Abschlussbericht Projekt: „Verminderung der ... - BLE

Antioxidant activity of tubers and tuber tissue. The deformation of the plasma membrane
might potentially increase some levels of ROS (6). Some ROS like HO - and O - 2 react
with the methylene group of PUFAs generating conjugated dienes, lipid peroxyl radicals
and hydroperoxides (33). We assumed that lipid peroxidation might delayed by antioxidant
compounds, which are able to advert HO - . In the present study, this ability was measured
by the H-ORAC method. Moreover, antioxidants have ferric reducing abilities and might
suspend branching of highly reactive peroxyl radicals (6), which was determined by the
FRAP method. In this study, the antioxidant activity was significantly higher in periderm.
Tuber periderm contains higher pectin concentration compared to non-periderm tissue (annex,
Tab. 10.58), whereby phenolic compounds interacting with pectin polysaccharides
(34) might be responsible for this higher antioxidant activity.
The relation between measured antioxidant activity and BSI was significant but not very
high because both FRAP and H-ORAC methods did not determine the O - 2 scavenging ability.
Singlet oxygen is more reactive than H 2 O 2 and less reactive than HO - (6) and promote
lipid peroxidation or is available for melanogenesis while FRAP and H-ORAC activity
-
have taken place. One protection mechanism against O 2 availability in higher concentrations
may be the induction of superoxide dismutase (SOD), which catalyses the dismutation
of O - 2 to O 2 and H 2 O 2 . Furthermore, peroxidase (POD) and catalase (CAT) catalyse
the breakdown of H 2 O 2 to H 2 O and O 2 (6). Nevertheless, both reaction pathways release
O 2 , which also become shareable for melanogenesis. Eighter PPO and tyrosine are available
and melanogenesis take place or remutated O 2 will prolong lipid peroxidation or will
-
be scavenged by low molecular mass antioxidants. O 2 scavenging ability was detectable
for low molecular mass antioxidants like quercitin (35, 36) and ß-carotenoid (33, 38),
which are significantly higher concentrated in pigmented potato tissue, compared to white
tuber tissue (9, 19). Due to the fact that the dark yellow coloured tubers have higher ß-
-
carotenoid content (37) a higher O 2 scavenging ability should be predictable resulting in
lower blackspot susceptibility. Assuming this hypothesis for the present results of the study
the dark yellow coloured cv. Gala revealed very low blackspot susceptibility throughout
the period of investigation.
Conclusion
Potato cultivars grown in 2005 and 2006 differed in their blackspot susceptibility after harvest
and after five and eight months of storage, respectively. During the entire period of
investigation the BSI tests revealed physical tuber parameters related to the percentage of
blackspot in potato tubers independent of pigment colour. The colour of the oxidized products
was measured as DP. DP results were influenced by the natural colour of the tissue
and therefore presented relationships between BSI and DP were significant but not very
high. The DP did not show cultivar specific blackspot susceptibility when different cultivars
were tested as reflected by the BSI test. Therefore the DP test is not practicable in
order to compare the blackspot susceptibility of different cultivars. As an immediate con-
231