ARTICLE IN PRESS JOURNAL OF FOOD COMPOSITION AND ANALYSIS Journal of Food Composition and Analysis 19 (2006) 11–19 www.elsevier.com/locate/jfca
Original Article
Seasonal variations in antioxidant components of cherry tomatoes (Lycopersicon esculentum cv. Naomi F1) Antonio Raffoa,, Giuseppe La Malfab, Vincenzo Foglianoc, Giuseppe Maiania, Giovanni Quagliaa a Istituto Nazionale di Ricerca per gli Alimenti e la Nutrizione, Via Ardeatina 546, 00178 Roma, Italy Dipartimento di Orto-Floro-Arboricoltura e Tecnologie Agroalimentari, Universita` di Catania, Via Valdisavoia 5, 95123 Catania, Italy c Dipartimento di Scienza degli Alimenti, Universita` di Napoli ‘‘Federico II’’, P.co Gussone, 80055 Portici, Napoli, Italy
b
Received 21 April 2004; received in revised form 11 January 2005; accepted 7 February 2005
Abstract To evaluate seasonal variations in antioxidant components of greenhouse cherry tomatoes, the compositional profile of fruits (‘‘Pomodoro di Pachino’’, cv. Naomi F1) harvested at six different times of the year was compared. Among tomato antioxidants, phenolic compounds (naringenin content ranged from 1.84 to 9.04 mg/100 g, rutin from 1.79 to 6.61 mg/100 g) and a-tocopherol (40–1160 mg/100 g) showed the greatest variability. Ascorbic acid (31–71 mg/100 g), carotenoids (8350–15119 mg/100 g), phenolics and a-tocopherol concentration did not show definite seasonal trends, nor correlation with solar radiation or average temperature. Nevertheless, tomatoes harvested in mid-summer were characterized by lowered lycopene levels. Greenhouse growing conditions induced the accumulation of relatively high level of antioxidants for most of the year: one serving of raw tomatoes (100 g) could provide from 50% to 120% of the recommended daily intake of vitamin C, from 13% to 27% of that of vitamin A, from 0.4% to 12% of that of vitamin E, and from 15% to 35% of the flavonoid daily intake estimated for an Italian diet. r 2005 Elsevier Inc. All rights reserved. Keywords: Cherry tomato; Season; Carotenoids; Ascorbic acid; Phenolic compounds; a-tocopherol; Antioxidant activity
1. Introduction Several epidemiologic studies suggest that consumption of tomatoes and tomato-based products reduces the risk of chronic diseases such as cardiovascular disease and cancer (Sesso et al., 2003; Weisburger, 2002; Willcox et al., 2003). In particular, intake of tomato and tomatobased products has been relatively consistently associated with a lower risk of cancers of the prostate, lung and stomach (Giovannucci, 1999). Recent intervention studies demonstrate that regular intake of small amounts of tomato products can increase cell protection from DNA damage induced by oxidant species (Riso Corresponding author. Tel.: +39 06 5149 4409; fax: +39 06 5149 4550. E-mail address:
[email protected] (A. Raffo).
