QUALITY OF TOMATO FERTI LIZED WITH NITROGEN
AND PHOSPHOROUS

Abstract
The influence of different levels of nitrogen (N1, N2), phosphorous (P1, P2) and N+P (N1P1, N1P2, N2P1, N2P2) mixed fertilizers was investigated on volatile substances, soluble sugars, organic acids, titratable acidity, dry matter and lycopene of “Corbarino” cherry-like tomatoes. The flavor volatiles reached the highest concentrations in red-ripe cherry-like tomatoes treated with N1. Glucose, fructose, dry matter and titratable acidity increased only in N+P fertilized samples. Among the organic acids, citric increased, malic decreased and oxalic was constant in all the fertilized samples. Lycopene reached the highest values in N2 and N2P2 samples.

INTRODUCTION
Tomato, a key vegetable in the Italian Mediterranean diet, has recently gaining been attention in relation to the prevention of some human diseases. This interest is due to the presence of carotenoids and particularly lycopene, which is an unsaturated alkylic compound that appears to be an active compound in the prevention of cancer and cardiovascular risk and in slowing down cellular aging, owing to its high antioxidant and antiradical power (GERSTER 1997; GIOVANNUCCI et al. 1995). Lycopene is found in fresh, redripe tomatoes as all-trans (79-91%) and cis- (9-21%) isomers (STAHH and SIES, 1992; SHI et al.
1999; BOILEAU et al. 2002). Lycopene and vitamins give a measure of the nutraceutical quality, while flavour volatiles, soluble sugars, organic acids, etc. express the nutritional quality.
In red-ripe tomato fruit, many volatile compounds have been identified [2(E)-hexenal, hexanal, 3(Z)-hexen-1-ol, β-ionone, 2(E)4(Z)-decadienal, 2 isobutylthiazole, 3(Z)-hexenol, linalool, methylsalicylate, 2-methoxyphenol, 6-methyl- 5-hepten-2-one, 6-methyl-5-hepten-2-ol, 2,3-epoxygeranial, neral, geranial, nerylacetone, β-damascenone, α-terpineol etc.] (DI CESARE et al. 2003).
Hexanal, 2(E)-hexenal, 3(Z)-hexen-1-ol, 2-isobutylthiazole, are considered to be responsible for the fresh tomato flavour (DIRINCK et al. 1976). While, according to other authors (BUTTERY et al. 1989; BUTT ERY, 1993; BUTT ERY and LING, 1993 a,b) 3(Z)-hexenal, β-ionone, hexanal, β-damescenone, 2(E)-hexenal, 1-penten-3-one, 2 and 3-methylbutanols, 2-isobutylthiazole, 2-isobutylcyanide, 2(E)-heptenal, phenylacetaldehyde, 6-methyl-5-hepten-2-one, 3(Z)-hexenol, 2 phenylethanol, methylsalycilate are considered to be important contributors to tomato flavour.
Soluble sugars and organic acids play an important role in the characterization of the tomato taste. Sugars (glucose, fructose and traces of sucrose) and organic acids (citric, malic and oxalic) represent half of the total dry matter of tomato fruit (SILVESTRI and SIVIERO, 1991).
In tomato cultivation, fertilizer application regimes can play an important role both to increase the yield and size and to improve the nutritional and nutraceutical quality of the fruit. A large amount of N is required for optimum production as the tomato root absorbs a great deal from the soil. N-deficiency can cause a decrease in production (number and size of tomatoes), a reduction in storage quality, colour, and tomato taste (SAINJU et al., 2003).
Secondary plant metabolites which lack N in their structure such as lycopene, β-carotene, phenolics and flavonols are favoured under Nlimiting conditions, although photosynthetic activity is not simultaneously reduced. However nitrogen-containing compounds are favoured when N is readily available and not limiting to growth (DORAIS et al., 2008).
As far as nutritional quality and suitability for processing are concerned, many authors have highlighted the negative effects of excessive N, such as an increase in pH and a decrease in soluble sugars, soluble solids, dry matter, sugars/dry matter ratio and firmness (Kaniszewski et al., 1987; KOONER and RANDHAWA, 1990;PARISI et al., 2006).
XU et al. (2001) found that by using an application of nitrogen within the proper range increased the concentration of the volatile compounds in tomato, while an excessive N application decreased their concentration.
