Catalytic effect of metal cations on the darkening reaction in ripe olive processing

The darkening step in ripe olive processing can be accelerated by using different metal cations, particularly cobalt, manganese and iron, in the aeration liquid. It was found that manganese and iron ions increased the rate of the darkening reaction as their content in the liquid increased from zero to 9 mM. Manganese cations only had a catalytic effect on the darkening reaction, while iron ions also fixed the dark colour formed when olives were bottled and sterilized. However, the rate of oxidation of the orthodiphenols in the olive flesh (hydroxytyrosol and caffeic acid) was slightly modified when manganese or iron was added to the aeration liquid. The better dark surface colour obtained when manganese or iron ions were added to the aeration liquid remained after bottling and sterilization of olives in a ferrous gluconate solution. These results suggest that manganese could be used to catalyse the darkening reaction since this cation is generally recognized as safe.     

Interactions between microbial iron reduction and metal geochemistry: effect of redox cycling on transition metal speciation in iron bearing sediments

Microbial iron reduction is an important biogeochemical process that can affect metal geochemistry in sediments through direct and indirect mechanisms. With respectto Fe(III) (hydr)oxides bearing sorbed divalent metals, recent reports have indicated that (1) microbial reduction of goethite/ferrihydrite mixtures preferentially removes ferrihydrite, (2) this process can incorporate previously sorbed Zn(II) into an authigenic crystalline phase that is insoluble in 0.5 M HCl, (3) this new phase is probably goethite, and (4) the presence of nonreducible minerals can inhibit this transformation. This study demonstrates that a range of sorbed transition metals can be selectively sequestered into a 0.5 M HCl insoluble phase and that the process can be stimulated through sequential steps of microbial iron reduction and air oxidation. Microbial reduction experiments with divalent Cd, Co, Mn, Ni, Pb, and Zn indicate that all metals save Mn experienced some sequestration, with the degree of metal incorporation into the 0.5 M HCl insoluble phase correlating positively with crystalline ionic radius at coordination number = 6. Redox cycling experiments with Zn adsorbed to synthetic goethite/ferrihydrite or iron-bearing natural sediments indicate that redox cycling from iron reducing to iron oxidizing conditions sequesters more Zn within authigenic minerals than microbial iron reduction alone. In addition, the process is more effective in goethite/ferrihydrite mixtures than in iron-bearing natural sediments. Microbial reduction alone resulted in a -3x increase in 0.5 M HCl insoluble Zn and increased aqueous Zn (Zn-aq) in goethite/ferrihydrite, but did not significantly affect Zn speciation in natural sediments. Redox cycling enhanced the Zn sequestration by approximately 12% in both goethite/ferrihydrite and natural sediments and reduced Zn-aq to levels equal to the uninoculated control in goethite/ferrihydrite and less than the uninoculated control in natural sediments. These data suggest that in situ redox cycling may serve as an effective method for     

5-羟甲基糠醛与氨基酸反应形成的风味物质

将5-羟甲基糠醛(HMF)分别与丝氨酸、苏氨酸、γ-氨基丁酸、丙氨酸反应,采用GC-MS共检测出21种挥发性成分,主要为羰基化合物、酮类、呋喃类和烃类化合物。在HMF-丝氨酸反应体系中,吡嗪、5-甲基-2-呋喃甲醛和壬醛在高底物浓度和长反应时间下生成量最高;而在HMF-苏氨酸反应体系中,苯乙酮、3-甲基-吡嗪与2,5-二甲基-吡嗪的生成量随反应时间延长而显著增加,反应物浓度对其没有显著影响;在HMF-氨基丁酸体系中,癸醛的生成量随着反应时间的延长而增多,反应物浓度要在长时间反应条件下才会有显著性差异;在HMF-丙氨酸反应体系中,壬醛和癸醛的生成量随反应时间延长而增多,但在相同反应时间下,却随浓度增加而减少。     

pH值和金属离子对大豆分离蛋白凝胶形成的影响

在90℃,研究了大豆分离蛋白浓度、pH值、金属离子、加热时间等因素对大豆分离蛋白凝胶形成的作用。结果显示,酸性条件下大豆分离蛋白形成凝胶的最适pH值为3.0,碱性条件下形成凝胶的最适pH值为9.0;凝胶溶液中CaCl2浓度为0.4%的时,形成凝胶的透明性最高,时间为22min。     

