scholarly journals Kinetics of non-enzymatic browning reaction from the l-ascorbic acid/l-cysteine model system

2016 ◽  
Vol 34 (No. 6) ◽  
pp. 503-510 ◽  
Author(s):  
A.-N. Yu ◽  
L.-P. Tang
Keyword(s):  
Ascorbic Acid ◽  
Order Reaction ◽  
Model Systems ◽  
Enzymatic Browning ◽  
Ascorbic Acid Concentration ◽  
First Order ◽  
Browning Reaction ◽  
Brown Colour ◽  
Colour Development ◽  
Kinetics Of

The kinetics of the non-enzymatic browning reaction from l-ascorbic acid/l-cysteine model systems was investigated at 125–155°C for 10–120 min by measuring the loss of reactants and monitoring the brown colour development. The result showed that the browning products were produced at the first order reaction kinetics requirement, with the E<sub>a</sub> being 114.33 kJ/mol. The mechanism for the browning development was proposed. The correlation coefficient between browning products and uncoloured intermediate products increased with the rising temperature. At temperatures below 110°C, the non-enzymatic browning reaction did not occur at all or the reaction was slow. Browning products could not be produced solely by self-degradation of l-cysteine. The amount of browning products negatively correlated with the l-ascorbic acid concentration.

scholarly journals Kinetics of degradation of ascorbic acid by cyclic voltammetry method

2015 ◽  
Vol 21 (2) ◽  
pp. 351-357 ◽  
Author(s):  
Veselinka Grudic ◽  
Nada Blagojevic ◽  
Vesna Vukasinovic-Pesic ◽  
Snezana Brasanac
Keyword(s):  
Ascorbic Acid ◽  
Cyclic Voltammetry ◽  
Rate Constant ◽  
Oxidation Reaction ◽  
Order Reaction ◽  
First Order Reaction ◽  
First Order ◽  
Other Substances ◽  
Kinetics Of Degradation ◽  
Kinetics Of

Cyclic voltammetry was used to examine the kinetics of degradation of ascorbic acid (AA) at different temperatures. It has been shown that the reduction of the concentration of AA in all temperatures follow the kinetics of the first order reaction. The rate constant of the oxidation reaction increases with temperature as follows: 5x10-5; 2x10-4; 1x10-3 and 3x10-3 min-1 at temperatures of 25?C, 35?C, 65?C and 90?C, respectively. The temperature dependence of the rate constant follows Arrhenius equation, and the value of activation energy of the reaction degradation is 48.2 kJ mol-1 . The effect of storage time at a temperature of 90 ?C on AA content in fresh juice of green peppers was investigated. It was shown that AA oxidation reaction in the juice is also the first order reaction, while the lower rate constant in relation to the pure AA (5x10-3 min-1) indicates the influence of other substances present in peppers.

The Kinetics of Glucose Decomposition with Sulfate Reduction in the Anaerobic Fluidized Bed Reactor

1993 ◽  
Vol 28 (2) ◽  
pp. 135-144 ◽  
Author(s):  
S. Matsui ◽  
R. Ikemoto Yamamoto ◽  
Y. Tsuchiya ◽  
B. Inanc
Keyword(s):  
Sulfate Reduction ◽  
Fluidized Bed ◽  
Kinetic Equations ◽  
Fluidized Bed Reactor ◽  
Order Reaction ◽  
First Order Reaction ◽  
First Order ◽  
Glucose Decomposition ◽  
Reaction Equations ◽  
Kinetics Of

Using a fluidized bed reactor, experiments on glucose decomposition with and without sulfate reduction were conducted. Glucose in the reactor was mainly decomposed into lactate and ethanol. Lactate was mainly decomposed into propionate and acetate, while ethanol was decomposed into propionate, acetate, and hydrogen. Sulfate reduction was not involved in the decomposition of glucose, lactate, and ethanol, but was related to propionate and acetate decomposition. The stepwise reactions were modeled using either a Monod expression or first order reaction kinetics in respect to the reactions. The coefficients of the kinetic equations were determined experimentally. The modified Monod and first order reaction equations were effective at predicting concentrations of glucose, lactate, ethanol, propionate, acetate, and sulfate along the beight of the reactor. With sulfate reduction, propionate was decomposed into acetate, while without sulfate reduction, accumulation of propionate was observed in the reactor. Sulfate reduction accelerated propionate conversion into acetate by decreasing the hydrogen concentration.

Kinetics and Mechanism of Hexachloroiridate(IV) Oxidation of Arsenic(III) in Acidic Perchlorate Solutions

1992 ◽  
Vol 57 (7) ◽  
pp. 1451-1458 ◽  
Author(s):  
Refat M. Hassan
Keyword(s):  
Ionic Strength ◽  
Fractional Order ◽  
Activation Parameters ◽  
Order Reaction ◽  
First Order Reaction ◽  
Intermediate Complex ◽  
Constant Ionic Strength ◽  
Kinetics Of Oxidation ◽  
First Order ◽  
Kinetics Of

The kinetics of oxidation of arsenic(III) by hexachloroiridate(IV) at lower acid concentrations and at constant ionic strength of 1.0 mol dm-3 have been investigated spectrophotometrically. A first-order reaction in [IrCl62-] and fractional order with respect to arsenic(III) have been observed. A kinetic evidence for the formation of an intermediate complex between the hydrolyzed arsenic(III) species and the oxidant was presented. The results showed that decreasing the [H+] is accompanied by an appreciable acceleration of the rate of oxidation. The activation parameters have been evaluated and a mechanism consistent with the kinetic results was suggested.

