Hydrothermal nanosilica in the production of environmentally friendly salad products with desired properties in a closed agrobiotechnological system
The possibility of controlling the quality of salad products under conditions of a closed agrobiotechnical system with controlled conditions by processing with silicon-containing preparations was tested experimentally: a complex preparation of hydrothermal nanosilica with synthetic analogue of phytohormone auxin, crezacin, in relation to silica, similar to organosilicon component 1-chloromethyl in Russia plant growth - the Energia M preparation. The use of hydrothermal nanosilica with synthetic phytohormone crezacin makes it possible to purposefully change the chemical composition and obtain products of a given quality. The effect of nanosilica on product quality is complex multilateral: organoleptic properties of the product are improved, the content of residual amounts of nitrates and the toxic element of lead is reduced, the proportion of solids, the level of antioxidant activity and the accumulation of vitamin C are increased. The content in leaves significantly (up to 2-3 times) vitamins of group B. The shelf life of products is increased by reducing water loss (dehydration) during storage. A significant stimulating effect on the test cultures of Paramecium caudatum and Daphnia magna was revealed, which gives reason to assume a high level of food safety, as well as the effect of the appearance of new properties in the salad - a manifestation of biological activity that improves the living environment for biotesting objects, which manifested itself in an increase in their vital activity and productivity. The data obtained can be used for practical purposes for growing salad products with a controlled enriched chemical composition and increased nutritional and biological value.
The issue of food quality management is of great scientific and practical importance. Product quality is defined as "the totality of the characteristics of food products that meet the stated requirements and including its safety, consumer properties, energy and nutritional value, authenticity, ability to meet human food needs under normal conditions of use in order to ensure the preservation of human health" . The "Strategy for improving the quality of food products in the Russian Federation until 2030" emphasizes that the consumption of food products with low consumer properties is the reason for the decline in the quality of life and the development of a number of diseases of the population, therefore, it is necessary to create mechanisms to ensure good nutrition, disease prevention, increase the duration and increase quality of life of the population through the production and circulation on the market of food products of appropriate quality .
Thus, in modern conditions there is an acute question of finding ways and means of managing the quality and food safety of products. However, in natural, natural conditions, yield and product quality are difficult to regulate due to sharp fluctuations in growing conditions [9–14]. In this aspect, technologies of growing plants in closed agrobiotechnological systems with controlled plant growth conditions (climate chambers, phytotrons, synergotrons, etc.) are of great interest. When growing plants under controlled conditions of a closed agroecosystem, a directed change in the plant metabolism and production with controlled chemical composition and biological activity is possible [15–18].
One of the elements of quality management technology in agrobiotechnological systems is the use of biological stimulators and plant growth regulators that increase metabolic activity and plant resistance to stress [19–23]. Particularly promising as plant growth stimulants are nanoscale forms of silicon (a review of studies in this direction was published by us in 2020 . Studies conducted with open and protected soil plants have shown high efficiency in the application of silicon-based preparations for foliar dressing, not only increasing productivity, but also increasing the accumulation of biologically valuable substances in products.
However, the characteristics of plant metabolism and the formation of product quality indicators in closed ecosystems remain virtually unstudied. Therefore, the aim of the work is to establish the ability to control the quality of products (for example, lettuce leaf) by using nanoscale silicon in closed agrobiotechnological systems with a controlled environment for the growth and development of plants. This work is a continuation of our research cycle on the use of silicon compounds in closed agrobiotechnological systems [17, 25–29].
MATERIALS AND METHODS
Experimental studies were carried out in the experimental installation ISR 0.1 design ANO "Institute for Development Strategies", Moscow, (see Fig.1). As an object of research, we used leaf lettuce (Lactuca sativa L.) of the Ballet variety, grown in hydroponic culture according to the generally accepted growing technology. The illumination intensity was 130–135 μmol/m2∙s, the duration of daylight hours was 17 hours, the spectrum was polychromatic with a predominance of red and blue lights. The composition of the nutrient solution (in mg/l): N–NH4 – 5; P is 41; K – 275; Ca – 100; Mg – 24; S – 30; Fe – 0.94; Mn – 0.14; B – 0.16; Cu – 0.03; Zn – 0.13; Mo – 0.03; pH – 5.7–6.0; EU – 1.5–2. Temperature was 25°C. The scheme of sowing seeds 100×80 mm, 3 seeds per nest. There were three repetitions. The duration of the growing period is 32 days from the moment of emergence of seedlings (the phase of full germination is fixed on 3 days after sowing seeds).
Silicon-containing preparations of different compositions were taken for study: natural hydrothermal nanosilica (GNA) and the product of the chemical synthesis Energia M (based on 1-chloromethylsilatran). In the composition of both drugs, the phytohormone krezacin (triethanolammonium salt of orthocresoxyacetic acid, a synthetic analogue of the auxin phytohormone) was used as the second component, which enhances the effectiveness of the main component. The treatment was carried out by the method of foliar spraying of lettuce with 0.005% solution of the preparations in distilled water in the phase of 4–5 leaves (18 day plant vegetation). Processing salad culture in the control was carried out with distilled water.
