果蔬酶促褐变机理的研究进展

酶促褐变对果蔬在加工保鲜过程中的品质有重大影响，有关酶促褐变机理的相关研究也越来越多。本文整理归纳了国内外围绕褐变机理进行的多酚氧化酶和酚类底物的相关研究，包括对多酚氧化酶种类、催化位点、提取、分离、纯化、活性测定方法的介绍；酚类化合物种类、含量变化及其变化原因的阐述；酚类酶促氧化反应、醌的生成途径、次级代谢过程、氧化终产物特性以及抗褐变剂抑制酶促褐变机理的报道，以期为酶促褐变机理的系统深入研究提供借鉴与参考。     

PPO酶促诱发因素对苹果多酚非酶褐变的影响

为探究苹果多酚氧化酶(PPO)酶促诱发因素对苹果多酚参与的非酶褐变的影响,以绿原酸和根皮苷为底物,以磷酸缓冲液为苹果汁模拟体系,通过控制PPO酶促诱发条件,进行酶促诱发反应,然后钝化酶,模拟体系于60℃进行非酶聚合反应,每隔24 h用色差计测定L*值、a*值、b*值和ΔE*值。结果表明,酶促诱发因素对绿原酸和根皮苷参与的非酶褐变的影响存在较大差异。p H在3.5~6.0,含有绿原酸和根皮苷的模拟体系,其褐变程度随酶促诱发p H升高而增大;酶促诱发温度20~60℃,诱发体系温度对绿原酸参与的非酶褐变影响不显著,而根皮苷在40℃时褐变程度较大;酶促诱发时间分别为40 min和30 min时绿原酸和根皮苷参与的非酶褐变程度较大;酶活14.25~171 U,酶活的增大加速两种多酚参与的非酶褐变。结果同时表明,根皮苷非酶褐变与果汁后浑浊有关,且较高的p H、温度、PPO酶活以及较长的酶促诱发时间加速果汁后浑浊形成。     

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。     

酶促诱发儿茶素对模拟苹果汁非酶褐变特性的影响

以苹果中含量较多的儿茶素为研究对象,以磷酸缓冲液为苹果汁褐变模拟体系,在多酚氧化酶（polyphenol oxidase,PPO）酶促诱发儿茶素后,钝化PPO,通过色差仪连续测定模拟体系亮度（L*）值、红度（a*）值、黄度（b*）值及总色差（ΔE*）值的变化趋势,研究酶促诱发条件对模拟果汁体系非酶褐变特性的影响。结果表明：酶促诱发时间及诱发体系温度对儿茶素参与的非酶褐变无显著性影响（P＞0.05）,而酶促诱发体系pH值以及儿茶素浓度对模拟体系褐变程度影响显著（P＜0.05）,pH 4.0时,模拟果汁体系褐变程度较大,褐变程度随儿茶素浓度的增大而增强;本实验同时发现,PPO诱发儿茶素发生非酶聚合,并与聚合产物相互作用而沉淀,导致果汁产生后浑浊。     

鸡腿菇的酶促褐变机理及其抑制研究

采用SPSS软件分析鸡腿菇贮藏过程中褐变与多酚氧化酶(PPO)、过氧化物酶(POD)活性变化的关系.用抗坏血酸(Vc)、亚硫酸钠和柠檬酸分别处理鸡腿菇,试图找到减轻鸡腿菇褐变的方法.结果表明:鸡腿菇在贮藏过程中褐变度逐渐增大,POD活性呈先上升后下降的趋势,其褐变度与PPO活性显著相关,均趋于上升,PPO活性的变化是引起鸡腿菇酶促褐变的主要原因;Vc、亚硫酸钠和柠檬酸三种处理均可不同程度地减轻鸡腿菇的褐变度,其中0.15-0.2mmol/L的柠檬酸处理效果最好,其次是亚硫酸钠和Vc.     

果蔬酶促褐变机理及其抑制方法研究进展

酶促褐变是果蔬深加工过程中存在的一个普遍且很严重的问题.本文介绍了酶促褐变的基本原理、影响因素,并从物理、化学、生物技术等方面介绍了一些酶促褐变的抑制方法.     