The effects of reaction parameters on the non-enzymatic browning reaction between l-ascorbic acid and glycine

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Yan Yang ◽  
Ya Li ◽  
Liang Feng ◽  
Ai-Nong Yu ◽  
Bao-Guo Sun ◽  
...  
Keyword(s):  
Ascorbic Acid ◽  
Reaction Pathway ◽  
Enzymatic Browning ◽  
Reaction Parameters ◽  
Remarkable Effect ◽  
Ph Values ◽  
Browning Reaction ◽  
Zero Order Kinetics ◽  
Volatile Products ◽  
Effects Of Temperature

AbstractThe non-enzymatic browning (NEB) reaction between l-ascorbic acid (ASA) and glycine (Gly), including the effects of temperature (110–150 °C), time (10–150 min) and pH (4.5, 6.8, 8.0 and 9.5) on the formation of un-colored intermediate products (UIPs), browning products (BPs) and volatile products (VPs), were investigated. The results showed that pH had a remarkable effect on the reaction. The characteristics of zero-order kinetics for the formation of UIPs and BPs were discussed, and the corresponding activation energy (Ea) was also calculated. When the pH was 4.5, the Ea for the formation of UIPs was approximate 53.76 kJ/mol and less than that at other pH values; while the Ea for BPs formation was approximate 94.06 kJ/mol and much higher than that at other pH values. The results suggested that an acidic environment facilitated the generation of UIPs, but did not remarkably promote the formation of BPs. The possible reaction pathway between ASA and Gly was proposed according to the experimental results.

Bacteriophage Conjugates: The Effect of Coupling Reaction and Specific Antibodies on the Kinetics of Inactivation and Reactivation

1973 ◽  
Vol 28 (1-2) ◽  
pp. 83-90
Author(s):  
Horst Mossmann ◽  
Dietrich K. Hammer
Keyword(s):  
Bacteriophage T4 ◽  
Covalent Binding ◽  
Coupling Reaction ◽  
Order Reaction ◽  
Direct Plating ◽  
Specific Antibodies ◽  
Coupling Process ◽  
First Order ◽  
Kinetics Of ◽  
Critical Site

The reaction of bacteriophage T4 with 1-fluoro-2,4-dinitrobenzene resulted in a covalent binding of 2,4-dinitrophenyl (DNP) determinants to the phage. From the kinetics of inactivation reflecting the coupling process it is concluded that attachment of more than one DNP group to the critical site(s) of the phage is required for inactivation (multi-hit reaction). Contrary to this the neutralization of DNP-T4 by anti-DNP antibody turned out to be a first order reaction, until 80 %> neutralization fitting one-hit kinetics. If compared with native T4, the susceptibility of DNP-T4 to neutralization by anti-T4 antibody is considerably higher, indicating that attachment of DNP groups to T4 amplifies the sensitivity to neutralization by anti-T4. Comparing neutralization kinetics of DNP-T4 and native T4 by anti-DNP-T4 antibody it is suggested that native determinants and DNP groups, as well as determinants resulting from alteration due to the coupling process, all together may contribute as targets for neutralization. Three characteristics strengthen the view that the velocity of T4 conjugates in infecting the host strain is markedly decreased if compared with that of native T4: (a) considerable discrepancy between direct plating and decision technique (b) increasing variety of plaque size and (c) decreased velocity of the first step of reproduction. The kinetics of neutralization observed can be reconciled with a model proposed by Krummel and Uhr. The kinetics of reactivation of neutralized DNP-T4 by the presence cf DNP-BSA has been investigated and the problems involved in the reaction are discussed.

scholarly journals The alcoholysis of 1,2,2-trimethylpropyl-methylfluorophosphonate

2000 ◽  
Vol 65 (12) ◽  
pp. 857-866
Author(s):  
Mladjen Micevic ◽  
Slobodan Petrovic
Keyword(s):  
Kinetic Data ◽  
Reaction Rate ◽  
Frequency Factor ◽  
Reaction Rate Constant ◽  
Order Reaction ◽  
Activation Entropy ◽  
Second Order Reaction ◽  
Third Order ◽  
First Order ◽  
Kinetics Of

The alcoholysis of 1,2,2-trimethylpropyl-methylfluorophosphonate (soman) was examined with a series of alkoxides and in corresponding alcohols: methanol, ethanol, 1-propanol, 2-propanol, 2-methoxyethanol and 2-ethoxyethanol. Soman reacts with the used alkoxides in a second order reaction, first order in each reactant. The kinetics of the reaction between 1,2,2-trimethylpropyl-methylfluorophosphonate and ethanol in the presence of diethylenetriamine was also examined. A third order reaction rate constant was calculated, first order in each reactant. The activation energy, frequency factor and activation entropy were determined on the basis of the kinetic data.

