棕色化反应的理论与实践

剖析了棕色化反应机理,梳理出棕色化反应认识上的不足。归纳出酶促棕色化反应发生的核心要素是细胞组织结构的解体。细胞组织结构解体有两种途径:一是细胞组织结构受到损伤;二是细胞组织衰老后的程序性死亡。对烟草调制过程中的棕色化进行了区分,并提出了调控棕色化反应的途径。     

儿茶素酶促制备茶黄素的研究进展

综述了儿茶素酶促制备茶黄素各反应条件的研究进展,旨在为确定儿茶素酶促制备茶黄素自动化提供科学依据,并就酶促制备茶黄素在选择多酚氧化酶方面以及同工酶方面做研究展望。     

茶叶氨基酸合成代谢及转化研究进展

氨基酸是茶叶重要的呈味物质,其在茶叶加工过程中也会发生各种酶促或非酶促反应而转化为茶叶香气及色素的重要组成物质。文章主要综述了近年来不同茶树种质资源、环境条件和加工工艺对氨基酸合成代谢及转化影响的相关研究进展,以为茶叶品质形成与调控提供一定参考。     

马铃薯酚类化合物的研究

综述了马铃薯酚类化合物的成分与分析。它的生物合成 ,它与植物的抗性 ,酶促褐化反应和煮后变黑及其它颜色变化之间的相关性 ,温度、光线及γ 射线照射对它的影响 ,如何抑制褐化反应以及酚类化合物的抗氧化性质和它对人体的保健作用。并且提出未来研究建议     

菜粕芥子碱酶降解反应的条件优化和机理研究

芥子碱是菜粕中的主要抗营养因子之一,为了绿色高效地降解芥子碱,选取了漆酶做催化剂,通过在线-紫外可见光谱实时监测的方法,测定了降解反应的动力学数据。该反应的动力学行为符合酶促反应过程,据此推导出酶解反应的米氏方程。利用薄层层析、高效液相色谱等分离手段,得到了纯化的降解产物,并进行了核磁共振波谱分析。根据动力学数据和产物信息,推测出反应机理可能是自由基过程。     

制茶中羰氨反应与焦糖化作用

制茶中褐变作用,按其发生机理可分为酶促褐变和非酶促褐变两大类。酶促褐变主要是多酚氧化酶催化儿茶素氧化聚合、缩合形成红褐色。最后生成褐黑色物质,这方面已有不少研究报导。非酶促褐变主要是羰氨反应和焦糖化作用,而这方面的研究报导很少。     

几丁寡糖对烟草赤星病的控制效应及其机制

在实验室条件下,采用菌丝生长速率法测定了几丁寡糖对烟草赤星病菌的抑制活性,继而在温室盆栽和人工接种条件下,分别研究了几丁寡糖、几丁寡糖＋木霉＋几丁质等5种方法处理对烟草赤星病的防治效果,同时分别系统测定了烟草植株施用几丁寡糖及人工接种赤星病菌后10d内SOD、POD、PPO和几丁质酶等4种防御酶的活性。结果表明,几丁寡糖对烟草赤星病菌的菌丝生长有一定抑制作用。单独施加几丁寡糖的处理对烟草赤星病的防治效果为53.60%,其次为几丁寡糖＋木霉处理,防治效果为38.28%。几丁寡糖处理后烟草体内的PPO、SOD、POD和几丁质酶的活性显著提高。以上结果说明,几丁寡糖对烟草赤星病有显著的控制效应,主要是通过诱导、提高烟草植株有关防御酶的活性从而增强烟草植株对赤星病的抗病性。     

水稻胚乳淀粉合成相关酶的结构、功能及其互作研究进展

淀粉作为稻米最主要的储藏物质,其生物合成过程直接影响水稻的产量和品质。水稻淀粉的生物合成在造粉体中通过一系列酶促反应完成。本文综述了淀粉合成过程中ADP-葡萄糖焦磷酸化酶(AGPase)、淀粉合酶(SSs)、淀粉分支酶(BE)及淀粉脱支酶(DBE)的结构、功能以及各酶之间的相互作用的最新研究进展,以期为稻米品质改良提供理论参考依据。     

