Three trays per light intensity were fully harvested to determine total fresh weight (FW) per m² using a precision analytical balance (AS 100/C/2, RADWAG, Radom, Poland). For dry weight (DW) measurements, a quarter of each tray was dried in a forced air oven (LDO-150F, Labtech, Gagok-ri, Korea) at 70°C until a constant mass was achieved. Both FM and DW values were recorded in grams (g). For dry matter content (DMC), the percentage of DW was calculated using the DW:FW ratio and expressed as a percentage.

Thirty cotyledons per light repetition (n = 90) were considered for cotyledon thickness. A micrometer with a 0.01 mm precision (JPT491, Mitutoyo, Japan) was used and expressed in millimeters (mm).

A 0–150 mm digital Vernier was used to determine microgreen length. Thirty microgreens per light repetition (n = 90) were considered and expressed in millimeters (mm).

Cotyledon leaf area was determined by image analysis of 20 cotyledons per replicated (n = 60). Images were analyzed using the ImageJ software, an open-source image processing program designed by the National Institutes of Health (NIH) (Bethesda, Maryland, United States). The specific version used was v. 1.51j8 (Schneider et al., 2012).

The determination of total phenolic content (TPC) was conducted according to the procedure described by Ainsworth and Gillespie (2007) with some modifications (Flores et al., 2022). The hydro-methanolic extract obtained in the previous steps was mixed with 10% Folin–Ciocalteu reagent, followed by a 0.7 mol L⁻¹ Na₂CO₃ solution. The reaction was left to react for 2 h, and 765 nm absorbance was recorded using a multi-plate spectrophotometer (Asys UVM 340, Biochrom, Cambridge, United Kingdom). A control mix without a sample was established for baseline correction purposes. The quantification of TPC was accomplished through a gallic acid calibration curve and was expressed in milligrams of gallic acid equivalent (GAE) per 100 g of fresh weight (FW). The final values were calculated as the average of nine data points, comprising three samples from each treatment replication.

Two distinct assays were conducted for the antioxidant capacity (AC) measurement. The ferric reducing antioxidant power (FRAP) and the 2,2-diphenyl-1-picrylhydrazyl (DPPH). A modified version of the method reported by Benzie and Strain (1996) was used for the FRAP assay. The FRAP reagent, comprised of 0.3 mol L⁻¹ acetate buffer (pH 3.6), 0.01 mol L⁻¹ 2,4,6-Tripyridyl-s-triazine (TPTZ) dissolved in 0.04 mL L⁻¹ HCl, and 0.02 mol L⁻¹ FeCl₃ 6H₂O, was prepared in a 10:1:1 ratio. The mixture was then heated at 37°C for 10 min. Subsequently, a sample aliquot was combined with the preheated FRAP reagent. The reaction mixture was transferred to a 96-well plate, and 593 nm absorbance was monitored with a multi-plate spectrophotometer (Asys UVM 340, Biochrom, Cambridge, United Kingdom) until it reached a stable reading.

The 2,2-diphenyl-1-picrylhydrazyl (DPPH) reagent was used for free radical scavenging activity, following the methodology that Gupta and Prakash (2009) described. In each reaction, an extract aliquot was mixed with a solution of 0.2 × 10⁻³ mol L⁻¹ DPPH, and the absorbance at 517 nm was recorded with a multi-plate spectrophotometer (Asys UVM 340, Biochrom, Cambridge, United Kingdom) until it stabilized.

To account for baseline variations, a control lacking samples was prepared and utilized for correction in both AC determination methods. The equivalent antioxidant capacity was determined using a calibration curve established with Trolox (Merck KGaA, Darmstadt, Germany). The resultant AC values were expressed in milligrams of Trolox equivalent (Trolox eq) per 100 g of fresh weight (mg 100 g⁻¹ FW).