YU-TAO et al. (2007) studied the effects of applications of N levels on volatile substances, taste compounds and firmness of fresh tomato fruits. The results pointed out that increasing N application increased the concentrations of 1-penten- 3-one, hexanal, 3(Z)-hexenal, 2-methyl-4-pentenal, 2(E)-hexenal, 6-methyl-5-hepten-2-one, titratable acidity, soluble sugars and soluble solids; under the same conditions the concentrations of phenylacetaldehyde decreased, whereas the concentration of 2(E)4(E)-hexadienal and firmness of fresh tomato fruit initially increased and then decreased.
WRIGHT and HARRIS (1985) pointed out that flavour scores indicated that increasing N and K fertilization had a detrimental effect on tomato flavour. An increase in titratable acidity and soluble solids was found with increasing fertilization. Concentrations of hexanal, 2-hexanone, benzaldehyde, phenylacetaldehyde, β-ionone and 6-methyl-5-hepten-2-one increased with increasing N+K levels.
Phosphorous fertilization is a key component in the metabolism and regulation of several pathways involved in the biosynthesis of secondary plant metabolites, many of which are nutraceuticals. P may increase the level of some phytochemicals such as ascorbic acid, anthocyanins, flavonoids and lycopene, although interaction with climatic factors and the growing season may occur (BR UULSEMA et al. 2004). SAITO AND KANO (1970) found that by increasing P-fertilization from 0 to 100 mg L-1 nutrient solution under hydroponic growth conditions, the colour of the tomato fruit greatly improved and consequently lycopene content was increased.
OKE et al. (2005) studied the effect of P fertilizer on the quality of tomato under field conditions for three consecutive years, evaluating the pH, titratable acidity, lycopene, vitamin C, flavor volatiles etc. They noted that the influence of P application on several of the quality parameters mentioned above was marginal, while climatic features had a more predominant effect.
In this study, the effects of two different levels of N and P and their mixture (N+P) on the nutritional and nutraceutical quality of “Corbarino” cherry-like tomatoes was evaluated.
MATERIALS AND METHODS
Plant source: The study was performed on “Corbarino” cherry-like tomatoes (accession PC05), a traditional ecotype originating in southern Italy (Campania region), characterized by small fruits (13-20 g) having a strong fruity odour and flavour, excellent health and nutritional properties and highly suitable for canning
(GIORDANO et al., 1999, 2000; ANDREAKIS et al., 2004; SINESIO et al., 2007).
The unfertilized tomatoes were grown in soil with a high content of organic matter (1.3% carbon) and available P (85 ppm), but low in available N (N Kjeldhal = 0.091%; NO3 = 7.0 ppm; NH4 = 11.5 ppm).
Fertilization was applied at two different levels of N (100 kg ha-1= N1; 200 kg ha-1= N2), P (150 kg ha-1= P1; 300 kg ha-1= P2) and their mixture (N1P1=100 kg ha-1 N+150 kg ha-1 P; N1P2= 100 kg ha-1 N+300 kg ha-1P; N2P1= 200 kg ha-1 N+150 kg ha-1 P and N2P2= 200 kg ha-1 N+300 kg ha-1 P).
Each level of P (P2O5) was applied before transplanting, while the amount of N for each treatment was applied in four doses during the crop cycle: 25% before transplanting as (NH4)2SO4, 25% at 30 DAT (days after transplanting), 25% at 60 DAT and 25% at 80 DAT as NH4NO3.
All the samples were cultivated, at Battipaglia (Sele Valley, SA) in open fields and harvested at the red-ripe stage between 20-24 August 2008.
The average yield of tomatoes (t/ha) according to the treatment applied is reported in Table 1.
Each test was repeated three times.
Extraction-concentration and analysis of volatile substances: The volatile compounds were extracted and concentrated by microwave-resin-solvent combined method and the extracts obtained were analyzed quali-quantitatively by GC/MS. The method and the operating conditions were reported in a previous note (DI CESARE et al., 2003).
Soluble sugars and organic acids: They were extracted with double distilled water and analyzed by HPLC (FORNI et al., 1992).
Lycopene: It was extracted using an hexane: acetone: ethanol mixture (2:1:1) and the hexane layer was analyzed by HPLC (MIGLIORI et al., 2008).
Dry matter: It was determined using a laboratory oven at 85°C up to a constant weight
(AOAC, 1980).
Statistical analysis: Tukey test was used to evaluate the differences among the different levels of fertilization. Mean values were considered significantly different when ρ≤0.05.
