Detection and quantification of pentosidine in foods

 Pentosidine, a crosslink amino acid in which one arginine and one lysine residue are linked together by a pentose, has been detected in foods for the first time using ion-exchange chromatography with direct fluorescence detection and subsequent ninhydrin derivatization. The method allows the simultaneous quantification of pentosidine along with all other amino acids of acid hydrolyzates at levels lower than 50 μg kg protein. Levels of pentosidine in all food samples investigated were very low (milk products between not detectable and 2–5 mg/kg protein; roasted coffee and some bakery products up to 35 mg/kg protein), indicating that pentosidine does not play a major part in the polymerization of food proteins. Received: 26 March 1996     

Chemopreventive effects of tea in prostate cancer: green tea versus black tea

The polyphenol compositions of green tea (GT) and black tea (BT) are very different due to post-harvest processing. GT contains higher concentrations of monomeric polyphenols, which affect numerous intracellular signaling pathways involved in prostate cancer (CaP) development. BT polymers, on the other hand, are poorly absorbed and are converted to phenolic acids by the colonic microflora. Therefore, after consumption of GT, higher concentrations of polyphenols are found in the circulation, whereas after BT consumption the phenolic acid levels in the circulation are higher. The majority of in vitro cell culture, in vivo animal, and clinical intervention studies examine the effects of extracts of GT or purified (-)-epigallocatechin-3-gallate (EGCG) on prostate carcinogenesis. These studies provide strong evidence supporting a chemopreventive effect of GT, but results from epidemiological studies of GT consumption are mixed. While the evidence for a chemopreventive effect of BT is much weaker than the body of evidence with regard to GT, there are several animal BT intervention studies demonstrating inhibition of CaP growth. This article will review in detail the available epidemiological and human clinical studies, as well as animal and basic mechanistic studies on GT and BT supporting a chemopreventive role in CaP.     

Bestandsaufnahme zum Vorkommen von Lysinoalanin in milcheiwei?haltigen Lebensmitteln

Zusammenfassung Mit einer verbesserten Analysen-methode wurde in ca. 350 milcheiweißhaltigen Lebensmittelproben des Handels Lysinoalanin (LAL) spezifisch und quantitativ bestimmt. Das Gros der Proben stammte aus dem mitteleuropäischen Raum. In Rohmilch und pasteurisierten Milchprodukten war LAL nicht nachweisbar. UHT-Produkte (Milch, Milcherzeugnisse, Sahne) enthielten in der Regel kaum LAL, Erzeugnisse mit 60 ppm LAL im Protein waren nachweislich stärker wärmebelastet worden als allgemein üblich. Ungezuckerte Kondensmilch enthielt durchschnittlich 150 bis 250 ppm LAL, in gezuckerter Kondensmilch wurde LAL meist nur in Spuren bis etwa 40 ppm gefunden. Autoklavierte Flüssigprodukte wie Sterilmilch, Kaffeesahne und vor allem Babymilch-Formulakost wiesen 200–1160 ppm LAL im Eiweiß auf, wodurch zum Teil intensive Eiweißschädigung indiziert wurde. Die große Schwankungsbreite im LAL-Gehalt dieser Produktgruppe war in erster Linie auf unterschiedliche Temperaturbelastungen und Erhitzungszeiten zurückzuführen. Die Herstellung von Milch- und Molkenpulver, Säure- und Labcasein, Käse und Käseprodukten, sowie Baby-Milchformulanahrung in Pulverform führte zu keiner nennenswerten LAL-Bildung. Caseinate und Kopräzipitate zeigten stark streuende Werte von 0 bis 1530 ppm LAL im Eiweiß. Caseinate, die mit Carbonat- und Citratsalzen oder durch vorsichtige stufenweise Zugabe von Natronlauge unter ständiger pH-Kontrolle (pH < 8) aufgeschlossen wurden, enthielten maximal 250 ppm LAL im Eiweiß. Direkte Zugabe von Natronlauge und Temperaturen über 100 °C führen zu hohen LAL-Werten. Zahlreiche untersuchte Lebensmittel mit Milcheiweißzusatz (z. B. Schlagcremepulver, Kaffeeweißer, Desserteremepulver) zeigten stark differierende LAL-Mengen von 0 bis 1300 ppm, hoher LAL-Gehalt ist dabei in der Regel auf die Verwendung stark alkalibehandelter Caseinate zurückzuführen. In diätetischen Eiweißkonzentraten (z. B. Formuladiät), die granuliertes Casein-oder Molkeneiweiß enthielten, wurden LAL-Mengen bis zu 1 180 ppm gefunden. Einige Schaumproteine auf der Basis von partiell alkalihydrolysiertem Milcheiweiß wiesen extrem hohe LAL-Mengen bis zu 53 000 ppm auf und enthielten zum Teil auch freies LAL. In allen anderen Lebensmitteln kommt LAL anscheinend nur proteingebunden vor.

