Interpretation of DSC data on protein denaturation complicated by kinetic and irreversible effects.

Thermal denaturation of Kunitz soybean trypsin inhibitor (KTI) and ribulose-1,5-biphosphate carboxylase (RBPC) from tobacco leafs was studied by the method of high-sensitivity differential scanning calorimetry (HS-DSC). The dependence of the denaturation temperature on the heating rate reveals in the case of both proteins a non-equilibrium character of the denaturation transition in applied conditions. Developed kinetic approach allows the determination of an equilibrium transition temperature as well as the rate constants of denaturation and renaturation from the complex data of HS-DSC. This method was applied to the analysis of the pH-induced change of the conformational stability of KTI within pH range from 2.0 to 11.0. It allowed the determination of the pH dependencies: of the excess free energy of denaturation, of the activation enthalpy and entropy of denaturation as well as of the denaturation rate constant. Conclusions have been made suggesting the contribution of side-chain hydrogen bonds in the stabilisation of the native and activated states of KTI.

The importance of glassy biopolymer components in food.

The glassy state is not just important in low moisture and frozen foods, where it influences the physical and chemical stability and the crispness of some foodstuffs: glassy biopolymer components affect the physical properties of most food systems and low moisture biological systems. Glassy foods are not always fragile and crispy in texture. Therefore, the relationship between mechanical behaviour and molecular dynamics in low-moisture biopolymer systems will be considered. Vitrification of a macromolecular system only requires a mutual fixation of a certain proportion of the chain segments. The higher the rigidity of the chains, the lower the number of the chain segments which must be mutually fixed to vitrify the system. Mechanical stress can help the thermal movement to re-activate the motion of mutually fixed segments and involves a long deformation of glassy material. The stress required to effect long deformation presumably increases up to the strength of the material as the temperature decreases from the glass transition to the temperatures of brittleness (crispness). Vitrification of a loaded viscoelastic system results in an accumulation of mechanical energy (memory effect), which can be released (elastic recovery) above the glass transition temperature due to heating and or addition of a plasticizer. The effects of memory and elastic recovery could be of particular importance for producing foodstuffs which change their form, e.g. self-stirring dry foods and drinks on re-hydration in hot water. The importance of glassy biopolymer ingredients from the viewpoint of food formulation and processing is discussed.

Effect of thermal denaturation on vanillin binding to some food proteins.

Interactions of food proteins--beta-lactoglobulin (BLG), bovine serum albumin (BSA) und ovalbumin (OA)--with vanillin and effect of thermal denaturation of the proteins on vanillin binding were studies by US-VIS spectrophotometry. This method has its origin in characteristic changes in the vanillin absorption spectrum at vanillin-protein complex formation and allows to calculate concentrations of the bound and free ligand in aqueous solutions. Thermodynamic parameters, the intrinsic association constants and the number of binding sites of the vanillin binding to the native and thermodenaturated proteins (monomers and clusters) were determined. It is shown that the vanillin affinity for the native proteins is decreased in the following order: BSA > BLG > OA. This sequence is reversed for the protein thermoclusters. The stepwise annealing allowing to derive complex protein mixtures composed of different types of the native and denatured protein mixtures composed of different types of the native and denatured protein particles was applied to thermodenaturation of BSA. The vanillin affinity for BSA is decreased in the order: native protein > denaturated monomer > denaturated clusters. Vanillin interaction with the proteins is mainly electrostatic in nature.

Physico-chemical modification of food proteins: food emulsions.

Physico-chemical protein modification involved in food processing is used for "engineering" the structure-property relationship of foods. The three main tools used for protein modification are food formulation, mechanical and thermal (heating/cooling) treatments. They correspond to the main stages of all food technologies. Food structural design is based upon incompatibility and complexing of food biopolymers as well as upon fundamental features of physico-chemical properties of biphasic aqueous systems. Some examples of functional biopolymer modification are considered in systems such as meat extenders, fat replacers, ice cream mixes and wheat flour doughs.

[Phase equilibria in water-defatted milk proteins-carboxymethylcellulose sodium salt systems]. / Fazovye ravnovesiia v sistemakh voda-belki obezzhirennogo moloka--natrievaia sol' karboksimetiltselliulozy.

