Influence of environmental and nutritional factors on the development of lettuce (Lactuca sativa L.) microgreens grown in a hydroponic system: A review

Abstract

Lettuce microgreens are one of the most popular vegetables due to them being perceived as a “healthy food”, with high concentrations of nutrients, beneficial vitamins, and minerals. With a short vegetation period, they can be cultivated with minimum investment, and they are increasingly accepted by consumers, as they are healthy and easy to prepare. Lettuce has high ecological plasticity, but, despite this, its phenotypic expression, morphology, physiology, and anatomy are significantly influenced by environmental conditions. Lettuce microgreens contain higher quantities of phytonutrients and minerals and lower quantities of nitrates at the early stage of development than at the completely developed stage. The environmental conditions that influence the development of lettuce microgreens (and their quality) in a hydroponic system are as follows (average ideal values): light (400 W), photoperiodicity (12 h), light intensity (400 µmol m−2 s−1), colour spectrum (440-460 nm), temperature (20 ± 2 °C), and humidity (80 ± 5 %). The nutritional solution in a hydroponic system must be carefully monitored, by checking certain essential parameters such as the following (average ideal values): pH (6.3 ± 0.4), electrical conductivity (1.8 ± 0.2 mS), dissolved oxygen (6 mg L−1), and temperature (18 ± 2 °C). The analysis of expert literature reveals that there is a need to establish certain protocols for cultivating microgreens in hydroponic systems, to minimize the factors that can negatively influence the plants, in order to obtain higher concentrations of active substances.

Trial Protocol for Evaluating Platforms for Growing Microgreens in Hydroponic Conditions

“…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]. Parameters defined and optimal ranges for different species of microgreens continuously monitored and controlled are presented in Table 1 [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].…”

“…The nutrient solution shall be monitored daily and manipulated in order to be maintained at the best parameters for the development of plants [55]. The level of the nutrient solution must be kept constant [19].…”

“…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] and nutrients valuable for human health [20][21][22]. This is why it is necessary to standardize certain cultivation protocols to ensure their quality [23][24][25].…”

“…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]. 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].…”

Desenvolvimento de um sistema de correção automático de solução nutritiva em sistema hidropônico NFT utilizando microcontroladores de baixo custo

“…A alface (Lactuca sativa L.) é a hortaliça cujas folhas são as mais consumidas no mundo (Menezes et al, 2022). No Brasil está sendo muito comercializada devido seu valor nutricional, além disso, cada vez mais a demanda dessa hortaliça cresce em função dessa segurança alimentar e por ser um alimento de fácil preparo (Rusu et al, 2021;Teng et al, 2021).…”