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initial fertilization, the second two weeks before the natural
June drop, and third after fruit picking. The cumulative rate
of nitrogen in this case reached 105 kg N/ha. Nitrogen fertilization
was equal in all years of the experiment.
b) Crop load regulation
Trees were selected according to their vegetative (trunk circumferences)
and generative parameters (number of flower
clusters, number of fruit after the natural June drop). In all
years of the experiment fruits were thinned by hand at a
diameter of 15 mm to the chosen crop load (CL: number of
fruit per tree) of 100 % (H: high), 70 % (M: moderate) or
40 % (L: low) of potential ceop load (yield).
c) Fruit sampling and quality characteristic determination
On each selected tree 4 fruits were chosen and marked by a
code, which consisted of the nitrogen rate, crop load, block
replication and number of fruits in the treatment (for instance:
N60-H-2-12). Fruit samples were taken from the 2 nd
to 4 th growing year (1999 to 2002) and were tested for skin
colour, fruit flesh firmness, soluble solids content, starch
degradation index, titratable acidity content and fruit mineral
composition.
d) Skin colour measurement
In the years 2001 and 2002 skin colour measurements were
performed. Sign L, marked on each selected fruit, represented
the exact spot where the colour was measured. This
method is a modification of the method, used by Tijskens
et. al (2003) for determination of chlorophyll degradation
dynamics in stored fruits.
A Minolta CR-200 chomameter linked to DATA DP 100
for data processing was used for skin colour measurement.
Fruit chromaticity was expressed in L* a* b* colour space
coordinates (CIELAB). L* correspondes to a dark/light
scale (0 = black, 100 = white) and represents the relative
lightness of colours, being low for dark and high for light
colours. The parameter a* is negative for green and positive
for red and b* is negative for blue and positive for yellow
(Hribar, 1989). L*a*b means were presented as:
L* = 116(Y/Yn) 1/3 – 16 (1)
a* = 50[(X/Xn) 1/3 – (Y/Yn) 1/3 ] (2)
b* = 200[(Y/Yn) 1/3 – (Z/Zn) 1/3 ] (3; Hribar, 1989).
The absolute colour difference between two measurements
was calculated as:
ΔE = (Δa* 2 +Δb* 2 +ΔL* 2 ) 1/2 (4)
ΔL = L*– L* n-1
(5)
Δa* = a*– a* n-1
(6)
Δb* = b*– b* n-1
(7; Hribar, 1989).
The initial colour measurement was made approximately
1 month before the predicted technological maturity of
fruits and continued up to the time of technological maturity
of the fruits.
e) Fruit maturity parameters
The fruit were collected at the optimal harvest date. 30 fruit
per treatment (10 per block) were selected for determination
of fruit maturity parameters.
Fruit flesh firmness was measured by a hand penetrometer
using a FRUIT PRESSURE TESTER mod. HT 327 (3–27
Lbs., 11 mm) at 4 spots on the equatorial cross-section
of the fruit, after removing the fruit skin (Hribar, 1989).
Means are expressed as kg/cm 2 . Soluble solids in apple
juice were measured by an ATAGO N1 hand refractomeret
and expressed as % Brix. The starch degradation index
was defined after dipping a cross-section of the fruit
into a 0,02 M solution of I 2 in potassium iodine (KI),
where the presence of starch results in a dark coloration of
the fruit-cross-section. The intensity and % of coloration
were determined according to the EVROFRU starch scale,
where unity 1 represents 100 % of unconverted starch in
the fruit.
Then the Streif maturity index was calculated:
STI = F/SSxS (8; Streif, 1996)
F: fruit flesh firmness, SS: soluble solids, S: starch
Total titratable acidity were measured by titration of apple
juice with 0,1 M NaOH using phenolphthalein as indicator
and expressed as malic acid.
f) Mineral composition of fruits
After picking the fruit were grated with a plastic grater and
frozen at –20 °C. Total fruit nitrogen content was determined
according to the Kjedahl method and Ca content by
means of atomic absorption spectroscopy.
Statistic evaluation
One way variance analysis was used to determine the influence
of nitrogen rate and crop load on the different parameters
of fruit quality. Duncan’s test (0.05) was used to determinate
differences between treatments. For processing of
statistical data the Statgraphic Plus 4.0 (Manigistics, ZDA)
package was used.
Results and Discussion
a) Fruit skin colour
The results in Table 1 show that nitrogen rate and crop
load significantly influenced the chromometric parameters
Tab. 1 Source of variability and their influence on chromometric parameters
L*a*b* with adjusted P-values and determination coefficient (R2)
Parameter N CL Y N x CL x Y R2
L* < 0.0001 < 0.0001 0.0458 < 0.0001 0.24
a* < 0.0001 < 0.0001 < 0.0001 < 0.0001 0.32
b* 0.0009 < 0.0001 0.0002 < 0.0001 0.30
P ≤ 0.001: very highly significant; P ≤ 0.01: highly significant; P ≤ 0.05: significant;
P > 0.05: not significant (N: nitrogen, CL: crop load, Y: year)
128 ı Originalarbeiten Deutsche Lebensmittel-Rundschau ı 104. Jahrgang, Heft 3, 2008