混浊苹果汁生产中的酶促褐变及其防止研究进展

介绍了苹果中与酶促褐变有关的多酚氧化酶及酚类物质,以及在混浊苹果汁生产中防止酶促褐变的各种方法。     

氧化白藜芦醇协同抗坏血酸抑制余甘子酶促褐变的机制研究

通过研究氧化白藜芦醇协同抗坏血酸对余甘子酶促褐变的抑制作用,以及对其多酚氧化酶的酶抑制动力学研究,探明氧化白藜芦醇联合抗坏血酸协同抑制褐变酶的作用机理。结果表明,0.02%氧化白藜芦醇、0.15%抗坏血酸、0.02%氧化白藜芦醇+0.15%抗坏血酸均能减缓余甘子的酶促褐变,对3种褐变酶即多酚氧化酶(PPO)、过氧化物酶(POD)、苯丙氨酸解氨酶(PAL)活性均有较好的抑制作用;0.02%氧化白藜芦醇+0.15%抗坏血酸联合处理对余甘子的酶促褐变及对PPO、POD、PAL的抑制活性强于单独使用。酶抑制动力学结果表明,氧化白藜芦醇对PPO的IC50为(3.300±0.010) μmol/L,抑制机理为可逆的混合型抑制,而氧化白藜芦醇+抗坏血酸(1∶7)的IC50为(1.600±0.020) μmol/L,抑制机理为可逆的竞争性抑制,协同使用导致抑制方式也发生改变。氧化白藜芦醇对PPO的抑制常数KI为0.904 μmol/L,对PPO-底物形成的复合物的抑制常数KIS为14.285 μmol/L,而氧化白藜芦醇+抗坏血酸(1∶7)对PPO的抑制常数KI为0.840 μmol/L,联合处理对PPO的抑制性加强。     

苹果酒中模拟体系下非酶氧化与酶促氧化对聚合度影响的研究

以苹果酒中单酚含量较多的4种酚（儿茶素、表儿茶素、绿原酸和咖啡酸）为研究对象。在模拟苹果酒pH体系环境下，对其在非酶氧化和酶促氧化下聚合度的变化进行了研究。结果表明，在非酶氧化过程中，以儿茶素和表儿茶素的聚合反应为主，而在酶促氧化过程中。则是以绿原酸和咖啡酸的聚合反应为主。     

鲜切果蔬酶促褐变关键酶研究进展

机械伤使得鲜切果蔬在生理生化方面出现各种变化,导致果蔬贮藏期间品质下降,其中酶促褐变是导致鲜切果蔬贮藏品质下降的重要原因之一。本文主要介绍了鲜切果蔬酶促褐变过程中4个关键酶,即多酚氧化酶(PPO)、苯丙氨酸解氨酶(PAL)、脂肪氧合酶(LOX)和过氧化物酶(POD)的特性、作用机理以及影响酶活性的因素,以期为进一步研究鲜切果蔬酶促褐变的机理及酶促褐变的控制方法提供理论基础。     

Dissolved oxygen content in apple must: technological implications in cider processing

Oxygen can influence the composition and quality of apple must and cider. In this study, the effect of unit operations on oxygen dissolution during apple must processing was investigated and the technological implications discussed. Oxygen dissolution after different apple must processing unit operations, and also the effect of enzymatic browning reaction on dissolved oxygen uptake were analysed. During pressing, the highest and first oxygen dissolution occurred in the must at 6.8 mg/L, on average. The enzymatic browning reaction after 10 min was responsible for an oxygen uptake above 80%. The addition of sulphur dioxide or maceration of crushed apple results in a must with more oxygen content, however the beverage colour is negatively affected. The incorporation of oxygen into the must by bubbling oxygen or the movement of liquid may not be effective owing to consumption by the reaction of residual polyphenol oxidase. Moreover, this can affect the alcoholic fermentation because of the oxidation of nutrients such as vitamins. If the apple must is depectinized, racked and filtered, there will be enough oxygen to obtain a quality cider. These results and observations can be useful for selecting unit operations in cider companies in order to improve the beverage quality. Copyright © 2014 The Institute of Brewing & Distilling     

Optimization of Vapor Induced Puffing in Apple Dehydration

Vapor induced puffing during high temperature fluidized bed (HTFB) dehydration of apple cubes was optimized using response surface methodology (RSM). Osmoblanching in sugar syrup prevented enzymatic browning. Successtil puffing was achieved by creating a surface barrier to vapor by dipping the cubes in starch solution and manipulating the temperature and time of exposure in the HTFB. Optimum conditions for minimum bulk density with acceptable levels of nonenzymatic browning included dipping osmoblanched apple cubes in 1% starch solution, followed by HTFB drying 11 min at 157°C. Product bulk density exhibited a minimum while nonenzymatic browning values did not display an optimum. Minimum value of bulk density predicted by RSM and browning values were very close to those verified experimentally for product processed under the identified optimum conditions.     

