苹果中多酚氧化酶的性质

苹果中的多酚氧化酶是引起苹果及苹果酒褐变的重要原因之一 ,用乳化剂及酚结合剂从苹果中提取多酚氧化酶 (PPO) ,研究其酶学性质 :不同底物的Km、Vm,反应的最适温度、pH及两种底物同时存在时的酶学效应 .结果表明 :4 甲基儿茶酚为最适底物 ,其最适温度 30℃ ,最适 pH4 .5 ,不同浓度咖啡酸对酶的影响不同 ,儿茶素对不同浓度绿原酸的酶促反应影响也不同 .研究几种效应物对酶活力的影响表明 :偏重亚硫酸钠、半胱氨酸、抗坏血酸为强烈抑制剂 ,羧酸类对酶具有抑制效应 ,肉桂酸比同一结构形式的苯甲酸抑制效果强     

蕨菜多酚氧化酶的性质

以冷冻丙酮制备蕨菜多酚氧化酶丙酮粉,用分光光度法研究pH、温度、底物浓度,抑制剂对酶活性的影响,结果表明,以邻苯二酚为底物,该酶的最适pH值为7.4,最适温度为25℃;Km为39.86 mmol/L,Vm为0.686 OD/min,90℃热处理50 s可钝化PPO的活性;抗坏血酸、亚硫酸钠为强烈抑制剂,175 mg/L的亚硫酸钠、225 mg/L的抗坏血酸能有效抑制PPO的活性.     

苹果多酚结构及褐变研究进展

本文对已报道的苹果多酚物质进行了归类。并列出了它们的结构图。在苹果加工业中,褐变备受关注,其直接影响着产品的营养、风味和感官。这种褐变主要由于多酚类物质在西每（多酚氧化酶PPO和过氧化酶POD）的氧化下生成了有色物质,文中对这两种酶氧化多酚机理进行了分析,并时褐变抑制剂及抑制机理作了阐述。     

苹果多酚对多酚氧化酶氧化特性的影响

本文以富士苹果中含量较多的绿原酸、儿茶素、表儿茶素和根皮苷为苹果多酚氧化酶（PPO）作用底物,以磷酸盐缓冲液为苹果汁酶促褐变模拟体系,通过连续测定酶促褐变模拟体系吸光度A420值的变化趋势,研究不同苹果多酚底物对PPO酶促催化特性的影响,并确定多酚氧化酶对该4种底物较适作用条件。结果表明,苹果多酚底物对PPO反应特性影响较大;PPO酶促氧化绿原酸、儿茶素、表儿茶素和根皮苷4种多酚底物适宜的pH分别为5.0、4.0、4.5、4.5;适宜的温度分别为55、70、60、50 ℃;PPO作用适宜的底物浓度分别为5、0.5、2、10 mM;适当提高酶活可促进酶促褐变反应,且该4种底物对多酚氧化酶的亲和力大小为：儿茶素>表儿茶素>绿原酸>根皮苷。该研究为苹果汁褐变控制提供理论依据。     

褐变抑制剂对果蔬多酚氧化酶的影响

果蔬贮藏过程中,褐变问题严重影响其经济价值及营养价值,由多酚氧化酶引起的酶促褐变备受关注,寻找合适的抑制方法是国内外研究的热点。一些化学抑制剂对于酶促褐变具有良好的抑制效果,本文综述了果蔬褐变的机理,抗坏血酸、半胱氨酸、柠檬酸抑制剂的作用原理及具体应用,旨在为解决由酶促褐变引起的果蔬生产加工问题提供参考,促进果蔬品质的提升。     

苹果多酚氧化酶的提取及其抑制作用的研究

以冷冻丙酮制备苹果多酚氧化酶(PPO), 通过以邻苯二酚为底物测定氧化产物的方法,对苹果果肉中多酚氧化酶的pH值、温度、热稳定性及抗氧化剂抑制作用进行了研究.结果表明:用真空冷冻干燥得到的酶粉能更好的保持多酚氧化酶活性;酶氧化邻苯二酚的最适pH为6.0,最适温度为25℃;PPO在20-25℃时对热较稳定,期后随着温度升高后,酶活迅速降低;在100℃维持1min酶全部失活;抗坏血酸和黄酮类物质能明显地抑制酶促褐变.     

香蕉中多酚氧化酶特性探讨

针对香蕉储运保鲜及加工过程中褐变问题研究了其中多酚氧化酶的反应速度、最适 pH值、热稳定性等方面的特性 ,从而可以为解决香蕉的褐变问题提供了科学依据。     

香蕉中多酚氧化酶特性探讨

针对香蕉储运保鲜及加工过程中褐变问题研究了其中多酚氧化酶的反应速度、最适pH值、热稳定性等方面的特性，从而可以为解决香蕉的褐变问题提供了科学依据。     

香蕉多酚氧化酶褐变性质的研究

以邻苯二酚为废物通过采用分光光度计测定氧化产物的方法,对香蕉果肉中多酚氧化酶(PPO)的催化特性、最适温度、最适pH值、热稳定性等性质进行了研究。结果表明,香蕉PPO的最适温度为 25℃,最适 pH为 5.0,75℃水浴处理 5 min酶基本完全失活,100℃水浴处理20s可钝化PPO的活性,且香蕉PPO存在同功酶。实验中同时考察了柠檬酸、抗坏血酸、NaHSO_3和半胱氨酸对PPO的褐变抑制效果。     