渥堆过程中黑茶生化成分变化及其影响因子研究进展

渥堆过程中,黑茶中的生化成分在湿热作用下发生剧烈变化,如茶多酚因多酚氧化酶引起的氧化聚合反应而含量锐减;儿茶素因微生物的酶促氧化与非酶促作用转化,其组分及比例发生明显改变;氨基酸和可溶性糖含量亦有所变化等。这些变化为形成黑茶外形棕褐油润,汤色橙黄或红浓,滋味醇和等独特品质奠定了重要的物质基础。本文对渥堆过程中,黑茶主要品质成分变化以及渥堆工艺关键影响因子等进行了综述,并对渥堆工艺研究趋势作了展望。     

菠萝果皮蛋白酶的活性研究

用丹宁沉淀法提取菠萝果皮蛋白酶，须经过多次洗涤、保护和激活，使酶从其复合物中游离出来，研究结果测得干酶得率约０．１７％，皮汁酶活性一般为０．０４万／ｇ，干酶活性约２０万／ｇ，果皮蛋白酶酶促反应最适条件为：ＰＨ５．５－６．５，温≤６０℃，在一般室温下，酶促反应达到最大速度时间，鲜汁的１ｈ，干酶约需１－１．５ｈ。     

葡萄糖-赖氨酸美拉德产物分级组分对香蕉酶促褐变的抑制

酶促褐变是香蕉加工中拟解决的关键问题,非硫安全高效抑制剂的筛选是目前的研究热点。美拉德产物（Maillard reaction products,简称MRPs）展示了其良好的抑制酶促褐变的能力,然而美拉德产物分级组分的相关研究尚未见报道。通过透析处理得到大于和小于3 500 u的分级组分,比较其抑制香蕉酶促褐变的相关能力,并对抑制机理进行研究。结果显示：3种MRPs中,MW>3 500 u的MRPs具有较好的还原力,MW<3 500 u的MRPs具有较好的DPPH·清除率、螯合铜离子能力以及抑制多酚氧化酶酶活的能力。MW<3 500 u的MRPs对游离酶抑制常数（KI）和对酶-底物络合物的抑制常数（KIS）分别为0.198 mmol/L和1.508 mmol/L,抑制类型属于混合型抑制。     

不同陈化条件下烤烟褐变与氨基酸含量变化关系

通过分光光度法测定不同陈化时间和不同温度、湿度、真空度等陈化条件下烤烟烟叶中氨基酸含量和颜色的变化,并探讨烤烟褐变与氨基酸含量变化间的相互关系。结果表明,烤烟云烟85和翠碧在有氧陈化条件下温度越高、湿度越大,氨基酸含量越低,褐变度越大。因此烤烟在陈化过程中适当保持低温、低湿和隔离空气可减少烟叶褐变。     

烘烤凋萎期失水速度对烟叶质量的影响

凋萎期失水速度在烟叶质量的形成过程中具有重要作用,是影响烟叶质量的关键指标。为了优化烘烤工艺,寻找最佳的凋萎期失水速度,以秦烟96为试验材料,2014~2015年在甘肃陇南地区应用变频技术通过风量调节研究了烘烤凋萎期7组失水速度对烟叶质量的影响。试验结果表明,凋萎期失水速度控制在5~7 g∕(kg·h)之间,不但可以让未变黄的烟叶继续变黄,消除青烟,让已变黄的烟叶适度失水,同时降低了变黄后烟叶的水分含量,为烟叶定色创造了条件,有利于防止棕色化反应的发生。     

杨桃果实过氧化物酶特性及其抑制条件研究

以愈创木酚为底物,采用分光光度法对杨桃果实过氧化物酶（POD）的酶学特性进行研究。结果表明,杨桃POD反应时间不宜超过3.5 min,最适pH为 5.6,最适温度为30 ℃,100 ℃处理 30 s 后 POD 活性完全丧失。POD催化的酶促褐变反应动力学符合米氏方程,动力学参数Km=1.68×10-2 mol/L,Vmax=15.267 U/min,相应的动力学方程为v=15.267[S]/(0.0168+[S])（U/min）。抑制剂对 POD活性的抑制效果从大到小依次为抗坏血酸＞L-半胱氨酸＞亚硫酸氢钠＞柠檬酸。本研究可为杨桃保鲜贮藏和深加工过程中的酶促褐变控制提供理论参考。     

荔枝果实干制加工的热烫和无硫护色工艺

荔枝是我国南方一种重要的热带、亚热带水果,具有较高的营养价值和商业潜力.然而,在高温高湿季节,采后荔枝果实极易发生腐烂变质、果皮褐变、病原菌侵染等品质劣变现象.因此,荔枝果实除鲜食外,常被加工成不同的商业产品,特别是荔枝果干.干制荔枝由于干制加工时间较长,易发生果皮褐变,导致其外观色泽、产品质量和风味丧失,最终限制荔枝...     

