Respective Threshold Values Research Articles

Analysis of wine primary aroma compounds by stir bar sorptive extraction

Due to the great importance of some primary aroma compounds on wine quality, these compounds which includes terpenes, C 13-norisoprenoids and C 6 compounds, have been analyzed by stir bar sorptive extraction (SBSE) followed by a thermal desorption-gas chromatography–mass spectrometry analysis. The stir bar sorptive extraction method was optimized in terms of temperature, time, pH and NaCl addition. The best SBSE sorption kinetics for the target analytes were obtained after submitting the solutions to 60 °C during 90 min. The addition of sodium chloride did not enhance the volatile extraction. The method proposed showed good linearity over the concentration range tested, with correlation coefficients higher than 0.98 for all the analytes. The reproducibility and repeatability of the method was estimated between 0.22 and 9.11%. The detection and quantification limits of all analytes were lower than their respective olfactory threshold values. The application of this SBSE method revealed that monovarietal white wines were clearly separated by two canonic discriminating functions when grape varieties were used as differentiating variable, the first of which explained 98.4% of the variance. The compounds which contributed most to the differentiation were limonene, linalool, nerolidol and 1-hexanol.

Stir bar sorptive extraction for the determination of volatile compounds in oak-aged wines

Stir bar sorptive extraction (SBSE) followed by a thermal desorption-gas chromatography–mass spectrometry analysis has been optimized for the determination of 13 of the most important oak volatiles in wine samples, all in a single run. The stir bar sorptive extraction method was optimized in terms of temperature, time, pH and NaCl addition, and the best results were obtained after stirring the wine sample with the polydimethylsiloxane stir bar during 90 min at room temperature. The addition of sodium chloride did not enhance the volatile extraction. The method proposed showed good linearity over the concentration range tested, with correlation coefficients ranging from 0.92 to 0.99 for all the analytes. The reproducibility and repeatability of the method was estimated between 0.11 and 5.45%. The detection and quantification limits of all analytes were lower than their respective olfactory threshold values, and, most importantly, no artifacts have been observed during the analysis as described in most extractions using other current methodologies.

The effects of selected aldehydes, ketones and carboxylic acids on off‐flavours in water

SummaryThe effects of selected aldehydes, ketones and carboxylic acids on the development of off‐flavours in water were studied. Combinations of hexanal, octanal, 2‐octanone, 5‐nonanone, hexanoic acid and nonanoic acid were rated by the off‐flavour intensities they created in water at concentrations just at or below the threshold value of each analyte. Two different sensory panels evaluated the off‐flavours induced by different combinations of the analytes. The observations of the two panels agreed well. From these studies, it could be concluded that aldehydes play an important role in the development of off‐flavours intensities in water. There were synergistic effects between aldehydes and ketones, as well as between aldehydes and carboxylic acids. Small amounts of aldehydes and carboxylic acids – well below their respective threshold values – caused an increase in the off‐flavour intensity. No synergism between ketones and carboxylic acids could be observed.

Electrical Taste Thresholds Established on the Medial Tongue using Two Sizes of Electrodes

The present study determined whether a 125 mm electrode would produce lower and more reliable electrical taste thresholds than a 25 mm electrode when measurement occurred in a medial tongue region relatively sparse in taste bud numbers. We hypothesized this would be the case and that the obtained threshold values would be higher than those previously reported for anterior and lateral tongue regions. Sixteen college-age subjects were tested twice, once using the 25 mm electrode and once using the 125 mm electrode on each of two sessions separated by 2 to 16 days. The order of presentation of the sessions was counterbalanced across subjects. Measurement was confined to the medial tongue, 0.7 cm lateral to the median furrow. As hypothesized, the larger electrode resulted in lower and more reliable threshold values than the smaller electrode (respective median threshold values = 20.06 microA & 33.59 microA, P = .001; respective test-retest rs = 0.78 [P < .001] and 0.46 [P < .05]). Also as hypothesized, the threshold values were higher (i.e., sensitivity lower) than previously reported for anterior and lateral tongue regions. The magnitude and reliability of electrical taste thresholds depends on the tongue region examined and the size of the electrodes used. These results suggest that relatively large electrodes should be considered for electrogustometric threshold testing, particularly when lingual regions not highly populated with taste buds are evaluated.

