Characterization of phenoloxidase activity of carapace and viscera from cephalothorax of Norway lobster (Nephrops norvegicus)

The characterization of phenoloxidase activity was performed in both carapace and viscera extracts of Norway lobster. Phenoloxidase activity rose with increasing temperature up to 60 °C. The carapace enzymatic extract showed the highest themostability, retaining about 80% of maximum activity at 45 °C and 40% at 65 °C. On the other hand, both enzymatic extracts showed a single peak activity at neutral-slightly alkaline pH and were quite resistant to inactivation at alkaline pH (pH > 8), but phenoloxidase activity became unstable at pH lower than 5.5. The enzymatic extract obtained from viscera showed a higher affinity for catechol (K_M 5.97 mM) than carapace extract (K_M 19.40 mM). Both mono- and diphenoloxidase activities were found in carapace and viscera. Polyphenoloxidase and converted-hemocyanin into PPO-like enzyme could be the main responsible for these activities.     

桃褐变调控方法的研究

本文对控制多酚氧化酶（ＰＰＯ）活力的方法进行了探索，证明利用三因子二次回归组合设计所得到的回归方程能准确反映因子与指标之间的关系，并能预示因子（氯化钠、柠檬酸、抗环血酸）用量的多少对指标（ＰＰＯ活力）影响的程度与趋势。在各因子对指标的重要性及交互效应的分析方面，也提供了完整、准确、严谨的分析方法。     

Thermal inactivation of polyphenoloxidase in pineapple puree

Prevention of browning in pineapple puree by thermal inactivation of enzyme, Polyphenoloxisase (PPO), was examined between 40 and 90 °C and in relation to exposure time. The amount of inactivation was measured as a function of time and temperature under isothermal conditions. Reaction rate constant and activation energy (E_a) as well as Decimal reduction time (D) and z-value of thermal inactivation, were determined. The rate of inactivation varied with temperatures and follows a logarithmic law. Kinetic studies showed that the thermal inactivation (40-90 °C) of the PPO followed first-order kinetics.     

Effect of ferulic acid on inhibition of polyphenoloxidase and quality changes of Pacific white shrimp (Litopenaeus vannamei) during iced storage

Effects of ferulic acid (FA) on polyphenoloxidase (PPO) and the quality changes of Pacific white shrimp (Litopenaeus vannamei) during iced storage for 10 days were investigated. Both FA and oxygenated FA (OFA) with different concentrations (0.1%, 0.5%, 1% and 2% (w/v)) showed PPO inhibitory activity in a dose dependent manner. FA was generally more effective in PPO inhibition than was OFA. Based on activity staining, white shrimp PPO with an apparent molecular weight of 210 kDa was inhibited by FA. When whole shrimps were treated with FA solution with concentrations of 1% or 2% and stored in ice for up to 10 days, the increase in psychrophilic and mesophilic bacterial count were retarded, in comparison with the control and those treated with 1.25% sodium metabisulphite (SMS). The coincidental lower rates of increase in pH and total volatile base content were obtained. Additionally, shrimps treated with 2% FA possessed the lowest peroxide value and thiobarbituric acid reactive substances (TBARS) value during the storage. After 10 days of storage, shrimps treated with 2% FA had the lower melanosis score and higher score for colour, flavour and overall likeness, compared with the control and SMS treated shrimps (P < 0.05).     

Steam blanching effect on polyphenoloxidase,peroxidase and colour of mango (Mangifera indica L.) slices

The heat stability of peroxidase (POD) and polyphenoloxidase (PPO) was investigated in mango (Mangifera indica L.) slices, and the relative colour was studied after different steam blanching times. There was complete inactivation after 5 min for POD and 7 min for PPO. Steam blanching of 3 min gave residual activity of 2.85% and 8.33% for PPO and POD, respectively, and when compared with samples blanched for 5 min had no effect on colour over 20 days of storage. Correlation was found between activities of PPO, POD and colour change over 20 days. After 7 min steam blanching the browning index was stable but less than at 3 and 5 min because non-enzymic browning had occurred. This research suggests that yellowness (b) and lightness (L) values contribute positively to the browning index (BI), compared to redness (a).     

