Abschlussbericht Projekt: „Verminderung der ... - BLE

were performed in tubers after harvest and in tubers stored for five and eight months, respectively,
at 4°C and 95 % relative humidity. Moreover, the tubers were divided into six
groups of specific gravity ranking from 1.095 kg L -1 , with 0.01 increments. The
separation was performed directly before testing (Wright et al. 2005). For this purpose tubers
were plunged in different vessels with demineralised water and adequate NaCl- concentrations,
respectively. Furthermore, the samples were divided into two parts. Tubers
from the first part were used to determine their blackspot index (BSI). Tubers from the
second part were used for analysis. Samples were sliced and used fresh or were shockfrozen
in liquid nitrogen and stored at -30 °C until testing or freeze-drying (Epsilon 2-40,
Christ).
Analyses. Blackspot index (BSI) of whole potato tubers of different specific gravities was
determined according to the method of the German “Bundessortenamt” (BSA) (Federal
Plant Variety Office). The tubers were cooled down to 4 to 5°C and mechanical treated for
50 s in a vegetable washing machine with a rotating drum (Flottwerk H.J. Dames GmbH &
Co. KG, Rotenburg a. d. F., Germany) with three replications. Each replication consisted
of an amount of tubers (Σ tuber ) adequate to a volume of 6 L. Afterwards, treated tubers were
stored at room temperature for 48 hours. For BSI determination they were cut into halves
length-wise and a half tuber was evaluated visually using a scale with four scores of discolouration:
No discolouration indicated no blackspot development and therefore no
blackspot bruise susceptibility (Σ 1 ). Discolouration till quarter of length and less than 5
mm in-depth showed slight blackspot bruise susceptibility (Σ 2 ). Medium blackspot bruise
susceptibility corresponded to a discolouration till quarter of length and above 5 mm indepth
or a half of the length and maximal 5 mm in-depth (Σ 3 ). Serious blackspot bruise
susceptibility was indicated by a stronger discolouration (Σ 4 ). The blackspot bruise susceptibility,
expressed as the percentage of discoloured tubers was calculated from following
equation (1):
( ) ( 0.3∑ + 0.5∑ + ∑ )/
∑
BSI % =
2 3 4 tuber*
100
(1)
BSI: blackspot index (%)
Σ: amount of analysed tubers
The dry matter concentration of potato tubers was analysed according to Naumann and
Bassler (1976). Starch analyses referred to the ICC- Standard method no. 123/ 1 (2006).
The pectin concentrations of potato tubers were analysed in potato tuber periderm, nonperiderm
as well as in whole tubers differing in their specific gravity. Samples were prepared
from fresh shock-frozen tissues. First of all the extraction of the ethanol insoluble cell
wall material has taken place with 60 g sliced tissue (tissue fresh ), which was mixed with
denatured ethanol using an ultra-turrax (Janke & Kunkel, IKA lab technics, Germany) (Keijbets
and Pilnik 1974). Two grams of the degreased ethanol insoluble cell wall material
(tissue degreased ) were cleaned up form starch using cold demineralised water and a nylon
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