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We use hydrodynamic cosmological zoom-in simulations from the Feedback in Realistic Environments project to explore the morphologies and kinematics of 15 Milky Way (MW)-mass galaxies. Our sample ranges from compact, bulge-dominated systems with 90 per cent of their stellar mass within 2.5 kpc to well-ordered discs that reach ≳15 kpc. The gas in our galaxies always forms a thin, rotation-supported disc at z = 0, with sizes primarily determined by the gas mass. For stars, we quantify kinematics and morphology both via the fraction of stars on disc-like orbits and with the radial extent of the stellar disc. In this mass range, stellar morphology and kinematics are poorly correlated with the properties of the halo available from dark matter-only simulations (halo merger history, spin, or formation time). They more strongly correlate with the gaseous histories of the galaxies: those that maintain a high gas mass in the disc after z ~ 1 develop well-ordered stellar discs. The best predictor of morphology we identify is the spin of the gas in the halo at the time the galaxy formed 1/2 of its stars (i.e. the gas that builds the galaxy). High- z mergers, before a hot halo emerges, produce some of the most massive bulges in the sample (from compact discs in gas-rich mergers), while later-forming bulges typically originate from internal processes, as satellites are stripped of gas before the galaxies merge. Moreover, most stars in z = 0 MW-mass galaxies (even z = 0 bulge stars) form in a disc: ≳60-90 per cent of stars begin their lives rotationally supported.

Unlike spiral galaxies such as the Milky Way, the majority of the stars in massive elliptical galaxies were formed in a short period early in the history of the Universe. The duration of this formation period can be measured using the ratio of magnesium to iron abundance ([Mg/Fe]) in spectra, which reflects the relative enrichment by core-collapse and type Ia supernovae. For local galaxies, [Mg/Fe] probes the combined formation history of all stars currently in the galaxy, including younger and metal-poor stars that were added during late-time mergers. Therefore, to directly constrain the initial star-formation period, we must study galaxies at earlier epochs. The most distant galaxy for which [Mg/Fe] had previously been measured is at a redshift of z ≈ 1.4, with [Mg/Fe] = . A slightly earlier epoch (z ≈ 1.6) was probed by combining the spectra of 24 massive quiescent galaxies, yielding an average [Mg/Fe] = 0.31 ± 0.12 (ref. 7). However, the relatively low signal-to-noise ratio of the data and the use of index analysis techniques for both of these studies resulted in measurement errors that are too large to allow us to form strong conclusions. Deeper spectra at even earlier epochs in combination with analysis techniques based on full spectral fitting are required to precisely measure the abundance pattern shortly after the major star-forming phase (z > 2). Here we report a measurement of [Mg/Fe] for a massive quiescent galaxy at a redshift of z = 2.1, when the Universe was three billion years old. With [Mg/Fe] = 0.59 ± 0.11, this galaxy is the most Mg-enhanced massive galaxy found so far, having twice the Mg enhancement of similar-mass galaxies today. The abundance pattern of the galaxy is consistent with enrichment exclusively by core-collapse supernovae and with a star-formation timescale of 0.1 to 0.5 billion years-characteristics that are similar to population II stars in the Milky Way. With an average past star-formation rate of 600 to 3,000 solar masses per year, this galaxy was among the most vigorous star-forming galaxies in the Universe.

A simple and accurate method for the determination of moisture in edible oils by differential FTIR spectroscopy has been devised based on the stoichiometric reaction of the moisture in oil with toluenesulfonyl isocyanate (TSI) to produce CO2. Calibration standards were devised by gravimetrically spiking dry dioxane with water, followed by the addition of neat TSI and examination of the differential spectra relative to the dry dioxane. In the method, CO2 peak area changes are measured at 2335 cm(-1) and were shown to be related to the amount of moisture added, with any CO2 inherent to residual moisture in the dry dioxane subtracted ratioed out. CO2 volatility issues were determined to be minimal, with the overall SD of dioxane calibrations being ∼18 ppm over a range of 0-1000 ppm. Gravimetrically blended dry and water-saturated oils analysed in a similar manner produced linear CO2 responses with SD's of <15 ppm on average. One set of dry-wet blends was analysed in duplicate by FTIR and by two independent laboratories using coulometric Karl Fischer (KF) procedures. All 3 methods produced highly linear moisture relationships with SD's of 7, 16 and 28 ppm, respectively over a range of 200-1500 ppm. Although the absolute moisture values obtained by each method did not exactly coincide, each tracked the expected moisture changes proportionately. The FTIRTSI-H2O method provides a simple and accurate instrumental means of determining moisture in oils rivaling the accuracy and specificity of standard KF procedures and has the potential to be automated. It could also be applied to other hydrophobic matrices and possibly evolve into a more generalized method, if combined with polar aprotic solvent extraction., (Copyright © 2016 Elsevier B.V. All rights reserved.)

