Download Testing of Mineral Green on fruit quality of tomatoes

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.