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1. INTRODUCTION Consumption of horticultural food crops has increased over the last few decades, especially as a result of changes in the consumer’s nutritional behaviour. Some researches pointed out, that consumers are more concerned about staying healthy and eating correctly. Some consumers may weight priority on how vegetables are produced, i.e. if vegetables are produced environmentally sound and/or organically, or on vegetable quality. Consequently, it is essential for growers to understand which segment of the market they are producing for. Nowadays, agricultural practices are focused on the optimisation of nutrient management through a better control of plant water and nutrient requirements to improve plant health and crop yield. In this sense, the use of hydroponic practices in tomatoes and bell peppers has demonstrated that quality was similar with respect to conventional or intensive practices, and reducing grown water pollution. Hydroponic commercial agriculture is a rapidly growing industry. The annual rate of growth is approximately 15-25%. Hydroponics is a soilless culture and can be considered as a special method within the different greenhouse crop production methods. Hydroponics is the method of cultivating plants using mineral nutrient solutions or/and in inert substrates. Nutrients are added to the water at the concentration which is suitable for plant growth. The International Society of Soilless Culture defines soilless culture as “the growth of non-aquatic plants with their roots in completely inorganic medium, where the roots are supplied with a nutrient solution”. Over the resent two decades, hydroponic growing systems have become increasingly popular among European commercial growers since they improve quantitative and qualitative characteristics of the final product. In comparison with traditional cultivation techniques in soil, the hydroponics has a lot of advantages. Most important are: production is very intensive, higher sanitary quality (without soil contaminants), higher yields, crop-rotation is abandoned, less problems with pests and diseases, better crop quality if optimal nutrient solution is used, lower production costs and better control of the cultivation process. The major advantages of hydroponics are therefore the elimination of the need for soil sterilization and more precise control of the application of nutrients and water. There are many types of hydroponic systems which use a variety of substrates: rock wool culture, NFT – Nutrient Film Technique (crop roots intake water and nutrients from a thin film of nutrient solution), PPH – Plant Plane Hydroponics (roots are developed over a thin layer of substrate, that is well penetrated with nutrient solution), VPH – Vertical Hydroponic Systems (similar to PPH, the substrate is wrapped in plastic film and positioned vertically) and aeroponics. Previous studies show that fruits and vegetables are a food source of several bioactive compounds (i.e. phytochemicals). Phytochemicals that possess antioxidant characteristics are believed to contribute to the improvement human health and disease prevention. For example, vegetables generally are a rich source of potent antioxidants. Antioxidants are agents, which scavenge the free radicals and may therefore help delay or prevent oxidative damage. It has been also shown that tomatoes and bell peppers are a valuable part of the diet owing to their nutritive values. They are a low-energy food containing small amounts of carbohydrates and fats and high proportion of dietary fibre, proteins, minerals and vitamins. Despite a relatively large market for tomatoes and bell peppers, alternative cultivation techniques such as hydroponics have not been sufficiently considered for improving their quality. Hydroponics are a good method for research under controlled conditions of nutrient availability. Most modern hydroponic solutions are based on the work of Hoagland and Arnon (1950) and have been adapted to numerous crops. In February 2016, As An d.o.o. (further known as applicant) has shown interest for testing Mineral green (Mineral). This products have a variety of uses for plant nutrittion, growing stimulator, plant protection and other purposes. So the objective of the present study was is to assess the influence of two hydroponic nutrient solution (modified Hoagland-Arnon solution and MINERAL GREEN) and conventionally produced bell peppers and tomatoes on selected plant metabolites. The experiment was undertaken in a multi-span greenhouse covered with double PE-film and passive climate control on a laboratory field of the Biotechnical Faculty in Ljubljana, Slovenia (46o 04' N, 14o 31' W, 300 m M.S.L.). The plants were grown under natural daylight condition, without additional illumination. 