0889-1575/$ - see front matter r 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jfca.2005.02.003
et al., 2004). This protective action is typically attributed to antioxidant components like lycopene and other carotenoids, ascorbic acid, flavonoids and vitamin E. Due to its relatively high average consumption tomato is an important source of these dietary antioxidants. Tomatoes are the most highly consumed vegetable in Italy, with the highest average consumption among European countries (NETTOX, 1998). In a study on the Italian food consumption patterns in the 1990s, a consumption of tomatoes (both for salad and ripe) of 75.5 g/day/capita has been estimated (Turrini et al., 2001). As a matter of fact, tomatoes have been assessed to be the second most important source of vitamin C in the Italian diet (La Vecchia, 1998). Moreover, in a recent study on dietary sources of vitamin C, vitamin E and specific carotenoid in Spain (Garcı´ a-Closas et al., 2004), tomatoes ranked first as a
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source of lycopene (71.6%), second as a source of vitamin C (12.0%), pro-vitamin A carotenoids (14.6%) and b-carotene (17.2%), and third as a source of vitamin E (6.0%). In Italy, cherry tomatoes are largely used for fresh consumption (more than 25% of the market), and their commercial importance is continuously increasing (Leonardi et al., 2000a, b). In Sicily, as well as in other regions of the Mediterranean basin, cherry tomatoes are grown year round in unheated greenhouses, which have no climate control systems and are covered with plastic film; consequently, development and ripening of fruits occur under varying climatic conditions. Temperature and light intensity exert a direct influence on the quality attributes of tomato fruit, such as appearance, firmness, texture, dry matter and sensory properties (Dorais et al., 2001). On the other hand, environmental factors can also affect the antioxidant content of tomatoes: Dumas et al. (2003) have recently reviewed the available knowledge about the effects of climatic and other preharvest factors on the antioxidant contents of tomatoes. At present, a thorough understanding of the influence of environmental factors and their interactions with agronomic practices on the accumulation of antioxidants during the fruiting period is still lacking, although some relationships have been observed in general. Light exposure is favourable to vitamin C accumulation (Dumas et al., 2003; Lee and Kader, 2000). Several studies have reported on the effect of shading (by leaves or artificial covers) in decreasing the ascorbic acid content (El-Gizawi et al., 1993; Venter, 1977), whereas greenhouse-grown tomatoes were usually found to have lower vitamin C levels than those grown outdoors, chiefly because of the lower light intensity (LopezAndreu et al., 1986). On the contrary, lycopene synthesis is severely inhibited by exposure to intense solar radiation, and it has been suggested that radiation injury to tomato fruit might be due to the general effects of overheating on irradiated tissues (Adegoroye and Jolliffe, 1987; Dumas et al., 2003). In fact, the formation of lycopene depends on the temperature range and seems to occur between 12 and 32 1C, whereas higher temperatures specifically inhibit its accumulation (Hamauzu et al., 1998; Leoni, 1992; Robertson et al., 1995). As regards phenolic compounds, although genetic control represents the main factor in determining their accumulation in vegetable foods, external factors may also have a significant effect on this (Macheix et al., 1990). In many plant species the flavonol content may be enhanced in response to elevated light levels, in particular to increased UV-B radiation (Brandt et al., 1995). As a matter of fact, it has been reported that cherry tomato plants grown in greenhouse under high light accumulated an approximately two-fold greater soluble phenols content (rutin and chlorogenic acid) than low-light plants (Wilkens et al., 1996).
On the other hand, it has been only infrequently been investigated whether these effects might produce definite seasonal trends in tomato antioxidant compositional profile. Only a few studies have investigated seasonal fluctuations of nutrients, and in particular the phytonutrient content of tomatoes. Vanderslice reported on seasonal differences in ascorbic acid content of tomato, with higher levels in summer than in spring (Vanderslice et al., 1990). Seasonal variations in vitamin C content were observed in greenhouse-grown tomatoes at the mature-green stage, and were directly correlated with temperature variations (Liptay et al., 1986). As regards phytonutrients, marked variations have been observed in the level of quercetin in cherry tomatoes grown at different times of the year, but no definite seasonal trends have been brought into evidence (Crozier et al., 1997; Stewart et al., 2000). Only very little information is available on the seasonal variations of carotenoid content in the tomato fruit (Heinonen et al., 1989). On the basis of the above observations, variations in climatic conditions between different seasons can be expected to significantly influence the compositional profiles of tomato typologies produced year round. Thus to better evaluate the real contribution of tomato consumption to total daily intake of antioxidants, it is interesting to know not only the average content of antioxidants, but also the extent of their seasonal fluctuations. To develop information on seasonal variations in cherry tomato antioxidant properties, we compared the detailed compositional profile (ascorbic acid, phenolic compounds, carotenoids, a-tocopherol) of greenhouse cherry tomatoes (cv. Naomi F1), grown in Sicily within the same geographical area (‘‘Pomodoro di Pachino’’), and harvested at six different times of the year. The aim of this work was to estimate the extent of variation in cherry tomato antioxidant content and antioxidant activity for 1 year of production, and to show possible relationships between antioxidant concentrations and climate factors such as temperature and solar radiation.
