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Mineral and Ascorbic AcidConcentrations of Greenhouse- andField-Grown Vegetables: Implications forHuman HealthF. Aghili a , A. H. Khoshgoftarmanesh b , M. Afyuni b & M. Mobli ca Soilless Culture Research Centre, Isfahan University of Technology,Isfahan, Iranb Department of Soil Sciences, College of Agriculture. 84154-83111,Isfahan University of Technology, Isfahan, Iranc Department of Horticulture, College of Agriculture. 84154-83111,Isfahan University of Technology, Isfahan, IranPublished online: 21 Dec 2011.

To cite this article: F. Aghili , A. H. Khoshgoftarmanesh , M. Afyuni & M. Mobli (2012) Mineral andAscorbic Acid Concentrations of Greenhouse- and Field-Grown Vegetables: Implications for HumanHealth, International Journal of Vegetable Science, 18:1, 64-77, DOI: 10.1080/19315260.2011.572147

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International Journal of Vegetable Science, 18: 64–77, 2012Copyright © Taylor & Francis Group, LLCISSN: 1931-5260 print / 1931-5279 onlineDOI: 10.1080/19315260.2011.572147

Mineral and Ascorbic AcidConcentrations ofGreenhouse- and Field-GrownVegetables: Implications forHuman Health

F. Aghili,1 A. H. Khoshgoftarmanesh,2 M. Afyuni,2 and M. Mobli3

1Soilless Culture Research Centre, Isfahan University of Technology, Isfahan, Iran2Department of Soil Sciences, College of Agriculture. 84154-83111, Isfahan Universityof Technology, Isfahan, Iran3Department of Horticulture, College of Agriculture. 84154-83111, Isfahan Universityof Technology, Isfahan, Iran

Vegetable nutritional quality is related to concentrations of antioxidants and otherphytonutrients. In Iran, vegetables can be produced in soil in climate-controlled green-houses. Limited information is available on the quality of greenhouse-grown vegetablescompared to field-grown vegetables. Concentrations of Ca, Mg, P, K, Fe, Zn, Cu, Mn,and ascorbic acid in greenhouse- and field-grown bell pepper (Capsicum annuum L.),cucumber (Cucumis sativa L.), and tomato (Solanum lycopersicum L.) were determined.Mean fruit K, P, and Mg concentrations in greenhouse-grown bell pepper, cucumber,and tomato were greater than expected levels. Mean fruit K concentrations in green-house-grown bell pepper, cucumber, and tomato were lower than that in field-grownvegetables. Greenhouse-grown vegetables accumulated greater amounts of P in fruitcompared to field-grown vegetables. More than 48%, 38%, 30%, and 54% of greenhousevegetables were Fe, Zn, Cu, and Mn deficient, respectively. Field-grown vegetables hadlower contents of Cu, Mn, Fe, Zn, and ascorbic acid compared to greenhouse-grownvegetables. Calcium, Fe, Cu, Mn, and Zn intakes through consumption of greenhouse–grown vegetables for population study groups accounted for a negligible fraction of therecommended daily allowance (RDA), whereas daily intake of ascorbic acid was greaterthan the RDA requirement. Intake of micronutrients and ascorbic acid from field–grown vegetables was less than that from greenhouse-grown vegetables. In general, thenutritional quality (contents of micronutrients and ascorbic acid) of greenhouse-grownvegetables was better than that of field-grown vegetables, although fruit micronutrientconcentrations of field- and greenhouse-grown vegetables were lower than expected

This research work was supported by Iran National Science Foundation, ProjectNo. 84105-25.Address correspondence to A. H. Khoshgoftarmanesh, Department of Soil Sciences,College of Agriculture. 84154-83111, Isfahan University of Technology, Isfahan, Iran.E-mail: amirhkhosh@cc.iut.ac.ir

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Mineral Concentrations in Vegetables 65

levels. The results indicated that bell pepper is an excellent source of ascorbic acidand potassium for humans. Despite a protected system of cultivation, poor fertilizermanagement in greenhouses could adversely affect the nutritional value of vegeta-bles. Improved nutritional management in greenhouses could enhance micronutrientconcentrations in these vegetables.

