Effect of lime on the dissolution of two phosphate rocks in acid soils

The effect of pH and calcium (Ca) on the dissolution of Gafsa (GPR) and Christmas Island A (CIPR) phosphate rocks (PR) was examined in closedincubation and open-leaching systems in six acid, Malaysian soils. The pH of the soils was increased to between 4.5 and 6.1 by incubating with calcium carbonate (CaCO₃); soil was also incubated with calcium chloride (CaCl₂) to provide equivalent amounts of Ca without causing any marked change in pH. In the closed-incubation system, dissolution of reactive GPR was overall higher (11–70%) than for the less reactive CIPR (12–43%) after 60 days of incubation. Dissolution of PR decreased with increasing levels of CaCO₃ or CaCl₂, but the decrease was more pronounced in CaCO₃-treated than in CaCl₂-treated soils. Increasing additions of CaCl₂ decreased the size of the available sink for Ca from 84.0 to 0 mmol (+) kg^–1 soil. Although the addition of CaCO₃ increased the cation-exchange capacity (CEC) of these variable-charge soils (from 23.0 to 199.0 mmol (+) kg^–1 soil), most of the newly-created exchange sites were occupied by Ca added through CaCO₃. This was responsible for the decrease in size of the sink for Ca. Addition of CaCO₃ also decreased the proton supply from 260.7 to 0 mmol (+) kg^–1 soil, which in conjunction with the decrease in size of the Ca sink decreased the dissolution of PR. The effect of CaCO₃ and CaCl₂ on PR dissolution varied between soils and was related to pH-buffering and the Ca-sink size. In an open-leaching system, large amounts of Ca (8–40%) added as CaCO₃ were removed in the leachate and hence the decrease in GPR dissolution with CaCO₃ addition was less in the open-leaching than in the closed-incubation system.     

The effect of soil Ph on olsen bicarbonate phosphate values

The effect of increases in soil pH by liming on Olsen bicarbonate phosphate (P) test values was investigated using two contrasting New Zealand soils: a highly P retentive Egmont soil and a Tokomaru soil with a low P retention capacity. After incubation with three rates of Ca(OH)₂, soil pH was increased, and a reduction in the Olsen P values was observed. The amounts of ³²P-exchangeable P, however, increased with increasing soil pH, and there was very little change in water-extractable P. The addition of lime had no significant effect on either the yield or uptake of P by ryegrass grown on the same soils in the glasshouse. It appears that the decline in Olsen P values in soils following liming is a result of an artefact in the Olsen procedure. High concentrations of Ca are involved in the decrease in Olsen P values in limed soils. It is suggested that the precipitation of calcium phosphates in the Olsen extracts of limed soils is responsible for the decrease in the Olsen P values. In a field experiment, increasing soil pH by lime addition also resulted in a decrease in the Olsen P values.     

Hydrophilic and hydrophobic sorption of organic acids by variable charge soils: effect of chemical acidity and acidic functional group

Sorption of organic acids by variable-charge soil occurs through both hydrophilic and hydrophobic sorption. In this study, the effect of chemical acidity and the type of acidic functional group on the relative contribution of hydrophilic and hydrophobic processes to sorption by a gibbsite-dominated and a kaolinite-dominated variable-charge soils was quantified by measuring sorption isotherms from different electrolytes (CaCl2, Ca(H2PO4)2, and KCl). The A1 soil is dominated by gibbsite whereas the DRC soil is primarily kaolinite. The organic acids investigated include five chlorinated phenols (pentachlorophenol, 2,3,4,6-tetrachlorophenol, 2,4,6-trichlorophenol, 2,4,5-trichlorophenol, and 2,4-dichlorophenol) with pKa values ranging from 4.69 to 7.85 and two acidic herbicides (2,4-D (pKa = 2.8) and prosulfuron (pKa = 3.76)) that contain carboxyl and urea functional groups, respectively. Anion exchange of chlorinated phenols and prosulfuron on both variable-charge soils as well as 2,4-D sorption on the A1 soil was linearly correlated to chemical acidity. The effective positive surface charge [AEC/(AEC + CEC)] and the anionic fraction of the organic acid in solution, which are both pH-dependent, were sufficient to estimate the contribution of anion exchange to organic acid sorption except for 2,4-D sorption by DRC soil. The latter was much greater than would be predicted from the pKa of 2,4-D. Calcium bridging between silanol edge group and 2,4-D was hypothesized and corroborated by differences in sorption measured from KCl and CaCl2 solutions. For predicting contributions from hydrophobic processes, a log-log linear relationship between pH-dependent octanol-water (Kow(pH)) and organic carbon-normalized sorption coefficients (Koc(pH)) appeared adequate.     

