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  • Author or Editor: D. Lőrinczy x
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Abstract  

Handbook of Thermal Analysis and Calorimetry, Volume :Applications to Inorganicand Miscellaneous Material, (Series Editor: Patrick K. Gallagher, Volume Editors: Michael E.Brownand Patrick K Gallagher)

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Abstract  

Force generation in muscle during contraction arises from direct interaction of the two main protein components of the muscle, myosin and actin. The process is driven by the energy liberated from the hydrolysis of ATP. In the presence of CaATP the energy released from hydrolysis produces conformational changes in myosin and actin, which can be manifested as an internal motion of myosin head while bound to actin. It is suggested that myosin heads attached to actin produce conformational changes during the hydrolysis process of ATP, which results in a strain in the head portion of myosin in an ATP-dependent manner. These structural changes lead to a large rotation of myosin neck region relieving the strain. Paramagnetic probes and EPR spectroscopy provide direct method in which the rotation and orientation of specifically labelled proteins can be followed during muscle activity. In order to find correlation between local and global structural changes in the intermediate states of the ATPase cycle, the spectroscopic measurements were combined with DSC measurements that report domain stability and interactions. In the review a detailed description of the application of EPR and DSC techniques in muscle protein research will be given. The measurements show that the small local structural changes detected by EPR after nucleotide binding influence the global structure of protein system responsible for muscle contraction.

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The quality of sour cream production from homogenised cream in the 1970's was highly improved. The heat resistance of product remained badly, that is, it precipitated in hot food. The Hungarian Dairy Research Institute (HDRI) has elaborated a technology that eliminates this disadvantageous characteristic: it is the use of exopolysaccharide (EPS)-producing lactic acid bacteria. This bacterium produces no aroma, and the proliferation optima of EPS-producing and aroma-producing lactic acid bacteria cultures do not coincide. Detection of these two bacteria was done until now by gene technology, that is expensive and long lasting one. We have applied (at first as we know) isotherm calorimetric method to follow the simultaneous proliferation of these bacteria and it was determined that: both lactic acid bacteria cultures proliferate well at the non-optimal temperature of 30°C and the thermophilic EPS-producing culture was faster than that of the mesophilic aroma-producer. The two cultures do not inhibit each other in mixed culture, and the ratio in mixed culture was 79% EPS-producer and 21% aroma-producer.

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Conventional and saturation transfer electron paramagnetic resonance spectroscopy (EPR and ST EPR) and differential scanning calorimetry (DSC) were used to study the motional dynamics and segmental flexibility of cardiac myosins.

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Summary  

While the basic fermented (sour) milk products, such as yogurt and kefir can be produced only in live flora version, the post heat-treatment is preferred in their flavored variations to increase the storage time. Casein being in sour coagulum precipitates during heat-treatment; therefore protective colloids surrounding the protein should be used to prevent it. Protective colloids are plant extracts, the most known of them are pectin and amylopectin. Basic requirement of protective colloid effect is the lower swelling temperature of hydrocolloid than the temperature of precipitation of sour coagulum. In this work we have examined the precipitation of sour coagulum as a function of the type of lactic acid bacteria cultures applied during fermentation as well as the swelling of heat protective plant hydrocolloids as a function of the composition (mainly of sugar content) of medium. To investigate the precipitation of fermented coagulum skimmed milk was fermented with mesophilic butter culture, thermophilic yogurt culture as well as with exopolysaccharide (EPS)-producing Prebiolact-2 culture. Precipitation was indicated in the increase of great extent of viscosity. Amylopectin was dispersed into aqueous solution of pH 4.5, the saccharose concentration of which was changed during the investigation of the swelling of heat protective hydrocolloids. A definite exothermic peak was assigned to the swelling of hydrocolloids during the DSC experiments. We could conclude that the precipitation temperature was increasing in the mesophilic-thermophilic-EPS producing microbes line, i.e. the heat stability and swelling temperature of hydrocolloids depend on the saccharose content of aqueous medium and they increase with rising the concentration of saccharose.

