Abschlussbericht Projekt: „Verminderung der ... - BLE

Compared to whole tubers several reports attribute the highest antioxidant activity to the
tuber periderm (11, 25). With respect to the formation of melanin pigments beneath the
cortex tissue two methods were used to study the antioxidant activity of tuber periderm in
comparison with tuber non-periderm and to study if a relationship with the BSI of whole
tubers exists. The tubers were not separated in specific gravities before analysing (Tab. 3,
4). In tubers harvested in 2005 relative H-ORAC and FRAP activities revealed significant
higher concentrations of antioxidant compounds in tuber periderm compared to nonperiderm
concentrations. Cultivars with a higher antioxidant activity in periderm showed
also a higher antioxidant activity in the non-periderm tissue. The relative H-ORAC compounds
as a result of single tissue antioxidant activity were slightly more concentrated in
tubers with a medium to high BSI of cvs. Adretta, Granola and Renate compared with cvs.
Nicola, Lolita, Marabel and Gala (r = 0.401, p ≤ 0.05). Antioxidant activity determined
with the FRAP method indicated significant lower concentrations of corresponding compounds
in cvs. Granola and Marabel compared to the other cultivars (Tab. 3).
Table 3 Antioxidant activity (relative H-ORAC, mmol GAE kg -1 FM; FRAP,
mmol kg -1 FM) of tuber tissue of potato cultivars differing in their blackspot susceptibility
(BSI, %) harvested in 2005
Relative H-ORAC FRAP BSI
Non-periderm Periderm* Non-periderm Periderm* Whole tuber
Afra 29.77 ± 2.14 38.15 ± 3.25 cd 0.89 ± 0.07 1.39 ± 0.28 ab 83 ± 7.05 a
Adretta 42.09 ± 3.53 59.59 ± 4.86 a 1.00 ± 0.05 1.24 ± 0.19 ab 58 ± 3.95 b
Granola 31.85 ± 2.00 57.94 ± 5.80 ab 0.64 ± 0.18 1.24 ± 0.16 b 50 ± 10.12 c
Renate 42.88 ± 9.53 56.46 ± 7.31 a 1.13 ± 0.34 1.73 ± 0.15 a 39 ± 11.59 d
Nicola 23.11 ± 5.92 30.99 ± 3.37 d 0.86 ± 0.16 1.44 ± 0.35 ab 3 ± 1.41 f
Lolita 32.80 ± 2.11 48.21 ± 2.29 bc 0.72 ± 0.03 1.52 ± 0.21 ab 4 ± 2.15 e
Marabel 24.63 ± 3.38 47.41 ± 0.83 c 0.74 ± 0.00 1.13 ± 0.12 b 2 ± 0.91 g
Gala 33.55 ± 4.61 37.53 ± 3.20 cd 1.18 ± 0.12 1.63 ± 0.47 a 2 ± 0.83 h
a,b,c different letters indicate significant differences of the whole tissue (on the basis of the sum of relative
H-ORAC and FRAP values in non-periderm and periderm, respectively) of cultivars by Tukey tests
(p ≤ 0.05),* the periderm showed always significant higher H-ORAC-values and FRAP activity compared to
the non-periderm tissue by Tukey tests (p ≤ 0.05), (H-ORAC, hydroxyl radical averting capacity;
GAE-equivalent, gallic acid equivalent; FRAP, ferric reducing ability of plasma; BSI, blackspot index)
Tubers harvested in 2006 were not significantly different in their BSI compared to tubers
harvested in 2005 (Tab. 2). Again, the concentration of antioxidant compounds in tuber
periderm was significantly higher than in tuber non-periderm (Tab. 4). However, the FRAP
data and the relative H-ORAC data revealed significantly higher concentrations of antioxidant
compounds in comparison with tubers harvested in 2005. The concentration of relative
H-ORAC antioxidants of periderm and non-periderm were slightly correlated with
tubers BSI (r = 0.514, p ≤ 0.05).
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