Measurement of urine pH and net acid excretion and their association with urine calcium excretion in periparturient dairy cows

Urine pH (U_pH) and net acid excretion (NAE) are used to monitor the degree of systemic acidification and predict the magnitude of resultant hypercalciuria when feeding an acidogenic ration to control periparturient hypocalcemia in dairy cattle. The objectives of this study were to evaluate the diagnostic performance of urine dipstick and pH paper for measuring U_pH, and to characterize the U_pH–NAE relationship and the association of urine Ca concentration ([Ca]) with U_pH and NAE. Urine samples (n = 1,116) were collected daily from 106 periparturient Holstein-Friesian cows fed an acidogenic ration during late gestation. Net acid excretion was measured by titration, and U_pH was measured by a glass-electrode pH meter (reference method), Multistix-SG urine dipsticks (Siemens Medical Solutions Inc., Ann Arbor, MI), and Hydrion pH paper (Micro Essential Laboratory Inc., Brooklyn, NY). Diagnostic performance was evaluated using Spearman correlation coefficient (r_s), Bland–Altman plots, and logistic regression. Urine pH measured by urine dipstick (r_s = 0.94) and pH paper (r_s = 0.96) were strongly associated with U_pH. Method-comparison studies indicated that the urine dipstick measured an average of 0.28 pH units higher, and pH paper 0.10 pH units lower, than U_pH. Urine [Ca] was more strongly associated with U_pH (r_s = −0.65) than NAE (r_s = 0.52). Goals for controlling periparturient hypocalcemia under the study conditions were U_pH <6.22 and <6.11, based on achieving urine [Ca] ≥5 mmol/L and estimated urinary Ca excretion ≥4 g/d, respectively. Urine pH was as accurate at predicting urine [Ca] as NAE when U_pH >6.11. We conclude that pH paper is an accurate, practical, and low-cost cow-side test for measuring U_pH and provides a clinically useful estimate of urine [Ca].     

Influence of the overall charge and local charge density of pectin on the complex formation between pectin and β-lactoglobulin

The complex formation between β-lactoglobulin (β-lg) and pectin is studied using pectins with different physicochemical characteristics. Pectin allows for the control of both the overall charge by degree of methyl-esterification as well as local charge density by the degree of blockiness. Varying local charge density, at equal overall charge is a parameter that is not available for synthetic polymers and is of key importance in the complex formation between oppositely charged (bio)polymers. LMP is a pectin with a high overall charge and high local charge density; HMP_B and HMP_R are pectins with a low overall charge, but a high and low local charge density, respectively. Dynamic light scattering (DLS) titrations identified pH_c, the pH where soluble complexes of β-lg and pectin are formed and pH_?, the pH of phase separation, both as a function of ionic strength. pH_c decreased with increasing ionic strength for all pectins and was used in a theoretical model that showed local charge density of the pectin to control the onset of complex formation. pH_? passed through a maximum with increasing ionic strength for LMP because of shielding of repulsive interactions between β-lg molecules bound to LMP, while attractive interactions were repressed at higher ionic strength. Potentiometric titrations of homo-molecular solutions and mixtures of β-lg and pectin showed charge regulation in β-lg–pectin complexes. Around pH 5.5–5.0 the pK_as of β-lg ionic groups are increased to induce positive charge on the β-lg molecule; around pH 4.5–3.5 the pK_a values of the pectin ionic groups are lowered to retain negative charge on the pectin. Since pectins with high local charge density form complexes with β-lg at higher ionic strength than pectins with low local charge density, pectin with a high local charge density is preferred in food systems where complex formation between protein and pectin is desired.     