2. Material and methods 2.1. Fruit sampling Cherry tomatoes (‘‘Pomodoro di Pachino’’, cv. Naomi F1) were sampled on plants grown in cold greenhouses, within farms belonging to the Association for the protection of the typical products of Pachino (Province of Siracusa, Sicily). ‘‘Pomodoro di Pachino’’ tomatoes, which have recently achieved the PGI (Protected Geographical Indication) European recognition (Official Journal of European Communities, 2002), are produced in a protected environment (glasshouses and/or tunnels) covered with polyethylene netting or
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other plastic material; planting out takes place throughout the year, at a density of 2–6 plants/m2. The plants are grown upright and have one or more branches; irrigation is carried out using groundwater taken from wells sunk with a salinity level ranging from 1500 to 10 000 mS. For our experiment, harvests were carried out at six different times of the year: April, June, July, December (1999), January and March (2000). Tomatoes were harvested at full ripeness, as usually occurs for marketing. To mediate the effects of technical growing conditions, within each sampling, fruits were harvested from ten different representative farms, selected for their uniformity, and pooled in one sample. Then, antioxidant content and antioxidant activity were determined on a group of 30 fruits taken at random from each pooled sample. On a separate group of fruits taken from the same pooled samples, dry matter and skin colour were determined. Dry matter content was determined by gravimetry; about 5 g of homogenized sample was dried in a thermoventilated oven at 70 1C until constant weight was reached. Chromatic coordinates (L*, a*, and b*) were determined on the equatorial part of the fruit as described by McGuire (1992), using a tristimulus Minolta Chroma meter (model CR-200, Minolta Corp.). Colour was described by the ratio a*/b*. 2.2. Biochemical analyses Whole tomatoes were homogenized in a Waring blender for 1 min. The homogenate was then frozen at 20 1C and stored until analysed. All data reported in tables were expressed on fresh weight basis. 2.2.1. Ascorbic acid Ascorbic acid, reduced and total (ascorbic plus dehydroascorbic acid), was extracted from freshly homogenized tomatoes and quantified by HPLC according to the method described by Margolis and Schapira (1997). HPLC separation was carried out using an ESA HPLC system with an eight-channel coulometric electrode array detector (ESA), on a Capcell Pak NH2 column (250 4.4 mm) (Shiseido) at a flow rate of 1 mL/min, at 40 1C; the mobile phase was as described in the above-mentioned paper. Pure standards (Sigma Chemicals) were used for identification of peaks and for quantification. 2.2.2. Phenolic compounds Phenolics were either hydrolysed or not, in order to obtain free (naringenin, caffeic, p-coumaric and ferulic acid) and conjugated (chlorogenic acid and rutin) forms, and extracted as described by Hertog et al. (1992). Quantitative analysis was performed using the ESA HPLC system previously mentioned. HPLC separation
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was carried out at a flow rate of 1 mL/min, at 30 1C, using a Supelcosil LC-18 column (250 4.6 mm) with a Perisorb Supelguard LC-18 (Supelco); the mobile phase and the elution programme were as described by Hertog et al. (1992). The calibration curve for quantification was obtained using authentic standards (Sigma Chemicals). 