Trial Protocol for Hydroponically Cultivated Microgreens: Comparison
Please note this is a comparison between Version 2 by Camila Xu and Version 1 by Teodor Rusu.

Microgreens are young plants that are consumed at the seedling stage, which have a short production cycle (about 14 days) and require little space for growth. The hydroponic production of microgreens has potential to develop, at both an industrial, and a family level, due to the improved production platforms.

  • microgreens
  • hydroponic
  • trial protocol

1. Introduction

Microgreens are young plants that are consumed at the seedling stage, which have a short production cycle (about 14 days) and require little space for growth [1]. Microgreens are emerging functional foods of the 21st century [2] that are gaining interest for their sustained nutraceutical properties and are an optimistic prospect for expanding especially for the consumption of the population in large urban areas and in terms of food security. Production of microgreens using hydroponic systems must be planned and controlled with care for controlling environmental factors in order to increase quality parameters [3,4,5,6][3][4][5][6]. This is in comparison to more conventional production methods using soil, considering all the controllable factors in hydroponic systems that have been shown to influence the accumulation of bioactive substances [7[7][8],8], the harvest timeframe [9[9][10][11],10,11], and the quality of the finished product [12,13,14][12][13][14]. Furthermore, the lack of a soil’s microbiome in hydroponic systems is also important to consider, as unsuccessful parameterization leaves the plants vulnerable to harmful spoilage by microorganisms [15,16,17][15][16][17].
However, the advantages of hydroponic platforms and the development of evaluation protocols can lead to a positive influence on the quality of microgreens with higher concentrations of active substances [18,19][18][19] and nutrients valuable for human health [20,21,22][20][21][22]. This is why it is necessary to standardize certain cultivation protocols to ensure their quality [23,24,25][23][24][25]. For instance, there is a wide range of environmental impact factors and variation in their relationships to downstream microgreens outputs, which means that there is no single prescription that will guarantee perfect results [26]. The litreserature review arch has demonstrated that there are optimal ranges within which one can begin the task of designing effective prescriptions for successful microgreen production [3,21,27][3][21][27].
The time from sowing to harvest is 7–21 days for microgreens [28], a period in which the control of vegetation factors is very important. Nutritional solution, temperature, and light regime have the most important role in seed germination [29,30][29][30] and development [31], while also summarizing the recent research on the many promising research trends in refining microgreen production to achieve optimal outputs along its phenological stages [32]. The nutritional solution, air, and water temperature, light regime, pH, electrical conductivity, dissolved oxygen, CO2 concentration, and relative humidity are all important factors which influence secondary metabolism from an incipient phase [33[33][34],34], which in the final stages increases both the perceived and actual value of the plants by contributing to human health and nutritional fortification [35,36][35][36].
Microgreen producers must integrate specific systematic hydroponic strategies to obtain high-quality microgreens and high quantity [37] and quality bioactive substances [38], while also avoiding the potential for spoilage and low-quality production [20,39][20][39] when moving too far beyond the noted parameter ranges [3].
Many authors in the literature reviewesearchers have noted that best practices have not been developed [40[40][41],41], which means that although there are many guidelines for producing microgreens, wresearchers do not have very clearly defined standards; this literature review research has therefore gathered critical information regarding hydroponically grown microgreen production that can be used by researchers and producers to improve the protocol for testing platforms used to obtain microgreens [18,42][18][42].
Microgreens are currently considered among the five most profitable crops, along with mushrooms, ginseng, saffron and goji berries [43]. Therefore, developing species-specific growth media to support year-round production and to enhance valuable antioxidant components is affordable and of utmost importance for the microgreens industry [19,22,43][19][22][43]. It is particularly important that the fundamental research into ensuring the safety and quality of this new addition to healthy diets, microgreens, is carried out so that the produce industry can avoid some of the problems that have challenged the mature produce and sprout industries during the past several decades [44,45][44][45].

2. Trial Protocol for Evaluating Platforms for Growing Microgreens

The trial protocol for evaluating platforms for growing microgreens in hydroponic conditions includes the procedures to be followed and the parameters considered useful for calibrating the platform. Hydroponic GoHydro systems (https://gohydro.org, accessed on 18 April 2022). have specific characteristics, such as the layer of crop used (nutrient solution), type of irrigation (closed), method of irrigation (immersing), irrigation level (root level) [47][46]. Plants are cultivated in a substrate membrane, over which the nutrient solution passes periodically [48][47]. The high-capacity tank helps to maintain a constant pH. The color of the tank must be white on the outside to maintain a constant temperature of the nutrient solution, and it is not affected by solar radiation [49][48]. The water pump is in the tank, and the nutrient solution reaches the surface of containers through a pipe system. The pump recirculates the whole solution within 30 min of a fertilization regime, and the result is the mixing of the solution in the system [50][49]. Microgreens can germinate and grow without any fertilizer application, up to the capacity of the specific seed’s capacity [39]. However, providing mineral nutrients to microgreens will increase yields and secondary metabolite concentration [51][50].