Keywords Antioxidant, Bell pepper, Cucumber, Minerals, Nutrients, Nutritionalquality, Tomato.

Protected cultivation plays an important role in production of fresh vegetablesworldwide and in Iran. In 2003, approximately 246.5 million metric tons offresh vegetables, excluding melons, were produced worldwide from 6.7 millionha of protected cultivation (Food and Agriculture Organization [FAO], 2005).The nutritional quality of vegetables is becoming increasingly important forgreenhouse growers who want to meet the ever-increasing demand of con-sumers in the highly competitive fresh vegetable market. Research has shiftedtoward the content of antioxidants, which are claimed to help in preventinghuman diseases (Etminan et al., 2004). Low vegetable intake is estimated tocause about 31% of ischemic heart disease and 11% of stroke occurrence world-wide (World Health Organization [WHO], 2002). It is estimated that up to2.7 million lives could potentially be saved each year if vegetable consumptionwere increased (WHO, 2003). Vegetables are a good source of many nutrientsand antioxidants that are essential for human health (WHO, 2003). Vegetablescan contribute 35%, 24%, and 11% of the total daily K, Mg, and P, respectively,to the human diet (Levander, 1990).

Antioxidants contain the enzymes selenium-dependent glutathione perox-idase (GPX); copper-zinc–dependent superoxide dismutase (SOD); the dietaryantioxidants vitamins C, E, and zinc; and phenolic compounds thought toquench free radicals (Bosland and Votava, 2000; Hessler et al., 1983). Dailyconsumption of vegetables in sufficient amounts might help in the preventionof major chronic diseases such as cancers (Weber and Bendich, 1996).

Dark green, leafy vegetables such as Spinacea oleracea (L.) are goodsources of iron (Serrano, 2003). Iron is a component of a number of proteins,including enzymes and hemoglobin, and the latter are important for transportof oxygen to tissues throughout the body (Institute of Medicine [IOM], 2000).Animal-based foods are the main source of Zn, an essential trace element; veg-etables are relatively poor in Zn (United States Department of Agriculture,Agricultural Research Service [USDA-ARS], 2001). Zinc is an essential cofactorfor enzymes controlling numerous cellular processes in plants, including DNAsynthesis, growth, reproduction, and development (Manfred et al., 2005). Leafyvegetables are rich sources of manganese (Ursel, 2001), an element that playsan important role in a number of physiologic processes as a constituent andan activator of enzymes (Ursel, 2001). The effects of calcium supplied throughmilk products on bone accrual is well known (Du et al., 2002), and the role ofvegetables in supplying Ca is emerging (McGartland et al., 2004).

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Although greenhouse-grown bell pepper (Capsicum annuum L.), cucum-ber (Cucumis sativa L.), and tomato (Solanum lycopersicum L.) constitute amajority of the vegetables consumed in Iran, there is a lack of informationon the nutritional quality of these vegetables. In Iran it is customary to growvegetables in soil in protected, climate-controlled greenhouses. However, thereare no reliable statistics for greenhouse vegetable area, production, nutritionalquality, and market value (Gruda, 2005).

This study was conducted to determine levels of macronutrients (Ca, Mg, P,and K) and micronutrients (Fe, Zn, Cu, and Mn) and the antioxidant ascorbicacid (vitamin C) in greenhouse-grown bell pepper, cucumber, and tomato, themost important nonleafy vegetables produced in Iran. The daily intake ofnutrients and ascorbic acid from these vegetables was estimated and com-pared to the recommended daily allowance (RDA) and tolerable upper intakelevel (UL).

MATERIALS AND METHODS

Study Site, Sample Collection and AnalysisA total of 70 bell pepper, cucumber, and tomato greenhouses were

randomly selected in Isfahan province, central Iran. Generally, productiontechniques used by the growers were similar. Various greenhouse and soil prop-erties were identified (Table 1). Soils in the various areas differed in texture,electrical conductivity (EC), and total P, K, and micronutrients. The attributesof soil texture, EC, total P, and available K, Fe, and Zn were used to group thedata and groups were compared to determine whether they affected outcomes.In addition, a total of 20 bell pepper, cucumber, and tomato fields were selectedin Isfahan. The area extends from easting of 510 15/ to 520 41/ longitude, nor-thing of 320 31/ to 320 59/ latitude. This province was selected because it

Table 1: The range of selected soil properties in the experimental fields andgreenhouses.

