Biomedical subjects
M Karel
Publications and source records attributed to M Karel.
Ultrasound appearance of the hip joint in newborns during the first week of life.
The frequency of different types of hip joints in newborns was determined on the basis of ultrasound screening examinations performed during the first week of life. A higher percentage (14.1%) of abnormal hip joints were seen in comparison with the groups examined in later weeks of life suggesting the possibility of natural improvement in a number of cases. The more frequent appearance of pathology in girls was confirmed. Further investigations on the natural history of hip joint development in the newborn and on the general principles of screening examinations are needed.
Effects of water on diffusion in food systems.
A number of operations in food processing, and the stability of stored foods, are affected by diffusional properties of food systems, which include the foods themselves, their immediate environment within a package, and any barriers (packaging or coating) used with the foods. Water content and "water activity" affect these diffusional properties dramatically, by plasticizing food and/or packaging polymers and affecting glass transition temperatures of components, and in some cases, water may serve as an internal transport medium. The present paper reviews the current state of knowledge of effects of water on diffusion in food systems, and in particular, changes in diffusivity above glass transition temperatures. The complexity of resultant effects on food stability in dry and frozen foods is discussed. Examples of potential effects of glass transitions on stability of frozen foods are provided by computer simulation of shelf life using specified assumptions.
Cryomicroscopic analysis of intracellular ice formation during freezing of mouse oocytes without cryoadditives.
Kinetics of intracellular ice formation (IIF) under various freezing conditions was investigated for mouse oocytes at metaphase II obtained from B6D2F1 mice. A new cryostage with improved optical performance and "isothermal" temperature field was used for nucleation experiments. The maximum thermal gradient across the window was less than 0.1 degrees C/10 mm at sample temperatures near 0 degrees C. The dependence of IIF on the initial concentration of the suspending medium was found to be pronounced. The mean IIF temperatures were found to be -9.56, -12.49, -17.63, -22.20 degrees C for freezing at 120 degrees C/min in 200, 285, 510, and 735 mosm phosphate-buffered saline, respectively. For concentrations higher than 735 mosm, the kinetics of IIF showed a break point at approximately -31 degrees C. Below -31 degrees C, all the remaining unfrozen oocytes underwent IIF almost immediately over a temperature range of less than 3 degrees C. This dramatic shift in the kinetics of IIF suggests that there were two distinct mechanisms responsible for IIF during freezing. The effect of the cooling rate on the kinetics of IIF was also investigated in isotonic PBS. At 1 degrees C/min none of the oocytes contained ice, whereas, at 5 degrees C/min all the oocytes contained ice. The mean IIF temperatures for cooling rates between 1 and 120 degrees C/min were almost constant with an average of -12.82 +/- 0.6 degrees C (SEM). In addition, constant temperature experiments were conducted in isotonic PBS. The percentages of oocytes with IIF were 0, 50, 60, and 95% for -3.8, -6.4, -7.72, and -8.85 degrees C. In undercooling experiments, IIF was not observed until approximately -20 degrees C (at which temperature the whole suspension was frozen spontaneously), suggesting the involvement of the external ice in the initiation of IIF between approximately -5 and -31 degrees C during freezing of oocytes.
A colorimetric method for the enzymatic analysis of gases: the determination of ethanol and formaldehyde vapors using solid alcohol oxidase.
A novel enzymatic approach to the direct determination of ethanol vapors in the gas phase is described. The system is composed of alcohol oxidase, peroxidase, and the color indicator 2,6-dichloroindophenol dispersed on microcrystalline cellulose (avicel). Simple devices are developed for the semiquantitative determination of ethanol in the breath. The devices are optimized to produce a sharp color change at a set time of 1 min for ethanol concentrations above the legal limit for driving (kinetic method) or a stable final color after 5 min (equilibrium method). Such color changes are detectable by simple visual observation. Using TLC plastic sheets and a transmittance densitometer, the system can also be used as a quantitative method for the determination of ethanol or formaldehyde vapors. Dehydrated enzymes may be useful for the analysis of hazardous gases.
Enzyme-catalyzed, gas-phase reactions.
Dehydrated preparations of alcohol oxidase adsorbed on DEAE-cellulose vigorously catalyze a gas-phase oxidation of ethanol vapors with molecular oxygen. The gas-phase reaction is strongly dependent on the water activity of the system. The enzymatic activity is severely inhibited by the product hydrogen peroxide. This inhibition can be alleviated, however, by an addition of catalase or peroxidase to the dry preparation. Such dehydrated, bienzymic catalysts afford a complete and selective conversion of the substrate to acetaldehyde. Dry alcohol oxidase is much more thermostable than in aqueous solution. The results of this work suggest that dehydrated enzymes have potential applications in the analysis of gaseous compounds and in the development of novel gas-solid bioreactors.