Comparison of polyphenol oxidase in tubers ofSolanum tuberosum and the non-browning tubers ofS. hjertingii

Solarium hjertingii, a wild potato species, does not exhibit enzymatic browning nor blackspot. Blackspot and enzymatic browning are physiological disorders that are caused by the reaction of the enzyme polyphenol oxidase with phenolic substrates, resulting in discoloration of tuber cortex. We determined thatS. hjertingii has a low amount of at least one of the polyphenol oxidases in its tubers compared toS. tuberosum. Less than 5 μg ofS. tuberosum polyphenol oxidase protein, as determined from Western blot staining, had measurable enzymatic activity. In contrast,S. hjertingii protein with comparable staining had no detectable activity.     

Genetic characterization of reduced melanin formation in tuber tissue ofSolatium hjertingii and hybrids with cultivated diploids

The degree of enzymatic browning in tubers was examined quantitatively in five plant introduction (PI) accessions ofSolanum hjertingii and in hybrids of this species with cultivated diploids that had high enzymatic browning. Polyphenol oxidase activity and melanin formation inS. hjertingii accessions was subjected to an analysis of variance. There was significant variation in melanin formation within accessions but the between accession component was not significant. This indicates that it would be most advantageous to select low melanin formation by evaluating individual genotypes within an accession. Significant variation for PPO activity existed between accessions, indicating that selection on the basis of accession means would be the best means of selecting for lower PPO activity. Both parameters were much lower in allS. hjertingii genotypes compared to tetraploid cultivars known for their susceptibility to internal blackspot when mechanically damaged. The reduced browning inS. hjertingii was due to a lack of PPO activity and not the shortage of substrate. Progenies, and parents of four crosses between selectedS. hjertingii genotypes and cultivated diploids were measured for PPO activity and melanin formation. The mean performance of the progenies was closest to theS. hjertingii parent in all cases. Degree of dominance indicated nearly complete dominance or overdominance in the direction of theS. hjertingii parent. These results are discussed in light of other work which indicates that protein antigenic to PPO antibody is present inS. hjertingii. It appears that inactive PPO is present in the tubers. The pronounced dominance of low PPO activity and suppression of melanin formation in the hybrids withS. hjertingii is promising for the utility of this wild species as a source of genetic factors that, upon introgression into the cultivated potato gene pool, would suppress browning.     

Polyphenol oxidase and peroxidase activities of apricots (Prunus armeniaca L.) as affected by cultivar,location, and year of harvest

A total of 22 samples of apricots belonging to ten cultivars from two locations and picked in the years 1975–78 were assayed for polyphenol oxidase (PPO) and partly for peroxidase (POD) activities, heat resistance of these enzymes,o-dihydroxy phenol (ODP) content, and initial rate of enzymatic browning (BA). Of these characteristics, ODP content showed the greatest and BA the least variation. PPO activity relative to fresh weight was found to depend on the year of harvest rather than on the cultivar, while POD activity relative to fresh weight was cultivar dependent. The values of BA and ODP content were markedly influenced by both cultivar and year. For a given cultivar, PPO and POD activities relative to fresh weight as well as BA were higher in the samples picked in 1976 at one location than in those picked in the other years at the other location.The initial rate of browning of apricots was primarily dependent on the ODP content as shown by linear regression analysis with two independent variables. The relative influence of ODP content as compared with that of PPO activity related to fresh weight was the stronger the higher the value of the ratio of PPO-ODP, i.e. the smaller the values of the endogenous substrate available to the enzyme in the tissues. This suggests substrate depletion to be the limiting factor in the enzymatic browning of apricots.Heat inactivation of PPO was found to be a simple exponential process, while that of POD a biphasic one. PPO was less heat resistant than POD: total inactivation occurred after 10-min heat treatment at 75°C and 85°C, respectively.