A primary Fourier transform infrared (FTIR) method capable of determining acidity in ester-based oils is described and evaluated. Absolute free fatty acid (%FFA) and acid value (AV) calibrations were devised by spiking oleic acid into a refined, acid-free oil and measuring ν COO(-) at ∼ 1569 and ν phenolate(-) at ∼ 1588 cm(-1), respectively, in the second-derivative differential spectra. The FTIR acidity predictions were compared to the AOCS titrimetric method using acid mixtures as well as acid containing used vendor oils of undefined makeup and provenance, using two spectroscopically divergent reference oils as AC0. Relative to the AOCS reference method, the FTIR procedure was found to be both more accurate (± 0.107 vs ± 0.122) and reproducible (± 0.025 vs ± 0.077) in determining %FFA and similar in predicting AV. The FTIR phenolate method overcomes a variety of limitations of earlier FTIR-based methods, being particularly simple and well suited to routine, semiautomated acidity analysis of ester-based oils using a basic FTIR spectrometer.

The Fluid Life Corporation assessed and implemented Fourier transform infrared spectroscopy (FTIR)-based methods using American Society for Testing and Materials (ASTM)-like stoichiometric reactions for determination of acid and base number for in-service mineral-based oils. The basic protocols, quality control procedures, calibration, validation, and performance of these new quantitative methods are assessed. ASTM correspondence is attained using a mixed-mode calibration, using primary reference standards to anchor the calibration, supplemented by representative sample lubricants analyzed by ASTM procedures. A partial least squares calibration is devised by combining primary acid/base reference standards and representative samples, focusing on the main spectral stoichiometric response with chemometrics assisting in accounting for matrix variability. FTIR(AN/BN) methodology is precise, accurate, and free of most interference that affects ASTM D664 and D4739 results. Extensive side-by-side operational runs produced normally distributed differences with mean differences close to zero and standard deviations of 0.18 and 0.26 mg KOH/g, respectively. Statistically, the FTIR methods are a direct match to the ASTM methods, with superior performance in terms of analytical throughput, preparation time, and solvent use. FTIR(AN/BN) analysis is a viable, significant advance for in-service lubricant analysis, providing an economic means of trending samples instead of tedious and expensive conventional ASTM(AN/BN) procedures., (© 2014 Society for Laboratory Automation and Screening.)

A Fourier transform infrared (FTIR) method developed for the analysis of moisture in edible oils using dry acetonitrile as the extraction solvent was re-examined with the objective of improving its overall sensitivity and reproducibility. Quantitation was based on the H-O-H bending absorption at ∼1630 cm(-1) instead of the bands in the OH stretching region, fewer interferences being an issue in the former as opposed to the latter region. In addition, a spectroscopic dilution correction procedure was developed to compensate for any miscibility of oil samples with acetonitrile, and gap-segment 2nd derivative spectra were employed to minimise the associated possibility of spectral interferences from absorptions of the oils. In comprehensive standard addition experiments using a variety of edible oils, the FTIR method was shown to recover the amounts of water quantitatively added to dry oil with an accuracy of ±20 ppm when the spectra of the acetonitrile extracts of the water-spiked oils were ratioed against the spectra of the acetonitrile extracts of the corresponding dry oils. The accuracy deteriorated substantially when the spectra of the acetonitrile extracts of the water-spiked oils were ratioed against the spectrum of the acetonitrile extraction solvent only. However, the primary variable affecting the apparent difference in the accuracy of the two approaches was determined to be the variability in the residual moisture content of the dried oils used in the standard addition experiments, as confirmed by an FTIR procedure based on H-D exchange with D(2)O. The FTIR method as structured is amenable to automation (>120 samples/h) and provides a very competitive means by which to routinely measure moisture present in a variety of hydrophobic materials that are normally the domain of Karl Fischer titration, such as edible oils, mineral oils, biodiesel and fuels., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