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Abstract  

The development of functional foods of probiotic effect based on the slime-producing strains isolated in the 1980s, and that of enriched with Ca on the utilization of the high Ca-containing whey of the quarg production in the Carpathian basin using fermentation. The probiotic properties of the slime-producing microbe strains isolated have been proved by in vitro and in vivo examinations. We have used an isotherm DSC method to identify the probiotic microbes. The percentile ratio of probiotic and other microbes was determined in the product by this technique. By utilization of quarg whey a special additive food for Ca-enrichment has been developed which is suitable to complete or enrich different foods (dairy, meat and bakery products). The products developed are: probiotic kefir (Synbiofir), probiotic sour cream, probiotic butter cream, poultry meat products completed with Ca, bakery products completed with Ca.

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Abstract  

In contrast with the traditional method of cheese processing, where Ca breaks down from the protein chain and protein is peptized, a new technology has been elaborated, during which cheese is dispersed without phosphate-containing processing salt, when the gel is formed by plant hydrocolloids. Raw material of constant composition was processed with a phosphate-containing salt or in the presence of hydrocolloids. Thermodynamic processes occurring during the processing and in the end-products were examined by an ultra-sensitive micro DSC method. The structures of end-products were also investigated by electronmicroscopy. The temperature ranges of the endothermal processes indicating the transformations of protein and hydrocolloids can be distinguished: 81-90C for peptization processing and 61-72C for processing without peptization. The differences are less in the end-products: 75-87C in traditional processed cheese and 68-74C in processed cheeses made without peptization. In contrast with the spongy structure of traditional processed cheeses consisting of peptized proteins, processed cheeses made without peptization involve structure-forming elements created by the interaction of linear macromolecules of hydrocolloids and cheese proteins.

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Abstract  

The effect of AMP.PNP on the thermal stability and dynamics of myosin head were investigated by using DSC and different spin label technique for chemically skinned muscle fibres prepared from rabbit. The thermal unfolding of the fibres in rigor, strong as well as weak-binding state showed a complex process characterizing at least three discrete domain regions with different stability (T m =54, 58.4 and 62.3°C). The unfolding at 54°C refers to the catalytic domain of myosin, whereas transition at T m =58.4°C represents the rod-like region. In the presence of AMP.PNP only the parameters of the last transition changed significantly (T m =70.4°C) showing an increased interaction between actin and myosin heads being attached to actin. Measurements on MSL-fibres (labelled at Cys-707 of myosin) in the presence of AMP.PNP showed that about half of the cross-bridges dissociated from actin. This fraction had a dynamic disorder, the other population had the same spectral feature as in rigor. In contrast, on TCSL-fibres AMP.PNP increased the orientational disorder of myosin heads, a random population of spin labels was superimposed on the ADP-like spectrum showing conformational and motional changes in the internal structure of myosin heads. ST EPR measurements reported increased rotational mobility of spin labels in the presence of AMP.PNP. The DSC and EPR results suggest that in the presence of AMP.PNP the attached heads have the same global orientation as in rigor, but the internal structure undergoes a local conformational change.

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Abstract  

The osteoporosis is regarded as a widespread disease all over the world. In the prevention therapy of this disease there is a primary role of the daily calcium intake with the proper Ca:P ratio (1:1–1:2). The primary source of Ca for people the dairy products are implied, from which only the processed cheeses have inadequate ratio of Ca:P. In cheeses processed without peptization developed in the Hungarian Dairy Research Institute (HDRI) the Ca:P ratio meets the requirements (1.5:1), moreover these products can be enriched with Ca. In this study we used both processing technologies. The electronmicroscopic photographs demonstrate the differences clearly. The traditionally processed cheese (with peptization) has a 'spongy’ structure well known from literature, while a space-net can be seen resulting from the casein-filamentous hydrocolloid interaction in the structure of heat-treated cheese without peptization. DSC curves are the same in the temperature range 0–40C, showing endotherm melting process in two well-distinguished temperature interval (0–20 and 22–40C). They are different in the temperature interval 40–100C: in the case of processed cheese with peptization the gel-sol transformation gives a higher endotherm peak in a narrow temperature range, while for heat-treated cheese without peptization this temperature range is wider with a lower endotherm peak. Both electronmicroscopic and DSC investigations have proved that contrary to the traditionally processed cheese where the structure is formed by the linked peptized protein, in the heat- processed cheese without peptization the frame-forming element is the huge hydrocolloid molecule interacted with the protein. The enthalpy change is substantially lower at the disintegration of the latter structure.

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