Pasting,thermal, gel texture,resistant starch and colour properties of unripe banana flour from 10 desert banana varieties cultivated in South Africa

Unripe banana flour is a potential commercial ingredient in various food products for increased resistant starch and reduced gluten contents. In the present study, the pasting (rapid visco-analysis), gel texture (penetration test), thermal (differential scanning calorimetry), colour (tri-stimulus colour indices) and the resistant starch properties of unripe banana flour produced from different dessert banana varieties (n?=?10) cultivated in South Africa, were analysed and juxtaposed to wheat and maize flour. The functional properties varied significantly (p?≤?0.05) between banana varieties, and from wheat and maize flours, to various extents. Selected functional property ranges of unripe banana, wheat and maize flours, respectively included; flour colour index (63.16–76.42, 77.34 and 80.96), paste viscosity (405.5–556.6, 124.7 and 115.6 RVU), gelatinization temperature (64.67–71.21, 71.11 and 69.95?°C), gel firmness (7.24–11.44?×?10^??2 N, 3.49?×?10^??2 N and 6.56?×?10^??2 N) and resistant starch content (19.9–47.4, 2.8 and 2.2% w/w). Multivariate analysis (principle component analysis) showed that the unripe banana flours from different varieties were distinguished from each other based on the pasting temperature. The unripe banana flours were distinguished from both wheat and maize flour based on breakdown and peak paste viscosities. The breakdown viscosity was the most positively related measure to the resistant starch content with a linear regression R-squared value of 0.898, indicating a significant role played by granule structure in resistance to enzymatic hydrolysis. The present research demonstrates that selection of appropriate dessert banana variety is important when replacing staple flours (wheat and maize) with unripe dessert banana flour as a functional ingredient.     

Electro-mechanical analysis of the audible noise of an inverter-fedsquirrel-cage induction motor

The audible noise emitted by a three-phase squirrel cage induction motor fed by a frequency inverter is determined by the electromagnetic and mechanical behavior of the components of the drive. A computerized analysis method is described that uses theoretical and experimental data for predicting the audible noise spectrum components. Starting from the inverter voltage and the motor data, the electromagnetic forces are predicted and analyzed. The mechanical natural frequencies are considered, either in a theoretical (finite element calculation) or in an experimental (modal analysis) methodology, to predict the vibrational behavior of the machine. The scheme contains the following steps: analysis of the frequency spectrum of the inverter used; synthesis of the magnetic force spectrum accounting for the motor data: calculation or measurement of the resonant data of the stator assembly; and comparison of the force spectrum and the resonant data. These various steps are discussed     

Modelling the effect of superatmospheric oxygen concentrations on in vitro mushroom PPO activity

The kinetics of polyphenol oxidase (PPO, EC 1.14.18.1) with respect to oxygen concentrations from 5 to 100% using chlorogenic acid (CGA) as substrate was examined. In vitro mushroom PPO activity was determined by measuring the consumption of oxygen during the oxidation reaction. A differential Michaelis–Menten model was fitted to the obtained total depletion curves. The product concentration as well as the concentration of oxygen had a clear inhibitory effect on the reaction rate. However, the inhibitory effect of oxygen was more evident at low product concentration. A linear mixed inhibition model that considered both the product (oxidised CGA) and oxygen as inhibitors was developed. A model with the product as a competitive inhibitor and oxygen as an uncompetitive inhibitor was the most appropriate to explain the reaction kinetics. The values of the inhibition constants calculated from the model were 0.0032 mmol L⁻¹ for K_m (Michaelis–Menten constant related to oxygen), 0.023 mmol L⁻¹ for K_mc (constant for competitive inhibition due to the product), 1.630 mmol L⁻¹ for K_mu (constant for uncompetitive inhibition due to oxygen) and 1.77 × 10⁻⁴ mmol L⁻¹ s⁻¹ for V_max (maximum reaction rate). The results indicate that superatmospheric oxygen concentrations could be effective in preventing enzymatic browning by PPO. Copyright © 2006 Society of Chemical Industry     

Predictive modelling and validation of Listeria innocua growth at superatmospheric oxygen and carbon dioxide concentrations

The effect of superatmospheric oxygen and carbon dioxide concentrations on the growth of Listeria innocua, which was used as a model organism for the pathogen Listeria monocytogenes, was evaluated. The bacteria were grown on a nutrient agar surface at 7 degrees C. Three carbon dioxide levels (0%, 12.5% and 25%) were combined with different levels of high oxygen concentrations (above 20%) based on a mixture design. The applied oxygen concentrations did not significantly influence the growth. High CO2 concentrations, on the contrary, reduced the maximum specific growth rate and prolonged the lag time. An overall model to describe the growth of L. innocua under high carbon dioxide conditions was constructed based on nine growth experiments, using a weighted one-step regression procedure. The influence of carbon dioxide on lag time and maximum specific growth rate was described using Ratkowsky-type models and inserted in the Baranyi equation. The model described the growth very well. To assess the validity of the model, 14 additional experiments were carried out. There was a good correlation of the model predictions and observed validation data.     