Complex coacervates obtained from lactoferrin and gum arabic: Formation and characterization

Proteins and polysaccharides are the most frequently used hydrocolloids in the food industry, and their interaction can provide products such as complexes coacervates, which can be used as ingredients and biomaterials or in microencapsulation systems. In the present work, the interaction between lactoferrin (0.1, 0.2, 0.3, 0.5 and 1% w/w) and gum arabic (0.1% w/w) with various concentrations of NaCl (0, 0.01, 0.25, 0.3 and 0.5 mol/L) and at various pH values (from 1.0 to 12.0) was studied. The pH for the formation (higher turbidity) of the insoluble complex coacervates (pH_Ø1) varied according to the amount of NaCl used in the system (pH 3.5 to 5.3); these values are below the isoelectric point of lactoferrin (8.0), at which the protein is more positively charged, generating electrostatic binding. At a pH of approximately 2.0, this bond weakens, leading to the solubilization of precipitates, resulting in a sudden decrease in the turbidity (pH_Ø2). Samples containing a lower concentration of lactoferrin (0.1, 0.2 and 0.3% w/w) showed greater turbidity and consequently a higher formation of precipitates or aggregates. Even these samples, which contained a salt concentration of 0.3 mol/L, showed higher turbidity and displacement points of pH_Ø1 and pH_Ø2. The zeta potential and particle size values were used to study the influence of the pH, ionic strength and temperature on the interaction between the biopolymers. It was observed that the formation of macromolecules occurred between the isoelectric point of the protein (8.0) and the pKa of the polysaccharide (2.0), and a certain salt concentration (0.25 mol/L) led to larger particle sizes. It was observed that, at pH 7.0, a concentration of 0.1% gum arabic was able to stabilize the denaturation of the protein in solutions containing 0.1% lactoferrin, resulting in a constant particle size at all temperatures studied.     

Improving the thermostability of β-lactoglobulin via glycation: The effect of sugar structures

This work studied the effects of sugar structure (size, position of carbonyl group, and charge state) on the thermostability of β-lactoglobulin (β-lg) when controlling the glycation extent of reducing sugars to the same level. Ribose, glucose, maltose, maltotriose, fructose and galacturonic acid were selected to react with β-lg at a_w of 0.53 at 45 °C for different periods to reach an average degree of saccharide attached per protein molecule β-lg (average DSP) of 5. β-Lg and the conjugates in pH 3, 5 and 7 were heated. The denaturation temperature was detected by differential scanning calorimeter (DSC), and the solubility was determined by Bradford assay. The results showed that all the conjugates exhibited higher denaturation temperature than β-lg. Larger molecular size, ketose and negative charge had significant effects on increasing the denaturation temperature. β-Lg and the conjugates at pH 3 and 7 could maintain their solubility when increased the temperature from 60 to 90 °C. The conjugates showed better thermostability than β-lg at pH 5 and sugar structure had effects on the improvement. Glycation by sugars with increasing size and negative charge stabilized β-lg. Ketose glycation did not show better thermostability than aldose, but caused more aggregates during mild or short time heating.     

Simultaneous application of dissolution/precipitation and surface complexation/surface precipitation modeling to contaminant leaching

This paper discusses the modeling of anion and cation leaching from complex matrixes such as weathered steel slag. The novelty of the method is its simultaneous application of the theoretical models for solubility, competitive sorption, and surface precipitation phenomena to a complex system. Selective chemical extractions, pH dependent leaching experiments, and geochemical modeling were used to investigate the thermodynamic equilibrium of 12 ions (As, Ca, Cr, Ba, SO4, Mg, Cd, Cu, Mo, Pb, V, and Zn) with aqueous complexes, soluble solids, and sorptive surfaces in the presence of 12 background analytes (Al, Cl, Co, Fe, K, Mn, Na, Ni, Hg, NO3, CO3, and Ba). Modeling results show that surface complexation and surface precipitation reactions limit the aqueous concentrations of Cd, Zn, and Pb in an environment where Ca, Mg, Si, and CO3 dissolve from soluble solids and compete for sorption sites. The leaching of SO4, Cr, As, Si, Ca, and Mg appears to be controlled by corresponding soluble solids.     