2.2.3. Carotenoids The procedure described by Tonucci et al. (1995) was followed with slight modification. Homogenized tomatoes were extracted in THF in the presence of butylated hydrohytoluene (BHT) (from Sigma Chemicals), and resuspended in 5 mL of CHCl3. A further 1:10 dilution of the extracted material in 40% CH3CN, 20% methanol, 20% hexane, and 20% CH2Cl2 was performed before the chromatographic analysis. HPLC separation was carried out at a flow rate of 0.8 mL/min and a temperature of 30 1C using a Shimadzu HPLC with diode array detection and a Supelcosil C18 column (250 4.6 mm). Carotenoid elution was achieved using the following linear gradient: starting condition, 82% A, 18% B; 20 min, 76% A, 24% B; 30 min, 58% A, 42% B; 40 min, 39% A, 61% B. ‘‘A’’ was CH3CN and ‘‘B’’ was methanol/hexane/CH2Cl2 1:1:1 v/v. Quantification of carotenoids was achieved by calibration curve obtained with authentic standard (b-carotene from Fluka) or HPLC-purified compounds (lycopene and other determined compounds). The concentration of the standards was calculated using the extinction coefficient. 2.2.4. a-tocopherol A-tocopherol from homogenized tomatoes was measured according to Baldini et al. (1996). Briefly, the extraction consists of base hydrolysis of the sample followed by C2H4Cl2 addition. The organic phase was dried, and the residue resuspended in 1 mL of CH3OH and run on HPLC column (Phenomenex Prodigy C18, 5 mm; 4.6 250 mm). The mobile phase was isocratic CH3OH: H2O (98:2) with a flow rate of 1 mL/min. Atocopherol was identified by comparison with a pure standard (Sigma Chemicals) and quantified by measuring absorbance at 290 nm. 2.2.5. Antioxidant activity A quantity of 10 mL of deionized water was added to 5 g of freshly homogenized tomatoes, and the suspension was centrifuged at 15 000 rpm for 15 min (4 1C). The supernatant (water-soluble fraction) was recovered, filtered, and after suitable dilution (1:5) with phosphate buffer (10 mM, pH 7.0), used for the crocin bleaching inhibition test (Tubaro et al., 1996). Antioxidant activity was expressed as equivalent millimolar Trolox (6hydroxy-2,5,7,8-tetramethyl-chroman-2-carboxylic acid) for 100 g of tissue fresh weight. The pulp resulting from centrifugation of the homogenate was extracted with
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10 mL of CH2Cl2, centrifuged at 15 000 rpm for 5 min (4 1C), filtered, and the supernatant was recovered; this extraction step was repeated three times, and supernatant fractions were pooled. The extract (waterinsoluble fraction) was used for the 2,20 -azinobis(3ethylbenzothiazoline-6-sulphonic acid) (ABTS) test (Pellegrini et al., 1999), and antioxidant activity was expressed as equivalent millimolar Trolox for 100 g of tissue fresh weight. 2.3. Statistical evaluation of data We performed analysis of variance (ANOVA) in order to test the significance of the observed differences. When the effects of harvesting date were significant (Pp0:05), the mean values for each parameter were compared by a multiple comparison Duncan test to look for grouping (at P ¼ 0:05).
3. Results and discussion The content of some tomato antioxidants and the antioxidant activity of tomato extracts are greatly affected by ripening stage (Cano et al., 2003; Dumas et al., 2003; Raffo et al., 2002). In our experiment, tomato fruits were harvested at full ripeness, the stage at which they are usually consumed, and chromaticity values determined on the skin showed only slight differences between different sampling times, denoting quite similar stage of ripeness. The a*/b* ratio, a simple and appropriate ripening index (Giovanelli et al., 1999), did not show significant differences at P ¼ 0:05 (a*/b* mean values were: 1.31 (April), 1.14 (June), 1.42 (July), 1.33 (December), 1.35 (January), 1.35 (March)). More marked variations between sampling times were observed in dry matter content (mean values were, respectively, 6.97%, 8.93%, 8.14%, 7.37%, 9.10%, 8.67%).
2.4. Climatic data 3.1. Ascorbic acid Climatic data in the area of production were recorded daily at the weather station in Santo Pietro. Average temperature and mean solar radiation detected during the month preceding the harvest are presented in Table 1.
