Analysis of free amino acids in green coffee beans

To investigate amino acid changes in green coffee beans in the post-harvest period, amino acid concentrations were determined in green beans and after modelled drying, fermentation and storage. After the drying at alternating temperatures up to maximally 40°C, considerable changes in the concentrations of individual amino acids were identified. At the beginning of the storage period, significant changes in concentration were found to a minor extent. Under the condition of drying, it was mainly the concentration of glutamic acid that changed considerably. There was an increase in all the samples by 500 mg/kg dry matter on average, which corresponds to an increase of about 50% of the original value. In contrast, the concentration of aspartic acid in most of the samples decreased clearly due to drying. For the predominant part of the coffee samples, there was a significant increase in the hydrophobic amino acids Val, Phe, Ile and Leu. Changes of the quantities of other amino acids were non-uniform and only insignificant. Constant drying at 80°C for most of the amino acids brought about only minor concentration changes compared to those values obtained at 40°C. Modelled fermentation had no significant effect on the concentrations of the individual amino acids. After a 4-week storage of dried beans, amino acid concentrations did not change further. It is very possible that different post-harvest treatment parameters may influence the amount of aroma precursor compounds in the coffee beans.     

Effect of aromatic precursor addition to wine fermentations carried out with different Saccharomyces species and their hybrids

This work explores the ability of different yeast strains from different species of the genus Saccharomyces (S. cerevisiae, S. uvarum and S. kudriavzevii) and hybrids between these species to release or form varietal aroma compounds from fractions of grape odourless precursors. The de novo synthesis by the yeasts of some of the varietal aroma compounds was also evaluated. The study has shown that de novo synthesis affects some lipid derivatives, shikimic derivatives and terpenes in all species and hybrids, with some remarkable differences amongst them. The release or formation of aroma compounds from precursors was found to be strongly linked to the yeast or hybrid used, and the triple hybrid S. cerevisiae × S. bayanus × S. kudriavzevii in particular and secondarily the hybrid S. cerevisiae × S. bayanus were highly efficient in the production of most varietal aroma compounds, including γ-lactones, benzenoids, volatile phenols, vanillin derivatives and terpenols. The presence of precursors in the fermenting media caused a surprising levelling effect on the fermentative aroma composition. Altogether, these results suggest that it is possible to modulate wine aroma by employing different yeast species in order to create new wines with different aromatic notes.     

花椒叶提取物对烤牛肉饼杂环胺形成的影响

以牛肉和花椒叶为研究对象,研究花椒叶提取物（Zanthoxylum bungeanum Maxim. leaf extract,ZME）添加量（0.015%、0.030%、0.045%）对烤牛肉饼中杂环胺（heterocyclic amines,HAs）形成的影响。结果表明,与对照组相比,ZME能够显著抑制烤牛肉饼中总HAs的形成（P＜0.05）,对其最大抑制率为39.87%,但对不同种类HAs形成的影响不同。其中,添加0.045% ZME对2-氨基-1-甲基-6-苯基咪唑并[4,5-b]吡啶、2-氨基-3-甲基咪唑并[4,5-f]喹啉、2-氨基-3,4-二甲基咪唑并[4,5-f]喹啉、1-甲基-9H-吡啶并[3,4-b]吲哚和2-氨基-9H-吡啶并[2,3-b]吲哚的抑制率分别达到71.76%、78.02%、49.07%、35.82%和100%;而0.045% ZME却促进2-氨基-3,8-二甲基咪唑并[4,5-f]喹喔啉和9H-吡啶并[3,4-b]吲哚的形成。进一步分析ZME对烤牛肉饼中HAs前体物的影响,结果显示前体物的消耗随着ZME添加量的增加呈降低趋势,相关性分析表明HAs的形成与多种游离氨基酸的消耗显著相关。上述结果表明ZME能显著抑制烤牛肉饼中HAs的形成,为其提高加工食品安全性及更广泛的应用提供理论依据。     

Synthesis and polymer‐to‐ceramic conversion of tailorable copolysilazanes

Tailorable copolysilazanes (CPSZs) with variable chemical structure and molecular weights were prepared by coammonolysis of dichloromethylsilane, dichloromethylvinylsilane, and trichloromethylsilane. The as‐synthesized CPSZ was characterized by gel permeation chromatography, Fourier transformed infrared (FTIR) spectroscopy, and nuclear magnetic resonance spectroscopy. The CPSZ could be cured in an inert atmosphere at 180°C for 24 h. Pyrolysis behavior and structure evolution of the cured CPSZ were studied by means of thermal gravimetric analysis and FTIR. Hydrosilylation, transamination, dehydrogenation, and demethanation reactions were involved in the polymer‐to‐ceramic conversion of CPSZ. The ceramization process was complete at 900°C with a ceramic yield of 81–84%. Elemental analysis indicated that the compositions of final ceramics can be tailored by controlling the feed ratios of the starting chlorosilanes. Moreover, the microstructural evolution of the resultant Si? C? N ceramics was further investigated by X‐ray diffraction, Raman spectroscopy, and transmission electron microscopy. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Centrifugal partition chromatography applied to the isolation of oak wood aroma precursors