Phase equilibria in water mixtures of skimmed milk with sodium salt of carboxymethylcellulose (CMC) was studied using two degrees of CMC polymerization (500 and 200) and substitution (0.8 and 0.5). The increase of the polymerization degree from 200 to 500 resulted in a higher protein yield in the protein phase, while the decrease of the substitution degree from 0.8 to 0.5 caused a noticeable decrease of asymmetry of phase diagrams. The phase separation was accompanied by ion exchange: potassium and calcium ions were mainly found in the protein phase. The highest yield of milk protein into the protein phase was 85% at a CMC concentration of 0.7%. The main protein component of the polysaccharide phase was alpha-lactalbumin.

Study of the conformational stability of 7S globulin from french beans (phaseolin) using high-sensitivity differential scanning microcalorimetry.

The change of the conformational stability and quaternary structure of the 7S globulin from french beans (phaseolin) has been investigated in the pH range 2.0-11.0 using the high-sensitivity differential scanning microcalorimetry technique. It has been established that each polypeptide chain of phaseolin consists of two thermodynamically unequivalent cooperative domains. The number and type of the side-chain hydrogen bonds which participate in the stabilization of the folded structure of each domain have been determined. The more stable domain contains six side-chain hydrogen bonds: four of the carboxylate-tyrosyl type and two of the carboxylate-histidyl type. The less stable domain contains four side-chain hydrogen bonds: two of the carboxylate-tyrosyl type and two of the carboxylate-histidyl type. All these side-chain hydrogen bonds appear to be localized within the hydrophobic interior of the domains. It has been found that the 3S form of phaseolin that is a product of the complete phaseolin dissociation at extreme pH values does not undergo any cooperative transition at heating. Consequently, this form probably has a conformation of 'molten globule' type.

Collagen and its rational content in meat products: Part 1. Analytical studies.

Computer-assisted simulation has been used to study the effect of collagen content on the biological value of meat proteins. It has been shown that an increase in the collagen content from 2·5% to 15-20% of the total amount of proteins contained in minced meat tangibly enhances protein utilization for tissue synthesis. Hence, the above collagen content in meat products heightens their nutritional and biological value and renders them more suited for human metabolism.

[Interpretation of thermograms of protein denaturation in non-equilibrium conditions]. / K voprosu ob interpretatsii termogramm denaturatsii belkov v neravnovesnykh usloviiakh.

Data are presented concerning the effect of heating rate on the denaturation parameters of small and oligomeric globular proteins: Kunitz trypsin inhibitor from soybeans and 1,5-Ribulose Bisphosphate Carboxylase from tobacco leaves. Substantional dependence of denaturation temperature on the heating rate reflects non-equilibrium pattern of denaturation of these proteins under experimental conditions. To interpret these data a kinetic approach is proposed, which permits determination of equilibrium value of the denaturation temperature and of the constant of de- and renaturation rate. The conformation transitions in the proteins studied are shown to be relatively slow processes. Their rate is comparable to the velocity of temperature change in a calorimeter, which is the cause of non-equilibrium effects in a calorimetric experiment.

[Thermodynamic and kinetic study of thermal denaturation of Kunitz soybean trypsin inhibitor by differential scanning microcalorimetry]. / Termodinamicheskoe i kineticheskoe issledovanie termicheskoi denaturatsii ingibitora tripsina Kunitsa iz bobov soi medodom differentsial'noi skaniruiushchei mikrokalorimetrii.

The thermal denaturation of soybean trypsin inhibitor (Kunitz inhibitor) has been studied in pH-region from 2.0 to 11.0 by differential scanning microcalorimetry. The thermodynamic characteristics have been determined. It has been established that the denaturation transition of protein may be described by a two-state model. It has been shown, that two side hydrogen bonds between carboxylate-ion and tyrosyl and carboxylate-ion and lysyl take part in the stabilization of the inhibitor's native structure. The activation of denaturation is accompanied by cleavage of one side hydrogen bond.

[Relation between ovalbumin hydration and the nature of cations, their concentration and temperature]. / Zavisimost' gidratatsii oval'bumina ot prirody kationov, ikh kontsentratsii i temperatury.