葡萄与葡萄酒中多酚氧化酶研究进展

在葡萄与葡萄酒的加工过程中,多酚氧化酶可以引起葡萄汁和葡萄酒的氧化,尤其是白葡萄酒,严重影响了葡萄酒的品质。本文总结了葡萄中多酚氧化酶的结构和功能及其在葡萄中的分布情况,并且揭示了在葡萄酒酿造工艺中其引起氧化褐变的机制,同时介绍了影响多酚氧化酶活性的因素和多酚氧化酶抑制剂应用等的研究进展,为进一步控制葡萄酒酿造过程中多酚氧化酶引起的氧化褐变提供参考。     

不同杂交后代苹果与富士苹果的多酚氧化酶特性比较

不同杂交后代苹果54号、45号及富士苹果多酚氧化酶特性比较结果表明：不同苹果的最适pH值不同，45号和富士为5．5，54号为6．0；45号、54号和富士最适温度分别为30，35，40℃；富士热稳定性最强，其次是45号，最次为54号；不同苹果PPO的最适底物依次为绿原酸、咖啡酸、儿茶酚；Na2S203对PPO活性抑制效果最佳，L-半胱氨酸与抗坏血酸的抑制效果较好，EDTA-2Na的抑制效果较差；不同苹果PPO同工酶酶带不同，染色深浅不同。富士有四条酶带，45号和54号只有一条共有酶带，富士酶带数最多，染色最深。     

Inactivation kinetics of apple polyphenol oxidase in different pressure–temperature domains

The impact of high hydrostatic pressure and temperature on the stability of polyphenol oxidase (PPO) was studied in cloudy apple juice. Application of 200–500 MPa near room temperature or heat treatment at 45–55 °C at ambient pressure caused an increase of PPO activity of up to 65% in freshly squeezed apple juice. Combined pressure–temperature inactivation experiments with fully activated PPO (5 min treatment at 400 MPa and 20 °C) were carried out in the range of 0.1–700 MPa and 20–80 °C. Enzyme inactivation kinetics followed a 2.2 order reaction scheme at all pressure–temperature conditions tested. A polynomial model was successfully applied to describe the rate of PPO inactivation as a function of pressure and temperature and was used to construct a pressure–temperature isokinetic diagram. This diagram clearly showed synergistic effects of pressure and temperature on the inactivation of apple PPO at pressures above 300 MPa and antagonistic effects at lower pressures. Compared to ambient pressure conditions, temperatures required to inactivate PPO in apple juice were increased 10–15 °C at 100–300 MPa.

Industrial relevance

High pressure processing of fresh fruits is gaining popularity in the food industry because of its ability to inactivate microorganisms and some enzymes near room temperature with little impact on flavour or nutritional attributes of the food. However, quantitative data regarding the impact of process parameters on the target reaction are required to economically utilise this technology. This paper provides a mathematical model describing the combined effect of pressure, temperature and treatment time on the inactivation of PPO in cloudy apple juice.     

Characterization of polyphenol oxidase from broccoli (Brassica oleracea var. botrytis italica) florets

Polyphenol oxidase (PPO) from broccoli florets was extracted and purified through (NH₄)₂SO₄ precipitation, ion-exchange and gel filtration chromatography. The molecular weight was estimated to lie between 51.3 and 57 kDa by sodium dodecyl sulphate-polyacrylamide gel electophoresis (SDS-PAGE) and gel filtration. The effects of substrate specificity, pH, and sensitivity to various inhibitors: citric acid, ascorbic acid, sodium sulphate and EDTA (sodium salt of ethylenediaminetetraacetic acid) of partially purified PPO were investigated. Polyphenol oxidase showed the best activity toward catechol (K_M = 12.34 ± 0.057 mM, V_max = 2000 ± 8736 U/ml/min) and 4-methyl catechol (K_M = 21 ± 0.087 mM, V_max = 28.20 ± 0.525 U/ml/min). The optimum pH for broccoli PPO was 5.7 with catechol and 4-methylcatechol as substrates. The most effective inhibitor was sodium sulphate.     

烟草多酚氧化酶的分离提纯及性质研究

本文用丙酮干粉,硫酸铵分级沉淀,阴离子交换层析,阳离子交换层析和凝胶过滤方法从新鲜的烟叶中分离纯化出了一种多酚氧化酶Ⅰ和多酚氧化酶Ⅱ(根据过DEAE-Sephadex A-50柱后的前后顺序,命名A-5柱先洗脱的活性组分为多酚氧化酶Ⅰ(PPOⅠ),后洗脱的为多酚氧化酶Ⅱ(PPOⅡ)).分离后多酚氧化酶Ⅰ的比活力是原来的71倍,而多酚氧化酶Ⅱ的比活力为原来的100倍.SDS-PAGE电泳显示分离所得的多酚氧化酶为纯品,其分子量分别为42kDa和42.5kDa.最后测量了分离得到的PPO的一些基本性质,结果表明多酚氧化酶Ⅰ在pH=7,t=40℃时具有最大活力,多酚氧化酶Ⅱ在pH=6,t=40℃时具有最大活力.动力学研究表明在pH=6.5,以邻苯二酚为底物的条件下,两种酶Km值分别为6.8mmol/L和1.2mmol/L.     