The yield on a fresh weight basis varied among species and cultivars (green or red). Green cabbage yield showed no significant differences among treatments; meanwhile, in red cabbage, the low intensity increased the yield compared to medium and high intensities by 17.9 and 5.7%, respectively (Table 2). In kale, significant differences were observed only for the red cultivar; specifically, the low and medium intensities raised the yield compared to the high intensity by 9.0 and 9.9%, respectively (Table 2). In mizuna, the yield did not show significant differences for the green and red cultivars (Table 2). On the other hand, in green mustard, the yield was significantly higher under medium and low intensities compared to high intensity by 26.6 and 16.1%, respectively. By contrast, high intensity produced the maximum yield of 46.7% for red mustard and 42.2% for low intensity, both of which were greater than the yield attained with medium intensity (Table 2).

Green cabbage and kale showed no significant differences among treatments for dry weight (Table 2). In red cabbage, low intensity diminished the yield compared to medium and high intensities by 25.6 and 23.3%, respectively. In red kale, no significant differences were observed (Table 2). In green mizuna and mustard, high intensity promoted a higher yield than medium and low intensities; in the red cultivars of both species, dry weight decreased significantly at low intensity by about 30% (Table 2).

Dry matter content showed similar results to dry weight. Green cabbage and kale cultivars showed no significant differences among treatments. On the other hand, low intensity significantly decreased DMC in red cabbage compared to medium and high intensities by 36.8 and 27.8%, respectively. Meanwhile, in red kale, no significant differences among treatments were found (Table 2). In green mizuna and mustard cultivars, high intensity promoted a higher DMC than low and medium intensities. In particular, DMC in green mizuna under high intensity was 50.6 and 33.7% higher than in low and medium intensities, respectively (Table 2). In green mustard, DMC under high intensity was 38.9 and 61.0% higher than in low and medium intensities, respectively (Table 2). In red mizuna and mustard cultivars, low intensity had a significant negative effect on DMC. The low intensity decreased the DMC in red mizuna compared to high and medium intensities by 35.7 and 24.4%, respectively. In addition, medium intensity significantly decreased DMC in red mizuna compared to high intensity by 14.9%. In red mustard, the low intensity diminished DMC by about 40% compared to the others intensities (Table 2).

Overall, the low intensity promoted a greater length of the microgreens in all species compared to the high intensity, except in red kale (Table 2). For instance, the hypocotyl length in green and red cabbages at the low intensity was 22.2 and 34.2% greater than at the highest intensity, respectively. In green kale, the low intensity stimulated the hypocotyl length by 11.5% compared to the high intensity. Meanwhile, green and red mizuna showed increased hypocotyl length of over 40% under low compared to high-intensity. Among all species, mustard hypocotyl length, independent of cultivar, had the greatest difference between low and high intensity. Specifically, hypocotyl length was 112.9 and 85% greater in green and red mustard, respectively, when comparing low and high intensities (Table 2).

Cotyledon thickness generally did not show significant differences among light intensity treatments, except for green cabbage, where medium intensity significantly increased cotyledon thickness compared to high intensity by 8.6% (Table 2).

Cotyledon area showed significant differences only in green and red mizuna and red kale (Table 2). Particularly, the low intensity increased the cotyledon area of green mizuna compared to medium and high intensities by 63.7 and 69.8%, respectively. In red mizuna, low intensity promoted higher cotyledon area than medium and high intensity by 35.7 and 83.9%, respectively. In addition, medium intensity significantly increased cotyledon area compared to high intensity by 35.5%. On the other hand, high intensity promoted a larger cotyledon area of red kale compared to low and medium intensities by 49.0 and 65.6%, respectively (Table 2).

