果汁非酶褐变的反应机制及其影响因素

果汁非酶褐变反应的机制有焦糖化反应，美拉德反应，抗坏血酸氧化分解和多元酚氧化缩合反应。本文分析了影响非酶褐变的主要因素。     

果汁非酶褐变及其影响因子

果汁非酶褐变反应的机制有焦糖化反应、美拉德反应、抗坏血酸氧化分解和多酚氧化缩合反应。影响非酶褐变的因子很多，如温度、pH值、金属离子和包装材料等。     

果汁褐变及其影响因素研究进展

果汁加工及贮藏过程中的褐变包括酶促褐变和非酶促褐变(美拉德反应,酚类物质氧化变色、焦糖化褐变和抗坏血酸氧化褐变)两种情况。影响酶促褐变的因素有温度、pH、氧气、抑制剂和酚类化合物等,非酶褐变的影响因素因褐变类型的不同存在差异。各种非酶褐变类型问存在复杂关系。     

果汁非酶褐变的机制及控制措施

本文阐述了果汁非酶褐变的机制：焦糖化反应、美拉德反应、抗坏血酸氧化分解和多元酚氧化缩合,并对目前常用的抑制果汁非酶褐变的方法进行了综述.     

南果梨果汁非酶促褐变反应机制研究

通过监测南果梨果汁在不同温度贮藏过程中非酶促褐变反应的褐变指数（browning index,BI）及5-羟甲基糠醛（5-hydroxymethylfurfural,5-HMF）、总酚、抗坏血酸、游离氨基酸、还原糖的含量,探究其非酶促褐变反应的主要反应机制和影响因素。通过动力学方程表达各反应进行的情况和主次关系,结果表明,南果梨果汁非酶促褐变的主要反应机制是美拉德反应和抗坏血酸氧化分解反应,多元酚氧化缩合反应和焦糖化反应在南果梨果汁非酶促褐变反应体系中影响较小。在不同的贮藏温度下,5-HMF和抗坏血酸的含量变化规律均符合零级反应动力学模型,随着贮藏温度的升高,南果梨果汁的非酶促褐变反应速度加快。     

中国白酒的非酶褐变反应的应用

食品在加热处理或长期贮存中，会产生不同程度的类黑精色素，这类反应没有酶的参与，故称非酶褐变反应。白酒在长期贮存中出现微黄色或淡黄色，属非酶褐变反应。白酒中的非酶褐变反应受白酒中微量成分的种类及含量、水分、pH值、温度、时间、金属离子和氧等因素影响。可利用非酶褐变反应鉴别酒曲培制温度及中挺时间、白酒香型和检测产品质量。     

储藏过程中百香果汁非酶褐变的研究

百香果汁在储藏过程中易发生非酶褐变,影响其品质。研究了储藏期间同非酶褐变相关的物质的变化规律及其与褐变的关系。结果显示,总糖、还原糖、氨基态氮和VC均随储藏温度升高或储藏时间延长而减少,褐变度及5-HMF含量则随储藏温度升高或储藏时间延长而增加,总酚含量变化不显著。因此,VC的氧化分解及Maillard反应是导致百香果汁储藏过程中非酶褐变的主要原因。     

橙汁非酶褐变机制及控制措施

阐述了橙汁非酶褐变的机制——美拉德反应,焦糖化反应,抗坏血酸的氧化分解和多酚类化合物氧化缩合反应。通过对杀菌方式,贮藏方式,褐变剂抑制剂的添加及加工中吸附树脂使用的分析,重点综述了在橙汁加工储藏过程中控制非酶褐变的措施。     

橙汁非酶褐变机制及控制措施

阐述了橙汁非酶褐变的机制：美拉德反应、焦糖化反应、抗坏血酸的氧化分解和多酚类化合物氧化缩合反应。通过对橙汁原料选择、杀菌方式、贮藏方式、褐变抑制剂添加及加工中吸附树脂使用的分析,重点综述了在橙汁加工储藏过程中控制非酶褐变的措施。     

影响荔枝汁非酶褐变的因素及其控制方法

通过测定荔枝汁加工和贮存过程中褐变度的变化,研究了影响荔枝汁非酶褐变的主要因素。结果表明,影响荔枝汁非酶褐变的主要因素有:多酚类物质、pH值、金属离子(Mg2+、Fe3+、Cu2+、Sn2+)、包装材料和贮藏温度。通过控制这些因素可有效抑制荔枝汁的非酶褐变。     

