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LYCOPENE CONTENT IN HYDROPONIC AND NON-HYDROPONIC
TOMATOES DURING POSTHARVEST STORAGE
S. Ajlouni 1, S. Kremer 2, and L. Masih 1.
Abstract
The initial lycopene content in hydroponic and non-hydroponic ripen tomato fruits
was about 36 μg/g fr. wt., and increased continuously during postharvest storage.
Maximum amounts of lycopene were recorded after 14 days of storage at 22oC,
and reached 89.75±4.51 μg/g fr. wt. and 115.13±2.08 μg/g fr. wt. for hydroponic
and non-hydroponic cultivars, respectively. Non-hydroponic tomatoes showed also
a significant increase (p<0.05) in red colour when stored at 22oC. Storage at
refrigeration temperature (4oC) suppressed lycopene formation and red colour
development in both cultivars.
1 The Department of Food Science and Agribusiness
Gilbert Chandler College
Institute of Land and Food Resources
The University of Melbourne
Sneydes Road, Werribee Victoria 3030
Tel: (03) 92175206 Fax: (03) 9741 9396
2 The Department of Home Economic and Nutrition
Fachhochschule Fulda
36012 Fulda
Germany
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Introduction
Carotenoids are natural pigments synthesized by plants and some microorganisms
and found in a wide variety of fruits and vegetables. Carotenoids act as light-
absorbing pigments during photosynthesis and protect cells against
photosensitization (Rao, 1999; Clinton, 1998). In addition, some carotenoids, such
as α- and β-carotene play an important role as vitamin A precursors (Van Niekerk,
1988).
Lycopene is one of these carotenoids found predominantly in tomatoes, and forms
the principal pigment responsible for the red colour. The content of lycopene
varries widely among tomato varieties and increases dramatically during ripening
(Clinton, 1998). The concentration of lycopene in ripe fruits of the common
variety lycopersicon esculentum ranges between 31-77 μg/g fresh weight (Nguyen,
1999). Recent research and nutritional studies revealed that lycopene exhibits the
highest anitoxidant effect among all major dietary carotenoids (Rao, 1999;
Clinton, 1998). It is believed that dietary lycopene can reduce the risk of chronic
diseases such as cancer and cardiovascular disease (Rao, 1999).
Lycopene is a acyclic carotenoid, insoluble in water, containing 11 conjungated
and 2 non-conjugated double bonds (Rao, 1999; Clinton, 1998). In most foods,
lycopene occurs mainly in the thermodynamical most stable all-trans
configuration. In raw tomatoes, for example, 94-96% of the lycopene can be found
in the all-trans form (Schierle, 1997). However the trans to cis isomerization
occurs mainly during cooking, processing and storage (Rao, 1999; Tonucci, 1995),
and improves the bioavailability of lycopene (Gaertner, 1997, Stahl, 1992).
Lycopene content in hydroponic tomatoes, which represent an important and
growing section in the tomato industry, has not been well investigated. The
production of hydroponic tomatoes has increased significantly during the last few
years. The annual turnover of hydroponic crops in Australia reached $3 million in
1998, with a ten-fold increment in the last decade (Wilson,1999). This study will
report changes in lycopene contents in hydroponic and non-hydroponic cultivars
during storage at refrigeration and room temperatures.
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Materials and Methods
Chemicals
Lycopene (90-95% pure) and HPLC grade methylene chloride were obtained from
Sigma Chemical Company (St. Louis, USA). Analytical grade solvents including
hexane, methanol, acetone and toluene as well as HPLC grade methanol were
purchased from British Drug House (BDH Laboratory Supplies, Poole, UK).
Sampling and preparation of lycopene extract
Medium size tomato fruits with similar degrees of maturity, and from two different
cultivars were used in this study. Hydroponic tomatoes (Pyramid) were obtained
from a local grower and non-hydroponic tomatoes were bought from a local
supermarket. Each group of tomatoes was divided into two halves and placed on
trays. One half was stored at room temperature (22°C), and the other half in a
fridge at 4°C. Changes in color and lycopene contents were measured on day zero
and after 7, 14, and 21 days of storage.
Due to the fact that pure lycopene is a very light-sensitive compound, the
extraction was performed under subdued lighting with a 25W red globe providing
the only illumination, following the method of Chen et al., (1995) with slight
modifications.