Color parameters, such as lightness, chroma, and hue, showed significant differences among intensity treatments for the different Brassicaceae species and cultivars, except for red mustard (Table 3). In general, green cabbage microgreens grown under medium intensity were greener than microgreens grown under low and high intensity (Table 3; Figure 2). Meanwhile, the low intensity promoted a lighter color of the microgreens in red cabbage (high lightness value) compared to medium and high intensities (Table 3; Figure 2). In green kale, medium intensity significantly increased the hue, turning it greener than the low and high intensities. In contrast, in red kale, the color remained green and enhanced under low intensity compared to medium and high intensities (Table 3; Figure 2). In green mizuna, microgreens grown under high intensity were greener than those grown under low and medium intensities. In contrast, in red mizuna, the low intensity increased the blue color of the cotyledons compared to medium and high intensities, which enhanced the purple color (Table 3; Figure 3). Finally, in green mustard, both medium and high intensities significantly increased the hue, which meant that microgreens were greener than microgreens grown under low intensity. In red mustard, the microgreens had a color closer to reddish, and no significant differences were observed among the intensity treatments (Table 3; Figure 3).

Brassicaceae microgreen chlorophyll a content varied between 55.6 and 212.2 μg g⁻¹ FW, and overall, the low intensity promoted a higher content in most of the species than the other intensities, except for the red kale and mustard cultivars (Table 4). Specifically, low intensity significantly increased the chlorophyll a content in green cabbage compared to medium and high intensities by 38.7 and 65.7%, respectively. Similar results were observed in red cabbage; were low intensity stimulated the chlorophyll a content compared to medium and high intensities by 27.6 and 33.0%, respectively. In green kale, low intensity also significantly increased the chlorophyll a content compared to medium and high intensities by 23.8 and 45.9%, respectively. In green mizuna, the chlorophyll a content at low intensity reached 12.6 and 64.7% more than at medium and high intensities, respectively. On the other hand, red mizuna grown in low and medium intensities showed a similar chlorophyll a content and was significantly higher than high intensity by 29%. For green mustard, the chlorophyll a content was significantly enhanced under low intensity compared to medium and high intensities by 16.7 and 27.9%, respectively (Table 4).

Chlorophyll b content showed higher values in all the microgreens of the species grown under the lowest intensity, but significant differences were observed only in the green cultivars and red mizuna (Table 4). Green cabbage grown under low intensity had higher chlorophyll b content than medium and high intensities by 32.8 and 50.9%, respectively. Meanwhile, in green kale, the content of chlorophyll b increased 52.7% when comparing low and high intensity. In green mizuna, both low and medium intensities significantly enhanced chlorophyll b content compared to high intensity by 37.5 and 33.5%, respectively. Similarly, the chlorophyll b content significantly increased by 22.3 and 20.2% in red mizuna cultivated in low and medium intensities compared to high intensity, respectively. The low intensity also improved chlorophyll b content in green mustard. In particular, the lowest intensity significantly increased chlorophyll b content by 25.9 and 29.0%, respectively, compared to medium and high intensities (Table 4).

Carotenoid content was significantly modified only in green cabbage and both cultivars of mizuna (Table 4). In green cabbage, carotenoid content significantly increased under low intensity compared to high intensity by 79.4%. Meanwhile, the low intensity significantly improved the carotenoid contents in both mizuna cultivars. Specifically, the low intensity in green mizuna increased carotenoid content compared to the medium and high intensities by 9 and 58.8%, respectively. Likewise, the medium intensity showed a significantly higher content of carotenoids than the high intensity by 45.6%. In red mizuna, carotenoid content under low intensity was significantly enhanced compared to medium and high intensities by 8.0 and 18.4%. In addition, medium intensity also significantly increased carotenoid content compared to high intensity by 9.6% (Table 4).

Total phenol content in Brassicaceae microgreens varied between 51.5 and 248.5 mg GAE 100 g⁻¹ FW. Among the green cultivars, green mustard was the species with the lowest TPC values (51.5–90.3 mg GAE 100 g⁻¹ FW), while green cabbage had the highest values (164.0–194.9 mg GAE 100 g⁻¹ FW) (Table 5). Among the red cultivars, red kale showed the lowest TPC values (86.9–110.6 mg GAE 100 g⁻¹ FW); the highest values were obtained in red cabbage (158.5–248.5 mg GAE 100 g⁻¹ FW) (Table 5). Overall, TPC was improved under high intensity in all Brassicaceae species, except in red cabbage and mustard. In these red cultivars, the TPC was enhanced by the medium intensity. In particular, red cabbage and mustard significantly improved under medium compared to low intensity by 56.8 and 54.9%, respectively (Table 5). On the other hand, green cabbage grown under high intensity significantly raised TPC compared to low intensity by 18.7%. In green kale, TPC significantly increased compared to low and medium intensities by 28.6 and 27.7%, respectively. In red kale, TPC enhanced under high intensity compared to low intensity by 27.3%. Similarly, TPC significantly increased by 52.5% in green mizuna microgreens grown at high compared to low intensity. In red mizuna, the high intensity also significantly increased the TPC compared to low and medium intensities by 54.7 and 27.5%, respectively. In the same way, high intensity significantly enhanced TPC in green mustard versus low and medium intensities by 75.3 and 59.5%, respectively (Table 5).