Table 1 Average climate data detected during the month preceding the harvest Date of harvest
Average temperature (1C)
Mean solar radiation (MJ m2 day1)
April 6 June 8 July 26 December 21 January 25 March 20
11.5 22.4 23.6 11.0 7.1 10.5
17.2 24.5 26.1 6.8 7.7 14.0
Fruits harvested at different times were characterized by markedly variable ascorbic acid levels (CV 34.5% and 24.4%, for reduced and total ascorbic acid); reduced ascorbic acid ranged from 16 to 44 mg/100 g (230–493 mg/100 g of dry weight), total ascorbic acid (the sum of ascorbic and dehydroascorbic acid, representing vitamin C content) from 31 to 71 mg/100 g (445–795 mg/100 g d.w.) (Table 2). A range of seasonal variation from 7 to 23 mg/100 g was observed by Liptay et al. (1986) on greenhouse grown fruits of cv. Jumbo at the mature-green stage. In the samples of our experiment, the level of total ascorbic acid was relatively high when compared with published data on different cultivars for fresh consumption grown in several countries. Davies and Hobson (1981) reported the range from 10 to 45 mg/100 g f.w. for reduced ascorbic acid
Table 2 Ascorbic acid, reduced and total, and phenolic compounds content (mg/100 g) in tomatoes harvested at different times of the year Compound
Apr
Jun
Jul
Dec
Jan
Mar
CV
Ascorbic acid Reduced Total
1673 aa 3177 a
4471 e 7179 c
2575 bc 6473 bc
2871 c 5573 b
2271 b 5571 b
3372 d 6175 bc
34.5 24.4
Phenolic compounds Chlorogenic acid Caffeic acid p-Coumaric acid Ferulic acid Rutin Naringenin
5.4470.70 0.2770.01 0.6870.04 0.1670.01 1.7970.07 9.0470.55
c a c a a d
3.0870.71 0.2870.09 0.4570.04 0.1570.02 2.0370.17 2.6770.41
ab a b a a b
3.1270.08 0.2470.10 0.3670.02 0.0970.02 2.7670.14 5.4070.35
ab a a a b c
3.7670.67 0.1770.01 0.4870.05 0.0970.02 2.9270.20 2.1870.21
ab a b a b ab
4.3570.13 0.2970.01 0.7970.05 0.2970.07 3.8770.17 1.9270.10
bc a d b c a
2.6770.08 0.5670.24 0.6370.08 0.0470.01 6.6170.07 1.8470.13
Values are means (7 standard deviations) of three samples; CV represents coefficient of variation of mean values. a In this and in the following tables, different letters indicate significant differences according to the Duncan test (P ¼ 0:05).
a b c a d a
28.0 44.3 28.6 63.6 53.0 74.8
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content in commercial cultivars from different parts of the world, whereas Souci et al. (1994) reported the range from 20.0 to 28.8 mg/100 g for vitamin C. Several factors could have contributed to the relatively high accumulation of ascorbic acid in the tomatoes of our experiment. The first factor is the cultivar, since it is known that tomatoes from cherry cultivars contain higher ascorbic acid levels, as well as dry matter and soluble solids, than normal-sized fruits (Kader et al., 1977). The second factor is the relatively high salinity of the irrigation water used in the considered production area (Leonardi et al., 2000a, b); it has been observed, in fact, that irrigation water of high salinity may enhance the ascorbic acid content, as well as dry matter, soluble solids and titratable acidity (Petersen et al., 1998; De Pascale et al., 2001). The third factor is the particularly sunny climate of the production area; it has been reported that the region where ‘‘Pomodoro di Pachino’’ are grown has the highest temperatures and receives the greatest amount of solar radiation, averaged out over the year, in mainland Europe (Official Journal of European Communities, 2002). As expected from its antioxidant-based functions in plant metabolism, the level of ascorbic acid is responsive to a wide variety of environmental stress factors, including light and temperature; in fact, several works have reported that plants increase their ascorbic acid levels in response to light (Davey et al., 2000) and that high light intensity is associated with a high vitamin C content in tomato fruit (Dumas et al., 2003; Lee and Kader, 2000). In our study, tomato samples harvested at different times did not show any significant