2. MATERIAL AND METHODS Fruits were collected from three commercial varieties of tomato (cv. Amaneta F1, cv. Buran F1 and Tadim F1) and bell peper (cv.'Blondy F1', cv. Bagoly F1 and Belladonna F1) in 2016, from three parallel experiments that were conducted from May to September. Flowers were tagged on fruit set, and fruits were harvested at diferent intervals from 18 days from fruit set (DFFS) until senescence on the plant (87 DFFS for peppers and 94 DFFS for tomato fruits). Tomato fruit at 94 DFFS were characterized by a very intense red color and a soft pulp. Bell peppers at 87 DFFS were pale green to yellowish and senescent in appearance. Plants were started in the greenhouse from seed and transplanted to raised beds on May 15 at a planting density of 0.5 × 0.5 m in an unheated three-span greenhouse with flap ventilation at the ridge and roll-up ventilation at the side walls. Each span was 6 m wide and 25 m long and covered with a transparent polycarbonate Lexan corrugated sheet (LCS100, SABIC Innovative Plastics, Netherlands), with 89% visible light transmittance and <3% UV transmission. On the side walls, polyethylene film was used for roll-up ventilation. The experiment consisted of a randomized block design in a side-by-side comparison of three different growing system (conventional and two hydroponics). Plants were trained on a single stem up a string according to the high wire system for a long extended growing cycle. Yellow sticky traps were used to monitor whiteflies (Bemisia tabaci) and other common greenhouse pests. The soil of conventionally produced site is classified as gleyic fluvisol and endogenic fluvisol containing 24 g kg−1 soil organic matter in the 0−0.3 m soil layer. At the beginning of the season, the average initial soil nitrate content was 5.2 mg kg−1 for the same depth, soil assimilable P and K was 22 and 28 mg kg−1, respectively, on the basis of which application rates of macronutrients were calculated according to the Regulations on Conventional Production of Vegetables. One day before transplanting, granulated mineral fertilizers were incorporated on the plots at a rate of 70 kg N ha−1, 50 kg P ha−1 and 235 kg K ha−1, and 20 kg Ca ha−1 as calcium ammonium nitrate, super phosphate, and potassium sulfate, respectively. The remaining N and Ca (150 and 184 kg ha−1) were applied via fertigation with the watersoluble fertilizer (WSF) calcium nitrate (Multi-Cal, Haifa Chemicals, Israel). Irrigation was applied as required through a drip tape (T-tape TSX 500 model, T-systems International) beneath the plastic mulch. Hydroponic treatment of plants with two types of nutrient solution (modified Hoagland-Arnon solution and MINERAL GREEN) was started right at the time of transplantation and continued till the end of the experiment. Plants were cultivated on rockwool slabs (Grodan BV), commonly used as the standard growing medium for tomato and bell pepers. Slab dimensions in all the cases were 100 x 15 x 7.5 cm (length x width x height). A simple drip irrigation system used a dripper with a capacity of 2 litres/hour, with one dripper per plant. A constant concentration of nutrient solution was delivered by a pumping fow method. Table 1: Composition of nutrient solution - macronutrients (Hoagland & Aronu) Component KNO3 KH2PO4 Ca(NO3)2 NH4NO3 MgSO4*7H2 O Sum Macronutrient stocks g/1000 l for 5 000 l 505.5 2 527.5 136.0 680.0 654.7 3 273.5 80. 400.0 486.5 2 432.5 N-NO3 84.0 N-NH4 PO4231.0 112.0 14.0 210.0 mg/l K+ 195.0 39.0 Ca++ Mg++ SO42- 48.0 64.0 48.0 64.0 160.0 14.0 14.0 31.0 234.0 160.0 Table 2: Composition of nutrient solution - micronutrients (Hoagland & Aronu) Component H3BO3 MnSO4 ZnSO4 CuSO4 Mo chlorid Fe chelate 2.1 Micronutrient stocks mg/l g for 10 000 l 1.9 19.0 2.2 22.0 1.4 14.0 0.19 1.9 0.12 1.2 17.0 170.0 Mn Zn B 330.0 μg/l Cu Mo Fe 550.0 327.0 48.0 48.0 840.0 Evaluation Immediately after harvest, fruit tissue (6 sub-samples of 5 fruits were made by homogenising) immediately frozen with liquid N2, lyophilized, and kept at -80oC for the chemical determinations. Tomato: Fruit pigments (neoxanthin, violaxanthin, antheraxanthin, zeaxanthin, lutein, carotene, -carotene, chlorophyll a, chlorophyll b) were determined using the method described in Tausz, Wonisch, Grill, Morales, and Jimenez (2003). Pigments were extracted from 100 mg of the dry fruit powder with 5 ml of ice-cold acetone on an ice bath, using T-25 Ultra-Turrax (Ika-Labortechnik, Staufen, Germany) homogenizer for 25 seconds. All extraction procedures were performed in dim light. Acetone extracts were filtered through 0,2 μm Minisart SRP 15 filter (Sartorius Stedim Biotech GmbH, Goettingen, Germany) and then subjected to HPLC gradient analysis (a Spherisorb S5 ODS-2 250 x 4.6 mm column with an S5 ODS-2 50 x 4.6 mm precolumn (Alltech Associaties, Inc., Deerfield, USA)), using the following solvents: solvent A; acetonitrile/methanol/water (100/10/5, v/v/v); solvent B; acetone/ethylacetate (2/1, v/v), at a flow rate of 1 mL.min-1, employing linear gradient