ARTICLE IN PRESS

LWT 39 (2006) 835–843
www.elsevier.com/locate/lwt

Effect of organic growing systems on sensory quality
and chemical composition of tomatoes
A.K. Thyboa,, M. Edelenbosa, L.P. Christensena, J.N. Sørensenb, K. Thorup-Kristensenb
a

Department of Food Science, Danish Institute of Agricultural Sciences, P.O. Box 102, DK-5792 Aarslev, Denmark
Department of Horticulture, Danish Institute of Agricultural Sciences, P.O. Box 102, DK-5792 Aarslev, Denmark

b

Received 29 April 2005; received in revised form 13 September 2005

Abstract
Tomato plants were grown in the greenhouse in the soil, in confined beds, or in combined beds where the roots could also develop in
the soil outside the bed. The beds were filled with compost based on clover grass hay, deep litter and peat and harvested in early summer
and autumn in 2002 and 2003, and in the soil treatment the same compost was incorporated into the soil. The tomato fruit quality was
assessed by sensory analysis and content of chemical components as, e.g. dry matter, soluble solids, citric acids and volatile components.
The content of minerals was mainly determined to evaluate possible limitations in nutrient supply. Due to only minor effects of growing
systems on sensory quality and chemical composition of tomato fruits it is concluded that it is possible to produce tomato fruits in
confined and combined soil bed systems without any loss in eating quality. Actually the results indicate that a slight increase in quality of
tomatoes from the confined and combined systems is obtained. The present result points to the fact that confined and combined growing
systems may be new relevant commercial growing systems, in which the quality of tomatoes seems to be ensured, and in which nutrient
loss and root diseases contamination can be reduced.
r 2005 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved.
Keywords: Tomato (Lycopersicon esculentum); Growing systems; Organic farming; Sensory quality; Physico-chemical composition;;  Volatile compounds;
Harvest time

1. Introduction
Consumers are becoming increasingly concerned about
how, where and when foods are produced. This has led to
an increased consumer interest in organically grown
vegetables including those produced in greenhouses.
Organic greenhouse tomatoes in Northern Europe are
often produced as intensive monocultures in soil. In this
system, it is not realistic to use crop rotation or crop
diversity to increase the sustainability of the production.
This has led to problems with soil-borne pests and diseases
(Forsberg, Sahlström, & Ögren, 1999) and problems
with nutrient supply, balance and losses (Gysi & von
Allmen, 1997). These problems may be handled by growing
greenhouse tomatoes in limited beds (Gäredal &
Corresponding author. Tel.: +45 89 99 34 05; fax: +45 89 99 34 95.

E-mail address: Anette.Thybo@agrsci.dk (A.K. Thybo).

Lundegårdh, 1997), which allows each new crop to be
established in fresh compost, and to collect and recycle the
drainage water and the compost itself.
In several studies the effect of growth media, fertilizers
and salinity sources on the chemical compositions and
sensory quality of tomatoes has been investigated (Basker,
1992; Auclair, Zee, Karam, & Rochat, 1995; Haglund,
Johansson, Gäredal, & Dlouhy, 1997; Petersen, Willumsen,
& Kaack, 1998; Auerswald, Schwarz, Kornelson, Krumbein, & Brükner, 1999; Granges, Azodanlou, Couvreur, &
Reuter, 2000; Gundersen, McCall, & Bechmann, 2001),
and it appears that the effect of nutrients is often
confounded with the effect of growth media. A few studies
have shown that there are no differences in the physicochemical and sensory quality of conventional tomatoes
grown in soil or in rock-wool slabs, except for the content
of cadmium, whereas other factors like the physiological
state of the tomato fruit at harvest and the electrical

0023-6438/$30.00 r 2005 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.lwt.2005.09.010

