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Greenhouse tomatoes in New Zealand

Tomatoes

Introduction


Tomato (Lycopersicon esculentum) is an important vegetable crop with its origins in elevated regions of Central and South America (Gould, 1983). The total world production of tomatoes in 2003 was 110 million metric tonnes (FAOSTAT Agriculture Statistics Database, 2003).
In New Zealand, tomatoes are the second most commonly consumed vegetable in the diet, after potatoes (VegFed, 2004) and are usually grown in greenhouses for fresh consumption. In 2003, tomatoes were planted in 167 hectares of greenhouses with a total production of 40,000 tonnes, and New Zealanders spent over $107 millions on the purchase of these fresh tomatoes (Hort Research, 2003). Tomatoes are a member of Solanaceae family and the tomato fruit is regarded as a berry because the seeds are formed within a fleshy mesocarp. The tomato fruit can be divided into skin, pericarp, and locular contents (Davies and Hobson, 1981) (Figure 1). The epidermal layer has a heavily cutinised outer surface and the skin consists of four or five layers of cells under a thin cuticle. The locular cavities are filled with jelly-like parenchyma cells that surround the seeds.
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Figure 1. Main anatomical features of mature tomato.


Figure 1. Main anatomical features of mature tomato.

Nutrient composition Tomatoes are 93 to 95% water. Half the dry matter is reducing sugars, with slightly more fructose than glucose tomatoes also contain citric, malic and dicarboxylic amino acids, lipids, minerals and alcohol-insoluble solids (AIS), which include cellulose, hemicellulose, pectic substances and proteins.

Composition of tomatoes
The concise NZ Food Composition Tables, 6th Edition, NZ Institute for Crop & Food Research Ltd.(2003).

Tomato, flesh, skin and seeds, raw


g
water
Ekj
Protein
Fat
CHO
Fibre
Sugar
Starch
1 tomato
127
120
86
1.1
0.3
3.4
1.5
3.4
0.1
1 cup chopped
190
179
129
1.7
0.5
5.1
2.3
5.1
0.1


Na mg
K mg
Ca mg
Fe mg
Zn mg
Se µg
1 tomato
5
337
14
0.2
0.1
0.1
1 cup chopped
7
504
21
0.3
0.2
0.2


Total vit. A equiv.
β carotene
equiv.
Thiam
mg
Ribo
mg
Total
niacin
mg
B6
mg
B12
mg
Folate
µg
Vit C
mg
1 tomato
117
697
0.03
0.01
0.8
0.01
0.00
18
30.1
1 cup chopped
175
1040
0.05
0.01
1.1
0.02
0.00
27
45.0

The sugar content of tomato fruit is closely associated with its soluble solids content. The sugars and acids are responsible for the taste of fresh tomatoes and play an important role in determining the overall sensory quality of tomatoes. Total solids and total sugars have been reported to increase progressively from the green to red stages of ripening and the balance between glucose and fructose shifts from about 2:1 in immature fruit to a predominance of fructose at maturity. In immature green fruit, malic acid is the predominant form, while citric acid contributes about 25% of the total acidity. However, the citric acid concentrations increase with the ripening of the fruit resulting in 45 and 66% of the total acidity in mature fruit. High sugars and relatively high acids are required for best flavour development. High acids and low sugars will produce a tart tomato, while high sugars and low acids will result in bland taste. When both sugars and acids are low, the result is a tasteless, insipid tomato.

Antioxidant components of tomato


The antioxidant compounds help scavenge excess free radicals and, thus, prevent abnormal oxidative changes in the human body. Oxygen-derived free radicals and other pro-oxidants are important mediators in signal transduction and have an important role in producing biologically active and essential compounds in the human body (Basu, 1999). Free radicals can be formed spontaneously in the body by many biological processes and their production may increase as a result of environmental sources such as cigarette smoke, UV radiation and oxidizing agents. Excessive accumulation of these pro-oxidants and free radicals may damage cells by the oxidation of lipids, proteins and DNA, and induce peroxidation and DNA strand-breaks. The body synthesis various endogenous antioxidants such as catalase, glutathione peroxidase and transferrin and the diet makes an important contribution to the levels of antioxidants in the body. Because high amounts of tomatoes and their products are in the diet, they may make a significant contribution to the supply of the antioxidants required by humans. Tomato fruit is a reservoir of a diverse range of antioxidant molecules, such as carotenoids, flavonoids, phenolic acids, ascorbic acid and vitamin E.

Carotenoids

Carotenoids are natural pigments synthesised by plants and microorganisms, but not by animals (Paiva and Russell, 1999). The major roles of carotenoids in plants are: (i) to help harvest light and protect from photo-oxidation, (ii) to provide colour to fruits and flowers to attract pollinators. In tomato fruits, more than 21 carotenoids, including lycopene, phytoene, phytofluene, neurosporene, α-, β-, γ-, δ- and ξ-carotene and lutein have been identified. Lycopene is the most abundant carotenoid present in ripe red tomatoes, comprising up to 90% of the pigments present.