A new transmission-based Fourier transform infrared (FTIR) spectroscopic method for the direct determination of free fatty acids (FFA) in edible oils has been developed using the developed spectral reconstitution (SR) technique. Conventional neat-oil and SR calibrations were devised by spiking hexanoic acid into FFA-free canola oil and measuring the response to added FFA at 1,712 cm(-1) referenced to a baseline at 1,600 cm(-1)(1,712 cm(-1)/1,600 cm(-1)). To compensate for the known oil dependency of such calibration equations resulting from variation of the triacylglycerol ester (C═O) absorption with differences in oil saponification number (SN), a correction equation was devised by recording the spectra of blends of two FFA-free oils (canola and coconut) differing substantially in SN and correlating the intensity of the ester (C═O) absorption at the FFA measurement location with the intensity of the first overtone of this vibration, measured at 3,471 cm(-1)/3,427 cm(-1). Further examination of the spectra of the oil blends by generalized 2D correlation spectroscopy revealed an additional strong correlation with an absorption in the near-infrared (NIR) combination band region, which led to the development of a second correction equation based on the absorbance at 4,258 cm(-1)/4,235 cm(-1). The NIR-based correction equation yielded superior results and was shown to completely eliminate biases due to variations in oil SN, thereby making a single FFA calibration generally applicable to oils, regardless of SN. FTIR methodology incorporating this correction equation and employing the SR technique has been automated.

A rapid method has been developed to extract and quantitatively measure the total oil content in poultry feeds using a domestic microwave oven. The optimized extraction procedure involves the replicate (6x) extraction of 5 g of ground feed with 12 ml of hexane for 20 s in a 900 W oven. Each replicate involves the collection of the resulting miscella and its replacement with fresh solvent for re-extraction. The collected extracts were centrifuged and transferred to a vial. The solvent was evaporated to a constant weight and the residual lipid weighed. In comparison to conventional Soxhlet extraction method, lipid contents obtained using the optimized microwave procedure was not significantly different. However, FTIR analysis indicated that the microwave procedure was superior in minimizing the formation of free fatty acids (FFA) relative to the Soxhlet procedure if the temperature of the sample was kept within the range of 45-50 degrees C. This simple, sequential extraction procedure is rapid, highly efficient and provides a simple mean of quantitating the lipid content of poultry feed in less than 40 min without the need for specialized microwave oven.

Substantive improvement in the sensitivity of the AOAC/AOCS spectral ratioing method for the determination of isolated trans isomers in edible oils was recently achieved by the application of a new spectral reconstitution (SR) technique that facilitates the FTIR analysis of edible oils in the transmission mode. However, the general applicability of the spectral ratioing method is still severely limited by the requirement to know the provenance of the oil to be analyzed and have on hand its trans-free counterpart so that the underlying triacylglycerol absorptions in the trans measurement region (990-945 cm(-1)), henceforth referred to as UAt , may be ratioed out. To eliminate the need for a trans-free reference oil, we have employed two-dimensional (2D) correlation spectroscopy to search for other spectral features that might correlate with and serve to estimate the UAt . The three-dimensional contour maps obtained by 2D correlation analysis of the spectra of 10 trans-free oils of different oil types, recorded using the SR procedure, revealed such correlations in two spectral regions, 1700-1600 and 4500-4300 cm(-1), exhibiting one maximum and two maxima, respectively, with wavenumber coordinates of (968, 4407), (968, 4299), and (968, 1650). The latter two correlations, when optimized, produced excellent linear regression relationships (r>0.95) with the UAt . The spectra of five sets of trielaidin-spiked oils were corrected for the UA t using these relationships, and their trans contents were predicted from the calibration equation generated for the spectral ratioing procedure. Linear regression of predicted versus added trans over the range of 0-1.6% trans, which is below the limit of quantitation of the AOAC/AOCS spectral ratioing method, yielded r=0.88-0.90 with an SD of approximately 0.2% trans. These results indicate that the combination of the SR technique with the UA t correction approach may provide a simple and accurate FTIR method for the analysis of the trans content of fats and oils that would be competitive with GC.