Bell pepper Cucumber TomatoGreenhouse Field Greenhouse Field Greenhouse Field

pH 6.8–7.4 7.3–8.7 6.6–7.5 7.4–8.3 6.9–7.5 7.4–8.5CaCO3 (%) 8–12 8–22 8–12 8–25 10–12 8–22Total N (%) 0.03–0.30 0.01–0.15 0.27–0.43 0.09–0.25 0.11–0.22 0.07–0.18P (mg·kg−1) 79–103 12–21 92–100 15–23 80–91 10–21K (mg·kg−1) 577–880 230–315 634–903 273–333 319–580 187–305Fe (mg·kg−1) 18.1–28.3 6.2–10.0 15.9–28.8 7.6–11.3 13.1–23.31 7.2–11.5Zn (mg·kg−1) 8.98–17.13 0.84–4.45 7.11–14.30 0.99–4.01 6.32–13.13 1.04–3.45Cu (mg·kg−1) 6.36–8.64 0.59–3.10 4.04–7.59 0.44–2.87 5.18–9.04 0.67–3.56Mn (mg·kg−1) 8.22–25.10 5.10–10.3 7.65–23.7 5.49–9.45 8.00–22.91 6.01–11.03

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Mineral Concentrations in Vegetables 67

is a major producer of greenhouse-grown vegetables. The bell pepper, cucum-ber, and tomato intake rates in this province have been reported previously(Mohammadifard et al., 2005). At harvest (15 Mar. to 30 Apr.), 10 freshfruit samples each of bell peppers, cucumbers, and tomatoes were randomlycollected from each greenhouse for analysis.

To measure mineral nutrient concentration, fresh fruit samples were cutinto small pieces, placed in an oven at 70◦C to dry until they reached a constantweight, and ground. Dry samples (1 g) were placed into ceramic vessels andcombusted in a muffle furnace at 550◦C for 8 h. Ashed samples were removedfrom the muffle furnace, cooled, and the ash dissolved in 2 M HC1 (Chapman,1996). The final solution was diluted to meet the range requirements of theanalytical procedures. Analyses of K, Ca, Mg, Fe, Zn, Cu, and Mn were carriedout with an atomic absorption spectrophotometer (model 3400, Perkin Elmer,Wellesley, Mass.). Potassium was determined in the emission mode of thespectrometer. The concentration of P was measured using a spectrophotometer(model UV-1601, Shimadzu Corp., Kyoto, Japan).

Ten grams of fresh fruit was crushed in a mortar and homogenized witha pestle. The homogenate was centrifuged at 2795 g for 10 min and thesupernatant was filtered using 541 Whatmann filter paper. Ascorbic acidconcentration was analyzed by titration using 2,6-dichlorophenol indophenol(Howard et al., 1994). The content of ascorbic acid was expressed as milligramsper 100 milliliters. All reagents were analytical grade and were from Merck AG(Darmstadt, Germany). Stock standard solutions containing 1000 mg L−1 ofthe metals K, Ca, Mg, Fe, Zn, Cu, and Mn in 2% HNO3 were used for prepara-tion of calibration standards. The certified standard materials of the NationalInstitute of Standards and Technology (NIST) were used to determine accu-racies of for metal analyses. Distilled deionized water was used throughoutfor sample preparation, dilution, and rinsing the apparatus prior to analysis.To minimize the risk of contamination all glassware was washed with distilleddeionized water followed by an acid wash. Digested solutions were kept in therefrigerator until analysis. The efficiency of the procedure was determined byadding known concentrations of each metal in a 1 g sample. Each samplewas analyzed for the spiked metals with an atomic absorption spectropho-tometer. Percentage recoveries of metals in the samples were determined(Table 2).

