Abschlussbericht Projekt: „Verminderung der ... - BLE

Water relations in potato (Solanum tuberosum) tubers in comparison to their
blackspot susceptibility
Antje Wulkow 1 , Werner B. Herppich 2 , Elke Pawelzik 1*
1 Quality of Plant Products Section, Department of Crop Sciences, University of Goettingen,
2 Department of Horticultural Engineering, Leibniz Institute for Agricultural Engineering
Potsdam-Bornim
Abstract
Tubers harvested 2006 and 2007 and stored for five and eight months at low temperatures
of 4°C avoided water losses and therefore losses of pressure potential due to cold accumulation
which is known as a common practice of vegetative organs of carrots and radish.
The performed mechanism of cold accumulation belonged to osmotic adjustment. Thereby
blackspot susceptibility of tubers increased with increasing specific gravity, irrespective of
whether cells were fully turgid or flaccid.
Keywords: water status, mechanical stress, cold storage
Introduction
Potato tubers are exposed to different environmental conditions during growth, harvest,
handling and storage which predetermine their physiological status. These combinations of
circumstances may affect the water status of the tuber as well as its variations due to metabolic
changes and, as a consequence, can directly influence processing operations and
product quality (Günel and Karadogan, 1998; Heuer and Nadler, 1998; Kolbe and Stephan-
Beckmann, 1997; Pawelzik and Delgado, 1999; Rasool et al., 2007). In potato tubers
blackspot is a major quality problem worldwide, caused by mechanical impact (Alvarez
and Canet, 2002; Lærke, 2001). This blue-black discolouration of cortical parenchyma
(Lulai, 2007) occurs without recognizable cell dissociation (Storey, 2007) contrary to other
types of bruise like crushing, shatter and cracking leading to visible cell deformation
(Baritelle and Hyde, 2003). However, intracellular membrane modification might be necessary
to synthesize the dark polyphenolic pigment melanin from phenols stored in the
vacuole catalysed by the amyloplast-located (Lærke et al., 2002) enzyme Polyphenol oxidase
(PPO, EC 1.10.3.1, EC 1.14.18.1) (Schmitz et al., 2008). It is highly probable that
tuber water status affects blackspot susceptibility (Bajema et al., 1998a; Baritelle and
Hyde, 2001; Corsini et al., 1999; Lærke, 2001; Olsen et al., 2003/4; Pawelzik and Delgado,
1999) where water loss change membrane integrity allowing enzymatic browning as obtained
in rambutan fruits (Nephelium lappaceum) (Landrigan et al., 1996). Moreover
blackspot development is interrelated with many other parameters concerning potato tubers
impact susceptibility (e.g. tuber mass, tuber shape, physiological tuber age) (Storey, 2007).
In the past, many studies investigated single features of tissue water status and their interactions
with tuber mechanical properties like pressure potential and impact susceptibility
180