Examination of growth of probiotic microbes by an isoperibolic calorimetry

Due to the increasing consumers’ interest in up-to-date nutrition nowadays the production of main part of fermented dairy products (e.g. yogurt, kefir) is made by using probiotic microbes. The majority of this product group are the flavoured variations, the sweetener of which is, first of all, still refined sugar (e.g. saccharose). Honey of natural origin, consequently preferred from the nutritional physiological point of view, is suitable to replace this refined carbohydrate. In our experiments we have sweetened the most frequently used milk containing of 1.6 and 3.6% fat with generally used saccharose of 10%, and the difference in the dry material content was equilibrated by drink water of 3% (control product). The experimental product was sweetened with robinia honey of 13% (dry material content was 77%). The fermentation was performed with a probiotic culture of 5%, which was clinically tested to be probiotic. The fermentation process was conducted in isotherm regime at 36 °C during 18 h in batch wessels using SETARAM Micro DSC II calorimeter. The calorimetric enthalpy was proportional to the probiotic microbe counts generated during the fermentation. Due to our experiments, we have come to the conclusion that honey instead of hindering much rather stimulates the growth of probiotic microbes. At sample pairs sweetened by saccharose and acacia honey, respectively, the higher enthalpy was measured at samples containing honey in all cases.     

Detection of probiotic microbes in probiotic cheese spreads by isothermic calorimetry

Summary The probiotic cheese spreads developed by the Hungarian Dairy Research Institute (HDRI) have a better Ca:P ratio than traditional brands and spread easily and without sticking even cold, further, their live lactic acid bacteria content gives them additional advantages as well. These advantages derive from the fact that a probiotic culture may also be employed during fermentation, through which the cheese spread may become probiotic if the culture proliferates. The international specification is a probiotic cell count of at least 10⁶/g. However, during fermentation the probiotic cheese spread must also use other non-probiotic cultures to produce the right taste. Given that the microorganisms in the cultures are all cocci, their indication in a mixed environment is difficult and time-consuming. It appears possible, therefore we have used the isothermic DSC method due to their differences in heat production. In order to analyze the calorimetric curves a deconvolutional program was devised which decomposed them into Gaussian curves. It was confirmed that probiotic bacteria proliferated in the probiotic cheese spreads, and their ratio was greater than 40% with a total plate count of 2-7·10⁸/g. Accordingly, the probiotic cheese spread developed by HDRI contains an order of magnitude more probiotic bacteria than the internationally accepted cell count of 10⁶/g.     

Examination of a coffee product enriched with calcium by the isoperibolic method

The main reason of osteoporosis, one of the most frequently occurring civilization disease nowadays, is the calcium-defficient and phosphorus-surplus nutrition, respectively. One of the possible preventions is to complete the foods with predominance of phosphorus with Ca at least till Ca:P ratio of 1:1. To complete foods with Ca today primarilly organic Casalts (e.g. Ca-malate, -lactate, -citrate) are used, their absoption has clinically been approved. These Ca-enrichers are food additives and have E-numbers. The raw material of a Ca-enricher has been developed by us is the Ca-rich whey of fermented fresh cheese being indigenous in the Carpathian basin, and which is further enriched in Ca (first of all in Ca-malate) during the technology. This product being under EU-patentization, contains the main adjuvants (milk protein, lactose, oligosaccharide, micro elements) promoting the Ca-absorption and incorporation in bones. It is an additive-food, its bioavailability has clinically been proved. Its further advantage is that owing to its colloidchemical stucture it can be instantized. In our experiments separately 20–20 mg from calcium-malate (CaM), fresh cheese whey powder enriched in Ca (QC), its instant version (QC_i), instant coffee (DE), mixture of 50–50% instant coffee and instant fresh cheese whey powder enriched in Ca (DEQCi) were measured into the bottom of a mixing batch vessel and 180 mg distilled water into the upper part of it (in the reference one 20 + 180 mg distilled water). Attaining the heat balance the two parts of the cell have been mixed and the isotherm solution curves have been plotted at 20oC. Our main results are: (i) There is no significant difference between the heat amounts liberated in CaM, QC and QCi plus water solutions. The average value of enthalpies is −28 J/g. (ii) There are one maximum peak at CaM and two peaks at QC during solution. The CaM, and the first maximum peaks of QC are in the range of 700–800 s after mixing, and the second peak is within 2000–4000 s. The total solution at both samples is over 6000 s. (iii) At instant sample (QC_i) there is one maximum at 100 s and the solution is completed at about 700 s. (iv) The slope of DE and DEQCi curves are the same.     