Direct Method for Determining Inorganic Phosphate in Serum with the "CentrifiChem"

1972 ◽  
Vol 18 (3) ◽  
pp. 263-265 ◽  
Author(s):  
John A Daly ◽  
Gerhard Ertingshausen
Keyword(s):  
Inorganic Phosphate ◽  
Direct Method ◽  
Order Reaction ◽  
First Order Reaction ◽  
First Order ◽  
Kinetics Of ◽  
A Direct Method

Abstract A direct method was developed for determining inorganic phosphate in serum, which requires only a single reagent addition. The method quantitates the unreduced phosphomolybdate heteropolyacid at 340 nm and is linear to at least 10 mg of phosphate per 100 ml. Only 10 µl of serum is required. The unique blanking capabilities of centrifugal analyzers permit the "on run" elimination of serum and reagent background absorbances, which are automatically subtracted. Data on precision, correlation, and recovery are presented. Kinetics of the reaction were studied, and theoretical limits of automatic blanking when applied to a first-order reaction are discussed.

Studies on the oxidative degradation of paracetamol by a μ-oxo-diiron(III) complex

2020 ◽  
Vol 98 (2) ◽  
pp. 98-105
Author(s):  
Bula Singh ◽  
Ranendu Sekhar Das
Keyword(s):  
Acetic Acid ◽  
Oxidative Degradation ◽  
Active Role ◽  
Order Reaction ◽  
Proton Abstraction ◽  
First Order ◽  
Initial Activation ◽  
Reaction Media ◽  
Kinetics Of ◽  
Reactivity Order

In higher organisms, metalloenzymes like cytochrome P450, containing a Fe(III) metal center, play an active role in metabolism of paracetamol (APAP). Here, we have chosen a mimicking μ-oxo-diiron complex, [Fe(III)2(μ-O)(phen)4(H2O)2]4+ (1, phen = 1,10-phenanthroline), to study spectrophotometrically the kinetics of the redox interactions with APAP. In acidic buffer media (pH = 3.4–5.1), APAP quantitatively reduces 1 following first-order reaction kinetics. Each molecule of 1 accepts two electrons from APAP and is reduced to ferroin [Fe(phen)3]2+. On oxidation, APAP produces N-acetyl-p-benzoquinone imine (NAPQI), which on hydrolysis results in a mixture of benzoquinone, quinone oxime, acetamide, and acetic acid. In reaction media due to successive deprotonations, 1 exists in equilibrium with the species [Fe(III)2(μ-O)(phen)4(H2O)(OH)]3+ (1a) and [Fe(III)2(μ-O)(phen)4(OH)2]2+ (1b) (pKa = 3.71 and 5.28, respectively). The kinetic analyses suggest for an unusual reactivity order as 1 < 1a ≫ 1b. The mechanistic possibilities suggest that although 1 is reduced by concerted electron transfer (ET) – proton transfer (PT) mechanism, 1a and 1b may be reduced by a concerted PT–ET mechanism where a slow proton-abstraction step is followed by a rapid ET process. It seems that the initial activation of the bridging μ-oxo group by a proton-abstraction results in the higher reactivity of 1a.

Development of Torrefaction Kinetics for British Columbia Softwoods

2012 ◽  
Vol 10 (1) ◽  
Author(s):  
Jianghong Peng ◽  
Xiaotao T. Bi ◽  
Jim Lim ◽  
Shabab Sokhansanj
Keyword(s):  
British Columbia ◽  
Weight Loss ◽  
Kinetic Model ◽  
Residence Time ◽  
Order Reaction ◽  
First Order Reaction ◽  
Chemical Components ◽  
First Order ◽  
One Step ◽  
Kinetics Of

Torrefaction is a thermal treatment without air or oxygen in the temperature range of 473-573 K. The pyrolysis kinetics of three chemical components (cellulose, hemicelluloses, and lignin) and wood at low temperatures of relevance to torrefaction conditions have been reviewed. A series of thermogravimetric (TG) experiments have been carried out to study the intrinsic torrefaction kinetics of major chemical components and British Columbia (BC) softwoods. The weight loss during BC softwood torrefaction was found to be mainly associated with the decomposition of hemicelluloses, although there was also certain degree of decomposition of cellulose and lignin. The weight loss of the BC softwoods during torrefaction could be approximately estimated from the chemical composition of wood species and the weight loss data for torrefaction of pure cellulose, hemicelluloses, and lignin, respectively. Based on the fitting of the TG curves of BC softwoods and three chemical components, two different torrefaciton models were proposed. The simple one-step (single-stage) kinetic model with the first order reaction can predict the reaction data reasonably well over the long residence time, with the final sample weight being strongly related to the torrefaction temperature. A two-component and one-step first order reaction kinetic model, on the other hand, gave improved agreement with data over short residence time, and can be used to guide the design and optimization of torrefaction reactors over the weight loss range of 0 to 40% at the temperature range of 533-573 K, which covers the typical range of industrially relevant operations.

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