Technique for finding the optimum geometry of electrostaticmicromotors

This paper presents a computer-based method for finding the optimum geometry of very small electrostatic motors based on the variable capacitance principle. Not only is the geometry taken into account, but different excitation schemes are studied, in order to find the maximum average output torque and/or the minimum vibration component in the output torque. Different combinations of stator and rotor poles are treated. The most important part of this optimization is automation of the procedure. For the actual calculation of the electrostatic field distribution, the finite-element method is used. The mesh generation for the machine as a function of the rotor position and the design parameters is automated. The extraction of the torque and capacitance values is done in batch procedure, constructed around a commercial finite-element CAD package. This automation makes the system an optimization tool of an otherwise very tedious technique     

Engineering An Experimental Platform For High Throughput Reactivity Screening

The genomics revolution coupled to advances in computational power, informatics and robotics is driving drug discovery programs to produce drug candidates faster. This need has resulted in advances in high throughput methods for performing organic chemistry such as combinatorial and parallel synthesis. Yet there has not been a corollary advance in the ability to collect quantitative information on reactions that can be used to produce these drug candidates. This lack of an efficient and robust analytical method has resulted in a significant chemistry bottleneck. This work outlines a set of methods that helps address this chemistry bottleneck by using analytical constructs to detect and quantify reaction outcomes. To accomplish this, an integrated experimentalcheminformatics platform has been developed which couples an experimental design system, automated high throughput parallel and combinatorial synthesis methodology, sample processing, quantitative mass spectroscopy and automated data analysis. This platform is being used to optimize single reactions and the syntheses of whole libraries of compounds, and to generate large databases on specific reaction classes.     

Calculation of the flux density and the unbalanced pull in two pole induction machines

Contents In this paper, the relationship between the homopolar flux generated by a statically eccentric rotor and the unbalanced magnetic pull in two-pole induction motors is considered. We will show that due to this kind of eccentricity, a homopolar flux is generated having the supply frequency, yielding a vibrational component of the unbalanced magnetic pull with the double supply frequency.

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Die Ermittlung der Induktionsverteilung und der Radialkräfte in zweipoligen Asynchronmaschinen

Übersicht In der vorliegenden Arbeit wird auf die Verknüpfung der Unipolarflüsse mit den Radialkräften bei 2poligen Drehstromasynchronmaschinen näher eingegangen. Es wird nachgewiesen, daß sich bei statisch exzentrischer Verlagerung des Läufers in zweipoligen Drehstromasynchronmaschinen netzfrequente Unipolarflüsse ausbilden können, die Rüttelkräfte von doppelter Netzfrequenz zur Folge haben.

     

Analysis of the requirements for class II-restricted T cell recognition of a single determinant reveals considerable diversity in the T cell response and degeneracy of peptide binding to I-Ed

The amino acid sequences recognized by five I-E(d)-restricted and one E alpha A beta d-restricted murine T cell clones were determined. The clones had been raised to a synthetic peptide representing amino acids 305-328 of influenza virus hemagglutinin. It was found that although all of the T cell clones recognized a single 10-residue region of the peptide, 307KYVKQNTLKL316, different clones could recognize minimal ("core") determinants spanning 8, 9, or 10 of these amino acids. To see whether particular amino acids within the sequence 307-316 were universally important for T cell recognition, the six clones were assayed for their ability to tolerate single amino acid substitutions of the 10 residue peptide. In all, 190 analogues of the peptide in which each amino acid in the sequence was replaced, in turn, by each of the other 19 naturally occurring amino acids were tested. It was shown that 1) the six T cell clones had very different requirements for recognition of the peptide, 2) substitutions at every single position within the peptide could be shown to affect recognition in a T cell-specific manner, and 3) every single position within the peptide could be replaced by a large number of amino acids and still be recognized by at least one T cell clone. These results demonstrate the great diversity exhibited by the T cell repertoire in recognizing a 10-amino acid determinant, as well as the degeneracy of peptide binding to I-E(d).