2.1. Setting the Optimal Ranges, in Controlled Settings

Setting the optimal ranges for microgreens, in controlled settings, between the limits of favorability for each species, aims to highlight the effects of the hydroponic platform [3]. As reported in the literature, special attention must be addressed to the choice of growth medium, which represents one of the key factors in the production process and could influence microgreens yield and quality [52][51]. Parameters defined and optimal ranges for different species of microgreens continuously monitored and controlled are presented in Table 1 [3,19][3][19]. The spectral output of the lighting system must be quantified using a spectrometer, at various points of growth of the trays of the platform [53][52].
Table 1.
Parameters defined for different species of microgreens continuously monitored and controlled.

References

  1. Wieth, A.R.; Pinheiro, W.D.; Da Silva Duarte, T. Purple Cabbage Microgreens Grown in Different Substrates and Nutritive Solution Concentrations. Rev. Caatinga 2019, 32, 976–985.
  2. Choe, U.; Yu, L.L.; Wang, T.T.Y. The Science behind Microgreens as an Exciting New Food for the 21st Century. J. Agric. Food Chem. 2018, 66, 11519–11530.
  3. Rusu, T.; Cowden, R.J.; Moraru, P.I.; Maxim, M.A.; Ghaley, B.B. Overview of Multiple Applications of Basil Species and Cultivars and the Effects of Production Environmental Parameters on Yields and Secondary Metabolites in Hydroponic Systems. Sustainability 2021, 13, 11332.
  4. Kyriacou, M.C.; El-Nakhel, C.; Soteriou, G.A.; Graziani, G.; Kyratzis, A.; Antoniou, C.; Ritieni, A.; De Pascale, S.; Rouphael, Y. Preharvest Nutrient Deprivation Reconfigures Nitrate, Mineral, and Phytochemical Content of Microgreens. Foods 2021, 10, 1333.
  5. Šamec, D.; Ljubej, V.; Redovniković, I.R.; Fistanić, S.; Salopek-Sondi, B. Low Temperatures Affect the Physiological Status and Phytochemical Content of Flat Leaf Kale (Brassica oleracea var. acephala) Sprouts. Foods 2022, 11, 264.
  6. Gómez, C.; Currey, C.J.; Dickson, R.W.; Kim, H.J.; Hernández, R.; Sabeh, N.C.; Raudales, R.E.; Brumfield, R.G.; Laury-Shaw, A.; Wilke, A.K.; et al. Controlled Environment Food Production for Urban Agriculture. HortScience 2019, 54, 1448–1458.
  7. Lam, V.P.; Kim, S.J.; Park, J.S. Optimizing the Electrical Conductivity of a Nutrient Solution for Plant Growth and Bioactive Compounds of Agastacherugosa in a Plant Factory. Agronomy 2020, 10, 76.
  8. Franzoni, G.; Cocetta, G.; Prinsi, B.; Ferrante, A.; Espen, L. Biostimulants on Crops: Their Impact under Abiotic Stress Conditions. Horticulturae 2022, 8, 189.
  9. Ciriello, M.; Formisano, L.; Pannico, A.; El-Nakhel, C.; Fascella, G.; Duri, L.G.; Cristofano, F.; Gentile, B.R.; Giordano, M.; Rouphael, Y.; et al. Nutrient Solution Deprivation as a Tool to Improve Hydroponics Sustainability: Yield, Physiological, and Qualitative Response of Lettuce. Agronomy 2021, 11, 1469.
  10. Levine, C.P.; Mattson, N.S. Potassium-Deficient Nutrient Solution Affects the Yield, Morphology, and Tissue Mineral Elements for Hydroponic Baby Leaf Spinach (Spinaciaoleracea L.). Horticulturae 2021, 7, 213.
  11. Neocleous, D.; Nikolaou, G.; Ntatsi, G.; Savvas, D. Impact of Chelated or Inorganic Manganese and Zinc Applications in Closed Hydroponic Bean Crops on Growth, Yield, Photosynthesis, and Nutrient Uptake. Agronomy 2020, 10, 881.
