Abschlussbericht Projekt: „Verminderung der ... - BLE

8453, Germany) at 595 nm. For comparison, standards of 1mM FeSO 4 *7H 2 O solutions
(20) were used, respectively solved in its extraction medium. The sum of the results represented
the total FRAP (mmol kg -1 FM) of the sample.
The hydroxyl radical averting capacity (H-ORAC) analysis followed Boxin et al. (24) and
was carried out in freeze-dried samples of periderm and non-periderm tissue, which was
mechanically ground to a fine powder. Sample extractions were performed in three replications.
Hundred mg of a sample were mixed with 2 ml solution of acetone: distilled water:
acetic acid in the ratio 70: 29.5: 0.5 (pH 5.0) for one hour. Afterwards, the mixture was
centrifuged at 2660g (Janetzki T-30, Germany) for 10 minutes and the clear supernatants
were analysed. The calculation of relative H-ORAC based on gallic acid equivalents
(GAE) per kilogram tuber fresh mass.
Statistics. The obtained data were analysed with Sigma Stat statistical program (STAT32).
All data sets were tested for normal distribution and variance homogeneity (p= 0.05). Following
analyses of variance were calculated for cultivar and specific gravity. Calculated
means were compared by Tukey-test (p ≤ 0.05). Correlation and multiple regression procedures
between normally distributed quality parameters were performed using Pearson correlation
coefficients.
Results
During the vegetation period of potatoes the specific gravity of tubers differs due to maturing
time of cultivars, physiological tuber age, environmental conditions and pathogenic
impact. Also tuber skin structures, gas concentration in the periderm and storage conditions
affects tuber specific gravity (25). With respect to these facts potato tubers of the studied
cultivars were separated according to their specific gravities after harvest and storage periods.
Results of BSI, DP and FRAP tests are shown in Figure 1 and statistical evaluations of
these tests are presented in Table 1. The standard deviations for BSI were not calculated
because the required volume of tubers was not always available for all groups of specific
gravity and it was therefore not possible to perform three replications. If the amount of
tubers was less than a corresponding volume of 6 L the FRAP and DP test were performed
only. In some cases, the standard deviation of FRAP and DP results tended to zero which is
not visible in the graphs.
The BSI tests revealed a highly significant increasing blackspot susceptibility of tubers
with increasing specific gravity after harvest 2005 and 2006 (Fig. 1, I, IV) and after five
(Fig. 1, II, V) and eight months of storage (Fig. 1, III, VI), respectively. The FRAP activity
tend to decrease with increasing specific gravity of the stored tubers (Fig. 1, III, VI). A
significant correlation between BSI and DP was detected after harvest in 2005 and after
five months of storage (Fig. 1, II, III), in tubers after harvest in 2006 and in stored tubers
(Fig. 1, IV, V, VI), respectively. In general, both FRAP and DP values did not consistently
represent the blackspot susceptibility of tubers differing in their specific gravity.
223