Spectral reconstitution (SR), a technique that has been developed to facilitate mid-FTIR transmission analysis of inherently viscous samples, was applied to simplify and automate a previously reported FTIR method for the determination of peroxide value (PV) of edible oils. The basis of the PV determination is the rapid reaction of triphenylphosphine (TPP) with the hydroperoxides present in an oil to produce triphenylphosphine oxide (TPPO), which exhibits a readily measurable absorption band at 542 cm(-1). In the SR procedure, the viscosity of oil samples is reduced by mixing them with a diluent, which allows them to be readily loaded into a flow-through transmission cell. The spectra of the neat oil samples are then reconstituted from those of the diluted samples by using the absorption of a spectral marker present in the diluent to determine the dilution ratio. For the SR-based PV method, the TPP reagent was added to the diluent, which consisted of odorless mineral spirits (OMS) containing methylcyclopentadienyl manganese tricarbonyl (MMT) as the spectral marker. Sample preparation for PV analysis involved mixing approximately 10 ml of oil with approximately 25 ml of the TPP-containing diluent; accurate weighing or delivery of precise volumes was not required because the dilution ratio was determined spectroscopically from the intensity of the nu(CO) absorption of MMT at 1942 cm(-1) in the spectrum of the diluted sample relative to that in the spectrum of the diluent. Calibration standards, prepared by gravimetric addition of TPPO to a peroxide-free oil, were handled in the same manner, and a linear calibration equation relating the concentration of TPPO (expressed as the equivalent PV) to the absorbance of TPPO at 542 cm(-1) relative to a baseline at 530 cm(-1) in the reconstituted spectra was obtained, with a regression S.D. of +/-0.15 meq/kg oil. PV determinations on two sets of validation samples, spanning PV ranges of 0-20 and 0-2 meq/kg oil, were carried out in parallel by the AOCS titrimetric and SR-based FTIR procedures, and comparison of the results of duplicate analyses by the two methods indicated that the latter was more reproducible and slightly more sensitive. The SR-based PV method, when implemented on an autosampler-equipped FTIR system, allowed for the automated analysis of approximately 90 samples per hour.

A simple, rapid, and reproducible method has been developed for the quantitative determination of free fatty acid (FFA) content in lipids extracted from poultry feeds by Fourier transform infrared (FTIR) spectroscopy with the use of a single-bounce attenuated total reflectance (SB-ATR) accessory. An FTIR calibration curve was prepared by gravimetrically adding oleic acid (15-37%) to pure refined, bleached, and deodorized (RBD) canola oil and measuring the area of the COOH absorption band at 1710 cm-1. The oil from each of 12 poultry feed formulations was extracted using conventional Soxhlet extraction, and after evaporation of the solvent, the FFA content was determined by the conventional AOCS titrimetric procedure and by the SB-ATR/FTIR method. The SB-ATR/FTIR FFA predictions were related to those determined by the AOCS titrimetric method by linear regression, producing an R value of 0.999 and a SD of +/-0.28% FFA. Time-course spectra collected as lipids extracted into hexane indicated that a 15 min extraction was adequate to obtain a representative sample for FFA determination, with further extraction resulting in little, if any, change in the proportion of FFA in the lipid extract. Only a small volume of the hexane extract ( approximately 20 mL) yielded sufficient material for the SB-ATR/FTIR analysis. Thus, by shortening the extraction time and taking a small sample so as to reduce solvent removal time, the SB-ATR/FTIR procedure provides a very simple and rapid means of determining the FFA content of poultry feed lipids.

This paper describes the development of a practical Fourier transform infrared (FT-IR) method for the determination of moisture in lubricants through the combined use of signal transduction and differential spectroscopy to circumvent matrix effects. The acid-catalyzed stoichiometric reaction of 2,2-dimethoxypropane (DMP) with moisture to produce acetone was used to provide IR signals proportional to the amount of moisture present in oils. Calibration standards were prepared by spiking polyalphaolefin (PAO) gravimetrically with water using dioxane as a carrier. For FT-IR analysis, standards and samples were diluted with acidified isooctane and then split, with one aliquot treated with DMP and the other with a blank reagent. The spectra of the two aliquots were collected, and a differential spectrum was obtained so as to ratio out the invariant spectral contributions from the sample. Quantitation for moisture was based on measurement of the peak height of the nu(C=O) absorption of acetone at 1717 cm(-1), yielding a standard error of calibration of approximately 40 ppm H2O. The method was validated by standard addition of water in dioxane to PAO containing added base as well as to new and used oils. In all cases the method responded quantitatively to standard addition, the average standard error of prediction being approximately 80 ppm, with the results showing only a minor dependence on the oil formulation. From an analytical perspective, the FT-IR method is both more reproducible and more accurate than Karl Fischer methods and has advantages in terms of environmental considerations, sample size, and speed of analysis as well as the variety of oil types that can be handled. Signal transduction/differential spectroscopy may have broader utility as an alternative means for the determination of low levels of moisture in complex matrices.

