Abschlussbericht Projekt: „Verminderung der ... - BLE

Table 4 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 2006
Relative H-ORAC FRAP BSI
Non-periderm Periderm* Non-periderm Periderm* Whole tuber
Afra 47.01 ± 7.16 64.34 ± 8.57 bc 1.07 ± 0.34 1.43 ± 0.15 ab 66 ± 1.80 b
Adretta 55.02 ± 9.07 109.47 ± 6.34 a 1.61 ± 0.08 2.04 ± 0.13 ab 74 ± 6.51 a
Granola 33.26 ± 4.38 75.74 ± 1.87 bc 1.26 ± 0.03 1.46 ± 0.11 ab 28 ± 0.76 c
Renate 30.47 ± 2.53 41.93 ± 3.39 d 1.70 ± 0.07 1.70 ± 0.27 a 20 ± 5.24 d
Nicola 44.32 ± 4.92 65.81 ± 3.95 bc 1.16 ± 0.31 1.84 ± 0.02 ab 5 ± 2.02 g
Lolita 55.01 ± 3.97 72.41 ± 2.63 b 1.01 ± 0.20 2.01 ± 0.79 a 5 ± 1.02 f
Marabel 27.04 ± 2.60 76.33 ± 4.33 c 0.72 ± 0.26 1.09 ± 0.07 b 10 ± 2.75 e
Gala 45.16 ± 3.05 53.75 ± 2.39 c 0.89 ± 0.04 1.13 ± 0.21 b 3 ± 0.75 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
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)
Discussion
BSI of freshly harvested tubers. The present investigation revealed a significant increase
of BSI with increasing tuber specific gravity. This result supports the findings of Lærke
(12) where tuber specific gravity of mechanical stressed cultivars may contribute to the
level of energy introduced to the tuber by the impact. In our study, the specific gravity of
tubers ranged between 1.095 kg L -1 . The cultivars can be characterized by cultivar-specific
mean specific gravities. For example, the cvs. Afra, Adretta and Lolita performed
many tubers with specific gravities from 1.075 to 1.085 kg L -1 . However, their BSI
was significantly different from each other. This observation was also done for cvs. Granola,
Renate and Nicola with tuber mean specific gravity from 1.065 to 1.075 kg L -1 . Tubers
of cvs. Gala and Marabel showed a mean specific gravity from 1.055 to 1.065 kg L -1 ,
whereby both cultivars had a low BSI. Results indicated that variation of tuber specific
gravity within a cultivar determined its BSI. Present findings are comparable to studies of
Wright et al. (26) who found that eight of ten tested cultivars showed a higher bruise score
with increasing specific gravity. Both studies revealed that impact resulted in high correlations
between blackspot susceptibility and tuber mass, irrespective of the applied test
method. Specific gravity is generally assumed to be a cultivar characteristic (24) and reflects
the dry matter concentration of potato tubers (r = 0.96) (27). The term dry matter
refers to all substances of the potato tuber, except water (28) and includes 80 % starch,
10 % cell wall and 10 % cytoplasmatic components (12). Lærke (12) described that cells
fully filled with starch granules are more violable to impact bruise. High dry matter con-
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