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836

conductivity (EC) in the growth media have more
pronounced effects on tomato quality (Künsch et al.,
1994; Petersen et al., 1998; Auerswald, Schwarz et al., 1999;
Gundersen et al., 2001; Thybo, Bechmann, & Brandt,
2005).
Organic tomatoes are mainly grown in soil. Many
consumers believe that greenhouse vegetables, grown in
soil are superior in sensory quality and content of vitamins
and minerals to those grown in other media (Johansson,
Haglund, Berglund, Lea, & Risvik, 1999). For this reason it
is important to investigate the effect of growing organic
tomatoes in compost. Flavour and firmness are important
quality criteria for tomatoes (Krumbein & Auerswald,
1998). Tomato flavour is attributed to the content of sugar,
acid and volatile compounds. Tomatoes have many odourimpact compounds, dominating the flavour (Krumbein &
Auerswald, 1998). Almost 400 volatile compounds have
been identified in tomato fruits (Whitfield & Last, 1993),
and some of them, such as (Z)-3-hexenal, (E)-2-hexenal,
hexanal, (Z)-3-hexen-1-ol, 1-hexanol, 2-isobutylthiazole
and 6-methyl-5-hepten-2-one, are considered important
contributors to the fresh tomato flavour (Buttery, 1993;
Baldwin, Goodner, Plotto, Pritchet, & Einstein, 2004; Ruiz
et al., 2005). There seem to be several major components to
tomato flavour, which are often opposing; the earthy,
musty, vine, green aroma and the fruity, tropical, floral,
ripe tomato and sweet tomato flavour (Baldwin et al.,
2004). Many factors affect the concentration of volatiles in
tomatoes, e.g. cultivar, maturity and harvest time, and
post-harvest treatments (Krumbein & Auerswald, 1998;
Auerswald, Peters, Brücker, Krumbein, & Kuchenbuch,
1999). Recently, Tando, Baldwin, Scott, and Shewfelt
(2003) reported that tomatoes described as full flavoured
were characterized by a low level of titratable acidity, a
high content of total sugars and soluble solids and an
intermediate content of hexanal, (Z)-3-hexenal, 2- and 3methyl-1-butanol, (E)-2-hexenal, (Z)-3-hexen-1-ol, geranyl
acetone, b-ionone and 1-penten-3-one.

Open

The objective of the present study was to evaluate the
physico-chemical and sensory properties of organic tomatoes, grown in compost beds to ensure that a change in
cultivation method toward a higher degree of sustainability
and more environmentally friendly growing method would
produce tomatoes of similar quality to those grown in soil.
To meet consumer demands, we also developed a system,
which combined the growing of plants in compost beds
with growing in soil. This system allowed the plant roots to
penetrate through the compost and out through the
sidewalls of the bed into the surrounding soil during
growth and development in the greenhouse.
2. Material and methods
2.1. Growing systems
Tomato plants (Lycopersicon esculentum Mill. cv.
‘Aromata’ grafted on cv. ‘Beaufort’ roots) were grown in
soil (open beds), in compost beds (confined beds) and in
compost beds with holes for root penetration (combined
beds) in a greenhouse compartment in 2002 and 2003
(Fig. 1). In the open beds compost made of chopped clover
grass hay, deep litter and peat (Sørensen & ThorupKristensen, 2006) was slightly incorporated into the top
0.2 m soil-layer in a length of 2.8 m and a width of 0.9 m.
The confined and combined beds consisted of containers
(2.8 m long, 0.5 m wide and 0.3 m deep) inserted into the
soil. The confined and combined beds were identical,
except that the combined beds had 8 cm holes in the
vertical sidewalls 5 cm below the soil surface with a
distance of 45 cm between holes (Sørensen & ThorupKristensen, 2006). The plants in the confined and combined
systems were grown in the same mixture of compost as in
the soil, except that a 0.15 m layer of wheat straw was
placed at the bottom of each bed to ensure sufficient
drainage. Drainage water was collected and re-circulated
from the confined and combined beds. The amount of

Confined

Combined

Fig. 1. Growing of tomatoes in an open, a confined and a combined bed systems.