Small heat shock protein degradation could be an indicator of the extent of myofibrillar protein degradation

The objective of the present study was to evaluate the relationship between small heat shock proteins (sHSP) degradation and tenderness development of beef loins at different ultimate pH (pH_u). A total of twelve loins (M. longissimus dorsi) from steers were obtained at 1 day post mortem. Shear force and proteolysis of each loin were analyzed at 1 and 28 days post mortem. The loins at intermediate pH_u (5.8 to 6.0) showed more variation in tenderness compared to the loins at low pH_u (< 5.8), where few samples were still tough (> 10 kgF) at 28 days. The intact sHSP20 was more pronounced (P < 0.05) in the intermediate pH_u loin compared to the low pH_u counterpart. Further, high correlations between the degradation of both sHSP and myofibrillar proteins were observed (e.g. r = 0.94; degraded sHSP27 and degraded desmin). The result of this study suggests that the extent of sHSP degradation could be an indicator of myofibrillar protein degradation and tenderness.     

A stochastic approach for integrating strain variability in modeling Salmonella enterica growth as a function of pH and water activity

Strain variability of the growth behavior of foodborne pathogens has been acknowledged as an important issue in food safety management. A stochastic model providing predictions of the maximum specific growth rate (μ_max) of Salmonella enterica as a function of pH and water activity (a_w) and integrating intra-species variability data was developed. For this purpose, growth kinetic data of 60 S. enterica isolates, generated during monitoring of growth in tryptone soy broth of different pH (4.0-7.0) and a_w (0.964-0.992) values, were used. The effects of the environmental parameters on μ_max were modeled for each tested S. enterica strain using cardinal type and gamma concept models for pH and a_w, respectively. A multiplicative without interaction-type model, combining the models for pH and a_w, was used to describe the combined effect of these two environmental parameters on μ_max. The strain variability of the growth behavior of S. enterica was incorporated in the modeling procedure by using the cumulative probability distributions of the values of pH_min, pH_opt and a_wmin as inputs to the growth model. The cumulative probability distribution of the observed μ_max values corresponding to growth at pH 7.0-a_w 0.992 was introduced in the place of the model's parameter μ_opt. The introduction of the above distributions into the growth model resulted, using Monte Carlo simulation, in a stochastic model with its predictions being distributions of μ_max values characterizing the strain variability. The developed model was further validated using independent growth kinetic data (μ_max values) generated for the 60 strains of the pathogen at pH 5.0-a_w 0.977, and exhibited a satisfactory performance. The mean, standard deviation, and the 5th and 95th percentiles of the predicted μ_max distribution were 0.83, 0.08, and 0.69 and 0.96 h^− 1, respectively, while the corresponding values of the observed distribution were 0.73, 0.09, and 0.61 and 0.85 h^− 1. The stochastic modeling approach developed in this study can be useful in describing and integrating the strain variability of S. enterica growth kinetic behavior in quantitative microbiology and microbial risk assessment.     

Effect of Water Activity on the Growth Kinetics of Staphylococcus aureus in Ground Bread Crumb

The kinetics of Staphylococcus aureus (strains A, B, D) growth in bread crumb were determined as a function of water activity (A_w) from 0.836 to 0.909 at pH 5.2 to 5.5 and at 35°c. Adding glycerol to the dough or equilibrating the bread over saturated salt solutions adjusted the A_w of the bread. Growth kinetics data, plotted as enumerated colony counts versus incubation time, were fitted using the logistic function to determine maximum growth rates. Similar maximum growth rates resulted, irrespective of the method used to adjust A_w. Extrapolation of growth rate‐A_w results predicts the A_w corresponding to a zero growth rate.     

