Abschlussbericht Projekt: „Verminderung der ... - BLE

Kelling, 2007; Neumann, 1995) and reflects the dry matter concentration of potato tubers
(Haase 2003/4). A higher dry matter concentration may result from a higher amount of cell
wall components, cytoplasmatic components or in case of potato tubers from a large size or
a high number of starch granules. This reportedly increases the susceptibility to mechanical
deformation of membranes as a direct effect of impact (Lærke, 2001; Olsen, 2003/4; Storey,
2007), regardless of tissue turgidity.
According to Scanlon et al. (1998) and Bajema et al. (1998a) it may be assumed that a
fully turgid vacuole presses protoplasm and starch granules against the cell walls more
than in flaccid cells. Compared to flaccid cells this may increase the shock wave speed
after impact. The cell walls could compensate the acceleration of shock wave due to the
chemical interactions between the various cell wall components or transferred the impact
energy into the parenchyma.
Contrary, in relaxed cells the vacuoles did not perform such a strong pressure and so starch
granules and protoplasm were not constricted. If the parenchyma was impacted, the starch
granules were highly variable to the parenchyma and extended the cell membrane (Galindo
et al., 2004b; Alvarez et al., 2000b) or dissipated the impact energy due to friction (Scanlon
et al., 1998). Therefore, in flaccid cells the specific gravity of cells influences impact
susceptibility. These findings are in agreement with results of Scanlon et al. (1998), who
observed a positive relationship between specific gravity and loss modulus, a component
of the modulus of elasticity.
A directly negative correlation between water concentration and blackspot was found in
tubers with specific gravities above 1.095 kg L -1 during the entire period of investigation.
The decreasing water concentration reduced stress threshold and enhanced impact susceptibility
of potato tubers. Similar results were reported for potato tubers (Alvarez et al.,
2000a), carrot roots (Herppich et al., 2004) and apples (Alvarez et al., 2000b).
Conclusion
From the present results we conclude that blackspot susceptibility of potato tissue is primary
associated with the starch concentration of cells and furthermore with the impact
susceptibility of the cell membrane of the cortical parenchyma. Presented data showed that
increasing impact thresholds and therefore lower blackspot susceptibilities were supported
by turgid cells achieved through a balanced water concentration of tubers during growth
and storage periods irrespective of cultivars.
References
Alvarez, M.D., Canet, W., 2002. Effect of osmotic adjustment on the rheology of potato
tissue. The use of discriminant analysis for interpretation. Eur. Food Res. Technol. 214,
83-90.
Alvarez, M.D., Saunders, D.E.J., Vincent, J.F.V., 2000a. Effects of turgor pressure on the
cutting energy of stored potato tissue. Eur. Food Res. Technol. 210, 331-339.
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