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nutrients applied with compost at the beginning of
the growing period was 117 g N m
2, 48 g P m
2 and
112 g K m
2 in 2002 and 196 g N m
2, 35 g P m
2 and
121 g K m
2 in 2003. Supplemental fertilizer was given
in two or three applications as dry clover-hay pellets
(Dangrønt Products A/S, Ølgod, Denmark) to half of the
beds beginning 7 August 2002 and 28 May 2003. A total
of 54 g N m
2, 7 g P m
2 and 49 g K m
2 in 2002 and
41 g N m
2, 5 g P m
2 and 36 g K m
2 in 2003 were applied
to the plants. The reason for the reduction in supplemental
fertilizer in 2003 was that the compost in 2003 had a higher
content of N, P and K. The root zone temperature was
5.2 1C higher in the confined and combined beds at
planting, decreasing to 2.2 1C 1 month later and to nearly
none 2 month after planting. Plants were transplanted on
21 March 2002 and on 18 February 2003. The plants were
grown using the layering system, which removes all leaves
below the upper truss of ripening fruits. Bumblebees were
used for pollination, and pest and diseases were controlled
by biological means. The experiment was arranged in a
Latin square with three replicates.
2.2. Harvest
The harvest period was between 24 May and 21 October
in 2002 and between 23 April and 3 October in 2003. The
plants were harvested three times weekly and the cumulated yield of red fruits was recorded for each system early
and late in the season. In 2002, fruits were harvested at
colour stage 5 and in 2003 at colour stage 6, using a colour
chart for tomatoes from 0 (yellow–green) to 7 (dark red).
For physico-chemical analysis and sensory evaluation, red
tomato fruits (size 40–70 mm) were harvested on 10 June
(early) and on 7 October (late) 2002 and on 19 May (early)
and on 22 September (late) in 2003. Samples of 40 firstclass fruits from each system were stored for 2 days at
18 1C. From each batch, two groups of 15 fruits were made;
each group representing fruits of nearly similar size and
biological age determined by expert evaluation of the visual
colour (Tijsken & Evelo, 1994).
2.3. Physico-chemical analysis
At each harvest time, 15 fruits were measured from each
sample. Fruit firmness was measured by a CNS Farnell
Texture Analyser (Borehamwood, UK) and expressed as
the average of the maximum force (kg) needed to penetrate
each fruit with an 8 mm cylindrical probe at a crosshead
speed of 50 mm min
1. All fruits were then divided into
quarters. One quarter from each of the 15 fruits was pooled
and used for measures of soluble solids content, pH and
titratable acidity. The second quarter of each 15 fruits was
used for determination of dry matter and content of major
and trace elements, the third for determination of vitamin
C and the fourth for volatile analysis.
Soluble solids content, pH and titratable acidity were
determined in a filtrate made from the tomatoes after 2 min

837

mixing in a Waring blender (Connecticut, USA). The
soluble solid content was determined using a Refractometer RFM 330 (Bellingham & Stanley Ltd., Kent, UK)
with automatic reading and temperature control at 20 1C,
while pH and titratable acidity were measured on a
Metrohm 719 S Titrino titrator (Metrohm Ltd., Herishau,
Switzerland). Titratable acidity was determined by titration
to pH 8.1 with a 0.1 N NaOH solution and expressed as %
citric acid. The dry matter content was determined after
drying in a ventilated oven at 80 1C for 20 h (Lytzen A/S,
Herlev, Denmark) and the dried material used for analysis
of major and trace element. Cd was determined according
to Gundersen et al. (2001), nitrogen according to AOAC
992.23 and all other elements according to AOAC 984.27.
The total ascorbic acid content (vitamin C) was determined
as described by Lento, Daugherty, and Denton (1993) and
Pongracz (1971).
2.4. Analysis of volatile compounds
Volatile compounds were collected from blended tomatoes after enzyme inactivation with salt using a modified
method of Buttery, Teranishi, and Ling (1987). A sample
of 250 g tomatoes was blended 30 s in a Waring blender
(Conneticut, USA), and then allowed to stand for 180 s
before 250 ml saturated CaCl2 solution was added and
blended for another 10 s. The mixture (500 g) was placed in
a 1 l flask and purified nitrogen (150 ml min
1) was led into
the flask and passed over the vigorously stirred mixture and
out of the flask through a trap containing 200 mg Porapak
Q 50–80 mesh (Waters Inc., Milford, MA, USA). Volatile
compounds were collected for 90 min at 25 1C in a
thermostatic incubator (Termaks 6000 Incubator, Lutzen
Lab, Herlev, Denmark). The trap was then removed and
eluted with 2 ml distilled CH2Cl2 and for quantitative
estimations, 10 ml of a 100 ppm internal standard solution
of 4-methyl-1-pentanol in CH2Cl2 was added. The headspace samples were concentrated to approximately 100 ml
before analysis by GC and GC–MS. A Hewlett-Packard
5890 GC (Hewlett-Packard, Avondale, PA, USA)
equipped with a FID-detector operating at 230 1C and a
split/splitless injector operation at 200 1C was used. The
volatile compounds were separated on a Chrompack
(Middleburg, The Netherlands) WCOT-fused silica capillary column (50 m  0.25 mm i.d.; DF ¼ 0.2 mm liquid
phase, CP-Wax 52CB) using the following temperature
program: isothermal for 3 min at 40 1C, followed by
1 1C min
1 to 60 1C, isothermal for 2 min, then 5 1C min
1
to 180 1C, isothermal for 10 min, then 10 1C min
1 to
220 1C, followed by constant temperature for 10 min.
Helium was applied as carrier gas with a flow rate of
1.4 ml min
1. One microlitre of each sample was injected
onto the column in splitless mode. The concentrations of
individual volatiles were estimated from the FID-peak
areas and the internal standard. The volatile compounds
were identified by GC–MS on a Varian Saturn 2000 ion
trap mass Spectrometer (70 eV) using the same conditions