  12. Birlanga, V.; Acosta-Motos, J.R.; Pérez-Pérez, J.M. Mitigation of Calcium-Related Disorders in Soilless Production Systems. Agronomy 2022, 12, 644.
  13. Liszka-Skoczylas, M.; Berski, W.; Witczak, M.; Skoczylas, Ł.; Kowalska, I.; Smoleń, S.; Szlachcic, P.; Kozieł, M. The Influence of Hydroponic Potato Plant Cultivation on Selected Properties of Starch Isolated from Its Tubers. Molecules 2022, 27, 856.
  14. Mau, L.; Junker, S.; Bochmann, H.; Mihiret, Y.E.; Kelm, J.M.; Schrey, S.D.; Roessner, U.; Schaaf, G.; Watt, M.; Kant, J.; et al. Root Growth and Architecture of Wheat and Brachypodium Vary in Response to Algal Fertilizer in Soil and Solution. Agronomy 2022, 12, 285.
  15. Riggio, G.M.; Jones, S.L.; Gibson, K.E. Risk of Human Pathogen Internalization in Leafy Vegetables during Lab-Scale Hydroponic Cultivation. Horticulturae 2019, 5, 25.
  16. Nissen, L.; Casciano, F.; Gianotti, A. Plant Volatiles of Lettuce and Chicory Cultivated in Aquaponics are Associated to their Microbial Community. Microorganisms 2021, 9, 580.
  17. Sathyanarayana, S.R.; Warke, V.G.; Mahajan, G.B.; Annapure, U.S. Comparative Studies of Microbial and Heavy Metal Safety Assessment of the Herbs Cultivated in Hydroponically and Regular Soil System. J. Food Saf. 2021, 41, e12936.
  18. Chen, H.; Tong, X.; Tan, L.; Kong, L. Consumers’ Acceptability and Perceptions Toward the Consumption of Hydroponically and Soil Grown Broccoli Microgreens. J. Agric. Food Res. 2020, 2, 100051.
  19. Rusu, T.; Moraru, P.I.; Mintas, O.S. Influence of Environmental and Nutritional Factors on the Development of Lettuce (Lactuca sativa L.) Microgreens Grown in a Hydroponic System: A Review. Not. Bot. Horti Agrobot. Cluj-Napoca 2021, 49, 12427.
  20. Renna, M.; Paradiso, V.M. Ongoing Research on Microgreens: Nutritional Properties, Shelf-Life, Sustainable Production, Innovative Growing and Processing Approaches. Foods 2020, 9, 826.
  21. Zhang, Y.; Xiao, Z.; Ager, E.; Kong, L.; Tan, L. Nutritional Quality and Health Benefits of Microgreens, a Crop of Modern Agriculture. J. Future Foods 2021, 1, 58–66.
  22. Ebert, A.W. Sprouts and Microgreens—Novel Food Sources for Healthy Diets. Plants 2022, 11, 571.
  23. Sugumaran, K.; Al-Roumi, A.; Thomas, B.; Kumar, V.; Albaho, M. Effect of Light Emitting Diodes (LED) Light on the Productivity and Quality of Selected Crops in a Modular Agricultural Production System. Acta Hortic. 2020, 1296, 951–958.
  24. Thuong, V.T.; Minh, H.G. Effects of Growing Substrates and Seed Density on Yield and Quality of Radish (Raphanus sativus) Microgreens. Res. Crops 2020, 21, 579–586.
  25. Bulgari, R.; Negri, M.; Santoro, P.; Ferrante, A. Quality Evaluation of Indoor-Grown Microgreens Cultivated on Three Different Substrates. Horticulturae 2021, 7, 96.
  26. Ghoora, M.D.; Srividya, N. Effect of Packaging and Coating Technique on Postharvest Quality and Shelf Life of Raphanus sativus L. and Hibiscus sabdariffa L. Microgreens. Foods 2020, 9, 653.
  27. Galieni, A.; Falcinelli, B.; Stagnari, F.; Datti, A.; Benincasa, P. Sprouts and Microgreens: Trends, Opportunities, and Horizons for Novel Research. Agronomy 2020, 10, 1424.
  28. Treadwell, D.D.; Hochmuth, R.; Landrum, L.; Laughlin, W. Microgreens: A New Specialty Crop. HS1164; Series of the Horticultural Sciences Department; UF/IFAS Extension: Gainesville, FL, USA, 2020.
