Comparison of Minerals and Bioactive Compounds of Six Vegetable Species in Microgreen Stage in Hydroponic and Soil Production Systems

Consumer’s demand for high valuable bioactive compounds have been increased in recent years.  Microgreen is a stage in the growth of vegetables that is popular among consumers for their high nutritional value. It can consider as young and tender edible seedling to enhance salad quality and safety. At the same time, it has been reported that microgreen can provide higher amount of phytonutrient (ascorbic acid, phenolics and carotenoids) and minerals. Hydroponics is defined as a system of growing plant in nutrient solution which could provide necessary micro- and macro-elements for early seedling growth. The use of hydroponic gardening by commercial growers is steadily increasing as the ability to control the growing factors while conserving space is of paramount importance to crop yields and commercial profits. It is also worth noting that hydroponic systems are good for the environment. As the water is recirculating, it is not being evaporated as readily or absorbed into the ground quickly. Therefore, it is important and valuable to study the growth of some common vegetable in hydroponics as microgreen in terms of higher bioactive compounds and minerals. The present study was conducted to evaluate two production systems (hydroponic and soil system) and also two growth stages (microgreen and mature) of 6 vegetable species (green basil, violet basil, lettuce, radish, dill and coriander). Different growth characteristics and bioactive compounds were measured as indices of yield and quality include: root dry/fresh weight, shoot dry/fresh weight, leaf area, ascorbic acid, total chlorophyll, carotenoids, phenolics, antioxidant activity and micro- and macro-nutrients in a factorial experiment based on completely randomized design with three replications. The weight of roots and shoots were measured at two stages during growth. Leaf area of vegetables were determined using a leaf area meter (CI-202, USA). Ascorbic acid determination was performed by 2, 6-dichlorophenolindophenol reagent. Chlorophyll, carotenoids, phenolics and antioxidant activity were tested spectrophotometric analysis. Samples of dry leaves were ground and dry-ashing at 550 °C for 4 h. The ashes were dissolved with 5 ml 2 N HCl and made up to 50 ml with distillated water. The concentrations of K were measured by flame photometry (Jenway, model PFP7). Analysis of Ca and P was carried out by titration and spectrophotometry (model T80 UV/VIS) , respectively. The Mg, Fe, Zn and Cu were identified by atomic absorption procedure. The results showed that growth characteristics of violet basil, green basil, lettuce, radish, dill and coriander were higher at the adult stage than microgreen stage. The results also showed that the growth characteristics of green basil, lettuce, radish, dill and coriander were higher in hydroponics than soil cultivation. Total chlorophyll content of violet basil, green basil, lettuce and dill were higher at microgreen stage than adult stage, while total chlorophyll content of leaf radish and dill plants were higher at the adult stage than microgreen stage. However, the chlorophyll content of the whole plants was higher in the conditions of soil cultivation than hydroponic conditions. Phenolic compounds and antioxidant activity of lettuce, radish and coriander leaves were higher at microgreen stage than adult stage, while these traits were higher in adult stage than in microgreens in violet basil, green basil and dill. Vitamin C was also higher in all vegetables in the microgreen stage compared to the mature stage in both cultures except for dill and coriander. Mineral elements content was higher at microgreen stage than in the mature stage, except for zinc element. Based on the results of this experiment, it can be concluded that the production and cultivation of these six vegetables in the microgreen stage could be considered as a suitable method for high nutritional value.