Dietary Intake AssessmentDaily intake of mineral and ascorbic acid through consumption of

greenhouse-grown bell pepper, cucumber, and tomato was calculated using thefollowing equation:

DI = FIR C

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68 F. Aghili et al.

Table 2: Recovery results for bell pepper, cucumber, andtomato samples.

% Recovery

Element Bell pepper Cucumber Tomato

Ca 103.9 96.2 96.7Mg 96.1 93.0 100.1K 93.0 97.0 97.2P 96.4 96.5 94.5Fe 101.4 93.6 91.9Zn 94.6 98.2 93.2Mn 94.3 99.0 101.0Cu 94.2 90.4 93.3

where DI is the daily intake of mineral nutrients or ascorbic acid(mg/person/day); FIR is the daily intake of vegetable (g/person/day); and Cis the the average concentration of nutrients or ascorbic acid in the vegetable(mg/100 g fruit weight).

It was assumed that bell pepper, cucumber, and tomato consumption isabout 80, 120, and 100 g/person >10 years old/d and 60, 100, and 80 60 g/child<10 years old/d, respectively. Bell pepper, cucumber, and tomato intake rateassumptions were from Mohammadifard et al. (2005), although there was somemodification due to use of greater amounts of vegetables. Field-grown vegeta-bles are a negligible fraction of vegetables consumed locally. The calculateddietary intakes of nutrients and ascorbic acid were compared to the RDA.

Statistical AnalysisSignificant differences between means were separated by analysis of vari-

ance followed by least significant difference (LSD) test. All data were analyzedusing the SPSS statistical package (SPSS, Inc., Chicago, Ill.). Correlation anal-ysis was performed on selected variable pairs. The Kruskal-Wallis test wasused to determine whether significant differences existed among greenhousesgrouped based on soil characteristics.

RESULTS AND DISCUSSIONS

Variations in soils due to texture, EC, total phosphorus, potassium, andmicronutrients did not produce significant differences in results among loca-tions, and the data were pooled.

Fruit Macronutrients ConcentrationsMacronutrients concentrations in field and greenhouse bell pepper, cucum-

ber, and tomato samples were determined (Table 3). Cucumber accumulated

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Mineral Concentrations in Vegetables 69

Table 3: Descriptive statistics of Ca, Mg, K, and P concentrations (mg/100 g FW) inbell pepper, cucumber, and tomato produced in greenhouses.

Max Min Mean ± sd

Element Greenhouse Field Greenhouse Field Greenhouse Field

Bell pepperCa 14.2 20.2 7.9 8.3 11.1 ± 1.8 13.4 ± 8.9Mg 25.0 26.5 9.9 7.9 16.2 ± 5.5 16.9 ± 8.7K 376 380 265 234 324 ± 38 339 ± 87P 70.1 45.6 20.3 11.7 34.5 ± 10.3 28.0 ± 8.5

CucumberCa 26.2 31.1 6.7 9.8 14.9 ± 4.6 18.7 ± 8.7Mg 23.0 16.7 13.1 14.4 16.2 ± 2.5 14.8 ± 5.9K 287 311 172 184 229 ± 31 246 ± 52P 46.5 32.1 24.5 12.5 36.1 ± 6.6 21.4 ± 8.9

TomatoCa 13.6 16.7 5.9 5.4 10.7 ± 2.4 9.6 ± 5.3Mg 18.2 17.8 9.2 7.8 14.3 ± 2.5 13.5 ± 3.1K 290 311 220 234 252 ± 25 269 ± 32P 50.4 33.4 23.3 14.5 35.2 ± 8.3 22.9 ± 6.9

Table 4: Mean concentrations (mg/100 g FW) of Ca, Mg, K, and P in field- andgreenhouse-grown bell pepper, cucumber, and tomato with their critical limits.