Optimization methods and available software. Part 1.
Optimization theories and generally applied optimization techniques are reviewed. The versatility and the complexity anticipated in actual problems are simplified to enable the food practitioners interested in the subject to overcome some of the barriers which prevented full utilization of optimization. The paper summarizes the various mathematical methods available for solving problems of product and process optimization and provides information and advice concerning the advantages and limitations of each technique. A compiled list of optimization subroutines, guidelines and criteria for choosing the proper software are furnished.
Effects of ionizing radiation on nitric oxide myoglobin. Part 1. Effects on the NO-haem moiety.
Bovine nitric oxide myoglobin (NOMb) was irradiated with 40-4000 krad of gamma-radiation, and the effects on the haem studied using absorption spectroscopy and electron spin resonance (e.s.r.) spectroscopy. The results show the following behaviour. The bright red colour of NOMb changes to brown upon irradiation. This is similar to changes observed in radiation sterilized. nitrite-containing meats. NOMb becomes progressively denitrosylated, with met-myoglobin (metMb) as the immediate product. Upon increasing doses of radiation (up to 800 krad) at 0 degrees C parallel to NOMb denitrosylation, metMb is gradually converted, by water radiolytic products, to other products, believed to be ferromyoglobin and ferrimyoglobin peroxide. A minor quantity of 'choleglobin-type' pigments may also be formed at the highest doses. Freezing of NOMb has a substantial protective effect against radiation. Native bovine NOMb behaves as a pentaco-ordinate (hfs of 3 peaks with equal intensity); the bond between iron and N epsilon is thus dramatically stretched and weakened. Using a thermal energy analyser, no NO could be detected over irradiated NOMb solution, indicating rapid reaction of NO liberated from NOMb by radiation, with radiolytic products of water.
Effects of ionizing radiation on nitric oxide myoglobin. Part 2. Effects on the globin moiety.
Irradiation of nitric oxide myoglobin (NOMb) induces changes in the haem as well as protein moiety of NOMb, especially at doses of 400-800 krad. The changes in the protein include: Conformational changes, with apparent partial denaturation of globin alpha-helix as evidenced by circular dichroism. Preferential scission of the polypeptide chain and dimerization via covalent bond(s) as evidenced by SDS-polyacrylamide gel electrophoresis. Products with a spectrum of hydrodynamic volumes between those of the monomer and the dimer are also formed. The shift of NOMb pIs toward more acidic pHs (probably due to modification and/or destruction of basic amino acid residues by water radiolytic products) as evidenced by isoelectric focusing.
Reactions between peroxidizing lipids and histidyl residue analogues: enhancement of lipid oxidation and browning by 4-methylimidazole.
As a part of our study on the interactions between peroxidizing lipids and the histidyl imidazole side-chain in simple, low-moisture model systems, 4-methylimidazole (4MI) was reacted with methyl linoleate (ML). This analogue was chosen to avoid interference from other functional groups in histidine (free base) or in proteins. Changes in the concentrations of lipid hydroperoxides, carbonyls, 4MI, and brown pigments were followed over a period of 24 days. The results indicate that 4MI exhibits significant prooxidative activity by reducing the induction period as well as by enhancing the formation of brown pigments. These effects are more pronounced at high 4MI/MI molar ratios and under basic pH's. Upon interactions with peroxidizing ML, as much as 44% of initially present 4MI was destroyed by the sixth day of incubation.
Free radical reactions of peroxidizing lipids with amino acids and proteins: an ESR study.
Free radical transfer from oxidizing methyl linoleate to amino acids and proteins was studied in dry model systems incubated for periods up to 20 days. Electron spin resonance was used to study free radical production. Free radicals were detectable in the amino acids lysine, arginine, histidine, tryptophan, and cysteine. Reduced glutathione and, to a limited extent, cystine also gave free radical signals. Free radicals produced in proteins primarily showed central singlet lines, attributable to carbon-centered radicals, with g= 2.004+/- 0.001. Sulfhydryl proteins also exhibited downfield shoulders at g approximately equal to 2.015 and 2.023 that were essentially identical to peaks observed in cysteine and reduced gluathione. The field positions of sulfur resonace in cysteine and proteins suggested a sulfur-oxygen complex rather than thiyl radicals.
Membrane separation processes and freeze concentration in the 1980s.
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Volatile retention during freeze drying of protein solutions.
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Volatile transport in frozen aqueous solutions. I. Development of a mechanism.
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Volatile transport in frozen aqueous solutions. II. Influence of system parameters.
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An improved method for the preparation of isomeric , -diaminopimelic acid from glutaraldehyde.
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Characterisation of macroglobulins IgM aggregates.
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Metal-catalyzed oxidation in the presence of water in foods.
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