This paper describes the development of practical Fourier transform infrared (FT-IR) methods for the determination of acid number (AN) and base number (BN) in lubricants through the combined use of signal transduction via stoichiometric reactions and differential spectroscopy to circumvent matrix effects. Trifluoroacetic acid and potassium phthalimide were used as stoichiometric reactants to provide infrared (IR) signals proportional to the basic and acidic constituents present in oils. Samples were initially diluted with 1-propanol, then split, with one half treated with the stoichiometric reactant and the other half with a blank reagent, their spectra collected, and a differential spectrum obtained to ratio out the invariant spectral contributions from the sample. Quantitation for AN and BN was based on measurement of the peak height of the v(C = O) or v(COO) absorptions, respectively, of the products of the corresponding stoichiometric reactions, yielding a standard error of calibration of < 0.1 mg KOH/g oil. The AN/BN FT-IR methods were validated by the analysis of a wide range of new and used oils supplied by third parties, which had been analyzed by ASTM methods. Good correlations were obtained between the chemical and FT-IR methods, indicating that the measures are on the whole comparable. From a practical perspective, these new FT-IR methods have significant advantages over ASTM titrimetric methods in terms of environmental considerations, sample size, and speed of analysis, as well as the variety of oil types that can be handled. FT-IR analysis combining stoichiometric signal transduction with differential spectroscopy may be of wider utility as an alternative to titration in the determination of acid or basic constituents in complex nonaqueous systems.

Dielectric properties of grapes at 2.45 GHz were measured at moisture contents varying from 80 to 15% (wet basis) at temperatures ranging from 25-80 degrees C using the Open Ended Coaxial Transmission Line Technique. Both dielectric constant and loss factor decreased with decreasing moisture content. In low moisture samples these properties were found to be considerably influenced by higher temperatures. Dielectric properties of sugar solutions of varying concentrations (20-250% by weight in water) were also determined at different temperatures, and these values were compared to those of grapes of corresponding moisture concentration. Predictive models of the dieletric properties as functions of moisture content and temperature were generated using response surface methodology. The results are useful in estimating the volumetric heating of grapes by microwave energy, and these methods can be extended to sugar-based foods in general.

Transmission infrared analysis, which has been successfully applied to milk analysis, was assessed for the quantitative analysis of fat and protein in meat products. Meats of varying fat and protein content were converted into milk-like emulsions, which were, in turn, analyzed by standard chemical methods and by a Multispec M infrared analyzer. The performance of the instrument for meat analysis using a standard milk calibration was also assessed and compared with the instrument set with a meat calibration. Both approaches provided a good estimate of the fat and protein content for a range of meat products, the meat calibration being more accurate than the milk calibration. The infrared method allowed for rapid and accurate analysis of meat and has future potential in the meat industry for quality control purposes., (Copyright © 1984. Published by Elsevier Ltd.)

Increased production of commercial goat milk in Ontario stimulated an investigation to determine a base freezing point for goat milk for quantifying added water. A method also was developed for detection and estimation of degree of adulteration of goat milk with bovine milk. The mean freezing point based on 228 fresh herd samples of goat milk taken over 1 yr was -.5527 degrees C (-.5719 degrees H). This mean was used to generate an added water table. A simple and direct polyacrylamide disc gel electrophoretic method was devised to determine semi-quantitatively bovine milk adulteration down to 5%. Both of these methods are currently in use for routine monitoring of goat milk adulteration in the province of Ontario.

The Mojonnier method was compared with the conventional Soxhlet method for the determination of fat in 7 different meat products to assess its use as a standard reference method for calibration of commercial quantitative infrared transmission analyzers (e.g., Multispec M, Milkoscan 300 or 104). Results for the meat samples obtained by the Mojonnier method did not differ significantly from those obtained by the Soxhlet method. In addition, the Mojonnier method was less time-consuming and more precise than the Soxhlet; therefore, it can be used as a standard reference procedure for the calibration and assessment of infrared milk analyzers in their potential application to the rapid determination of fat in meat and meat products.

