean continuous gelatin phase. At a TPS comparable with Tgel (4/5%), phase separation occurred during gel formation, which led to a varying microstructure and competition between the phase separation and the gel formation. At a TPS below Tgel (4/3%), gel formation proceeded faster than the phase separation and the microstructure had many, small inclusions and a diffuse microstructure, and the phase separation was incomplete. It was established that the microstructure was determined by the relative rates of the phase separation and the gel formation. Three different zones of phase separation could be distinguished based on comparisons of TPS and Tgel, and results from CLSM, TEM and image analysis.     

Mechanical properties of films and three-dimensional scaffolds made of fibroin and gelatin

Silk fibroin is a biocompatible and biodegradable material, which can be used in surgery and tissue engineering. To improve the cell adhesion on fibroin surface, gelatin can be added to the items made of fibroin. This work compares the mechanical properties of films and three-dimensional scaffolds made of fibroin and fibroin with gelatin. The addition of 30% gelatin to the fibroin scaffold does not change its microstructure or swelling. The addition of gelatin decreases the mechanical properties of films (decreases the Young’s modulus, the maximum strain and elongation) but increases the shear modulus of the scaffolds.     

Comparative immunochemical and immunocytochemical study of 3 soluble granulocytic proteins in blood cells and serum

Using immunofluorescence, it has been shown that leukocyte thermostable alpha-glycoprotein (LTAG) and leukocyte beta-globulin (LBG) are, like lactoferrin, components of polynuclear leukocytes. These proteins were found in the perinuclear zone, cytoplasm membrane and extracellularly. Serum LTAG concentration increases in immune inflammatory diseases. In severe forms of diabetes and glomerulonephritis there is a rise in LBG concentration. The biological role of LTAG and LBG is unknown.     

Bridging the divide between the high- and low-solid analyses in the gelatin/kappa-carrageenan mixture

Over the past few years, a considerable amount of work has been done in several laboratories on the measurement of structural properties of low-solid biopolymer mixtures or high-solid materials of a single biopolymer in the presence of co-solute. The main objective of this work has been to establish a correlation between the two types of systems and extend it to a binary mixture in a high-solid environment. In doing so, it employed well-characterized kappa-carrageenan and gelatin samples in an aqueous preparation or in the presence of glucose syrup and sucrose. The phase behavior of the composite gel was ascertained using small-deformation dynamic oscillation, differential scanning calorimetry, and light microscopy. Experimental observations were built into polymer blending laws that argued for an explicit phase topology and distribution of solvent between the two networks. A working hypothesis was formulated and applied to high-solid mixtures thus identifying phase or state transitions in the time/temperature function. This led to the development of a mechanical glass transition temperature as the threshold of two distinct molecular processes governing the "rubber-to-glass" transformation. A stage was reached at which the predictions of the hypothesis were found to be in good agreement with the experimental development of viscoelasticity in the high-solid kappa-carrageenan/gelatin mixture ranging from the rubbery plateau and the transition region to the glassy state.     

Solution properties of the galactomannans extracted from the seeds of Caesalpinia pulcherrima and Cassia javanica: comparison with locust bean gum.

The galactomannans from the seeds of Caesalpinia pulcherrima and Cassia javanica were extracted from the milled seeds in water at room temperature. Both products, as well as a commercial sample of locust bean gum (LBG), were purified by precipitation in isopropyl alcohol. The intrinsic viscosity determined for LBG, [eta] = 15.2 dl/g, was slightly higher than those for the other two galactomannans. The dependence of the specific viscosity at zero shear rate on the coil overlap parameter, C[eta], revealed a similar behaviour for the three galactomannans. A master curve was obtained with a critical concentration, C*, at C*[eta] = 3.3. The slope of the curve in the concentrated regime is higher than the values in the range of 3.9-6.6, obtained for the generalized behaviour of several random coil polysaccharides. Dynamic experiments showed that, at the concentrations studied, the behaviour of the galactomannans was typical of systems with predominant entanglement networks in the region between the terminal and plateau zones of frequency response. The correlation between dynamic and steady shear properties (Cox Merz rule) was satisfactory for the three galactomannans.     

Rheological properties of mixtures of kappa-carrageenan from Hypnea musciformis and galactomannan from Cassia javanica

Mixed gels of κ-carrageenan (κ-car) from Hypnea musciformis and galactomannans (Gal) from Cassia javanica (CJ) and locust bean gum (LBG) were compared using dynamic viscoelastic measurements and compression tests. Mixed gels at 5 g/l of total polymer concentration in 0.1 M KCl showed a synergistic maximum in viscoelastic measurements for κ-car/CJ and κ-car/LBG at 2:1 and 4:1 ratios, respectively. The synergistic maximum obtained from compression tests carried out for mixed gels at 10 g/l of total polymer concentration in 0.25 M KCl was the same for both κ-car/CJ and κ-car/LBG gels. An enhancement in the storage modulus (G′) and the loss modulus (G″) was observed in the mechanical spectra for the mixtures in relation to κ-car. The proportionally higher increase in G″ compared with G′, as indicated by the values of the loss tangent (tan δ), suggests that the Gal adhere non-specifically to the κ-car network.