Search Results

You are looking at 1 - 7 of 7 items for :

  • "activation energy" x
  • Materials and Applied Sciences x
  • All content x
Clear All

penetration. The diffusion of copper varies as an inverse function of carbon composition. Activation energies of carbon diffusion in steel are also found to increase with increasing braze temperatures and the corresponding carbon content [ 2 ]. Yoshida et al

Open access

In this work the influence of addition of different plant extracts (olive leaf, green tea, pine bark PE 95%, pine bark PE 5:1, red wine PE 30%, red wine PE 4:1, and bioflavonoids) to blackberry juice during heating (at 30, 50, 70 and 90 °C) on the anthocyanin and phenol contents, polymeric colour, and antioxidant activity was investigated. Also, reaction rate constant, half-lives of degradation, and activation energy were calculated. Control sample was juice without addition of extracts. The highest anthocyanin content at 30 °C was in samples with the addition of olive leaf and green tea. At 90 °C the highest anthocyanin content was measured in samples with the addition of extract of red wine and bioflavonoides. Samples supplemented with the extracts had much higher antioxidant activity in comparison to the control sample. Results showed that at 90 °C the sample with green tea supplementation had the lowest reaction rate constant and the highest half-life. Activation energy ranged from 29 to 44 kJ mol−1.

Restricted access

In this study, limonene was encapsulated by using gelatine, Na-alginate, polyvinyl alcohol, lactalbumin or xanthan gum with the uniaxial electrospinning process. The highest encapsulation efficiency was obtained for the sample containing polyvinyl alcohol. The release kinetic studies of nanofibre encapsulated limonene were carried out at 5.5, 20, and 38.5 °C. The Peppas equation expressed the release behavior of limonene for all systems very well, indicating quasi-Fickian diffusion. The modelling data suggested that maybe more than one mechanism was involved for the release at 20 °C. The activation energy for releasing limonene from the electrospun polyvinyl alcohol-alginate encapsulation system was found to be 6.2 kJ mol–1 from the Arrhenius equation.

Restricted access

The extractable (ASTA) colour retention of four different milled spice paprikas was evaluated at 10, 20, 35, 50, and 60 °C storage temperature. The ASTA colour stability during long-term storage period strongly depended on the temperature, primary handling and drying of the fresh crop, and the applied production technology. The cooled (10 °C) or temperature-controlled (20 °C) conditions appeared to be a reasonable solution to preserve the quality of paprika powder. The kinetics study on the temperature dependence of ASTA colour loss estimated the apparent reaction order, rate constants, predicted half-life times and activation energy. The Q10 approach and shelf life-plot resulted in useful data, which can be suitable for quick and economical evaluation of further spice paprika products.

Restricted access

The texture changes during the initial phase of blanching of potatoes, carrots and green peas at different blanching times (0–240 s) and temperatures (85 °C, 95 °C, 100 °C) were investigated. The breaking force (N) was determined by compression or Back extrusion tests with an Instron texture tester. Electronmicroscopic studies (SEM) were made to support the interpretation of the results.For each vegetable several sections of changes of the breaking force (lnF) were identified. For potatoes a three phase change of the breaking force by all temperatures (85 °C, 95 °C, 100 °C) was observed. In the first of the 3 different observed stages of potato blanching the breaking forces increased with time (0–40 s). In the second and third stage of the blanching process of potato a linear relationship was found between the logarithm of the breaking force and the blanching time. The second phase observed was faster (40–160 s) than the consecutive slower third phase (160–240 s).For green peas the change of the breaking force (lnF) can be described by two consecutive first rate reactions. A faster decreasing period between 0–25 s was followed by a slower decreasing one between 70–140 s. Between the first and second stage of the blanching process there was an initial lag period (25–70 s), which will not be described here. In the period after 140 s, there was not any change, this period is constant.For carrots the fastest change can be observed at 100 °C compared to the results at 85 and 95 °C. A three-phase curve was observed as well. An initial lag period (0–90 s) was followed by a faster (90–190 s) and a slower (190–240 s) decreasing one. In the second and third stage of the blanching process of carrots a linear relationship was found. For the changes of the breaking force (lnF) a kinetical approach was applied, reaction rate constants and apparent activation energies were calculated. The kinetical approach helps to compare and forecast changes at different process conditions.

Restricted access

The texture changes during the initial phase of blanching of potatoes, carrots and green peas at different blanching times (0–240 s) and temperatures (85 °C, 95 °C, 100 °C) were investigated. The breaking force (N) was determined by compression or Back extrusion tests with an Instron texture tester. Electronmicroscopic studies (SEM) were made to support the interpretation of the results.For each vegetable several sections of changes of the breaking force (lnF) were identified. For potatoes a three phase change of the breaking force by all temperatures (85 °C, 95 °C, 100 °C) was observed. In the first of the 3 different observed stages of potato blanching the breaking forces increased with time (0–40 s). In the second and third stage of the blanching process of potato a linear relationship was found between the logarithm of the breaking force and the blanching time. The second phase observed was faster (40–160 s) than the consecutive slower third phase (160–240 s).For green peas the change of the breaking force (lnF) can be described by two consecutive first rate reactions. A faster decreasing period between 0–25 s was followed by a slower decreasing one between 70–140 s. Between the first and second stage of the blanching process there was an initial lag period (25–70 s), which will not be described here. In the period after 140 s, there was not any change, this period is constant.For carrots the fastest change can be observed at 100 °C compared to the results at 85 and 95 °C. A three-phase curve was observed as well. An initial lag period (0–90 s) was followed by a faster (90–190 s) and a slower (190–240 s) decreasing one. In the second and third stage of the blanching process of carrots a linear relationship was found. For the changes of the breaking force (lnF) a kinetical approach was applied, reaction rate constants and apparent activation energies were calculated. The kinetical approach helps to compare and forecast changes at different process conditions.

Restricted access

( Oryza sativa L.) and their degradation kinetics . Food Res. Int. , 50 , 691 - 697 . 10.1016/j.foodres.2011.07.037 Janković , B. , Marinović-Cincović , M. & Jankovic , M. ( 2017 ): Distribution of apparent activation energy counterparts during

Restricted access