correlation between ascorbic acid content and climatic parameters. Nevertheless, the effect of relatively high light and temperature (Table 1) could have contributed, at least partly, to the relatively high level of total ascorbic acid observed in the fruits harvested in June and July. The effects induced by climatic variations were probably superimposed upon other factors, such as sanitary and nutritional status of the plant, and changes in water availability. We found, moreover, a relatively high amount of dehydroascorbic acid (40–60% of total ascorbic acid), whereas lower proportions have been previously reported for ripe tomatoes: 20–30% according to Vanderslice et al. (1990) and Davies and Hobson (1981), whereas even lower proportions have been observed by Cano et al. (2003) and Jimenez et al. (2002). On the contrary, over 90% of the vitamin C was found as dehydroascorbic acid in fresh tomatoes grown in warm climates (De Serrano et al., 1993). In any case, it is evident that, in the tomatoes we considered, the simple ascorbic acid quantification would lead to a substantial underestimation of vitamin C content. From a nutritional point of view, one serving of the considered raw cherry tomatoes (100 g) may provide from 50% to 120%
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of the recommended daily intake of vitamin C for the Italian people (Societa` Italiana di Nutrizione Umana, 1996). 3.2. Phenolic compounds Among main tomato antioxidants, phenolic compounds showed the greatest variations between different sampling times (Table 2). Naringenin content varied from 1.84 to 9.04 mg/100 g (21–130 mg/100 g d.w.) with a CV of 74.8%, and chlorogenic acid from 2.67 to 5.44 mg/100 g (31–78 mg/100 g d.w.) with a CV of 28.0%. Rutin level ranged from 1.79 to 6.61 mg/100 g (0.99–3.66 mg/100 g when expressed as conjugated quercetin), with a range of variation (CV of 53.0%) similar to that found by Stewart et al. (2000) in Spanish field-grown cherry tomatoes (cv. Paloma) sampled over a period of 13 months. Rutin concentration relative to dry weight ranged from 27 to 76 g/100 g. Hertog et al. (1992) observed variations in flavonol levels associated with seasonal influences in some leafy vegetables (lettuce, endive and leek), with the highest levels in summer. On the other hand, in our experiment, as well as in that on Spanish cherry tomatoes, no definite seasonal trends were evidenced in the main phenolic level; moreover, we did not observe any correlation between rutin, naringenin and chlorogenic acid content and climatic parameters. Limited amounts (less than 1 mg/100 g f.w.) of other hydroxycinnamic acids (pcoumaric, caffeic and ferulic acid) were also found in all samples. As observed in the case of ascorbic acid, it is possible that phenolic concentration was affected by a wide range of cultural and environmental factors. In plants, moreover, phenolic biosynthesis is particularly sensitive to induction by various biotic and abiotic stresses (Dixon and Paiva, 1995): for instance, flavonols like quercetin and kaempferol can be synthesized in response to a pathogen attack or to wounding, whereas wound-induced chlorogenic acid and phenolic esters may act directly as defence compounds or may serve as a precursor for the synthesis of polyphenolic barriers. Consequently, a limited number of samples are not adequate to evidence significant relationships with single climatic factors. Interestingly, the phenolics pattern showed noticeable variations between different sampling times, suggesting that each compound was affected in a different way by the same environmental changes. From our data, it resulted that one serving of cherry tomatoes provided from 3.7 to 10.3 mg of flavonoids (conjugated quercetin plus naringenin), which was equal to approximately 15–35% of the flavonoid daily intake estimated for the Italian diet (23–34 mg/diet) (Hertog et al., 1995), confirming the relevance of tomatoes as dietary sources of flavonoids.
