Feasibility Study for a Chemical Process Particle Size Characterization System for Explosive Environments Using Low Laser Power.

The industrial particle sensor market lacks simple, easy to use, low cost yet robust, safe and fast response solutions. Towards development of such a sensor, for in-line use in micro channels under continuous flow conditions, this work introduces static light scattering (SLS) determination of particle diameter using a laser with an emission power of less than 5 µW together with sensitive detectors with detection times of 1 ms. The measurements for the feasibility studies are made in an angular range between 20° and 160° in 2° increments. We focus on the range between 300 and 1000 nm, for applications in the production of paints, colors, pigments and crystallites. Due to the fast response time, reaction characteristics in microchannel designs for precipitation and crystallization processes can be studied. A novel method for particle diameter characterization is developed using the positions of maxima and minima and slope distribution. The novel algorithm to classify particle diameter is especially developed to be independent of dispersed phase concentration or concentration fluctuations like product flares or signal instability. Measurement signals are post processed and particle diameters are validated against Mie light scattering simulations. The design of a low cost instrument for industrial use is proposed.

Characterization of volatile metabolites formed by molds on barley by mass and ion mobility spectrometry.

The contamination of barley by molds on the field or in storage leads to the spoilage of grain and the production of mycotoxins, which causes major economic losses in malting facilities and breweries. Therefore, on-site detection of hidden fungus contaminations in grain storages based on the detection of volatile marker compounds is of high interest. In this work, the volatile metabolites of 10 different fungus species are identified by gas chromatography (GC) combined with two complementary mass spectrometric methods, namely, electron impact (EI) and chemical ionization at atmospheric pressure (APCI)-mass spectrometry (MS). The APCI source utilizes soft X-radiation, which enables the selective protonation of the volatile metabolites largely without side reactions. Nearly 80 volatile or semivolatile compounds from different substance classes, namely, alcohols, aldehydes, ketones, carboxylic acids, esters, substituted aromatic compounds, alkenes, terpenes, oxidized terpenes, sesquiterpenes, and oxidized sesquiterpenes, could be identified. The profiles of volatile and semivolatile metabolites of the different fungus species are characteristic of them and allow their safe differentiation. The application of the same GC parameters and APCI source allows a simple method transfer from MS to ion mobility spectrometry (IMS), which permits on-site analyses of grain stores. Characterization of IMS yields limits of detection very similar to those of APCI-MS. Accordingly, more than 90% of the volatile metabolites found by APCI-MS were also detected in IMS. In addition to different fungus genera, different species of one fungus genus could also be differentiated by GC-IMS.

Contrast enhancement of surface layers with fast middle-infrared scanning.

In this study, we present an efficient and innovative method to visualize absorption differences in the mid-infrared range with spatial resolution using laser technology. We focus on only two lasers with wavelengths between 3.4 µm and 3.6 µm and a spatial resolution of 20 µm and thus achieve a scanning speed up to 300 kS/s for fast image generation. In this article, we focus especially on the detection of C-H bands in this region of the absorption spectrum. Concealed structures are examined by calculating the measured structures with both wavelengths. In our results, we demonstrate exemplary measurements on 130-µm-thick polyvinyl chloride layers. In turn, these structures are suitable for further processing in rapid quantitative quality control.

Effect of Malt-Derived Potential Antioxidants on Dimethyl Sulfide Oxidation.

During malt kilning, dimethyl sulfide (DMS) is partly oxidized to dimethyl sulfoxide (DMSO), which can be reduced by yeast to generate DMS during fermentation. The aim of this study was to test the effect of malt-derived potential antioxidants on DMS oxidation and to assess their applicability for DMSO minimization. In the presence of 18 µM copper, all tested antioxidants (250 µM) catalyzed DMS oxidation to deviating extents (sulfite > ascorbic acid (Asco) > gallic acid (GA) > L-cysteine (Cys) > L-glutathione (GSH)). Hydrogen peroxide was found as primary DMS oxidant for each substance except for sulfite. Electron spin resonance spectroscopy provided evidence for the formation of bisulfite radicals and peroxymonosulfate radicals, which are proposed as being capable of exhaustive DMS oxidation (∼100%) over a wide concentration. The data demonstrate that use of antioxidants per se cannot be suggested for the minimization of DMSO formation in malt and other foodstuffs. Potential shifts from pro- to antioxidative behavior of antioxidants and their implications on malt quality are discussed.