About 500 g of tomato were homogenized in a Waring blender (800 E, Dynamics
Corporation of America, Connecticut, USA) and three samples of the homogenate
(4 g each) were collected and treated separately. The homogenate was mixed with
30 ml of hexane:acetone:methanol:toluene, 10:7:6:7 v/v/v/v in a 100ml volumetric
flask, 6 ml of a 4% methanolic KOH was added and the flask was shaken for 1
min and left in the dark at room temperature for 16 h saponification. After
saponification, 30 ml of hexane were added to the flask, followed by gentle
swirling for 1 min, before the mixture was diluted to volume with 1% Na2So4. The
flask was left to stand in the dark for an additional 1h until two phases had
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separated. The upper phase was transferred into a rotary evaporator and evaporated
to dryness at 50°C. The dried concentrate was then dissolved in 10 ml of
methanol-methylene chloride 45:55 v/v and filtered through a 0.2 μm membrane.
To minimize oxidation or degradation of the extracted lycopene, 20 μl of that
filtrate were immediately injected into the HPLC.
HPLC system
The chromatographic analyses were performed using a Shimadzu High
Performance Liquid Chromatograph equipped with a workstation computer (Class-
VP) and a photodiode array (PDA) detector (SPD-M10Avp). The column used
was a NOVA PAK C18 stainless steel column of 3.9 x 150 mm packed with C18
reversed-phase material with a particle size of 4 μm (Millipore-Waters Associates,
USA).
Lycopene standard was dissolved in chloroform containing 0.1% Butylated
Hydroxytoluene (BHT), divided into 1 ml aliquots and stored at – 80°C. The
elution was performed at room temperature with an isocratic solvent,
methanol:(methanol:methylene chloride, 45:55 v/v) 99:1 v/v, at a constant flow
rate of 1.5 ml/min. The peak response of lycopene was detected at 472nm and the
quantification of the lycopene was performed using the programm Excel
(Microsoft, USA).
Colour measurement
A Minolta Chroma Meter CR-300 (Minolta Co., Ltd., Japan) was used to measure
the L, a & b color space values of whole tomato fruits before homogenisation.
Statistical Analysis of Data
Data were statistically analyzed using SPSS 8.0. for WIN 95/NT and a student T-
test was performed to compare between the means at 95% confidence level.
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Results
a. Lycopene Contents:
The initial lycopene content in ripe hydroponic tomatoes (HT) was 36.15±4.17
μg/g fresh weight (fr. wt.) on day zero of storage. Lycopene content in HT
(Pyramid) increased continuously during storage at room temperature and reached
a maximum value of 89.75 ± 4.51μg/g fr. wt. after 14 days of storage (Fig 1). The
same data revealed also that lycopene content started to decrease after 21 days of
storage, while the tomato fruits were still in a good quality for consumption.
Storage at refrigeration temperature did not affect lycopene content (36.15 ± 4.17
μg/g fr. wt.) in Hydroponic tomatoes, which showed very little changes throughout
the storage period (Fig 1). However, severe senescence and deterioration in the
quality of hydroponic tomatoes were observed after 21 days of storage at 4oC.
Changes in lycopene contents in non-hydroponic tomato (non-HT), as affected by
storage temperature, showed similar patterns to those observed in the hydroponic
cultivars. However the increments in lycopene contents in non-HT stored at room
temperature were significantly (P<0.05) higher than those recorded in HT
throughout the storage period. Lycopene content increased dramatically in non-HT
after 14 days of storage at room temperature and reached a maximum value of
115.13 ± 2.08 μg/g fr. wt. (Fig 1).
Deleted: changes
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Figure 1. Changes in lycopene contents of hydroponic (Pyramid) and non-
hydroponic tomatoes during storage at two different temperatures.
HT(4C): Hydroponic tomato stored at 4oC; Non-HT(22C): Non-
hydroponic tomato stored at 22oC.
Storage Time (day)
0
20
40
60
80
100
120
0 7 14 21
Non-HT (22C)
HT (22C)
Non-HT (4C)
HT (4C)
Storage Time (day)
Lycopene content (ug/g fr wt)
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b. Colour Measurments
In addition to visual evaluation of the degree of ripeness of tomato fruits, colour
measurements were also recorded throughout the storage period to monitor
changes in tomato red colour as a quality parameter. The three colour space values
(L, a and b) were measured using Minolta Chroma Meter. Positive L, a and b
colour space values reflect the degree of lightness, redness and yellowness,
respectively. Since mature and high quality tomato fruits are usually associated
with intense red colour, the a values can be used as an indicator to estimate
changes in tomato quality during maturation and storage. The larger the a value,
the more intense the red colour of tomato fruits.
Data form colour measurements in hydroponic tomatoes revealed slight changes in
L and b values during storage at 4oC and 22oC. However, changes in a values were
significant (p<0.05) during storage at 22oC. The a values in HT increased from
11.83±2.45 to 17.68±1.05 after the first 7 days of storage (Table 1), and remained
relatively stable thereafter. No significant changes in a values were recorded in HT
stored at 4oC (Table 1).