from 10% solvent B to 70% solvent B in 18 min, with a run time 30 min, and photometric detection at 440 nm. The HPLC analysis was performed on a Spectra-Physics HPLC system with Spectra Focus UV-VIS detector (Fremont, USA). Identification of compounds was achieved by comparing the retention times and the spectra as well as by the addition of standards. The concentrations of pigments were calculated with the help of corresponding external standards. Concentrations of tocopherols (α-tocopherol, γ-tocopherol, δ-tocopherol) were measured following the method reported in Tausz et al. (2003). Tocopherols were extracted from the dry leaf powder with ice-cold acetone exactly as described for chloroplast pigments. The acetone extracts were then subjected to isocratic HPLC analysis on a Spectra-Physics HPLC system equipped with Spectra System FL 2000 detector. Separations of tocopherols were achieved on a Spherisorb S5 ODS-2 (250 x 4.6 mm) column with an S5 ODS-2 (50 x 4.6 mm) precolumn, using methanol as solvent. Tocopherols were detected directly by fluorometry (excitation 295, emission 325) and identified by comparison of retention times as well as by the addition of standards. The concentrations of tocopherols were calculated with the help of corresponding external standards. The average structure of carotenoids and tocopherols was analyzed using compositional data analysis. The geometric mean was used as the measure of the central tendency for four components of carotenoid composition and three components of tocopherol composition. The data were transformed with additive log ratio (alr) transformation before ANOVA. 3. RESULTS 3.1 Tomato Figure 1: Cv. Buran (left), cv. Amaneta (middle) and cv. Tadim (right) (photo: D.Žnidarčič) The content of antioxidant compounds has today become an important quality parameter of fruits and vegetables. As reported by many authors, the antioxidant activity of various fruits and vegetables may differ with varieties and agronomic conditions. Tomato is known as an important source of antioxidants, especially carotenoids. Among them, lycopene is predominant and plays an important role in reducing cardiovascular diseases and digestive tract tumors, as the most efficient singlet oxygen quencher. Another important lipophilic antioxidant in tomato fruit is vitamin E, which has been proved to be important in reducing the risk of cardiovascular diseases, enhancing immune status and modulating important degenerative conditions associated with aging. It consists of four tocopherols (R-, β-, δ- and γ-tocopherol), of which R-tocopherol is the most biologically active form. It has also been observed that the beneficial effects associated with the consumption of tomatoes are attributed to the synergistic effects of the tomato compounds, especially lycopene and R-tocopherol, which have been shown to inhibit prostate carcinoma cell proliferation, HL-60 leukemic cell differentiation and low-density lipoprotein (LDL) oxidation. Figure 2: Average amounts of neoxanthin (with SE bars) for three tomato varieties Figure 3: Average amounts of violaxanthin (with SE bars) for three tomato varieties Figure 4: Average amounts of antheraxanthin (with SE bars) for three tomato varieties Figure 5: Average amounts of lutein (with SE bars) for three tomato varieties Figure 6: Average amounts of zeaxanthin (with SE bars) for three tomato varieties Figure 7: Average amounts of chlorophyll b (with SE bars) for three tomato varieties Figure 8: Average amounts of chlorophyll a (with SE bars) for three tomato varieties Figure 9: Average amounts of -carotene (with SE bars) for three tomato varieties Figure 10: Average amounts of δ-tocopherol (with SE bars) for three tomato varieties Figure 11: Average amounts of γ-tocopherol (with SE bars) for three tomato varieties Figure 12: Average amounts of α-tocopherol (with SE bars) for three tomato varieties 3.2 Bell peppers Figure 13: Cv. Blondy (left), cv. Bagoly (middle) and cv. Belladonna (right) (photo: D.Žnidarčič) Figure 14: Experiments on bell peppers (photo: D.Žnidarčič) Chemicals used in extraction of compounds were obtained from Sigma-Aldrich Corp., St Luis, Mo., U.S.A. (methanol, formic acid, sulfuric acid, metaphosphoric acid, acetone, ethyl acetate). Purified water used in extraction was obtained with Milli-Q Direct 8 system by Millipore (Merck KGaA, Darmstadt, Germany). Extraction of sugars, organic acid, and vitamin C was carried out as reported by Cunja and others (2015), with some modifications. For each cultivar 6 replicates were made. For the extraction of ascorbic acid 1 g of pericarp was extracted with 10 mL of 2% metaphosphoric acid. In analysis of organic acids and sugars standards of citric acid, and quinic acid, were from Sigma-Aldrich Co.; glucose, fructose, and sucrose from Fluka (Fluka Chemie AG, Buchs, Switzerland); malic acid from Merck (Merck KGaA, Darmstadt, Germany). The following organic acids