Characterization of fish myosin aggregates using static and dynamic light scattering

Myosin was extracted from Atlantic Cod (Gadus morhua) using different methods resulting in small aggregates of pure myosin. These aggregates consisted of between 8 and 20 myosin molecules and were relatively stable at low temperatures (T<20 °C) in dilute (C<5 g/L) solutions containing 0.5 M KCl in the pH range 6.0–8.0. At higher concentrations precipitation or gelation was observed. Heat-induced aggregation at low concentrations was studied using turbidimetry and light scattering. In most cases the aggregation stagnated at longer heating times, but in some cases the aggregation continued until it led to precipitation of large flocs. Cooling led to further growth of the aggregates, which was, however, reversed upon heating.     

Physicochemical properties of low sodium frankfurter with added walnut: effect of transglutaminase combined with caseinate, KCl and dietary fibre as salt replacers

This study compares the effects of combinations of microbial transglutaminase (TGase) and various non-meat ingredients (caseinate, KCl and wheat fibre) used as salt replacers, with the effects of NaCl on the physicochemical properties (cooking loss, emulsion stability, texture and colour) of frankfurters with added walnuts. The combination of TGase with caseinate, KCl or fibre led to harder, springier and chewier (P < 0.05) frankfurters with better water- and fat-binding properties (emulsion stability and cooking loss) (P < 0.05) than those made with TGase only. Ranking of ingredient efficiency in combination with TGase showed that caseinate > KCl > fibre. Frankfurters with caseinate presented the highest lightness and the lowest redness values. Frankfurter with NaCl had a harder, springier and chewier gel/emulsion network with lower cooking loss than those NaCl free.     

Dielectric properties of soybean protein isolate dispersions as a function of concentration, temperature and pH

Dielectric properties of commercial soy protein isolate (SPI) dispersions were measured over the frequency range of 200-2500 MHz by the open-ended coaxial probe method using a network analyzer as a function of concentration (5, 10 and 15 g/100 g water), temperature (20-90 °C) and pH (4.5, 6.6 and 10). Results indicated that the dielectric constant (ε′) decreased with temperature (except at 90 °C) and frequency while increased with concentration. The loss factor (ε″) increased with frequency and concentration; however, temperature showed mixed effect. Both ε′ and ε″ data were related to frequency using a polynomial model. The significant change in ε′ and ε″ at 90 °C was a result of protein denaturation which was identified by differential scanning calorimetry (DSC). Change in the association/dissociation behavior of SPI dispersions due to electrostatic attraction/repulsion among protein molecules on heating as a function of pH was assumed to be responsible for the significant increase in dielectric parameters. Penetration depth (D_p) was estimated under various conditions and it decreased with an increase in frequency, concentration, temperature and pH. The minimum D_p was found at alkaline pH at a temperature of 90 °C and frequency of 2450 MHz.     

Modeling the growth kinetics of Bacillus cereus as a function of temperature, pH, sodium lactate and sodium chloride concentrations

Mathematical models describing the growth kinetic parameters (lag phase duration and growth rate) of Bacillus cereus as a function of temperature, pH, sodium lactate and sodium chloride concentrations were obtained in this study. In order to get a residual distribution closer to a normal distribution, the natural logarithm of the growth kinetic parameters were used in modeling. For reasons of parsimony, the polynomial models were reduced to contain only the coefficients significant at a level of p相似文献   

Power generation in fed-batch microbial fuel cells as a function of ionic strength, temperature, and reactor configuration

Power density, electrode potential, coulombic efficiency, and energy recovery in single-chamber microbial fuel cells (MFCs) were examined as a function of solution ionic strength, electrode spacing and composition, and temperature. Increasing the solution ionic strength from 100 to 400 mM by adding NaCl increased power output from 720 to 1330 mW/m2. Power generation was also increased from 720 to 1210 mW/m2 by decreasing the distance between the anode and cathode from 4to 2 cm. The power increases due to ionic strength and electrode spacing resulted from a decrease in the internal resistance. Power output was also increased by 68% by replacing the cathode (purchased from a manufacturer) with our own carbon cloth cathode containing the same Pt loading. The performance of conventional anaerobic treatment processes, such as anaerobic digestion, are adversely affected by temperatures below 30 degrees C. However, decreasing the temperature from 32 to 20 degrees C reduced power output by only 9%, primarily as a result of the reduction of the cathode potential. Coulombic efficiencies and overall energy recovery varied as a function of operating conditions, but were a maximum of 61.4 and 15.1% (operating conditions of 32 degrees C, carbon paper cathode, and the solution amended with 300 mM NaCl). These results, which demonstrate that power densities can be increased to over 1 W/m2 by changing the operating conditions or electrode spacing, should lead to further improvements in power generation and energy recovery in single-chamber, air-cathode MFCs.     

