*2.5. Antioxidants and Antioxidant Activity*

*2.5. Antioxidants and Antioxidant Activity*  The content of the main antioxidants (polyphenols, carotenoids, and ascorbic acid) was measured in this experiment. Significant differences were found for total polyphenols in relation to species, light, and their interaction (Table 4, Figure 5). On average across light conditions, the antioxidant content was slightly but significantly higher in turnip greens (>145 mg GAE·100 g**−**1 FW vs. 124 mg·g**−**1 in amaranth). Polyphenols were maximized under blue light (B, >165 mg·g**−**1 FW) in both species. Red light (R) somehow depressed the biosynthesis of polyphenols, leading to a final content that was overall the lowest in amaranth (<75 mg·g**−**1 FW), but did not differ from that in W (128.2 and 135.9 The content of the main antioxidants (polyphenols, carotenoids, and ascorbic acid) was measured in this experiment. Significant differences were found for total polyphenols in relation to species, light, and their interaction (Table 4, Figure 5). On average across light conditions, the antioxidant content was slightly but significantly higher in turnip greens (>145 mg GAE·100 g−<sup>1</sup> FW vs. 124 mg·<sup>g</sup> −1 in amaranth). Polyphenols were maximized under blue light (B, >165 mg·g <sup>−</sup><sup>1</sup> FW) in both species. Red light (R) somehow depressed the biosynthesis of polyphenols, leading to a final content that was overall the lowest in amaranth (<75 mg·g <sup>−</sup><sup>1</sup> FW), but did not differ from that in W (128.2 and 135.9 mg·<sup>g</sup> <sup>−</sup><sup>1</sup> FW in R and W, respectively) in turnip greens (*S* × *L*, *p* ≤ 0.01).

**Table 4.** Main effects of species (amaranth and turnip greens) and LED treatment (W = white, B = blue, R = red) on total phenolic content (TPC), ascorbic acid (Asc), and antioxidant activity (DPPH) of microgreens.

mg·g**−**1 FW in R and W, respectively) in turnip greens (*S* × *L*, *p* ≤ 0.01).


Values (mean ± *se*) within each column, followed by the same letter, do not significantly differ at *p* ≤ 0.05 according to Tukey's test; significant at *p* ≤ 0.01 (\*\*) and 0.001 (\*\*\*). Three biological replicates were used for the analysis (*n* = 3).

 **TPC** 

replicates were used for the analysis (*n* = 3).

of microgreens.

LED treatment (*L*)

*Significance*

**Figure 5.** Interaction effect of *species* × *light treatment* (W = white, B = blue, R = red) on TPC (mg GAE·100 g<sup>−</sup>1 FW) of microgreens. Data are means ± standard error (*n* = 3). Three biological replicates were used for the analysis. Different letters indicate significance at *p* ≤ 0.05 according to Tukey's test. **Figure 5.** Interaction effect of *species* × *light treatment* (W = white, B = blue, R = red) on TPC (mg GAE·100 g−<sup>1</sup> FW) of microgreens. Data are means <sup>±</sup> standard error (*<sup>n</sup>* = 3). Three biological replicates were used for the analysis. Different letters indicate significance at *p* ≤ 0.05 according to Tukey's test.

Ascorbic acid (Asc) is another antioxidant that was detected in the microgreens of the

**Table 4.** Main effects of species (amaranth and turnip greens) and LED treatment (W = white, B = blue, R = red) on total phenolic content (TPC), ascorbic acid (Asc), and antioxidant activity (DPPH)

> **Asc (mg·g<sup>−</sup>1 FW)**

0.51 ± 0.1 b 82.3 ± 15.7 c

**DPPH (mg TE·100 g<sup>−</sup>1 FW)** 

168.5 ± 42.9 a

**(mg GAE·100 g<sup>−</sup>1 FW)** 

Species (*S*) Amaranth 124.8 ± 13.5 b 0.20 ± 0.0 b 54.6 ± 5.2 b

B 168.6 ± 6.2 a 0.20 ± 0.0 c

Values (mean ± *se*) within each column, followed by the same letter, do not significantly differ at *p*