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3.3. Carotenoids Carotenoid content was also characterized by marked variations between different harvesting times, ranging from 8350 to 15 119 mg/100 g (101.9–175.5 mg/100 g d.w.) (Table 3). In all samples, lycopene was by far the main component of carotenoid fraction (76–85%), ranging from 7061 to 11 969 mg/100g (86.7–138.1 mg/ 100 g d.w.). The coefficient of variation was 20.4%, 20.1% and 25.2% for total carotenoids, lycopene and bcarotene contents, respectively. Our results were similar to previously published data: lycopene content of 24 tomato varieties grown in southern Italy in 1998 ranged from 3400 to 15 000 mg/100 g (mean value 8600 mg/ 100 g), whereas in 29 varieties grown in 1999 it varied from 4500 to 16 300 mg/100 g (mean value 8700 mg/100 g) (Dumas et al., 2003). Few data have been reported in literature on seasonal fluctuations of carotenoid levels in tomatoes. Heinonen et al. (1989) observed that lycopene concentration was relatively high in summer (June to August) (3800–6600 mg/100g) and low in winter (October to March) (2600–3100 mg/100 g) in tomatoes purchased from retail food stores in Finland; on the contrary, they found the minimum level of b-carotene and lutein in summer. Our results did not evidence clear seasonal trends of carotenoid content or any association with climatic parameters. Nevertheless, lycopene content was at the lowest in July (Table 3), similar to that observed by Martinez-Valverde et al. (2002) on tomato samples harvested in mid-summer, confirming that the high radiation level and hot temperatures reached in this period of year in the Mediterranean area, may exert a significant inhibition effect on lycopene accumulation. Moreover, total carotenoid and lycopene content did not correlate with dry matter content nor with chromaticity values; as previously observed, tomatoes showing similar fruit colour (a*/b* determined on the
skin) do not necessarily contain similar amounts of total carotenoids or lycopene (Leonardi et al., 2000a, b; Giovanelli et al., 1999). Different from phenolic compounds, carotenoid profile was similar in all samples, whereas it was reported to change quite rapidly during the ripening process (Raffo et al., 2002). It was confirmed the absence of z-carotene, and the presence of phytoene and phytofluene, in relevant amounts, and of g-carotene, lutein, neurosporene and lycopene 1,2-epoxide, in minor quantities (Table 3). Our data confirmed that cherry tomatoes are important source of carotenoids, not only lycopene but also b-carotene, one serving providing from 13% to 27% of the recommended daily intake of vitamin A (Societa` Italiana di Nutrizione Umana, 1996). 3.4. a-tocopherol a-tocopherol level was rather low at each sampling time, with a considerable variation from December, 40 mg/100 g (0.54 mg/100 g d.w.), to June, 1160 mg/100 g (13.0 mg/100 g d.w.) (Table 3). Previous papers on several tomato varieties cultivated in Hungary reported a less marked extent of variation, from 90 to 612 mg/ 100 g (Abushita et al., 1997; Abushita et al., 2000). However, our data confirmed that a-tocopherol contribution to the antioxidant properties of tomato is of minor relevance, while the contribution to vitamin E intake of one serving of fruits ranged from 0.4% to 12% of the recommended daily intake (Societa` Italiana di Nutrizione Umana, 1996). Moreover, in tomatoes, vitamin E is present mainly within seeds, which are not readily digested by humans, so the nutritional relevance of the vitamin E content of cherry tomatoes could be lower than the whole fruit content would suggest.
Table 3 Carotenoid and a-tocopherol content (mg/100 g) in tomatoes harvested at different times of the year Compound
Apr
Jun
Jul
Dec
Jan
Mar
CV
Carotenoids Lycopene b-Carotene Phytoene Phytofluene Lutein Neurosporene g-Carotene Lycopene 1,2-epoxide
81007140 b 950724 c 733710 c 386717 b 1772 a 2971 a 3572 c 134715 c
10818778 d 1063733 d 608713 b 41274 b —* 3675 a 3874 c 13379 c
70617271 a 519730 a 36777 a 30078 a 2574 b —* 1172 a 7178 a
101927233 c 8437127 bc 1215719 d 52575 c 1473 a 3272 a 2374 b 91718 ab
82027427 b 623735 a 1231756 de 563725 d 1676 a 3578 a 1573 a 91721 ab
119697218 e 820719 b 1284741 e 846723 e 2072 ab 4573 b 2472 b 11079 bc
20.1 25.2 42.8 38.1 55.0 52.4 43.9 24.1
103847190 b
131087116 d
83537315 a
129357400 c
107757550 b
151197340 e
20.4
1100720 e
1160710 f
800710 c
40710 a
1000720 d
100710 b
71.9
Total carotenoids a-Tocopherol
*Below the detection limit. Values are means (7 standard deviations) of three samples; CV represents coefficient of variation of mean values.