Analysis of light scattering data on the sodium caseinate assembly as a response to the interactions with likely charged anionic surfactant

We report on the modification of the parameters of sodium caseinate nanoparticles, measured basically by static and dynamic light scattering (the weight-average molar mass M_w; the radius of gyration R_G, the hydrodynamic radius R_h, their ratio (ρ=R_G/R_h), reflecting the shape of the scattering particles; and the thermodynamic affinity for an aqueous medium (the second virial coefficient A₂)), as a response to the interactions with the likely charged anionic surfactant–CITREM (the equimass mixtures of the esters of the stearic and palmitic acids with a citric acid) over a wide range of the surfactant low concentrations at pH 7.2. We found that the protein association, induced by the interactions with the likely charged anionic surfactant, was most pronounced at the medium value of the ionic strength under the ionic strength variation from 0.005 to 0.1 M, namely, at 0.05 M. The detailed dependence of the parameters of the surfactant-modified sodium caseinate on the CITREM concentration allowed recognizing the three concentration regions with the specific parameters of the complex (protein+surfactant) nanoparticles at the ionic strength that is peculiar to the most marked protein association (0.05 M). The first concentration region is at C_CITREM<1.75 mg L⁻¹, which is rather far from the original cmc region for CITREM (cmc_CITREM≈15 mg L⁻¹), where the formation of the most large and linear complex (protein+surfactant) nanoparticles, possessing the highest thermodynamic affinity for the aqueous medium, is revealed. The second concentration range is from C_CITREM=1.75 mg L⁻¹ up to the original cmc point for the surfactant, where the less rigid linear complex (protein+surfactant) nanoparticles, possessing both the lower molar mass and the lower thermodynamic affinity for the aqueous medium, than those in the region (I), were generally formed. The third concentration region, which is defined in the close vicinity to the original surfactant cmc (cmc_CITREM⩾15 mg L⁻¹), is characterized, by a slight decrease in the molar masses of the modified protein nanoparticles and by their quite close thermodynamic affinity for the aqueous medium as compared with the same parameters observed in the second region. The sharp collapse of the complex (protein+surfactant) nanoparticles is found to be in the third concentration region. This collapse apparently suggests the cluster formation of the surfactant molecules in the interior of the protein associates in the close vicinity to the surfactant cmc region. The further measurements of the enthalpy of the protein–surfactant interactions along with the intrinsic viscosity and the apparent net charge of the surfactant-modified protein nanoparticles support the light scattering data obtained.     

Characterisation of a high acyl gellan polysaccharide using light scattering and rheological techniques

Two high acyl gellan samples, one obtained from the aerobic fermentation using milk permeate-based medium, and the other, a commercial gellan (LT100, CPKelco), were converted to the sodium form (referred to as Na-31461 and Na-LT100, respectively) using a cation exchange resin. The Na-gellan solutions were characterised using rheological and static light scattering techniques. The shear rate dependence of viscosity master flow curve obtained for Na-LT100 solution gave an exponent value (1−n) of the Cross equation (∼0.76) typical of flexible random coil polymers. A higher exponent value (∼0.82) was obtained for Na-31461 suggesting that the molecules had a lower degree of flexibility than that of Na-LT100. The intrinsic viscosity ([η]) and molar mass (M_w) values for Na-31461 ([η]∼3950 ml/g, M_w∼5.2×10⁵ Da) were approximately twice that of Na-LT100 ([η]∼2360 ml/g; M_w∼2.5×10⁵ Da). The mechanical spectra (G′, G″) of Na-LT100 solution was characteristic of entangled random coil polymers whereas a weak gel characteristic (G′>G″) was obtained for Na-31461 solution. All these suggest that Na-LT100 molecules were single-stranded, while Na-31461 molecules were double-stranded. Both Na-LT100 and Na-31461 formed gels when the Na⁺ concentration was further increased. The complex moduli of Na-LT100 and Na-31461 superimposed closely at all Na⁺ concentrations implied that the conformation of Na-gellan molecules (from single to double-stranded to three-dimensional gel network) were highly dependent on Na⁺ concentration.     