The following quality parameters were analyzed: organoleptic assessment according to GOST R. 547032011, dry matter content – according to GOST 28561-90, nitrate content – according to GOST 29270-95, vitamin C – according to GOST 24556-89, group B vitamins – by capillary electrophoresis on the device "Drops 105", antioxidant activity – with a PHOTOCHEM Analytik Jena AG photocolorimeter, lead content – according to GOST R 51301-99. Additionally, the solids content and residual moisture were determined using a MX-50 moisture analyzer, A&D Company (Japan). In the study of lettuce samples, samples were prepared for analysis, subjecting them to air-shadow drying at room temperature (22 ± 3 °C) for 3 weeks. To determine the solids content in lettuce samples and residual moisture, 6 g of coarsely cut lettuce leaves were prepared and IR-dried at a fixed temperature of 105°C to constant weight. For a comprehensive assessment of product quality, a biotesting method was used using Paramecium caudatum and Daphnia magna according to the method described in . Mass losses during storage were determined after 11 days of storage (in % of the initial mass). Storage was carried out in desiccators with ground covers at room temperature.
RESULTS AND DISCUSSION
The possibility of controlling the quality of salad products under conditions of a closed agrobiotechnological system with controlled conditions by processing with silicon-containing preparations and plant growth regulators (PPP) was experimentally verified. The results of the studies showed the prospects of this approach, since natural nanosilica and the product of the chemical synthesis of Energia M have a comprehensive multilateral impact and contribute to the formation of products with improved properties:
The positive effect of hydrothermal nanosilica on the formation of organoleptic properties of products
Assessment of the appearance of marketable products was carried out according to a comprehensive indicator: the appearance, taking into account color, size, shape, development of the leaf system, the presence of small, substandard leaves, the level of marketability of the product as a whole.
The results of the experiment show the possibility by using hydrothermal nanosilica to improve the appearance of lettuce leaves, thereby increasing the marketability of products and their attractiveness to consumers (see Table 1, Fig.2). Appearance reflects the general condition of plants and is a marker of metabolic activity, photosynthetic and growth processes. Thus, nanosilica contributed to the formation of plants with greater leaf mass, more developed due to a complex of physiological and biochemical effects.
We note that silicon in the form of an organosilicon compound: 1-chloromethylsilatran with crezacin (Energia M preparation) was also effective in increasing the level of presentation of the product, however it was inferior in quantitative terms to the new form of the binary plant growth stimulator when replacing a synthetic organosilicon compound with hydrothermal nanosilica obtained on nature-friendly technologies from Kamchatka thermal waters using ultrafiltration technology.
The increase in the proportion of solids in the treatment of plants with hydrothermal nanosilica
The solids content and moisture loss during drying were evaluated in two ways – according to GOST 28561-90 and using a moisture analyzer MX-50, A&D Company (Japan) with drying of the samples at a constant temperature of 105 °С.
When assessing GOST 28561-90, the solids content increased when using the composition of GNA + crezacin by 1.2% compared with the control. Note that the use of the Energia M preparation was less effective compared to the use of hydrothermal nanosilica. The increase in the solids content in lettuce was only 0.3% (see Fig.3).
During infrared drying of lettuce leaf samples at 105 °C, the increase in dry matter (r.v.) had a similar value – 1.2% for GNK and 0.4% for the Energia M preparation (Table 2).
The absolute values of the mass fraction of r.v. were slightly lower than when determined by drying according to GOST (for example, in control, these values were 7.4% according to GOST and 6.0% on an IR analyzer), which can be explained by the difference in drying conditions with different methods. However, despite some differences in the absolute values of r.v., the nature of the influence of the studied drugs had similar trends.
The accumulation of nitrates and toxic elements in lettuce when using silicon-containing preparations with crezacin
The accumulation of nitrates in lettuce decreased after treatment with silicon-containing preparations (see Table 3). The excess of MPC for lead was not noted either in the control or in the experimental versions.
The accumulation of the toxic element of lead decreased 8.5 times (GNA + krezacin), 7 times (Energia M). The excess of MPC for lead was not observed in the control nor in experimental versions.
The effect of increasing the antioxidant activity of products during the processing of lettuce plants with hydrothermal nanosilica
The most important function of antioxidants is to prevent reactions involving reactive oxygen species (ROS); they act as an antagonist of unregulated ROS transformations. ROS play an important role in plant physiology, are involved in the regulation of growth processes and protect plants from adverse factors, but the formation of large amounts of ROS is detrimental to living systems. Many ROS are free radicals and activate the course of free radical reactions.
During oxidative stress, over-accumulation of AFO can occur in plants, which can destroy membranes and other cellular structures. Therefore, the important role of plant antioxidants is to interrupt radical oxidative processes. In plants, ROS are formed in the electron transport chain of chloroplasts. In addition, various biochemical reactions occur in plant organisms as a result of which free radicals of different nature are formed, antioxidants with different mechanisms of action also protect them. Therefore, the importance of antioxidants is to ensure the adaptation of plants to adverse factors, the utilization of ROS and the prevention of the accumulation of free radicals in cells. Antioxidant activity is determined by the activity of enzymes of the antioxidant system and the content of chemical compounds of non-enzymatic nature. Non-enzymatic antioxidants include phenolic substances, bioflavonoids, carotenoids, vitamin C and many others. More than 5000 compounds with antioxidant effect have been found in plants.