包装材料对苹果浓缩汁贮藏期非酶褐变的影响

研究了苹果浓缩汁贮藏过程中,3种包装材料对褐变指数(A420)、氨基态氮、还原糖和5-羟甲基糠醛含量的影响。结果表明,3种包装材料对苹果浓缩汁的非酶褐变阻遏作用玻璃瓶最佳;20d内,PE/TIE/PA/TIE/PE5层共挤蒸煮袋>PE(聚乙烯)袋;20d后,PE袋>蒸煮袋。     

对灌装果汁褐变的初步研究

以马口铁涂料罐灌装草莓汁为例,对果汁中发生褐变的影响因素和不同抑制剂对防止褐变的作用进行了研究.结果表明金属离子和温度是促进马口铁涂料罐灌装草莓汁发生褐变的重要因素;酸性添加剂有加快褐变的趋势;而EDTA-Na2对抑制褐变有良好的作用.     

Reaction pathways and factors influencing nonenzymatic browning in shelf-stable fruit juices during storage

The occurrence of nonenzymaticbrowning in fruit juices during storage is a major quality defect. It negatively affects consumer acceptance and consumption behavior and determines the shelf-life of these products. Although nonenzymatic browning of fruit juices has been the subject of research for a long time, the exact mechanism of the nonenzymatic browning reactions is not yet completely understood. This review paper aims to give an overview of the compounds and reactions playing a key role in nonenzymatic browning during the storage of fruit juices. The chemistry of the plausible reactions and their relative importance will be discussed. To better understand nonenzymatic browning, factors affecting these reactions will be reviewed and several strategies and methods to evaluate color changes and browning will be discussed. Nonenzymatic browning involves three main reactions: ascorbic acid degradation, acid-catalyzed sugar degradation, and Maillard-associated reactions. The most important NEB pathway depends on the matrix. Nonenzymatic browning is affected by many factors, such as the juice composition, the pH, the oxygen availability (packaging material), and the storage conditions. Nonenzymatic browning can thus be considered as a complex problem. To characterize color changes and browning and obtain insight into the browning mechanism of fruit juices, food scientists applied several approaches and strategies. These included the use of model systems with/without the addition of labeled compound and real systems as well as advanced analytical methods.     

Effect of storage on nonenzymatic browning reactions in carob pekmez

Carob pekmez was stored at 5, 25, 35 and 45 °C for studying the reaction kinetics of nonenzymatic browning reactions. Hydroxymethylfurfural (HMF) formation, browning index (A₄₂₀) and CIE (International Commission on Illumination) colour parameters were analysed to evaluate nonenzymatic browning reactions. HMF formation and A₄₂₀ values increased linearly with the storage time and temperature and both followed zero‐order reaction. No fitting model was found for the changes in visual CIE parameters. The dependence of rate constant of nonenzymatic reactions on temperature was represented by an Arrhenius equation and the activation values were found as 114.87 kJ mol^?1 and 86.62 kJ mol^?1 for HMF formation and A₄₂₀ values, respectively. The excellent linear correlations (r = 0.728–0.99) among colour parameters, browning index and HMF were found.     

Effect of pH control on the intermediates and melanoidins of nonenzymatic browning reaction

The effect of pH control on the intermediates and melanoidins of nonenzymatic browning reaction was investigated. A solution of glucose (36.03 g/l) and lysine (36.53 g/l) was refluxed by heating for 24 h with the pH controlled at pH 7.0 by three methods: running the reaction in 2 mol/l phosphate buffer (buffer-melanoidin), adding a sodium hydroxide solution through a pH stat (pH stat-melanoidin) or initial pH control with NaHCO₃ at the start of reaction (NaHCO₃-melanoidin). The three resulting model melanoidins were monitored by pH, color intensity, reducing activity, gel permeation chromatography (GPC), and electrofocusing. The color intensity and reducing activity in the buffer- and pH stat-melanoidins were both higher than those of the NaHCO₃-melanoidin. The two intermediates, 5-hydroxymethyl-pyrrole-2-aldehyde and lysylpyrraline, were produced in the early stage of the reaction and are likely to have been incorporated in the melanoidin formation during heating. Electrofocusing showed that the melanoidins prepared under pH control were separated into 14 bands in the pI range of 3.5–4.85, and that the NaHCO₃-melanoidin consisted of 30 bands in the pI range of 3.5–8.35. The bands with pI of more than 4.85 were formed during the stage of decreasing pH in the reaction solution and disappeared after freezing preservation at −20°C for 6 months.     