有机相中脂肪酶的催化反应及其应用

有机相中脂肪酶的催化反应是非水相酶催化反应中一个重要方面,介绍了有机相中脂肪酶的催化反应及主要影响因素,并综述了脂肪酶的固定化及其固定方法。对有机相中固定化脂肪酶催化技术在脂肪酸酯的合成、食品、制药和新能源等领域的应用作了概述,最后对有机相中脂肪酶的催化技术进行了展望。     

Effects of enzymatic modification of wheat protein on the formation of pyrazines and other volatile components in the Maillard reaction

Enzymatically hydrolysed wheat gluten hydrolysate (WGH) was deamidated using glutaminase to produce deamidated wheat gluten hydrolysate (DWGH). Volatile components were analysed in WGH and DWGH thermally reacted with glucose or fructose. In the reaction system containing glucose, 19 pyrazines, 2 furans, and 5 sulphur-containing components were detected in WGH, while 34 pyrazines, 4 furans, and 7 sulphur-containing components were found in DWGH. In the system containing fructose, 24 pyrazines, 3 furans, and 6 sulphur-containing components were identified in the thermal reaction of WGH, whereas 36 pyrazines, 4 furans, and 8 sulphur-containing components were found in DWGH. The volatile components increased in DWGH, both qualitatively and quantitatively, mainly due to free ammonia released by deamidation. More volatiles were also developed in WGH and DWGH with fructose than with glucose. It was found that ammonia released from wheat protein via deamidation participated in the generation of diverse volatile components including pyrazines in the Maillard reaction.     

Phase transition in foods: effect of pressure and methods to assess or control phase transition

Food systems can be defined as heterogeneous and complex systems in which multiple interactions take place. In addition, food systems are unstable due to chemical and physical reactions. Food components (proteins carbohydrates, lipids, water …) might undergo phase transitions due to a pressure or temperature change. The effect of temperature and pressure on phase transitions of selected food components is discussed with emphasis on high pressure processing of food systems. The possibilities of Nuclear Magnetic Resonance and Magnetic Resonance Imaging in assessing phase transitions in food are highlighted.     

纺织纤维与金属离子的配位反应及其应用进展

总结并评述了聚丙烯腈纤维、聚乙烯醇纤维、聚醋酸乙烯酯纤维、棉纤维和羊毛纤维等与金属离子的配位反应.介绍了几种纺织纤维与金属离子的配位反应在责金属回收、工业废水中重金属离子去除以及高分子金属催化剂的制备等方面的应用.     

Coprecipitation of arsenate with metal oxides: nature, mineralogy, and reactivity of aluminum precipitates