Flavours extracted from oak wood during barrel ageing contribute to the organoleptic character of wines and spirits. The aim of this work was to identify the glycosidic precursors of the key volatile compounds responsible for oak wood aroma. Oak extract is a very complex matrix and, furthermore, precursors are present in very small quantities. Preparative centrifugal partition chromatography (CPC) is a promising solution for purifying the oak extract. The solvent system was selected on the basis of the partition coefficient of glycosidase enzyme activity (K_ca). Thanks to the efficacy of CPC separation, three glucoside gallates were subsequently isolated by HPLC chromatography. Vanillin-(6′-O-galloyl)-O-β-d-glucopyranoside, 3,4,5-trimethoxyphenyl-(6′-O-galloyl)-O-β-d-glucopyranoside, and (6R,9R)-3-oxo-α-ionol-9-O-(6′-O-galloyl)-β-glucopyranoside (macarangioside E) were isolated and identified. This was the first time that vanillin-(6′-O-galloyl)-O-β-d-glucopyranoside was identified and the first time that macarangioside E was isolated from oak wood. Heating macarangioside E resulted in the formation of megastigmatrienone, which has an aroma reminiscent of tobacco.     

Improvement on ferroelectric properties of metal-organic decomposited PZT thin film prepared by using prenucleation layer

Abstract

Perovskite SrRuO₃ (SRO) layer was, for the first time, been successfully synthesized by using metal-organic decomposition (MOD) process. The presence of SRO buffer layer on Pt(Si) substrates has significantly enhanced the crystallization and densification behavior of the subsequently deposited Pb(Zr_0.52Ti_0.48)O₃ films. The pyrochlore free perovskite phase can be obtained by post-annealing the PZT/SRO/Pt(Si) films at 500°C, which is 50°C lower than that needed in PZT/Pt(Si) films. The fine grain (～0.3 μm) microstructure can be attained by post-annealing at 650°C for PZT/SRO/Pt(Si) films and 700°C for PZT/Pt(Si) films. The ferroelectric hysteresis properties of the two PZT films are comparable to each other. The leakage current properties of PZT/SRO/Pt(Si) films increased pronouncedly with post-annealing temperature, resulting in inferriar leakage behavior to PZT/Pt(Si) films.     

聚丙烯腈原丝纺丝溶液的合成

以偶氮二异丁腈 (AIBN)为引发剂 ,研究了丙烯腈与丙烯酸甲酯在二甲基亚砜溶剂中的自由基均相溶液共聚合反应。考察了单体浓度、引发剂浓度、单体配比 ,反应温度和时间等对共聚反应的影响。分别用称重法和乌氏粘度计测定了反应的转化率和产物的相对分子质量。研究结果表明 ,制备高性能聚丙烯腈纺丝溶液最佳的反应条件是 :总单体浓度2 5 % ,AIBN占总单体浓度 1% ,反应温度为 6 0℃ ,时间为 30h     

Er:YAl3(BO3)4 glassy thin films from polymeric precursor and sol-gel methods: Waveguides for integrated optics

This paper presents the characterization of single-mode waveguides for 980 and 1550 nm wavelengths. High quality planar waveguide structure was fabricated from Y_1 − xEr_xAl₃(BO₃)₄ multilayer thin films with x = 0.02, 0.05, 0.1, 0.3, and 0.5, prepared through the polymeric precursor and sol-gel methods using spin-coating. The propagation losses of the planar waveguides varying from 0.63 to 0.88 dB/cm were measured at 632.8 and 1550 nm. The photoluminescence spectra and radiative lifetimes of the Er^{3+ 4}I_13/2 energy level were measured in waveguiding geometry. For most samples the photoluminescence decay was single exponential with lifetimes in between 640 μs and 200 μs, depending on the erbium concentration and synthesis method. These results indicate that Er doped YAl₃(BO₃)₄ compounds are promising for low loss waveguides.     

液相先驱体制备ZrC粉末研究

采用氯氧化锆、丙醇、丙三醇和乙酰丙酮为基本原料合成了锆的先驱体溶液,通过液相先驱体转化法合成了ZrC粉末.研究了先驱体溶液组成和热处理温度对合成ZrC粉末的成分和显微结构的影响,结果表明,随丙三醇用量的增加,干燥时间延长,提高碳和锆的物质的量比和温度都能够提高ZrC粉末的生成率.在高温热处理后合成了面心立方的ZrC粉末,1500℃处理后,粉末颗粒呈不规则的形状.1800℃热处理后,颗粒为球型,颗粒长大的趋势明显.     

新型腈纶油剂ASY—2在聚丙烯腈基碳纤维上的应用

介绍了新型腈纶油剂ASY－2在聚丙烯腈基碳纤维生产线上的试用情况,试用结果显示,ASY－2腈纶油剂能有效提高原丝的亲水性,改善纤维的集束性、分纤性,减少纤维加工毛丝率。