Mean

Element Vegetable Greenhouse Field Critical level T

Ca Bell pepper 11.1b 13.4b 12.0 NSCucumber 14.9a 18.7a 16.0 −2.2∗Tomato 10.7b 9.6c 12.0 NS

Mg Bell pepper 16.2a 16.9a 14.0 NSCucumber 16.2a 14.8b 14.0 2.1∗Tomato 14.3a 13.5bc 9.2 3.7∗

K Bell pepper 324a 339a 260 5.4∗∗Cucumber 229c 246c 147 10.2∗∗Tomato 252b 269b 220 6.1∗∗

P Bell pepper 34.5a 28.0a 25.0 2.2∗Cucumber 36.1a 21.4b 24.0 10.3∗Tomato 35.2a 22.9b 23.3 5.2∗

Values in a column and for each element followed by the same letter are not significantlydifferent at P ≤ 0.05, LSD test.NS, ∗, ∗∗Nonsignificant or significant at P ≤ 0.05 or P ≤ 0.01 according to LSD test.

greater amounts of Ca in its edible parts than tomato and bell pepper. Theone-sample t-test analysis indicated that Ca concentration in greenhousecucumber was significantly lower than its expected level of 16 mg/100 g FW(Khoshgoftarmanesh, 2007; Table 4).

More than 65% of cucumber samples were Ca deficient, but there wasno significant difference between Ca concentration in tomato and bell pep-per samples and the expected Ca level. This may be due to the different

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70 F. Aghili et al.

maturity levels of bell pepper, cucumber, and tomato samples. Calcium defi-ciency can be caused by salinity and high temperature (Willats et al., 2001).Impaired Ca transportation in the xylem and unstable environmental con-ditions are the main reasons for Ca deficiency in cucumber fruit (Gruda,2005; Willats et al., 2001). Despite an advantage in comparison to outdoorproduction, greenhouses are never completely free from influences of stress,especially with respect to heat and light energy (Peet, 1999; Tognoni et al.,1999). The environmental stresses inside greenhouses can affect nutrition andperformance quality indices. Calcium regulates leaf senescence and ripening(Bramlage, 1993; Fallahi and Simons, 1996). Ca improves cell wall and mem-brane integrity and regulates ripening and leaf senescence (Marschner, 1995).Calcium also plays a role in binding polysaccharides and proteins of cell walls(Marschner, 1995). Field-grown bell pepper and cucumber accumulated greaterCa compared with greenhouse-grown bell pepper and cucumber, and Ca con-centration in greenhouse tomato fruit was greater than that in field-growntomato.

Potassium concentration in bell pepper was significantly higher thanin cucumber and tomato (Table 4). Potassium concentration in bell pepper,tomato, and cucumber has been reported to be in the 176–260 range (Medicaland Nutrition Experts, Mayo Clinic, 2004; Rubio et al., 2002; USDA-ARS,1999), 222–244 (Medical and Nutrition Experts, Mayo Clinic, 2004; Nonnecke,1989), and 144–147 mg/100 g FW (Medical and Nutrition Experts, MayoClinic, 2004), respectively. Potassium concentrations in bell pepper, cucumber,and tomato were significantly (P < 0.01) greater than the expected normalranges (Table 4). Fruit K concentration of field-grown vegetables was greaterthan that of greenhouse-grown vegetables.

There was no significant difference in P and Mg concentrations among veg-etables (Table 4). The P and Mg contents in bell pepper from various partsof the world range from 24.0 to 30.5 (Medical and Nutrition Experts, MayoClinic, 2004) and 12 to 16 mg/100 g FW (Rubio et al., 2002; USDA-ARS,1999), respectively. Phosphorus concentrations in tomato and cucumber arereported to be in the range of 24–27 (Nonnecke, 1989; Rubio et al., 2002)and 20–24 mg/100 g FW (Khoshgoftarmanesh, 2007; Medical and NutritionExperts, Mayo Clinic, 2004), respectively. The mean fruit P and Mg concentra-tions in the three vegetables were significantly greater than expected levels(Table 4). Field-grown vegetables accumulated greater P in the fruit comparedto greenhouse-grown vegetables. A reason for elevated concentrations of K, P,and Mg in greenhouse-grown cucumber, tomato, and bell pepper may be poorfertilizer management and high application of manure and synthetic fertiliz-ers. Some producers apply more than 2 kg/1000 m2 of P before each irrigationperiod.