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Study on the occurrence of lysinoalanine in food which contain milk proteins

Summary In 350 commercial samples of food and food ingredients containing milk protein lysinoalanine (LAL) was determined by an improved method. Most of the samples originated from the central European market. LAL was not detectable in fresh milk and pasteurized milk products. Ultra-High-Temperature(UHT)-products (milk, mixed milk and cream) generally did not contain LAL, samples with 60 ppm LAL i.p. (i.p. = in the protein) evidently had been heat treated to a greater extent than usual. In unsweetened evaporated and condensed milk LAL was present at an average of 150 ppm to 250 ppm i.p., whereas in most sweetened condensed milk samples there were only from traces up to 40 ppm LAL. Autoclave sterilized products such as sterilized milk, coffee cream and above all liquid infant milk formulas contained 200 to 1,160 ppm LAL i.p., the higher levels indicating intensive protein damage. The wide range of LAL in these samples was attributed to the diverse heat treatment — both in temperature and time. The production of powdered milk and whey, acid and rennet casein, cheese and cheese products as well as powdered infant milk formulas induced no appreciable LAL formation. LAL-levels in caseinates and coprecipitates diverged widely (0–1,530 ppm LAL i.p.). Conversion of casein curd into caseinate dispersion by carbonate and citrate salts or by a careful and gradual addition of hydroxide led to maximum LAL-levels of 250 ppm i.p. High LAL values resulted from direct addition of hydroxide and temperatures above 100 °C. In numerous food samples containing milk protein as an ingredient (e.g. whipped topping mix, coffee creamer, dessert cream) the degree of LAL varied from 0 to 1,300 ppm i.p.; the high values were attributed to the use of strong alkali treated cascinates. In dietetic protein concentrates (e.g. formula diet) containing granulated casein or whey protein LAL was found in relatively large amounts up to 1,180 ppm i.p. Some whipping agents from partially alkali hydrolyzed milk protein showed extremely high levels of LAL up to 53,000 ppm i.p. and some of the samples contained also free LAL. In all other kinds of food LAL seems to be exclusively present as protein-bound LAL.

     

Closed-form inverse kinematics of 6R milling robot with singularity avoidance

For a 6R milling robot, it is necessary to convert the postprocessing cutter locations (CL) into the robot’s revolute joint variables. This paper introduces an algorithm for calculating the forward and inverse kinematics of a 6R robot according to the CL data generated by conventional CAD/CAM systems. A redundant mechanism is analyzed to avoid the singular configurations and joint limits. The Denavit–Hartenberg (D–H) convention is referred to for developing the forward kinematics, and a closed-form solution of the inverse kinematics is presented by means of kinematic decoupling. A fundamental approach with modifying factor for avoiding singularity are developed with regard to three-axis and five-axis CL data. A gap bridging strategy is applied to reduce the jerk motion caused by tool retraction and cut paths connection. Finally, the result is conducted to simulation and machining test to verify the algorithms.     