Biochemical characterization and process stability of polyphenoloxidase extracted from Victoria grape (Vitis vinifera ssp. Sativa)

Polyphenol oxidase (PPO) was isolated from Victoria grapes (Vitis vinifera ssp. Sativa) grown in South Africa and its biochemical characteristics were studied. Optimum pH and temperature for grape PPO activity were pH 5.0 and T = 25 °C with 10 mM catechol in McIlvaine buffer as substrate. PPO showed activity using the following substances: catechol, 4 methyl catechol, d, l-DOPA, (+) catechin and chlorogenic acid. K_m and V_max values were 52.6 ± 0.00436 mM and 653 ± 24.0 OD_400 nm/min in the case of 10 mM catechol as a substrate. Eight inhibitors were tested in this study and the most effective inhibitors were found to be ascorbic acid, l-cysteine and sodium metabisulfite. Kinetic studies showed that the thermal inactivation of Victoria grape PPO followed first-order kinetics, with an activation energy, E_a = 225 ± 13.5 of kJ/mol. Both in semipurified extract and in grape juice, PPO showed a pronounced high pressure stability.     

无核白葡萄多酚氧化酶特性研究

从新疆无核白葡萄中分离出多酚氧化酶（ＰＰＯ）并对其部分特性进行了研究。结果表明其最适ｐＨ为７,且在ｐＨ３处存在相对活力的４５％,最适温度为２０℃。酶催化反应动力学方程为Ｖ＝０．０９１「ｓ」／５４．０１＋「ｓ」,对「ｓ」来说属于分数级反应ｐｐｏ对儿茶素和咖啡酸的催化能力强于绿原酸和邻苯二酚,对一元酚和对间二酚,对一元酚和对间二酚不起作用。本研究为探明新疆无核白葡萄荫干过程中酶促褐变的内部原因提供了理     

The Deglet-Noor Date Polyphenoloxidase Activity Is Very Thermolabile and Exhibits Peculiarities in Its Thermal Inactivation Kinetics

In our current research on the preservation of the Deglet-Noor date quality during thermal processing, the heat inactivation of the polyphenoloxidase in enzyme extracts of this fruit was investigated. In contrast to previous studies on this enzyme in this exotic fruit, we performed full kinetic analyses at different temperatures (25-70°C) and enzyme activity was measured by the initial velocity methodology. The heat-inactivation of the polyphenoloxidase from the Deglet-Noor date does not obey a simple “one step-two stages” mechanism. All the recorded kinetics were described using a simple three parameters-biexponential model that we previously showed to be a common arranged form of kinetic expression for the known wide diversity of mechanisms of enzyme deactivation. The values of the two rate constants of the model were collected for four temperatures, ranging from 25 to 70°C and their variation was analyzed through the ARRHENIUS's law to determine the Ea values (11.83 and 54.71 kJ mol^-1, respectively). Possible explanations and implications of such low values are discussed. These results are compared to other results from laboratory as well as elsewhere in the literature.     

Effect of reactant concentrations on the Maillard reaction in a fructose–glycine model system and the inhibition of black tiger shrimp polyphenoloxidase

The characteristics and the inhibitory activity towards black tiger shrimp polyphenoloxidase of Maillard reaction products (MRPs), prepared by heating an equimolar mixture of fructose and glycine at various concentrations (0.75–30 mM) at 100 °C for 12 h, were investigated. Increase in the intermediate products was observed with increasing reactant concentration, as evidenced by the increase in A₂₉₄ and fluorescence intensity. Furthermore, development of browning (A₄₂₀) was noticeable when the reactant concentration increased. The inhibitory activity of MRPs towards PPO gradually increased when the concentration of each reactant increased and reached a maximum at 30 mM (80% inhibition). The increase in the inhibitory activity of MRPs was coincidental with the increase in the reducing power, A₂₉₄, fluorescence intensity, as well as browning intensity. Generally, the development of Maillard reaction products was associated with decrease in pH and loss of reducing sugar and free amino groups, with coincidental increase in reducing power and copper-chelating property. MRPs with the reactant concentration of 4.5–30 mM were able to chelate the copper ion. Therefore, the inhibitory activity of MRPs towards browning, induced by PPO, was most likely due to their copper-chelating property as well as reducing power.     

微生物发酵酸浆对马铃薯浆液的防褐研究

用豌豆自然发酵酸浆对马铃薯浆液进行防褐研究，结果表明，豌豆自然发酵酸浆对马铃薯浆液具有显著防褐作用，其他主褐因子并非酸浆中主要代谢产物－－有机酸，而是微生物菌体和上清液中某种热敏性物质，且该物质能有效抑制马铃薯多酚氧化酶活性。