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A.K. Thybo et al. / LWT 39 (2006) 835–843

as described above. Compounds suggested by the mass
spectral NIST database (version 6.0) were verified by
comparison with mass spectra and retention indices of
authentic reference compounds.
2.5. Sensory evaluation
A selected group of ten assessors (seven females and
three males, aged 25–57 years) was trained in descriptive
analysis according to guidelines in ISO (1993). The panel
had several years of experience with sensory analysis of
fruits and vegetables and specific experience with sensory
analysis of tomatoes (Thybo et al., 2005). Samples of half a
tomato each were served on white plates coded with a
3-digit number in random order to each assessor. Two
evaluations of the samples (replicates) were carried out per
day. The assessors worked in single cabinets under
standard conditions (20 1C and 60–70% rh) and red light
to avoid eventual colour bias. The assessors developed a
list of profiling attributes and agreed on: redness of the
surface skin, redness of the fruit tissue evaluated as the
1 cm layer just below the skin, firmness, crispness,
mealiness, sourness, sweetness and tomato flavour. The
panel was trained for 4–5 h in the profile with respect to
reproducibility and ability to discriminate. The evaluation
was carried out using a 15-cm unstructured line scale with
anchor points ‘none’ on the left side and ‘very much’ on the
right side.
2.6. Statistical analysis
All physico-chemical and sensory data were analysed by
analysis of variance (ANOVA), using the GLM and the
MIXED model procedures (SAS version 8.00, Gary USA).
All data were checked for outliers and data on volatile
compounds were transformed to the logarithms of the
concentrations to ensure variance homogeneity. For all
data at the early harvest, ANOVA included the effects of
growing system, blocks and interaction. For the late
harvest, a mixed ANOVA model including the effects of
growing system, blocks, supplemental fertilizer and interactions was used to examine the data. Statistical differences
were determined by F tests statistics. LSD was used to
assess the location of the significant differences at P ¼ 0:05.
3. Results and discussion
3.1. Effect of growing systems on fruit yield and element
content
At early harvest the highest production was obtained
from plants grown in the combined beds, and in 2003 the
lowest production was obtained from plants in the confined
beds (Table 1). At late harvest, especially in 2003, plants
grown in the confined beds produced a lower fruit yield
than plants in the other systems. A lower production of
fruits from the plants grown in the confined beds could be

Table 1
Effect of growing system and fertilizer supplement on the cumulated yield
(kg/m2) of tomatoes, harvested early and late in 2002 and 2003a
Systems

2002

2003

Early harvest
Open
Confined
Combined
System

2.2 bb
2.1 b
2.6 a
*c

4.9 b
4.3 c
5.5 a
**

Late harvesta
Open
Confined
Combined

32.2 a
29.8 b
33.1 a

37.8 a
30.3 b
39.2 a

–Supplement
+Supplement

31.4 B
32.1 A

35.8 A
35.8 A

System
Supplement

*
*

***
ns

a

a

At the early harvest, yield was cumulated in 2002 from 24 May to 10
June and in 2003 from 23 April to 19 May. At the late harvest, yield was
cumulated in 2002 from 24 May to 7 October and in 2003 from 23 April to
22 September.
b
Different letters within columns at each harvest indicate significant
differences at P ¼ 0:05. Small letters are used for systems and capital
letters for fertilizer supplement.
c
Significance levels: ***: Pp0:001, **: Pp0:01, *: Pp0:05, ns: nonsignificant.

