香蕉皮多酚氧化酶和过氧化物酶特性的研究

分别以邻苯二酚、愈创木酚为底物,采用分光光度计测定氧化产物的方法对香蕉皮多酚氧化酶(PPO)和过氧化物酶(POD)的性质进行研究。结果表明,PPO最适温度为30℃、最适pH5.5、Km=22.42mmol/L、Vmax=0.027OD420/min,75℃水浴处理5min基本完全失活,100℃水浴处理20s可钝化PPO活性,并且香蕉皮PPO有同工酶;香蕉皮过氧化物酶(POD)的最适pH6.0、最适温度30℃,其在80℃下处理5min后基本失活,在沸水浴25s后酶被钝化。     

Browning in processed yams: peroxidase or polyphenol oxidase?

Polyphenol oxidase and peroxidase were purified from white yam (Dioscorea rotundata) using DEAE‐cellulose ionexchange chromatography. Thermoinactivation curves for polyphenol oxidase showed monophasic kinetics, while those for peroxidase were biphasic. Urea partially stabilised peroxidase against irreversible thermoinactivation, but did not do so in the case of polyphenol oxidase. Only peroxidase was capable of regenerating activity after thermoinactivation. The results showed that thermoinactivation of peroxidase was mainly due to conformational changes, while that of polyphenol oxidase was probably due to covalent damage. Peroxidase reactivation might play an important role in the browning of processed yam. © 2002 Society of Chemical Industry     

Peroxidase and Polyphenoloxidase Activities in Papaya During Postharvest Ripening and After Freezing/Thawing

Changes in peroxidase (POD) and polyphenoloxidase (PPO) activities of papaya (Caricu papava), cv Sunrise, during ripening, freezing and short frozen storage were studied. Fruits were stored at 14°C and 85 90 % RH until maturity for processing was reached (about 21 days). Fruit were frozen cryogenically and frozen slices were stored at — 18°C. POD activity increased in pulp tissue up to the ripe stage, showing a maximum value after 7 days cold storage. Similarly, PPO activity showed an important increase (4 × initial value) on the same date. The quantity of extractable proteins was at a maximum after 15 days storage at 14°C. Freezing and frozen storage (-18°C) produced an increase of POD activity while EPO activity was only slightly affected.     

化学抑制剂对果蔬食品多酚氧化酶性质影响的研究进展

多酚氧化酶(polyphenol oxidase,PPO)引起的酶促褐变会导致果蔬食品色泽劣变,营养成分降低,甚至使其丧失商品价值.化学抑制剂对PPO具有较好的抑制效果,并且使用方便,在果蔬食品中广泛使用,因此对它的研究具有理论和实际意义.该文论述了羧酸、抗坏血酸及其衍生物、含硫氨基酸、酚酸及其他抑制剂对PPO的抑制作...     

虾体多酚氧化酶特性及其抑制技术研究进展

多酚氧化酶是虾体中普遍存在的一种含铜金属蛋白,它是虾体发生黑变的主要原因,也是虾保鲜品质控制中亟待解决的技术关键。研究多酚氧化酶的酶学特性,抑制酶促褐变,对于提高虾的食用价值和商品价值至关重要。本文综合介绍了多酚氧化酶的虾体分布、活性特征、分离纯化、分析测定、黑变机理及其抑制方法。     

Oxidation of polyphenols in unfermented and partly fermented cocoa beans by cocoa polyphenol oxidase and tyrosinase

Unfermented and partly fermented dried cocoa beans have an excessively astringent and bitter flavour owing to their high polyphenol content. Studies on the remaining polyphenol oxidase activity and the oxidation of polyphenols in these beans have been conducted in relation to two factors, ie incubation time (0, 1, 2, 4, 8 and 16 h) and pH of incubation (3.5, 4.5, 5.5 and 6.5). Owing to unsuccessful polyphenol oxidation during incubation of partly fermented beans, incubation–enrichment treatments were carried out by combining incubation time (0, 8, 16, 24 and 32 h) and addition of crude cocoa polyphenol oxidase and purified tyrosinase from mushroom at 88 and 8800 units g^?1 and pH 5.5. Results showed that the remaining polyphenol oxidase activities of unfermented and partly fermented dried beans were 1 and 0.08% with specific activities of 9 and 1% respectively. The polyphenols of unfermented beans were effectively oxidised by incubation at 45 °C and pH 3.5–6.5 without enzyme enrichment; while those of partly fermented beans required enzyme enrichment. Both crude cocoa polyphenol oxidase and tyrosinase could be used for enzyme enrichment, but tyrosinase seemed to be more effective. © 2002 Society of Chemical Industry     