≤ 0.05 according to Tukey's test; significant at *p* ≤ 0.01 (\*\*) and 0.001 (\*\*\*). Three biological

R 104.4 ± 12.2 c

Turnip greens 145.6 ± 7.7 a 0.78 ± 0.2 a 180.5 ± 22.2 a

*S* \*\* \*\*\* \*\*\* *L* \*\*\* \*\*\* \*\*\* *S* × *L* \*\* \*\*\* \*\*

W 135.6 ± 2.3 b 0.79 ± 0.2 a 102.4 ± 26.5 b

two species. Unlike carotenoids, much greater contents of Asc (up to 1.3 mg·g**−**1 FW) were found in turnip greens (*p* ≤ 0.001) (Table 4, Figure 6). Light strongly affected (*L*, *p* ≤ 0.001) the content of this antioxidant, being significantly higher under blue light (B) in both species. A significant *S* × *L* interaction (*p* ≤ 0.001) was found according to ANOVA, indicating that, unlike amaranth, whose microgreens had the same Asc in W and R, white light (W) significantly reduced the accumulation of this metabolite in shoots of turnip greens, whose final content was <0.3 mg·g**−**1 FW. Antioxidant activity (AA), expressed as DPPH free-radical scavenging activity, was Ascorbic acid (Asc) is another antioxidant that was detected in the microgreens of the two species. Unlike carotenoids, much greater contents of Asc (up to 1.3 mg·g <sup>−</sup><sup>1</sup> FW) were found in turnip greens (*p* ≤ 0.001) (Table 4, Figure 6). Light strongly affected (*L*, *p* ≤ 0.001) the content of this antioxidant, being significantly higher under blue light (B) in both species. A significant *S* × *L* interaction (*p* ≤ 0.001) was found according to ANOVA, indicating that, unlike amaranth, whose microgreens had the same Asc in W and R, white light (W) significantly reduced the accumulation of this metabolite in shoots of turnip greens, whose final content was <0.3 mg·g <sup>−</sup><sup>1</sup> FW. *Plants* **2021**, *10*, x FOR PEER REVIEW 8 of 19

seemingly correlated to Asc (*r* = 0.82\*) more than to other antioxidants (*r* = 0.54ns vs.

**Figure 6.** Interaction effect of *species* × *light treatment* (W = white, B = blue, R = red) on ascorbic acid (Asc, mg·100 g<sup>−</sup>1 FW) of microgreens. Data are means ± standard error (*n* = 3). Three biological replicates were used for the analysis. Different letters indicate significance at *p* ≤ 0.05 according to Tukey's test. **Figure 6.** Interaction effect of *species* × *light treatment* (W = white, B = blue, R = red) on ascorbic acid (Asc, mg·100 g−<sup>1</sup> FW) of microgreens. Data are means <sup>±</sup> standard error (*<sup>n</sup>* = 3). Three biological replicates were used for the analysis. Different letters indicate significance at *p* ≤ 0.05 according to Tukey's test.

Antioxidant activity (AA), expressed as DPPH free-radical scavenging activity, was seemingly correlated to Asc (*r* = 0.82\*) more than to other antioxidants (*r* = 0.54ns vs. carotenoids, *r* = 0.41ns vs. TPC). As a result, on average across light conditions, higher AA corresponded to turnip greens (up to 260 mg TE·100 g−<sup>1</sup> FW) with respect to microgreens of amaranth (AA <74%) (Figure 7). Light also exerted a significant effect on this trait, with AA being higher in microgreens grown under blue light (B). However, a significant *S* × *L* interaction (*p* ≤ 0.001) revealed that, while no differences were observed for AA between W and R in amaranth (46 mg TE·100 g−<sup>1</sup> FW, on average), red light (R) adversely affected the antioxidant activity in amaranth, which was the 55% and 27% lower than AA in B and W, respectively.