Mobility of heavy metals in harbour sediments: an environmental aspect for the reuse of contaminated dredged sediments

Different methods to determine the source strength of two harbour sediment fractions were applied and are discussed with a focus on As, Cd, Cr, Co, Cu, Mo, Ni, Pb, and Zn. Four different batch experiments were performed with both the sandy and the silty fractions of harbour sediments sampled at the disposal site for dredged material in Bremen Seehausen, north Germany. In addition to the batch experiments a modified centrifugation tube was used in order to obtain pore water from the unsaturated silty fraction. Column experiments were run with the sandy fraction of the material under saturated and unsaturated conditions, irrigated with artificial acid rain water. The results show that the legal threshold value applying to Mo and Pb is not exceeded in any of the methods applied to the sandy or the silty fractions. As for the sandy fraction, Cr and Co were also below this limit. Cd, Ni, Cu and Zn exceeded the threshold values in some of the batch experiments applied to both fractions, depending on the pH value and the elution agent used in the experiment. All results obtained from saturated column leaching were below the respective threshold values; however, it should be noted that the pH was between 7 and 8 throughout the entire experiment. This pH also applied to the unsaturated column, with the exception of the ‘first flush’. This first sample had a pH value of 3.8, which was due to sulphide oxidation at the beginning of the experiment and led to strong leaching of all the elements under study. As a consequence, arsenic, Cu and Ni values exceeded their respective threshold values.

Fatigue crack growth mechanisms in steels

Fatigue crack growth behavior of structural steels is examined by using the Unified Approach developed by the authors. In this approach, fatigue requires two-load parameters involving maximum stress intensity, K max, and stress intensity amplitude, △ K. For a fatigue crack to grow, both K max and △ K must exceed their respective threshold values. Similarly, for any other crack growth rate, two limiting values, K max∗ and △ K∗ are required to enforce the growth rate. The variation of these two critical values forms the crack growth trajectory map, which is defined by plotting △ K∗ vs. K max∗ as a function of crack growth rate. In this trajectory map, the line defined by △K ∗=K max∗ represents pure fatigue crack growth behavior induced by cyclic strains. It is shown that this line provides a reference norm for defining deviations in the trajectory resulting from environmental and/or monotonic fracture modes superimposed on fatigue. Using this approach, we have examined the crack growth behavior of many structural steels. The trajectory maps of these steels show deviations due to superimposed environmental effects. These effects vary with grain size, yield strength, microstructure, and chemistry. In addition, for a given material, changes in the trajectory paths occur because of changing crack growth mechanisms. Analysis of material behavior using trajectory maps provides a clear understanding of the relative magnitude of cyclic and environmental damage and how the microstructure, chemistry, and crack tip plasticity affect fatigue crack growth behavior of steels.

An indirect conductimetric screening method for the detection of antibiotic residues in bovine kidneys.

An indirect conductimetric screening method using three test bacterium-medium combinations was developed for rapid detection of antibiotic residues in bovine carcasses. The detection time (DT), i.e. the point when the growth of the test bacterium was detected, was determined by observing the rate of change in the conductance plotted against time. This detection time averaged half of the reference time recorded by the instrument software. Total change in conductance (TC) was used as a further measure of growth. Threshold values for DT and TC were determined with inhibitor-free kidney samples. The presence of a residue was indicated if the DT exceeded the respective threshold value and was confirmed if the TC remained below the TC threshold value. The limits of detection (LODs) determined with fortified samples were at about or below the MRLs for cephalexin, chlortetracycline, ciprofloxacin, dihydrostreptomycin, enrofloxacin, oxytetracycline and penicillin G. The LODs for penicillin G, oxytetracycline and the sum of enrofloxacin and ciprofloxacin were also estimated with incurred samples; these samples were also analysed using liquid chromatography. The LODs determined with fortified and incurred samples were in close agreement. Given its rapid detection, good sensitivity to a wide range of antibiotics and ease of performance, the indirect conductimetric method developed here would seem to offer an appealing alternative to agar diffusion tests.

