How Do Xanthan and Hydroxypropyl Methylcellulose Individually Affect the Physicochemical Properties in a Model Gluten‐Free Dough?

To better understand the physicochemical changes imparted by hydrocolloids on gluten-free dough, 2 hydroxypropyl methylcelluloses (HPMCs) and xanthan gum were added at 2%, 3%, and 5% to rice cassava dough without the addition of alternative proteins. The formulated doughs were analyzed using thermoanalytic and rheological techniques to determine the role of water and subsequent flow behavior upon hydrocolloid addition. The baked loaves were then measured for specific loaf volume and tensile strength to determine bread quality. Thermogravimetric analysis (TGA) results revealed that hydrocolloid-added dough held water more tightly than the rice cassava control with an additional water distribution at 85 to 88 °C. Rheologically, the increase of elastic moduli in the low methoxy HPMC and xanthan-added dough became more pronounced with gum addition; however, both HPMC formulations had increased viscous moduli allowing the gas cells to expand without collapsing. In the bread, the final specific loaf volume increased with high methoxy HPMC (2% to 5%) and low methoxy HPMC (2%) but was depressed with increased addition of low methoxy HPMC (5%) and xanthan (3% and 5%). Crumb hardness was decreased in high methoxy HPMC loaves but was increased significantly in low methoxy HPMC (5%) and xanthan (5%) formulations. From the gums studied, it was concluded that high methoxy HPMC was the optimum hydrocolloid in the rice cassava gluten-free dough. PRACTICAL APPLICATION: Two types of hydrocolloids, xanthan gum and HPMC, were individually added to a gluten-free rice cassava formulation. Based on the thermoanalytic and rheological studies on dough, as well as the bread quality studies, high methoxy HPMC at 5% addition was determined to optimally improve the bread quality when only gum addition was considered. This study indicates the potential use of high methoxy HPMC as an additive in gluten-free bread formulations prior to considering alternative proteins.     

Synthesis of an ionic N-nitrosamine and a method for its determination in foodstuffs

Summary A model ionic N-nitrosamine (N-nitroso-N¹N¹-dimethylpiperazinium iodide) was synthesised in order to develop an appropriate analytical method for examining the possible incidence of this class of compounds in food. A procedure suitable for its analysis in biological samples is described and is based on preparation of an aqueous extract, ion-pair extraction into an organic solvent, separation by high-performance liquid chromatography and detection with a thermal-energy analyzer. The average recovery of the ionic N-nitrosamine from cured meat was 83% at 200 g/kg; the detection limit was 50 gm/kg. bei den Muskelproben nahezu 30% der mit Hilfe der

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Synthese eines Ionischen N-Nitrosamins und eine Methode für dessen Analyse in Lebensmitteln

Zusammenfassung Ein Modell eines ionischen N-Nitrosamins (N-Nitroso-N¹N¹-dimethylpiperaziniodid) wurde synthetisiert, um die entsprechende analytische Methode zur Prüfung des möglichen Auftretens von Verbindungen dieser Klasse in Lebensmitteln zu entwickeln. Es wird ein für die Analyse dieses Stoffes in biologischen Proben geeignetes Verfahren beschrieben, das auf der Zubereitung eines wäßrigen Extrakts, Ionenpaar-Extraktion in einem organischen Lösungsmittel, Trennung durch Hochleistungs-Flüssigkeitschromatographie und Nachweis mit Hilfe eines thermischen Energieanalysators beruht. Aus geräuchertem Fleisch mit einem Gehalt von 200 g ionischem N-Nitrosamin/kg wurden im Durchschnitt 83% des Stoffes extrahiert, die Methode hat eine Nachweisgrenze von 50 g/kg.

     

Does a two-year period of orthokeratology lead to changes in the endothelial morphology of children?

Purpose

To compare changes in endothelial morphology in the central and superior cornea in subjects wearing single-vision spectacles and orthokeratology lenses over two years.

A Comparison of the Work of Adhesion Obtained from Wetting and Vapor Adsorption Measurements

Some of the limitations to determining experimental values of the work of adhesion are discussed. Wetting measurements appear to provide the most direct means of assessing the work of adhesion for a solid-liquid system, but they require the formation of a finite contact angle by the liquid against the solid of interest, and the need for independent knowledge of the equilibrium spreading pressure of the liquid's vapor on the solid further limits their applicability. Vapor adsorption measurement using the technique of inverse gas chromatoraphy (IGC) provides a promising alternative means of determining the work of adhesion not subject to these limitations. The measurements are, furthermore, amenable to solids which are difficult to use with wetting measurements, e.g., those which are porous or granular. An attempt is made here to compare values of the work of adhesion determined using both wetting and vapor adsorption measurements. Good agreement is attained between the two methods for diiodomethane in contact with poly (vinyl chloride), poly (methyl methacrylate), and chemi-thermo-mechanical wood pulp fibers, suggesting that the technique of IGC is particularly well-suited for rapid determination of the work of adhesion.     