Arsenic mobilization in soils is mainly controlled by sorption/desorption processes, but arsenic also may be coprecipitated with aluminum and/or iron in natural environments. Although coprecipitation of arsenic with aluminum and iron oxides is an effective treatment process for arsenic removal from drinking water, the nature and reactivity of aluminum- or iron-arsenic coprecipitates has received little attention. We studied the mineralogy, chemical composition, and surface properties of aluminum-arsenate coprecipitates, as well as the sorption of phosphate on and the loss of arsenate from these precipitates. Aluminum-arsenate coprecipitates were synthesized at pH 4.0, 7.0, or 10.0 and As/Al molar ratio (R) of 0, 0.01, or 0.1 and were aged 30 or 210 d at 50 degrees C. In the absence of arsenate, gibbsite (pH 4.0 or 7.0) and bayerite (pH 10.0) formed, whereas in the presence of arsenate, very poorly crystalline precipitates formed. Short-range ordered materials (mainly poorly crystalline boehmite) formed at pH 4.0 (R = 0.01 and 0.1), 7.0, and 10.0 (R= 0.1) and did not transform into Al(OH)3 polymorphs even after prolonged aging. The surface properties and chemical composition of the aluminum precipitates were affected by the initial pH, R, and aging. Chemical dissolution of the samples by 6 mol L(-1) HCl and 0.2 mol L(-1) oxalic acid/ oxalate solution indicated that arsenate was present mainly in the short-range ordered precipitates. The sorption of phosphate onto the precipitates was influenced by the nature of the samples and the amounts of arsenate present in the precipitates. Large amounts of phosphate partially replaced arsenate only from the samples formed at R = 0.1. The quantities of arsenate desorbed from these coprecipitates by phosphate increased with increasing phosphate concentration, reaction time, and precipitate age butwere always lessthan 30% of the amounts of arsenate present in the materials and were particularly low (<4%) from the sample prepared at pH 4.0. Arsenate appeared to be occluded within the network of short-range ordered materials and/or sorbed onto the external surfaces of the precipitates, but sorption on the external surfaces seemed to increase by increasing pH of sample preparation and aging. Furthermore, at pH 4.0 more than in neutral or alkaline systems the formation of aluminum arsenate precipitates seemed to be favored. Finally, we have observed that greater amounts of phosphate were sorbed on an aluminum-arsenate coprecipitate than on a preformed aluminum oxide equilibrated with arsenate under the same conditions (R = 0.1, pH 7.0). In contrast, the opposite occurred for arsenate desorption, which was attributed to the larger amounts of arsenate occluded in the coprecipitate.     

Effects of supercritical carbon dioxide on volatile formation from Maillard reaction between ribose and cysteine

BACKGROUND: Supercritical carbon dioxide (SC‐CO₂) technology is being used in an increasing number of food‐manufacturing applications; however, its effect on the Maillard reaction is not well studied. The objective of this study was to investigate the effect of SC‐CO₂ treatment (140 °C, 40 MPa) on the Maillard reaction of an aqueous ribose–cysteine model system under varying pH conditions (5.6, 7.0 and 8.0), with emphasis on the formation of volatile compounds. RESULTS: SC‐CO₂ had a suppressing effect on the browning stages of the reaction under acidic and neutral pH conditions, while it appeared to have an accelerating effect at pH 8.0. Over 70 volatile compounds were positively identified from the headspace of the model system by gas chromatography–mass spectrometry. The volatiles were dominated by sulfur‐containing compounds including thiophenes and fused bicyclic sulfur‐containing compounds under all experimental conditions. Several compounds, including 2‐methyl‐3‐furanthiol, 2‐furanmethanethiol, 3‐thiophenethiol, and 2‐methyl‐3‐thiophenethiol, and one of the intermediates, furfural, were generated in much higher amounts in the SC‐CO₂‐treated samples, especially at alkaline and neutral pH values. CONCLUSION: SC‐CO₂ treatment was inhibitory to the formation of most volatiles in the Maillard reaction, but enhanced the formation of some intermediates and well‐known meaty flavoured compounds. Copyright © 2007 Society of Chemical Industry     

The formation and performance of auxetic textiles. Part I: theoretical and technical considerations

Auxetic textiles belong to a class of extraordinary materials that become fatter when stretched. Sustained efforts to fabricate auxetic fabric structures are limited. Indeed, several geometrical configurations have been previously proposed but none has been engineered into functional auxetic textile fabrics. The use of auxetic materials has been limited because of problems with deploying them in their fabricated forms. Our thrust in this research is to combine our knowledge of geometry and fabric structural characteristics to engineer auxetic textiles and to determine the properties of such auxetic textile fabrics. In this paper, we have presented the technique we developed for producing several knit structures in which filling yarn inlays are used to effect compound repeating units. In these productions, the chain is used as a base structure and a minimum of two guide bars and maximum of six guide bars are deployed to produce such warp knit auxetic fabrics.     

