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][8][7,8], the harvest timeframe ^[9][10][11][9,10,11], 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 literesearchature review 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][34][33,34], 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 authoresearcherss in the literature review have noted that best practices have not been developed ^[40][41][40,41], which means that although there are many guidelines for producing microgreens, rwesearchers do not have very clearly defined standards; this researchliterature review 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) ^[46][47]. Plants are cultivated in a substrate membrane, over which the nutrient solution passes periodically ^[47][48]. 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 ^[48][49]. 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 ^[49][50]. 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 ^[50][51].

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 ^[51][52]. 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 ^[52][53].