Nachhaltigkeit in der Pflanzenproduktion

The purpose of part II is to develop and to discuss a methodological approach for the practical implementation of sustainable crop production. In part I the term “sustainable crop production” has been defined and explained. Based on this definition the approach presented here entails several steps starting with the identification of the whole range of crop management measures and the emissions and other releases associated with them. Through an impact pathway assessment these releases are traced from their point of origin, the farm or production level, to their end points, namely agroecosystems and adjacent ecosystems. At the ecosystem level condition-indicators, which describe the condition of the ecosystems affected by agricultural crop production measures, need to be selected. For these condition-indicators threshold values (i.e. maximally tolerable values) have to be determined. These should not be exceeded if irreversible changes in the respective ecosystems and ecosystem compartments are to be avoided. By tracing the maximally tolerable values back along their impact pathway, they are transposed to the level of crop production. At the farm level they prescribe a framework within which agricultural crop production must remain to prevent irreversible changes in the affected ecosystems. The framework consists of production indicators and their respective threshold values (i.e. critical uses of farm inputs), which have to be adhered to in order to ensure sustainable crop production.

Detection of simultaneous self-administration of testosterone and epitestosterone in healthy men

Combined self-administration of testosterone (T) and epitestosterone (ET) by athletes counteracts the efficiency of the corresponding urinary glucuronides (G) ratio, (T/ET)G, as an indicator of T abuse. I therefore propose 5-androstene-3 beta, 17 alpha-diol (5A3 beta 17 alpha), the immediate metabolic precursor of ET, as a new reference compound for the expression of relative excretions of T and ET. Thus (T/5A3 beta 17 alpha)G and (ET/5A3 beta 17 alpha)G become potential criteria to indicate joint administration of T and ET, since their respective threshold values (2.5 and 1.5) are exceeded even when (T/ET)G remains below the critical value of 6.

Quantitation of liquid-crystalline ordering in F-actin solutions.

Actin filaments (F-actin) are important determinants of cellular shape and motility. These functions depend on the collective organization of numerous filaments with respect to both position and orientation in the cytoplasm. Much of the orientational organization arises spontaneously through liquid crystal formation in concentrated F-actin solutions. In studying this phenomenon, we found that solutions of purified F-actin undergo a continuous phase transition, from the isotropic state to a liquid crystalline state, when either the mean filament length or the actin concentration is increased above its respective threshold value. The phase diagram representing the threshold filament lengths and concentrations at which the phase transition occurs is consistent with that predicted by Flory's theory on solutions of noninteracting, rigid cylinders (Flory, 1956b). However, in contrast to other predictions based on this model, we found no evidence for the coexistence of isotropic and anisotropic phases. Furthermore, the phase transition proved to be temperature dependent, which suggests the existence of orientation-dependent interfilament interactions or of a temperature-dependent filament flexibility. We developed a simple method for growing undistorted fluorescent acrylodan-labeled F-actin liquid crystals; and we derived a simple theoretical treatment by which polarization-of-fluorescence measurements could be used to quantitate, for the first time, the degree of spontaneous filament ordering (nematic order parameter) in these F-actin liquid crystals. This order parameter was found to increase monotonically with both filament length and concentration. Actin liquid crystals can readily become distorted by a process known as "texturing." Zigzaging and helicoidal liquid crystalline textures which persisted in the absence of ATP were observed through the polarizing microscope. Possible texturing mechanisms are discussed.