Phenolic compounds

Flavonoids and phenolic acids are the two major classes of phenolics. Phenolic compounds are secondary plant metabolites that are highly variable in their structure and occurrence. Phenolics are synthesised from phenylalanine. The phenolic compounds are relevant to the appearance, taste and flavour of food products, as well as to their health-promoting properties

Health benefits of tomato and tomato products


Antioxidant functions of lycopene, phenolic compounds, and ascorbic acid are associated with reducing DNA damage, malignant transformation and biological oxidative damage of proteins, lipids, and other cell components in vitro (Shi and Le Maguer, 2000). Many tissue culture studies and animal studies have also shown that lycopene helps to inhibit tumour formation (Rao and Agarwal, 1999). The interest in tomato antioxidants and their potential protective role in prevention of chronic diseases stems largely from the epidemiological observations on normal and at risk populations (Rao and Agarwal, 1999). Many epidemiological studies have suggested that a diet rich in a variety of fruits and vegetables results in a lower risk of cancer and other chronic diseases (Steinmetz and Potter, 1996; World Cancer Research Fund, 1997; Lister, 2003). Based on consumption of more than 10 servings of tomato products per week, an almost 35% reduction in risk of prostate cancer has been observed and the protective effect was even stronger when the analysis was focused on more advanced or aggressive prostate cancer (Giovannucci, 1999). Oxidatively modified low-density lipoproteins have been reported to be involved in heart diseases (atherosclerosis) (Rao and Agarwal, 1999). Dietary antioxidant vitamins, flavonoids and carotenoids may protect low-density lipoproteins from oxidative damage and may, thus, contribute to reducing the risk of heart diseases.
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Research at Lincoln University


New Zealand glasshouse tomatoes contained similar amounts of lycopene, total phenolics and ascorbic acid to tomatoes grown in other countries and under different conditions although there is a wide range of values reported. At Lincoln University we have carried out a range of experiments looking at what factors affect the antioxidant composition of tomatoes.

Does it matter which type of tomato you choose?
Answer
The amount of antioxidant vitamins C and E were measured in 4 cultivars of tomatoes. These tomatoes were Excell and Tradiro which are large sized salad tomatoes, Flavourine a medium sized table tomato and Campari, a small cocktail cultivar commonly sold on the vine. The vitamin C content ranged from 153-193 mg/100 g DM (dry matter). The vitamin C content ranged from 153-193 mg/100 g DM and was not significantly different between cultivars. Excell tomatoes had significantly higher vitamin E compared to the other cultivars. The 4 cultivars ranged from 8-31 mg/100 g DM. The antioxidant activity of the 4 cultivars was measured in both a hydrophilic extract and a lipophilic extract using the ABTS assay.Ascorbic acid and flavonoids contributed to approximately one third the antioxidant activity activity in the hydrophilic extracts. Compari the smallest cultivar had significantly higher antioxidant activity, total phenolics and flavonoids than the larger cultivars.
The lycopene was highest in Flavorine which had the brighter red colour.
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Is the antioxidant content affected by the environment used to grow the tomatoes?
Answer
Tomatoes grown at different times of the year differ in their antioxidant activity. Even when they are grown in a glasshouse variations in radiation, temperature and fruit load affect the antioxidant capacity. The antioxidant activity was nearly 40% higher in summer than spring. The lycopene was 31% lower in summer than spring. The ability to change glasshouse conditions by increasing light on spring/winter days and decreasing temperature in summer may allow consistently higher antioxidant activity and lycopene levels (respectively).
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What if you use different fertilisers?
Answer
Another factor that can be changed while growing tomatoes is the fertilizer used. The type of fertilizer was shown to have a significant effect on the nutrient concentration, taste and antioxidant components present.
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What’s the best way to keep the tomatoes after picking?
Answer
Post harvest storage of tomatoes at 7, 15 and 25 C does not have any deleterious effect on tomato antioxidant activity, vitamin C, total phenolics and flavonoids. Storage at 15 or 25 C showed an increase in the lycopene content and red colour of the tomato but after 4 days storage the firmness of the tomato declined. Refrigeration at 7 C inhibits ripening, colour development and lycopene accumulation.
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Just where in the tomato is the lycopene?
Answer
The skin fraction of all cultivars tested had significantly higher levels of total phenolics, total flavonoids, lycopene, ascorbic acid and antioxidant activity compared to their pulp and seeds. This occurred in both the hydrophilic and lipophilic fractions as measured by ABTS.

The skin and seed fraction contained:
53% Total phenolics
52% Total flavonoids
48% Total lycopene
43% Ascorbic acid
52% Total anitoxidant acitivity
These results demonstrate the significance from a nutritionist’s perspective of using the whole tomato and developing new products with the pulp and skins.
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What happens when you process tomatoes?
Answer
Experiments using 2 cultivars, Excell and Arancea looked at the effects of home processing on colour, vitamin C, total phenolics,lycopene and antioxidant activity. Boiling and baking had only small effect on ascorbic acid, total phenolics and lycopene contents and antioxidant activity, but frying significantly reduced the ascorbic acid, phenolic and lycopene contents. Soaking of sliced tomato with olive oil, white vinegar or olive oil and white vinegar had the following effects. Olive oil alone reduced the amount of lycopene able to be extracted (this may not be physiologically significant) while vinegar had no effect. Oil and vinegar marinade significantly reduced ascorbic acid, total phenolic and antioxidant activity of the tomatoes. Semi-dried tomatoes were produced at 42 C. On a dry weight basis the dry tomatoes had lower total phenolics, total flavonoids, lycopene and ascorbic acid content and total antioxidant capacity than the fresh tomatoes.The lower drying temperature was gentle and helpful in refraining colour and vitamin C. Comparison of cultivars suggested Tradiro was more suitable for semi-drying than Excell and Flavourine. The percentage of total phenolics and flavonoids available after digestion (as determined by in vitro digestion) was much higher than for lycopene.

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