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Abstract  

Light emission during the dissolving of irradiated sugars (lyoluminescence, LL) allows the estimation of absorbed dose. The use of 1-mannose as LL substance and the correlation between the concentration of paramagnetic centres and LL yield in the presence of [Fe(CN)6]4− and CNS anions demonstrated the possibility to measure relative rate constants of the reaction of mannose peroxy-radicals with different substances soluble in water.

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Fibre-rich fruit juices are playing an increasing role in healthy nutrition, and consumers are regarding them, especially citrus juices of 100% fruit content, as reliable sources of vitamin C. Nevertheless relatively few scientific data are available on vitamin C retention during the heat treatment of aseptically packed fruit juices made from fruit concentrates. Authors investigated this problem within the scope of OTKA T 014965 research project (Körmendy et al., 1998, 1999a, 1999b; Pátkai, 1998).

Instead of separate case studies on different types of fruit juices and technologies, authors analysed the vitamin C content of model solutions with similar composition to real citrus juices as a function of temperature and duration of heat treatment and that of initial oxygen and ascorbic acid concentration. Based on the measured data, they elaborated kinetic relations and determined the reaction rate constants of vitamin C decomposition under the experimental conditions. By means of the calculated kinetic relations and reaction rate constants one can estimate the losses of vitamin C in the case of known parameters of the heat treatment, packaging material, oxygen and vitamin C concentration within the investigated domain. Results may promote technology and product development in the field of citrus fruit juices.

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radicals. With an average tropospheric OH concentration of [OH] global ≈ 1 × 10 6 radicals cm −3 (24 h average) [ 11 ] and by utilizing the OH reaction rate constants from our current work, the atmospheric lifetime, τ ≈ ( k 1 × [OH] global ) −1 , of 4

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completion of cure, t is the reaction time, f (α) is the model-dependent function of α or reaction model, and k ( T ) is the reaction rate constant which follows the Arrhenius relation ( Eq. 3 ). (3) In Eq. 3 , A denotes the preexponential

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kinetic parameters such as activation energy ( E a ), pre-exponential factor ( Z ) and reaction rate constants ( k ). Using the information presented in Table 4 and according to Eqs. 2 – 4 : 2 3 4 where R is the gas constant, β is the heating rate

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used the second-order reaction rate constants in our calculations. Fig. 1 Schematic representation of the BG + fading reaction Results and

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first-order reaction rate constant, found from the slope of the regression lines by plotting the natural log of nitrate concentration changes versus with reaction time according to Eq. 6 . The obtained rate constant, k obs , was used to calculate the

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Abstract  

On the basis of results of kinetic investigates of many compounds general temperature dependence of Gibbs free energy of activated complexes created in thermal decomposition processes and the reaction rate constant were calculated.

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catalyst surface. The HDO reaction of phenol on these catalysts mainly proceeded with the hydrogenation–dehydration route. The conversion and the total deoxygenation rate were 100 and 99.6%, respectively. The pseudo first-order reaction rate constant of the

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.0% aromatics. But the hydrogenation reaction would be suppressed because the excess promoter covered the Ni site, which resulted in the increase of intermediate products and the decrease of conversion. The pseudo first-order reaction rate constant of the phenol

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