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Biomedical subjects

M Karel

Publications and source records attributed to M Karel.

At least 19 recordsLinked to original sources
PubMed2000

Photic entrainment of circadian activity patterns in the tropical labrid fish Halichoeres chrysus.

Yellow wrasses (Halichoeres chrysus) show clear daily activity patterns. The fish hide in the substrate at (subjective) night, during the distinct rest phase. Initial entrainment in a 12h:12h light-dark (12:12 LD) cycle (mean period 24.02h, SD 0.27h, n = 16) was followed by a free run (mean period 24.42h, SD 1.33h) after transition into constant dim light conditions. Light pulses of a comparable intensity as used in the light part of the LD cycles did not result in significant phase shifts of the free-running rhythm in constant darkness. Application of much brighter 3h light pulses resulted in a phase-response curve (PRC) for a fish species, with pronounced phase advances during late subjective night. The PRCs differed from those mainly obtained in other vertebrate taxa by the absence of significant phase delays in the early subjective night. At that circadian phase, significant tonic effects of the light pulses caused a shortening of the circadian period length. Entrainment to skeleton photoperiods of 1:11 LD was observed in five of six wrasses exposed, also after a 3h phase advance of this LD cycle. Subsequently, a 1:11.25 LD cycle resulted in entrainment in four of the six fish. It is suggested that the expression of the circadian system in fish can be interpreted as a functional response to a weak natural zeitgeber, as present in the marine environment. This response allows photic entrainment as described here in the yellow wrasse.

Animals↗
PubMed1997

Preservation of biological materials under desiccation.

A number of life forms, including seeds, certain nematodes, bacterial and fungal spores, and cysts of certain crustaceans, show an ability to survive desiccation. The present article reviews the literature available on this subject and critically evaluates the evidence for various mechanisms that may be responsible for these phenomena. Specific mechanisms considered include vitrification (glass formation) by sugars and other polyhydroxy compounds that are accumulated by the desiccated structures, specific effects of polyhydroxy compounds on membranes, effect of "compatible solutes" on conformation of key proteins, as well as other biochemical mechanisms. The article presents potential applications relevant to food technology and to biotechnology and reviews the research required to materialize more effective use of desiccation in food and biopreservation.

Animals↗
PubMed1995

An empirical test of telephone screening to identify potential dementia cases.

Thirty-seven subjects, 15 with a clinical diagnosis of Alzheimer's disease and 22 normal controls, participated in a study of the accuracy of telephone screening in identifying potential dementia cases. The telephone protocol and scoring algorithm resulted in 100% sensitivity and 91% specificity. The findings suggest that a brief telephone interview can serve as an efficient screening device to locate dementia cases in the context of a large-scale community-based investigation.

Aged↗
PubMed1993

Cellular response of mouse oocytes to freezing stress: prediction of intracellular ice formation.

Successful protocols for cryopreservation of living cells can be designed if the physicochemical conditions to preclude intracellular ice formation (IIF) can be defined. Unfortunately, all attempts to predict the probability of IIF have met with very limited success. In this study, an analytical model is developed to predict ice formation inside mouse oocytes subjected to a freezing stress. According to the model, IIF is catalyzed heterogeneously by the plasma membrane (i.e., surface catalyzed nucleation, SCN). A local site on the plasma membrane is assumed to become an ice nucleator in the presence of the extracellular ice via its effects on the membrane. This interaction is characterized by the contact angle between the plasma membrane and the ice cluster. In addition, IIF is assumed to be catalyzed at temperatures below -30 degrees C by intracellular particles distributed throughout the cell volume (i.e., volume catalyzed nucleation, VCN). In the present study, these two distinctly coupled modes of IIF, especially SCN, are applied to various experimental protocols from mouse oocytes. Excellent agreement between predictions and observations suggests that the proposed model of IIF is adequate.

Animals↗
PubMed1991

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.

Female↗
PubMed1991

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.

Chemical Phenomena↗
PubMed1991

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.

Animals↗
PubMed1991

Applying state diagrams to food processing and development.

The physical state of food components affects their properties during processing, storage, and consumption. Removal of water by evaporation or by freezing often results in formation of an amorphous state (Parks et al., 1928; Troy and Sharp, 1930; Kauzmann, 1948; Bushill et al., 1965; White and Cakebread, 1966; Slade and Levine, 1991). Amorphous foods are also produced from carbohydrate melts by rapid cooling after extrusion or in the manufacturing of hard sugar candies and coatings (Herrington and Branfield, 1984). Formation of the amorphous state and its relation to equilibrium conditions are shown in Fig. 1 [see text]. The most important change, characteristic of the amorphous state, is noticed at the glass transition temperature (Tg), which involves transition from a solid "glassy" to a liquid-like "rubbery" state. The main consequence of glass transition is an increase of molecular mobility and free volume above Tg, which may result in physical and physico-chemical deteriorative changes (White and Cakebread, 1966; Slade and Levine, 1991). We have conducted studies on phase transitions of amorphous food materials and related Tg to composition, viscosity, stickiness, collapse, recrystallization, and ice formation. We have also proposed that some diffusion-limited deteriorative reactions are controlled by the physical state in the vicinity of Tg (Roos and Karel, 1990, 1991a, b, c). The results are summarized in this article, with state diagrams based on experimental and calculated data to characterize the relevant water content, temperature, and time-dependent phenomena of amorphous food components.