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Mineral Concentrations in Vegetables 71

Fruit Micronutrient ConcentrationsMean concentrations of Fe and Zn in the vegetables varied from 0.28 to

0.60 and 0.19 to 0.27 mg/100 g FW, respectively (Table 5). Bell pepper accu-mulated the highest amounts of Fe and Zn in fruit and the lowest fruit Fe andZn concentrations were in cucumbers. Iron and zinc levels in bell pepper havebeen reported to range from 0.31 to 0.77 (Medical and Nutrition Experts, MayoClinic, 2004; Rubio et al., 2002; USDA-ARS, 1999) and 0.17 to 0.26 mg/100 gFW (Rubio et al., 2002; USDA-ARS, 1999), respectively. In regards to thesufficient range of Fe in tomato and cucumber (0.27–0.50 mg/100 g FW)(Khoshgoftarmanesh, 2007; Nonnecke, 1989) and Zn critical deficiency levelin tomato (0.2 mg/100 g FW; Nonnecke, 1989), about 48% and 35% of fruitsamples were Fe and Zn deficient, respectively.

There was no significant difference among vegetables in fruit Cu andMn concentrations, although field-grown vegetables had lower amounts of Cuand Mn in their fruit compared to greenhouse-grown vegetables (Table 5).Mean concentrations of Mn in bell pepper, tomato, and cucumber comparedto expected levels (0.09, 0.11, and 0.10 mg/100 g FW, respectively; Nonnecke,1989) indicated that about 54% of samples were Mn deficient. In com-parison to normal fruit Cu levels for bell pepper, cucumber, and tomato(0.10, 0.08, and 0.06, respectively) (Khoshgoftarmanesh, 2007; Nonnecke,1989), more than 30% of greenhouse-grown vegetables were Cu deficient.

Table 5: Descriptive statistics of Fe, Zn, Cu, Mn, and ascorbic acid concentrationsin bell pepper, cucumber, and tomato (mg/100 g FW) in greenhouse-grown bellpepper, cucumber, and tomato.

Max Min Mean ± SD

Element Greenhouse Field Greenhouse Field Greenhouse Field

Bell pepperFe 0.68 0.56 0.55 0.44 0.61 ± 0.09 0.48 ± 0.07Zn 0.32 0.25 0.02 0.07 0.25 ± 0.03 0.17 ± 0.02Cu 0.15 0.09 0.01 0.05 0.10 ± 0.02 0.06 ± 0.01Mn 0.18 0.16 0.03 0.07 0.08 ± 0.01 0.10 ± 0.01Ascorbic acid 303 297 194 221 246 ± 53 251 ± 49CucumberFe 0.50 0.23 0.17 0.13 0.28 ± 0.03 0.13 ± 0.01Zn 0.24 0.14 0.12 0.11 0.18 ± 0.02 0.12 ± 0.01Cu 0.15 0.09 0.04 0.04 0.09 ± 0.01 0.06 ± 0.02Mn 0.18 0.12 0.05 0.07 0.10 ± 0.01 0.09 ± 0.01Ascorbic acid 4.2 1.9 1.1 1.6 3.2 ± 0.9 1.2 ± 0.3TomatoFe 0.42 0.23 0.12 0.11 0.32 ± 0.06 0.17 ± 0.03Zn 0.18 0.10 0.11 0.07 0.15 ± 0.02 0.07 ± 0.01Cu 0.10 0.05 0.02 0.04 0.05 ± 0.01 0.04 ± 0.01Mn 0.16 0.12 0.09 0.10 0.12 ± 0.03 0.11 ± 0.01Ascorbic acid 24.0 14.9 11.0 12.7 21.0 ± 6.1 14.2 ± 3.9

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72 F. Aghili et al.

Copper and Mn deficiency results in reduced yield and quality (Marschner,1995).

Poor nutrition management and high application of phosphate fertilizersin soil may be the main reasons for fruit micronutrient deficiencies. Somefarmers apply high amounts of manure fertilizer before planting. Almostall greenhouses have been established on P-enriched local soils previouslyused for cereal production. Phosphorus forms insoluble complexes with Znand Fe in soil that in turn cause decreases in available concentrations ofthese micronutrients. Alkaline soils and high amounts of CaCO3 may bereasons for low availability of micronutrients to plants in calcareous soils(Khoshgoftarmanesh, 2007).