Estimating Water Activity in Systems Containing Multiple Solutes Based on Solute Properties

A water activity (a_w) model for multicomponent systems expressed as a linear first order sum of molalities and requiring only data from binary solutions was tested. The model was developed based on a linear relationship between a_w and molality for each solute. Water activity predictions were validated and compared with Ross’equation using a_w data reported of different complex electrolyte and nonelectrolyte solutions. The equation proved to have a good predictive application, was extremely simple and exhibited comparable accuracy to Ross’equation in the mixtures considered.     

A two-front leach model for cement-stabilized heavy metal waste

Quantitative scanning electron microscope (SEM) studies of cement-stabilized waste specimens exposed to a leaching solution at constant pH in the range 4-7 have shown that the acid neutralization capacity (ANC) of the waste matrix is consumed at two consecutive leaching fronts. The first front is associated with the dissolution of portlandite (Ca(OH)2) and the partial reaction of calcium silicate hydrate (CSH) gel. The second front marks the dissolution of Ca-Al hydroxy sulfate minerals. The advancement of the first front is limited by the diffusion of OH- ions from the first front toward the leaching solution. The advancement of the second front, however, is controlled by the diffusion of H+ ions from the leaching solution toward the second front. Leaching of copper, zinc, and lead only occurs between the second front and the specimen surface. The leaching behavior of metals is modeled by considering that metals are leached from the waste matrix as a result of the advancement of the second front. The proposed model takes into account the leachable metal fraction in the waste matrix and the effect of metal remineralization on metal mobility.     

Variation of cardinal growth parameters and growth limits according to phylogenetic affiliation in the Bacillus cereus Group. Consequences for risk assessment

The growth rates of strains covering the seven major phylogenetic groups of Bacillus cereus sensu lato (as defined by Guinebretiere et al., 2008) at a range of temperature (7 °C–55 °C), pH (4.6–7.5) and a_w (0.929–0.996, with 0.5%–10% NaCl as humectant) were determined. Growth rates were fitted by non-linear regression to determine the cardinal parameters T_min, T_opt, T_max, pH_min, pH_opt, a_wmin and μ_opt. We showed that cardinal parameters reflected the differences in the temperature adaptation observed between B. cereus phylogenetic groups I to VII. The ability of growing at low pH (up to 4.3) or low a_w (from a_w 0.929 and up to 10% NaCl) varied among strains. The strains of groups III and VII, the most tolerant to heat, were also the most adapted to high NaCl (all strains growing at 8% NaCl) and the ones of groups I and VI the least adapted (no growth at 7% NaCl). All strains of groups II and VII were able to grow at pH 4.6, and only a few strains of group VI. Phenotypic differences between the two psychrotrophic groups II and VI were revealed by contrasted acid and salt tolerance. The cardinal values determined in this work were validated by comparing with cardinal parameters of a panel of strains published elsewhere and with predictions of growth in a range of foods.     

牛乳中酪蛋白的分离及其特性的研究

以鲜牛乳高速离心得到的酪蛋白为原料,配置成不同pH的溶液,进而研究了样品的Zeta电势、电导率、黏度、平均粒径和稳定性的变化。实验结果表明:酪蛋白溶液的Zeta电势值(绝对值)、电导率值和黏度值都是随着pH的增加而逐渐增加;平均粒径值是先减小后增加,在pH6.2时有最小值,为26.03nm;溶液的pH为5.8～6.6时,体系较稳定。初步认为,当pH<7时,降低pH会导致胶体磷酸钙的溶解,使得体系的平均粒径变小;继续降低pH会导致静电斥力的减小,酪蛋白会发生凝集,平均粒径增大,体系也会变得不稳定。     

On the selection of relevant environmental factors to predict microbial dynamics in solidified media