Rheological,gelling and emulsifying properties of a glycosylated and cross‐linked caseinate generated by transglutaminase

The impacts of oligochitosan glycosylation and cross‐linking on some properties of a commercial caseinate were investigated in this study. The glycosylated and cross‐linked caseinate with glucosamine content of 4.74 g kg^?1 protein was generated by transglutaminase (TGase) and oligochitosan at pH 7.5 and 37 °C, with fixed substrate molar ratio of 1:3 (acyl donor to glucosamine acceptor), caseinate content of 50 g L^?1, TGase of 10 kU kg^?1 protein and reaction time of 3 h, respectively. In comparison with the caseinate, the glycosylated and cross‐linked caseinate had decreased reactable amino groups (0.58 vs. 0.51 mol kg^?1 protein), higher apparent viscosity, decreased emulsifying activity index (about 14.5%) and statistically unchanged emulsion stability index (92.6 vs. 90.5%). Based on the mechanical spectra of the acid‐induced gels, the glycosylated and cross‐linked caseinate showed shorter gelation time (95 vs. 200 or 220 min) than the caseinate or cross‐linked caseinate. The gels prepared from the glycosylated and cross‐linked caseinate also had enhanced hardness, springiness and cohesiveness. The results indicated that TGase‐mediated oligochitosan glycosylation and cross‐linking has the potential to obtain new protein ingredients.     

Effects of temperature and concentration on particle size in a lactose solution using dynamic light scattering analysis

Nucleation, as well as the processes affecting it, is a constant source of interest for scientists dealing with crystallisation. The majority of published material focuses on secondary nucleation because of the complexity of the crystallisation process. The influence of temperature and different levels of concentration, from highly supersaturated solutions down to lactose solutions below the supersaturated level, on lactose primary cluster was investigated using the dynamic light scattering (DLS) method. The minimum particle size in the solution was found; it varied from 0.89 to 1.17 nm and matched the size of a single lactose molecule (1.18 nm), which was estimated by using molecular modelling techniques. Using the DLS technique, it was confirmed that particle size increased with the decrease of temperature and increasing of concentration of the solution. Theoretical calculations were made to estimate a predicted number of molecules that form particles of primary clusters with different sizes.     

Use of an autobioluminescent Campylobacter jejuni to monitor cell survival as a function of temperature, pH, and sodium chloride

The effects of storage temperature (4, 22, and 30 degrees C), pH (4.0 to 8.5), and sodium chloride concentration (0.25 to 7.5%, wt/vol) on the survival of a strain of Campylobacter jejuni ATCC 35921 with an autobioluminescent phenotype (generated from the fusion of luxCDABE genes from Xenorhabdus luminescens to the C. jejuni flaA promoter) in Mueller-Hinton broth under aerobic conditions were determined. At comparable pHs, autobioluminescent C. jejuni cells die most rapidly at 30 degrees C and most slowly at 4 degrees C. For example, at pH 5.5, a 1.2-log decrease in the cell count was observed after 4 days of storage at 4 degrees C, while 3.7- and 4.8-log reductions in cell numbers were observed after 4 days of storage at 22 and 30 degrees C, respectively. At 4 degrees C, C. jejuni was sensitive to NaCl concentrations of > or = 2.5%. However, the degree of inactivation at this storage temperature was also significantly lower than that observed at 22 degrees C, which, in turn, was substantially lower than that observed at 30 degrees C. In the presence of different NaCl concentrations at 22 and 30 degrees C, a strong correlation (r = 0.98) between plate count and bioluminescence output was obtained. However, at low pHs (4.0 and 4.5) and/or a low storage temperature (4 degrees C), bioluminescence did not correlate well with plate count. Despite these limitations, an autobioluminescent phenotype of C. jejuni proved to be a useful tool for studying the behavior of C. jejuni exposed to environmental stresses.     