Ascorbic Acid Concentration in Greenhouse-GrownVegetablesThe mean ascorbic acid concentration in bell pepper (246 mg/100 g)

was higher than in tomato (21 mg/100 g) and cucumber (3.2 mg/100 g;Table 5). Concentrations of ascorbic acid in field-grown vegetables werelower than in greenhouse-grown vegetables. Considering the normal con-centration of ascorbic acid in tomato, cucumber, and bell pepper (20, 3,and 189 mg/100 g FW, respectively; Khoshgoftarmanesh, 2007; Medical andNutrition Experts, Mayo Clinic, 2004), all vegetables accumulated significantlygreater amounts of ascorbic acid over expected levels. Bosland and Votva(2000) reported that bell pepper consumption is increasing and that bell peppermay become an important source of vitamins in the human diet. Bell pepperis an excellent source of bioactive nutrients such as vitamin C, provitamin A(carotenoids), and phenolic compounds, which confirms its nutritional qualityand antioxidant capacity (Howard et al., 1994). High ascorbic acid content invegetables may be attributed to high K concentration in fruit. A positive rela-tionship between fruit K and ascorbic acid concentration was found (r2 = 0.82).Potassium is a key element in organic acid synthesis (Marschner, 1995). Caseroet al. (2004) reported a positive relationship between leaf and fruit K andascorbic acid concentration in Golden Smoothie apples. Winsor (1979) reportedthat K concentration had a positive effect on fruit organic acid concentration.

Daily Intake of Macronutrients From Greenhouse-GrownVegetablesCalcium intake through consumption of bell pepper, cucumber, and tomato

produced in greenhouses was below the RDA and accounted for a negligiblefraction of the calcium RDA (Table 6). This indicates that vegetables can partlycontribute to calcium intake but cannot replace key foods such as milk (Weaverand Plawecki, 1994).

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Mineral Concentrations in Vegetables 73

Table 6: Daily intake (mg/day) of Ca, K, P, and Mg through consumption ofgreenhouse-grown bell pepper, cucumber, and tomato.

Age group Ca Mg P K

Bell pepper4–10 Years old 6.7 9.7 20.7 194>10 Years old 8.9 14.3 35.2 252

Cucumber4–10 Years old 14.9 16.2 36.1 229>10 Years old 17.9 19.5 43.3 275

Tomato4–10 Years old 8.6 11.4 14.1 201>10 Years old 10.7 12.9 27.6 260

Total4–10 Years old 30.1 27.4 70.9 625>10 Years old 37.5 46.7 106 787

RDAa

4–8 Years old 800 130 500 38009–18 Years old 1300 240 1250 4500>18 Years old 1000–1200 Men 400 700 4700

Women 300Contribution to the nutrient RDA (%)

4–8 Years old 3.8 21.0 14.2 16.59–18 Years old 2.9 19.5 8.0 17.5>18 Years old 3.4 Men 11.7 15.0 16.7

Women 15.6

aData from IOM (2000).

Although more cucumber and tomato were consumed than bell pepper,all vegetables provided relatively equal contributions of the potassium RDA(Table 6). Flores et al. (2004) reported that pepper is an excellent source ofpotassium. Tucker et al. (1999) reported that vegetables contributed more thanhalf of the total potassium consumed by humans. It was estimated that con-sumption of greenhouse-grown bell pepper, cucumber, and tomato can supply4.3%–5.4%, 5.1%–5.8%, and 4.5%–5.5% of the total K RDA for children andadults.

Greenhouse-grown vegetables contributed about 15% of the phosphorousRDA for children and adults >18 years old and about 8% of the RDA for 8- to18-year-olds (Table 6).