biological replicates were used for the analysis. Different letters indicate significance at *p* ≤ 0.05

Multifactorial ANOVA showed that the mineral contents were significantly affected by species and the LED treatments, as well as by their interaction (Table 5). Most of the mineral elements were different in the two species except for Fe and Ni. Amaranth showed higher concentrations of Mg, K, Cu, Zn, and P, but lower concentrations of Na,

Light treatments significantly influenced the concentration of Mg, Ca, Mn, Fe, Ni, and P. In particular, R light increased the concentrations of Mg, Mn, Fe, and Ni, while W

The effect of LED treatment was more pronounced for Mg and the microelements (Mn, Fe, and Cu), which were significantly higher in turnip greens under the red LED. Amaranth grown under the red and blue LED showed a high Fe concentration. No

Ca, and Mn compared to turnip greens (Table 5).

light increased the concentrations of Ca and P (Table 5).

significant differences were observed for Ni, Zn, and P (Table 5).

according to Tukey's test.

*2.6. Mineral Composition* 

**Figure 7.** Interaction effect of *species* × *light treatment* (W = white, B = blue, R = red) on the antioxidant activity (DPPH, mg TE·100 g<sup>−</sup>1 FW) of microgreens. Data are means ± standard error (*n* = 3). Three biological replicates were used for the analysis. Different letters indicate significance at *p* ≤ 0.05 according to Tukey's test. **Figure 7.** Interaction effect of *species* × *light treatment* (W = white, B = blue, R = red) on the antioxidant activity (DPPH, mg TE·100 g−<sup>1</sup> FW) of microgreens. Data are means <sup>±</sup> standard error (*<sup>n</sup>* = 3). Three biological replicates were used for the analysis. Different letters indicate significance at *p* ≤ 0.05 according to Tukey's test.

**Figure 6.** Interaction effect of *species* × *light treatment* (W = white, B = blue, R = red) on ascorbic acid (Asc, mg·100 g<sup>−</sup>1 FW) of microgreens. Data are means ± standard error (*n* = 3). Three biological replicates were used for the analysis. Different letters indicate significance at *p* ≤ 0.05 according to

#### *2.6. Mineral Composition 2.6. Mineral Composition*

Tukey's test.

Multifactorial ANOVA showed that the mineral contents were significantly affected by species and the LED treatments, as well as by their interaction (Table 5). Most of the mineral elements were different in the two species except for Fe and Ni. Amaranth showed higher concentrations of Mg, K, Cu, Zn, and P, but lower concentrations of Na, Ca, and Mn compared to turnip greens (Table 5). Multifactorial ANOVA showed that the mineral contents were significantly affected by species and the LED treatments, as well as by their interaction (Table 5). Most of the mineral elements were different in the two species except for Fe and Ni. Amaranth showed higher concentrations of Mg, K, Cu, Zn, and P, but lower concentrations of Na, Ca, and Mn compared to turnip greens (Table 5).

Light treatments significantly influenced the concentration of Mg, Ca, Mn, Fe, Ni, and P. In particular, R light increased the concentrations of Mg, Mn, Fe, and Ni, while W light increased the concentrations of Ca and P (Table 5). Light treatments significantly influenced the concentration of Mg, Ca, Mn, Fe, Ni, and P. In particular, R light increased the concentrations of Mg, Mn, Fe, and Ni, while W light increased the concentrations of Ca and P (Table 5).

The effect of LED treatment was more pronounced for Mg and the microelements (Mn, Fe, and Cu), which were significantly higher in turnip greens under the red LED. Amaranth grown under the red and blue LED showed a high Fe concentration. No significant differences were observed for Ni, Zn, and P (Table 5). The effect of LED treatment was more pronounced for Mg and the microelements (Mn, Fe, and Cu), which were significantly higher in turnip greens under the red LED. Amaranth grown under the red and blue LED showed a high Fe concentration. No significant differences were observed for Ni, Zn, and P (Table 5).