Non-contact Raman spectroscopy for in-line monitoring of glucose and ethanol during yeast fermentations.

The monitoring of microbiological processes using Raman spectroscopy has gained in importance over the past few years. Commercial Raman spectroscopic equipment consists of a laser, spectrometer, and fiberoptic immersion probe in direct contact with the fermentation medium. To avoid possible sterilization problems and biofilm formation on the probe tip, a large-aperture Raman probe was developed. The design of the probe enables non-contact in-line measurements through glass vessels or inspection glasses of bioreactors and chemical reactors. The practical applicability of the probe was tested during yeast fermentations by monitoring the consumption of substrate glucose and the formation of ethanol as the product. Multiple linear regression models were applied to evaluate the Raman spectra. Reference values were determined by high-performance liquid chromatography. The relative errors of prediction for glucose and ethanol were 5 and 3%, respectively. The presented Raman probe allows simple adaption to a wide range of processes in the chemical, pharmaceutical, and biotechnological industries.

Effect of l-Cysteine and Transition Metal Ions on Dimethyl Sulfide Oxidation.

During malt kilning, significant amounts of dimethyl sulfide (DMS) oxidize leading to the formation of dimethyl sulfoxide (DMSO), a precursor of DMS during fermentation. Yet, knowledge regarding reaction mechanisms of DMSO formation during malt production is limited. The role of thiols in sulfide oxidation is unclear as they possess sulfoxide reducing ability as well as pro- and antioxidative properties. This study investigated the effects of the thiol l-cysteine (Cys), molecular oxygen, transition metal ions, and EDTA on DMS oxidation in aqueous model solutions. Highest oxidative DMS consumption was observed when Cys was combined with iron(II) (∼12%) and copper(II) (∼40%). Response surface modeling (RSM) revealed that Cys together with copper(II) had a strictly prooxidative effect and no antioxidative behavior was found. Hydrogen peroxide, as generated via autoxidation of Cys-Cu(I)-Cys complexes, was supposed to be the primary DMS oxidant in this work. Based on redox kinetics, potential reaction mechanisms, and their impact on oxidative processes in thermal food processing, such as malt and beer production, are discussed.

Relevance of Oxygen for the Formation of Strecker Aldehydes during Beer Production and Storage.

Off-flavor in beer is often associated with the appearance of staling aldehydes. In this study, the factors amino acid concentration, carbohydrate concentration, Fe2+ concentration, and oxygen concentration were investigated in terms of their effect on the formation of carbonyl compounds during storage using response surface methodology. From all factors tested, only amino acid concentration and oxygen concentration promoted Strecker aldehyde formation during storage, while all other carbonyls measured were unaffected. A mixture of glucose/xylose, representing carbohydrate sources, as well as Fe2+ concentration were insignificant factors, though carbohydrate additions exhibited a significant role in the formation of 2-furfural. De novo formation of phenylacetaldehyde from phenylalanine during beer storage was observed using labeling experiments and a linear relationship between Strecker aldehydes formed and total packaged oxygen was identified. Capping beers with oxygen barrier crown corks and addition of 10 mg/L EDTA to beers effectively diminished Strecker aldehyde formation. Oxygen was additionally shown to significantly promote Strecker aldehyde formation during sweet wort production. A pathway for the reactive oxygen species-induced degradation of amino acids yielding Strecker aldehydes was proposed and was further scrutinized in buffered model solutions. The insignificant role of Fe2+ in the response surface experiments is discussed.

Characterization of the Migration of Hop Volatiles into Different Crown Cork Liner Polymers and Can Coatings.