RESULTS AND CONCLUSIONS
Volatile substances: Table 2 shows the volatile compounds identified in unfertilized and fertilized cherry-like tomatoes (alcohols, carbonyl compounds (aldehydes and ketones), phenolic derivatives, heterocyclic compounds and terpenes). Results are in agreement with what was found in fresh tomato fruits by BUTTERY et al. (1989), BUTTERY (1993), BUTTERY and LING
(1993 a,b).
As for alcohols, 3-methyl-1-butanol decreased in all the fertilized samples and this trend was more evident in N2P1 and N2P2. All the other alcohols increased only in N1 samples, and they decreased in all the other fertilized samples, with respect to the unfertilized one.
Among the carbonyl compounds, 1-penten-3- one, 2(E)-hexenal, 2(E)-heptenal, 2(E)4(E)-decadienal increased with all the fertilized samples.
Hexanal and 6-methyl-5-hepten-2-one increased in both levels of N, but decreased or were similar in the other fertilizations, with respect to the unfertilized sample.
Methyl salicylate increased with both levels of
N and in the N+P samples, but decreased with both levels of P.
2-isobutylthiazole increased in N1 samples, but decreased in all the other fertilized samples.
Concerning terpenes, linalool increased in N1,
N2, P1 and P2 samples, but decreased in the N+P samples. All the other terpenes increased in N1 and N2 samples and decreased or were constant in P1 and P2 and N+P fertilized samples.
As reported above, it can be seen that most of the contributor volatile compounds showed the highest concentration in N fertilized samples especially at the lower level. As N supply increased, so did the similar behaviour of increasing concentrations of several volatile compounds, in agreement with YU-TAO et al. (2007). A lot of studies have demonstrated that the concentrations of amino acids and fatty acids increased with increasing N supply (MOZAFAR, 1993). Samino acids (cysteine and methionine) are precursor of thiazole, as 2-isobutylthiazole. Aromatic amino acids are precursors of phenolic volatile compounds (ESC HIN, 1990). Leucine and valine are precursors of 2-methyl-1-butanol, 3-methyl-
1-butanol and lycopene whose conversion gives 6-methyl-5-hepten-2-one, 6-methyl-5-hep-
Table 1 - Tomato yield (t/ha) according to the treatment applied. Different letters indicate significant difference
(ρ≤ 0.05).
Treatment Average yield
(t/ha)
Unfertilized 36.8 a
N1 60.4 ab
N2 64.7 ab
P1 39.0 a
P2 44.3 a
N1P1 59.0 ab
N1P2 59.9 ab
N2P1 69.6 b
N2P2 73.4 b
Ital. J. Food Sci. n. 2, vol. 22 - 2010 189 ten-2-ol and terpenes. Fatty acids are precursors of lipids, whose degradation gives aldehydes and ketones (WRIGHT and HARRIS, 1985; CARBALLO et al., 1994; WESTON and BART H, 1997).
This could explain why the concentration of all classes of volatile compounds increased with increasing
N supply.
Except for linalool and 2(E)-hexenal, which showed the highest concentrations in P1 and
P2 samples, all the other volatile compounds showed lower values with respect to unfertilized and/or N1 and N2 ones. In N+P samples, the values were always lower than the unfertilized sample, apart from some carbonyl compounds and methyl salycilate. These results agree with OKE et al. (2005) who observed no major differences in the volatile concentrations vs. various phosphorous supplementations. Chemico-physical and nutraceutical parameters:
The values of soluble sugars, organic acids, titratable acidity, dry matter and lycopene are reported in Table 3. The concentrations of glucose and fructose were quite comparable with the unfertilized sample in the cherry-like tomatoes fertilized with N or P. On the contrary, in the samples fertilized with both N + P, there was an increase of glucose in N2P1 and N2P2, and fructose in N2P1. No effects on sugar contents of N fertilization up to 200 kg/ha were found in peeled tomato by PARISI et al. (2006).
Table 2 - Quali-quantitative composition (μg/100 g d.m.) of volatile compounds identified in “Corbarino” cherry-like tomatoe samples, treated with N and P fertilizers. Different letters indicate significant difference (ρ≤ 0.05).
