Modelling the effect of superatmospheric oxygen concentrations onin vitro mushroom PPO activity (original) (raw)
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Inhibition kinetics of polyphenol oxidase by glutamic acid
European Food Research and Technology, 2007
The inhibition of polyphenol oxidase (PPO) by glutamic acid was investigated. Application of different concentrations of glutamic acid to mushroom solution and Ocimum basilicum L. extract showed that glutamic acid appeared to be an effective browning inhibitor. Glutamic acid showed uncompetitive inhibition for mushroom and Ocimum basilicum L. polyphenol oxidases using 4-methylcatechol as a substrate, for mushroom PPO using catechol as a substrate and for Ocimum basilicum L. polyphenol oxidase using pyrogallol as a substrate; mixed-type inhibition for mushroom polyphenol oxidase using pyrogallol as a substrate; and noncompetitive inhibition for Ocimum basilicum L. polyphenol oxidase using catechol as a substrate. Furthermore, sodium azide was used as an inhibitor for comparison with the inhibition potency of glutamic acid. It was found that glutamic acid was a more power inhibitor than sodium azide. The type of inhibition observed depended on the substrate, inhibitor and enzyme source used.
International Journal of Food Science & Technology, 2008
Inhibition kinetics and mechanism of polyphenol oxidases (PPO) partially purified from various sources such as Thymbra spicata L. var. spicata and Ocimum basilicum L., and of mushroom PPO bought from Sigma by diethyldithiocarbamic acid have been described using catechol, 4-methylcatechol and pyrogallol as substrates. The inhibition type was competitive for O. basilicum L. PPO using catechol and 4-methylcatechol as substrates, for mushroom PPO using catechol, 4-methylcatechol and pyrogallol as substrates, and for T. spicata L. var. spicata PPO using 4-methylcatechol as a substrate; uncompetitive inhibition for T. spicata L. var. spicata PPO using pyrogallol as a substrate; and non-competitive inhibition for O. basilicum L. and T. spicata L. var. spicata PPO using pyrogallol and catechol as substrates, respectively. The inhibition effect of diethyldithiocarbamic acid on enzymatic browning varied greatly from one phenol to another and from one enzyme to another. Hence, no general rule can easily be established with regard to the type of inhibition observed.
Food and Bioprocess Technology, 2017
Polyphenol oxidase (PPO) is one of the most important food enzymes, it is responsible for the browning of many foods. Pulsed light (PL) is a non-thermal method of food preservation that is able to inactivate PPO. The aim of this work was to gain insight into the mechanism of PPO inactivation by PL. To this, the kinetics of PPO inactivation by PL was measured, together with associated changes in tryptophan fluorescence, KI fluorescence quenching and turbidity; and results were analysed by parameter A and phase diagram methods. Enzyme inactivation followed the Weibull model. Tryptophan fluorescence decreased during PL treatment, as well as the parameter A, while Stern-Volmer constants increased and turbidity was constant. The phase diagram showed only two populated states. There was a high correlation between the loss of activity and parameter A. Results indicate that under the experimental conditions, the inactivation of PPO by PL is an all-or-none process where the enzyme progressively unfolds with no evidence of aggregation.
2014
Enzymatic browning is a major quality issue in fruit and vegetable processing and can be counteracted by different 9 natural inhibitors. Often, model systems containing a single polyphenol oxidase (PPO) are used to screen for new inhibitors. To 10 investigate the impact of the source of PPO on the outcome of such screening, this study compared the effect of 60 plant extracts 11 on the activity of PPO from mushroom (Agaricus bisporus, AbPPO) and PPO from potato (Solanum tuberosum, StPPO). Some 12 plant extracts had different effects on the two PPOs: an extract that inhibited one PPO could be an activator for the other. As an 13 example of this, the mate (Ilex paraguariensis) extract was investigated in more detail. In the presence of mate extract, oxygen 14 consumption by AbPPO was found to be reduced >5-fold compared to a control reaction, whereas that of StPPO was increased 15 >9-fold. RP-UHPLC-MS analysis showed that the mate extract contained a mixture of phenolic compounds and saponins. Upon 16 incubation of mate extract with StPPO, phenolic compounds disappeared completely and saponins remained. Flash 17 chromatography was used to separate saponins and phenolic compounds. It was found that the phenolic fraction was mainly 18 responsible for inhibition of AbPPO and activation of StPPO. Activation of StPPO was probably caused by activation of latent 19 StPPO by chlorogenic acid quinones. 20 KEYWORDS: enzymatic browning, tyrosinase, LC-MS, plant extracts, Ilex paraguariensis 21 ■ INTRODUCTION 22
