Kinetic studies on the isothermal high hydrostatic pressure (HHP) inactivation of Escherichia coli in liquid whole egg (LWE) were performed at 5 and 25 degrees C in the pressure range of 250-400 MPa. The characteristic tailing inactivation curves were described by a first-order biphasic model. As compared to a previous rheological study, it is suggested that the phase change of LWE during pressure treatment affects the inactivation rate of E. coli. Within the processing criteria where the rheological properties of LWE were still comparable to those of fresh LWE, HHP treatments at 5 degrees C induced more E. coli inactivations than those at 25 degrees C. From the results of approximately 3 log reductions of E. coli and over 5 log reductions of Pseudomonas and Paenibacillus, HHP treatment of LWE at 5 degrees C is regarded to be as effective as conventional thermal pasteurization. However, no post-process contamination and the consistency of temperature during preparation, HHP treatment, and storage provide clear processing advantages.

Colony Count, Microbial↗

PubMedDate not supplied

Metastable states of water and ice during pressure-supported freezing of potato tissue.

Different ice modifications were obtained during freezing processes at several pressure levels from atmospheric pressure up to 300 MPa. In the pressure range between 210 and 240 MPa, a metastable ice I modification area was observed, as the nucleation of ice I crystals in the thermodynamically stable region of ice III was reached. A significant degree of supercooling was obtained before freezing the tissue water to ice III, which has to be considered when designing pressure-supported freezing processes. The effect of supercooling phenomenon on the phase transition time is discussed using a mathematical model based on the solution of the heat transfer governing differential equations. Phase transition and freezing times for the different freezing paths experimented are compared for the processes: freezing at atmospheric pressure, pressure-assisted freezing, and pressure-shift freezing. Different metastable states of liquid water are defined according to their process-dependent stability.

Computer Simulation↗

PubMedDate not supplied

Electrophysiological model of intact and processed plant tissues: cell disintegration criteria.

Frequency versus conductivity relationships of food cell system, based on impedance measurements as characterized by polarization effects of the Maxwell-Wagner type at intact membrane interfaces, are presented. The electrical properties of a biological membrane (represented as a resistor and capacitor) are responsible for the dependence of the total conductivity of the cell system on the alternating current frequency. Based on an equivalent circuit model of a single plant cell, the electrical conductivity spectrum of the cell system in intact plant tissue (potato, carrot, banana, and apple) was determined in a frequency range between 3 kHz and 50 MHz. The electrical properties of a cell system with different ratios of intact/ruptured cells could also be predicted on the basis of a description of a cell system consisting of elementary layers with regularly distributed intact and ruptured cells as well as of extracellular compartments. This simple determination of the degree of cell permeabilization (cell disintegration index, p(o)) is based upon electric conductivity changes in the cell sample. For accurate calculations of p(o), the sample conductivities before and after treatment, obtained at low- (f(l)) and high-frequency (f(h)) ranges of the so-called beta-dispersion, were used. In this study with plant cell systems, characteristic conductivities used were measured at frequencies f(l) = 3 kHz and f(h) = 12.5 MHz. The disintegration index was used to analyze the degree of cell disruption after different treatments (such as mechanical disruption, heating, freeze-thaw cycles, application of electric field pulses, and enzymatic treatment) of the plant tissues.

Cell Fractionation↗

PubMedDate not supplied

Diagnosis and monitoring of therapy of the various enzymatic defects causing congenital adrenal hyperplasia by semiautomatic capillary gas-liquid chromatography.

A semiautomatic capillary gas-liquid chromatographic method for the determination of urinary steroids has been developed. Trimethylsilylenol ethers were used as steroid derivatives instead of the more common methoxime trimethylsilyl ethers. The diagnosis of the various enzymatic defects causing congenital adrenal hyperplasia can be made using the characteristic pattern of urinary steroid chromatograms. Furthermore, the method presented can be used routinely to monitor therapeutic control in congenital adrenal hyperplasia. Reference data for patients of different age groups under good therapeutic control are presented.

3-Hydroxysteroid Dehydrogenases↗