Properties of peroxidase and polyphenol oxidase in natural complexes from walnuts (Juglans regia) and in active DL-DOPA copolymers

Black polymers were extracted from walnut husk homogenates (Juglans regia L) in a phosphate buffer (pH 8.0) after air-bubbling for 24 h. After several purification stages, ultrafiltration and gel chromatography (Sephadex and Ultrogel), three extracts (two soluble and one insoluble) were isolated. At the same time, a synthetic DL DOPA/POD/PPO copolymer was prepared. Two walnut extracts exhibited POD and PPO activity. Both DL DOPA/POD/PPO copolymers (soluble and insoluble) only presented a POD activity. The insoluble and more complex extracts (either natural or synthetic) presented the lowest oxidase activities. The soluble walnut extract exhibited low though not negligible PPO and POD activities. It was observed using electrophoresis and gel chromatography that both enzymes were present in phenolic complexes. The high level of adsorption observed on polyacrylamide gel, as well as the elementary composition of these complexes enabled a comparison with phytomelanins. PPO and POD in the soluble copolymers (from both natural and synthetic sources) were governed by Michaelis-Menten kinetics. Apparent constants were calculated using the Lineweaver-Burk method. The use of limited proteolysis and an inhibitor showed good resistance of POD activity in walnut and synthetic copolymers and exceptional resistance of PPO activity in walnut extracts (particularly insoluble extract).     

Peroxidase and polyphenol oxidase thermal inactivation by microwaves in green coconut water simulated solutions

Enzymes from coconut water such as peroxidase (POD) and polyphenol oxidase (PPO) when in contact with oxygen begin reactions causing nutritional and color losses. Solutions simulating the chemical constituents of coconut water were submitted to a batch process in a microwave oven. PPO and POD inactivation data could be characterized by: PPO/water D_93 °C=16.5 s (z=35.5 °C); PPO/sugars D_91 °C=18 s (z=33°C); POD/water D_91.5 °C=44 s (z=24 °C) and POD/sugars D_92 °C=20.5 s (z=19.5 °C). The contact between salts and enzymes promoted a drastic reduction of the initial activity. After the incidence of microwave energy at temperatures above 90 °C, enzymes activity was not detected. These results can indicate an adequate choice of temperature conditions to inactivate coconut water enzymes. The knowledge of how green coconut water constituents influence POD and PPO activity will supply useful information about microwave processing of coconut water.     

贮藏期香椿中多酚类物质含量与相关酶活变化的关系

将新鲜香椿于0、5、10℃及20℃系列温度下贮藏,定期取样,测定香椿中的多酚类物质的含量,并对与多酚含量变化密切相关的酶类-多酚氧化酶(PPO)、过氧化物酶(POD)的酶活变化趋势进行考察。结果显示,各贮藏温度下,香椿中的多酚含量随着贮藏时间的延长呈现先上升后下降的趋势,而多酚氧化酶的酶活也呈现先上升后下降趋势,过氧化物酶的酶活则呈现出持续上升的趋势。同时发现贮藏于0℃下的香椿贮藏时间最长,生理变化最为缓慢,且其中多酚含量及多酚氧化酶(PPO)、过氧化物酶(POD)酶活变化最为平缓,可以确定香椿最宜存放于0℃条件下。     

In-vitro studies on the effect of polyphenol oxidase and peroxidase on the formation of polyphenolic black tea constituents

Flavanols (catechins and gallocatechins) isolated from green tea leaves (Camellia sinensis) (L) O Kuntze) were treated in vitro with polyphenol oxidase, peroxidase and a combination of both. The flavanol levels and those of the products formed were monitored by reversed-phase high-performance liquid chromatography (HPLC using spectrophotometric detection at 280 and 380 nm. Flavanols and theaflavins were quantified, whilst integrated peak areas are given for the remaining compounds. After fermentation in the presence of polyphenol oxidase higher levels of theaflavins and resolved thearubigins were obtained, whilst peroxidase produced higher amounts of chromatographically unresolved thearubigins of higher molecular weight, observed as a rise in the HPLC baseline, in the presence of peroxidase a significant decrease in the levels of all flavonol glycosides was observed, whilst in the presence of polyphenol oxidase only myricetin glycoside levels decreased.     