In green cabbage, the antioxidant capacity measured by FRAP and DPPH exhibited a similar trend across intensity treatments, significantly increasing AC at high intensity compared to low intensity. The increase by FRAP reached 32.1%, while by DPPH, it was 26.1% (Table 5). In red cabbage, both medium and high intensities raised AC compared to low intensity. Specifically, AC under medium significantly increased compared to low intensity by 55.2% (FRAP) and 57.9% (DPPH), respectively (Table 5). In both kale cultivars, high intensity promoted higher AC by FRAP and DPPH compared to low and medium intensities. Particularly, AC measured by FRAP increased under high intensity versus the other intensities in a range of 21.2–27.7%. Similarly, AC measured by DPPH enhanced under high compared to low and medium intensities in a range of 16.1–30.5% (Table 5). In both mizuna cultivars, AC measured by FRAP showed no significant differences among intensity treatments. Meanwhile, AC measured by DPPH showed a substantial worsening under high intensity compared to low and medium intensities. In green mizuna, high intensity significantly raised AC compared to the other intensities by about 36%. In red mizuna, the high intensity increased AC compared to low and medium intensities by 52.9 and 30.1%, respectively. Furthermore, medium intensity also significantly raised AC compared to low intensity by 17.6% (Table 5). In general, in both mustard cultivars, high intensity promoted AC by FRAP and DPPH compared to low and medium intensities. In green mustard, the AC by FRAP under high intensity was 46.5 to 76.4% higher than at low and medium intensities, respectively. Meanwhile, the AC by DPPH under high intensity was 57.4–50.3% higher than at low and medium intensities, respectively. In red mustard, AC by FRAP under high intensity significantly enhanced compared to low intensity by 32.3%. On the other hand, AC by DPPH significantly raised under medium intensity compared to low by 40.5% (Table 5).

Leaf pigments, such as chlorophylls and carotenoid concentration, can vary due to internal factors and as an indicator of response to light conditions (Sumanta et al., 2014). Choi (2021) showed in strawberries that photosynthetic pigments as chlorophyll a (Chl a), chlorophyll b (Chl b), and carotenoid contents changed under various light intensity conditions and presented significantly lower concentrations at high light intensity. On the other hand, Meas et al. (2020) show that the increase in light intensity between 130 and 280 μmol m⁻² s⁻¹ did not affect the concentration of total chlorophyll a, b, (a + b), and total carotenoids of red amaranth microgreens. These studies showed the differential response to light intensity of these pigments among species. In the current study, the content of Chl a showed a significant reduction at high light intensity (210 μmol m⁻² s⁻¹) in green and red cabbages, green kale, green and red mizuna, and green mustard (Table 4). On the other hand, Chl b obtained with high light intensity was significantly lower than at lower intensity in green cabbage, kale, mizuna, mustard, and red mizuna. Moreover, total carotenoids were reduced in green cabbage and green and red mizuna at high light intensity. Green cabbage reached 40 and 33% higher Chl a and Chl b, respectively, at low compared to high intensity. On the other hand, red cabbage had a higher content of Chl a and Chl b at low compared to high intensity by 25 and 22%, respectively. As cabbage, low intensity promoted a higher concentration of Chl a and Chl b in green and red kale grown at low compared to high intensity by 31 and 34%, respectively. Red kale also showed a reduction in Chl a and Chl b concentrations when grown at low intensity compared to high intensity by 9 and 13%, respectively (Table 4). For green mizuna, the reduction of Chl a and b between low and high intensity reached 39 and 24%, respectively, while for the red cultivar, it reached 22 and 18%, respectively. For mustard, only the green cultivar showed a significant decrease in Chl a and b due to the light intensity. In particular, the Chl a and Chl b concentrations decreased from low to high intensity by 21 and 22%, respectively. These results confirm those reported by Jones-Baumgardt et al. (2021), who observed that Chl a and Chl b content was reduced in the range of 24 and 30% between 100 and 400 μmol m⁻² s⁻¹ light intensities in cabbage, kale, mustard, and arugula.