Fertilized
COMPOUNDS Unfertilized
N1 N2 P1 P2 N1P1 N1P2 N2P1 N2P2
ALCOHOLS
3-methyl-1-butanol 409.62 c 373.52 b 264.15 ab 270.03 ab 299.40 ab 287.96 ab 301.79 ab 230.16 a 220.12 a
2-methyl-1-butanol 28.63 bc 55.32 e 20.90 d 11.95 a 25.83 b 23.32 c 21.16 b 24.72 b 20.67 c
6-methyl-5-hepten-2-ol 8.17 d 17.92 d 7.16 c 7.47 c 6.33 b 4.41 a 5.21 ab 5.58 ab 4.15 a phenethyl alcohol 112.91 d 255.79 e 109.00 d 100.33 d 43.65 b 63.48 bc 29.43 a 72.07 c 71.42 c
CARBONYL COMPOUNDS
1-penten-3-one 4.21 b 13.10 c 16.78 d 11.85 a 13.16 c 14.03 c 16.01 d 11.81 c 15.06 d hexanal 214.90 b 256.43 c 284.60 c 198.09 a 204.48 ab 213.32 b 224.52 b 186.90 a 176.16 a
2(E)-hexenal 28.86 b 47.62 c 43.71 c 37.37 a 41.91 ab 38.04 bc 46.58 c 33.59 ab 28.86 b
2(E)-heptenal 22.04 b 40.43 c 51.10 d 29.68 bc 38.94 c 43.66 c 40.25 c 21.83 b 24.67 a
6-methyl-5-hepten-2-one 212.43 ab 333.52 c 262.32 b 191.46 a 173.16 a 195.81 a 183.16 a 159.62 a 162.13 a
2(E).4(E)-decadienal 35.45 a 70.26 c 75.37 c 34.69 a 41.42 ab 54.15 b 67.81 bc 36.65 a 58.53 b
PHENOLIC DERIVATIVES methyl salicylate 79.32 b 227.06 e 173.04 d 67.38 a 72.40 ab 146.27 cd 151.34 cd 124.95 c 131.66 c
HETEROCYCLIC COMPOUND
2-isobutylthiazole 242.93 b 288.35 c 215.22 b 200.86 b 182.81 b 204.82 b 201.11 b 100.13 a 115.86 a
TERPENES
linalool 51.04 b 91.49 c 87.84 c 180.98 d 163.65 d 44.80 b 8.47 a 55.77 b 52.31 b neral 30.07 b 50.39 c 39.13 ab 24.14 a 25.66 a 24.31 b 27.00 ab 20.43 a 18.92 a geranial 54.19 c 95.44 e 67.31 d 44.63 b 38.18 ab 36.29 a 47.71 b 32.11 a 44.37 b β-damascenone 25.86 b 52.13 d 42.93 c 17.39 a 18.12 a 16.59 a 27.50 b 23.99 b 24.56 b neryl acetone 26.29 b 37.86 cd 40.42 d 21.16 b 20.09 c 11.97 a 29.50 bc 19.53 b 24.91 b β(Z)-ionone 41.41 c 48.22 c 51.33 d 24.25 a 31.99 b 19.53 a 25.13 a 21.99 a 18.75 a
Table 3 - Effect of N and P fertilizers on chemical-physical and nutraceutical parameters of “Corbarino” cherry-like tomatoes.
Soluble sugars are expressed in g/100 g f.w., organic acids and lycopene in mg/100 g f.w., titratable acidity in meq/100 g f.w.
Different letters indicate significant difference (ρ≤ 0.05).
Fertilized
Unfertilized
N1 N2 P1 P2 N1P1 N1P2 N2P1 N2P2
SOLUBLE SUGARS
Glucose 2.37 a 2.37 a 2.27 a 2.19 a 2.39 a 2.54 a 2.50 a 2.91 b 2.64 b
Fructose 2.64 a 2.43 a 2.38 a 2.59 a 2.63 a 2.64 a 2.62 a 2.91 b 2.64 a
ORGANIC ACIDS
Oxalic 5.72 b 5.41 b 6.04 b 5.88 b 5.90 b 5.44 b 6.10 b 4.84 a 6.15 b
Citric 346.28 b 422.63 c 466.74 c 317.90 a 407.91 c 442.82 c 411.18 c 508.33 d 472.54 d
Malic 55.11 b 43.27 a 51.03 ab 43.51 a 51.73 c 49.34 b 45.77 a 46.72 ab 44.02 a
TITATRABLE ACIDITY 8.06 a 10.31 c 10.39 c 9.13 b 8.69 a 8.02 a 9.84 b 12.28 d 11.43 d
D.M. % 9.28 b 9.60 b 9.88 b 8.68 a 8.73 a 10.12 c 9.90 b 9.93 b 10.29 c
LYCOPENE 6.84 a 10.49 bc 15.15 d 8.96 b 12.68 c 9.38 b 9.17 b 11.56 c 14.62 d
190 Ital. J. Food Sci. n. 2, vol. 22 - 2010
For organic acids, oxalic acid was constant in all the samples except N2P1, where it decreased in comparison to the unfertilized sample. Citric acid showed the lowest value only in the unfertilized sample, while malic acid decreased in all samples, except in N2 where it was similar to the unfertilized sample.