Current Topics in Peptide and Protein Research , 2023
Enzymatic browning is a biochemical process catalyzed by polyphenol oxidase (PPO), employing endogenous phenolic compounds and molecular oxygen as substrates. This intriguing reaction leads to the formation of brown or black pigments, commonly referred to as melanins, specifically occurring on the surfaces of certain fruits and vegetables. This research focuses on investigating the kinetic parameters of PPO, also known as tyrosinase, extracted from Agaricus bisporus (Paris mushroom) and Terfezia leonis (Desert truffle). The study explores the effects of pH, temperature, and substrate concentration (L-tyrosine) on PPO activity from both sources. The results demonstrate that the activity of PPO from Agaricus bisporus reaches its maximum at pH 5 and a temperature of 45 °C, with inhibition observed in the presence of excess substrate. The kinetic parameters, Vmax and Km, for Agaricus bisporus PPO were determined to be 0.07587 ΔAbs.Min^(-1) and 0.1386 mmol.l^(-1), respectively. On the other hand, the activity of PPO from Terfezia leonis reaches its peak at pH 5 and a temperature of 40 °C, and the corresponding kinetic parameters are Vmax = 66.35 μM/min and Km = 0.17 mM. Enzymatic browning has been a subject of interest for numerous scientists who have explored various techniques to inhibit or eliminate the compounds responsible for the reaction, such as oxygen, copper, substrate, or the enzyme itself. Overall, this study provides valuable insights into the kinetic behavior of PPO from Agaricus bisporus and Terfezia leonis, shedding light on potential strategies for inhibiting enzymatic browning to preserve the visual appeal and quality of food.
Journal of Food Biochemistry, 2013
Polyphenol oxidase (PPO) was purified from Lactarius piperatus (L.) Pers. by using Sepharose 4B-L-tyrosine-p-amino benzoic acid affinity column. Optimum pH and temperature of purified PPOs of L. piperatus were found to be 7.0 and 20C, respectively, by using catechol as a substrate. The enzyme retained 100% of its original activity at 4C and its optimum pH value for 24 and 72 h. L. piperatus PPO was also quite stable at 20C after 4 h incubation. The Km and Vmax values were calculated as 1 mM and 25 U/mg protein, respectively. Ascorbic acid was found to be the most potent inhibitor for the enzyme. The mushroom PPO was an effective biocatalyst in the selected organic solvents such as dichloromethane, heptane and toluene when using catechin as a substrate. All data support that L. piperatus has a highly active PPO possessing similar biochemical and kinetic characteristics to some plant PPO enzymes.
Controlled or modified packaging (CA/MA) of lettuce is simulated in model solutions containing lettuce polyphenol oxidase (PPO), chlorogenic acid (CG), and/or (-)-epicatechin (EPI) under various combinations of CO 2 , O 2 , N 2 , temperature, and pH conditions. Enzymatic browning is measured by PPO activity, color formation, substrate consumption, and development of products. Results were analyzed by multiway data analysis. CO 2 minimized the chemical polymerization and reduced PPO activity slightly. CG was a better substrate for PPO than EPI. CG was, in particular, involved in the primary enzymatic catalyzed oxidation, whereas EPI was important for the subsequent chemical polymerization in mixtures of CG and EPI. A very descriptive five-parameter multiplicative model was obtained from the PPO data by the multivariate method PARAFAC. This model describes the importance of substrate, atmospheric composition, pH, and temperature for PPO activity. Low pH (3.0) reduced PPO activity strongly (89%), whereas low temperature (5 °C) had a weaker effect on PPO activity (40% reduction of activity). The prediction of PPO activity (O 2 consumption) by kinetic UV-vis spectra correlated well (r 2) 0.87) with traditional polarographic PPO assay.
Control of Enzymatic Browning in Processed Mushrooms (Agaricus bisporus
Journal of Food Science, 1983
Control of polyphenol oxidase (E.C. 1.14.18) activity by the use of citric acid was investigated. The enzyme was inactivated at pH 4.0 and was stable to 10 min exposures at 25°C in the pH range 4.0–8.0. At pH 6.5 the enzyme was active at 45°C but not at 70°C and thermal inactivation followed pseudo first-order kientics. At pH 6.5 the activation energy (Ea) for enzyme inactivation was 41.1 Kcal/mole while at pH 3.5 two rate constants and hence two values for Ea were observed. Between 0–5 min Ea for inactivation of polyphenol oxidase was 8.7 Kcal/mole and >5 min Ea was 21.8 Kcal/mole.