The red colour of non-hydroponic tomatoes was also affected by storage
temperature as indicated by some significant changes in colour space values. The
a values increased from 5.75±2.61 to 9.26±1.49 after the first 7 days of storage at
4oC, and such increment was more significant at 22oC (Table 2). The L value in
non-hydroponic tomatoes decreased from 48.32±2.22 to 40.86±0.81 during storage
at 22oC, while no major changes in b values were detected in non-HT throughout
the storage period.
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Table 1. Changes in colour space values (L, a & b) in hydroponic tomatoes during storage for 21 days at two different temperatures.
Storage Temperature
4oC
22oC
Storage Time (days)
L a b L a b
0
7
14
21
42.60 ± 1.72 *
42.95 ± 0.73
43.96 ± 1.24
41.38 ± 1.81
11.83 ± 2.45
8.22 ± 1.80
9.25 ± 1.51
10.77 ± 3.23
20.89 ± 1.01
24.25 ± 1.16
24.12 ± 1.04
24.81 ± 3.10
42.60 ± 1.72
39.77 ± 0.96
38.64 ± 0.96
37.91 ± 0.22
11.83 ± 2.45
17.68 ± 1.05
18.54 ± 1.83
18.35 ± 0.95
20.89 ± 1.01
20.98 ± 2.18
20.65 ± 1.87
19.52 ± 1.03
* Values represent the average of six measurements followed by the standard deviation.
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Table 2. Changes in colour space values (L, a & b) in non-hydroponic tomatoes during storage for 21 days at two different
temperatures.
Storage Temperature
4oC
22oC
Storage Time (days)
L a b L a b
0
7
14
21
48.32 ± 2.11 *
46.31 ± 2.12
44.55 ± 2.27
46.42 ± 1.54
5.75 ± 2.61
9.26 ± 1.49
11.36 ± 2.73
10.94 ± 3.83
23.19 ± 3.60
27.55 ± 5.08
30.67 ± 1.74
28.67 ± 3.10
48.32 ± 2.11
40.86 ± 0.81
39.06 ± 1.07
38.59 ± 0.38
5.75 ± 2.61
21.06 ± 2.39
22.66 ± 1.70
21.53 ± 2.45
23.19 ± 3.60
23.42 ± 2.06
21.32 ± 1.40
20.66 ± 1.55
* Values represent the average of six measurements followed by the standard deviation.
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Discussion:
Tomato fruits of both cultivars (hydroponic and non-hydroponic) appeared to have a
similar amount of lycopene at the start of the storage period. The average lycopene
contents were 36.15±4.17 and 36.25±1.24 μg/g fr wt for hyroponic and non-hyroponic,
respectively. These values are in agreement with those reported by Nguyen in 1999, who
indicated that the content of lycopene in ripe fruits of the common variety Lycopersicon
esculentum ranges between 31 and 77 μg/g fr wt.. Lycopene content increased
continuously in both cultivars during storage at 22oC, and reached its maximum values
after 14 days of storage (Fig 1). However, the rate of lycopene formation in non-
hyroponic tomatoes was higher than that in the hyroponic cultivar. The amount of
lycopene in non-HT reached a maximum value of 115.13±2.08 μg/g fr wt in comparison
to 89.75 ±4.51 μg/g fr wt in HT under the same storage conditions. These findings may
suggest that the substrate for lycopene formation (phytoene) was more readily available
in non-HT, and/or the lycopene biosynthesis enzymatic systems were more active in non-
HT. Results of lycopene formation at 4oC may support these suggestions. No significant
changes (p>0.05) in lycopene contents were detected in HT during storage at 4oC, while
non-HT revealed a 68% increase in the amount of lycopene after 14 days of storage at
4oC. However, this percentage increment in lycopene content in non-HT at 4oC was much
smaller than that detected at 22oC (217%) after the same storage period.
These results may indicate that ripe tomatoes “red colour” stored at room temperature
would have higher lycopene contents than tomato fruits kept at refrigeration temperature.
Similar conclusion was reported by Hamauzu et al., (1998) who indicated that lycopene
contents were high in ripe tomatoes stored at 20°C for 10 days. Lycopene is usually
synthesized from phytoene and regarded as the common precursor for β-carotene.
Because the cycle of lycopene formation and degradation is highly regulated by several
biosynthetic enzymes, it can be postulated that storing tomato fruits at refrigeration
temperature may reduce these enzymatic activities and maintain lycopene contents
relatively stable.