  29. Mlinarić, S.; Gvozdić, V.; Vuković, A.; Varga, M.; Vlašiček, I.; Cesar, V.; Begović, L. The Effect of Light on Antioxidant Properties and Metabolic Profile of Chia Microgreens. Appl. Sci. 2020, 10, 5731.
  30. Ayeni, A. Nutrient Content of Micro/Baby-Green and Field-Grown Mature Foliage of Tropical Spinach (Amaranthus sp.) and Roselle (Hibiscus sabdariffa L.). Foods 2021, 10, 2546.
  31. Kelly, N.; Vaštakaitė-Kairienė, V.; Runkle, E.S. Chapter 18—Indoor Lighting Effects on Plant Nutritional Compounds. In Plant Factory Basics, Applications and Advances; Kozai, T., Niu, G., Masabni, J., Eds.; Academic Press: Cambridge, MA, USA, 2022; pp. 329–349.
  32. Pignata, G.; Casale, M.; Nicola, S. Water and Nutrient Supply in Horticultural Crops Grown in Soilless Culture: Resource Efficiency in Dynamic and Intensive Systems. In Advances in Research on Fertilization Management of Vegetable Crops; Tei, F., Nicola, S., Benincasa, P., Eds.; Advances in Olericulture; Springer: Cham, Switzerland, 2017.
  33. Ramakrishna, A.; Ravishankar, G.A. Influence of Abiotic Stress Signals on Secondary Metabolites in Plants. Plant Signal. Behav. 2011, 6, 1720–1731.
  34. Na, L.; Bernardo, E.L.; Tippayadarapanich, C.; Takagaki, M.; Kagawa, N.; Yamori, W. Growth and Accumulation of Secondary Metabolites in Perilla as Affected by Photosynthetic Photon Flux Density and Electrical Conductivity of the Nutrient Solution. Front. Plant Sci. 2017, 8, 708.
  35. Wojdyło, A.; Nowicka, P.; Tkacz, K.; Turkiewicz, I.P. Sprouts vs. Microgreens as Novel Functional Foods: Variation of Nutritional and Phytochemical Profiles and Their in Vitro Bioactive Properties. Molecules 2020, 25, 4648.
  36. Newman, R.G.; Moon, Y.; Sams, C.E.; Tou, J.C.; Waterland, N.L. Biofortification of Sodium Selenate Improves Dietary Mineral Contents and Antioxidant Capacity of Culinary Herb Microgreens. Front. Plant Sci. 2021, 12, 716437.
  37. Weber, C.F. Broccoli Microgreens: A Mineral-Rich Crop that can Diversify Food Systems. Front. Nutr. 2017, 4, 7.
  38. Hemathilake, D.M.K.S.; Gunathilake, D.M.C.C. Chapter 32—High-Productive Agricultural Technologies to Fulfill Future Food Demands: Hydroponics, Aquaponics, and Precision/Smart Agriculture. In Future Foods; Bhat, R., Ed.; Academic Press: Cambridge, MA, USA, 2022; pp. 555–567.
  39. Li, T.; Lalk, G.T.; Arthur, J.D.; Johnson, M.H.; Bi, G. Shoot Production and Mineral Nutrients of Five Microgreens as Affected by Hydroponic Substrate Type and Post-Emergent Fertilization. Horticulturae 2021, 7, 129.
  40. Ciuta, F.; Arghir, L.D.; Tudor, C.A.; Lagunovschi-Luchian, V. Research on Microgreens Farming in Vertical Hydroponic System. J. Hortic. For. Biotechnol. 2020, 24, 27–34.
  41. Tan, L.; Nuffer, H.; Feng, J.; Kwan, S.H.; Chen, H.; Tong, X.; Kong, L. Antioxidant Properties and Sensory Evaluation of Microgreens from Commercial and Local Farms. Food Sci. Hum. Wellness 2020, 9, 45–51.
  42. Kyriacou, M.C.; De Pascale, S.; Kyratzis, A.; Rouphael, Y. Microgreens as a Component of Space Life Support Systems: A Cornucopia of Functional Food. Front. Plant Sci. 2017, 8, 1587.
  43. Kyriacou, M.C.; El-Nakhel, C.; Pannico, A.; Graziani, G.; Soteriou, G.A.; Giordano, M.; Palladino, M.; Ritieni, A.; De Pascale, S.; Rouphael, Y. Phenolic Constitution, Phytochemical and Macronutrient Content in Three Species of Microgreens as Modulated by Natural Fiber and Synthetic Substrates. Antioxidants 2020, 9, 252.