Application of isothermal and isoperibolic calorimetry to assess the effect of zinc on cement hydration

The amount of zinc in the clinker or in the secondary raw materials has been increasing in recent years. Zinc can get to Portland cement from solid waste or tires which are widely used as a fuel for burning in a rotary kiln. The aim of this work was to determine the effect of zinc on Portland cement hydration. This effect was studied by isothermal and isoperibolic calorimetry. Both calorimetry methods are suitable for measurements during the first days of hydration. Isoperibolic calorimetry monitors hydration process in real-life conditions, while isothermal calorimetry does it at a defined chosen temperature. Zinc was added to the cement in the form of two soluble salts of Zn(NO₃)₂, ZnCl₂ and a poorly soluble compound ZnO. The concentration of zinc added was chosen as 0.05, 0.1, 0.5 and 1 mass%. The results show that increasing amounts of zinc ions in cement pastes lead to hydration retardation and reduce both the maximum temperature and the maximum heat flow due to the retarding effect of zinc. The newly formed compounds during hydration were identified by X-ray diffraction method.     

Analysis by calorimetry

The last years have seen the development of differential calorimetry into a scanning technique for routine analysis. In order of ease of determination heats of fusion, heats of reaction, phase diagrams, purity analysis, heat capacity and similar heat effects are added to the list of quickly measurable quantities. Accuracies of the order of 1–5% of heats of fusion and heat capacity are obtainable under favorable conditions. Special topics which have been discussed are instrumentation, transition temperatures, heat capacities, glass transitions, heats of transitions, and phase diagrams.     

Comparison of thermokinetic data obtained by isothermal, isoperibolic, adiabatic and temperature programmed measurements

In this paper isothermal, isoperibolic and adiabatic calorimeters and a Power-Compensating DSC are compared by determining kinetic data of a simple test reaction. First, the kinetic parameters were analyzed using a conventional isothermal method, based on the analytic determination of the course of reaction. Subsequently, the kinetic data of the performed reaction were determined for the different types of calorimeters by simultaneously evaluating several measurements with identical initial conditions but different temperature courses. The kinetic parameters obtained by the different calorimeters agree reasonable well, indicating the reliability of kinetic data derived from thermokinetic methods.The authors are thankful for the financial support by the Department of Education and Research of the Federal Republic of Germany (BMBF).     

Hydration of thermally denatured lysozyme studied by sorption calorimetry and differential scanning calorimetry

We have studied hydration (and dehydration) of thermally denatured hen egg lysozyme using sorption calorimetry. Two different procedures of thermal denaturation of lysozyme were used. In the first procedure the protein was denatured in an aqueous solution at 90 degrees C, in the other procedure a sample that contained 20% of water was denatured at 150 degrees C. The protein denatured at 90 degrees C showed very similar sorption behavior to that of the native protein. The lysozyme samples denatured at 150 degrees C were studied at several temperatures in the range of 25-60 degrees C. In the beginning of sorption, the sorption isotherms of native and denatured lysozyme are almost identical. At higher water contents, however, the denatured lysozyme can absorb a greater amount of water than the native protein due to the larger number of available sorption sites. Desorption experiments did not reveal a pronounced hysteresis in the sorption isotherm of denatured lysozyme (such hysteresis is typical for native lysozyme). Despite the unfolded structure, the denatured lysozyme binds less water than does the native lysozyme in the desorption experiments at water contents up to 34 wt %. Glass transitions in the denatured lysozyme were observed using both differential scanning calorimetry and sorption calorimetry. Partial molar enthalpy of mixing of water in the glassy state is strongly exothermic, which gives rise to a positive temperature dependence of the water activity. The changes of the free energy of the protein induced by the hydration stabilize the denatured form of lysozyme with respect to the native form.     