due to differences in the nutrient availability and nutrient
uptake from the different systems. Compost is a very
diverse product and the release of nitrogen, phosphorus
and sulphur is very much dependent on the content of
carbon. At low carbon content, the release of nitrogen,
phosphorus and sulphur is fast, but at high carbon content
the release is slow. The challenge in using compost as
nutrient source for plant growth is to time the nutrient
release when the crop needs it (Båth, 2000). The plants in
the open and combined system in our study had access to
nutrient uptake from the soil, and roots could expand and
utilize a greater quantity of nutrient substrate than in the
confined system. The content of most of the major and
trace elements in the tomato fruits (Table 2) are found
within the normal range for tomatoes grown in soil
(Gundersen et al., 2001). The yield and the content of
elements show that the plant nutrition has been sufficient.
At the early harvest the growing system had a significant
effect on calcium, phosphorous, cadmium and total
nitrogen in 2002. It seems that the highest concentration
of these elements was found in the soil grown tomatoes,
however the differences were small. For both years, the
content of Cd was significantly lower in the confined and
combined bed, which is important information for health
insurance. The content of Cd in the soil bed was
comparable with results obtained by Gundersen et al.
(2001), who also showed that soil-grown tomatoes contained higher levels of Cd (approx. 24 mg/100 g dm) than
tomatoes grown on rock-wool slabs (approx. 1.2 mg/
100 g dm).

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839

Table 2
Effect of growing system on the concentrations of major and trace elements in tomato fruits harvested in 2002 and 2003
Early harvest 2002a

Compound

Early harvest 2003a

Open

Confined

Combined

Open

Confined

Combined

Major elements
N (g 100 g dm
1)
K (g 100 g dm
1)
P (mg 100 g dm
1)
S (mg 100 g dm
1)
Ca (mg 100 g dm
1)
Mg (mg 100 g dm
1)
Na (mg 100 g dm
1)

2.53 ab
4.77
560 a
113
147 a
160
17

2.20 b
4.77
453 b
117
157 a
160
17

2.30 ab
4.50
477 c
103
113 b
153
10

2.03
4.10
433
110
193
137
—

1.90
4.00
380
100
157
137
—

1.87
3.90
400
100
173
133
—

Minor elements
Cd (mg 100 g dm
1)

28 a

15 b

18 b

18 a

8b

17 a

a

Early harvest 2002: 10 June; early harvest 2003: 19 May.
Different letters within rows at each year harvest indicate significant differences at P ¼ 0:05.

b

Table 3
Effect of growing system and fertilizer supplement on sensory attributes of tomatoes harvested early and late in 2002 and 2003a
Systems/suppl fert