  44. Turner, E.R.; Luo, Y.; Buchanan, R.L. Microgreen Nutrition, Food Safety, and Shelf Life: A Review. J. Food Sci. 2020, 85, 870–882.
  45. Di Gioia, F.; Petropoulos, S.A.; Ferreira, I.C.F.R.; Rosskopf, E.N. Microgreens: From Trendy Vegetables to Functional Food and Potential Nutrition Security Resource. ActaHortic 2021, 1321, 235–242.
  46. Eldridge, B.M.; Manzoni, L.R.; Graham, C.A.; Rodgers, B.; Farmer, J.R.; Dodd, A.N. Getting to the Roots of Aeroponic Indoor Farming. New Phytol. 2020, 228, 1183–1192.
  47. Silber, A.; Bar-Tal, A. 8—Nutrition of Substrate-Grown Plants. In Soilless Culture; Raviv, M., Lieth, J.H., Eds.; Elsevier: Amsterdam, The Netherlands, 2008; pp. 291–339.
  48. Giurgiu, G.M. Research on Hydroponic Cultivation of Some Medicinal and Aromatic Plant Species and the Influence of the Technology on the Bioactive Substance. Ph.D. Thesis, USAMV Cluj-Napoca, Cluj-Napoca, Romania, 2016.
  49. Yang, T.; Kim, H.-J. Characterizing Nutrient Composition and Concentration in Tomato-, Basil-, and Lettuce-Based Aquaponic and Hydroponic Systems. Water 2020, 12, 1259.
  50. Johnson, S.A.; Prenni, J.E.; Heuberger, A.L.; Isweiri, H.; Chaparro, J.M.; Newman, S.E.; Uchanski, M.E.; Omerigic, H.M.; Michell, K.A.; Bunning, M.; et al. Comprehensive Evaluation of Metabolites and Minerals in 6 Microgreen Species and the Influence of Maturity. Curr. Dev. Nutr. 2021, 5, nzaa180.
  51. Di Gioia, F.; De Bellis, P.; Mininni, C.; Santamaria, P.; Serio, F. Physicochemical, Agronomical and Microbiological Evaluation of Alternative Growing Media for the Production of Rapini (Brassica rapa L.) Microgreens. J. Sci. Food Agric. 2016, 97, 1212–1219.
  52. Bölter, B.; Seiler, F.; Soll, J. Analysis of Arabidopsis Thaliana Growth Behavior in Different Light Qualities. J. Vis. Exp. 2018, 132, 57152.
  53. Ehret, D.; Alsanius, B.; Wohanka, W.; Menzies, J.; Utkhede, R. Disinfestation of Recirculating Nutrient Solutions in Greenhouse Horticulture. EDP Sci. 2001, 21, 323–339.
  54. Sakamoto, M.; Suzuki, T. Effect of Nutrient Solution Concentration on the Growth of Hydroponic Sweetpotato. Agronomy 2020, 10, 1708.
  55. Yang, T.; Kim, H.-J. Effects of Hydraulic Loading Rate on Spatial and Temporal Water Quality Characteristics and Crop Growth and Yield in Aquaponic Systems. Horticulturae 2020, 6, 9.
  56. Ibañez, C.A.; Zafraa, J.C.G.; Sachta, H.M. Natural and Artificial Lighting Analysis in a Classroom of Technical Drawing: Measurements and HDR Images Use. Procedia Eng. 2017, 196, 964–971.
  57. Orlando, M.; Trivellini, A.; Incrocci, L.; Ferrante, A.; Mensuali, A. The Inclusion of Green Light in a Red and Blue Light Background Impact the Growth and Functional Quality of Vegetable and Flower Microgreen Species. Horticulturae 2022, 8, 217.
  58. Beeson, R.C., Jr.; Chen, J. Quantification of Daily Water Requirements of Container-Grown Calathea and Stromanthe Produced in a Shaded Greenhouse. Water 2018, 10, 1194.
  59. Jans-Singh, M.; Fidler, P.; Ward, R.M.; Choudhary, R. Monitoring the Performance of an Underground Hydroponic Farm. In Proceedings of the International Conference on Smart Infrastructure and Construction 2019 (ICSIC), Cambridge, UK, 8–10 July 2019; pp. 133–141.
More
ScholarVision Creations