have been determined in investigated pepper fruits: citric, malic, quinic acid. Analysis revealed significant differences among cultivars and production system. Extraction and determination of phenolic compounds was performed with HPLC/MS as described before by Cunja and others (2015). For each individual cultivar 6 repetitions were made. Compounds were identified by comparing retention times and absorption spectra, by fragmentation and by adding authentic standard solution to the sample. The content was calculated from peak areas and response factors of calibration curves of corresponding external standards. Figure 14: Average amounts of citric acid (with SE bars) for three bell peppers varieties Figure 15: Average amounts of malic acid (with SE bars) for three bell peppers varieties Figure 16: Average amounts of quinic acid (with SE bars) for three bell peppers varieties Figure 17: Average amounts of glucose (with SE bars) for three bell peppers varieties Figure 18: Average amounts of fructose (with SE bars) for three bell peppers varieties Figure 19: Average amounts of sacharose (with SE bars) for three bell peppers varieties Figure 20: Average amounts of C-vitamin (ascorbic acid) (with SE bars) for three bell peppers varieties Figure 21: Average amounts of quercetin (with SE bars) for three bell peppers varieties Figure 22: Average amounts of luteolin (with SE bars) for three bell peppers varieties Figure 23: Average amounts of apigenin (with SE bars) for three bell peppers varieties Figure 23: Average amounts of chrysoeriol glycoside (with SE bars) for three bell peppers varieties 4. CONCLUSION In the face of a global market economy, obtaining high yields of tomato and bell pepper fruit of very high quality and flavor is essential for ensuring consumer satisfaction and for the success of the greenhouse industry. Fruit quality may be affected by several factors such as genotype, fruit maturity and different external factors. Relationships between greenhouse environment and mineral nutrition of the tomato plant are extremely complex. A way to improve organoleptic and nutraceutic qualities of greenhouse tomato and bell pepper fruit without yield reduction is to maintain proper environmental parameters in the greenhouse (light, temperature, humidity, CO2 enrichment) and to implement new growing methods - nutrient solution. Very little attention has been given to the influence of nutrient solution and environmental factor interactions on fruit flavour and health benefit. Better knowledge of the spatial and temporal changes of the status of water and nutrients both in the plant and in the root environment is essential to guarantee an optimal growth, yield and fruit quality under different greenhouse growing conditions. In commercial hydroponic culture, growers generally provide plants with nutrient solutions having constant mineral nutrient concentrations and they control the volume of nutrient solution provided based on time or amount of solar radiation. Most growers rely on standardized recommendations to set the composition and concentration of nutrient solution. Over recent years, recommended concentrations of mineral nutrients in solutions have increased, especially in production of high-quality vegetables such as tomato and bell pepper. Hydroponics are a good method for research under controlled conditions of nutrient availability. Most modern hydroponic solutions are based on the work of Hoagland and Arnon and have been adapted to numerous crops. Seventeen elements are considered essential for normal growth and development of higher plants. All of these elements are absorbed by the roots through the root-zone media, except C, which is absorbed from the atmosphere by the shoots. The elements Mg, Ca, K, P, N, and S are considered macronutrients because they are required in relatively large concentrations in plant tissue. The remaining elements (Fe, CI, B, Mn, Zn, Cu, Mo, and Ni) are considered micronutrients because they are required in lower concentrations. The objective of our research was to determine the effect of nutrient solution (standard Hoagland-Arnon composition for the nutrient solution and MINERAL GREEN) and conventionally produced bell peppers and tomatoes on on selected plant metabolites. The null hypothesis for this experiment is that nutrient solution, production system, and variety will not significantly influence fruits quality. The primary results of the present study demonstrate significant differences in chemical composition (primary and secundary metabolites) and basic quality parameters between production systems. The results of the study may be useful to the producers who strive to improve their production technology, for food and processing industry and for consumers. It can be concluded that fruit quality could be optimised by modifing the concentration of some nutrients (Ca2+, K+, NO3-, NH4+ ...) present in MINERAL GREEN.