Redness surface

Redness tissue

Firmness

Crispness

Mealiness

Sourness

Sweetness

Tomato flavour

Early harvest 2002a
Open
Confined
Combined

8.5
8.7
9.2

9.1
8.7
9.2

7.0
7.2
7.6

7.1
7.2
7.7

0.7
0.6
0.4

5.2 abb
5.6 a
4.7 b

5.3
5.8
5.9

5.7 ab
6.2 a
5.6 b

Late harvest 2002a
Open
Confined
Combined

8.6
7.2
9.1

8.3 a
6.6 b
8.5 a

9.5
9.9
9.4

8.9
9.7
8.6

1.0
0.8
1.1

8.6
8.3
8.1

3.3
3.6
3.6

6.0
5.6
6.3

–Suppl fert
+Suppl fert

8.4
8.5

8.0
7.5

9.7
9.5

9.4
8.8

0.9
1.0

8.6
8.0

3.3
3.7

6.0
5.9

7.4 b
8.5 a
7.5 b

7.6 b
8.8 a
7.8 b

1.2 a
0.9 b
1.0 ab

6.0
5.9
5.9

6.4
7.1
6.7

6.8 b
7.7 a
7.7 a

7.6
7.9
7.2

6.8
7.2
6.7

0.7
1.1
1.2

6.0
5.9
6.3

6.4
6.3
6.4

6.3
6.3
6.6

7.4
7.7

6.6
7.2

0.8
1.2

6.3
5.8

6.5
6.2

6.8
6.0

Early harvest 2003a
Open
Confined
Combined

9.7 b
10.6 a
11.0 a

Late harvest 2003a
Open
Confined
Combined

9.7
10.0
10.0

–Suppl fert
+Suppl fert

10.7 B
9.0 A

9.7 b
10.1 ab
10.9 a
9.0
9.4
9.5
10.6 B
8.0 A

a

Harvest dates in 2002 were: 10 June and 7 October and in 2003: 19 May and 22 September.
Different letters within columns at each harvest indicate significant differences at P ¼ 0:05. Small letters are used for systems and capital letters for
fertilizer supplement.
b

3.2. Effect of growing systems on sensory quality
The effect of growing systems on the sensory quality of
the tomatoes is given in Table 3. Only few significant effects
of growing systems were observed, which are concordant
with the general lack of significant differences in the
physico-chemical components (Table 4). At the early
harvest time in 2003, the tomatoes from the confined and
combined beds were rated higher in surface colour, red
tissue colour, crispness and tomato flavour than the fruits

from the open system. The same tendency was seen for the
late harvest in 2003. The tomatoes grown in the combined
growing system in 2002 also seemed to have a slightly
higher intensity in red surface colour, red tissue colour
(only significant at the late harvest in 2002) and sweetness
and a lower intensity for sourness (only significant at the
early harvest in 2002) than the fruits from the open and
confined system. In 2003, the tomatoes were harvested at a
stage of advanced ripeness than those in 2002 at a maturity
level closer to that preferred by consumers and this could

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840

Table 4
Effect of growing system on the concentration of physico-chemical and volatile compounds collected by dynamic headspace technique in tomatoes
harvested early in 2002 and 2003
Compound

Early harvest 2002a
Open

Physico-chemical compounds
Firmness (kg)
Dry matter (g 100 g fw
1)
Soluble solids (g 100 g fw
1)
Titratable acidity (g 100 g fw
1)
PH
Vitamin C (mg 100 g fw
1)

2.13
5.64
4.53
0.43
4.32
11.8

Volatile compounds (mg kg fresh weight
1)
1-Penten-3-one
28
Hexanal
283
2-Methyl-2-butenal
12.5
(Z)-3-hexenal
402
2- and 3-Methyl-1-butanol
65
(E)-2-Hexenal
90
2-Pentyl-furan
0.56
1-Octen-3-one
0.48
6-Methyl-5-hepten-2-one
8.3
(Z)-3-hexen-1-ol
1.2
6-Methyl-5-hepten-2-ol
0.71 a
Camphor
0.11
Linalool
0.23
Dimethyl sulfoxide
0.26
b-Caryophyllene
0.72
b-Cyclocitral
0.10
Geranyl acetone
0.32
b-Ionone
0.045
a

Early harvest 2003a

Confined

Combined

2.08
6.04
4.97
0.46
3.58
15.0

2.14
5.92
4.77
0.43
4.32
13.3

30
304
13.9
445
68
96
0.66
0.55
6.7
2.4
0.60 c
0.12
0.25
0.23
0.68
0.12
0.25
0.036

31
308
13.2
424
66
98
0.58
0.55
8.2
1.8
0.67 b
0.11
0.26
0.14
1.05
0.17
0.39
0.038

Open

1.99
5.67
4.27 ab
0.38
4.19 a
14.6 a
19.5
310
10.9 a
352
39
59
0.56
0.61
12.7
1.6
0.34
0.09 b
0.15
0.18
0.32
0.05
0.25 b
0.018

Confined

Combined

1.99
5.87
4.58 b
0.39
4.17 b
16.0 ab

1.97
5.89
4.43 ab
0.39
4.16 b
16.6 b

19.3
308
5.3 b
328
42
54
0.58
0.66
14.6
1.3
0.42
0.15 a
0.11
0.23
0.24
0.03
0.19 c
0.020

19.4
323
5.3 b
336
38
56
0.75
0.59
11.4
1.6
0.34
0.11 a
0.15
0.25
0.28
0.02
0.31 a
0.024

Early harvest 2002:10 June; early harvest 2003: 19 May.
Different letters within rows at each year indicate significant differences at P ¼ 0:05.