The influence of temperature, nature and concentration and alkali metal chlorides on the hydration degree of ovalbumin (W) was studied by the method of proton magnetic relaxation. It is shown that W of ovalbumin at low temperatures is conditioned by the sum of W by strong and weak water binding sites of the protein molecule. The standard binding enthalpy of water by weak sites is independent of the nature and concentration of the low-molecular weight salt and comprises about 40 KJ mol-1. The addition of such salts to the protein solution leads to changes of W conditioned by the changes of the strong site hydration. The liotropic effect of Li+ and Cs+ on the protein solution is complicated by their interactions with the peptide groups of protein.

Properties of oil/water emulsions stabilized by casein-acid polysaccharide mixtures.

Properties of oil/water emulsions stabilized with the soluble casein-acid polysaccharide mixtures were investigated. Compared to initial protein solutions, higher emulsifying properties of the mixtures are demonstrated. A study is made on the influence of the properties of the mixtures for obtaining thermostable emulsions of hard consistency which could be applied in production of a great variety of foodstuffs. The role of the formation of protein-acid polysaccharide complexes is discussed.

Thermodynamic compatibility of proteins in aqueous media. Part 3. Studies on the role of intermolecular interactions in the thermodynamics of compatibility of proteins according to the data of dilution enthalpies.

The flow microcalorimetric method was used to determine the enthalpies of diluting solutions of ovalbumin, bovine serum albumin, casein, soybean globulin fraction, thermotropic aggregates of ovalbumin, mixtures of ovalbumin-bovine serum albumin, casein-soybean globulin fraction, and ovalbumin-thermotropic aggregates of ovalbumin in water. The calorimetric data obtained were compared with the data on phase equilibrium in the systems Water-Ovalbumin-Bovine serum albumin, Water-Casein-Soybean globulin fraction, Water-Ovalbumin-Thermotropic aggregates of ovalbumin. Intermolecular interactions have been shown to play a significant role in the thermodynamics of protein compatibility.

A study on gelation of soybean globulin solutions. Part 4. Effect of gelation conditions on the visco-elastic properties and structure of thermotropic gels of soybean globulin fraction.

To the study of the structure and properties of the thermotropic soybean globulin fraction (SGF) gels the stress relaxation and electron microscopy techniques has been applied. The value of slope of normalized relaxation function was used as a characteristic of relaxation properties of SGF gels. This value characterizes the velocity of the gels relaxation processes. It has been found that this characteristic is determined only by the gels' heating temperatures. Using the differential scanning microcalorimetric technique it was shown that the changes of the slope of normalized relaxation function of SGF gels are controlled only by heating temperature. The reason for this lies in the changes of the composition of the denaturation product of SGF gels. The increase is shown of the shear moduli of gels prepared at other than optimum temperatures by additional heating under optimal gelation conditions. That is a result of existence of a sol-fraction. The most significant increase of shear moduli is found for the SGF gels, sol-fraction of which is native 11S globulin. A correlation has been established between the changes of SGF gels' structure obtained from the dates of rheological measurements and electron microscopy technique.

Thermodynamic compatibility of proteins in aqueous media. Part. I. Phase diagrams of some water--protein A--protein B systems.

The thermodynamic compatibility of proteins belonging to different classes according to Osborne has been investigated in aqueous media. Phase equilibrium for water--ovalbumin--soybean globulin fraction, water--ovalbumin--casein, water--casein--gliadin and water--casein--soybean globulin fraction systems has been investigated. The data obtained were analysed according to the theoretical concepts of Scott, Patterson and Prausnitz concerning the effect of polymer molar masses and the solvent quality on the phase equilibrium in similar systems. The analysis performed indicates that these concepts can be applied to the water--protein A--protein B systems. The phase equilibrium in water--protein A--protein B systems has some distinctive features as compared to that in systems containing two synthetic polymers in the single solvent. Firstly, proteins are usually compatible in a broader concentration range as compared to common polymers. Moreover, the separation of water--protein A--protein B systems into two phases often results in a considerable concentration of one of the protein components. Apparently, the latter fact can be associated with the marked difference in the interaction parameter of proteins belonging to different classes with the solvent, and, hence, with the marked difference in the hydrophilicity of the proteins investigated.

Thermodynamic compatibility of proteins in aqueous media. Part 2. The effect of some physicochemical factors on thermodynamic compatibility of casein and soybean globulin fraction.