Coordinate contribution of lipid oxidation and Maillard reaction to the nonenzymatic food browning

Lipid oxidation and the Maillard reaction are probably the two most important reactions in Food Science. Both include a whole network of different reactions in which an extraordinary complex mixture of compounds are obtained in very different amounts and produce important changes in food flavor, color, texture, and nutritional value, with positive and negative consequences. This article analyzes the interactions between both reactions, with special emphasis in nonenzymatic browning development, by discussing the influence of lipid oxidation products in the Maillard pathway and vice versa, as well as the existence of common intermediates and polymerization mechanisms in both reactions. The existing data suggest that both reactions are so interrelated that they should be considered simultaneously to understand the products of the Maillard reaction in the presence of lipids and vice versa, and should be included in one general pathway that can be initiated by both lipids and carbohydrates.     

Non-enzymatic browning of oligogalacturonides in apple juice models

Summary Apple juice models, consisting of galacturonides (reaction products of enzymatic pectin degradation), sugars, amino acids and organic acids, were subjected to heat treatment for 2 h in a boiling water bath and the decrease in the galacturonide concentration, the formation of the reaction products and the colour were established.Unsaturated galacturonides were found to be much more reactive than saturated galacturonides. 2-Furoic acid and 5-formyl-2-furoic acid were the main detectable products formed by the degradation of unsaturated galacturonides. The formation of these products was independent of the presence of amino acids and increased with decreasing pH. It is indicated that unknown degradation products of unsaturated galacturonides are the cause of increased browning when asparagine is present in the reaction mixture. The reaction constants for the degradation of unsaturated galacturonides under the various reaction conditions were determined. It was demonstrated that unsaturated oligogalacturonides contribute largely to non-enzymatic browning. The colour formation in fructose models was particularly enhanced by the presence of unsaturated galacturonides. Hydroxymethylfurfural (HMF) was a major reaction product and was produced, to a larger extent, from fructose rather than from glucose. HMF formation from glucose and fructose was found to be independent of the presence of galacturonides and amino acids and was greater at lower pH.

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Nicht-enzymatische Bräunung von Oligo-Galakturoniden in Apfelsaft-Modellen

Zusammenfassung Apfelsaft-Modelle, bestehend aus Galakturoniden (Reaktionsprodukte des enzymatischen Pectinabbaus), Zuckern, Aminosäuren und organischen Säuren wurden einer Hitzebehandlung von 2 h in einem kochenden Wasserbad unterzogen. Dabei wurde die Abnahme der Galakturonid-Konzentration und die Entstehung von Reaktionsprodukten und Färbung ermittelt.Im Vergleich zu den gesättigten Verbindungen erwiesen sich ungesättigte Galakturonide als wesentlich reaktionsfähiger, bei denen als hauptsächliche Reaktionsprodukte Brenzschleimsäure und 5-Formylbrenzschleimsäure nachgewiesen werden konnten. Die Bildung dieser Stoffe war unabhängig von der Gegenwart von Aminosäuren, jedoch abhängig von pH-Wert, denn diese nehmen bei Erniedrigung zu. Ergebnisse deuteten darauf hin, daß unbekannte Abbauprodukte der ungesättigten Galakturonide Ursache für eine verstärkte Bräunung in Reaktionssystemen mit Asparagin sind. Die Reaktionsgeschwindigkeitskonstanten beim Abbau der ungesättigten Galakturonide wurden bei unterschiedlichen Reaktionsbedingungen ermittelt. Es konnte gezeigt werden, daß ungesättigte Galakturonide maßgeblich zur nicht-enzymatischen Bräunung beitragen. Die Farbbildung in Modellen mit Fructose wurde insbesondere durch die Anwesenheit ungesättigter Galakturonide verstärkt. HMF, als Hauptreaktionsprodukt, wurde aus Fructose in größerer Menge als aus Glucose gebildet. Die Bildung von HMF aus Glucose und Fructose erwies sich als unabhängig von der Anwesenheit von Galakturonide und Aminosäuren und erhöhte sich bei Erniedrigung des pH-Wertes.