Influence of temperature,pH and ionic strength on the production of isoflavone-rich soy protein isolates

Soy protein isolates (SPI) may present different isoflavone profiles and contents, depending on processing conditions. In the present work, seven different SPI, resulting from changes in the processing steps, were obtained. The best parameters for obtaining isoflavone-richer SPI were: extraction at pH 9 and temperature of 55 °C, acid precipitation performed at pH 4.5, acid-washing of the precipitate and mild centrifugation conditions for the separation of acid-precipitated proteins. Isoflavones were soluble in aqueous solution in the pH range 2–10 (73–93% of the amount solubilized in 80% methanol). The profile of isoflavones was dependent on the temperature used for the aqueous extraction. Temperatures below 50 °C caused hydrolysis of β-glucosides with increase of aglucones, by endogenous β-glucosidase activity.     

Survival and growth of Listeria monocytogenes in broth as a function of temperature, pH, and potassium lactate and sodium diacetate concentrations

The objective of this study was to determine the antimicrobial effect of a combination of potassium lactate and sodium diacetate (0, 1.8, 3, and 4.5%; PURASAL P Opti.Form 4, 60% solution) on the survival and growth of Listeria monocytogenes Scott A in pH-adjusted broth (5.5, 6.0, 6.5, and 7.0) stored at 4, 10, 17, 24, 30, and 37 degrees C. Appropriate dilutions of broth were enumerated by spiral plating on tryptose agar and counted with an automated colony counter. Growth data were iteratively fit, using nonlinear regression analysis to a three-phase linear model, using GraphPad PRISM. At pH 5.5, the combination of lactate-diacetate fully inhibited (P < 0.001) the growth of L. monocytogenes at all four levels and six temperatures. At pH 6.0, addition of 1.8% lactate-diacetate reduced (P < 0.001) the specific growth rate of L. monocytogenes and increased lag time; however, 3 and 4.5% completely inhibited the growth at the six temperatures studied. Efficacy of the lactate-diacetate mixture was decreased as pH increased and incubation temperature increased. Thus, at pH 6.5, at least 3% was required to retard (P < 0.001) the growth of L. monocytogenes in broth. There was a limited effect of the lactate-diacetate level on the specific growth rate of the pathogen at pH 7.0. However, 1.8 and 3% significantly lengthened the lag time at 4 and 10 degrees C. These results suggest that 1.8% of lactate-diacetate mixture can be used as a substantial hurdle to the growth of L. monocytogenes when refrigerated temperatures are maintained for products with pH less than 6.5.     

Functionality of myofibrillar proteins as affected by pH, ionic strength and heat treatment - a low-field NMR study

Myofibrills were extracted from porcine muscle, and their water properties were characterized using low-field nuclear magnetic resonance (NMR) T(2) relaxometry. A T(2) relaxation pattern very similar to the pattern observed in intact meat and water contents comparable to the water content in meat were observed, implying that the myofibrillar structures are responsible for retaining the majority of water in meat. The effect of pH and ionic strength in the samples was investigated as pH was adjusted to 5.4, 6.2, and 7.0 and ionic strength to 0.29, 0.46 and 0.71 M, respectively. Even though there were interactions between pH and ionic strength, the water content in the samples increased significantly with increasing pH and ionic strength. Moreover, mean T(2) relaxation times likewise increased with increasing pH and ionic strength, which reveals that the increased water retention could be ascribed to a swelling of the myofibrils and thereby increased spacing between filaments. The present study demonstrates that NMR T(2) relaxometry is a potential tool to explore how processing factors such as pH and ionic strength affect the microstructure of meat.     