Polymerization rates by calorimetry. II

By means of isothermal kinetic calorimetry, an automatic instantaneous record of polymerization rate can be obtained, independent of conversion. A large improvement in resolving kinetic events is thereby realized. Certain abrupt changes in rate due to electrolyte level have been observed.     

Purity determination by differential scanning calorimetry

A review of the literature on the DSC method for purity determination is presented, with a discussion of the most important aspects, i.e. theory, sample handling, calibration of the instrument, evaluation of melting curves, and the conditions and accuracy of the measurement of eutectic impurities.     

Investigation of run-away reactions by precision calorimetry

Investigations in chemical safety are necessary in case that the reaction course depends on changes of the reaction conditions sensitively. To break off a conversion in a hazardous situation, the precision calorimeter ACTRON 5 is equipped with two safety pumps. They empty and rinse the reactor with cold solvent. The pumps will be activated automatically. For testing the calorimeter the complex reaction of chloronitrobenzene with alkalined alcohol was used and break off at predefined conditions. The possibility of the kinetic estimation of these break-off files is shown.     

Isoperibol calorimetry as a tool to evaluate the impact of the ratio of exopolysaccharide-producing microbes on the properties of sour cream

Summary 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.     

Monitoring soybean seed germination by calorimetry

A method to monitor seed germination that combines isothermal calorimetry and imbibition measurements is reported. Individual seeds of three cultivars of soybean seeds (A7636RG, Munasqa and DM5.8RR) and one of radish were used. Imbibition curves were performed on individual seeds in a germination chamber at 25 °C. Calorimetric specific thermal power (p)–time (t) curves of germination were also obtained at 25 °C for 10 or more individual seeds after 30 min of equilibration of the system. Calorimetric experiments of germination in 5 mM KCN were performed to estimate specific imbibitions enthalpies (Δ_i h). The p–t curves could be extrapolated to t = 0 by relating the rate of water uptake as determined from imbibitions curves with p values. Then, p–t curves were integrated to determine the specific metabolic enthalpies Δh which in turn were related to the water content (WC) of seeds at the corresponding times. The method allows determination of specific enthalpy change due to germination, Δ_g h, which apparently is species related. Besides, the standard deviation (SD) of the Δ_g h value gives an indication of seed quality. On the other hand, the water content that seeds need to germinate and the moment at which seeds are fully imbibed can also be determined. This is very important when breeding new cultivars for water stress tolerance. The water content needed for each cultivar to germinate was 74, 57, 35 and 64% for soybean seeds cvs. A7636RG, Munasqa, DM5.8RR and radish, respectively.     

Rates of crystallization of polyethylene fractions by calorimetry

Rates of crystallization of polyethylene fractions have been studied at high undercoolings by differential calorimetry to demonstrate the utility of this technique for fast crystallization analysis. It has been shown that there is continuity in the crystallization kinetics from low to high undercoolings. On the other hand, the influence of molecular weight on the crystallization rates, as the undercooling increases, is very moderate, as would be expected.     

Binding isotherm determination by isothermal titration calorimetry

Journal of Thermal Analysis and Calorimetry - A simple method for determination of binding isotherm in the protein-ligand interaction was introduced using isothermal titration calorimetric data....     