A study has been made on the effect of temperature, sodium chloride, pH and cysteine on the thermodynamic compatibility of casein and soybean globulin fraction in aqueous medium. The section of miscibility gap characterizing the influence of the indicated factors on the compatibility of proteins has been determined. Assessment has been made of the influence of pH and cysteine on a) the effective molecular weights of casein and soybean globulin fraction and b) the difference in the intensity of interaction between each protein and a solvent. The experimental data obtained on the compatibility of proteins were found in good agreement with the theoretical concepts which establish the dependence of the compatibility of polymers on the ratio of their molecular weights, the intensity of interactions between polymers, as well as on the difference in the intensities of interaction between each of them and a solvent, i.e. on the difference of protein hydrophilicities.

Isolation of lactic whey proteins in the form of complexes with apple pectin.

The possibility of isolating lactic whey proteins (LWP) in the form of insoluble complexes (IC) with apple pectin was studied. The effect of pH, ionic strength (mu, NaCl), temperature (T degree C), pectin weight fraction (X3%) and the total concentration of macromolecular components in the system (Ws) on isolation has been considered. The process has been characterized by LWP yield in the composition IC--P, percentage and the extent of protein concentration in the concentrated phase (IC)--F. The mixing of lactic whey with a pectin solution usually yielded an IC (10% less than or equal to X3 less than or equal to 90%). The dependence of P on X3 is of an extreme nature with a maximum of 85% at X3 = 60%. The following conditions correspond to the maximum LWP yield (90%) in the complex composition: pH 3.4, mu = 0.01, T = 5-20 degrees C, X3 = 60%, Ws = 0.5%. At compositions of the system corresponding to the maximum P value (X3 = 60%) practically all the LWP fractions are present in the concentrated phase. If X3 much greater than 60% or X3 much less than 60% alpha-lactalbumin is practically absent in the concentrated phase. Usually, minimum F values (2.5-4.0) correspond to maximum protein yield at X3 = 60%. At X3 greater than 70% and X3 less than 50% F values may be considerably higher (20 times and more). A decrease in the pectin methylation degree from 56.7% down to 15.4% does not affect F. The maximum protein yield (94%) occurs when low methylated pectin is used. The character of the dependence of F on X3 is explained according to similar processes of complex gel formation and the processes of gel formation in polymer solutions.

Solubility of protein fibers obtained from casein solutions and liquid two-phase water-casein-sodium alginate systems.

The solubility of protein and protein-polysaccharide matrix fibers obtained from casein solutions and two-phase water-casein-sodium alginate (W-C-A) systems in water and in 1 M NaCl solutions at different pH at 20 and 100 degrees C has been studied. The matrix fibers obtained from the two-phase W-C-A system are shown to be considerably less soluble than those from the casein solutions. This difference is seen particularly clearly when pH amounts to 5-7. However, it disappears with the spinning two-phase system at temperature above 80 degrees C. An assumption has been made about the matrix fibers being either mixed gels of the thermo-reversible, soluble calcium caseinate and thermo-irreversible insoluble calcium alginate, or complex protein-polysaccharide gels formed with the participation of the calcium ions. This latter assumption is in conformity with the negligible solubility of the protein fibers obtained as a result of the lyotropic gelation of the skimmed milk proteins.

[Rheological properties of a calcium alginate-potato starch hydrolysate-water system]. / Rheologische Eigenschaften des Systems Calciumalginat-Kartoffelstärke-hydrolysat-Wasser.

The rheological properties of liquid solutions and gels of sodium alginate, calcium gluconate and gelling maltodextrin were investigated and compared with the behaviour of pastes and gels of non-degraded potato starch. The dependence of the rheological properties upon the calcium gluconate concentration is extreme. A marked increase in the viscosity of the liquid solutions and maximal values for the hardness and the breaking strength of the gels are obtained at a calcium gluconate/sodium alginate ratio of 0.3. As to breaking strength, elasticity and hardness, the maltodextrin-based gels are many times inferior to the potato starch-based gels. The breaking strength, hardness and elasticity of maltodextrin gels are increased by the addition of sodium alginate and calcium gluconate, which increases their effectiveness when used in foods.

[Artificial food. I. Development of a new course in food production-reasons and advantages]. / Künstliche Lebensmittel. 1. Mitt. Entwicklung einer neuen Richtung der Lebensmittelproduktion--Gründe und Vorteile.

The causes for the development of a new course in the food production are discussed. The characteristic features and the specific contradictions are dealt with that are connected with the traditional production methods of food. The character of the new methods of food production as well as their economic and technological advantages are considered.