The effect of switching individual cow Record of Performance milk samples from on-farm Babcock analytical system to centralized infrared analysis was investigated. The effects of lipolytic activity on the signals of the fat (5.73/5.58 and 3.48/3.56 microns) and protein (6.46/6.68 microns) wavelengths of filter instruments showed that lipolysis decreased the infrared fat signal and concurrently increased the protein signal. The chain length (3.48/3.56 microns) signal was unaffected by lipolysis due to the concordant movement of the reference wavelength baseline with the changes in the sample wavelength signal. Storage trials (3 d) of preserved milk samples indicated no direct relation between fat signal depression and chemically determined free fatty acid levels. Microbial growth and agitation also contributed to changes observed in samples studied under controlled conditions. Based on concurrent infrared, Babcock, and Mojonnier analyses of approximately 900 samples on d 1 and 3, there was a consistent but marginal drop in the carbonyl (5.73/5.56 microns) fat signal and an increase in the amide (6.46/6.68 microns) protein signal, but these changes were of limited significance. A study of 3-d and older samples indicated that significant levels of acid were produced, indicative of microbial growth. A comparison of Babcock results carried out on-farm, Mojonnier analyses in the laboratory, and their corresponding infrared results did not show statistically significant differences. Other than the inherent variability present in the individual cow samples, there were minor quality changes occurring under the present sample handling system due to a combination of lipolysis, microbial growth, and acid production. Refrigeration of Record of Performance samples during transport and at the central laboratory is recommended to minimize these changes.

An investigation was undertaken to determine whether ammonium ion could be quantitated in aqueous solution by using commercially available infrared filter instruments such as the Multispec M1 analyzer. Ammonium salt solutions were scanned using an infrared spectrophotometer modified specifically to facilitate the study of aqueous systems and were shown to have 2 main absorption bands at 3.49 microns (2865 cm-1) and 6.89 microns (1451 cm-1). The 3.49 microns band did not correspond to any individual band noted in the literature and was concluded to be a composite of fundamental bands and Fermi resonances due to hydrogen bonding affecting the ion in solution. The response of the 6.89 microns band to NH4+ concentration was approximately twice that of the 3.49 microns band, and quantitation of the ammonium ion was assessed by the dual wavelength method as employed in filter-based commercial infrared analyzers. Good quantitation was obtained using 5.56 microns as a reference wavelength, and the slope of the standard curve of ammonium sulfate was not significantly affected by pH in the pH 3-8 region. A 6.86 microns sample filter and a 5.56 microns reference filter were installed in a Multispec M1 analyzer and a linear response was obtained for concentrations of up to 0.6% ammonium sulfate. Accurately weighed samples of ammonium sulfate were converted to ammonia by using the micro-Kjeldahl procedure and then distilled into standard acid, diluted to volume, and assessed by titration and transmission infrared analysis. The infrared method was more accurate than the titration method in replicating the initial weights.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of infrared absorption by the use of a CH stretch filter which isolates wavelengths in the order of 3.4-3.5 microns has been suggested as a replacement for the conventional carbonyl stretch absorption measurement or as an additional measurement for the estimation of fat in aqueous fat emulsions. To determine the merits of this CH stretch measurement, a study was conducted with a series of natural fats selected for their differences in average molecular weight, fatty acid composition, and degree of unsaturation. In this study, the use of the CH stretch filter, the C = O stretch filter, or the combination thereof could predict the fat content with equal accuracy if the fat was consistent in average molecular weight and degree of unsaturation. For a fat which varied in its degree of unsaturation, the CH filter measurement could be used in conjunction with the iodine value to produce accurate results. The combination C = O filter, CH filter, and the iodine value produced the most accurate results when the intent was to analyze a variety of fats on a single calibration.

The reaction kinetics of microbial destruction in food products are generally determined by the Thermal Death Time method (TDT), while chemical changes have traditionally been calculated by the more widely accepted Arrhenius approach. These two methods do not reconcile mathematically, and simply stated, one is the inverse of the other. It was of interest therefore to consider the relationship of these methods relative to each other on a mathematically simulated and experimental basis. The kinetic parameters of Saccharomyces uvarum were determined experimentally and used to calculate simulated processes in accordance to the relationships dictated by the TDT and Arrhenius models. The simulation results indicated a discrepancy between the methods, the Arrhenius approach requiring about 16% more time to complete a process. Based on five processing trials carried out using S. uvarum the actual process times were compared to those predicted by the TDT and Arrhenius methods. The Arrhenius method predicted the correct process times on the average, while the TDT predictions were short by about 8% in terms of time. From a microbiological standpoint, these differences are not likely to be singificant, however, they may be important if the TDT method is used to characterize the kinetic parameters of more rigerously defined chemical systems.