The intensity and variability of the growing season on Iceland

Abstract Climatic statistical material from seven lowland stations and one highland station in Iceland was analyzed for the period 1960–1984 with regard to length, intensity, and variability of the growing season. The latter is defined in terms of means with at least ten days with mean daily temperatures above +3°, +5°, and +10°C respectively. Apart from a distinct difference between the more continental, arctic highland situation and that of the subarctic oceanic lowlands, differentiations between the coastal areas can also be demonstrated. From the south and west toward the northwest not only does the growing season become shorter but the incoming degree day totals also become lower. In contrast to this, relatively higher cumulative heat totals are attained within shorter periods in the sheltered settings of the northern and eastern fjords and valleys. This applies especially to the +10°C threshold. The variability of the number of days with daily mean temperatures above the respective threshold values increases as the threshold values increase: The lowest variability in terms of the lower temperature thresholds is reached in the south and southwest and in terms of the +10°C threshold in the north and east. With the exception of Reykjavik, a minimum for degree day heat totals during the growing season was recorded at all stations in the mid‐sixties, followed by a peak in the mid‐seventies, and another decrease to the lowest minima recorded, in the early eighties.

On direct initiation of gaseous detonations

A simple theoretical model is presented to determine the correlation between the igniter's critical energy and power necessary for direct initiation of detonations and to predict their respective threshold values. The model comprises a constant-velocity piston which is set in motion at time t = 0. The resulting constant-velocity shock wave heats up the explosive mixture and triggers the chemical reaction. It is shown that for direct initiation, the piston should remain in motion for a time interval at least equal to the induction period. The predictions based on this simple model are in good qualitative agreement with the experimental findings reported in the literature on cylindrical detonations.

Determination of Flavor Threshold Levels and Sub‐Threshold, Additive, and Concentration Effects

SUMMARY— The flavor threshold concentrations were determined for 23 compounds composing an artificial peach beverage base. The threshold levels ranged from 52 ppm to 0.4 ppb. The threshold values were used in sub‐threshold, additive sub‐threshold, and concentration trials. Sub‐threshold and additive sub‐threshold effects resulted from only a few of the flavor combinations tried. Change in concentration of one compound in a mixture of six compounds was not readily detectable organoleptically. The difference in concentration could be detected gas chromatographically, but only if the mixtures were extracted with pentane and concentrated.By dividing the respective threshold values into the amount of each compound present in the beverage, a factor was calculated, called the “unit flavor base,” which indicated the relative importance of each compound as a flavor substance in the peach beverage. By dividing the gas chromatographic peak heights by the respective threshold values, gas chromatographic response was weighted for flavor importance. When the unit flavor base and weighted gas chromatographic response were converted into logarithms, the relation between the values was nearly linear. The correlation coefficient was 0.8691 (significant @ 0.01).

A New Procedure for the Investigation of Experimentally Induced Acoustic Trauma in Man

A procedure is described by means of which the time interval during which a given temporary threshold shift produced by a high level traumatizing noise and the time required for the threshold to recover to near normal threshold values can be determined with useful accuracy. Initially, the subject's threshold values are ascertained for the noise and for the “test” tone. The levels of the two sounds are then raised to the desired intensity levels, e.g., the noise to 110 db and the test tone to 40 db above their respective threshold values. The two sounds are then presented alternately, the noise for ten seconds, the test tone for one second, this cycle being repeated until the subject reports inaudibility of the test tone. By instructing the subject to depress “yes” or “no” switches when the test tone is or is not heard and by connecting the switches to an appropriate recording mechanism, the time (in terms of ten-second intervals) over which 10-, 20-, 30-, and 40-db threshold shifts result are readily obtained. Also, by discontinuing the traumatic tone and attenuating the test tone (now presented continuously) in, e.g., 10-db steps whenever the subject responds with the “yes” button, the acceleration of the recovery curve is obtained. An almost infinite number of parameters result from varying the duration, intensity level, and frequency composition of the noise and the test tone. The procedure, with reasonable care, eliminates the possibility of producing permanent traumatic damage to the ear. Experimental results reveal marked individual differences in the length of time over which a given temporary threshold shift for the tone occurs. Curves of experimental data will be presented. It is anticipated that this procedure will constitute a significant noise susceptibility test by means of which “tender” ears can be differentiated from “tough” ears.