In indoor conditions, 80 and 350 μmol m⁻² s⁻¹ were considered normal and high light intensity, respectively (Jiang et al., 2020). In this sense, high light exposure could disrupt the normal light reactions of photosynthesis. This disruption leads to an increase in the number of oxidized Photosystem I (PSI) reaction centers, which in turn contributes to photo-inhibition leading to the production of reactive oxygen species (ROS) such as singlet oxygen and superoxide radicals. These ROS can damage the chlorophyll molecules and other photosynthetic components, ultimately leading to a decrease in chlorophyll content (Janeeshma et al., 2022). In this study, the loss of chlorophyll a and b of microgreens exposed to high light intensities could likely attributable to enzyme-mediated degradation. Sato et al. (2015) report that in A. thaliana under high light intensities, the chlorophyll b is degraded by chlorophyll b reductase, which is proposed to be crucial for disassembling light-harvesting complexes as a strategy to minimize damage to light-capturing photosystems in the chloroplast.

Carotenoids are liposoluble pigments present in numerous fruits and vegetables. Some of these carotenoids, like β-carotene, serve as precursors to vitamin A and have antioxidant functions that effectively scavenge free radicals and extinguish singlet oxygen (Xiao et al., 2019). According to Xiao et al. (2012, 2019), the major carotenoids found in these Brassicaceae microgreens were β-carotene, lutein/zeaxanthin, and violaxanthin, which is very similar to the carotenoid profile of many mature Brassicaceae samples. The total carotenoid concentration was significantly reduced by light intensity in green cabbage and green and red mizuna (Table 4). Specifically, in green cabbage, the concentration of total carotenoids was reduced by 44% when they grow at high rather low intensity. Also, in green and red mizuna, the total carotenoid concentration decreased under low compared to high intensity by 37 and 15%, respectively. The reduction in β-carotene concentration can be attributed to the specific regulation of carotenoid biosynthesis and accumulation by light. Under high light stress, the activity of carotenoid cleavage dioxygenases (CCDs) is enhanced, thereby regulating carotenoid levels. Moreover, enzymatic oxidation via peroxidases/lipoxygenases or non-enzymatic photochemical processes in photosynthetic tissues also contributes to carotenoid homeostasis (Nisar et al., 2015). Furthermore, Arabidopsis leaves exposed to high light stress produce bioactive, volatile plant compounds such as β-cyclocitral and dihydroactinidiolide, which are derived from the oxidation of β-carotene. This oxidation process contributes to the observed reduction in β-carotene concentration. Also, these compounds, originating from carotene, function as stress signals, leading to the modulation of gene expression and activation of cellular defense mechanisms in plants (Nisar et al., 2015). The other evaluated species showed a similar trend, with no significant differences observed between light intensities. Likewise, Jones-Baumgardt et al. (2021) noted that total carotenoid concentrations were unaffected in kale, cabbage, mustard, and arugula microgreens exposed to variable PPFD from 100 to 600 μmol m⁻² s⁻¹.