Drip loss,peroxidase and sensory changes in kiwi fruit slices during frozen storage

The biochemical, sensory and drip loss changes that occur during processing and prolonged frozen storage of kiwi fruit slices (cvs Abbott and Hayward) were studied. Fruit slices were frozen at ?40°C, packed in polyethylene bags and stored at ?18°C for 11 months. Maturity characteristics (pH, acidity, dry matter, soluble solids) were determined on raw fruit. Objective (proteins, peroxidase (EC 1.11.1.7) activity, drip loss) and subjective (sensory tests) analyses were carried out during processing and storage, and indicated a good quality of the frozen kiwi fruit slices after 11 months of storage. There were significant differences (P < 0.05) between the studied varieties with respect to drip loss during frozen storage and colour after 11 months. Best results were obtained with cv Hayward. This variety showed less drip loss after thawing and after 11 months storage presented the same green colour as after freezing, while cv Abbott became yellowish-green.     

苹果多酚氧化酶特性及无硫护色脱水研究

脱水苹果片在加工过程中极易发生褐变。在对苹果多酚氧化酶特性进行分析的基础上,通过设计正交实验得到最佳无硫护色剂组合,并初步确定真空干燥的条件。结果表明,苹果多酚氧化酶的最适pH为6.0,最适温度为36℃,100℃热烫60s可使其完全失活。苹果片的最佳无硫护色剂组合为0.6%柠檬酸、0.06%L-半胱氨酸、1.5%氯化钠,在真空度为0.09MPa,温度为50℃的条件下,可得到色泽较好的苹果片。     

新收获稻谷储藏期间蛋白含量及PPO活性的变化

分析了40℃、RH80%条件处理4d后置于15℃和23℃的籼稻和糯稻发芽率、多酚氧合酶(PPO)活性及蛋白质含量的变化。结果表明,40℃、85%RH温湿处理4d,显著提高2个稻谷品种发芽率,降低稻谷PPO活性。PPO活性在60～90d期间出现高峰,籼稻PPO活性对高温高湿敏感度高于糯稻。水溶性、盐溶性、醇溶性蛋白在30d出现一峰值,60d之后还有积累高峰;谷蛋白60d前急剧积累,之后积累缓慢。储藏期间稻谷巯基含量呈现下降趋势。短时间老化处理降低籼稻谷蛋白/醇蛋白比率峰值和巯基含量,却提高糯稻谷蛋白/醇蛋白比率峰值和巯基含量,即籼稻和糯稻陈化过程存在差别。     

基于视频与数字图像比色的甘薯多酚氧化酶活力检测

多酚氧化酶(polyphenol oxidase,PPO)是引起甘薯酶促褐变的主要原因,常用的PPO活力检测方法操作繁琐,建立一种简便快捷的检测方法意义重大。实验采用手机拍摄甘薯切片的褐变视频,提取视频图像RGB变化数据,建立了PPO活力预测模型。研究发现,0～30 s图像R值的变化量(ΔR)与PPO活力呈极强的正相关(相关系数0. 946),G值与B值的变化量(ΔG和ΔB)与PPO活力呈中等强度正相关(相关系数分别为0. 799和0.620)。采用多元线性回归模型对ΔR、ΔG、ΔB与PPO活力间的关系进行拟合,所得模型的拟合确定系数(R²)达到0. 903,模型的预测相关系数(r_p)、预测均方误差和标准偏差比分别为0. 956,2. 079和3. 459。结果表明,采用视频与数字图像比色快速检测甘薯多酚氧化酶活力是可行的。     

Degradation of pelargonidin 3‐glucoside in the presence of chlorogenic acid and blueberry polyphenol oxidase

Oxidation of both chlorogenic acid (CG) and pelargonidin 3‐glucoside (Pg 3‐glc) as well as their mixture, in the presence of blueberry polyphenol oxidase (PPO) was studied in model solutions. The reactions were monitored by spectrophotometric, polarographic and HPLC methods. In the absence of CG, Pg 3‐glc is not oxidised by blueberry PPO, but pigment degradation is induced by the presence of chlorogenic acid. Kinetic studies showed that Pg 3‐glc was degraded by a mechanism involving a reaction between chlorogenoquinone and/or secondary products of oxidation formed from the quinone and the pigment. Therefore, no coupled oxidation mechanisms occurred with Pg 3‐glc, as expected of its structure. The oxidation of CG by PPO in the presence of Pg 3‐glc involved the consumption of 0.6 μmol of oxygen per μmol of CG oxidised, which is close to the stoichiometry calculated from the oxidation of CG alone (0.63 μmol of oxygen per μmol). The initial phase of the pigment degradation showed a delay which did not correspond to cresolase activity. This phase could be explained by a quinone/anthocyanin reaction which is dependent on the chlorogenoquinone concentration and/or a reaction involving secondary products of oxidation (formed from the chlorogenoquinone) and Pg 3‐glc. © 1999 Society of Chemical Industry     

Some characteristics of polyphenol oxidase purified from edible yam (Dioscorea cayenensis-rotundata cv. Longbô) cultivated in Côte d'Ivoire

