A review on the effects of light-emitting diode (LED) light on the nutrients of sprouts and microgreens

Quality Evaluation of Indoor-Grown Microgreens Cultivated on Three Different Substrates

The microgreens are innovative products in the horticultural sector. They are appreciated by consumers thanks to their novelty and health-related benefits, having a high antioxidant concentration. This produce can be adopted for indoor production using hydroponic systems. The aim of the present work was to investigate the influence of three growing media (vermiculite, coconut fiber, and jute fabric) on yield and quality parameters of two basil varieties (Green basil—Ocimum basilicum L., Red basil—Ocimum basilicum var. Purpurecsens) and rocket (Eruca sativa Mill.) as microgreens. Microgreens were grown in floating, in a Micro Experimental Growing (MEG®) system equipped with LED lamps, with modulation of both energy and spectra of the light supplied to plants. Results showed high yield, comprised from 2 to 3 kg m−2. Nutritional quality varied among species and higher antioxidant compounds were found in red basil on vermiculite and jute. Coconut fiber allowed the differentiation of crop performance in terms of sucrose and above all nitrate. In particular, our results point out that the choice of the substrate significantly affected the yield, the dry matter percentage and the nitrate concentration of microgreens, while the other qualitative parameters were most influenced by the species.

Postharvest UV-B and Photoperiod with Blue + Red LEDs as Strategies to Stimulate Carotenogenesis in Bell Peppers

Background: Our objective was to evaluate carotenoid accumulation in bell peppers during shelf life under different light conditions. Methods: Fruit stored for 6 d at 7 °C received a 9 kJ m−2 UV-B treatment, while non-UV-treated were used as control (CTRL). Subsequently, all peppers were disposed for a retail sale period of 4 d at 20 °C with a photoperiod of 14 h under fluorescent light (FL) + 10 h under darkness (D), FL, or blue + red LEDs (BR LED). Results: Total antioxidant capacity (TAC) was increased by the UV-B treatment and the photoperiods supplemented with FL and BR LED, which was directly related to the carotenoid content. In fact, CTRL peppers (225 mg β-carotene kg−1) under FL+BR LED showed an increase of ~33% of 13-cis-β-carotene, ~24% of all-trans-β-carotene, and ~27.5% of 9-cis-β-carotene compared to FL + D and FL + FL. Capsaicinoids showed an increase by ~22%, ~38%, and ~27% in the content of capsanthin, capsanthin laurate, and capsanthin esters, respectively, after the UV-B treatment, which was even enhanced after the LED-supplemented photoperiod by ~18% compared to FL+D. Conclusions: Illumination with BR LEDs + UV-B during the retail sale period nights is recommended to increase the bioactive content of bell peppers via carotenoid accumulation to 270 mg β-carotene kg−1.

Effect of Different Ratios of Blue and Red LED Light on Brassicaceae Microgreens under a Controlled Environment

The consumption of microgreens has increased due to their having higher levels of bioactive compounds and mineral nutrients than mature plants. The lighting conditions during the cultivation of microgreens, if optimally selected, can have a positive effect by further increasing their nutritional value. Thus, our study aimed to determine the changes in mineral nutrients contents of Brassicaceae microgreens depending on different blue–red (B:R) light ratios in light-emitting diode (LED) lighting and to evaluate their growth and nutritional value according to different indexes. Experiments were performed in controlled environment growth chambers at IH LRCAF, 2020. Microgreens of mustard (Brassica juncea ‘Red Lace’) and kale (Brassica napus ‘Red Russian’) were grown hydroponically under different B:R light ratios: 0%B:100%R, 10%B:90%R, 25%B:75%R, 50%B:50%R, 75%B:25%R, and 100%B:0%R. A 220 μmol m⁻² s⁻¹ total photon flux density (TPFD), 18 h photoperiod, 21/17 ± 2 °C temperature and 60% ± 5% relative humidity in the growth chamber were maintained during cultivation. We observed that an increasing percentage of blue light in the LED illumination spectrum during growth was associated with reduced elongation in the microgreens of both species and had a positive effect on the accumulation of mostly macro- and micronutrients. However, different B:R light ratios indicate a species-dependent response to changes in growth parameters such as leaf area, fresh and dry mass, and optical leaf indexes such as for chlorophyll, flavonol, anthocyanin, and carotenoid reflectance.