Consumption of microgreens has increased due to appreciation for their concentrated functional components, such as phenolics, compared to mature leafy greens (Mir et al., 2017). The phenolic content in the plant is determined by the plant’s biosynthetic processes, which are influenced by various factors, such as cultivar, climate, postharvest treatments, and agricultural and environmental conditions (Olsen et al., 2010). Among the phenols, flavonoids constitute the most abundant and varied category in our dietary intake (Olsen et al., 2010), where the most prevalent subgroups are flavanols and anthocyanins. The latter are responsible for the red and purple in the red cultivars of Brassicaceae species as cabbage, kale, mizuna, and mustard (Olsen et al., 2010; Sun et al., 2013). Total phenolic content in green and red cabbages increased under high compared to low intensity by 18 and 44%, respectively. As reported by Sun et al. (2013), different anthocyanins present in red cabbage microgreens correspond to cyanidin-3-diglucoside-5-glucoside derivatives. Compounds that, according to Olsen et al. (2010), represent 10.3% of the total phenol equivalents per 100 g of fresh weight. Also, Zhang et al. (2019) mentioned that light treatment, especially short-wavelength light, can improve anthocyanin accumulation and antioxidant capacity. In this context, the light spectrum used (Figure 1) contributed to the wavelength in the range between 380 and 420 nm, which corresponds to the UV-A region (Kozai and Zhang, 2016) and is thus capable of stimulating the synthesis of this kind of compound. This might explain the higher increase in total phenolics in the red cultivar over the green one.

Kale cultivars had similar total phenolic concentrations between 85 and 110 mg GAE 100 g⁻¹ FW and showed an increase of 29 and 27% when high light intensities were compared with low for green and red cultivars, respectively (Table 5). Olsen et al. (2010) determined that red kale had a total phenolic content between 614 and 730 mg GAE 100 g⁻¹ FW, and Xiao et al. (2019) found 220.8 ± 9.0 mg GAE 100 g⁻¹ FW. These results were almost 7- and 2-fold, respectively, higher than values in this study for the same species at high light intensity (Table 5).

For green mizuna, the higher total phenolic concentration was registered at high light intensity and represented a 53% increase compared to low intensity. Also, the green mustard cultivated in this study had the most significant increase in total phenolic content, reaching an increase of 75% when cultivated at high over low intensity (Table 5). On the other hand, in red mizuna, total phenolic concentrations showed an increase of 55% when high and low intensities were compared and the total phenolic concentration in red mustard increase 28% at high intensity compared to low intensity. Lin et al. (2011) showed that, as in cabbage, the phenolic composition of red mustard was glycosylated hydroxycinnamic acid derivatives, and different flavonol glycoside derivatives that correspond to kaempferol quercetin or isorhamnetin. Lin et al. (2011) also showed that different anthocyanins present in red mustard correspond to acylated cyanidin 3-sophoroside-5-mono-di or tri-glucosides. These same authors mentioned that nearly all the structurally identified anthocyanins from the colored brassica plants corresponded to cyanidin with a similar chemical structure. Additionally, Zhang et al. (2019) said these compounds are accumulated by short-wavelength light (Figure 1).

Dannehl and Josuttis (2014) highlight that the quantity (intensity) and quality (spectrum) of light play a major role in terms of the accumulation of secondary plant compounds in fruits and vegetables. Also, according to Flores et al. (2022), high intensities can stimulate the increase in the concentration of total phenolic, total flavonoids, and the antioxidant capacity of lettuce and endive, especially when the light spectrum has an adequate intensity at wavelengths corresponding with blue color (400–500 nm) (Figure 1). Also, Appolloni et al. (2021) analyzed the effects of indoor LED lighting recipes and management on the specialized metabolite content in different groups of crop plants and found that most studies applied a combination of red and blue light (22%) or monochromatic blue (23%) with a 16 h day⁻¹ photoperiod (78%) and an intensity greater than 200 μmol m⁻² s⁻¹ (77%) and concluded that these treatment features were often the most efficient in enhancing specialized metabolite content. Additionally, Verlinden (2020) mentioned that high light intensities and UV-A exposure treatments appear to trigger antioxidant accumulation, and wavelength in the range between 380 and 420 nm (Figure 1) can stimulate the synthesis of anthocyanins (Zhang et al., 2019). In addition, Oh et al. (2009) showed in lettuce that a high light intensity of 800 μmol m⁻² s⁻¹ applied for 1 day can increase the concentration of total phenolics and antioxidant capacity. The same authors showed that high light intensity, compared to other stresses, like chilling and heat shock, can be more effective in increasing the concentration of compounds such chlorogenic acid, caffeic acid, chicoric acid, quercetin 3-O-glucoside, and luteolin-7-O-glucoside, which belong to the phenylpropanoid pathway. These changes consequently can explain the increase in the recorded values of total phenolic content.