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Table 4 Antioxidant activity (equivalent mM Trolox/100 g of fresh weight of food) in tomatoes harvested at different times of the year Fraction
Apr
Jun
Jul
Dec
Jan
Mar
CV
Water-soluble fraction Water-insoluble fraction
0.19170.009 a 0.02970.001 b
0.26370.010 c 0.02770.001 a
0.21070.006 b 0.02670.001 a
0.17170.005 a 0.03470.001 c
0.17070.013 a 0.02970.001 b
0.42070.020 d 0.03470.001 c
40.3 11.5
Values are means (7 standard deviations) of three samples; CV represents coefficient of variation of mean values.
3.5. Antioxidant activity Several studies have investigated the effects of ripening stage, genotype and processing on hydrophilic and lipophilic antioxidant activity of tomato (Cano et al., 2003; George et al., 2004; Lavelli et al., 2000; Leonardi et al., 2000a, b; Raffo et al., 2002) by using different test reactions for antioxidant activity measurement. Generally, hydrophilic antioxidant activity was significantly affected by genotype and processing, and almost independent of the ripening stage; on the other hand, lipophilic antioxidant activity was more influenced by ripening stage than by genotype. In our experiment, total antioxidant activity (the sum of activity of both water-soluble and water-insoluble fractions, Table 4) varied from 0.199 to 0.454 equivalent mM Trolox/100 g, and in all samples the water-soluble fraction represented by far the main percentage contribution (83–92%) to total activity. Similar ratios between hydrophilic and lipophilic tomato antioxidant activity were previously observed in full ripened tomatoes (Cano et al., 2003; Raffo et al., 2002). The water-soluble fraction showed more variable antioxidant activity between different samples than the waterinsoluble fraction (CV of 40% and 11.5%, respectively); moreover, the antioxidant activity of the two fractions was not correlated with climatic data. Tomato sample harvested in March showed a markedly higher total activity than other samples, due to a higher activity of the water-soluble fraction. This high value could be, at least partly, due to a relatively high content of rutin and a medium–high level of reduced ascorbic acid. In fact, rutin is characterized by the highest antioxidant activity among main phenolics of tomato (rutin 2.4 TEAC, naringenin 1.53 TEAC, chlorogenic acid 1.24 TEAC, as determined using in vitro test by Rice-Evans et al. (1996)). Nevertheless, it is hard to explain changes in antioxidant activity of water-soluble fractions on the basis of variations in ascorbate and phenolics content. First, it has been observed that the antioxidant activity of food extracts depends on both concentrations and synergistic effects (Diplock et al., 1998). Secondly, test reactions for antioxidant activity measurement might be affected by other components (glutathione and enzymatic components) that are involved in complex antioxidant systems of tomato fruits (Jimenez et al.,
2002). Already in a previous study, we did not observe significant correlation between the antioxidant activity of water-soluble fraction and any hydrophilic antioxidant compounds (Raffo et al., 2002). On the other hand, lipophilic antioxidant activity is, generally, well correlated to total carotenoid content, or to lycopene content, in tomato samples (Cano et al., 2003, George et al., 2004, Raffo et al., 2002). In our data, the sample with the lowest carotenoid content (July) showed the lowest water-insoluble antioxidant activity, and that one with the highest content (March) had the highest activity, even though the correlation between the two parameters was lower (R ¼ 0:68, Po0:1) than that observed on tomato sampled at different ripening stages (Cano et al., 2003; Raffo et al., 2002).
4. Conclusions In summary, cherry tomatoes of the same cultivar, greenhouse-grown under similar conditions in the same geographical area, and harvested at similar stage of ripeness but at different times of the year showed marked differences in the antioxidant content. In spite of wide variations in antioxidant content according to the season having been observed, neither a clear seasonal trend, nor a correlation between antioxidant content and mean solar radiation or average temperature, was found. In practice, for an accurate assessment of effects of climate factors on phytonutrient content, large-scale field trials over several years and in several locations would be necessary. Nevertheless, our results confirmed that the hot temperatures of mid-summer in the Mediterranean basin may produce a significantly negative effect on lycopene accumulation. Despite the marked variability showed by antioxidants content, greenhouse-growing conditions in Sicily induced the accumulation of relatively high levels of ascorbic acid, phenolic compounds and carotenoids in cherry tomatoes for most of the year.
Acknowledgements We are indebted to Elena Azzini and Aldo Bertone for technical assistance.
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