Crystallization↗
PubMed1989

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.

2,6-Dichloroindophenol↗
PubMed1989

The future of irradiation applications on Earth and in space.

What needs to be done to establish food irradiation on a truly commercial basis so that those living on planet Earth can fully realize the benefits of this versatile process? This question is answered in the first part of this paper. The second part covers the potential contributions of irradiated foods to feed humans in space.

Earth, Planet↗
PubMed1989

Potential utilization of algal protein concentrate as a food ingredient in space habitats.

Green alga Scenedesmus obliquus was studied as one of the potential sources of macronutrients in a space habitat. Algal protein concentrate (70.5% protein) was incorporated into a variety of food products such as bran muffins, fettuccine (spinach noodle imitation) and chocolate chip cookies. Food products containing 20 to 40% of incorporated algal proteins were considered. In the sensory analysis the greenish color of the bran muffins and cookies was not found to be objectional. The mild spinachy flavor (algae flavor) was less detectable in chocolate chip cookies than in bran muffins. The color and taste of the algae noodles were found to be pleasant and compared well with commercially available spinach noodles. Commercially available spray-dried Spirulina algae was also incorporated so the products can be compared with those containing Scenedesmus obliquus concentrate. Food products containing commercial algae had a dark green color and a "burnt after taste" and were less acceptable to the panelists.

Biomass↗
PubMed1987

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.

Alcohol Oxidoreductases↗
PubMed1987

Non-conventional approaches to food processing in CELSS. I--Algal proteins; characterization and process optimization.

Protein isolate obtained from green algae (Scenedesmus obliquus) cultivated under controlled conditions was characterized. Molecular weight determination of fractionated algal proteins using SDS-polyacrylamide gel electrophoresis revealed a wide spectrum of molecular weights ranging from 15,000 to 220,000. Isoelectric points of dissociated proteins were in the range of 3.95 to 6.20. Amino acid composition of protein isolate compared favorably with FAO standards. High content of essential amino acids leucine, valine, phenylalanine and lysine makes algal protein isolate a high quality component of CELSS diets. To optimize the removal of algal lipids and pigments supercritical carbon dioxide extraction (with and without ethanol as a co-solvent) was used. Addition of ethanol to supercritical CO2 resulted in more efficient removal of algal lipids and produced protein isolate with a good yield and protein recovery. The protein isolate extracted by the above mixture had an improved water solubility.

Amino Acids↗
PubMed1987

Lipid content and fatty acid composition of green algae Scenedesmus obliquus grown in a constant cell density apparatus.

The lipids of alga Scenedesmus obliquus grown under controlled conditions were separated and fractionated by column and thin-layer chromatography, and fatty acid composition of each lipid component was studied by gas-liquid chromatography (GLC). Total lipids were 11.17%, and neutral lipid, glycolipid and phospholipid fractions were 7.24%, 2.45% and 1.48% on a dry weight basis, respectively. The major neutral lipids were diglycerides, triglycerides, free sterols, hydrocarbons and sterol esters. The glycolipids were: monogalactosyl diglyceride, digalactosyl diglyceride, esterified sterol glycoside, and sterol glycoside. The phospholipids included: phosphatidyl choline, phosphatidyl glycerol and phosphatidyl ethanolamine. Fourteen fatty acids were identified in the four lipid fractions by GLC. The main fatty acids were C18:2, C16:0, C18:3(alpha), C18:1, C16:3, C16:1, and C16:4. Total unsaturated fatty acid and essential fatty acid compositions of the total algal lipids were 80% and 38%, respectively.

Chlorophyta↗
PubMed1987

Supercritical fluid extraction and characterization of lipids from algae Scenedesmus obliquus.

Supercritical carbon dioxide (SC-CO2) extractions (with and without ethanol as an entrainer) were carried out to remove lipids and pigments from protein concentrate of green algae (Scenedesmus obliquus) cultivated under controlled conditions. The content and fatty acid composition of algal lipids using column, thin-layer (TLC) and gas-liquid chromatography (GLC) were determined. Absorption spectra of extracted fractions showed the predominance of chlorophyll A (lambda max at 410 nm). Single step supercritical carbon dioxide (SC-CO2) extraction resulted mostly in removal of neutral lipids and a part of glycolipids, but phospholipids were not extracted. Addition of ethanol to SC-CO2 increased the amount of glycolipids and phospholipids in the extract. TLC pattern of algal lipids showed that the main part of neutral lipids consisted of diglycerides, triglycerides, hydrocarbons, free sterols, and sterol esters. The glycolipids were mostly monogalactosyl diglyceride, digalactosyl diglyceride, esterified sterol glycoside, and sterol glycoside. In phospholipids, phosphatidyl choline, phosphatidyl glycerol, and phosphatidyl ethanolamine were the main compounds. Fatty acid composition patterns indicated the main fatty acids to be 16:0, 16:1, 16:2, 16:3, 16:4, 18:1, 18:2, and 18:3(a). Relatively high recovery of polyunsaturated fatty acids and essential fatty acids in supercritical fluid extracted algal lipids and proteins isolates were observed.

Carbon Dioxide↗
PubMed1984

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.

Computers↗