Milk pH as a function of CO2 concentration, temperature, and pressure in a heat exchanger

Raw skim milk, with or without added CO2, was heated, held, and cooled in a small pilot-scale tubular heat exchanger (372 ml/min). The experiment was replicated twice, and, for each replication, milk was first carbonated at 0 to 1 degree C to contain 0 (control), 600, 1200, 1800, and 2400 ppm added CO2 using a continuous carbonation unit. After storage at 0 to 1 degree C, portions of milk at each CO2 concentration were heated to 40, 56, 72, and 80 degrees C, held at the desired temperature for 30 s (except 80 degrees C, holding 20 s) and cooled to 0 to 1 degree C. At each temperature, five pressures were applied: 69, 138, 207, 276, and 345 kPa. Pressure was controlled with a needle valve at the heat exchanger exit. Both the pressure gauge and pH probe were inline at the end of the holding section. Milk pH during heating depended on CO2 concentration, temperature, and pressure. During heating of milk without added CO2, pH decreased linearly as a function of increasing temperature but was independent of pressure. In general, the pH of milk with added CO2 decreased with increasing CO2 concentration and pressure. For milk with added CO2, at a fixed CO2 concentration, the effect of pressure on pH decrease was greater at a higher temperature. At a fixed temperature, the effect of pressure on pH decrease was greater for milk with a higher CO2 concentration. Thermal death of bacteria during pasteurization of milk without added CO2 is probably due not only to temperature but also to the decrease in pH that occurs during the process. Increasing milk CO2 concentration and pressure decreases the milk pH even further during heating and may further enhance the microbial killing power of pasteurization.     

NaCl离子强度、Mg2+浓度、热变温和pH对云南地方黄牛肌肉盐溶蛋白凝胶保水性的影响

以肉牛的背最长肌(LD)和股二头肌(BF)为材料.研究了NaCl离子强度、Mg2+浓度、热变温度和pH对牛肉背最长肌和股二头肌盐溶蛋白凝胶保水性的影响.结果表明,在一定范围内,背最长肌和股二头肌盐溶蛋白热诱导凝胶的保水性与NaCl离子强度、热变温度呈正相关;Mg2+浓度对凝胶保水性的影响不明显;pH越高,偏离肉蛋白的等电点越远,保水性越好.     

Oil-in-water emulsions stabilized by sodium caseinate: Influence of pH,high-pressure homogenization and locust bean gum addition

The effect of pH, addition of a thickening agent (locust bean gum) or high-pressure homogenization on the stability of oil-in-water emulsions added by sodium caseinate (Na-CN) was evaluated. For this purpose, emulsions were characterized by visual analysis, microstructure and rheological measurements. Most of the systems were not stable, showing phase separation a few minutes after emulsion preparation. However, creaming behavior was largely affected by the pH, homogenization pressure or locust bean gum (LBG) concentration. The most stable systems were obtained for emulsions homogenized at high pressure, containing an increased amount of LBG or with pH values close to the isoelectric point (pI) of sodium caseinate, which was attributed to the size reduction of the droplets, the higher viscosity of continuous phase and the emulsion gelation (elastic network formation), respectively. All the studied mechanisms were efficient to decrease the molecular mobility, which slowed down the phase separation of the emulsions. In addition, the use of sodium caseinate was also essential to stabilize the emulsions, since it promoted the electrostatic repulsive interactions between droplets.     

Transformation of two-line ferrihydrite to goethite and hematite as a function of pH and temperature

Under oxic aqueous conditions, two-line ferrihydrite gradually transforms to more thermodynamically stable and more crystalline phases, such as goethite and hematite. This temperature- and pH-dependent transformation can play an important role in the sequestration of metals and metalloids adsorbed onto ferrihydrite. A comprehensive assessment of the crystallization of two-line ferrihydrite with respect to temperature (25, 50, 75, and 100 °C) and pH (2, 7, and 10) as a function of reaction time (minutes to months) was conducted via batch experiments. Pure and transformed phases were characterized by X-ray diffraction (XRD), X-ray absorption near-edge spectroscopy (XANES), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The rate of transformation of two-line ferrihydrite to hematite increased with increasing temperature at all pHs studied and followed first-order reaction kinetics. XRD and XANES showed simultaneous formation of goethite and hematite at 50 and 75 °C at pH 10, with hematite being the dominant product at all pHs and temperatures. With extended reaction time, hematite increased while goethite decreased, and goethite reaches a minimum after 7 days. Observations suggest two-line ferrihydrite transforms to hematite via a two-stage crystallization process, with goethite being intermediary. The findings of this study can be used to estimate rates of crystallization of pure two-line ferrihydrite over the broad range of temperatures and pH found in nature.