Polyphenol oxidase (PPO_Y) of edible yam ( Dioscorea cayenensis-rotundata cv. Longbô ) cultivated in Côte d'Ivoire was purified to homogeneity by a procedure that included ion exchange chromatography, ammonium sulphate fractionation, gel filtration and hydrophobic chromatography using dopamine as a substrate. The relative molecular weight of the PPO_Y was estimated to be 94.75 ± 0.63 and 151.56 ± 2.75 kDa by SDS–PAGE and gel filtration on Sephacryl S100 HR, respectively, indicating this PPO_Y as a multimer. Maximal PPO_Y activity occurred at 30 °C and pH 6.6. The enzyme was stable at 25 °C and its pH stability was in the range of 6.0–7.0. The values V _max/ K _m showed that the enzyme had the greatest reactivity towards dopamine among the substrates used. PPO_Y showed no activity toward the monophenols and was completely inhibited by beta-mercaptoethanol, sodium thiosulphate, l -ascorbic acid, sodium bisulphite and l -cysteine. Data generated by this study might help to better prevent edible yam browning.     

多酚氧化酶及超氧化物歧化酶与花生霉变的关系

探讨多酚氧化酶(PPO)及超氧化物歧化酶(SOD)活力变化与花生霉变进程的关系,为食品质量检测及食品的储藏安全提供理论依据。分别采用邻苯二酚显色法和邻苯三酚自氧化法测定PPO及SOD的酶活力。结果表明,PPO及SOD酶活均随着花生霉变进程变化而变化,呈现出特定的规律性。安全可食阶段的花生PPO酶活最高,而SOD酶活则最低。当花生微量长霉时,PPO酶活减少率为38.42%,而SOD酶活增加率则超过500%。这些数据可以作为花生是否霉变的评判依据。     

大麦酚类化合物及相关酶类的研究进展

大麦作为重要的粮食作物和啤酒酿造原料,其中的酚类化合物及其相关酶类（如酚类合成酶——苯丙氨酸解氨酶,酚类氧化酶——过氧化物酶和多酚氧化酶）对大麦的生长发育起重要的调节和保护作用,而在大麦的加工过程中会影响产品质量,如过氧化物酶和多酚氧化酶的氧化产物（苯醌和聚合产物）直接影响食品的质量。本文综述了大麦籽粒中酚类化合物及相关酶的种类和功能,并分析了对食品工业和啤酒酿造的影响。     

Improvement of frozen banana (Musa cavendishii, cv. Enana) colour by blanching: relationship between browning, phenols and polyphenol oxidase and peroxidase activities

 Browning in banana (Musa cavendishii, cv. Enana) processed products is a result of phenol oxidation catalysed by polyphenol oxidase (PPO) and peroxidase (POD) or of other non-enzymatic reactions (Maillard and Strecker mechanisms). Microwave and steam blanching significantly reduced PPO and POD activities and phenol levels in banana flesh, steam blanching being the most effective method for enzyme inactivation. Freezing/thawing processes produced a significant increase in phenol levels in all samples, due to cellular breakdown. After microwave heating browning processes occurred while steam-treated samples did not exhibit a significant colour change. Extractable PPO and POD activities in all banana samples increased as a consequence of freezing/thawing: steam-blanched slices exhibited lower residual activities. High correlations occurred between phenols and browning (r=0.86) in control samples. Blanched samples (microwave or steam) only exhibited correlations between PPO (r=0.80) and POD (r=0.80) activities and browning. Received: 22 February 1996     

Improvement of frozen banana (Musa cavendishii, cv. Enana) colour by blanching: relationship between browning, phenols and polyphenol oxidase and peroxidase activities

 Browning in banana (Musa cavendishii, cv. Enana) processed products is a result of phenol oxidation catalysed by polyphenol oxidase (PPO) and peroxidase (POD) or of other non-enzymatic reactions (Maillard and Strecker mechanisms). Microwave and steam blanching significantly reduced PPO and POD activities and phenol levels in banana flesh, steam blanching being the most effective method for enzyme inactivation. Freezing/thawing processes produced a significant increase in phenol levels in all samples, due to cellular breakdown. After microwave heating browning processes occurred while steam-treated samples did not exhibit a significant colour change. Extractable PPO and POD activities in all banana samples increased as a consequence of freezing/thawing: steam-blanched slices exhibited lower residual activities. High correlations occurred between phenols and browning (r=0.86) in control samples. Blanched samples (microwave or steam) only exhibited correlations between PPO (r=0.80) and POD (r=0.80) activities and browning. Received: 22 February 1996