Absorption of hop volatiles by crown cork liner polymers and can coatings was investigated in beer during storage. All hop volatiles measured were prone to migrate into the closures, and the absorption kinetics was demonstrated to fit Fick's second law of diffusion well for a plane sheet. The extent and rate of diffusion were significantly dissimilar and were greatly dependent upon the nature of the volatile. Diffusion coefficients ranged from 1.32 × 10(-5) cm(2)/day (limonene) to 0.26 × 10(-5) cm(2)/day (α-humulene). The maximum amounts absorbed into the material at equilibrium were in the following order: limonene > α-humulene > trans-caryophyllene > myrcene ≫ linalool > α-terpineol > geraniol. With the application of low-density polyethylene (LDPE) liners with oxygen-scavenging functionality, oxygen-barrier liners made up from high-density polyethylene (HDPE) or liner polymers from a different manufacturer had no significant effect on the composition of hop volatiles in beers after prolonged storage of 55 days; however, significantly higher amounts of myrcene and limonene were found in the oxygen-barrier-type crown cork, while all other closures behaved similarly. Can coatings were demonstrated to absorb hop volatiles in a similar pattern as crown corks but to a lesser extent. Consequently, significantly higher percentages of myrcene were found in the beers.

Biochemical heterogeneity of malt is caused by both biological variation and differences in processing: I. Individual grain analyses of biochemical parameters in differently steeped barley (Hordeum vulgare L.) malts.

Using individual grain analyses, the degree of inherent biological variation in germinating barley seeds has been established. Even under homogenous laboratory conditions, the activities of the germination-related enzymes α-amylase, ß-amylase and ß-glucanase varied by a factor of two to three. The comparison with single grain analyses of different industrially produced malts (steeping systems without aeration, with air suction and pressurised aeration) revealed that the heterogeneity of these malts nearly tripled. This increase may be due to the gradients in O2 and CO2 that arise in large industrial steeping vessels. The most homogenous malting in the industrial systems was achieved without any aeration during steeping. Therefore, to improve homogeneity, the common practise of steep aeration should be omitted. Germination progression was quite different within the three exhaustively aerated attempts, which indicated that gaseous composition was not the only factor affecting germination progression.

Formation of styrene dependent on fermentation management during wheat beer production.

Styrene is formed by the thermal decarboxylation of cinnamic acid during wort boiling or by enzymatic decarboxylation during fermentation. The enzymatic reactions proceed in parallel to the decarboxylation of ferulic- and p-cumaric acid to 4-vinylguaiacol and 4-vinylphenol by the same decarboxylase enzyme. However, the formation of styrene occurs much faster and all available cinnamic acid in wort was converted completely within a few hours. Moreover, the comparison of various manufacturing parameters shows that a higher fermentation temperature of 25 °C compared to 16 °C and an open fermentation management lead to a rapid decrease of styrene. This allows minimising the content of styrene in beer while maintaining the typical wheat beer flavours.

Application of a short intracellular pH method to flow cytometry for determining Saccharomyces cerevisiae vitality.

The measurement of yeast's intracellular pH (ICP) is a proven method for determining yeast vitality. Vitality describes the condition or health of viable cells as opposed to viability, which defines living versus dead cells. In contrast to fluorescence photometric measurements, which show only average ICP values of a population, flow cytometry allows the presentation of an ICP distribution. By examining six repeated propagations with three separate growth phases (lag, exponential, and stationary), the ICP method previously established for photometry was transferred successfully to flow cytometry by using the pH-dependent fluorescent probe 5,6-carboxyfluorescein. The correlation between the two methods was good (r(2) = 0.898, n = 18). With both methods it is possible to track the course of growth phases. Although photometry did not yield significant differences between exponentially and stationary phases (P = 0.433), ICP via flow cytometry did (P = 0.012). Yeast in an exponential phase has a unimodal ICP distribution, reflective of a homogeneous population; however, yeast in a stationary phase displays a broader ICP distribution, and subpopulations could be defined by using the flow cytometry method. In conclusion, flow cytometry yielded specific evidence of the heterogeneity in vitality of a yeast population as measured via ICP. In contrast to photometry, flow cytometry increases information about the yeast population's vitality via a short measurement, which is suitable for routine analysis.