Colour space values (L, a & b) of both cultivars were also affected by storage
temperature, and showed similar changes to those observed in lycopene. Storage at low
temperature suppressed red colour development in tomato fruits, as indicated by the
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smaller a values at 4oC in comparison with a values at 22oC for both cultivars (Tables 1
& 2). Maximum a values were obtained after 14 days of storage at 22oC. The net
increment in a values were 6.71 and 16.91 units for hydroponic and non-hydrponic
tomatoes, respectively. These observations correlate well with the previous results of
lycopene analysis, which showed more significant increase in non-HT. The fact that
lycopene is the principal pigment responsible for the red colour in tomato, supports these
findings, because more lycopene formation is expected to yield higher a values.
However, it should be noted that such positive relationship between lycopene content and
a values was observed throughout the storage period, except on day zero. Although both
hyroponic and non-hyroponic tomatoes showed similar lycopene contents on day zero
(Fig 1), the a value in HT was larger than that in non-HT (Tables 1 & 2). Such variations
in a values may be related to L values which showed some difference on that day of
measurement. The L values were 42.60 and 48.32 unit for hyroponic and non-
hydroponic, respectively. As L value represents the degree of lightness, larger L values
would be associated with brighter colour and smaller a values. This may explain the
reason for the smaller a values in non-HT compared to HT on day zero of storage.
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Conclusion:
The higher lycopene contents detected in non-HT compared to the HT fruits during
storage at room temperature may be related to variations in physiological characteristics
between the two cultivars, as well as growing conditions. Lessin reported in 1997 that
carotenoid concentration in fruits and vegetables vary within plant variety, degree of
ripeness, time of harvest, and growing and storage conditions. Storage at refrigeration
temperature (4oC) suppressed lycopene formation and red colour development in both
cultivars. These findings support the recommendations that tomato fruits in general
should be stored at room temperature in order to obtain better red colour and higher level
of lycopene.
Further investigation is needed to thoroughly evaluate chemical composition,
biochemical and physiological changes, and nutritional values of hydroponic tomatoes, as
compared to non-hyrodponic cultivars. The proposed future research project will use
tomato samples of well-identified cultivars, harvested at similar stage of maturity.
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References
Chen, BH, Peng, HY, and Chen, HE. 1995. Changes of carotenoids, color, and vitamin A
contents during processing of carrot juice. J. Agric. Food Chem. 43:1912-1918.
Clinton, KS. 1998. Lycopene: chemistry, biology, and implications for human health and
disease. Nutrition Reviews, Vol. 56, No.2: 35-51.
Gartner, C, Stahl, W, and Sies, H. 1997. Lycopene is more bioavialable from tomato
paste than from fresh tomatoes. Am J Clin Nutr. 66:116-22.
Hamauzu, Y, Chachin, K and Ueda, Y. 1998. Effect of postharvest storage temperature
on the conversion of 14C-mevalonic acid to carotenes in tomato fruit. J. Japan. Soc.
Hort. 67(4): 549-555.
Lessin, WJ, Catigage, GL, and Schwartz, SJ. 1997. Quantification of cistrans isomers of
provitamin A carotenoids in fresh and processed fruits and vegetables. J. Agric. Food
Chem. 45: 3728-3732.
Nguyen, NL, and Schwartz, SJ. 1999. Lycopene: Chemical and biological properties.
Food Technology. Vol. 53, No. 2: 38-44.
Rao, VA, Waseem, Z, & Agarwal, S. 1999. Lycopene content of tomatoes and tomato
products and their contribution to dietary lycopene. Food Research International, Vol.
31, No. 10: 737-741.
Schierle, J, Bretzl, w, Buhler, I, Faccin, N, Hess, Denise, Steiner, K & Schuep, w. 1997.
Content and isomeric ratio of lycopene in food and human blood plama. Food
Chemistry, Vol. 59, No. 3: 459-465.
Stahl, W, and Sies, H. 1992. Uptake of Lycopene and its geometrical isomers is greater
from heat-processed than from unprocessed tomato juice in humans. American
Institute of Nutrition. July 1992, P. 2161-2166.
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Tonucci, LH, Holden, JM, Beecher, GR, Khachik, F, Davis, CS, and Mulokozi, G. 1995.
Carotenoid content of thermally processed tomato-based food products. J. Agric.
Food Chem. 43:579-586.
Van Niekerk, PJ. 1988. Determination of vitamins. In Macrae, R. (ed). HPLC in food
analysis. Academic press, London: 133-140.
Wilson, A. 1999. Personal communication. Hyroponic tomato. The president of
hyroponic tomato group. Geelong, Victoria.
