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Blackspot susceptibility in comparison with the antioxidant activity of potato
(Solanum tuberosum) tubers
Antje Wulkow 1 , Anna J. Keutgen 2 , Ivan Goshev 3 , Boryana Mihaylova 3 , Elke Pawelzik 1
1 Quality of Plant Products Section, Department of Crop Sciences, University of Goettingen,
Germany; 2 Department of Storage and Processing of Plant Products, University of
Technology and Life Sciences, Bydgoszcz, Poland; 3 Institute of Organic Chemistry and
Center of Phytochemistry, Sofia, Bulgaria
Abstract
Mechanical impact enhanced melanogenesis, which caused blackspot occurrence in potato
tubers resulting in quality losses of fresh and processed products. Performed impact tests
revealed the same blackspot susceptibility of cultivars after harvest in 2005 and after harvest
in 2006. During a storage period of five months blackspot significantly decreased in
tubers harvested in 2005 and contrary increased in tubers harvested in 2006. Long-term
storage of eight months changed the blackspot susceptibility of tubers similar to freshly
harvested tubers. Blackspot was significantly correlated with tuber specific gravity.
Melanogenesis as a consequence of soluble oxidised substances was determined as discolouration
potential. The obtained results pointed out that a cultivar specific periodical determination
of its discolouration potential became essential to mirror their blackspot susceptibility.
Present findings indicated that melanogenesis takes place as a part of antioxidant
network or it is even a result. Some antioxidant systems were detected, which may
avoid melanogenesis, respectively. The performed FRAP and H-ORAC- tests showed a
slightly but significant correlation to mechanical stressed tubers.
Keywords: Solanum tuberosum, specific gravity, dormancy, melanogenesis, FRAP,
H-ORAC
Introduction
After harvest potato tubers are exposed to mechanical impact. Insensitive handling operations
as well as storage conditions and time influence the susceptibility of tubers to mechanical
impact (1, 2). The level of initiation of mechanical stress is determined by genotypes
and environmental conditions (3-5). Impact potentially increases the production of
reactive oxygen species (ROS) (6, 7). The term describes free radicals (superoxide radical,
O .- 2 , peroxyl radical, ROO - and hydroxyl radical, HO - ), as well as molecules like hydrogen
peroxide (H 2 O 2 ), singlet oxygen ( 1 O 2 ) and ozone (O 3 ) (6). The function of the plant generated
ROS is associated with the disease resistance mechanisms of cells (7) as well as the
lipid peroxidation of polyunsaturated fatty acids (PUFAs) of cell membranes (9). Increasing
generation of ROS under stress conditions induces both sub cellular damage and protective
response (7). To protect cells against stress conditions the ROS level is controlled
by an antioxidant system. In the cell, antioxidant compounds are closely linked with a
powerful antioxidant activity. The effect based on their redox properties and is a result of
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