金属氧化物气敏薄膜的厚度效应(Ⅱ)--扩散反应理论和气敏晶体的介观效应

通过对扩散反应方程的求解和无量纲分析出了响应时间和恢复时间随膜厚、气体变化的关系式，由于气敏晶体尺寸ｒ０→０时不能满足热力学极限，于是对Ｆermi统计公式提出了修正，并由此推出了最佳晶粒尺寸r0^*的计算公式，推导出了电导激活能随膜厚变化的曲线。     

金属罐装饮料中11种双酚类物质的污染调查与风险分析

目的 了解市场流通领域金属罐装饮料中11种双酚类物质的污染状况并进行风险分析。方法 在市场流通领域随机采集30批次金属罐装饮料样品, 采用高效液相色谱-串联质谱法进行分析。结果 30批次样品中有9批次检出双酚类物质, 总体检出率为30%, 检出的双酚类物质为双酚A-二缩水甘油醚(bisphenol A diglycidyl ether, BADGE)·2H2O和BADGE·H2O·HCl, 其最大检出值分别为4.002 mg/kg和1.254 mg/kg。结论 市场流通领域金属罐装饮料中双酚类物质存在一定程度的污染, 需加强风险监测。     

Interaction of lipid in the maillard reaction between cysteine and ribose: The effect of a triglyceride and three phospholipids on the volatile products

The inclusion of phospholipid in the Maillard reaction between cysteine and ribose is known to modify the volatile aroma compounds produced. The contributions made to the headspace volatiles by 60 major products of this reaction have been compared for four different lipids and their effect on aroma quality noted. The results described demonstrate marked dissimilarities between the behaviour of the four lipids. The most noticeable distinction was between the effect of triglyceride and the three phospholipids, but there were also variations in the way that each of the three phospholipids participated in the Maillard reaction. As well as displaying marked differences in volatile products, reaction mixtures containing the four lipids possessed distinct aroma characteristics; the phospholipids containing phosphatidylethanolamine conferred the most meat-like odour. These differences appear to be caused by the dissimilar fatty acid compositions and polar moieties. Thus this study underlines the importance of lipid interaction in the Maillard reaction for the formation of flavour.     

温度对“半胱氨酸-木糖”模型体系初始美拉德中间体及挥发性风味物质形成的影响

采用"半胱氨酸-木糖"模型反应,在p H 5.5、温度分别为120、130、140、150、160℃的条件下,考察初始美拉德中间体2-木糖基噻唑烷-4-羧酸、半胱氨酸-Amadori及原料半胱氨酸的含量随反应时间的变化,发现2-木糖基噻唑烷-4-羧酸、半胱氨酸的含量在各个温度下均呈下降趋势,温度越高下降越快;但半胱氨酸Amadori的含量在120、130、140℃时呈钟形曲线变化,150、160℃则一直呈陡峭的下降趋势。比较半胱氨酸利用率、反应产物的颜色、气味特征和检测到的挥发性化合物总量,尤其含硫化合物的量,得出采用140℃反应60 min为模型反应较佳条件。采用双柱定性、保留指数比对、标准谱库检索,从140℃反应60 min的产物中检测出含硫化合物40种,含氮杂环化合物5种,含氧杂环化合物8种,含量较高的为2-甲基-3-呋喃硫醇、2-糠硫醇、2-噻吩硫醇、2-甲基噻吩并[2,3-b]噻吩、2,5-噻吩二甲醛等。     

Evaluation of acrylamide formation in potatoes during deep-frying: The effect of operation and configuration

It is nowadays well known that heating, which is carried out to improve the hygienic, sensory and nutritional properties of foods, can be also responsible for the development of acrylamide. Acrylamide levels between a few ppb and in excess of 1000 ppb have been found in many heated foods. As acrylamide is classified as a probable human carcinogen, the knowledge of critical processing variables leading to its formation is needed to ensure safety requirements.