Dannehl and Josuttis (2014) emphasized that increased light intensity increases anthocyanins and flavonoids compounds, which is related to the antioxidant capacity. Therefore, the high antioxidant capacity found in Brassicaceae microgreens grown under high light intensity (210 μmol m⁻² s⁻¹) may be due to the accumulation of these molecules (Table 5). All Brassicaceae species evaluated in this study reached the highest antioxidant capacity by DPPH at 210 μmol m⁻² s⁻¹ and showed the same behavior as total phenolic compounds (Table 5). In general, red cultivars had higher antioxidant capacity by DPPH than green ones (Table 5). Only green and red mustards registered similar values among cultivars.

At high light intensity (210 μmol m⁻² s⁻¹), green and red cabbages showed a significant increase in DPPH values of 26 and 53% compared with low intensity (120 μmol m⁻² s⁻¹). Also, for green cabbage, AC by FRAP was higher at high light intensity, representing a 32% increase compared to low light intensity. Conversely, red cabbage reached the highest FRAP value at medium intensity, increasing 55% compared to low intensity and 8% compared to high intensity (Table 5).

Green and red kale also reached the highest DPPH values at 210 μmol m⁻² s⁻¹, which represents an increase of 21 and 24%, respectively, compared with the values reported at low intensity (Table 5). AC by FRAP also had higher values at high intensity, showing an increase of 28 and 25% in green and red kales, compared to low intensity. For this species, FRAP did not show differences among light-intensity treatments. Instead, DPPH showed an increase in green and red mizuna of 36 and 53% at high compared to low intensity (Table 5). According to Olsen et al. (2010), red kale had complex hydroxycinnamic acids derivatives, and disinapoyl-diglucoside was the main one, reaching 4.9% of the total amount of polyphenol equivalents per 100 g of fresh weight. These authors also showed that the main flavonol in red kale was kaempferol-3-sinapoyl-diglucoside-7-diglucoside, which represented 9.8% of the total amount of polyphenol equivalents per 100 g of fresh weight, being the mayor secondary compound responsible for the antioxidant capacity registered for this specie. Also, according to Verlinden (2020), this type of favonol can be accumulated at high light intensities. For green mustard, an increase in DPPH and FRAP of 47 and 57% at high intensity was observed compared to low intensity. Red mustard also showed the highest FRAP value at high intensity, increasing by 32% compared to low intensity. However, the highest DPPH values were reached at medium intensity representing an increase of 40 and 4% compared to low and high intensities, respectively.

Samuolienė et al. (2013) reported that a PPFD of 110 μmol m⁻² s⁻¹ suppresses normal growth and diminishes the nutritional value of Brassicaceae microgreens (Kohlrabi, mustard, red pak choi, and tatsoi). According to these authors, the most suitable conditions for growth and nutritional quality of the microgreens were higher intensities of 330–440 μmol m⁻² s⁻¹, resulting in a larger leaf surface area, higher total phenols, and antioxidant capacity. Similarly, in this study, 110 μmol m⁻² s⁻¹ reached the lowest concentration of total phenols and antioxidant capacity measured by DPPH and FRAP (Table 5).

Despite the high intensity increasing dry matter and dry weight percentage and also increase the TPC promoting a higher antioxidant activity, long photoperiods at low intensities can be better in terms of energy and financial efficiency than shorter photoperiods at high intensities (Filatov and Olonin, 2023; Lanoue et al., 2023).