Thermal polymerization of acrylamide by differential scanning calorimetry

Thermal polymerization of acrylamide was studied by differential scanning calorimetry. Latent heat of fusion ΔH_f and enthalpy of polymerization ΔH_p values were found to be 36 and ?18.0 kcal mol^?1, respectively. The overall activation energy E for the polymerization was calculated to be 19 k cal mol^?1 up to 60% conversion. The added free-radical inhibitor (benzoquinone) was found to desensitize the thermal polymerization of acrylamide suggesting the polymerization to be a free-radical type. The existing rate equation for the heterogeneous bulk polymerization in the presence of initiators has been modified for the thermally initiated bulk polymerization of acrylamide. The experimental overall E value was found to agree well with the calculated E value when considering only the propagation and termination steps, thereby suggesting the process to be similar to postpolymerization of acrylamide.     

Morphology characterization of emulsions by differential scanning calorimetry

This article is a review of some results obtained by Differential Scanning Calorimetry (DSC) for characterizing the morphology of emulsions. In a classical DSC experiment, an emulsion sample is submitted to a regular cooling and heating cycle between temperatures that include freezing and melting of the dispersed droplets. By using the thermograms found in the literature for various emulsions, how to get information about the solidification and melting, the presence of solute, the emulsion type, the transfer of matter, the stability and the droplet size is shown.     

Melting of indium by temperature-modulated differential scanning calorimetry

The melting and crystallization of a sharply melting standard has been explored for the calibration of temperature-modulated differential scanning calorimetry, TMDSC. Modulated temperature and heat flow have been followed during melting and crystallization of indium. It is observed that indium does not supercool as long as crystal nuclei remain in the sample when analyzing quasi-isothermally with a small modulation amplitude. For standard differential scanning calorimetry, DSC, the melting and crystallization temperatures of indium are sufficiently different not to permit its use for calibration on cooling, unless special analysis modes are applied. For TMDSC with an underlying heating rate of 0.2 K min^–1 and a modulation amplitude of 0.5–1.5 K at periods of 30–90 s, the extrapolated onsets of melting and freezing were within 0.1 K of the known melting temperature of indium. Further work is needed to separate the effects originating from loss of steady state between sample and sensor on the one hand and from supercooling on the other.On leave from Toray Research Center, Inc., Otsu, Shiga 520, Japan.This work was supported by the Division of Materials Research, National Science Foundation, Polymers Program, Grant # DMR 90-00520 and the Division of Materials Sciences, Office of Basic Energy Sciences, U.S. Department of Energy at Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp. for the U.S. Department of Energy, under contract number DEACOS-960R22464. Support for instrumentation came from TA Instruments, Inc. and Mettler-Toledo Inc. Research support was also given by ICI Paints.     

微生物降解塑料的研究进展

聚羟基脂肪酸酯(PHAs)是许多原核微生物在不平衡生长条件下合成的细胞内能量和碳源储藏性物质,作为完全可生物降解的热塑性聚酯而倍受关注。它除了具有与化学合成高分子相似的性质外,还具有比重大、光学活性好、透氧性低、抗紫外线辐射、生物可降解性、生物组织相溶性、压电性和抗凝血性等特点,因而在电子、光学、农业、生物医学、食品包装等领域具有广阔的应用前景。本文主要综述了近几年来国内外对PHAs微生物合成的研究进展,同时对PHAs的应用前景进行了展望。     

Starch-lipid interactions studied by differential scanning calorimetry

The amylose-lipid complex shows an endothermic transition around 100 °C in excess water. Complexes were prepared by adding lipids to an amylose-solution, and the precipitated complex was studied in the DSC during a heating and cooling sequence. The thermal stability of the complex depends on the lipid part, and the reversibility during cooling depends on presence of excess lipids.The influence of lipids on the gelatinization of starch was studied by adding lipids to wheat and potato starch, respectively, before the DSC-analysis. Depending on the lipid, an earlier as well as a delayed gelatinisation could be obtained.