L- and D-stereoisomers of amicetose were generated by combining sugar biosynthesis genes from four different antibiotic gene clusters and both sugars were transferred to the elloramycin aglycone by the sugar flexible ElmGT glycosyltransferase. 相似文献
Arrowroot starch (AA)-based films incorporated with a carnauba wax nanoemulsion (CWN), cellulose nanocrystals (CNCs), and essential oils (EOs) from Mentha spicata (MEO) and Cymbopogon martinii (CEO) were produced using the casting technique and then characterized in terms of their water barrier, tensile, thermal, optical, and microstructural properties and in vitro antifungal activity against Rhizopus stolonifer and Botrytis cinerea. Whereas the incorporation of CNCs decreased the moisture content and water vapor permeability of the AA/CWN/CNC film, the additional incorporation of either EO decreased the transparency and affected the microstructure of the AA/CWN/CNC/EO nanocomposites. MEO and CEO incorporation improved the thermal stability of the films and provided excellent protection against fruit-spoiling fungi. Because of their excellent barrier properties against fungal growth, water vapor permeability, and ultraviolet and visible light, these AA/CWN/CNC/EO films have promising potential for application as active food packaging or coating materials.
Xylitol is a sweetener with important technological properties like anticariogenicity, low caloric value, and negative dissolution
heat. Because it can be used successfully in food formulations and pharmaceutical industries, its production is in great demand.
Xylitol can be obtained by microbiological process, since many yeasts and filamentous fungi synthesize the xylose reductase
enzyme, which catalyses the xylose reduction into xylitol as the first step in the xylose metabolism. The xylitol production
by biotechnological means has several economic advantages in comparison with the conventional process based on the chemical
reduction of xylose. The efficiency and the productivity of this fermentation chiefly depends upon the microorganism and the
process conditions employed. In this mini-review, the most significant upstream parameters on xylitol production by biotechnological
process are described. 相似文献
We present the analysis of an interior-point method to decide feasibility problems of second-order conic systems. A main feature of this algorithm is that arithmetic operations are performed with finite precision. Bounds for both the number of arithmetic operations and the finest precision required are exhibited. 相似文献
A KSr2Nb5O15 nanopowder was synthesized by a chemical route based on a modified polyol method. The nanopowder exhibits the space group P4bm (ferroelectric) ascribed to the displacement of Nb from the central position of an [NbO6] octahedron, parallel to the c-axis (polarization axis). The magnitude of the niobium off-center, ∆z, was determined by X-ray diffraction and mid-infrared spectroscopy (FTIR). Analysis of the infrared spectrum carried out using curve fitting based on Gaussian functions has revealed a very strong vibration at 413 cm–1, ascribed to a bond of the Nb off-center with apical oxygen. A classical molecular theory was applied to derive the force constant of this bond from the vibrational frequency. Using the calculus of energies for the wavelength and the harmonic oscillator, we alternatively derived the ∆z parameter. 相似文献
In this paper we define a new condition number ?(A) for the following problem: given a m by n matrix A, find x∈ℝn, s.t. Ax<0. We characterize this condition number in terms of distance to ill-posedness and we compare it with existing condition
numbers for the same problem.
Received: November 5, 1999 / Accepted: November 2000?Published online September 17, 2001 相似文献
We investigate the physical meaning of some of the texture zeros which appear in most of the ansatzes on leptonic masses and their mixing. It is shown that starting from arbitrary lepton mass matrices and making suitable weak basis transformations one can obtain some of these sets of zeros, which therefore have no physical content. We then analyse four-zero texture ansatzes where the charged lepton and neutrino mass matrices have the same structure. The four texture zeros cannot be obtained simultaneously through weak basis transformations, so these ansatzes do have physical content. We show that they can be separated into four classes and study the physical implications of each class. 相似文献