مرکزی صفحہ Lebensmittel-Wissenschaft und-Technologie / Food Science and Technology Effect of organic growing systems on sensory quality and chemical composition of tomatoes
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 ARTICLE IN PRESS A.K. Thybo et al. / LWT 39 (2006) 835–843 836 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. ARTICLE IN PRESS A.K. Thybo et al. / LWT 39 (2006) 835–843 nutrients applied with compost at the beginning of the growing period was 117 g N m2, 48 g P m2 and 112 g K m2 in 2002 and 196 g N m2, 35 g P m2 and 121 g K m2 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 m2, 7 g P m2 and 49 g K m2 in 2002 and 41 g N m2, 5 g P m2 and 36 g K m2 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 min1. 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 min1) 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 min1 to 60 1C, isothermal for 2 min, then 5 1C min1 to 180 1C, isothermal for 10 min, then 10 1C min1 to 220 1C, followed by constant temperature for 10 min. Helium was applied as carrier gas with a ﬂow rate of 1.4 ml min1. 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 ARTICLE IN PRESS 838 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). ARTICLE IN PRESS A.K. Thybo et al. / LWT 39 (2006) 835–843 839 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 dm1) K (g 100 g dm1) P (mg 100 g dm1) S (mg 100 g dm1) Ca (mg 100 g dm1) Mg (mg 100 g dm1) Na (mg 100 g dm1) 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 dm1) 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 ARTICLE IN PRESS A.K. Thybo et al. / LWT 39 (2006) 835–843 840 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 fw1) Soluble solids (g 100 g fw1) Titratable acidity (g 100 g fw1) PH Vitamin C (mg 100 g fw1) 2.13 5.64 4.53 0.43 4.32 11.8 Volatile compounds (mg kg fresh weight1) 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. ARTICLE IN PRESS 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 ARTICLE IN PRESS 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. References AOAC 992.23, 984.27. (1997). Official Methods of Analysis of AOAC International. Maryland, USA: AOAC International. Auclair, L., Zee, J. A., Karam, A., & Rochat, E. (1995). Nutritive value, organoleptic quality and productivity of greenhouse tomatoes in relation to their production methods: Organic–conventional–hydroponic. Sciences des Aliments, 15, 511–528. Auerswald, H., Peters, P., Brücker, B., Krumbein, A., & Kuchenbuch, R. (1999). Sensory analysis and instrumental measurements of short-term stored tomatoes (Lycopersicon esculentum Mill.). Postharvest Biology and Technology, 15, 323–334. Auerswald, H., Schwarz, D., Kornelson, C., Krumbein, A., & Brückner, B. (1999). Sensory analysis, sugar and acid content of tomato at different EC values of the nutrient solution. Scientia Horticulturae, 82, 227–242. Baldwin, E. A., Goodner, K., Plotto, A., Pritchett, K., & Einstein, M. (2004). Effect of volatiles and their concentration on perception of tomato descriptors. Journal of Food Science, 69, S310–S318. Basker, D. (1992). Comparison of taste quality between organically and conventionally grown fruits and vegetables. American Journal of Alternative Agriculture, 7, 129–136. Båth, B. (2000). Matching the Availability of N Mineralised from GreenManure Crops with the N-Demand of Field Vegetables. Agraria Doctoral Dissertation (Ph.D.), Swedish University of Agricultural Sciences, Uppsala 222, 29-1. Buttery, R. G. (1993). Quantitative and sensory aspects of ﬂavor of tomato and other vegetables and fruits. In T. E. Acree, & R. Teranishi (Eds.), Flavor science: Sensible principles and techniques (pp. 259–286). Washington, DC: American Chemical Society. Buttery, R. G., Teranishi, R., & Ling, L. C. (1987). Fresh tomato aroma volatiles: A quantitative study. Journal of Agricultural and Food Chemistry, 35, 540–544. Edelenbos, M., Thybo, A. K., & Christensen, L. P. (2005). Flavour quality of organic tomatoes grown in different systems. In: Proceeding of the 11th Weurman flavour symposium, Roskilde, Denmark, 21–24 June 2005. Forsberg, A. S., Sahlström, K., & Ögren, E. (1999). Rotröteproblem i ekologisk tomatodling. Jordbruksinformation, 12, 1–14. Gäredal, L., & Lundegårdh, B. (1997). A test system with limited