Convenient partial purification of polyphenol oxidase from apple skin by cationic reversed micellar extraction

Polyphenol oxidase (PPO) was selectively extracted from reconstituted freeze-dried apple skin using reverse micelles formed by a cationic surfactant, dodecyl trimethyl ammonium bromide (DTAB). An optimum forward extraction was achieved with sodium phosphate buffer (pH 6, 100 mM, no added KCl) and an organic phase (isooctane:hexanol at a ratio of 5:1) containing 100 mM DTAB. The solubilised PPO was efficiently recovered by a stripping solution (pH 6, 1 M KCl) containing 10% ethanol. Under the optimised conditions, the purification fold and recovered activity of PPO were 12.6% and 71%, respectively. This purification fold and recovery were maintained when the extraction volume increased from 10–200 ml. Overall, reversed micellar extraction can be used as an efficient first step for the purification of PPO from apple skin.     

叠氮活化烟草多酚氧化酶II的机理

至今人们一直报道叠氮作为金属蛋白(特别是铜蛋白)的一种抑制剂,本研究表明叠氮也可以作为烟草多酚氧化酶Ⅱ (简称PPOⅡ)的激活剂。在天然PPOⅡ、叠氮-PPOⅡ络合物和过氧化物-PPOⅡ络合物的方波电位学研究中,从硝基蓝四唑(nitro bluetetrazolium)能被酶还原和PPOⅡ能被过氧化物激活的试验结果可以看出,叠氮与PPOⅡ的结合诱导了天然PPOⅡ活性中心的CuO₂2-Cu生成了CuO₂2-Cu活性中心结构。叠氮作为激活剂的原因应归因于叠氮分子与PPOⅡ的络合反应导致了CuO₂2-Cu的生成,它恰是过氧化物-PPOⅡ络合物的活性中心,其实质是过氧负离子起到激活剂的作用。      

蓝莓多酚氧化酶的部分纯化及其酶学特性研究

目的：明确蓝莓多酚氧化酶(PPO)的酶学特性。方法：分别采用硫酸铵分级沉淀法和疏水层析法分离纯化蓝莓PPO,比较两者的纯化效果,并对蓝莓PPO的酶促反应动力学、最适反应温度和pH以及稳定性进行研究。结果：硫酸铵分级沉淀法与疏水层析法的纯化倍数相近,但两者的得率分别为61%和84%。以绿原酸和邻苯二酚为底物时,蓝莓PPO的米氏常数(K_m)分别为23.38mM和6.13mM。该酶的最适pH值为6.0,最适反应温度为25℃。该酶在40℃以上不稳定,而在70℃时,其酶活在60s后残余酶活仅为7.23%。随着pH值的不断降低,其稳定性会不断下降。结论：疏水层析法对蓝莓PPO的分离纯化效果更好。蓝莓PPO对邻苯二酚的亲和力更高,该酶对温度和pH都较为敏感。     

Inhibition of polyphenol oxidase and peroxidase activities on fresh-cut apple by simultaneous treatment of ultrasound and ascorbic acid

The effects of ultrasound and ascorbic acid on activity changes of polyphenol oxidase and peroxidase, of fresh-cut apple during storage, were investigated. The combined treatment of ultrasound and ascorbic acid inactivated monophenolase, diphenolase, and peroxidase, whilst the individual treatment of ultrasound or ascorbic acid had inverse and limited inhibitory effect on the enzymes. The main protein bands had a molecular weight of approximately 63 kDa. A diffuse band, lacking the electrophoretic mobility of proteins, was observed after combined treatment. This investigation revealed that simultaneous treatment with ultrasound and ascorbic acid had synergistic inhibitory effects on several enzymes related to enzymatic browning.     

Quantification and characterisation of polyphenol oxidase from vanilla bean

Polyphenol oxidase (PPO) of Vanilla planifolia Andrews beans was extracted and purified through ammonium sulphate precipitation, dialysis, and gel filtration chromatography. PPO activity was measured by improved UV technique using 4-methylcatechol and catechol as substrates increasing substantial sensitivity of previous procedure. The optimum pH and temperature for PPO activity were found to be 3.0 and 3.4 and 37 °C, respectively. K_m and V_max values were found to be 10.6 mM/L and 13.9 OD₃₀₀ min⁻¹ for 4-methylcatechol and 85 mM/L and 107.2 OD₃₀₀ min⁻¹ for catechol. In an inhibition test, the most potent inhibitor was found to be 4-hexylresorcinol followed by ascorbic acid. The thermal inactivation curve was biphasic. Activation energy (E_a) and z values were calculated as 92.10 kJ mol⁻¹ and 21 °C, respectively.