The antioxidant activity of lettuce plants treated with hydrothermal nanosilica in combination with crezacin increased by 14.4% compared with the control (see Fig.4). Note that the use of the preparation Energia M in the treatment of plants turned out to be less effective in terms of antioxidant activity (an increase of 7.1% compared with the control). At present, it is difficult to talk about biological mechanisms that cause an increase in the antioxidant activity of plant tissues in the presence of silicon compounds, however, the total visible effect is obvious.
The effect of increasing the content of vitamins in salad products when processing salad plants with hydrothermal nanosilica
The experiment established a significant (up to 3 times in comparison with the control) increase in the content of B vitamins in lettuce due to the use of GNK with crezacin (see Fig.5). The mechanisms for such a drastic change have yet to be identified.
The content of ascorbic acid in lettuce when using the composition of GNA + crezacin also increased (10.3% compared with 8.95% in the control), but to a lesser extent than vitamins of group B. The use of the Energia M preparation was not effective in terms of increasing vitamin C content.
Improving the keeping quality of salad products by treating plants with GNC with crezacin after treatment
Lettuce is a perishable product, even if the recommended storage temperature is observed. This is due primarily to the high moisture content and large leaf area (total evaporation surface). Therefore, the search for ways to reduce moisture loss during storage is of great economic importance.
In the experiments, the natural weight loss over 11 days of storage decreased by 8.1% when using the composition of GNA + Crezacin, in the case of using the Energia M preparation – by 5.4% compared with the control (see Fig.6).
It is likely that treatment with silicon-containing preparations affects the structure of plant cells and tissues and increases their water-holding ability. These results are of great practical importance, can be successfully used to develop technology for post-harvest storage of salads in retail, restaurant business and farms.
Integrated product quality assessment using biotesting techniques
The results of biotesting of grown products (test culture Daphnia magna) showed that the treatment of leaf lettuce plants with experimentally studied plant growth regulators not only does not cause an increase in biotoxicity compared to the control, but also has a stimulating effect on the development of protozoa (see Fig.5). GNA preparations with krezacin and Energia M significantly (up to 5 times) increase the activity of Daphnia magna test cultures, which suggests that salad grown in conditions has a higher nutritional value, a high level of food safety compared to control. After processing the Ballet leaf variety after processing with the indicated preparations, it acquired a new quality, namely biologically active properties that increase the physiological capabilities of biological test cultures with respect to control. This suggests the presence of biological activity in lettuce leaves, i.e. emergence of a new quality in vegetable plants treated with growth regulators. The effect is most pronounced when treated with the composition of GNK + crezacin. The effectiveness of the Energia M preparation is also quite large, but inferior to nanosilica in combination with crezacin.
The use of another test culture (Paramecium caudatum) also showed the presence of a stimulating effect of the studied drugs (the number of cells in 100 μl of the medium in the control was 11.7, with the use of the Energia M preparation – 18.7, the composition of GNA + crezacin – 22.3).
Comparison of the results of chemical analyzes of quality and biotesting showed that through processing by growth regulators the quality of products improves, and this quality management method can be used when growing green crops.
The possibility of controlling the quality of lettuce salad products in closed agrobiotechnological systems by using hydrothermal nanosilica and a silicon-containing composition Energia M.
The use of drugs changes the metabolism of plants and leads to the formation of products with high nutritional and biological value.
Hydrothermal nanosilica in combination with crezacin increased the solids content in lettuce leaves and increased their antioxidant activity by 1.2 times, vitamin C by 1.2 times, vitamin B2 by 2.3 times, and vitamin B5 by 1.6 times, vitamin B6 – 3.3 times, vitamin B9–2.8 times; reduced mass loss after storage by 2 times, heavy lead metal by 8.6 times compared with control (untreated plants).
An increase in the biological activity of the products (stimulation of the development of test cultures), i.e. emergence of a new quality in vegetable plants treated with silicon-containing nanostructured growth regulators. According to the results of biotesting, toxic effects from the use of growth regulators were absent. At the same time, the number of test culture Daphnia magna in 100 ml of medium was 55.6 pcs. against 12.3 pcs. in the control version.
It was revealed that a plant growth stimulator based on hydrothermal nanosilica obtained using nature-like ultrafiltration technologies in combination with synthetic phytohormone krezacin is superior in efficiency to the Energia M growth stimulator existing in the Russian Federation, consisting of crezacin and organosilicon compound 1-chloromethylsilatrane.
The perspective of the possibility of controlling the quality of plant products in closed agrobiotechnological systems with a controlled environment by using non-root treatments with these growth regulators is shown. Their use is considered an environmentally friendly tool to reduce the load of chemicals in agriculture (fertilizers and pesticides), and at the same time to increase the resistance of plants to stress, increase plant productivity with the achievement of a higher level of quality of environmentally friendly products for a healthy diet. ■