Studies on the Effect of Physico‐Chemical Soot Properties and Feed Gas Composition on the Kinetics of Soot Oxidation on Fe2O3 Catalyst

Three commercial carbon black samples as well as self‐made C₃H₆ soot were investigated for their reactivity in the oxidation on an α‐Fe₂O₃ catalyst. These studies were performed by temperature programmed oxidation (TPO) using a packed bed. For reference purposes, TPO studies in the absence of the catalyst were made as well. The carbon black samples were characterized towards the content of C, H, N and O as well as higher heating value, specific surface area, moisture and volatile matter and were deemed to be suitable model substances for diesel soot of different maturity. The correlation of these physico‐chemical properties with the kinetics in catalytic TPO indicated that the soot oxidation on Fe₂O₃ is significantly affected by the initial number of surface oxygen compounds of the soot. The decomposition of these surface species causes the formation of active carbon sites, which are supposed to accelerate the soot oxidation.     

Synthesis of random or tapered solution styrene–butadiene copolymers in the presence of sodium dodecylbenzene sulfonate as a polar modifier

Random or tapered solution styrene–butadiene copolymer (SSBR) is very difficult to prepare in an isothermal batch process without the use of polar modifiers because of the diverse reactivity ratios of the styrene and the butadiene in hydrocarbon solvents. In the presence of polar modifiers, the random SSBR can be synthesized by anionic living polymerization with the variety of microstructures, which results in the change of glass transition temperature (T_g). This article will discuss the use of sodium dodecylbenzene sulfonate as a polar modifier in isothermal batch process that controls the microstructure of the SSBR resulting in a random as well as tapered SSBR with low T_g (?67°C to ?80°C). The T_g of SSBR was controlled by the styrene content rather than the microstructure of polybutadiene. Physical properties of SSBR compounding were discussed for tire tread applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Uncertainty assessment in friction factor measurements as a tool to design experimental set-ups

The promising performance of microchannels has given rise to intensive research on pressure drop and heat transfer characteristics of flows at the small scale. To check the classical models and to validate new ones, experiments need to be conducted, which are particularly difficult given the characteristic dimensions involved and the magnitude of the fluxes to be measured. Although more care has been devoted lately to the design of experiments in terms of control of the geometry and of the boundary conditions, the uncertainties which inevitably affect each measurement do not seem to have been given the proper consideration. Correctly calculating uncertainties not only allows a correct assessment of the experimental data obtained, but can also be used to decide which measurements need to have the highest precision to achieve a certain accuracy, thus saving money on the others. In this paper, a quantitative criterion is given to assess the accuracy achievable in the determination of the friction factor in the laminar regime for the flow of a fluid in a circular microtube. The influence of the six quantities (pressure drop, outlet pressure, temperature, length, diameter and volume flow rate) measured to determine f in the laminar regime are studied separately and when combined. It is found that at low Reynolds numbers flow rate and pressure drop measurements are determinant for the final value of the uncertainty, while at larger Reynolds numbers the influence of the accuracy in measuring the hydraulic diameter prevails and also limits the minimum value that the total uncertainty can take.     

A novel self-aligned fabrication process for microwave static induction transistors in silicon carbide

A novel multiple-self-aligned fabrication process is developed for recessed gate microwave static induction transistors (SITs) in silicon carbide (SiC). This process is demonstrated by fabricating 4H-SiC SITs having record f/sub T/ of 7 GHz.     

Operating strategy for a hydrogen engine for improved drive-cycle efficiency and emissions behavior

Due to their advanced state of development and almost immediate availability, hydrogen internal combustion engines could act as a bridging technology toward a wide-spread hydrogen infrastructure. Extensive research, development and steady-state testing of hydrogen internal combustion engines has been conducted to improve efficiency, emissions behavior and performance. This paper summarizes the steady-state test results of the supercharged hydrogen-powered four-cylinder engine operated on an engine dynamometer. Based on these results a shift strategy for optimized fuel economy is established and engine control strategies for various levels of hybridization are being discussed. The strategies are evaluated on the Urban drive cycle, differences in engine behavior are investigated and the estimated fuel economy and NO_x emissions are calculated. Future work will include dynamic testing of these strategies and powertrain configurations as well as individual powertrain components on a vehicle platform, called ‘Mobile Advanced Technology Testbed’ (MATT), that was developed and built at Argonne National Laboratory.