beds for evaluation of growing methods, applied to ecologically cultivated greenhouse tomatoes (Lycopersicon esculentum Mill.). Biological Agriculture and Horticulture, 14, 291–301. Granges, A., Azodanlou, R., Couvreur, F., & Reuter, E. (2000). Cultivation methods and organoleptic quality of tomatoes grown in the greenhouse and in the ﬁeld (Methods de culture et qualite organoleptique de tomates cultivees en serre et en plein champ). Revue Suisse de Viticulture, d’Arboriculture et d’Horticulture, 32(3), 175–180. Gundersen, V., McCall, D., & Bechmann, I. E. (2001). Comparison of major and trace element concentrations in Danish greenhouse tomatoes (Lycopersicon esculentum cv Aromata F1) cultivated in different substrates. Journal of Agriculture and Food Chemistry, 49, 3808–3815. Gysi, C., & von Allmen, F. (1997). Wasser- und Nährstoffbilanzen von Hors-sol Tomaten. Agrarforschung, 4, 1–6. Haglund, A., Johansson, L., Gäredal, L., & Dlouhy, J. (1997). Sensory quality of tomatoes cultivated with ecological fertilizing systems. Swedish Journal of Agricultural Research, 27, 135–145. ISO, International Standard 8586-1. (1993). Sensory analysis—general guidance to for the selection, training and monitoring of assessors Ref. No. ISO 8586-1: 1993. Genève: International Organization for Standardization. Johansson, L., Haglund, A., Berglund, L., Lea, P., & Risvik, E. (1999). Preference for tomatoes, affected by sensory attributes and information about growth conditions. Food Quality and Preference, 10, 289–298. Krumbein, A., & Auerswald, H. (1998). Characterization of aroma volatiles in tomatoes by sensory analyses. Nahrung, 10, 395–399. Künsch, U., Schärer, H., Dürr, P., Hurter, J., Martinoni, A., Jelmini, G., et al. (1994). Qualitätsuntersuchungen an Tomaten aus erdelosem und konventionellem Glashausanbau (Quality investigation of tomatoes from soil-less and conventional culture). Gartenbauwissenschaft, 59, 21–26. Lento, H. G., Daugherty, C. E., & Denton, A. E. (1993). Ascorbic acid measurement. Polargraphic determination of total ascorbic acid in foods. Journal of Agricultural and Food Chemistry, 11, 22–26. Lippert, F. (1993). Amounts of organic constituents in tomato cultivated in open and closed hydroponic systems. Acta Horticulturae, 339, 113–123. Petersen, K. K., Willumsen, J., & Kaack, K. (1998). Composition and taste of tomatoes as affected by increased salinity and different salinity sources. Journal of Horticultural Science and Biotechnology, 73, 205–215. Pongracz, G. (1971). Neue potentiometrische Bestimmingsmetode für Ascorbinsaüre und deren Verbindungen. Zeitschrift für Analytische Chemie, 253, 271–274. Ruiz, J. J., Alonso, A., Garcia-Martinez, S., Valero, M., Blasco, P., & Ruiz-Bevia, F. (2005). Quantitative analysis of ﬂavour volatiles detects differences among closely related traditional cultivars of tomato. Journal of the Science of Food and Agriculture, 85, 54–60. Schnitzler, W. H., Eichin, B., & Hanke, A. (1994). Inﬂuence of substrates and ripeness on taste and aroma of tomatoes. Gartenbauwissenschaft 5, 214–220. Sørensen, J. N. (1999). Nitrogen effects on vegetable crop production and chemical composition. Acta Horticulturae, 506, 41–49. Sørensen, J. N., & Thorup-Kristensen, K. (2006). An organic and environmentally friendly growing system for greenhouse tomatoes. Biological Agriculture and Horticulture, submitted for publication. ARTICLE IN PRESS A.K. Thybo et al. / LWT 39 (2006) 835–843 Tando, K. S., Baldwin, E. A., Scott, J. W., & Shewfelt, R. L. (2003). Linking sensory descriptors to volatile and non-volatile components of fresh tomato ﬂavour. Journal of Food Science, 68, 2366–2371. Thybo, A. K., Bechmann, I. E., & Brandt, K. (2005). Integration of sensory and objective measurements of tomato quality: Quantitative assessment of the effect of harvest data as compared with growth medium (soil versus rockwool), EC, variety, and maturity. Journal of the Science of Food and Agriculture, 85, 2289–2296. 843 Tijsken, L. M. M., & Evelo, R. G. (1994). Modelling colour of tomatoes during postharvest storage. Postharvest Biology and Technology, 4, 85–98. Whitﬁeld, F. B., & Last, J. H. (1993). Vegetables. In H. Maarse (Ed.), Volatile compounds in foods and beverages (pp. 203–281). New York: Marcel Dekker, Inc.