b

have made the sensory differences between the growing
systems more obvious in 2003.
Contrary effects of growing systems on tomato flavour
were observed in 2002. Tomatoes from the confined system
scored significantly higher in tomato flavour early in the
season but lower at the later harvest probably because the
fruits were less ripe in the confined system at this harvest
time. It is documented that the maturity of tomatoes at
harvest has a significant effect on tomato quality (Künsch
et al., 1994; Schnitzler, Eichin, & Hanke, 1994). Our results
indicate that even though the tomatoes from each growing
system were harvested at a similar colour stage, the sensory
panel were able to depict even small differences in visual
colour (Table 3), which were probably related to differences in the physiological maturity of the tomatoes
harvested on the different systems.
In conclusion, the differences in sensory quality between
the growing systems were very small, but there seemed to
be some consistency in the effect of growing systems
between the harvest times and years. In general, the
data point to the fact that the combined and confined
growing system produced tomatoes with slightly higher
intensity in sweetness and tomato flavour and lower

intensity in sourness compared to those from the open
system.
3.3. Effect of growing system on physico-chemical
compounds
The levels of pH, dry matter, soluble solids, titratable
acidity and vitamin C in the organic tomatoes grown in soil
and compost (Table 4) were within the levels reported for
conventional tomatoes grown in soil and on rock-wool slab
(Lippert, 1993; Petersen et al., 1998; Tando et al., 2003).
The tomatoes were firmer in 2002 than in 2003 (Table 4),
which reflected that the tomatoes were harvested at a stage
of advanced ripeness and higher maturity in 2003.
Very few significant effects of growing systems on the
physico-chemical components were obtained at either
harvest time in 2002 and 2003 in concordance with the
general lack of significant differences in the sensory
attributes (Table 3). The physico-chemical composition of
tomatoes from the first harvest in 2002 and 2003 are given
in Table 4. In 2003, the contents of soluble solids and
vitamin C were significantly higher and pH was lower in
the tomatoes grown in the combined and confined system.

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A.K. Thybo et al. / LWT 39 (2006) 835–843

The contents of dry matter and soluble solids were also
slightly higher (but nonsignificant) in the tomatoes from
the confined and the combined system in 2002, indicating
that the tomatoes contained higher levels of sugars,
primarily glucose and fructose (Tando et al., 2003). The
results of the sensory evaluation at the early harvest
showed that the tomatoes from the confined and combined
systems were harvested slightly more red than those from
the open system (Table 3). So differences in maturity at
harvest could be part of an explanation. Differences in the
plant growth rate at the beginning of the season could be
another explanation. The root-media temperatures in the
confined and combined beds were slightly higher compared
with the open system, which may have increased the
growth and development of constituents in the tomato
fruits from these systems. However, it was expected that
some of the differences in chemical composition of fruits
from the confined and in part also the combined beds could
be due to nutrient limitations or imbalances especially in
the confined system, where the tomatoes were fully
dependent on the content and availability of nutrients in
the compost. Analyses of the compost in confined beds
during the growing period showed nutrient imbalances
during the first 5 weeks of harvest and again during the last
7–8 weeks of harvest (Sørensen & Thorup-Kristensen,
2006). During the growing period the EC decreased from
about 3 to 1 and the ion activity ratio decreased from 0.4 to
less than 0.1, which is considered as low. Nutrient
imbalances were mostly observed in plants grown in the
confined system. In the combined system, the compost also
showed low ion activity ratios during the final growing
period, but plants did not suffer because they had the
possibility to escape from the adverse nutrient conditions
prevailing in the compost. The content of nitrogen was
found in significantly lower concentration in the fruits from
the confined (and the combined) system in 2002 (Table 2).
In 2002, yield was slightly increased by application of extra
fertilizer, indicating that plants were slightly deficient in N
at the late sampling this year. However, N deficiency was
probably also prevailing during the early growth stages. It
is well-known that a low level of nitrogen during growth
and development increases the dry matter content of
vegetables (Sørensen, 1999).
As for the nonvolatile constituents, very few significant
effects of growing system were found on the content of
volatile compounds. Totally 31 volatile compounds were
quantified in and identified from headspace samples of
organic tomatoes (Edelenbos, Thybo & Christensen, 2005)
including many of those considered to be important for
tomato flavour (Baldwin et al., 2004; Tando et al., 2003).
The concentrations of 18 individual volatile compounds in
headspace samples of tomatoes are given in Table 4. The
amount of volatile compounds was quantified by adding an
internal standard to the collected headspace samples.
Hence, our quantitative data correspond to the amount
directly emitted from tomatoes in contrast to studies where
the internal standard is added prior to collection of volatile