Dry matter decreased in P1 and P2 samples and increased in N1P1 and N2P2, while it remained constant in the other samples, compared to the unfertilized one. Taking into account the effects of N on this quality trait, these results are in agreement with those of PARISI et al. (2006).
Titratable acidity increased in all the fertilized samples, and the highest values were in
N2P1 and N2P2.
WRIGHT and HARR IS (1985) and LI et al. (1997) reported that organic acids, soluble sugars and titratable acidity increased with increasing rates of N and K application. In our research, a different response of soluble sugars, organic acids and titratable acidity can be observed with respect to the cited literature. In fact, the highest concentrations of glucose, fructose and titratable acidity were achieved by mixing N and P.
The unfertilized sample showed the lowest concentration (6.84 mg/100 g f.w.) of lycopene whereas it increased up to 10.49 mg/100 g f.w. in N1 and 15.15 mg/100 g f.w. in N2 in the fields fertilized with N.
In the fields fertilized with P, lycopene increased up to 8.96 mg/100 g f.w. in P1, and
12.68 mg/100 g f.w. in P2. These values were higher than the unfertilized samples, but lower than the samples treated with N.
When the fields were treated with both N + P fertilizations, in N1P1 and N1P2, lycopene ranged
9.17 to 9.38 mg/100 g f.w. But in N2P1 and N2P2, the values were 11.56 and 14.62 mg/100 g f.w., respectively. The latter value and that of N2 were the highest ones observed among all the samples.
Similar behaviour was observed by KOBR YN et al. (2004) in three tomato types (cluster, cherry and large-fruit), cultivated on rockwool and fertilized with different levels of nitrogen. The N supply increased the content of lycopene in all tomato types, but this effect was more evident in the cluster one.
The same results were obtained by ELKNER et al. (2004) in two tomato types (Fanny F1 and
Dual plus F1) fertilized with N+K and drip irrigated, fertigated and broadcast irrigated. Drip irrigation and fertigation with N+K and complex fertilizers had a positive effect on ascorbic acid, pectin and hemicelluloses and in particular on lycopene content in Dual plus F1.
DE PASCALE et al. (2008) studied the effects of three different rates of N supply (0, 100, 200 kg/ha) on the nutritional value of organically and conventionally grown tomatoes. They observed that carotenoids and antioxidant activity increased in organic tomatoes, even if the yields were lower than conventional ones.
Recent studies have pointed out that lycopene, as well as other carotenoids, are synthesized from isoprenoids that are products of mevalonic acid (MVA) and methylerythritol-4-phosphate
(MEP) pathway (BOTELLA-PAVIA and RODRIGUEZ-
CONCEPCION, 2006). Increasing of N fertilization could most likely enhance the action of enzymes involved in these pathways such as deoxyxylulose 5-phosphate synthase.
Our results indicate that the effect of N supplementation is more evident than P and mixing
(N+P) fertilizations in carotenoid biosynthesis, even if phosphorous is a key component
(ATP, NADP(H)2). However OKE et al. (2005) found that P supplementation may not significantly affect the processing quality parameters of tomato fruit. This may depend on the starting
P content in the soil, which is already adequate for complete synthesis of nutraceutical compounds (Vegetable Production Recommendations,
1999), as reported above.
Under these experimental conditions, besides the total yield (Table 1), N fertilization positively influenced the physico-chemico-organoleptic and nutraceutical parameters, compared to
P fertilization and N+P mixings. In fact, cherrylike tomatoes fertilized only with N had a higher concentration of volatile substances and lycopene in their tissues. These compounds improve the organoleptic characteristics and, perhaps most importantly, prevent chronic diseases, such as cancer, cardiovascular and neurodegenerative diseases. Our data clearly shows that, even if P fertilization in combination with nitrogen increases the nutraceutical quality, it can be limited or avoided if the P content in the soil is enough to regulate the cellular metabolism of tomatoes.
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Revised paper received October 2, 2009 Accepted December 16, 2009
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