Several studies have shown that food structure causes slower growth rates and narrower growth boundaries of bacteria compared to laboratory media. In predictive microbiology, both a_w or corresponding solute concentration (mainly NaCl) have been used as a growth influencing factor for kinetic models or growth/no growth interface models. The majority of these models have been based on data generated in liquid broth media with NaCl as the predominant a_w influencing solute. However, in complex food systems, other a_w influencing components might be present, next to NaCl. In this study, the growth rate of Salmonella typhimurium was studied in the growth region and the growth/no growth response was tested in Tryptic Soy Broth at 20 °C at varying gelatin concentration (0, 10, 50 g L⁻¹ gelatin), pH (3.25–5.5) and water activity (a_w) (0.929–0.996). From the viewpoint of water activity, the results suggest that NaCl is the main a_w affecting compound. However, gelatin seemed to have an effect on medium a_w too. Moreover, there is also an interaction effect between NaCl and gelatin. From the microbial viewpoint, the results confirmed that the a_w decreasing effect of gelatin is less harmful to cells than the effect of Na⁺ ions. The unexpected shift of the growth/no growth interface to more severe conditions when going from a liquid medium to a medium with 10 g L⁻¹ gelatin is more pronounced when formulating the models in terms of a_w than in terms of NaCl concentrations. At 50 g L⁻¹ gelatin, the model factored with NaCl concentration shifts to milder conditions (concordant to literature results) while the model with a_w indicates a further shift to more severe conditions, which is due to the water activity lowering effect of gelatin and the interaction between gelatin and NaCl. The results suggest that solute concentration should be used instead of a_w, both for kinetic models in the growth region and for growth/no growth interface models, if the transferability of models to solid foods is to be increased.     

Investigation of pyrochlore-based U-bearing ceramic nuclear waste: uranium leaching test and TEM observation

A durable titanate ceramic waste form (Synroc) with pyrochlore (Ca(U,Pu)Ti2O7) and zirconolite (CaZrTi2O7) as major crystalline phases has been considered to be a candidate for immobilizing various high-level wastes containing fissile elements (239Pu and 235U). Transmission electron microscopy study of a sintered ceramic with stoichiometry of Ca(U(0.5)Ce(0.25)Hf(0.25))Ti2O7 shows the material contains both pyrochlore and zirconolite phases and structural intergrowth of zirconolite lamellae within pyrochlore. The (001) plane of zirconolite is parallel to the (111) plane of pyrochlore because of their structural similarities. The pyrochlore is relatively rich in U, Ce, and Ca with respect to the coexisting zirconolite. Average compositions for the coexisting pyrochlore and zirconolite at 1350 degrees C are Ca(1.01)(Ce3+(0.13)Ce4+(0.19)U(0.52)Hf(0.18))(Ti(1.95)Hf(0.05))O7 (with U/(U + Hf) = 0.72) and (Ca(0.91)Ce(0.09))(Ce3+(0.08)U(0.26)Hf(0.66)Ti(0.01))Ti(2.00)O7 (with U/(U + Hf) = 0.28), respectively. A single pyrochlore (Ca(U,Hf)Ti2O7) phase may be synthesized at 1350 degrees C if the ratio of U/(U + Hf) is greater than 0.72, and a single zirconolite (Ca(Hf,U)Ti2O7) phase may be synthesized at 1350 degrees C if the ratio of U/(U + Hf) is less than 0.28. The synthesized products were used for dissolution tests. The single-pass flow-through dissolution tests show that the dissolution of the U-bearing pyrochlore is incongruent. All the elements are released at differing rates. The dissolution data also show a decrease in rate with run time. The results indicate that a diffusion-controlled process may play a key role during the release of U. TEM observation of the leached pyrochlore directly proves that an amorphous leached layer that is rich in Ti and Hf formed on the surface after the ceramic was leached in pH 4 buffered solution for 835 days. The thickness of the layer ranges from 6 to 10 nm. A nanocrystalline TiO2 phase also forms in the leached layer. The U leaching rate (g/(m2 day)) in acidic solutions can be expressed as log(NR) = -5.36-0.20 pH, where NR is the normalized rate. Conservative leaching rates of uranium [log(NR)] for the U-bearing ceramic at pH 2 and pH 4 solutions are -5.76 and -6.16 g/(m2 day), respectively. The results show that the U release rate of the ceramic waste is 10 times slower than that of defense high-level waste glass and about 1000 times slower than that of spent fuel. The pyrochlore-based ceramic is an ideal waste form for immobilizing long-lived radionuclides of 239Pu and 235U due to the Ti- and Hf-rich leached layer that forms on the ceramic surface. The leached layer functions as a protective layer and therefore reduces the leaching rate as thickness of the leached layer increases.     