841

compounds by dynamic headspace technique, corresponding to quantification of the total amounts of volatile
compounds in tomatoes (Buttery et al., 1987).
In 2002, growing systems had a significant effect on the
content of 6-methyl-5-hepten-2-ol. In 2003, significant
effects were observed on the contents of 2-methyl-2butenal, camphor and geranyl acetone, so there did not
seem to be any consistency in the effect of growing system
on the concentration of individual volatile compounds.
Despite the lack of significance, the volatile compounds
hexanal, 1-octen-3-one, linalool, dimethyl sulfoxide and bcyclocitral were the ones, mostly affected by growing
system, when investigating tomatoes from the early to the
late harvest in 2002, using multivariate data techniques
(Edelenbos et al., 2005). Tomato flavour is very complex
and many attempts have been made to suggest a
combination of compounds, giving tomatoes its unique
odour characteristics (Buttery, 1993; Krumbein & Auerswald, 1998; Baldwin et al., 2004). Ruiz et al. (2005)
suggested that hexanal and (Z)-3-hexenal in combination
with sugars and organic acids in a balanced ratio were the
most important contributors to tomato flavour and
consumer acceptance. Tomatoes grown in the confined
and combined beds had slightly higher concentrations of
hexanal (nonsignificant) than those grown in soil.
Despite the lack of significance of growing system on
many of the physico-chemical and volatile compounds, the
results illustrate that the confined and the combined
growing system could produce tomatoes with at least as
high a concentration of individual compounds than those
grown directly in soil. In summary, the tomatoes from the
combined system, and to some extent tomatoes from the
confined system, had a slightly higher concentration of
some of the chemical components relevant for quality of
tomatoes, and in concordance, tomatoes from the combined system had slightly higher scores for sensory quality.
Even though we do not know the reasons for these
differences, it is expected that the combined system allows
more balanced plant nutrition than the other systems as
plants in this system had excess to both compost and soil.
A healthier root system in the compost beds may be
another explanation, which gives the crop ability to
assimilate more nutrients from the surrounding growing
media than less healthy roots.
3.4. Effect of extra supply of fertilizer
Supplemental fertilizer was applied to the plants late in
the season to ensure a sufficient nutrient supply. The total
production of fruits increased slightly in 2002 as a result of
extra fertilizer but not in 2003 (Table 1) indicating that
plants had very little nutrient deficiencies during the final
growing period. There was no interaction between growing
system and extra fertilizer, and no significant effect of extra
fertilizer on the concentration of minerals, nitrogen and
potassium (data not shown). Few effects of extra fertilizer
were seen on the sensory and chemical components, e.g. the

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842

A.K. Thybo et al. / LWT 39 (2006) 835–843

tomatoes were less red (Table 3) and had a higher content
of titratable acidity in 2003 (data not shown) when extra
fertilizer was applied during growth and development. The
lack of substantial effects of supplemental organic fertilizer
on sensory and physico-chemical quality of tomatoes was
in accordance with the very limited effects of extra fertilizer
supply on total yield and contents of minerals and
nitrogen. This indicates that the basic nutrient supply
from the compost was sufficient to secure a high quality
and production of organic tomatoes late in the growing
season.

4. Conclusion
The results show small effects of growing system on
tomato quality; one interesting exception was the significantly lower content of cadmium in the tomatoes from the
confined system. There were indications that tomatoes
from the combined or confined systems were superior in a
few quality parameters, but generally the differences were
small, indicating that tomato quality is rather robust across
growing systems when harvested at comparable maturity.
This means that different cropping systems such as the
confined or the combined system can be employed without
changing the eating quality of tomatoes significantly. This
improves the possibilities for organic growers of tomatoes
to switch to a compost bed system in order to control soilborne pests and diseases and to improve the nutrient
balance in an intensive greenhouse production system.

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