Epidermal 1-O-acylceramides appear with the establishment of the water permeability barrier in mice and are produced by maturating keratinocytes

1-O-Acylceramides (1-OACs) have a fatty acid esterified to the 1-hydroxyl of the sphingosine head group of the ceramide, and recently we identified these lipids as natural components of human and mouse epidermis. Here we show epidermal 1-OACs arise shortly before birth during the establishment of the water permeability barrier in mice. Fractionation of human epidermis indicates 1-OACs concentrate in the stratum corneum. During in vitro maturation into reconstructed human epidermis, human keratinocytes dramatically increase 1-OAC levels indicating they are one source of epidermal 1-OACs. In search of potential enzymes responsible for 1-OAC synthesis in vivo, we analyzed mutant mice with deficiencies of ceramide synthases (Cers2, Cers3, or Cers4), diacylglycerol acyltransferases (Dgat1 or Dgat2), elongase of very long fatty acids 3 (Elovl3), lecithin cholesterol acyltransferase (Lcat), stearoyl-CoA desaturase 1 (Scd1), or acidic ceramidase (Asah1). Overall levels of 1-OACs did not decrease in any mouse model. In Cers3 and Dgat2-deficient epidermis they even increased in correlation with deficient skin barrier function. Dagt2 deficiency reshapes 1-OAC synthesis with an increase in 1-OACs with N-linked non-hydroxylated fatty acids and a 60% decrease compared to control in levels of 1-OACs with N-linked hydroxylated palmitate. As none of the single enzyme deficiencies we examined resulted in a lack of 1-OACs, we conclude that either there is functional redundancy in forming 1-OAC and more than one enzyme is involved, and/or an unknown acyltransferase of the epidermis performs the final step of 1-OAC synthesis, the implications of which are discussed.     

A Comparison of the Work of Adhesion Obtained from Wetting and Vapor Adsorption Measurements

Some of the limitations to determining experimental values of the work of adhesion are discussed. Wetting measurements appear to provide the most direct means of assessing the work of adhesion for a solid-liquid system, but they require the formation of a finite contact angle by the liquid against the solid of interest, and the need for independent knowledge of the equilibrium spreading pressure of the liquid's vapor on the solid further limits their applicability. Vapor adsorption measurement using the technique of inverse gas chromatoraphy (IGC) provides a promising alternative means of determining the work of adhesion not subject to these limitations. The measurements are, furthermore, amenable to solids which are difficult to use with wetting measurements, e.g., those which are porous or granular. An attempt is made here to compare values of the work of adhesion determined using both wetting and vapor adsorption measurements. Good agreement is attained between the two methods for diiodomethane in contact with poly (vinyl chloride), poly (methyl methacrylate), and chemi-thermo-mechanical wood pulp fibers, suggesting that the technique of IGC is particularly well-suited for rapid determination of the work of adhesion.     

Speciation analysis of arsenic in landfill leachate

As environmental impacts of landfill last from beginning of cell filling to many years after, there is an increasing interest in monitoring landfill leachate composition especially with regards to metals and metalloids. High-performance liquid chromatography (HPLC) coupled with inductively coupled plasma mass spectrometry (ICP-MS) has been applied to the speciation of arsenic in landfill leachates. The difficulty is related to the complexity and heterogeneity of leachate matrices. A soft sample preparation protocol with water dilution and filtration of leachates has proved to be sufficient for the achievement of identification and quantification of arsenic species without matrix effect. The cationic-exchange separation method developed has enabled the detection of six arsenic species (AsIII, MMA, AsV, DMA, AsB, TMAO) in different landfill leachates. The wide range of concentrations of arsenic species (from 0.2 to 250 microg As L(-1)) and their repartition illustrate the high variability of these effluents depending on the nature of the wastes, the landfill management, the climatic conditions and the degradation phase, to list a few. These results provide new information about the chemical composition of these effluents which is useful to better adapt their treatment and to achieve the risk assessment of landfill management.