Formation of nanostructured colloidosomes using electrostatic deposition of solid lipid nanoparticles onto an oil droplet interface

This study describes the assembly of colloidosomes by adsorbing solid lipid nanoparticles (SLN) onto the interfaces of oil-in-water emulsion droplets via electrostatic deposition technique. Oil-in-water emulsions (10% w/w corn oil, 1% w/w whey protein isolate in water) and SLN (10% octadecane, 1% sodium dodecyl sulfate in water) were prepared using a microfluidizer. The surface saturation concentration (C_sat) of negatively charged SLN adsorbed onto the positively charged oil-in-water emulsions (at oil droplet concentration of 0.5%) at pH 3 was investigated by measuring ζ-potential, and particle size, as well as assessing the microstructure by optical microscopy. Each of these methods depicted C_sat between 1.1–1.5% (w/w). The results were explained by calculating theoretical C_sat using molecular forces acting between the adsorbed droplets as described by the DLVO theory. We demonstrated that the surface saturation of SLN on emulsion droplets depends on the particle size population.     

The protection of bovine skeletal myofibrils from proteolytic damage post mortem by small heat shock proteins

This study aimed to determine how small heat shock proteins (sHSPs) protect myofibrillar proteins from μ-calpain degradation during ageing. Immunoprecipitation experiments with M. longissimus dorsi (LD) from Angus heifers (n = 14) examined the interaction between αβ-crystallin, desmin, titin, HSP20, HSP27 and μ-calpain. Results showed that αβ-crystallin associated with desmin, titin, HSP20, HSP27 and μ-calpain. Exogenous αβ-crystallin reduced desmin and titin degradations in myofibrillar extracts and attenuated μ-calpain activity. In a second experiment, bull LD (n = 94) were aged at − 1.5 °C for up to 28 days post mortem. μ-Calpain autolysed faster in high ultimate pH (pH_u) meat (pH_u ≥ 6.2) and this was concomitant with the more rapid degradation of titin and filamin in this pH_u group. Desmin stability in intermediate pH_u meat (pH_u 5.8 to 6.19) may be due to the protection of myofibril-bound sHSPs combined with the competitive inhibition of μ-calpain by sHSPs.     

The effect of ionic strength on the rheology of pH-induced bovine serum albumin/κ-carrageenan coacervates

Protein/polysaccharide coacervates are frequently applied to food products to control the rheology. This study investigated the effect of ionic strength (I) on the rheology of pH-induced protein/polysaccharide coacervates. Bovine serum albumin (BSA) and κ-carrageenan were used as a model protein and a polysaccharide, respectively. As the formation of BSA/κ-carrageenan coacervates increased the turbidity of an aqueous mixture, pH_c, pH_?, and pH_max values were identified corresponding to the pH of the formation of soluble coacervates, insoluble coacervates, and large insoluble coacervates respectively. Based on pH_c, pH_?, and pH_max, a state diagram of BSA/κ-carrageenan coacervation versus pH and I was constructed. Involvement of salt in coacervation screened out the electrostatic interaction between BSA and κ-carrageenan coacervation, resulting in the shift of pH_c, pH_?, and pH_max to lower pH. The shift was linearly changed to 1/I^1/2 that corresponded to the Debye length. BSA/κ-carrageenan coacervates were more elastic than viscous. The transition from insoluble coacervates to large insoluble coacervates contributed to enhancement of the rheology, especially in elasticity. An increase in the I of a BSA/κ-carrageenan mixture reduced the degree of coacervation and the elasticity, and the viscosity of BSA/κ-carrageenan coacervates.