Dietary intake of Mg through consumption of greenhouse-grown bell pep-per, cucumber, and tomato contributed 11.7%–21.0% of the Mg RDA (Table 6).Magnesium is found in a wide variety of foods, particularly in those closeto their unrefined state (Tucker et al., 1999). The percentage categories forthe Mg RDA are 100% or more, provided for informational purpose only;40%–99%, excellent source; 25%–39%, good source; and 10%–24%, significantsource (USDA-ARS, 1999). Greenhouse-grown vegetables were classified as“significant sources” to supply the magnesium RDA.

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74 F. Aghili et al.

Daily Intake of MicronutrientsDietary intake of Fe, Zn, Cu, and Mn through consumption of greenhouse-

grown vegetables was 0.9–1.13, 0.45–0.56, 0.19–0.23, and 0.24–0.30 mg/dayfor the 4-10 years old and > 10 years old population groups. Greenhouse-grown vegetables can supply about 43% and 25% of the copper RDA forchildren and adults, respectively (Table 7). These vegetables were relativelypoor, contributing only 5%–9% of Zn RDA for the population groups (Table 7).Vegetables provide <10% of Zn (USDA-ARS, 2001) and 6.1%–14.2% of the ironRDA. Vegetables contribute about 24% of the iron RDA in the United States(USDA-ARS, 1999).

Daily Intake of Ascorbic AcidDietary intake of ascorbic acid through consumption of bell pepper, cucum-

ber, and tomato was 166–190 mg/day for different population groups (Table 7).

Table 7: Daily intake (mg/day) of Fe, Zn, Cu, Mn, and ascorbic acid throughconsumption of bell pepper, cucumber, and tomato.

Age groups Fea Zn Cu Mn Ascorbic acid

Cucumber4–10 Years old 0.28 0.18 0.09 0.10 3.2>10 Years old 0.33 0.21 0.10 0.12 3.8

Tomato4–10 Years old 0.25 0.12 0.04 0.09 16.0>10 Years old 0.32 0.15 0.05 0.12 21.0

Bell pepper4–10 Years old 0.37 0.15 0.06 0.05 147>10 Years old 0.48 0.20 0.08 0.06 197

Total4–10 Years old 0.90 0.45 0.19 0.24 166>10 Years old 1.13 0.56 0.23 0.30 191

RDAb

4–8 Years old 10 5 0.44 —c 1009–18 Years old

Boy 9 9 0.70 — 100Girl 12 8

>18 years oldMan 8 11 0.90 — 100Woman 18 8

Contribution to nutrient RDA (%)4–8 Years old 9 9 43 — 1009–18 Years old

Boys 12.5 6.2 33 — 100Girls 9.4 7.0

>18 Years oldMan 14.1 5.1 25 — 100Woman 6.2 7.0

aThe iron RDA for women >50 years old is 8 mg/day.bData from IOM (2000).cThere were insufficient data to set an RDA for manganese.

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Mineral Concentrations in Vegetables 75

Jullian et al. (1999) reported that a daily intake of 200 mg of vitamin Cis sufficient to provide the maximum body retention of the nutrient andoptimal immune function. Recommended dietary allowances for ascorbic acidare 45 mg/day for children and 60 mg/day for adolescents and adults. Thedietary intake of vitamin C for different population groups from consump-tion of greenhouse-grown bell pepper and cucumber was considerably greaterthan the RDA; this value did not reach the UL (Table 7). These vegetablescan supply the total ascorbic acid requirement without risk of adverse effects.The UL of ascorbic acid for children, adolescents, and adults is 650, 1200, and2000 mg/day (IOM, 2000). According to the IOM (2000), no evidence is avail-able to confirm that ascorbic acid is carcinogenic or teratogenic or that it causesadverse reproductive effects. It has been reported that antioxidant vitamins A,C, and E are present in high concentrations in various types of pepper (Boslandand Votava, 2000). Green to red pepper pods contain enough vitamin C to meetor exceed the adult recommended daily allowance. The amount of vitamin Cobtained from one medium-sized pepper fruit is six times as much as that ofan orange. One medium green bell pepper (148 g) provides 180% of the vita-min C RDA (Bosland and Votava, 2000). Improved nutritional management ingreenhouses will enhance micronutrient concentrations in vegetables.

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