| 1. |
- Ahrné, Lilia, et al.
(författare)
-
Improvement of texture by modifying processing conditions
- 2003
-
Ingår i: Acta Hortic.. - : International Society for Horticultural Science. - 9789066059764 ; 604, s. 277-277
-
Konferensbidrag (refereegranskat)abstract
- Fruit and vegetable processors, faced with the challenge of gaining and maintaining a healthy position in the competitive fruit and vegetable sector, are optimising traditional processes towards product quality. Using frozen potatoes as a case study, the aim of this study was to evaluate the potential of improving the texture of potatoes by modifying the processing conditions. The texture of processed frozen potatoes is the result of the integral effect of the unit operations applied through the production chain. Production of frozen potatoes includes a blanching, a freezing, thawing/cooking step before being served. In this study, blanching temperatures from 70 to 97 °C up to 10 minutes were tested and combined with freezing by two freezing methods, impingement and air-blast freezing. The texture was measured after cooking of frozen potatoes in boiling water. Besides texture, water holding capacity, microstructural evaluation and pectinmethylesterase (PME) activity were determined. Blanching of potatoes prior to freezing can both improve water holding capacity and texture of potatoes, but this effect depends on the freezing rate and blanching temperature. Potatoes frozen with fastest freezing method are firmer and hold more water than the ones frozen by air-blast freezing. Blanching at 70 °C can lead to potatoes that after cooking retain a firmer texture, compared with blanching at 90 °C. The duration of the blanching treatment has also an important effect on texture changes. The studies of PME activity showed a good correlation between texture and PME for blanching at 90 °C, but for blanching at 70°C and longer times, the development of texture does not seem to be solely related to PME activity. Microstructural studies showed that the differences in texture are due to differences in the degree of starch gelatinisation and integrity of the cellular structure.
|
|
| 2. |
- Martinez, D. M., et al.
(författare)
-
Dryness and physical properties of paper webs in laboratory-scale impulse processing
- 2001
-
Ingår i: Drying Technology. - 0737-3937 .- 1532-2300. ; 19:10, s. 2435-2450
-
Tidskriftsartikel (refereegranskat)abstract
- This investigation evaluates the changes in dryness and physical properties of impulse processed paper webs. A laboratory-scale platen press was used to process 60 g/m2 webs under a wide range of pressure impulses and temperatures (23-380°C). The heat transfer rate to the web was also varied by using two different platen materials (steel and copper). Both thermomechanical and bleached kraft pulps were tested, and the dryness, density, surface roughness, and Scott bond were measured for each trial. Results show that dewatering is enhanced with increased temperature, pressure, and nip residence time, while pressure pulse shape and platen material have little influence. An empirical correlation is given to relate sheet dryness to the key process variables. This correlation suggests that resulting dryness values are not unique; that is, different combinations of temperature, pressure, and nip residence time can be used to obtain a similar level of dryness. Physical reasoning was used to develop a second correlation that links the resulting dryness to the density of the completely dried web. Surface roughness decreased with increasing surface temperature, while Scott bond rose sharply under conditions of high temperature and long nip residence time.
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
- Nilsson, Hans-Erik, et al.
(författare)
-
Numerical modeling of hole interband tunneling in wurtzite GaN and SiC
- 2001
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 90:6, s. 2847-2852
-
Tidskriftsartikel (refereegranskat)abstract
- The time evolution of Bloch electrons (holes) moving in a constant electric field has been studied for GaN and 2H-SiC using a numerical model based on realistic band structures. The large band gap of GaN and the SiC polytypes provide much larger critical fields than in conventional semiconductors, which allows device operation at very high electric fields. At sufficiently high electric fields the carriers may change band during drift due to tunneling. GaN has a direct band gap, while the hexagonal SiC polytypes have indirect band gaps. In spite of this difference the valence band structure is very similar due to the wurtzite symmetry. In this work the GaN and the 2H-SiC polytype are considered as wurtzite prototype semiconductors in order to study valence band to band tunneling in wurtzite semiconductors for electric fields directed along the c axis. A large valence band to band tunneling probability was found for both materials at electric fields above 400 kV/cm. This shows the importance of considering band to band tunneling in studies of high field hole transport in wide band-gap hexagonal semiconductor materials. The proposed numerical approach can be used to enhance the interband tunneling models used in Monte Carlo simulation of carrier transport in hexagonal semiconductors.
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
|
|