Nonenymatic Browning, Fluorescence Development, and Formation of Pyrrole Derivatives in Phosphatidylethanolamine/ Ribose/Lysine Model Systems

Browning, fluorescence, and pyrrole formation were determined in 4 mixtures of phosphatidylethanolamine (PE), ribose (RI), and/or lysine (lys) incubated at 60°C to study the contribution of lipid oxidation to food browning when lipid oxidation products are formed in the presence of other food components. The 4 assayed systems (PE/lys, PE/RI, RI/lys, and PE/RI/lys) were also extracted with chloroform‐methanol (2:1) to distinguish between the nonenzymatic browning produced with the amino group of PE and that produced with the amino groups of lys. Under the assay conditions, both the RI and the oxidized products produced in the fatty acid chains of PE contributed to the development of browning in the assayed systems. However, RI and oxidation products of PE exhibited different reactivities for the different amino groups involved in these reactions. Thus, the oxidized lipids reacted with the amino group of PE with preference for the amino group of lys, and this preference was reversed for RI. These results suggest that the contribution of both carbohydrates and lipid oxidation products to food browning may be distinguished. In addition, determination of oxidized lipid/ethanolamine derivatives in phospholipids may be an alternative procedure to evaluate oxidative damage in foods.     

Preliminary Study on Glucose Oxidase-Catalase Enzyme System to Control the Browning of Apple and Pear Purées

Oxygen is a key factor in fruit purées browning. The use of a commercial glucose oxidase-catalase enzyme system (GOX) for oxygen removal and browning control of Golden Delicious apple and Kaiser pear purées during storage has been investigated. The effect of ascorbic acid and peroxidase has also been tested and results compared with control (no treatment). Colour change was quantified using the CIE L^*, a^*, b^* system. Heating has been the unique treatment able to control the enzymatic browning of fruit purées, whereas GOX was the most efficient in reducing to low level the dissolved oxygen content in apple and pear purées (99% oxygen removed), and showed an interesting capability to control the nonenzymatic browning during fruit processing and purées storage. However, ascorbic acid decreased the nonenzymatic browning of fruit purées to a larger extent than any other chemical treatment used in this study. The Kaiser pear shows a fast enzymatic browning thus may represent a good ‘standard’ to measure browning kinetics.     

硫酸氨基葡萄糖非酶褐变的初步研究

将硫酸氨基葡萄糖样品分别在60、70、75、80℃下加热10h,测定加热过程中褐变指数、5- 羟甲基糠醛含量、硫酸氨基葡萄糖含量、pH 值的变化,用来表征非酶褐变进行的程度,将结果应用零级动力学方程拟合。结果表明,随着加热温度升高、时间延长,褐变指数、5- 羟甲基糠醛的含量逐渐增加,而pH 值和硫酸氨基葡萄糖的含量逐渐下降,硫酸氨基葡萄糖的非酶褐变反应符合零级动力学,褐变指数和5- 羟甲基糠醛含量变化的反应活化能分别为85.127、136.973kJ/mol,NaHSO3 对硫酸氨基葡萄糖的非酶褐变有一定的抑制作用。     

Nonenzymatic Browning in Dried Apples During Storage

This investigation into the effects of various treatments on nonenzymatic browning of dried apples determined that cysteine incorporation did not reduce browning during storage. Calcium treatment reduced rate of darkening but as Ca⁺⁺ concentration increased the effssects diminished. Manganese and tin compound addition was ineffective on product darkening. Packaging of dried apples with oxygen-scavengers markedly decreased product darkening during storage. About 20% of the nonenzymatic browning reaction occurring during storage was attributed to nonoxidative, or Maillard, reaction, and about 70% to oxidation.     

香蕉汁储藏过程中非酶褐变的研究

本文探讨了香蕉汁储藏中非酶褐变的原因与动力学。结果表明还原糖与氨基化合物发生的Maillard反应是造成香蕉汁储藏期间非酶褐变的主要原因。经与一级动力学和零级动力学模型拟合，推测香蕉汁储藏期间的非酶褐变符合零级动力学方程，其发生非酶褐变的活化能为80．46kJ／mol。     

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。