Effects of Different LED Light Recipes and NPK Fertilizers on Basil Cultivation for Automated and Integrated Horticulture Methods

This study aims to optimize the conditions for “Genovese” basil (Ocimum Basilicum) germination and growth in an indoor environment suitable for horticulture through a synergic effect of light and fertilizers addition. In fact, several studies determined that specific light conditions are capable of enhancing basil growth, but this effect is highly dependent on the environmental conditions. In this study, the effect of different light sources was determined employing a soil with a negligible amount of fertilizer, demonstrating substantial improvement when light-emitting diode (LED) lights (hyper red and deep blue in different combinations) were applied with respect to daylight (Plants height: +30%, Total fresh mass: +50%). Thereafter, a design of experiment approach has been implemented to calculate the specific combination of LED lights and fertilizer useful to optimize the basil growth. A controlled-release fertilizer based on nitrogen, phosphorus, and potassium (NPK) derived from agro-residues was compared with a soil enriched in macronutrients. The results demonstrate significant improvements for the growth parameters with the employment of the controlled-release NPK with respect to enriched soil combined with a ratio of hyper red and deep blue LED light equal to 1:3 (Total fresh mass: +100%, Leaves number: +20%).

Small Functional Foods: Comparative Phytochemical and Nutritional Analyses of Five Microgreens of the Brassicaceae Family

Microgreens are the seedlings of herbs and vegetables which are harvested at the development stage of their two cotyledonary leaves, or sometimes at the emergence of their rudimentary first pair of true leaves. They are functional foods, the consumption of which is steadily increasing due to their high nutritional value. The species of the Brassicaceae family are good sources of bioactive compounds, with a favorable nutritional profile. The present study analyzed some phytochemical compounds with nutritional values, such as chlorophylls, polyphenols, carotenoids, anthocyanins, ascorbic acid, total and reducing sugars, and the antioxidant activity of five Brassicaceae species: broccoli (Brassica oleracea L.), daikon (Raphanus raphanistrum subsp. sativus (L.) Domin), mustard (Brassica juncea (L.) Czern.), rocket salad (Eruca vesicaria (L.) Cav.), and watercress (Nasturtium officinale R.Br.). Broccoli had the highest polyphenol, carotenoid and chlorophyll contents, as well as a good antioxidant ability. Mustard was characterized by high ascorbic acid and total sugar contents. By contrast, rocket salad exhibited the lowest antioxidant content and activity. The essential oil (EO) composition of all of these species was determined in order to identify their profile and isothiocyanates content, which are compounds with many reported health benefits. Isothiocyanates were the most abundant group in broccoli (4-pentenyl isothiocyanate), mustard (allyl isothiocyanate), and watercress (benzyl isothiocyanate) EOs, while rocket salad and daikon exhibited higher contents of monoterpene hydrocarbons (myrcene) and oxygenated diterpenes (phytol), respectively. Broccoli microgreens exhibited the overall best nutritional profile, appearing as the most promising species to be consumed as a functional food among those analyzed.

LED Illumination Spectrum Manipulation for Increasing the Yield of Sweet Basil (Ocimum basilicum L.)

Manipulation of the LED illumination spectrum can enhance plant growth rate and development in grow tents. We report on the identification of the illumination spectrum required to significantly enhance the growth rate of sweet basil (Ocimum basilicum L.) plants in grow tent environments by controlling the LED wavebands illuminating the plants. Since the optimal illumination spectrum depends on the plant type, this work focuses on identifying the illumination spectrum that achieves significant basil biomass improvement compared to improvements reported in prior studies. To be able to optimize the illumination spectrum, several steps must be achieved, namely, understanding plant biology, conducting several trial-and-error experiments, iteratively refining experimental conditions, and undertaking accurate statistical analyses. In this study, basil plants are grown in three grow tents with three LED illumination treatments, namely, only white LED illumination (denoted W*), the combination of red (R) and blue (B) LED illumination (denoted BR*) (relative red (R) and blue (B) intensities are 84% and 16%, respectively) and a combination of red (R), blue (B) and far-red (F) LED illumination (denoted BRF*) (relative red (R), blue (B) and far-red (F) intensities are 79%, 11%, and 10%, respectively). The photosynthetic photon flux density (PPFD) was set at 155 µmol m⁻² s⁻¹ for all illumination treatments, and the photoperiod was 20 h per day. Experimental results show that a combination of blue (B), red (R), and far-red (F) LED illumination leads to a one-fold increase in the yield of a sweet basil plant in comparison with only white LED illumination (W*). On the other hand, the use of blue (B) and red (R) LED illumination results in a half-fold increase in plant yield. Understanding the effects of LED illumination spectrum on the growth of plant sweet basil plants through basic horticulture research enables farmers to significantly improve their production yield, thus food security and profitability.

Current trends and innovations

LEDs achieved success in creating a mesmerizing life for humans. LEDs with low output are relatively cheap, and hence, they are used for many temporary purposes such as glow sticks, photonic textiles, and LED art by artists. Besides the basic applications, LEDs have made strong strides in several new fields of applications and emerged as leaders in the technological growth. The LED industry has experienced tremendous change since its inception in the commercial market. In over a decade, the LED efficiencies have improved and their cost has lowered down. This has created numerous growth opportunities to implement LEDs for multiple businesses and newer products.